2.6 – Responses to Public Comments on Testing and Monitoring

This file contains responses to public comments on testing and monitoring (comment 

codes 4600 to 4670). This section includes comments on testing and monitoring plans, 

well testing, ground water quality monitoring, carbon dioxide plume tracking, and air 

and soil monitoring.

The table below presents all of the EPA-assigned comment codes that are included in 

this section of the comment and response summary. Use the bookmarks in the PDF to 

move among the comment codes. 

Topics included in this summary and associated comment codes

Topic Code

2.6 Proposed Plume and Pressure Front Monitoring Requirements (40 CFR 146.90) 4600

2.6.1 Testing and monitoring plan requirement 4610

2.6.2 Injectate monitoring 4620

2.6.3 Corrosion monitoring 4630

2.6.4 Pressure fall-off testing 4640

2.6.5 CO2 plume and pressure front tracking 4650

2.6.5.1 Plume tracking techniques/geophysical methods 4655

2.6.6 Geochemical monitoring 4660

2.6.7 Surface air monitoring and/or soil gas monitoring 4670

Every comment on these topic areas and the associated response is included in this 

summary; there is some repetition where multiple commenters made the same 

comment.

Responses to letters from individual commenters or organizations are also available in 

the rulemaking docket.
Comment Code: 4600 2.6 Proposed Plume and Pressure Front Monitoring Requirements (40 CFR

146.90) 

Individual Comments

Commenter Name: Iain Wright Letter ID: 0118

Commenter Organization: BP Alternative Energy Comment ID: 22067

Other EPA Comment Codes and Descriptions: 4655 2.6.5.1 Plume tracking

techniques/geophysical methods (seeking comment) 

Comment: MONITORING 

Moving on to my second point: Monitoring. Monitoring is important, but there is 

a common mis-perception that if you want secure storage, you need to do lots of 

monitoring. Well, the UN says that "the proportion of CO2 retained by 

appropriately selected and managed sites is likely to exceed 99% over 1,000 

years". SO THE KEY TO SECURE STORAGE IS THE APPROPRIATE SELECTION AND

MANAGEMENT 

OF THE SITE. If that is done properly, the site will be very secure and the need 

for monitoring can be appropriately reduced. Monitoring is like the speedometer 

on your car. It does contribute to your safety, but more important is the design 

of the car, the road and how you drive the car. 

Having said that, at In Salah, we are doing a big research project into 

monitoring, so the program is much more extensive than would be appropriate for 

a commercial project. We are trying out new technologies (such as satellite 

imagery, micro-seismic), so that we can see how they perform against 

conventional oilfield monitoring technologies (such as tracers and conventional 

seismic). 

But as you can probably hear from my accent, I’m a Scotsman, and Scotsmen don’t 

like to waste money, so every technology that we use at in Salah has been 

carefully chosen to represent good value for money. Before we started injection 

at In Salah, we did a site-specific assessment of leakage risk and then we 

tailored the monitoring program to address those risks. Mandating any specific 

monitoring technology could waste a great deal of money and resources without 

contributing to the protection of USDWs. SO WE WOULD CAUTION AGAINST A UNIVERSAL 

MANDATE FOR ANY SPECIFIC MONITORING TECHNOLOGY. 

Many of you will have heard of the other two monitored, industrial-scale CO2 

injection projects in the world, at Sleipner and Weyburn. If you compare the 

monitoring activities at these sites, you can see that something which works 

well in one location, may not work at all in another location. WE ENCOURAGE EPA 

TO USE RISK-ASSESSED, PERFORMANCE-BASED CRITERIA TO DETERMINE SITESPECIFIC 

MONITORING PROGRAMS. 

Response: EPA agrees with commenters and believes that flexibility is important in developing and

implementing a monitoring plan that is appropriately tailored for a specific GS site. The purpose of
the requirement at §146.90 to develop site-specific testing and monitoring plans is to ensure that the

monitoring performed at a site is appropriate for site operational conditions and the geologic setting.

EPA believes that this is the best approach for addressing potential risks at GS sites. These flexible

provisions in the monitoring requirements for Class VI wells enable the owner or operator to tailor

monitoring programs to the specific needs of each project in consultation with the Director.

The final regulation provides for flexibility in: 1) methodologies used to collect these data, 2) the

spatial resolution at which the data should be collected, and 3) how often the data should be

collected. The number and placement of monitoring wells will be based on site-specific information

such as the calculated AoR, injection rate and volume, site geology, baseline data, and the presence

of artificial penetrations within the AoR. In some instances, there may be a limited number of

options for complying with EPA's minimum requirements. For example, monitoring for geochemical

changes will require use of monitoring wells and collection of groundwater samples for chemical

analysis. Many options currently exist for complying with other requirements, such as tracking the

position of the plume and pressure front within the injection zone.

Flexibility is also provided regarding how to monitor for the specific data required by the final rule.

The testing and monitoring plan is developed by the owner or operator in consultation with the

Director and is designed to ensure that a detailed, Director-approved document describing how

monitoring will be conducted during the lifetime of the project exists. 

EPA also agrees that good site selection and management are crucial elements of a successful GS

project, but disagrees that this is an effective substitute for rigorous site monitoring. 

EPA does not believe that prescribing specific technologies to be used in all cases for GS would be

appropriate given the variability in sites. Rather EPA is developing guidance on testing and

monitoring to assist owners or operators and Directors in evaluating requirements under §146.90,

including proposed monitoring plans. The guidance describes available technologies and

recommended approaches for implementing a testing and monitoring plan, including pre-operational

geophysical logging and testing of injection wells, MITs, injection well testing during operation,

groundwater quality monitoring, tracking the CO2 plume and pressure front, and soil gas and

surface air monitoring which may be required by the UIC Director for specific GS projects. The

guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm. In addition, in January 2009,

DOE published a best practices manual entitled "Monitoring, Verification, and Accounting of CO2

Stored in Deep Geologic Formations" (DOE/NETL-311/081508); this manual is included in the

docket for the final GS rule.

Commenter Name: Leslie Savage Letter ID: 0122

Commenter Organization: Railroad Commission of Texas (RRC) Comment ID: 24749

Comment: 6. EPA should provide more flexibility in the requirements for monitoring, 

testing and reporting. For example, 

Response: EPA agrees that monitoring plans and methods need to be site-specific and believes that

the monitoring requirements for GS sites at §146.90 provide an appropriate level of flexibility in

structuring a testing and monitoring plan that protects USDWs from endangerment. 

The final regulation provides for flexibility in: 1) methodologies used to collect these data, 2) the

spatial resolution at which the data should be collected, and 3) how often the data should be

collected. The number and placement of monitoring wells will be based on site-specific information
such as the calculated AoR, injection rate and volume, site geology, baseline data, and the presence

of artificial penetrations within the AoR. In some instances, there may be a limited number of

options for complying with EPA's minimum requirements. For example, monitoring for geochemical

changes will require use of monitoring wells and collection of groundwater samples for chemical

analysis. Many options currently exist for complying with other requirements, such as tracking the

position of the plume and pressure front within the injection zone.

Flexibility is also provided regarding how to monitor for the specific data required by the final rule.

The testing and monitoring plan is developed by the owner or operator in consultation with the

Director and is designed to ensure that a detailed, Director-approved document describing how

monitoring will be conducted during the lifetime of the project exists. EPA is developing guidance

on testing and monitoring to assist owners or operators and Directors in evaluating requirements

under §146.90, including proposed monitoring plans. The guidance describes available technologies

and recommended approaches for implementing a testing and monitoring plan, including preoperational geophysical logging and testing of injection wells, MITs, injection well testing during

operation, groundwater quality monitoring, tracking the CO2 plume and pressure front, and soil gas

and surface air monitoring which may be required by the UIC Director for specific GS projects.

Commenter Name: John Stormon Letter ID: 0123

Commenter Organization: Washington State Dept. of Ecology Comment ID: 23002

Other EPA Comment Codes and Descriptions: 3310 2.2.1.1 Comments in favor of requiring

computational models to delineate the AoR (seeking comment) 

Comment: Area of Review: The proposed standards correctly require not just modeling, but 

tracking of the actual CO2 plume and pressure front, with periodic reevaluation 

of the modeled behavior as additional experience is gained at a sequestration 

project. Modeling is a good method of predicting the behavior of injected CO2 

but should not be relied upon without monitoring to verify the accuracy of the 

modeled predictions. The model will be continually refined throughout the life a 

sequestration project. 

Response: EPA acknowledges the commenter’s support of the modeling approach, and agrees that

reevaluation of the AoR as required at 146.84(e) must incorporate monitoring and operational data

gathered since the last model run. 

EPA agrees with commenters on the importance of monitoring at GS sites and emphasizes that

monitoring of injection activities will be an important component of every GS project. Monitoring

associated with injection wells and the movement of the CO2 plume is necessary to verify that the

injectate is confined in the target formations and does not endanger USDWs. 

EPA agrees that monitoring data should be used to review model assumptions, verify computational

model projections, and, when necessary, provide input for model refinements. As data are collected

at an injection site, model parameters can be adjusted to match observations (i.e., for model

calibration), which in turn improves the predictive capability of the model. As a GS project proceeds,

both monitoring and modeling will evolve, with monitoring results supporting effective AoR

reevaluations and leading to improved model predictions.

Commenter Name: John Hanger Letter ID: 0130

Commenter Organization: Pennsylvania Dept. of Env. Protection Comment ID: 21509
Comment: Proposed Plume and Pressure Front Monitoring Requirements 

-EPA should specifically identify (by technology) what type of monitoring would 

be necessary and applicable to verify containment of the CO2 and any failures 

away from the injection wells themselves. 

Response: EPA does not believe that prescribing specific technologies to be used in all cases for GS

would be appropriate given the variability in sites. Rather EPA is developing guidance on testing and

monitoring to assist owners or operators and Directors in evaluating requirements under §146.90,

including proposed monitoring plans. The guidance describes available technologies and

recommended approaches for implementing a testing and monitoring plan, including pre-operational

geophysical logging and testing of injection wells, MITs, injection well testing during operation,

groundwater quality monitoring, tracking the CO2 plume and pressure front, and soil gas and

surface air monitoring which may be required by the UIC Director for specific GS projects. The

guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm. In addition, in January 2009,

DOE published a best practices manual entitled "Monitoring, Verification, and Accounting of CO2

Stored in Deep Geologic Formations" (DOE/NETL-311/081508); this manual is included in the

docket for the final GS rule.

Commenter Name: John Hanger Letter ID: 0130

Commenter Organization: Pennsylvania Dept. of Env. Protection Comment ID: 25077

Comment: -Language is included in the proposed rule detailing how the injection well will 

be monitored during its operation, but there is no language included that 

regulates the monitoring of areas surrounding the injection well. There is also 

concern about how deep and how close to the capping (sealing) formation the 

surrounding monitoring wells and other wells should be allowed to approach the 

capping formation. 

Response: EPA clarifies that the final GS regulation, at §146.90(g)(1), requires all GS project

owners or operators to monitor for pressure changes in the injection zone. Specific monitoring

locations will be identified by the owner and operator and approved by the Director in the

monitoring and testing plan, but EPA expects that monitoring wells will be placed throughout the

AoR. EPA believes that pressure monitoring in the injection zone is necessary to track the

development and movement of the pressure front and CO2 plume and eliminates the need for

monitoring in the locations mentioned by the commenter. 

Pressure monitoring within the injection zone is also necessary because any such monitoring above

the confining zone would not detect movement of the pressure front unless a breach of the confining

zone occurs. EPA believes that monitoring using wells in the injection zone (i.e., that penetrate the

confining zone) can be safely performed if the wells are constructed to prevent flow between the

injection zone and USDWs or other layers above the confining zone. Such construction technologies

exist and have been used in the oil and gas industry for years. EPA believes that the benefits of

monitoring in the injection formation outweigh the manageable risk of those monitoring wells

serving as conduits for fluid movement. EPA is developing guidance on well construction that will

include recommendations for monitoring well construction. The guidance will be available on EPA’s

website at http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

EPA adds that owners or operators may consider performing additional pressure monitoring in wells
that are above the confining zone (e.g., in the same wells used to perform ground water quality

monitoring required at §146.90(d)) to provide additional verification that no pressure changes are

occurring above the confining zone due to CO2 leakage. Monitoring also identifies needed remedial

actions, provides inputs for AoR reevaluation modeling, and targets additional geochemical and

surface monitoring needs. Knowledge of the location of the CO2 plume and the associated pressure

front will assure the public that GS projects are proceeding according to plan, provide sufficient

information to the owner or operator and Director, or allow for appropriate actions to address any

indication that USDWs may be endangered.

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil gas and surface air monitoring, which may be required by the UIC Director

for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm. In addition, in January 2009,

DOE published a best practices manual entitled "Monitoring, Verification, and Accounting of CO2

Stored in Deep Geologic Formations" (DOE/NETL-311/081508); this manual is included in the

docket for the final GS rule.

Commenter Name: Christine Reimer Letter ID: 0142

Commenter Organization: National Ground Water Association Comment ID: 22553

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Fluid Movement 

The UIC regulations have, from the beginning, included two standards of 

prohibition of fluid movement that may be appropriate for geological 

sequestration of carbon dioxide. The fluid movement requirement for Class I 

injection wells states: 

The well must be constructed, operated, maintained, and plugged such 

that injection activities will not cause movement of any contaminant 

into a USDW 

The fluid movement requirement for Class V injection wells states: 

No owner or operator shall construct, operate, maintain, convert, plug, 

abandon, or conduct any other injection activity in a manner that allows 

the movement of fluid containing any contaminant into underground 

sources of drinking water, if the presence of that contaminant may cause 

a violation of any primary drinking water regulation under 40 CFR part 

142 or may otherwise adversely affect the health of persons. The 

applicant for a permit shall have the burden of showing that the 

requirements of this paragraph are met. 

The NGWA recommendation for carbon sequestration well permitting includes an 

experimental phase for each location that will be used for geological 
sequestration of carbon dioxide. Wells constructed during the experimental 

phase at each location will have extensive testing requirements and exploratory 

objectives that will not be needed during the operational phase. It will not be 

necessary or practical to apply the same standard of fluid movement to both the 

experimental phase and the operational phase of carbon sequestration. 

The NGWA recommendations also include early warning monitoring to detect 

movement of fluids containing carbon dioxide or contaminants before the fluids 

reach a USDW. The advantage of early warning monitoring is in the ability to 

detect fluid movement before a drinking water supply is impacted. The 

identification of a geological unit that can serve as secondary containment for 

the injected fluid is addressed in the NGWA recommendations for geologic 

characterization. It is recommended that early warning monitoring be included 

in the requirements for operation of Class V experimental carbon sequestration 

wells, as well as Class VI operational carbon sequestration wells. The 

requirement for early warning monitoring should include authorization for action 

by the regulatory agency when fluid movement is detected by the early warning 

monitoring system. 

Class V Experimental Carbon Sequestration Well: During the experimental phase 

of injection, while the well is permitted as a Class V well, the following fluid 

movement criterion should apply: 

No owner or operator shall construct, operate, maintain, convert, plug, 

abandon, or conduct any other injection activity in a manner that allows 

the movement of fluid containing carbon dioxide or any contaminant into 

underground sources of drinking water, if the presence of carbon dioxide 

or that contaminant may cause a violation of any primary drinking water 

regulation under 40 CFR part 142 or may otherwise adversely affect the 

health of persons. The applicant for a permit shall have the burden of 

showing that the requirements of this paragraph are met. 

Class VI Operational Carbon Sequestration Well: During the operational phase of 

injection, while the well is permitted as a Class VI well, the following fluid 

movement criterion should apply: 

No owner or operator shall construct, operate, maintain, convert, plug, 

abandon, or conduct any other injection activity in a manner that allows 

the movement of fluid containing carbon dioxide or any contaminant into 

underground sources of drinking water, if the presence of carbon dioxide 

or that contaminant may cause a violation of any primary drinking water 

regulation under 40 CFR part 142 or may otherwise adversely affect the 

health of persons. Additionally, no owner or operator shall construct, 

operate, maintain, convert, plug, abandon, or conduct any other 

injection activity in a manner that allows the movement of carbon 

dioxide in gaseous phase to land surface, nor limit the extraction of 

drinking water from a underground sources of drinking water by reduction 

of porosity or changes in pH or water quality due to geochemical 

reactions, or by causing a buildup of gas in the underground sources of 

drinking water. The applicant for a permit shall have the burden of 
showing that the requirements of this paragraph are met. 

If any water quality monitoring of an underground source of drinking 

water indicates the movement of any contaminant into the underground 

source of drinking water, or a violation of any part of the preceding 

paragraph, except as authorized under part 146, the Director shall 

publish a notice in newspapers of general circulation in whose service 

area the fluid movement was detected. If a meritorious request is 

submitted by the public, the Director shall prescribe such additional 

requirements for construction, corrective action, operation, monitoring, 

or reporting (including closure of the injection well) as are necessary 

to prevent such movement. 

Response: EPA does not agree that each GS site must first be permitted as an experimental Class V

well before being authorized to operate a full-scale Class VI well. Following the promulgation of the

final rule, EPA will allow the use of Class V experimental technology permits only for experimental

purposes; i.e., to test new, unproven technologies. EPA does not consider it appropriate to permit

CO2 injection wells that are testing the injectivity or appropriateness of an individual formation (e.g.,

as a prelude to a commercial-scale operation) as Class V experimental technology wells. Such wells

should be permitted as Class VI wells. 

The final rule at §146.90(g) requires owners or operators to track the extent of the CO2 plume and

pressure front. The owner or operator must use direct methods to monitor for pressure changes in the

injection zone. Indirect methods (e.g., seismic, electrical, gravity, or electromagnetic surveys and/or

down-hole CO2 detection tools) are required unless the Director determines, based on site-specific

geology, that such methods are not appropriate.

EPA believes that pressure monitoring in the injection zone is necessary to track the development

and movement of the pressure front and CO2 plume. Monitoring can also identify needed remedial

actions, provide inputs for AoR reevaluation modeling, evaluate predictions of plume movement,

and target additional geochemical and surface monitoring needs. Knowledge of the location of the

CO2 plume and the associated pressure front will also assure the public that GS projects are

proceeding according to plan, provide sufficient information to the owner or operator and Director,

or allow for appropriate actions to address any indication that USDWs may be endangered. 

In addition to monitoring to track the movement of the CO2 plume and pressure front, EPA believes

that monitoring above the confining layer is an important part of a rigorous monitoring program and

can help detect potential breaches of the confining zone. Such monitoring can provide an early

warning that the plume or other substances may be approaching a USDW. The final rule, at

§146.90(d), requires periodic monitoring of the ground water quality and geochemical changes

above the confining zone(s). Monitoring in additional formations, e.g., the injection zone, may also

be necessary, and if the Director believes such monitoring is warranted he/she has the authority to

require that it be included in the testing and monitoring plan. EPA adds that the baseline

geochemical data required at §146.82(a)(6) will help owners or operators interpret the results of this

monitoring.

EPA acknowledges that there are potential risks associated with GS, including the potential for

leakage of CO2 or other substances into USDWs. However, the purpose of the UIC regulations

including the Class VI requirements is to protect USDWs from endangerment. In order to protect

USDWs from endangerment §144.12 prohibits the movement of fluid into USDWs. Consistent with
§144.12, EPA is finalizing the Class VI requirements in order to ensure that USDWs are protected by

minimizing and mitigating potential/identified risks through proper site characterization, well

construction, operation, monitoring, post-injection site care, and site closure. The GS rule

accomplishes this through requirements tailored to address the unique nature of GS, including the

large volumes of CO2 injected, its buoyancy and potential corrosivity in the presence of water, and

impurities in the CO2 stream. Furthermore, if any water quality monitoring of a USDW indicates the

movement of any contaminant into the underground source of drinking water, except as authorized

under part §146, the Director shall prescribe such additional requirements for construction, corrective

action, operation, monitoring, or reporting (including closure of the injection well) as are necessary

to prevent such movement.

Commenter Name: Christine Reimer Letter ID: 0142

Commenter Organization: National Ground Water Association Comment ID: 22555

Other EPA Comment Codes and Descriptions: 3820 2.3.1 Well construction procedures 

Comment: Construction 

Regardless of the site specific component the new wells will need to be designed 

to meet the overarching goals for all projects. The goals for and injection 

well will be to inject CO2 and to keep fluid from moving along the wellbore 

between formations or to the surface. The goals for a monitoring well are to 

monitor the injection or other formations and also to keep fluids from moving 

along the wellbore. To accomplish these goals the design of the well needs to 

address site-specific, objective-specific (monitoring or injection), and fluidspecific considerations. All injection wells should be cased and cemented to 

Response: EPA agrees that appropriate injection well construction will depend on site-specific

factors. In determining whether to grant a Class VI permit, the Director will evaluate the

appropriateness of the proposed injection well construction based on site-specific information about

the injection project, including injection pressures, injection and confining zone lithology, and

information about the carbon dioxide stream as provided in §146.86(b)(1). In addition to the

flexibility given to the owner and operator, Director's discretion is specifically provided in

§146.86(b)(1) for casing and cementing and §146.86(c)(2 and 3) for tubing and packer location and

type. 

EPA believes that monitoring using wells in the injection zone (i.e., that penetrate the confining

zone) can be safely performed if the wells are constructed to prevent flow between the injection zone

and USDWs or other layers above the confining zone. To mitigate the risk of fluid movement, EPA

requires owners and operators to submit a testing and monitoring plan that describes how the owner

or operator plans to site and construct monitoring wells. 

EPA has developed a brief technical paper on construction of monitoring wells that perforate the

confining zone; this paper can be found in the rulemaking docket. EPA is developing guidance on

well construction that will include recommendations for monitoring well construction. The guidance

will be available on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Christine Reimer Letter ID: 0142

Commenter Organization: National Ground Water Association Comment ID: 22557
Other EPA Comment Codes and Descriptions: 3820 2.3.1 Well construction procedures 

Comment: The materials used for construction need to be compatible with the injected 

fluid and compatible with the formation fluids. Both injection and monitoring 

wells should be constructed to the same material standard unless there is an 

objective-specific reason not to, because they may both be subjected to similar 

aggressive down-hole conditions. In order to insure that proper wellbore 

construction materials are always selected a standard should be adopted that 

specifies wellbore materials should resist the expected downhole conditions to a 

sufficient degree such that degradation will not lead to leakage. The 

thicknesses of the casing and tubing must be sufficient to handle the pressure 

associated with the injected CO2. Although materials are an important aspect in 

well construction centralization of the casing is also important for insuring 

the cement job is successful. It is very important that the casing is 

centralized over the entire cemented section. This will provide the best 

condition to achieve full radial coverage of the cement between the casing and 

the formation. 

Response: EPA agrees that well materials need to be compatible with injected fluids and formation

fluids. The GS rule at §146.86(b)(1) requires that all injection well materials be compatible with

fluids with which the materials may be expected to come into contact. Further, the rule, at

§146.82(a)(7), requires owners or operators to submit information on planned injection pressures,

that the Director will use in evaluating the proposed casing, tubing, and packer design. EPA adds

that, in determining the suitability of well materials and the design of the well, the Director must

consider various aspects of the injection project, including injection pressure, external pressure,

internal pressure and axial loading in §146.86(b)(1)(ii), corrosiveness of the CO2 stream and

formation fluids in §146.86(b)(1)(v). 

EPA requires under §146.90 that owners or operators submit proposed testing and monitoring plans

to the Director at the time of the permit application. The operator will need to demonstrate that the

monitoring wells will be constructed and operated in a manner that will be sufficiently protective of

USDWs from endangerment. Monitoring wells will differ from injection wells in their purpose,

casing sizes, and depth, although their casing and cementing will likely be similar. Unlike injection

wells, monitoring wells will not need to be built to withstand CO2 injection, but, nonetheless, will

need to be built with materials and a design that ensure integrity of the well throughout its planned

life so that the well does not serve as a conduit for movement of the CO2 stream or formation fluids.

As described above, EPA is developing guidance on testing and monitoring at GS sites, which will

discuss monitoring well construction. The guidance will be available on EPA's web site, at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Christine Reimer Letter ID: 0142

Commenter Organization: National Ground Water Association Comment ID: 22565

Comment: Monitoring, Measurement, and Verification 

Measurement, monitoring, and verification (MMV) will be a key task for all 

geologic carbon sequestration operations. MMV should be looked at as a 

continuation of the measurements that were collected during the characterization 

and construction phases as described in the sections on well construction, 

testing, and closure and geologic characterization. Characterization and 

construction measurements will provide the baseline for comparison during the 
injection and post injection phases of the sequestration project. The data 

collected during the MMV will be used to insure the site is not leaking or for 

the identification and remediation of leaks. The data will also be used to 

calibrate and reduce uncertainty in models of the site. 

During the operational injection phase of a CCS project, MMV can be broken into 

operational monitoring, which is the monitoring of the injected CO2, and 

environmental monitoring, which is the monitoring of the subsurface including 

the sequestered CO2 and the associated pressure front. 

Operational MMV includes; monitoring the volume, flow rate, and composition of 

CO2 that is injected. The injection pressure must be low enough that injection 

does not propagate new fractures and does not open existing faults or fractures 

for flow through the caprock or damage the containment properties of the 

injection well. The operational monitoring will also have to monitor the 

injection and monitoring wells to ensure they are functioning properly and not 

allowing any leakage. The integrity of the injection well must be monitored 

internally and externally to ensure that there is no degradation that could 

allow CO2 to leave the target formation. Well integrity monitoring through the 

use of logs, annulus pressure monitoring, and mechanical integrity tests is 

covered in detail in the section on well construction, monitoring and 

abandonment. 

Environmental MMV needs to be implemented to collect data from the four or more 

geologic formations that comprise the subsurface site: the storage formation, 

the primary cap rock, the monitoring formation, and the secondary cap rock. MMV 

must also provide information on shallow formations, including the lowermost 

USDW, that contain drinking water, the surface and, any potential leakage 

pathways between the storage formation or monitoring formation and any drinking 

water formations or the surface (this may include additional monitoring of wells 

above what is required for operational monitoring). 

Response: EPA agrees that multi-faceted monitoring, as described by the commenter, is a key

element of ensuring that USDWs are protected from endangerment. The GS rule, at §146.90,

requires injectate monitoring, mechanical integrity testing, corrosion monitoring, tracking the CO2

plume and area of elevated pressure, monitoring geochemical changes above the confining zone,

and, at the discretion of the Director, surface air and soil gas monitoring for CO2 fluctuations, and

any additional tests necessary to ensure USDW protection from endangerment. EPA also agrees with

the commenter that data collected during site characterization (such as baseline geochemistry, preinjection reservoir pressure, etc.) are appropriate to ensure that baseline information is available to

form the basis for comparison during GS operation and post-injection. For example, the baseline

geochemical information will allow the owner or operator and permitting authority to evaluate

monitoring data and identify any changes in subsurface geochemistry that may indicate fluid

movement.

EPA agrees that the ground water geochemical monitoring outlined in §146.90(d) will maximize

protection of USDWs from endangerment at GS sites. Direct geochemical sampling is an important

part of a monitoring program. EPA agrees that direct monitoring for ground water quality above the

confining zone is important, and the GS rule requires this at §146.90(d). Monitoring in additional

formations, e.g., the injection zone, may also be necessary, and if the Director believes such
monitoring is warranted he/she has the authority to require that it be included in the testing and

monitoring plan.

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil gas and surface air monitoring which may be required by the UIC Director

for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm. In addition, in January 2009,

DOE published a best practices manual entitled "Monitoring, Verification, and Accounting of CO2

Stored in Deep Geologic Formations" (DOE/NETL-311/081508); this manual is included in the

docket for the final GS rule.

Commenter Name: Patrick Nugent Letter ID: 0143

Commenter Organization: Texas Pipeline Association (TPA) Comment ID: 23135

Comment: 3. One-size-fits-all testing and monitoring requirements should not be 

established. The required level of testing and monitoring should be determined 

on a site-by-site basis. Imposition of an across-the-board requirement would be 

inappropriate given the variations in geologic formations, and such a 

requirement would inhibit the development and use of geologic sequestration with 

little or no corresponding environmental benefit in certain cases. Regulatory 

bodies and operators should be free to tailor monitoring techniques to the 

specific conditions at each particular site, upon a determination that the 

techniques would produce reliable data. In addition. there should be no blanket 

Response: EPA agrees with commenters and believes that flexibility is important in developing and

implementing a monitoring plan that is appropriately tailored for a specific GS site. The purpose of

the requirement at §146.90 to develop site-specific testing and monitoring plans is to ensure that the

monitoring performed at a site is appropriate for site operational conditions and the geologic setting.

EPA believes that this is the best approach for addressing potential risks at GS sites. These flexible

provisions in the monitoring requirements for Class VI wells enable the owner or operator to tailor

monitoring programs to the specific needs of each project in consultation with the Director.

The final regulation provides for flexibility in: 1) methodologies used to collect these data, 2) the

spatial resolution at which the data should be collected, and 3) how often the data should be

collected. The number and placement of monitoring wells will be based on site-specific information

such as the calculated AoR, injection rate and volume, site geology, baseline data, and the presence

of artificial penetrations within the AoR. In some instances, there may be a limited number of

options for complying with EPA's minimum requirements. For example, monitoring for geochemical

changes will require use of monitoring wells and collection of groundwater samples for chemical

analysis. Many options currently exist for complying with other requirements, such as tracking the

position of the plume and pressure front within the injection zone.

Flexibility is also provided regarding how to monitor for the specific data required by the final rule.

The testing and monitoring plan is developed by the owner or operator in consultation with the

Director and is designed to ensure that a detailed, Director-approved document describing how

monitoring will be conducted during the lifetime of the project exists. EPA is developing guidance
on testing and monitoring to assist owners or operators and Directors in evaluating requirements

under §146.90, including proposed monitoring plans. The guidance describes available technologies

and recommended approaches for implementing a testing and monitoring plan, including preoperational geophysical logging and testing of injection wells, MITs, injection well testing during

operation, groundwater quality monitoring, tracking the CO2 plume and pressure front, and soil gas

and surface air monitoring, which may be required by the UIC Director for specific GS projects. The

guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: James Devine Letter ID: 0166

Commenter Organization: United States Geological Survey (USGS) Comment ID: 21351

Other EPA Comment Codes and Descriptions: 4655 2.6.5.1 Plume tracking

techniques/geophysical methods (seeking comment) 

Comment: Section 146.90 (g), Testing and Monitoring Requirements, FR page 43540 

This section requires the owneror operator "to track the extent ofthe carbon 

dioxide plume and the position ofthe pressure front" by direct or indirect 

monitoring. Indirect, geophysical techniques include, for example, seismic, 

electrical, gravity, or electromagnetic surveys.. ." It is unclear if surface 

deformation measurement techniques, such as repeat topographic 

surveys,satellite-based elevation measurements, and tiltmeters, are included as 

acceptable indirect monitoring techniques. Surface deformation techniques are in 

use, for example, at In Salah, Algeria (Onuma et al., 2008, abstract, Detection 

of surface deformation related with CO2 injection by DInSAR at In Salah, 

Algeria, Proceedings of 33rd International Geological Congress, Oslo, Norway). 

It is suggested that the proposed regulations allow for techniques beyond the 

realm of"traditional" geophysics and techniques not yet developed. 

Response: The final rule, at §146.90(g), requires owners or operators to perform monitoring to track

the extent of the CO2 plume and pressure front. The owner or operator must use direct methods to

monitor for pressure changes in the injection zone. Indirect methods (e.g., seismic, electrical, gravity,

or electromagnetic surveys and/or down-hole CO2 detection tools) are required unless the Director

determines, based on site-specific geology that such methods are not appropriate. EPA is affording

Director's discretion regarding the use of geophysical techniques at some sites because the Agency

recognizes that geophysical methods are not appropriate in all geologic settings. EPA clarifies that

this determination will be made by the Director based on the site-specific geologic information

submitted by the owner or operator with the permit application. 

EPA is not prescribing that deformation measurement techniques be used. However, if the owner or

operator believes they would enhance the monitoring regime, they may be proposed in the testing

and monitoring plan. Likewise, if the Director had reason to believe such methods are necessary to

ensure protection of USDWs, he/she is afforded discretion to require the use of additional

monitoring techniques at §146.90(i). 

EPA believes that this approach provides flexibility to develop a site-specific monitoring plan,

ensures that direct monitoring is available to track the movement of the CO2 and validate models,

and recognizes that indirect techniques are not appropriate in all situations. The owner or operator's

approved testing and monitoring plan will include the site-specific details, technologies, testing and

monitoring frequencies, and other pertinent information.
EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil gas and surface air monitoring which may be required by the UIC Director

for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm. In addition, in January 2009,

DOE published a best practices manual entitled "Monitoring, Verification, and Accounting of CO2

Stored in Deep Geologic Formations" (DOE/NETL-311/081508); this manual is included in the

docket for the final GS rule.

Commenter Name: Michael Mudd Letter ID: 0167

Commenter Organization: FutureGen Alliance (FGIA) Comment ID: 22458

Other EPA Comment Codes and Descriptions: 3300 2.2.1 Delineating the AoR/Modeling CO2

movement 

Comment: Area of Review (AoR) and Area of Monitoring (AoM) 

p. 43493, c. 2 The Proposed Rule defines Area of Review (AoR) as "The region 

surrounding the geologic sequestration project that may be impacted by the 

injection activity". The area of review is based on computational modeling that 

accounts for the physical and chemical properties of all phases of the injected 

carbon dioxide stream. 

The proposed regulation uses the Area of Review (AoR) for defining both 

monitoring requirements and corrective actions: 

p. 43499, c. 1 Area of Review (AoR) and Corrective Action: The Agency requires 

examination of both the vertical and horizontal extent of the area that will 

potentially be influenced by injection and storage activities and identification 

of all artificial penetrations in the area that may act as conduits for fluid 

movement into USDWs (e.g., active and abandoned wells) and, as needed, perform 

corrective action to these open wells (i.e., artificial penetrations). 

p. 43539, c. 3 (d)(2) The monitoring frequency and spatial distribution of 

monitoring wells must be based on baseline geochemical data that has been 

collected under §146.82(a)(6) and any modeling results in the area of review 

evaluation required by §146.84(b); 

Comment: 

- EPA should define two regulatory regions surrounding the geologic 

sequestration project and provide specific definitions for those regions; 1) 

Area of Monitoring (AoM) and 2) Area of Review; where the AoM is used to define 

the spatial distribution of monitoring wells and the AoR is used to define the 

limit of Corrective Action: 

- Area of Monitoring (AoM): The region surrounding the geologic sequestration 
project that contains 95% of the carbon dioxide mass. The area of monitoring is 

based on monitoring data and computational modeling that accounts for the 

physical and chemical properties of all phases of the injected carbon dioxide 

stream. In the absence of monitoring data, the area of monitoring is based on 

computational modeling. 

- Area of Review (AoR): The region surrounding the geologic sequestration 

reservoir that has or is indicated to develop pressures that are greater than 

10% different from the pre-injection formation fluid pressure, but no less than 

the Area of Monitoring. The area of review is based on monitoring data and 

computational modeling that accounts for the physical and chemical properties of 

all phases of the injected carbon dioxide stream. In the absence of monitoring 

data, the area of review is based on computational modeling. 

• The proposed definitions of AoM and AoR have several important components: 

- The AoM has a mass-based definition. 

- The AoR has a pressure-differential-based definition. 

- The AoR is never smaller than the AoM. 

- The AoR and AoM may be asymmetrical around the injection well(s). 

- The AoR and AoM may vary over time. 

- The carbon dioxide mass should be determined using a combination of monitoring 

data and computational modeling. 

- Pressure differentials are based on equilibrium hydrostatic conditions. 

Relative to existing UIC regulations governing waste disposal, EPA is 

introducing fundamentally new concepts for defining the area of review (AoR) for 

CO2 injection. The newly proposed concept is flawed and will pose an 

unjustifiable barrier to CO2 injection projects unless the approach for defining 

the AoR is addressed in the regulation. It is neither possible, nor practical, 

to predict where every molecule of CO2 will migrate; therefore, a threshold 

levels are required. In the case of large-scale injection projects, changes in 

formation pressures could be expected dozens to hundreds of miles from the 

injection well. It would not be practical for the AoR to comprise the entire 

area experiencing changes in formation pressure. A reasonable threshold for 

establishing the AoM might be where pressure changes are greater than 10% of the 

standard formation pressure. 

The proposed regulation defines the Area of Review (AoR) as being the region 

that may be impacted by the injection activity, without defining or quantifying 

impact. To be useful the bounding areas for corrective actions and monitoring 

activities must have specific definitions. Under deep geologic sequestration 

conditions the injected fluid (i.e., supercritical CO2) has low compressibility, 

the displaced fluid (i.e., brine) has low compressibility, and the reservoir 
formation (e.g., sandstone) generally has low compressibility, all of which 

suggest that the impact (i.e., pressure change) of the injection activity could 

be detected at great distances from the injection well(s). 

Injection of CO2 into deep saline formations is driven by differences between 

the well injection pressure and formation pressure. To avoid inducing fractures 

or opening existing fractures in the formation and caprock, well injection 

pressure will be limited to some fraction below the fracturing pressure. As 

CO2 migrates into the formation the formation pressure increases around the 

injection well. The pressure distribution in the formation around the injection 

well depends on the formation properties, structure, and injection rate. 

Injection formations will be required to be confined vertically and/or 

horizontally to prevent the vertical migration of injected fluids and saline 

reservoir fluids into USDWs. 

Confined formations (e.g., a caprock overlying a horizontally extensive 

formation) allow the formation fluid to be displaced laterally by the injected 

fluid. Injecting CO2 will result in elevated pressures both inside and beyond 

the CO2 plume. Elevated pressures within the CO2 plume have the potential to 

force CO2 and formation fluid through permeable wells, fractures, or faults that 

penetrate the formation. Elevated pressures outside the CO2 plume have the 

potential to force formation fluid through permeable wells, fractures or faults 

that penetrate the formation. The higher the formation pressure is above the 

ambient formation pressure, the greater the potential for CO2 and formation 

fluid to leak through permeable wells, fractures, and faults. The lateral 

pressure distribution is a function of the injection rate and the lateral 

distribution of formation permeability. When CO2 injection is halted, elevated 

pressures decay over time as the injected and formation fluids migrate away from 

the injection well(s). 

The proposed regulations define an AoR and Corrective Action as being an area 

within which artificial penetrations may act as conduits for fluid movement into 

USDWs (e.g., active and abandoned wells) and, as needed, require the applicant 

to perform corrective action to seal these open wells. The potential for fluid 

movement into USDWs from the injection of CO2 into the injection formation is 

correlated with the area of elevated formation pressure, which is usually larger 

than the area that contains the injected CO2 mass. For confined formations, this 

area is defined by the lateral pressure distribution around the injection 

well(s). 

Response: EPA believes that, while the commenter offers different terminology for the AoR and the

area to be monitored, the GS rule addresses the commenter's suggestions. Notably, the owner or

operator is required (under 146.90) to develop and implement a testing and monitoring plan for each

GS project that must consider the delineated AoR that includes both the CO2 plume and associated

pressure front and incorporates many of the attributes suggested by the commenter. EPA clarifies

that delineation of the AoR, as required at 146.84(c), must account for the physical and chemical

properties of all phases of the injected CO2 stream, based on available site characterization,

monitoring, and operational data. 

Furthermore, any changes to the AoR would necessitate a review of and potential change in the
testing and monitoring plan, consistent with the commenter's assertion that the AoR may vary over

time. The final GS regulation includes a requirement at 146.84(e) that the AoR be reevaluated at

least every 5 years, and also requires that the owner or operator review the AoR and corrective

action, testing and monitoring, and emergency and remedial response plans within one year of an

AoR reevaluation (as well as following significant changes to the facility, or when required by the

Director). The relationship between the AoR reevaluation and the testing and monitoring plan should

allow for considerations suggested by the commenter. 

EPA believes that by linking development and review of the testing and monitoring plan to the AoR

evaluation and reevaluation process, the GS rule, in effect, incorporates and addresses many of the

commenter's considerations for an area of monitoring.

Commenter Name: Theresa Pugh Letter ID: 0169

Commenter Organization: American Public Power Association Comment ID: 23373

Comment: Monitoring -- Pg. 46 

APPA believes it makes common sense to place monitors close enough to detect 

the leak before it can negatively affect the USDW. 

Response: Regarding monitoring locations, section §146.90(d) requires periodic monitoring of the

ground water quality and geochemical changes above the confining zone(s). EPA clarifies that this

monitoring requirement does not include the confining layer itself. Monitoring above the confining

layer will provide an indication of upward movement of CO2 that might endanger a USDW. In

addition, the final GS regulation, at §146.90(g)(1), requires all GS project owners or operators to

monitor for pressure changes in the injection zone. Monitoring of pressure in the injection zone gives

even greater advance warning of fluid movement that could potentially affect impact USDWs. The

exact number and location of monitoring locations to be tested will, however, be based on sitespecific characteristics and vulnerabilities and described in the Director-approved testing and

monitoring plan.

The GS rule stipulates that the monitoring frequency and spatial distribution of monitoring wells

must be based on baseline geochemical data that were collected during the initial site

characterization and the area of review evaluation, at §146.90(d)(2). The details of the geochemical

monitoring will be based on site-specific information and described in the Director-approved testing

and monitoring plan.

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil gas and surface air monitoring, which may be required by the UIC Director

for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Theresa Pugh Letter ID: 0169

Commenter Organization: American Public Power Association Comment ID: 23432

Comment: Monitoring 
APPA does not have great expertise in monitoring in GS commercial settings. 

However, it makes common sense to place monitors close enough to detect the leak 

before it can negatively affect the USDW. APPA realizes that some local 

jurisdictions may require surface monitoring or that OSHA may require surface 

monitoring for safety purposes. However, we doubt that surface monitoring would 

do much to protect USDWs. 

Response: Baseline characterization of the site, including the geochemical data and initial modeling,

will be highly valuable in selection of monitoring well locations and in refining plans for monitoring

frequency. The GS rule stipulates that the monitoring frequency and spatial distribution of

monitoring wells must be based on baseline geochemical data that were collected during the initial

site characterization and the area of review evaluation at §146.90(d)(2). The details of the

geochemical monitoring will be based on site-specific information and described in the Directorapproved testing and monitoring plan.

The Agency believes that surface air and soil gas monitoring, when coupled with subsurface

monitoring, may be appropriate at some GS projects to ensure USDW protection. EPA also

acknowledges that surface air and soil gas measurements are subject to variability and may not be

suitable in all settings as a method to ensure USDW protection. However, EPA does not believe that

this should entirely preclude their use. The decision to use surface monitoring and the selection of

monitoring methods will be site-specific (e.g., may be influenced by geology, injection depth, and

operational conditions) and must be based on potential risks to USDWs within the AoR.

Commenter Name: Kyle Isakower Letter ID: 0170

Commenter Organization: American Petroleum Institute Comment ID: 24188

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Rule Provision: 146.90(b) 

API Comments: (b) Installation and use, except during well workovers as defined 

in §146.868(d), of continuous recording MONITORING devices (INCLUDING DIGITAL 

DEVICES CAPTURING PERIODIC DATA) to monitor injection pressure, rate and volume; 

AND RECORD AT LEAST DAILY the pressure on the annulus between the tubing and the 

long string casing; and the annulus fluid volume;

Rationale: §146.86(d) does not exist; perhaps §146.88(d) is what was apparently 

intended. 

There is concern regarding what constitutes continuous monitoring. Industry 

agrees that regular monitoring of the parameters identified by EPA is 

appropriate. Our experience with CO2 EOR strongly shows that daily monitoring of 

most of these parameters is adequate (exceptions to this would be on a sitespecific basis). Recording should generally be done on a daily basis and 

reporting on a semi-annually basis. 

Response: EPA believes that a monitoring regime that includes continuous pressure monitoring of

GS wells, as required at §146.88(e), is important and appropriate because the potentially corrosive

nature of CO2 streams in the presence of water makes it critical to immediately identify corrosion-
related well mechanical integrity loss. 

Regarding the question of what constitutes continuous monitoring, EPA expects that Class VI

injection wells under §146.88(e) will be equipped with dedicated computer-based continuous

pressure monitoring devices (in concert with the Director-approved shut-off systems required for GS

wells), which typically take readings several times per second and record them electronically in a

computer system. EPA did not specify the types of devices in the final rule, however.

EPA adds that the final GS rule references §146.88(e), as the commenter suggests.

Commenter Name: Kyle Isakower Letter ID: 0170

Commenter Organization: American Petroleum Institute Comment ID: 24193

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Rule Provision: 149.90(e) - (f) 

API Comments: (e) A demonstration of external mechanical integrity pursuant to 

§146.89(c) at least once per year UNTIL THE WELL IS PLUGGED; 

(f) IF CONDITIONS WARRANT, A pressure fall-off test OR OTHER EQUIVALENT TEST 

THAT IDENTIFIES RESERVOIR CONDITIONS WITH RESPECT TO FLOW DYNAMICS at

least once 

every five years unless more frequent testing is required by the Director based 

on site specific information; 

Rationale: Technical clarifications. 

Response: Regarding pressure testing, EPA believes that pressure fall-off testing is necessary for GS

wells. Pressure fall-off tests are designed to verify that modeled projections of reservoir pressure

decline agree with measured pressure decline profiles. These tests can be useful in AoR calculations

and reevaluations and may also indicate mischaracterization of site geology and the presence of

leakage pathways. Therefore, EPA is requiring that pressure fall-off testing be conducted every five

years at a minimum, and the final GS regulation includes this requirement at §146.90(f). Pressure

fall-off tests may be conducted in conjunction with other well performance tests (i.e., mechanical

integrity testing) to ensure safe and effective operations. EPA disagrees that the rule should provide

specifics of the test at the degree suggested, however.

Based on its evaluation of all public comments and input on the proposed rule and NODA and

Request for Comment, EPA has made many revisions to the GS Rule. See the final rule and

preamble for further discussion on EPA's final approach.

Commenter Name: James Rower Letter ID: 0173

Commenter Organization: Utility Solid Waste Activities Group (USWAG) Comment ID: 23498

Comment: Plume and pressure front monitoring - USWAG appreciates the importance of 

accurate monitoring of the subsurface extent of the plume and pressure front. 

Id. at 43514. We believe, however, that over time constant monitoring may prove 

unnecessary as more information is gained regarding the accuracy of initial 

modeling. Any requirements for plume and pressure front modeling in the Final 

Rule should be flexible enough to adjust in the coming years as industry and 
regulators become more knowledgeable regarding the reliability of the modeling 

techniques initially used. 

Response: EPA agrees that flexibility is appropriate, and clarifies that the specific plume and

pressure front monitoring requirements will be established in the monitoring and testing plan

submitted by the owner or operator along with the permit application. EPA believes that the

monitoring requirements for GS sites at §146.90 provide an appropriate level of flexibility in

structuring a testing and monitoring plan that protects USDWs from endangerment. 

In addition, EPA is using an adaptive approach to regulating GS. EPA will collect and review

project data on early GS projects to determine whether the appropriate amount and types of

information and appropriate documentation are required and being collected. The Agency will

evaluate the information and determine if modifications to the requirements are necessary.

EPA believes that this approach provides flexibility to develop a site-specific monitoring plan,

ensures that direct monitoring is available to track movement of the CO2 and validate models, and

recognizes that indirect techniques are not appropriate in all situations. The owner or operator's

approved testing and monitoring plan will include the site-specific details, technologies, testing and

monitoring frequencies, and other pertinent information.

Pressure monitoring in the injection zone is necessary to track the development and movement of the

pressure front and CO2 plume. When combined with information on temperature, pressure data

provide an indication of the phase (e.g., gas, supercritical) and distribution of the injected CO2 (73

FR 43515). Monitoring can also identify needed remedial actions, provide inputs for AoR

reevaluation modeling, evaluate predictions of plume movement, and target additional geochemical

and surface monitoring needs.

Commenter Name: Kenneth Nemeth Letter ID: 0176

Commenter Organization: Southern States Energy Board Comment ID: 23542

Comment: Regarding specific points, we concur with the establishment of a threshold of a 

seabed up to three miles offshore, but no farther, and we support a requirement 

that the project operator should be able to demonstrate that the CO2 is 

contained within the storage zone. We do not support the need to monitor the 

exact location with in-zone monitoring wells, the CO2 plume, or displace brine 

pressure front. CO2 monitoring should be fit for purpose. Air and soil gas 

Response: EPA agrees that the owner or operator should be able to demonstrate that CO2 is

contained within the injection zone. For this reason, the final rule, at §146.90(g) requires owners or

operators to perform CO2 plume and pressure front tracking.

The final rule, at §146.90(g), requires owners or operators to perform monitoring to track the extent

of the CO2 plume and pressure front. The owner or operator must use direct methods to monitor for

pressure changes in the injection zone. Indirect methods (e.g., seismic, electrical, gravity, or

electromagnetic surveys and/or down-hole CO2 detection tools) are required unless the Director

determines, based on site-specific geology that such methods are not appropriate. 

Pressure monitoring in the injection zone is necessary to track the development and movement of the

pressure front and CO2 plume. When combined with information on temperature, pressure data

provide an indication of the phase (e.g., gas, supercritical) and distribution of the injected CO2 (73
FR 43515). Monitoring can also identify needed remedial actions, provide inputs for AoR

reevaluation modeling, evaluate predictions of plume movement, and target additional geochemical

and surface monitoring needs.

EPA disagrees that knowing the location of the plume and pressure front is unnecessary; plume

tracking and pressure monitoring are key components of monitoring at GS sites. A rigorous plume

tracking and pressure monitoring scheme, such as one that meets the requirements at §146.90(g), is

imperative for ensuring that the CO2 plume is contained within the injection zone. 

EPA clarifies that the limitation of the Class VI requirements not applying beyond the three-mile

limit offshore reflects the UIC program's authority under SDWA. See the preamble for additional

information about sub-seabed sequestration.

Commenter Name: Frederick R. Eames Letter ID: 0178

Commenter Organization: CCS Alliance Comment ID: 23871

Comment: F. PLUME AND PRESSURE FRONT MONITORING REQUIREMENT 

EPA proposes monitoring sequestration sites to track the location of the CO2 

plume and associated pressure front over time. Plume monitoring is important to 

the long-term stability of CCS sites. However, we submit that such a requirement 

should be flexible to accommodate growing knowledge about injection and CO2 

plumes. Monitoring has limited usefulness in some settings (e.g., 4D seismic 

often does not have the resolution to detect CO2 in some deep or complex 

settings or where hydrocarbon gases are present). Moreover, data gathering 

requirements related to plume tracking and testing should not unduly burden 

owners or operators, either in time or cost, and should be essential to 

evaluation of the plume's stability and safety. 

Response: EPA agrees with commenters on the importance of monitoring at GS sites and

emphasizes that monitoring of injection activities will be an important component of every GS

project. Monitoring associated with injection wells and the movement of the CO2 plume is necessary

to verify that the injectate is confined in the target formations and does not endanger USDWs.

EPA agrees with commenters that flexibility is important in developing and implementing a

monitoring plan that is appropriately tailored for a specific GS site. The purpose of the requirement

at §146.90 to develop site-specific testing and monitoring plans is to ensure that the monitoring

performed at a site is appropriate for site operational conditions and the geologic setting. EPA

believes that this is the best approach for addressing potential risks at GS sites. These flexible

provisions in the monitoring requirements for Class VI wells enable the owner or operator to tailor

monitoring programs to the specific needs of each project in consultation with the Director.

EPA agrees that seismic monitoring is not applicable to all sites. The final rule, at §146.90(g),

requires owners or operators to perform monitoring to track the extent of the CO2 plume and

pressure front. The owner or operator must use direct methods to monitor for pressure changes in the

injection zone. Indirect methods (e.g., seismic, electrical, gravity, or electromagnetic surveys and/or

down-hole CO2 detection tools) are required unless the Director determines, based on site-specific

geology that such methods are not appropriate.

EPA is affording Director's discretion regarding the use of geophysical techniques at some sites
because the Agency recognizes that geophysical methods are not appropriate in all geologic settings.

For example, geophysical methods are difficult to execute in areas that are structurally and

topographically complex or where lithologies have limited contrast in density, porosity,

permeability, and other physical properties. EPA clarifies that this determination will be made by the

Director based on the site-specific geologic information submitted by the owner or operator with

their permit application.

Commenter Name: Thomas Curtis Letter ID: 0181

Commenter Organization: American Water Works Association (AWWA) Comment ID: 23655

Comment: In its comments, AWWA makes several recommendations for the following specific 

items to be included in the final regulation: 

- Inclusion of detailed monitoring requirements in the final regulation; 

Response: EPA disagrees that the rule should specify the monitoring techniques for all GS sites.

EPA believes that flexibility is important in developing and implementing a monitoring plan that is

appropriately tailored for a specific GS site. The purpose of the requirement at §146.90 to develop

site-specific testing and monitoring plans is to ensure that the monitoring performed at a site is

appropriate for site operational conditions and the geologic setting. EPA believes that this is the best

approach for addressing potential risks at GS sites. These flexible provisions in the monitoring

requirements for Class VI wells enable the owner or operator to tailor monitoring programs to the

specific needs of each project in consultation with the Director.

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil gas and surface air monitoring which may be required by the UIC Director

for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm. In addition, in January 2009,

DOE published a best practices manual entitled "Monitoring, Verification, and Accounting of CO2

Stored in Deep Geologic Formations" (DOE/NETL-311/081508); this manual is included in the

docket for the final GS rule.

Commenter Name: Thomas Curtis Letter ID: 0181

Commenter Organization: American Water Works Association (AWWA) Comment ID: 23696

Other EPA Comment Codes and Descriptions: 4500 2.5 Proposed Mechanical Integrity Testing

(MIT) Requirements (40 CFR 146.89) 

Comment: Category: Monitoring 

EPA Request for Comment: EPA’s proposal would require owners or operators of 

Class VI GS projects to monitor internal mechanical integrity of their injection 

wells by continuously monitoring injection pressure, flow rate, and injected 

volumes, as well as the annular pressure and fluid volume to assure that no 

anomalies occur that may indicate an internal leak. EPA requests comment on the 

practicability of this requirement. EPA Notice 43513. 
EPA seeks comment on the appropriate frequency of internal and external MITs for 

GS injection wells, the appropriate types of MITs, and how to optimize MIT 

methods for GS. EPA Notice 43514. 

EPA seeks comment on the requirement for monitoring of GS sites for the purpose 

of tracking the location of the CO2 plume and associated pressure front over 

time. EPA Notice 43514 

EPA’s proposal would require that owners or operators perform a pressure falloff test at least once every five years. EPA seeks comment on the use and 

frequency of pressure fall-off testing for GS wells. EPA Notice 43515. 

Specifically, EPA seeks comment regarding the usefulness of indirect geophysical 

monitoring and surface air and soil gas monitoring. In addition, EPA seeks 

comment regarding the use of a Director-approved monitoring plan for GS sites. 

EPA Notice 43517. 

AWWA Response: Detailed monitoring guidelines were developed as part of a joint 

research project by AwwaRF and AWWA. These guidelines are provided in Section 

III of these comments and EPA should include the named tests and frequencies in 

the final regulation to ensure that protection of USDWs is consistent across all 

geologic sequestration projects. Based upon these requirements, owner/operators 

would develop testing and monitoring plans, which should be reviewed and updated 

at the same time as the re-evaluation of the Area of Review. The costs 

associated with monitoring of a sequestration project should not be a major 

consideration when determining the types and frequency of required monitoring. 

The goal of the monitoring requirements should be on preventing degradation of 

USDWs, not minimizing the cost to the owner/operator. 

AWWA strongly recommends both that both internal and external mechanical 

integrity testing should be required to prevent leakage of carbon dioxide from 

the injection well. Monitoring of the plume and pressure front over time is 

absolutely required as part of the system operation and a project shouldn't even 

be considered unless this monitoring is included. All of the monitoring 

Response: EPA agrees with the commenter; the final rule requires both internal and external

mechanical integrity testing. Mechanical integrity testing is one of the cornerstones of the existing

EPA UIC program. MIT requirements at §146.89 ensure protection of USDWs from endangerment

and provide an important early warning of potential problems in the injection well. Routine

mechanical integrity testing of injection wells provides data that enables the identification and

remediation of well integrity problems before they lead to leakage and/or endangerment of USDWs.

The GS rule's requirements for MITs encompass many of the same tests mentioned in the AwwaRF

and AWWA monitoring guidelines, including an approved tracer log, or noise logs and temperature

logs. EPA believes that the MITs described in the rule at §146.89(c) are effective methods to

demonstrate external MI. They have been used successfully by injection well operators for decades

and provide an important early warning of potential problems in the injection well system. While the

oxygen activation log is not explicitly required in the rule, the regulations do provide flexibility at

§146.89(e) to allow the Director to require additional test methods or, with the approval of the

Administrator, to approve the use of alternative MIT methods. These additional methods could
include the annual pressure test recommended in the AwwaRF/AWWA guidelines. The specific

MITs required prior to start-up of injection or at well workovers would be identified in the permit by

the Director. For additional information, please see the discussion of MITs in the final rule preamble.

As stated above, EPA disagrees that the rule should specify the monitoring techniques for all GS

sites. 

EPA agrees that tracking the plume and the position of the pressure front during injection operations

and the post-injection site care period will provide important data for determining that the injectate is

confined within the target formation, as well as for evaluating any risks within the AoR. EPA also

agrees with the commenter that data collected during site characterization (such as baseline

geochemistry, pre-injection reservoir pressure, etc.) are appropriate to ensure that there is a baseline

with which to compare GS operation and post-injection data. 

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes recommended approaches for implementing a testing and monitoring plan, including preoperational geophysical logging and testing of injection wells, MITs, injection well testing during

operation, groundwater quality monitoring, tracking the CO2 plume and pressure front, and soil gas

and surface air monitoring which may be required by the UIC Director for specific GS projects. The

guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm. In addition, in January 2009,

DOE published a best practices manual entitled "Monitoring, Verification, and Accounting of CO2

Stored in Deep Geologic Formations" (DOE/NETL-311/081508); this manual is included in the

docket for the final GS rule. 

EPA also agrees that periodic updates to the plan are appropriate. EPA clarifies that the final GS

regulation includes a requirement that the AoR be reevaluated every 5 years, and it specifies at

§146.90(j) that the operator revise the testing and monitoring plan to incorporate the results of the

most recent AoR reevaluation and recent operational and monitoring data.

EPA clarifies that cost-benefit analyses are not used to determine the most appropriate monitoring

technologies, location, or frequency. Instead, the Agency believes that the flexibility afforded the

owner or operator at §146.90 to develop a testing and monitoring plan tailored to site-specific

characteristics is appropriate for GS.

Commenter Name: Thomas Curtis Letter ID: 0181

Commenter Organization: American Water Works Association (AWWA) Comment ID: 24339

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Part 146.90(d)(1) AWWA recommends revising this part to read: 

The location and number of monitoring wells must be based on specific 

information about the geologic sequestration project, including injection rate 

and volume, geology, the presence of natural discontinuities and artificial 

penetrations and other factors. 

Response: Based on its evaluation of all public comments and input on the proposed rule and

NODA and Request for Comment EPA has made many revisions to the GS rule. See the final rule
and preamble for further discussion on EPA's final approach.

EPA's guidance on testing and monitoring will provide guidance on monitoring well placement. The

guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Wendy Jacobs Letter ID: 0183

Commenter Organization: Harvard Law School Environmental Law and Policy

Center

Comment ID:

25140

Comment: impurities) that can compromise the structure of the well and result in leaks of

stored CO2. ELPC and ETIP laud other precautionary measures required in the

proposed regulation, including down-hole shut off valves, continuous and

frequent monitoring of the integrity of the internal and external portions of

the well, tracking the plume and pressure front, and detailed electronic record

keeping. Id. at 43,511, 43,538-40 (proposed 40 C.F.R. §§ 146.88-.91). The

Response: EPA agrees with commenters on the importance of monitoring at GS sites, including

continuous monitoring and MITs. EPA emphasizes that monitoring of injection activities will be an

important component of every GS project. Monitoring (and related reporting and recordkeeping)

associated with injection wells and the movement of the CO2 plume is necessary to verify that the

injectate is confined in the target formations and does not endanger USDWs. 

After evaluating the risks and benefits of down-hole shut-off systems and considering additional

research, EPA will not require automatic down-hole shut-off devices for onshore Class VI wells.

Instead, the final rule, at §146.88(e)(2), requires that owners or operators of onshore Class VI wells

install automatic surface shut-off devices. The rule affords Director's discretion to mandate

automatic down-hole shut-off devices in onshore situations that may warrant their use. EPA believes

that requiring the installation of automatic surface shut-off devices for onshore wells (and affording

Director's discretion to require down-hole devices where necessary) ensures that proper precautions

are taken to prevent subsurface fluid movement and ensure protection of USDWs, human health, and

the environment.

Additionally, the GS rule, at §146.88(e)(3), requires the installation of down-hole shut-off devices

for Class VI wells located in the offshore submerged lands within the jurisdiction of a State UIC

program. The Agency believes that the unique construction and operational conditions for offshore

Class VI wells, including isolation from shorelines and the need to construct wells through the water

column and the subsurface, may delay response time in the event of well difficulties. These

conditions merit requiring automatic down-hole shut-off devices for offshore wells in the submerged

lands of a State. 

EPA believes that requiring the installation of automatic surface shut-off devices for onshore wells

(and affording Director's discretion to require down-hole devices where necessary) ensures that

proper precautions are taken to prevent subsurface fluid movement and ensure protection of USDWs,

human health, and the environment.

Commenter Name: Bradley J. Field Letter ID: 0186

Commenter Organization: New York State Dept. of Environmental Conservation

Div. of Mineral Resources

Comment ID:

25204
Other EPA Comment Codes and Descriptions: 4760 2.7.6 Proposed reporting frequency (seeking

comment) 

Comment: FF. EPA seeks comment on the appropriate amount and types of monitoring that should 

be conducted at a GS site. 

NYSDEC-DMN Response: NYSDEC-DMN agrees with EPA’s proposal to require operators 

to report semi- annually on the characteristics of injection fluids, injection 

pressure, flow rate, temperature, volume and annular pressure, and on the 

results of MITs, ground water monitoring, and any required atmospheric/soil gas 

monitoring. However, the amount and types of monitoring to be required should be 

site specific. 

Response: EPA agrees that monitoring plans and methods need to be site-specific and believes that

the monitoring requirements for GS sites at §146.90 provide an appropriate level of flexibility in

structuring a testing and monitoring plan that protects USDWs from endangerment. 

The final regulation provides for flexibility in: 1) methodologies used to collect these data, 2) the

spatial resolution at which the data should be collected, and 3) how often the data should be

collected. The number and placement of monitoring wells will be based on site-specific information

such as the calculated AoR, injection rate and volume, site geology, baseline data, and the presence

of artificial penetrations within the AoR. In some instances, there may be a limited number of

options for complying with EPA's minimum requirements. For example, monitoring for geochemical

changes will require use of monitoring wells and collection of groundwater samples for chemical

analysis. Many options currently exist for complying with other requirements, such as tracking the

position of the plume and pressure front within the injection zone.

Flexibility is also provided regarding how to monitor for the specific data required by the final rule.

The testing and monitoring plan is developed by the owner or operator in consultation with the

Director and is designed to ensure that a detailed, Director-approved document describing how

monitoring will be conducted during the lifetime of the project exists. EPA is developing guidance

on testing and monitoring to assist owners or operators and Directors in evaluating requirements

under §146.90, including proposed monitoring plans. The guidance describes available technologies

and recommended approaches for implementing a testing and monitoring plan, including preoperational geophysical logging and testing of injection wells, MITs, injection well testing during

operation, groundwater quality monitoring, tracking the CO2 plume and pressure front, and soil gas

and surface air monitoring which may be required by the UIC Director for specific GS projects.

EPA is retaining the semi-annual reporting requirements as proposed at §146.91(a). These

requirements ensure the Director has the information needed to take preventive action in a timely

manner to protect USDWs from endangerment. EPA notes that operators who want to streamline

their reporting schedules can negotiate with the permitting authority to establish a schedule that

allows reporting on all wells in a GS project at the same time; however, data for each well must be

reported separately and at least as frequently as required at §146.91. For additional information,

please see the final rule and the preamble for a discussion of EPA's final approach to recordkeeping

and reporting.

EPA agrees that some monitoring types and frequencies (e.g., associated with ground water

monitoring and plume tracking) will be site-specific. These activities must be established in the

approved testing and monitoring plan, which will be incorporated as a condition of the Class VI

permit.
Commenter Name: Daniel Plath Letter ID: 0188

Commenter Organization: NiSource, Inc. Comment ID: 25230

Comment: aspects. The following points summarize four primary lessons learned through 

operation of natural gas storage that would be applicable to GS: 

2. NiSource's Columbia subsidiary has performed many of the pre-activation and 

monitoring, measuring and verification (MMV) activities EPA discusses. While 

these technologies are useful, a number are primarily applicable to the initial 

development of a new field or as niche diagnostic tools for specific problems. 

Applying a large number of MMV techniques is appropriate for pilot projects 

though it is rarely a best practice for an established commercial application 

where the historical risks are well known and where there are practical limits 

on staff's time, budgets and other resources. Ultimately, the cost of GS will be 

passed on to electric customers and government regulations need to provide a 

balanced perspective. 

Response: EPA agrees with commenters and believes that flexibility is important in developing and

implementing a monitoring plan that is appropriately tailored for a specific GS site. The purpose of

the requirement at §146.90 to develop site-specific testing and monitoring plans is to ensure that the

monitoring performed at a site is appropriate for site operational conditions and the geologic setting.

EPA believes that this is the best approach for addressing potential risks at GS sites. These flexible

provisions in the monitoring requirements for Class VI wells enable the owner or operator to tailor

monitoring programs to the specific needs of each project in consultation with the Director.

The final regulation provides for flexibility in: 1) methodologies used to collect these data, 2) the

spatial resolution at which the data should be collected, and 3) how often the data should be

collected. The number and placement of monitoring wells will be based on site-specific information

such as the calculated AoR, injection rate and volume, site geology, baseline data, and the presence

of artificial penetrations within the AoR. In some instances, there may be a limited number of

options for complying with EPA's minimum requirements. For example, monitoring for geochemical

changes will require use of monitoring wells and collection of groundwater samples for chemical

analysis. Many options currently exist for complying with other requirements, such as tracking the

position of the plume and pressure front within the injection zone.

Flexibility is also provided regarding how to monitor for the specific data required by the final rule.

The testing and monitoring plan is developed by the owner or operator in consultation with the

Director and is designed to ensure that a detailed, Director-approved document describing how

monitoring will be conducted during the lifetime of the project exists. EPA is developing guidance

on testing and monitoring to assist owners or operators and Directors in evaluating requirements

under §146.90, including proposed monitoring plans. The guidance describes available technologies

and recommended approaches for implementing a testing and monitoring plan, including preoperational geophysical logging and testing of injection wells, MITs, injection well testing during

operation, groundwater quality monitoring, tracking the CO2 plume and pressure front, and soil gas

and surface air monitoring which may be required by the UIC Director for specific GS projects.

Commenter Name: Robert F. Van Voorhees Letter ID: 0190

Commenter Organization: Carbon Sequestration Council Comment ID: 24479

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule
language 

Comment: Rule Provision: 146.90(a) & (b) 

Proposed CCS Group Recommendations: (B) THE TESTING AND MONITORING PLAN MUST,

AT 

A MINIMUM, INCLUDE: 

(a) (1) analysis of the carbon dioxide stream with sufficient frequency to 

yield data representative of its chemical and physical characteristics; 

(b) (2) Installation and use, except during well workovers as defined in 

section 146.88(d), of continuous monitoring devices (INCLUDING DIGITAL DEVICES 

CAPTURING PERIODIC DATA) to monitor injection pressure, rate and volume; AND 

RECORD AT LEAST DAILY the pressure on the annulus between the tubing and the 

long strong casing; 

(3) A DEMONSTRATION OF EXTERNAL MECHANICAL INTEGRITY PURSUANT TO

§146.89(C) 

UNTIL THE WELL IS PLUGGED; 

(4) MONITORING OF THE PRESSURE BUILDUP IN THE INJECTION ZONE ANNUALLY,

INCLUDING 

AT A MINIMUM, A SHUT DOWN OF THE WELL FOR A TIME SUFFICIENT TO CONDUCT

A VALID 

OBSERVATION OF THE PRESSURE FALL-OFF CURVE AT LEAST ONCE EVERY FIVE

YEARS; AND 

(5) A QUALITY ASSURANCE PLAN FOR ALL TESTING AND MONITORING

REQUIREMENTS. 

Basis for CCS Group Comments: There is concern regarding what constitutes 

continuous monitoring. Industry agrees that regular monitoring of the parameters 

identified by EPA is appropriate. Experience with CO2 EOR strongly shows that 

daily monitoring of most of these parameters is adequate (exceptions to this 

would be on a site-specific basis). Recording should generally be done on a 

daily basis and reporting on a semi-annual basis. 

Response: EPA believes that continuous pressure monitoring of GS wells, as required at §146.88(e),

is important and appropriate because the potentially corrosive nature of CO2 streams in the presence

of water makes it critical to immediately identify corrosion-related well mechanical integrity loss.

Class VI injection wells must be equipped with dedicated computer-based continuous pressure

monitoring devices (in concert with the Director-approved shut-off systems required for GS wells),

which typically take readings several times per second and record them electronically in a computer

system.. 

EPA believes that a frequency of five years, as specified at §146.90(f), is an appropriate interval for

pressure fall-off testing (particularly given the suite of tests operators will perform on the well and

the site). EPA clarifies that the Director may require more frequent pressure fall-off tests at a

specific project if necessary, based on site-specific circumstances. Pressure fall-off tests may be

conducted in conjunction with other well performance tests (i.e., mechanical integrity testing) to

ensure safe and effective operations. All monitoring data collected, including information from
pressure fall-off tests, will be incorporated in AoR reevaluations at least every five years. EPA

disagrees that the rule should provide specifics of the testing to the degree suggested, however.

EPA clarifies that periodic MITs will not be required following plugging of the well. 

Based on its evaluation of all public comments and input on the proposed rule and NODA and

Request for Comment, EPA has made many revisions to the GS rule. See the final rule and preamble

for further discussion on EPA's final approach.

Commenter Name: Robert F. Van Voorhees Letter ID: 0190

Commenter Organization: Carbon Sequestration Council Comment ID: 24482

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Rule Provision: 146.90(e) & (f) 

Proposed CCS Group Recommendations: (e) A demonstration of external mechanical 

integrity pursuant to § 146.89(c) at least once per year throughout the duration 

of the geologic sequestration project; 

(f) A pressure fall-off test at least once every five years unless more frequent 

testing is required by the Director based on site specific information;

Basis for CCS Group Comments: Redundant to section 146.89 

These issues are addressed in recommended subsection (b)(3) and (4). 

Response: Based on its evaluation of all public comments and input on the proposed rule and

NODA and Request for Comment, EPA has made many revisions to the GS Rule. See the final rule

and preamble for further discussion on EPA's final approach. EPA adds that the purpose of including

all testing and monitoring requirements in §146.90 is to clarify and to specify the content of the

required testing and monitoring plan.

Commenter Name: Jeff W. Sheets Letter ID: 0192

Commenter Organization: ConocoPhillips Comment ID: 23897

Comment: Monitoring 

ConocoPhillips supports EPA's proposed rules to prepare, maintain, and comply 

with a testing and monitoring plan, including chemical analysis of CO2 streams 

and allowing for fit-for-purpose monitoring. We recommend some changes as 

described in detail in API's submittal. API's recommendations emphasize careful 

site selection and characterization, which create the strongest protection for 

USDWs while still handling well construction and monitoring with the most cost 

effective protective measures. Specific monitoring requirements detailed in 

API's recommendation maintain appropriate rigor to protect USDWs while allowing 

for site specific details. EPA's flexibility around operator developed plans is 

appropriate, and API acknowledges the directors discretion and ability to add 

prescriptive requirements as appropriate for specific sites. The recommendations 

provide balance, since too many prescriptive elements in the requirements 
themselves, would run the risk of becoming too broadly applied and add 

unnecessary cost. Preserving the environmental benefits of CCS relies on 

managing cost-effective protective solutions. 

Response: EPA agrees and believes that flexibility is important in developing and implementing a

monitoring plan that is appropriately tailored for a specific GS site. The purpose of the requirement

at §146.90 to develop site-specific testing and monitoring plans is to ensure that the monitoring

performed at a site is appropriate for site operational conditions and the geologic setting. EPA

believes that this is the best approach for addressing potential risks at GS sites. These flexible

provisions in the monitoring requirements for Class VI wells enable the owner or operator to tailor

monitoring programs to the specific needs of each project in consultation with the Director. Please

also see EPA's response to API's comment.

Commenter Name: John R. Baza Letter ID: 0193

Commenter Organization: Utah Division of Oil, Gas, and Mining Comment ID: 23915

Other EPA Comment Codes and Descriptions: 4700 2.7 Proposed Recordkeeping and Reporting

Requirements (40 CFR 146.91) 

Comment: Monitoring 

EPA seeks comments on proposed pressure plume and pressure front monitoring 

including issues such as the amount and type of monitoring, the usefulness of 

geophysical, air and soil monitoring, post-injection site monitoring, and 

frequency of reporting requirements. The IOGCC comments of December 23, 2008 

have addressed all of these issues in great detail, and the Division concurs 

with their recommendations. 

Response: Based on its evaluation of all public comments and input on the proposed rule and

NODA and Request for Comment, EPA has made many revisions to the GS Rule. See the final rule

and preamble for further discussion on EPA's final approach.

EPA agrees with commenters that developing and following testing and monitoring plans is an

important part of assuring that a GS project is operating properly and is crucial for the early

detection of potential endangerment to USDWs. EPA also agrees that periodic updates to the plan are

appropriate. EPA clarifies that the final GS regulation includes a requirement that the AoR be

reevaluated at least every five years, and it specifies at §146.90(j) that the operator revise the testing

and monitoring plan to incorporate the results of the most recent AoR reevaluation and recent

operational and monitoring data.

EPA acknowledges the comment and the final rule retains the text as proposed. Please see the final

rule and the discussion of testing and monitoring in the preamble for additional information.

Commenter Name: Andy Horn Letter ID: 0196

Commenter Organization: Colorado Ground Water Association (CGWA) Comment ID: 23926

Comment: Issue 6. Buffer Zone monitoring wells need to be addressed in the regulation. 

The regulations do not specifically identify the need for monitoring to verify 

performance of the repository. Monitoring wells to detect potential migration 

from the repository need to be incorporated into the proposed rule. Early 
implementation of GS should incorporate the concept of multiple barrier zones. 

This allows implementation of monitoring in zones below a USDW that can serve as 

a guard zone. These are critical in a zone between the repository and USDWs to 

allow for the early detection of a problem while mitigation is still an option. 

Even highly effective monitoring of GS reservoirs for failure may only inform 

operators after "the horse has left the barn." In addition to buffer-zone 

monitoring, pressures in confining units should be monitored to provide allow 

detection of failure of the GS reservoir. 

Response: EPA clarifies that the final rule requires monitoring to ensure that CO2 or injection zone

formation fluids remain in the injection zone. EPA believes that the ground water geochemical

monitoring above the confining zone required in §146.90(d) will maximize protection of USDWs

from endangerment at GS sites. Direct geochemical sampling is an important part of a monitoring

program. EPA adds that the baseline geochemical data required at §146.82(a)(6) will provide a basis

for comparison. EPA is not requiring monitoring in the confining zone itself. However, monitoring

in additional formations, e.g., the injection zone, may also be necessary, and if the Director believes

such monitoring is warranted he/she has the authority to require that it be included in the testing and

monitoring plan. 

EPA believes that geochemical monitoring above the confining zone should not be restricted to areas

near the plume. Research, both EPA-funded and external, has shown that the zone of elevated

pressure may be much larger than the plume (e.g., Birkholzer, et al. 2008). This area of elevated

pressure may cause migration of native brines from the target formation into overlying formations.

Careful placement of monitoring wells within the delineated AoR (which includes areas beyond the

extent of the CO2 plume) would allow for detection of changes in water quality related to GS

activities. EPA acknowledges that very thick confining zones would reduce the chance that CO2 or

other fluids will move from the injection zone; however, to increase protectiveness, a multiplebarrier approach to protecting USDWs from endangerment that includes both proper site

characterization and a detailed monitoring regime is warranted.

EPA believes that geochemical monitoring in and above the confining zone complements pressure

monitoring in the injection zone. EPA believes that pressure monitoring in the injection zone is

necessary to track the development and movement of the pressure front and CO2 plume. The final

rule, at §146.90(g), requires owners or operators to perform monitoring to track the extent of the

CO2 plume and pressure front. The owner or operator must use direct methods to monitor for

pressure changes in the injection zone. Indirect methods (e.g., seismic, electrical, gravity, or

electromagnetic surveys and/or down-hole CO2 detection tools) are required unless the Director

determines, based on site-specific geology that such methods are not appropriate.

EPA believes that pressure monitoring within the injection zone is necessary because any such

monitoring above the confining zone would not detect movement of the pressure front unless a

breach of the confining zone occurs.

Commenter Name: Andy Horn Letter ID: 0196

Commenter Organization: Colorado Ground Water Association (CGWA) Comment ID: 23932

Comment: While detailed geologic modeling is planned, monitoring wells should be 

installed into the injection zone, and into buffer zones above the injection 

zone, including fluid bearing zones below any potential USDW zone. In addition, 

pressure sensors should be installed in the confining units above the GS 
reservoir. The data collected from the monitoring wells and pressure monitoring 

points can be used to confirm the accuracy of a model and to monitor the zone 

above the injection zone for CO2 leakage. Monitoring wells should be installed 

into the buffer zone to provide early detection in the event CO2 or the 

associated pressure front begins to migrate into zones above the proposed 

injection zone. All monitoring wells should be designed to similar standards as 

injection well and will need pressure shut-in equipment. 

Clustered monitoring wells should be considered to allow a single borehole to be 

used to monitor several different vertically discrete zones. For example, there 

is a potential that the injection zone, one or more buffer zones, and the USDW 

zone could be monitored from clustered monitoring wells installed into a single 

borehole. In the event such technology is used, equipment should be installed, 

maintained, and tested on a designated frequency to prevent migration of fluids 

between zones. 

Response: EPA agrees that pressure monitoring in the injection zone is appropriate. The final GS

regulation, at §146.90(g)(1), requires all GS project owners or operators to monitor for pressure

changes in the injection zone. EPA believes that pressure monitoring in the injection zone is

necessary to track the development and movement of the pressure front and CO2 plume. Pressure

monitoring within the injection zone is necessary because any such monitoring above the confining

zone would not detect movement of the pressure front unless a breach of the confining zone occurs. 

EPA adds that, although it is not required in the GS rule, owners or operators may consider

performing additional pressure monitoring in wells that are above the confining zone (e.g., in the

same wells used to perform ground water quality monitoring required at §146.90(d)) to provide

additional verification that no pressure changes are occurring above the confining zone. Monitoring

also identifies needed remedial actions, provides inputs for AoR reevaluation modeling, and targets

additional geochemical and surface monitoring needs. Knowledge of the location of the CO2 plume

and the associated pressure front will assure the public that GS projects are proceeding according to

plan, provide sufficient information to the owner or operator and Director, or allow for appropriate

actions to address any indication that USDWs may be endangered. 

EPA acknowledges that, at certain sites, there may be a need for more or different monitoring

schemes (which may include monitoring in the confining or buffer zones), and adds that it is

important to balance the need for adequate monitoring that ensures USDW protection from

endangerment against too many artificial penetrations which could serve as conduits for fluid

migration. EPA expects site-specific testing and monitoring plans to describe the proposed

monitoring regime, which must be approved by the Director. EPA recognizes that wells with

multiple completions (i.e., what the commenter refers to as "clustered monitoring wells") may offer

benefits; nothing in the rule precludes their use. 

EPA believes that monitoring using wells in the injection zone (e.g., for pressure monitoring as

required at §146.90(g)(1)) can be safely performed if the wells are constructed to prevent flow

between the injection zone and USDWs or other layers above the confining zone. Such construction

technologies exist and have been used in the oil and gas industry for years. EPA believes that

properly constructed monitoring wells will be a safe way to obtain the data that is essential to ensure

that the injected CO2 remains confined in the injection zone and that pressure changes are not

causing movement of formation or other fluids. To mitigate the risk of fluid movement, EPA

requires owners and operators to submit a testing and monitoring plan that describes how the owner
or operator plans to site and construct monitoring wells. EPA is developing guidance on well

construction that will include recommendations for monitoring well construction. The guidance will

be available on EPA’s website at http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil gas and surface air monitoring which may be required by the UIC Director

for specific GS projects. The guidance can also be found on EPA’s website.

Commenter Name: Craig R. Walters Letter ID: 0200

Commenter Organization: Anadarko Petroleum Corporation Comment ID: 24701

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Rule Provision: 146.90(b) 

Anadarko Petroleum Corporation (APC) Comments: (b) The testing and monitoring 

plan must, at a minimum, include: 

(a1) Analysis of the carbon dioxide stream with sufficient frequency to 

yield data representative of its chemical and physical characteristics; 

(b2) Installation and use, except during well workovers as defined in § 

146.86(d), of continuous recording MONITORING DEVICES (INCLUDING DIGITAL 

DEVICES CAPTURING PERIODIC DATA) to monitor injection pressure, rate and volume; 

AND TO RECORD AT LEAST DAILY the pressure on the annulus between the tubing and 

the long string casing; and the annulus fluid volume;

(3) A DEMONSTRATION OF EXTERNAL MECHANICAL INTEGRITY PURSUANT TO

§146.89(C) 

UNTIL THE WELL IS PLUGGED; 

(4) MONITORING OF THE PRESSURE BUILDUP IN THE INJECTION ZONE ANNUALLY,

INCLUDING 

AT A MINIMUM, A SHUTDOWN OF THE WELL FOR A TIME SUFFICIENT TO CONDUCT

A VALID 

OBSERVATION OF THE PRESSURE FALLOFF CURVE AT LEAST ONCE EVERY FIVE

YEARS; AND 

(5) A QUALITY ASSURANCE PLAN FOR ALL TESTING AND MONITORING

REQUIREMENTS. 

(b) Installation and use, except during well workovers as defined in §146.88(d), 

of continuous monitoring devices (including digital devices capturing periodic 

data) to monitor injection pressure, rate and volume; and RECORD AT LEAST DAILY 

the pressure on the annulus between the tubing and the long string casing; 

Rationale: §146.86(d) does not exist; perhaps §146.88(d) is what was apparently 

intended. 

There is concern regarding what constitutes continuous monitoring. Industry 
agrees that regular monitoring of the parameters identified by EPA is 

appropriate. Our experience with CO2 EOR strongly shows that daily monitoring of 

most of these parameters is adequate (exceptions to this would be on a sitespecific basis). Recording should generally be done on a daily basis and 

reporting on a semi-annually basis. As a guiding principle, the frequency of 

monitoring should be determined by the level of risk posed by the injection 

operation. 

Response: EPA believes that continuous pressure monitoring of GS wells, as required at §146.88(e),

is important and appropriate because the potentially corrosive nature of CO2 streams in the presence

of water makes it critical to immediately identify corrosion-related well mechanical integrity loss.

Class VI injection wells must be equipped with dedicated computer-based continuous pressure

monitoring devices (in concert with the Director-approved shut-off systems required for GS wells),

which typically take readings several times per second and record them electronically in a computer

system.. 

EPA believes that a frequency of at least once every five years, as specified at §146.90(f), is an

appropriate interval for pressure fall-off testing (particularly given the suite of tests operators will

perform on the well and the site). EPA clarifies that the Director may require more frequent pressure

fall-off tests at a specific project, if necessary based on site-specific circumstances. Pressure fall-off

tests may be conducted in conjunction with other well performance tests (i.e., mechanical integrity

testing) to ensure safe and effective operations. All monitoring data collected, including information

from pressure fall-off tests, will be incorporated in AoR reevaluations, at least every five years. EPA

disagrees that the rule should provide specifics of the testing at the degree suggested, however.

EPA clarifies that periodic MITs are not be required following plugging of the well. 

Based on its evaluation of all public comments and input on the proposed rule and NODA and

Request for Comment, EPA has made many revisions to the GS rule. See the final rule and preamble

for further discussion on EPA's final approach.

Commenter Name: Craig R. Walters Letter ID: 0200

Commenter Organization: Anadarko Petroleum Corporation Comment ID: 24705

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Rule Provision: 146.90(e) 

Anadarko Petroleum Corporation (APC) Comments: (e) A demonstration of external 

mechanical integrity pursuant to § 146.89(c) at least once per year throughout 

the duration of the geologic sequestration project;

Rationale: See 146.90(b)(3) 

Response: Based on its evaluation of all public comments and input on the proposed rule and

NODA and Request for Comment, EPA has made many revisions to the GS rule. See the final rule

and preamble for further discussion on EPA's final approach. EPA adds that the purpose of including

all testing and monitoring requirements in §146.90 is to clarify and to specify the content of the

required testing and monitoring plan.
Commenter Name: Craig R. Walters Letter ID: 0200

Commenter Organization: Anadarko Petroleum Corporation Comment ID: 24706

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Rule Provision: 146.90(f) 

Anadarko Petroleum Corporation (APC) Comments: (f) A pressure fall-off test at 

least once every five years unless more frequent testing is required by the 

Director based on site specific information;

Rationale: See 146.90(b)(4) 

Response: Based on its evaluation of all public comments and input on the proposed rule and

NODA and Request for Comment, EPA has made many revisions to the GS rule. See the final rule

and preamble for further discussion on EPA's final approach. EPA adds that the purpose of including

all testing and monitoring requirements in §146.90 is to clarify and to specify the content of the

required testing and monitoring plan.

Commenter Name: Brad Castleberry Letter ID: 0203

Commenter Organization: Water Environment Association of Texas (WEAT)Comment ID: 22179

Other EPA Comment Codes and Descriptions: 3100 2.1 Proposed Geologic Siting Requirements

(40 CFR 146.83) 

Comment: groundwater quality as well as public drinking water sources. Careful 

consideration should he given to ensure an adequate assessment is made of each 

proposed injection well site. This consideration should come in the form of 

detailed site studies. sophisticated computer modeling, and other tools used to 

predict hydrogeology. Careful consideration should also he given to ensure that 

adequate ongoing monitoring and reporting is provided for any site ultimately 

permitted pursuant to the proposed rules. Given the unique circumstances 

surrounding this type of pollutant, and the lack of a significant body of longterm evidence to support the proposed activity, we would encourage EPA to 

include significant monitoring and reporting provisions to ensure the long-term 

viability of any permitted site with respect to surrounding groundwater quality. 

Response: EPA agrees with the commenter regarding the importance of site characterization, and

believes that the extensive requirements for geologic site characterization (at §146.82), AoR

evaluation (§146.84), and testing of the well during drilling (§146.87) are appropriate to ensure that

permitting authorities have the necessary information to evaluate whether a specific site will allow

safe injection of CO2. EPA adds that submittal and review of monitoring data (as required at

§146.90) and the AoR reevaluation process (§146.84(e)) will provide an opportunity for an ongoing

review of the site and a dialogue between the Director and the owner or operator to ensure that the

project is being operated in a manner that protects USDWs from endangerment.

EPA believes that monitoring plans and methods need to be site-specific and that the monitoring

requirements for GS sites at §146.90 provide an appropriate level of flexibility in structuring a

testing and monitoring plan that protects USDWs from endangerment. 

The GS rule, at §146.90, requires injectate monitoring, mechanical integrity testing, corrosion

monitoring, tracking the CO2 plume and area of elevated pressure, monitoring geochemical changes
above the confining zone, and, at the discretion of the Director, surface air and soil gas monitoring

for CO2 fluctuations, and any additional tests necessary to ensure USDW protection from

endangerment. 

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil gas and surface air monitoring which may be required by the UIC Director

for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Christopher Murray Letter ID: 0207

Commenter Organization: Pacific Northwest National Laboratory Comment ID: 22443

Other EPA Comment Codes and Descriptions: 3300 2.2.1 Delineating the AoR/Modeling CO2

movement 

Comment: Injection of CO2 into deep saline formations is driven by differences between 

the well injection pressure and formation pressure. To avoid inducing fractures 

or opening existing fractures in the formation and caprock, well injection 

pressure will be limited to some fraction below the fracturing pressure. As CO2 

migrates into the formation the formation pressure increases around the 

injection well. The pressure distribution in the formation around the injection 

well depends on the formation properties, structure, and injection rate. 

Injection formations will be required to be confined vertically and/or 

horizontally to prevent the vertical migration of injected fluids and saline 

reservoir fluids into USDWs. 

Confined formations (e.g., a caprock overlying a horizontally extensive 

formation) allow the formation fluid to be displaced laterally by the injected 

fluid. Injecting CO2 results in elevated pressures both inside and beyond the 

CO2 plume. Elevated pressures within the CO2 plume have the potential to force 

CO2 and formation fluid through permeable wells, fractures, or faults that 

penetrate the formation. Elevated pressures outside the CO2 plume have the 

potential to force formation fluid through permeable wells, fractures or faults 

that penetrate the formation. The higher the formation pressure is above the 

ambient formation pressure, the greater the potential for CO2 and formation 

fluid to leak through permeable wells, fractures, and faults. The lateral 

pressure distribution is a function of the injection rate and the lateral 

distribution of formation permeability. When CO2 injection is halted, elevated 

pressures decay over time as the injected and formation fluids migrate away from 

the injection well(s). 

The proposed regulations define an AoR and Corrective Action as being an area 

within which artificial penetrations may act as conduits for fluid movement into 

USDWs (e.g., active and abandoned wells) and, as needed, require the applicant 

to perform corrective action to seal these open wells. The potential for fluid 

movement into USDWs from the injection of CO2 into the injection formation is 

correlated with the area of elevated formation pressure, which is usually larger 
than the area that contains the injected CO2 mass. For confined formations, this 

area is defined by the lateral pressure distribution around the injection 

well(s). 

PNNL RECOMMENDATION 

EPA should define two regulatory regions surrounding the geologic sequestration 

project and provide specific definitions for those regions; 1) Area of 

Monitoring (AoM) and 2) Area of Review; where the AoM is used to define the 

spatial distribution of monitoring wells and the AoR is used to define the limit 

of corrective actions: 

Area of Monitoring (AoM): The region surrounding the geologic sequestration 

project that The area of monitoring is based on monitoring data contains 95% of 

the carbon dioxide mass. and computational modeling that accounts for the 

physical and chemical properties of all phases of the injected carbon dioxide 

stream. In the absence of monitoring data, the area of monitoring is based on 

computational modeling. 

Area of Review (AoR): The region surrounding the geologic sequestration 

reservoir that has or is indicated to develop pressures that are greater than 

10% different from the original hydrostatic formation fluid pressure, but no 

less than the Area of Monitoring. The area of review is based on monitoring data 

and computational modeling that accounts for the physical and chemical 

properties of all phases of the injected carbon dioxide stream. In the absence 

of monitoring data, the area of review is based on computational modeling. 

The proposed definitions of AoM and AoR have several important components: 

- The AoMhas a mass-based definition. - The AoR has a pressure-differential-based 

definition. - The AoR is never smaller than the AoM. - The AoR and AoM may be 

asymmetrical around the injection well(s). - The AoR and AoM may vary over time. - 

The carbon dioxide mass should be determined using a combination of monitoring 

data and computational modeling. - Pressure differentials are based on 

equilibrium hydrostatic conditions. 

Response: EPA believes that, while the commenter offers different terminology for the AoR and the

area to be monitored, the GS rule addresses the commenter's suggestions. Notably, the owner or

operator is required (under 146.90) to develop and implement a testing and monitoring plan for each

GS project that must consider the delineated AoR that includes both the CO2 plume and associated

pressure front and incorporates many of the attributes suggested by the commenter. EPA clarifies

that delineation of the AoR, as required at 146.84(c), must account for the physical and chemical

properties of all phases of the injected CO2 stream, based on available site characterization,

monitoring, and operational data. 

Furthermore, any changes to the AoR would necessitate a review of and potential change in the

testing and monitoring plan, consistent with the commenter's assertion that the AoR may vary over

time. The final GS regulation includes a requirement at 146.84(e) that the AoR be reevaluated at

least every 5 years, and also requires that the owner or operator periodically review the AoR and

corrective action, testing and monitoring, and emergency and remedial response plans within one
year of an AoR reevaluation (as well as following significant changes to the facility, or when

required by the Director). The relationship between the AoR reevaluation and the testing and

monitoring plan should allow for considerations suggested by the commenter. 

EPA believes that by linking development and review of the testing and monitoring plan to the AoR

evaluation and reevaluation process, the GS rule, in effect, incorporates many of the commenter's

considerations for an area of monitoring.

Commenter Name: John King Letter ID: 0211

Commenter Organization: Shell Exploration and Production Company

(SEPCo)

Comment ID:

22776

Comment: F. Testing and Monitoring Requirements 

The preamble to the proposed rule indicates, "EPA considers CO2 plume and 

associated pressure front monitoring to be necessary for verification of model 

predictions." 73 Fed. Reg. at 43514. This is difficult to understand because the 

regulatory regime for Class I hazardous waste injection wells do not require 

elaborate modeling, and plume or pressure front monitoring have never been 

considered necessary and are not required in that context. In fact, extensive 

experience with Class I hazardous waste injection demonstrates that plume and 

pressure front monitoring is not necessary, either to provide confidence in 

modeling results or otherwise. By suggesting otherwise, the proposed rule 

unnecessarily undermines confidence in the modeling demonstrations that can and 

should be relied upon to support determinations that injected CO2 will not 

endanger USDWs. 

The suggestion that it makes sense to monitor the movement of injected CO2 in 

the subsurface also does not consider the nature and utility of modeling used to 

evaluate injection well projects and of the technical difficulties and 

uncertainties such monitoring would involve. The root of the problem relates to 

the fact that modeling provides a conservative assessment of the potential for 

movement of injected fluids in the subsurface, not a precise "prediction" of 

actual fate and transport that can or should be "verified" on the basis of 

elaborate, costly, and uncertain efforts to observe the actual movement of 

fluids in the subsurface. As experience with hazardous waste injection shows, 

injection well operational data and the results of pressure fall-off tests 

provide ample data to validate the results of modeling. The additional 

monitoring requirements proposed in the GS context are excessive and 

unjustified. 

Response: EPA disagrees that plume and pressure front monitoring are not justified for Class VI

wells. The Agency recognizes that while there are similarities between injection of wastes for

disposal (Class I) and GS (Class VI), there are significant differences as well. Important unique

considerations for GS include the buoyancy of CO2, its corrosivity when in contact with water, its

low viscosity (i.e., high mobility), and the very large injection volumes that are anticipated. There is

also a degree of uncertainty regarding the behavior of large volumes of CO2 in the subsurface after

injection. Given these characteristics of anticipated GS projects, EPA believes that plume and

pressure front monitoring at §146.90(g) are justified to provide early warning of any unforeseen

fluid movement that might endanger USDWs. 
EPA believes that pressure monitoring in the injection zone is necessary to track the development

and movement of the pressure front and CO2 plume. Monitoring can also identify needed remedial

actions, provide inputs for AoR reevaluation modeling, evaluate predictions of plume movement,

and target additional geochemical and surface monitoring needs. Knowledge of the location of the

CO2 plume and the associated pressure front will also assure the public that GS projects are

proceeding according to plan, provide sufficient information to the owner or operator and Director,

or allow for appropriate actions to address any indication that USDWs may be endangered. 

The final rule, at §146.90(g)(2) requires owners or operators to track the position of the CO2 plume

using indirect methods (e.g., seismic, electrical, gravity, or electromagnetic surveys and/or downhole CO2 detection tools), unless the Director determines based on site-specific geology, that such

methods are not appropriate. For example, geophysical methods are difficult to execute in areas that

are structurally and topographically complex or where lithologies have limited contrast in density,

porosity, permeability, and other physical properties. EPA clarifies that this determination will be

made by the Director based on the site-specific geologic information submitted by the owner or

operator with the permit application.

EPA believes that this approach provides flexibility to develop a site-specific monitoring plan,

ensures that direct monitoring is available to track the movement of the CO2 and validate models,

and recognizes that indirect techniques are not appropriate in all situations. The owner or operator's

approved testing and monitoring plan will include the site-specific details, technologies, testing and

monitoring frequencies, and other pertinent information.

EPA agrees that good site selection, modeling, and management are crucial elements of a successful

GS project, but disagrees that this is an effective substitute for rigorous site monitoring. EPA

disagrees that pressure fall-off tests are an appropriate substitute for monitoring pressure changes in

the injection zone. Pressure fall-off tests provide information only in the vicinity of the injection

well(s) and measure pressure conditions within the injection zone only. Direct monitoring of

pressure changes in the injection zone can provide advance warning of movement of CO2 or brine

that might ultimately endanger a USDW.

Commenter Name: John King Letter ID: 0211

Commenter Organization: Shell Exploration and Production Company

(SEPCo)

Comment ID:

22779

Comment: a. Monitor Wells 

Monitor wells reaching the deep subsurface are problematic in a variety of 

respects. They are expensive to install, create potential pathways for vertical 

fluid migration, and -- in the deep subsurface where natural fluid movement may 

be very slow or effectively non-existent -- they have little potential to 

provide more than an isolated "point measurement." If the object is to track 

injected fluid within an injection zone, a monitor well could be placed in the 

path of the waste front to detect the waste front when it goes by, but the 

exercise would amount to a very expensive way to generate a single data point. 

There would be less likelihood of any benefit from monitoring wells designed to 

detect potential leakage from an injection zone, because the ability to detect 

such leakage is at best a hit-or-miss (if not a needle in a haystack) 

proposition. Monitor wells also have built-in confounding factors that include 
both the potential for well construction to impact fluid quality in the target 

sampling interval and the fact that sampling may itself cause fluid movement 

that might not otherwise occur. Because pressure fronts extend much further than 

injected fluid plume fronts during injection, pressure monitoring is more likely 

to be useful than fluid sampling, but costs would till be very high and the 

ability to detect relevant changes would still be very much hit-or-miss. For 

these reasons, EPA chose not to impose monitor well requirements for Class I 

hazardous waste injection wells, though it did allow monitor wells to be 

required at the discretion of the Administrator to address particular 

circumstances at the site. See 52 Fed. Reg. 32446 at 32463-64 (August 27, 1987), 

53 Fed. Reg. 28118 at 28141, 28144-45 (July 26, 1988). Experience with hazardous 

waste injection does not commend the use of monitor wells even in that context, 

and there is no justification to impose as stringent an approach -- let alone a 

more stringent approach -- for the injection of CO2. 

Response: As described above, EPA believes that monitoring using wells in the injection zone, e.g.,

for pressure monitoring as required at §146.90(g)(1), can be safely performed if the wells are

constructed to prevent flow between the injection zone and USDWs or other layers above the

confining zone. Such construction technologies exist and have been used in the oil and gas industry

for years. EPA believes that properly constructed monitoring wells will be a safe way to obtain the

data that is essential to ensure that the injected CO2 remains confined in the injection zone and that

pressure changes are not causing movement of formation or other fluids. To mitigate the risk of fluid

movement, EPA requires owners and operators to submit a testing and monitoring plan that

describes how the owner or operator plans to site and construct monitoring wells. EPA is developing

guidance on well construction that will include recommendations for monitoring well construction.

The guidance will be available on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil gas and surface air monitoring which may be required by the UIC Director

for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm. 

EPA also acknowledges that complete coverage of the potential plume area or leakage in the

subsurface is not possible through the use of monitoring wells. However, data from an appropriate

number of monitoring wells sited based on site-specific information will provide direct information

that is not otherwise obtainable and, along with other monitoring data, will support a broader

understanding of fluid behavior at the site. 

EPA adds that the iterative process of monitoring, modeling, and AoR reevaluation is appropriate to

verify that the CO2 plume and pressure front are moving through the subsurface as predicted, verify

the accuracy of the delineation model (or identify needed changes), and refine testing and monitoring

activities to ensure that USDWs are protected from endangerment and that there would be adequate

warning of potential problems at the site before any endangerment could occur. 

EPA acknowledges the commenters' concern about the cost of monitoring. However, EPA believes
that monitoring is essential for protection of USDWs at GS sites. Although a significant cost in

absolute terms, monitoring costs are expected to be a small fraction of site operating costs, according

to EPA's cost analysis for the GS rulemaking (which is available in the docket).

Commenter Name: Ronald Evans Letter ID: 0215

Commenter Organization: Denbury Resources, Inc. (DRI) Comment ID: 24311

Comment: 4. EPA Proposed §146.90(i) Any additional monitoring, as required by the 

Director, necessary to support, upgrade, and improve computational 

modeling of the area of review evaluation required under § 146.84(b) and 

to determine compliance with standards under 40 CFR 144.12 

This section effectively proposes a "catch all" to allow the Director undefined 

discretion to order unlimited and unspecified additional monitoring to improve 

modeling and ensure compliance. Vesting the Director with such additional 

undefined discretionary authority increases the regulatory risks of the Class VI 

permitting process and accordingly increases costs. In the event that experience 

implementing the proposed rule requires some future revisions to include 

additional monitoring requirements, such changes should be proposed and adopted 

through appropriate rulemaking procedures and based on an adequate factual and 

scientific record. However, adopting an open-ended power to require "any" 

additional monitoring, at this early stage, undermines the purpose of providing 

a defined set of rules that members of the public may evaluate prior to making 

the large investments that will be involved in Class VI projects. Such 

uncertainty can only tend to increase costs, creating a barrier to capital 

formation and discouraging geologic sequestration. Accordingly, Denbury 

recommends deleting this section. 

Response: EPA does not believe that UIC Directors should have undefined discretion when ordering

additional monitoring requirements. EPA believes that, given the variety of site-specific

circumstances that may be encountered at GS sites, it is reasonable to afford the Director discretion

only when additional testing and monitoring requirements are required to ensure the protection of

USDWs. 

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil gas and surface air monitoring which may be required by the UIC Director

for specific GS projects. The guidance will discuss how the Director may exercise any discretion.

The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Edward Steadman Letter ID: 0220

Commenter Organization: The Energy and Environmental Research Center at the

University of North Dakota

Comment ID:

21626

Comment: Page 43515 to 43516. Regarding monitoring. In general, this section is overly 

prescriptive with respect to the selection and application of monitoring 
techniques. One of the things that is lost in this discussion is that if the 

geometry of the trapping structure is well understood and the overlying seal has 

been demonstrated to be competent and thick, then plume monitoring should be 

relatively straightforward and less complicated. Consider, for example, 

injection into a thoroughly characterized high-relief structure, such as an 

anticline or pinnacle reef encased in impermeable anhydrite. Migration of the 

CO2 would be minimal, and plume stabilization would be relatively rapid. A few 

carefully instrumented and placed monitoring wells, some above the seal and 

others just outside and below the structure, would be enough to ensure the plume 

does not leak through the seal or slip beneath the spill point at the bottom of 

the structure. With this in mind, it can be reasonably argued that seismic 

surveys (which may or may not provide useful insight regarding the plume, 

depending on the lithology) would not offer any additional data that would 

further ensure the protection of USDWs. If there is no significant structural 

element to the trap, then plume stabilization could very well take many decades, 

and in such a case, a more robust and comprehensive suite of monitoring tools 

may have to be applied. Many examples of both types of sites, and many more that 

fall in between, have been identified throughout the United States, and it is 

because of this variety that it is critical that UIC regulations for GS allow 

flexibility in choosing plume-tracking methods. The EPA acknowledges the need 

for flexibility in a paragraph in the middle of page 43516, but many of the 

requirements laid out in the document do not reflect that need. 

Response: EPA agrees that flexibility is important in developing and implementing a monitoring

plan that is appropriately tailored for a specific GS site, and believes that the final regulation

provides for flexibility in: 1) methodologies used to collect these data, 2) the spatial resolution at

which the data should be collected, and 3) how often the data should be collected. The number and

placement of monitoring wells will be based on site-specific information such as the calculated AoR,

injection rate and volume, site geology, baseline data, and the presence of artificial penetrations

within the AoR. In some instances, there may be a limited number of options for complying with

EPA's minimum requirements. For example, monitoring for geochemical changes will require use of

monitoring wells and collection of groundwater samples for chemical analysis. Many options

currently exist for complying with other requirements, such as tracking the position of the plume and

pressure front within the injection zone.

Flexibility is also provided regarding how to monitor for the specific data required by the final rule.

The testing and monitoring plan is developed by the owner or operator in consultation with the

Director and is designed to ensure that a detailed, Director-approved document describing how

monitoring will be conducted during the lifetime of the project exists. EPA is developing guidance

on testing and monitoring to assist owners or operators and Directors in evaluating requirements

under §146.90, including proposed monitoring plans. The guidance describes available technologies

and recommended approaches for implementing a testing and monitoring plan, including preoperational geophysical logging and testing of injection wells, MITs, injection well testing during

operation, groundwater quality monitoring, tracking the CO2 plume and pressure front, and soil gas

and surface air monitoring which may be required by the UIC Director for specific GS projects.The

guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm. In addition, in January 2009,

DOE published a best practices manual entitled "Monitoring, Verification, and Accounting of CO2

Stored in Deep Geologic Formations" (DOE/NETL-311/081508); this manual is included in the

docket for the final GS rule.
With specific regard to plume tracking and pressure monitoring, EPA maintains that they are key

components of monitoring at GS sites. A rigorous plume tracking and pressure monitoring scheme,

such as one that meets the requirements at §146.90(g), is imperative for ensuring that the CO2 plume

is contained within the injection zone. 

The final rule at §146.90(g) requires owners or operators to perform monitoring to track the extent of

the CO2 plume and pressure front. The owner or operator must use direct methods to monitor for

pressure changes in the injection zone. Indirect methods (e.g., seismic, electrical, gravity, or

electromagnetic surveys and/or down-hole CO2 detection tools) are required unless the Director

determines, based on site-specific geology that such methods are not appropriate 

Pressure monitoring in the injection zone is necessary to track the development and movement of the

pressure front and CO2 plume. When combined with information on temperature, pressure data

provide an indication of the phase (e.g., gas, supercritical) and distribution of the injected CO2 (73

FR 43515). Monitoring can also identify needed remedial actions, provide inputs for AoR

reevaluation modeling, evaluate predictions of plume movement, and target additional geochemical

and surface monitoring needs.

Commenter Name: Edward Mehnert Letter ID: 0221

Commenter Organization: Illinois State Geological Survey Comment ID: 21637

Other EPA Comment Codes and Descriptions: 3300 2.2.1 Delineating the AoR/Modeling CO2

movement 

Comment: p.43506, IIIA2 Proposed Area of Review: Does the area of review need to be one 

contiguous area? For a deep saline aquifer with no structural trap, it may be 

beneficial to have two separate areas of review--one for the CO2 plume and 

another for the pressure front at a distant USDW boundary. In this setting, the 

pressure front may move brine upgradient into a portion of the aquifer that 

contains fresher water (<10,000 mg/L TDS). The distance between the injection 

well and the "freshwater" section of the aquifer may be more than 100 miles. 

Response: EPA clarifies that the requirements for AoR delineation incorporate both the CO2 plume

and associated pressure front. EPA agrees that both of these should be taken into account in

determining corrective action needs and developing a testing and monitoring plan, and that the

requirement to delineate the AoR at 146.84(c) addresses the potential risks raised by the

commenters. EPA believes that the final GS requirements for delineating the AoR provide sufficient

protection to USDWs, without introducing an overly complex regulatory process.

Commenter Name: Edward Mehnert Letter ID: 0221

Commenter Organization: Illinois State Geological Survey Comment ID: 21639

Comment: p.43514, IIIA6 Monitoring Requirements: The complete list of monitoring 

procedures may not be necessary in all settings, such as deep saline aquifers 

(>5,000 ft below ground surface). I hope that these rules will remain flexible 

such that they can benefit from the research currently being conducted by the 

USDOE-funded partnerships. Their Phase III efforts should provide valuable 

information on the feasibility and value of various monitoring methods. 

Response: EPA agrees with commenters and believes that flexibility is important in developing and
implementing a monitoring plan that is appropriately tailored for a specific GS site. The purpose of

the requirement at §146.90 to develop site-specific testing and monitoring plans is to ensure that the

monitoring performed at a site is appropriate for site operational conditions and the geologic setting.

EPA believes that this is the best approach for addressing potential risks at GS sites. These flexible

provisions in the monitoring requirements for Class VI wells enable the owner or operator to tailor

monitoring programs to the specific needs of each project in consultation with the Director.

The final regulation provides for flexibility in: 1) methodologies used to collect these data, 2) the

spatial resolution at which the data should be collected, and 3) how often the data should be

collected. The number and placement of monitoring wells will be based on site-specific information

such as the calculated AoR, injection rate and volume, site geology, baseline data, and the presence

of artificial penetrations within the AoR. In some instances, there may be a limited number of

options for complying with EPA's minimum requirements. For example, monitoring for geochemical

changes will require use of monitoring wells and collection of groundwater samples for chemical

analysis. Many options currently exist for complying with other requirements, such as tracking the

position of the plume and pressure front within the injection zone.

EPA believes, however, that implementing a testing and monitoring plan that includes all of the

required elements under §146.90 is essential to ensuring USDW protection. Please see the preamble

to the final rule for a complete justification of the elements of a GS testing and monitoring regime.

Flexibility is also provided regarding how to monitor for the specific data required by the final rule.

The testing and monitoring plan is developed by the owner or operator in consultation with the

Director and is designed to ensure that a detailed, Director-approved document describing how

monitoring will be conducted during the lifetime of the project exists. EPA is developing guidance

on testing and monitoring to assist owners or operators and Directors in evaluating requirements

under §146.90, including proposed monitoring plans. The guidance describes available technologies

and recommended approaches for implementing a testing and monitoring plan, including preoperational geophysical logging and testing of injection wells, MITs, injection well testing during

operation, groundwater quality monitoring, tracking the CO2 plume and pressure front, and soil gas

and surface air monitoring which may be required by the UIC Director for specific GS projects. The

guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm. 

EPA is using an adaptive approach to regulating GS. EPA will collect and review project data on

early GS projects to determine whether the appropriate amount and types of information and

appropriate documentation are required and being collected. The Agency will evaluate the

information and determine if modifications to the requirements are necessary.

Commenter Name: Darrick Eugene Letter ID: 0223

Commenter Organization: Texas Carbon Capture and Storage Association Comment ID: 23991

Comment: EPA Proposed §146.90(i) Any additional monitoring, as required by the 

Director, necessary to support, upgrade, and improve computational 

modeling of the area of review evaluation required under § 146.84(b) and 

to determine compliance with standards under 40 CFR 144.12 

This section effectively proposes a "catch all" to allow the Director undefined 

discretion to order unlimited and unspecified additional monitoring to improve 

modeling and ensure compliance. Vesting the Director with such additional 
undefined discretional authority increases the regulatory risks of the Class VI 

permitting process and accordingly increases costs. In the event that experience 

implementing the proposed rule requires some future revisions to include 

additional monitoring requirements, such changes should be proposed and adopted 

through appropriate rulemaking procedures and based on an adequate factual and 

scientific record. However, adopting an open- ended power to require "any" 

additional monitoring, at this early stage, undermines the purpose of providing 

a defined set of rules that members of the public may evaluate prior to making 

the large investments that will be involved in a Class VI projects. Such 

uncertainty can only tend to increase costs, creating a barrier to capital 

formation and discourage geologic sequestration. Accordingly, TxCCSA would 

recommend deleting this section: 

§146.90(i) Any additional monitoring, as required by the Director, 

necessary to support, upgrade, and improve computational modeling of the 

area of review evaluation required under § 146.84(b) and to determine 

compliance with standards under 40 CFR 144.12.

Response: EPA does not believe that Directors should have undefined discretion when ordering

additional monitoring requirements. EPA believes that, given the variety of site-specific

circumstances that may be encountered at GS sites, it is reasonable to afford the Director discretion

only when additional testing and monitoring requirements are added to ensure the protection of

USDWs. EPA is developing guidance on testing and monitoring to assist owners or operators and

Directors in evaluating requirements under §146.90, including proposed monitoring plans. The

guidance describes available technologies and recommended approaches for implementing a testing

and monitoring plan, including pre-operational geophysical logging and testing of injection wells,

MITs, injection well testing during operation, groundwater quality monitoring, tracking the CO2

plume and pressure front, and soil gas and surface air monitoring which may be required by the UIC

Director for specific GS projects. The guidance will discuss how the Director may exercise any

discretion. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Tiffany Rau Letter ID: 0224

Commenter Organization: Hydrogen Energy International Comment ID: 21676

Other EPA Comment Codes and Descriptions: 1250 1.1.1.4 Flexibility is needed (performancebased standards) 

Comment: With respect to monitoring requirements in general, EPA should adopt regulations 

that are performance and risk-based and will result in a site-specific 

monitoring program that is designed to understand the location, movement and 

stabilization of the CO2 plume in the subsurface as well as the early 

identification of any leakage for appropriate corrective action. HEI commends 

EPA for its efforts in this regard, but believes that further modification is 

necessary. HEI agrees with the proposal to allow a phased approach to conduct 

Response: EPA agrees with commenters and believes that flexibility is important in developing and

implementing a monitoring plan that is appropriately tailored for a specific GS site. The purpose of

the requirement at §146.90 to develop site-specific testing and monitoring plans is to ensure that the

monitoring performed at a site is appropriate for site operational conditions and the geologic setting.

EPA believes that this is the best approach for addressing potential risks at GS sites. These flexible
provisions in the monitoring requirements for Class VI wells enable the owner or operator to tailor

monitoring programs to the specific needs of each project in consultation with the Director.

The final regulation provides for flexibility in: 1) methodologies used to collect these data, 2) the

spatial resolution at which the data should be collected, and 3) how often the data should be

collected. The number and placement of monitoring wells will be based on site-specific information

such as the calculated AoR, injection rate and volume, site geology, baseline data, and the presence

of artificial penetrations within the AoR. In some instances, there may be a limited number of

options for complying with EPA's minimum requirements. For example, monitoring for geochemical

changes will require use of monitoring wells and collection of groundwater samples for chemical

analysis. Many options currently exist for complying with other requirements, such as tracking the

position of the plume and pressure front within the injection zone.

Flexibility is also provided regarding how to monitor for the specific data required by the final rule.

The testing and monitoring plan is developed by the owner or operator in consultation with the

Director and is designed to ensure that a detailed, Director-approved document describing how

monitoring will be conducted during the lifetime of the project exists. EPA is developing guidance

on testing and monitoring to assist owners or operators and Directors in evaluating requirements

under §146.90, including proposed monitoring plans. The guidance describes available technologies

and recommended approaches for implementing a testing and monitoring plan, including preoperational geophysical logging and testing of injection wells, MITs, injection well testing during

operation, groundwater quality monitoring, tracking the CO2 plume and pressure front, and soil gas

and surface air monitoring which may be required by the UIC Director for specific GS projects. The

guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Brian Williams Letter ID: 0225

Commenter Organization: BP Alternative Energy North America, Inc. (BP) Comment ID: 21721

Other EPA Comment Codes and Descriptions: 1250 1.1.1.4 Flexibility is needed (performancebased standards) 

Comment: With respect to monitoring requirements in general, EPA should adopt regulations 

that are performance and risk-based and will result in a site-specific 

monitoring program that is designed to understand the location, movement and 

stabilization of the CO2 plume in the subsurface as well as the early 

identification of any leakage for appropriate corrective action. BP commends 

EPA for its efforts in this regard, but believes that further modification is 

necessary. BP agrees with the proposal to allow a phased approach to conduct 

Response: EPA agrees with commenters and believes that flexibility is important in developing and

implementing a monitoring plan that is appropriately tailored for a specific GS site. The purpose of

the requirement at §146.90 to develop site-specific testing and monitoring plans is to ensure that the

monitoring performed at a site is appropriate for site operational conditions and the geologic setting.

EPA believes that this is the best approach for addressing potential risks at GS sites. These flexible

provisions in the monitoring requirements for Class VI wells enable the owner or operator to tailor

monitoring programs to the specific needs of each project in consultation with the Director.

The final regulation provides for flexibility in: 1) methodologies used to collect these data, 2) the

spatial resolution at which the data should be collected, and 3) how often the data should be

collected. The number and placement of monitoring wells will be based on site-specific information
such as the calculated AoR, injection rate and volume, site geology, baseline data, and the presence

of artificial penetrations within the AoR. In some instances, there may be a limited number of

options for complying with EPA's minimum requirements. For example, monitoring for geochemical

changes will require use of monitoring wells and collection of groundwater samples for chemical

analysis. Many options currently exist for complying with other requirements, such as tracking the

position of the plume and pressure front within the injection zone.

Flexibility is also provided regarding how to monitor for the specific data required by the final rule.

The testing and monitoring plan is developed by the owner or operator in consultation with the

Director and is designed to ensure that a detailed, Director-approved document describing how

monitoring will be conducted during the lifetime of the project exists. EPA is developing guidance

on testing and monitoring to assist owners or operators and Directors in evaluating requirements

under §146.90, including proposed monitoring plans. The guidance describes available technologies

and recommended approaches for implementing a testing and monitoring plan, including preoperational geophysical logging and testing of injection wells, MITs, injection well testing during

operation, groundwater quality monitoring, tracking the CO2 plume and pressure front, and soil gas

and surface air monitoring which may be required by the UIC Director for specific GS projects. The

guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Andrew Duguid Letter ID: 0226

Commenter Organization: Schlumberger Carbon Services Comment ID: 24053

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: §146.90 Testing and monitoring requirements. 

Proposed Rule: (b) Installation and use, except during well workovers as defined 

in §146.86(d), of continuous recording devices to monitor injection pressure, 

rate and volume; the pressure on the annulus between the tubing and the long 

string casing; and the annulus fluid volume; 

Schlumberger Suggested Revision: - 

Schlumberger Rationale: 146.86(d) does not exist; perhaps 146.88(d) is what was 

intended. 

Response: EPA acknowledges the comment; the final rule contains the suggested revision.

Commenter Name: Neeraj Gupta Letter ID: 0229

Commenter Organization: Battelle Energy Technology (BET) Comment ID: 21850

Other EPA Comment Codes and Descriptions: 4610 2.6.1 Testing and monitoring plan

requirement (seeking comment) 

Comment: Page 102, Pressure monitoring in overlying zones- Implicit in this monitoring 

requirement is that network of deep monitoring wells will be required with the 

injection well. We know of no other method to accurately measure deep 

pressures. As such, this requirement will be costly to implement and should be 

spelled out clearly for planning purposes. It may also be pertinent to make 

this optional depending on identified risks. 
Response: EPA acknowledges the commenters' concern about the cost of monitoring. However,

EPA believes that monitoring is essential for protection of USDWs at GS sites. Although a

significant cost in absolute terms, monitoring costs are expected to be a small fraction of site

operating costs, according to EPA's cost analysis for the GS rulemaking (which is available in the

docket).

EPA believes that monitoring using wells in the injection zone, e.g., for pressure monitoring as

required at §146.90(g)(1), can be safely performed if the wells are constructed to prevent flow

between the injection zone and USDWs or other layers above the confining zone. Such construction

technologies exist and have been used in the oil and gas industry for years. EPA believes that

properly constructed monitoring wells will be a safe way to obtain the data that is essential to ensure

that the injected CO2 remains confined in the injection zone and that pressure changes are not

causing movement of formation or other fluids. To mitigate the risk of fluid movement, EPA

requires owners and operators to submit a testing and monitoring plan that describes how the owner

or operator plans to site and construct monitoring wells. EPA is developing guidance on well

construction that will include recommendations for monitoring well construction. The guidance will

be available on EPA’s website at http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, and tracking the CO2 plume

and pressure front. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm. In addition, in January 2009,

DOE published a best practices manual entitled "Monitoring, Verification, and Accounting of CO2

Stored in Deep Geologic Formations" (DOE/NETL-311/081508); this manual is included in the

docket for the final GS rule.

Commenter Name: Neeraj Gupta Letter ID: 0229

Commenter Organization: Battelle Energy Technology (BET) Comment ID: 21857

Comment: Page 103, Monitoring within the confining zone- In our experience it is very 

difficult to measure parameters in confining layers like pH, salinity, minerals, 

heavy metals, and organic contaminants on a routine basis. Confining zones 

typically consist of very low permeability carbonates that do not produce water 

or unstable shale not suitable for sampling due to borehole stability concerns. 

Response: EPA recognizes that the collection of representative ground water samples from depth

poses challenges and that special methods, such as U-tubes, will be needed to preserve the integrity

of such samples. EPA is developing guidance on testing and monitoring to assist owners or operators

and Directors in evaluating requirements under §146.90, including proposed monitoring plans. The

guidance describes available technologies and recommended approaches for implementing a testing

and monitoring plan, including pre-operational geophysical logging and testing of injection wells,

MITs, injection well testing during operation, groundwater quality monitoring, tracking the CO2

plume and pressure front, and soil gas and surface air monitoring which may be required by the UIC

Director for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.
Regarding the comment about the difficulty of sampling within the confining zone, EPA clarifies

that §146.90(d) requires owners and operators to monitor ground water quality and geochemical

changes above the confining zone(s), rather than within the confining zone.

Commenter Name: Steven B. Corneli Letter ID: 0234

Commenter Organization: NRG Energy, Inc. Comment ID: 23169

Other EPA Comment Codes and Descriptions: 4660 2.6.6 Geochemical monitoring 

Comment: Monitoring Requirements 

The preamble of the proposed rule states that the "monitoring of subsurface 

geochemistry and the position of the CO2 plume and pressure front are necessary 

to verify predictions of plume movement, provide inputs for modeling, identify 

needed corrective actions, and target geochemical and surface monitoring 

activities." 73 Fed. Reg. at 43514. NRG believes that the proposed monitoring 

requirements are excessive and unjustified. The use of monitor wells or seismic 

data would be needed to verify the model predictions. In particular, it is 

Response: EPA disagrees that the monitoring requirements in the GS rule are excessive or

unjustified. In addition to monitoring to track the movement of the CO2 plume and pressure front,

EPA believes that monitoring above the confining layer is an important part of a rigorous monitoring

program. Such monitoring can provide an early warning that the plume may be approaching a

USDW. The final rule, at §146.90(d), requires periodic monitoring of the ground water quality and

geochemical changes above the confining zone(s). EPA also believes that geophysical (e.g., seismic)

methods are useful for plume tracking at GS sites. For this reason, the final rule at §146.90(g)

requires the use of indirect methods (e.g., seismic, electrical, gravity, or electromagnetic surveys

and/or down-hole CO2 detection tools) unless the Director determines, based on site-specific

geology that such methods are not appropriate

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil gas and surface air monitoring which may be required by the UIC Director

for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

EPA also acknowledges that complete coverage of the potential plume area or leakage in the

subsurface is not possible through the use of monitoring wells. However, data from an appropriate

number of monitoring wells sited based on site-specific information will provide direct information

that is not otherwise obtainable and, along with other monitoring data, will support a broader

understanding of fluid behavior at the site. 

EPA adds that the iterative process of monitoring, modeling, and AoR reevaluation is appropriate to

verify that the CO2 plume and pressure front are moving through the subsurface as predicted, verify

the accuracy of the delineation model (or identify needed changes), and refine testing and monitoring

activities to ensure that USDWs are protected from endangerment and that there would be adequate

warning of potential problems at the site before any endangerment could occur.
Commenter Name: Steven B. Corneli Letter ID: 0234

Commenter Organization: NRG Energy, Inc. Comment ID: 23171

Comment: The preamble of the proposed rule states that the "monitoring of subsurface 

geochemistry and the position of the CO2 plume and pressure front are necessary 

to verify predictions of plume movement, provide inputs for modeling, identify 

needed corrective actions, and target geochemical and surface monitoring 

activities." 73 Fed. Reg. at 43514. NRG believes that the proposed monitoring 

requirements are excessive and unjustified. The use of monitor wells or seismic 

data would be needed to verify the model predictions. In particular, it is 

impractical and cost prohibitive to measure the exact location of the CO2 plume 

and pressure front using monitor wells. The monitor wells would be very 

expensive to install and may create a potential pathway for migration of CO2. In 

addition, plume or pressure front monitoring have never been necessary or 

required under the Class I hazardous waste injection well program because 

experience has shown that it is not necessary to verify the model predictions. 

Response: EPA disagrees that plume and pressure front monitoring are not justified for Class VI

wells. The Agency recognizes that while there are similarities between injection of wastes for

disposal (Class I) and GS, there are significant differences as well. Important unique considerations

for GS include the buoyancy of CO2, its corrosivity when in contact with water, its low viscosity

(i.e., high mobility), and the very large injection volumes that are anticipated. There is also a degree

of uncertainty regarding the behavior of large volumes of CO2 in the subsurface. Given these

characteristics of anticipated GS projects, EPA believes that plume and pressure front monitoring at

§146.90(g) are justified to provide early warning of any unforeseen fluid movement that might

endanger USDWs. 

The final rule at §146.90(g) requires owners or operators to perform monitoring to track the extent of

the CO2 plume and pressure front. The owner or operator must use direct methods to monitor for

pressure changes in the injection zone. Indirect methods (e.g., seismic, electrical, gravity, or

electromagnetic surveys and/or down-hole CO2 detection tools) are required unless the Director

determines, based on site-specific geology that such methods are not appropriate.

EPA believes that pressure monitoring in the injection zone is necessary to track the development

and movement of the pressure front and CO2 plume. Knowledge of the location of the CO2 plume

and the associated pressure front will also assure the public that GS projects are proceeding

according to plan, provide sufficient information to the owner or operator and Director, or allow for

appropriate actions to address any indication that USDWs may be endangered. 

EPA believes that monitoring using wells in the injection zone, e.g., for pressure monitoring as

required at §146.90(g)(1), can be safely performed if the wells are constructed to prevent flow

between the injection zone and USDWs or other layers above the confining zone. Such construction

technologies exist and have been used in the oil and gas industry for years. EPA believes that

properly constructed monitoring wells will be a safe way to obtain the data that is essential to ensure

that the injected CO2 remains confined in the injection zone and that pressure changes are not

causing movement of formation or other fluids. 

§146.90(g)(2) requires owners or operators to track the position of the CO2 plume using indirect

methods (e.g., seismic, electrical, gravity, or electromagnetic surveys and/or down-hole CO2

detection tools), unless the Director determines based on site-specific geology, that such methods are

not appropriate. For example, geophysical methods are difficult to execute in areas that are
structurally and topographically complex or where lithologies have limited contrast in density,

porosity, permeability, and other physical properties. EPA clarifies that this determination will be

made by the Director based on the site-specific geologic information submitted by the owner or

operator with the permit application.

EPA believes that this approach provides flexibility to develop a site-specific monitoring plan,

ensures that direct monitoring is available to track the movement of the CO2 and validate models,

and recognizes that indirect techniques are not appropriate in all situations. The owner or operator's

approved testing and monitoring plan will include the site-specific details, technologies, testing and

monitoring frequencies, and other pertinent information.

EPA also acknowledges that complete coverage of the potential plume area or leakage in the

subsurface is not possible through the use of monitoring wells. However, data from an appropriate

number of monitoring wells sited based on site-specific information will provide direct information

that is not otherwise obtainable and, along with other monitoring data, will support a broader

understanding of fluid behavior at the site.

Commenter Name: Robert F. Voorhees Letter ID: 0243

Commenter Organization: Underground Injection Technology Group (UIT

Group)

Comment ID:

23339

Comment: B. Stringency of the Proposed Rule 

The UIT Group is concerned by the overall level of stringency of the proposed 

requirements for Class VI injection wells. Carbon dioxide is among the most 

innocuous materials injected under the UIC program, and yet the proposed rules 

for carbon dioxide injection would be among the most elaborate and burdensome in 

the entire UIC program. This approach is incongruous at best, and certainly 

seems ill-suited to the goal of encouraging responsible development of geologic 

sequestration projects. However, the UIT Group’s specific concern is that the 

proposed Class VI regulations are so excessive in some respects that they could 

effectively undermine public confidence in the UIC program for other classes of 

injection wells, including Class I injection wells. 

The UIT Group is particularly concerned with the proposed Class VI monitoring 

requirements, which are based upon the premise that it is necessary to track the 

physical location of injected fluids and observationally "verify" that USDWs are 

not being endangered. These requirements would appear to make elaborate 

monitoring through the use of monitor wells or indirect geophysical "plume 

tracking" techniques mandatory for all geologic sequestration projects. In 

general, it simply isn't true that this kind of monitoring is necessary, and - 

again as a general rule - such monitoring would be burdensome, costly, and of 

limited utility. 

Any discussion of monitor well requirements must start with an understanding of 

how the UIC program works: injection can't even commence unless there has been 

an adequate demonstration that the injection zone is separated from USDWs by a 

confining zone sufficient to prevent the movement of fluids from the injection 

zone into a USDW. Operators of hazardous waste injection wells must go a step 

further: they must demonstrate - to a reasonable degree of certainty - that 
there will be no migration of hazardous constituents from the injection zone for 

as long as the waste remains hazardous. 

Decades of experience with Class I injection has demonstrated that this 

regulatory approach is effective: under current regulatory standards, injectionrelated contamination of USDWs is virtually unknown, and EPA itself has 

concluded - after reviewing a broad range of studies - that properly-permitted 

Class I injection wells "provide an extremely low-risk" waste management option. 

See Class I Underground Injection Control Program: Study of the Risks Associated 

with Class I Underground Injection Wells (EPA, March 2001) at p. 42. In the 

face of such well-documented success it is difficult to see why there should be 

any crisis of confidence sufficient to justify the suggestion that the required 

"up-front" technical evaluation and controls on injection activity are somehow 

so unreliable that elaborate monitoring to track injected fluids and "verify" 

non-endangerment is necessary and should be required in every case. 

It would be one thing if the kind of monitoring at issue were relatively easy 

and cost-effective, but it is not. In the deep subsurface, such monitoring is 

difficult, costly, and generally yields relatively limited information. 

Accordingly, while there may be specific circumstances under which the use of 

monitor wells or indirect geophysical methods can make sense, it is important to 

consider both the potential utility of such monitoring and the burdens and 

technical challenges involved, as the regulations for Class I hazardous waste 

injection wells reflect. To suggest that elaborate monitoring efforts should 

be mandatory at every site, as the proposed Class VI regulations appear to 

suggest, is unjustified and does disservice to the demonstrated effectiveness 

and success of the detailed site selection, characterization and pre-injection 

technical evaluation the UIC program requires. 

Response: EPA disagrees that monitoring at GS sites will undermine public confidence in GS and

the UIC Program. EPA believes that appropriately designed and implemented monitoring plans will

increase public confidence in the safety of GS, helping to assure the public that any problems are

detected early and that appropriate measures are taken to protect USDWs from endangerment.

Knowledge of the location of the CO2 plume and the associated pressure front will enable EPA to

assure the public that GS projects are proceeding according to plan, provide sufficient information to

the owner or operator and Director, or allow for appropriate actions to address any indication that

USDWs may be endangered.

EPA disagrees that plume and pressure front monitoring are not justified for Class VI wells. The

Agency recognizes that while there are similarities between injection of wastes for disposal (Class I)

and GS (Class VI), there are significant differences as well. Important unique considerations for GS

include the buoyancy of CO2, its corrosivity when in contact with water, its low viscosity (i.e., high

mobility), and the very large injection volumes that are anticipated. There is also a degree of

uncertainty regarding the behavior of large volumes of CO2 in the subsurface after injection. Given

these characteristics of anticipated GS projects, EPA believes that plume and pressure front

monitoring at §146.90(g) are justified to provide early warning of any unforeseen fluid movement

that might endanger USDWs. 

The final rule, at §146.90(g), requires owners or operators to perform monitoring to track the extent

of the CO2 plume and pressure front. The owner or operator must use direct methods to monitor for
pressure changes in the injection zone. Indirect methods (e.g., seismic, electrical, gravity, or

electromagnetic surveys and/or down-hole CO2 detection tools) are required unless the Director

determines, based on site-specific geology that such methods are not appropriate.

EPA believes that pressure monitoring in the injection zone is necessary to track the development

and movement of the pressure front and CO2 plume. Monitoring can also identify needed remedial

actions, provide inputs for AoR reevaluation modeling, evaluate predictions of plume movement,

and target additional geochemical and surface monitoring needs. 

In addition, §146.90(g)(2) requires owners or operators to track the position of the CO2 plume using

indirect methods (e.g., seismic, electrical, gravity, or electromagnetic surveys and/or down-hole CO2

detection tools), unless the Director determines, based on site-specific geology, that such methods

are not appropriate. EPA is affording Director's discretion regarding the use of geophysical

techniques at some sites because the Agency recognizes that geophysical methods are not appropriate

in all geologic settings. EPA clarifies that this determination will be made by the Director based on

the site-specific geologic information submitted by the owner or operator with the permit

application.

EPA believes that this approach provides flexibility to develop a site-specific monitoring plan,

ensures that direct monitoring is available to track movement of the CO2 and validate models, and

recognizes that indirect techniques are not appropriate in all situations. The owner or operator's

approved testing and monitoring plan will include the site-specific details, technologies, testing and

monitoring frequencies, and other pertinent information.

EPA acknowledges the commenters' concern about the cost of monitoring. However, EPA believes

that monitoring is essential for protection of USDWs at GS sites. Although a significant cost in

absolute terms, monitoring costs are expected to be a small fraction of site operating costs, according

to EPA's cost analysis for the GS rulemaking, which is available in the docket).

Commenter Name: Robert F. Voorhees Letter ID: 0243

Commenter Organization: Underground Injection Technology Group (UIT

Group)

Comment ID:

23342

Comment: regulations themselves do not impose. The UIT Group also urges EPA to: (1) 

acknowledge the demonstrated and well-documented success of the existing UIC 

program regulations for Class I hazardous waste injection wells; and (2) avoid 

regulatory excesses in the proposed rule that could potentially undermine public 

confidence in the established effectiveness of the Class I regulations and the 

requirements for other UIC classes of wells. 

Response: As described above, EPA disagrees that monitoring at GS sites will undermine public

confidence in GS and the UIC Program. EPA believes that appropriately designed and implemented

monitoring plans will increase public confidence in the safety of GS, helping to assure the public that

any problems are detected early and that appropriate measures are taken to protect USDWs from

endangerment. Knowledge of the location of the CO2 plume and the associated pressure front will

enable EPA to assure the public that GS projects are proceeding according to plan, provide sufficient

information to the owner or operator and Director, or allow for appropriate actions to address any

indication that USDWs may be endangered.

As described above, the Agency recognizes that while there are similarities between injection of
wastes for disposal (Class I) and GS (Class VI), there are significant differences as well. Important

unique considerations for GS include the buoyancy of CO2, its corrosivity when in contact with

water, its low viscosity (i.e., high mobility), and the very large injection volumes that are anticipated.

There is also a degree of uncertainty regarding the behavior of large volumes of CO2 in the

subsurface after injection. Given these characteristics of anticipated GS projects, EPA believes that

plume and pressure front monitoring at §146.90(g) are justified to provide early warning of any

unforeseen fluid movement that might endanger USDWs. 

EPA believes that this approach provides flexibility to develop a site-specific monitoring plan,

ensures that direct monitoring is available to track movement of the CO2 and validate models, and

recognizes that indirect techniques are not appropriate in all situations. The owner or operator's

approved testing and monitoring plan will include the site-specific details, technologies, testing and

monitoring frequencies, and other pertinent information.

Commenter Name: Kurt Waltzer Letter ID: 0250

Commenter Organization: Clean Air Task Force Comment ID: 22318

Comment: The proposed rule outlines several different types of monitoring requirements: 

(a) analysis of the CO2 stream; (b) continuous monitoring of injection pressure, 

rate and volume as well as other quantities; (c) corrosion monitoring for the 

well materials; (d) groundwater and geochemistry monitoring above the confining 

zone; (e) mechanical integrity testing; (f) pressure fall-off tests;(g) CO2 

plume and pressure front tracking; and (h) surface air monitoring. 

We do not wish to comment on (c). We consider subpart (i), enabling the Director 

to require additional forms of monitoring, as well as subpart (j), calling for a 

quality assurance and surveillance plan, entirely appropriate. We consider (a), 

(b), (d), (e), and (f) and (g) to be essential elements of a sound monitoring 

system. 

Response: EPA acknowledges the commenter’s support. Based on its evaluation of all public

comments and input on the proposed rule and NODA and Request for Comment EPA has made

many revisions to the GS rule. See the final rule and preamble for further discussion on EPA's final

approach.

EPA agrees with commenters on the importance of monitoring at GS sites and emphasizes that

monitoring of injection activities will be an important component of every GS project. Monitoring

associated with injection wells and the movement of the CO2 plume is necessary to verify that the

injectate is confined in the target formations and does not endanger USDWs.

Commenter Name: Kurt Waltzer Letter ID: 0250

Commenter Organization: Clean Air Task Force Comment ID: 22319

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: In particular, monitoring above the caprock, sometimes informally referred to as 

"above-zone monitoring, and covered in (d), is a tested monitoring method [FN23], and 

one that can be key to verifying the integrity and lateral extent of the caprock 

(or confining zone). We support its inclusion, but also recognize that it might 

not be necessary to employ this method every time. We would only consider its 
omission acceptable only if another method capable of testing and verifying the 

integrity of the confining zone is being used. Subpart (d) would also cover 

groundwater monitoring near the surface, at a long distance from the caprock. It 

is our understanding that researchers from the Lawrence Livermore National 

Laboratory are already confident in the merits of this approach and its accuracy 

in detecting small amounts of CO2. We therefore recommend the following minor 

changes to §146.90(d): 

[In the paragraph below the text 

in all CAPS denotes added text. See also EPA-HQ-OW-0390-0250.pdf to see the 

original formatting.] 

"Periodic monitoring of the ground water quality and GEOPHYSICAL, geochemical OR 

OTHER changes above the confining zone(s) that may be a result of carbon dioxide 

OR OTHER INDUCED fluid movement through the confining zone or additional 

identified zones; provided however that the DIRECTOR MAY INSTEAD REQUIRE THE 

INCLUSION OF OTHER METHODS THAT TEST AND/OR VERIFY THE INTEGRITY OF

THE 

CONFINING ZONE(S) WITH SIMILAR ACCURACY AND TO THE SAME OR LARGER

AREAL 

EXTENT.(1) [...]" 

[FN23: Used successfully at the Frio pilot project, and already being 

considered for other projects.] 

Response: EPA clarifies that direct monitoring of ground water quality above the confining zone is

important, and the GS rule requires this at §146.90(d). EPA believes that the ground water

geochemical monitoring outlined in §146.90(d) will maximize protection of USDWs from

endangerment at GS sites. Additional monitoring above the confining zone, as well as monitoring in

additional formations, e.g., the injection zone, may also be necessary, and if the Director believes

such monitoring is warranted he/she has the authority under §146.90(i) to require that it be included

in the testing and monitoring plan. 

EPA adds that the baseline geochemical data required with the permit application at §146.82(a)(6)

will provide information on predicting potential interactions between rocks and CO2 as the

commenter suggests, and also expects that this information will inform the development and

approval of a site-specific testing and monitoring plan. EPA expects that the data will also help

determine whether any changes are occurring above the confining zone and whether they might be

associated with the CO2 plume or pressure front.

EPA further clarifies that the final rule at §146.90(g) requires indirect monitoring not above the

confining zone but in the injection zone, unless the Director determines, based on site-specific

geology, that indirect methods are not appropriate. Indirect methods can include geophysical

methods.

Commenter Name: Michel Paque Letter ID: 0259

Commenter Organization: Ground Water Protection Council Comment ID: 24829

Comment: There should not be a requirement for monitor wells into the injection zone, and 

monitor wells should not be required for the purpose of tracking the plume or 
pressure front. 

Response: EPA maintains that plume tracking and pressure monitoring are key components of

monitoring at GS sites. A rigorous plume tracking and pressure monitoring scheme, such as one that

meets the requirements at §146.90(g), is imperative for ensuring that the CO2 plume is contained

within the injection zone. The final GS rule, at §146.90(g)(1), requires GS well owners or operators

to use direct methods to monitor for pressure changes in the injection zone. The purpose of

monitoring in the injection zone is to track the development and movement of the pressure front and

CO2 plume. This will support an understanding of site performance and verify predictive modeling.

Pressure monitoring within the injection zone is necessary because any such monitoring above the

confining zone would not detect movement of the pressure front unless a breach of the confining

zone occurs.

Commenter Name: Michel Paque Letter ID: 0259

Commenter Organization: Ground Water Protection Council Comment ID: 24923

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Rule Provision: 146.90 

EPA Proposal: (a) Analysis of the carbon dioxide stream with sufficient 

frequency to yield data representative of its chemical and physical 

characteristics; 

(b) Installation and use, except during well workovers as defined in § 

146.86(d), of continuous recording devices to monitor injection pressure, rate 

and volume; the pressure on the annulus between the tubing and the long string 

casing; and the annulus fluid volume; 

GWPC Recommendations: Support the proposed EPA language in (a) 

(b) Installation and use, except during well workovers as defined in §146.88(d), 

of continuous monitoring devices (including digital devices capturing periodic 

data) to monitor injection pressure, rate and volume; and record at least daily 

the pressure on the annulus between the tubing and the long string casing; 

Rationale: 146.86(d) does not exist; perhaps 146.88(d) is what was apparently 

intended. 

Response: EPA acknowledges the comment; the final rule retains the language in §146.90(a) as

proposed. EPA adds that the final GS rule references §146.88(e), as the commenter suggests. 

Regarding §146.90(b), based on its evaluation of all public comments and input on the proposed rule

and NODA and Request for Comment EPA has made many revisions to the GS rule. See the final

rule and preamble for further discussion on EPA's final approach.

Commenter Name: Michel Paque Letter ID: 0259

Commenter Organization: Ground Water Protection Council Comment ID: 24927

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule
language 

Comment: Rule Provision: 146.90 

EPA Proposal: (e) A demonstration of external mechanical integrity pursuant to § 

146.89(c) at least once per year throughout the duration of the geologic 

sequestration project; 

(f) A pressure fall-off test at least once every five years unless more frequent 

testing is required by the Director based on site specific information; 

GWPC Recommendations: (e) A demonstration of external mechanical integrity 

pursuant to §146.89(c) at least once per year until the well is plugged; 

(f) A pressure fall-off test or other equivalent test that identifies reservoir 

conditions with respect to flow dynamics at least once every five years unless 

more frequent testing is required by the Director based on site specific 

information; 

Rationale: Redundant to section 146.89 

Response: Based on its evaluation of all public comments and input on the proposed rule and

NODA and Request for Comment EPA has made many revisions to the GS rule. See the final rule

and preamble for further discussion on EPA's final approach.

EPA believes that pressure fall-off testing is necessary for GS wells. Pressure fall-off tests are

designed to verify that modeled projections of reservoir pressure decline agree with measured

pressure decline profiles. These tests can be useful in AoR calculations and reevaluations and may

also indicate mischaracterization of site geology and the presence of leakage pathways. EPA

therefore believes that pressure fall-off testing is necessary every five years at a minimum, and the

final GS regulation includes this requirement at §146.90(f). Pressure fall-off tests may be conducted

in conjunction with other well performance tests (i.e., mechanical integrity testing) to ensure safe and

effective operations.

Commenter Name: Iain Wright Letter ID: 0508

Commenter Organization: BP Alternative Energy Comment ID: 21183

Comment: Moving on to my second point, monitoring. Monitoring is very important, because 

a common mis-perception that if you want secure storage you need to do lots of 

monitoring. Well, the U.N. says that a proportion of CO2 obtained by 

appropriately selected and managed sites is likely to exceed 99 percent over a 

thousand years. 

So the key to secure storage is the appropriate selection and management of the 

site. If that's done properly the site will be very secure and the need for 

monitoring can be appropriately reduced. 

Monitoring is kind of like the speedometer on your car. It does contribute to 

your safety, but more important is the design of the car, the road, and how you 

drive the car. Having said that, at In Salah we are doing a big research project 

into monitoring. And so the program is much more extensive than it would be 
appropriate for a commercial project. 

We're trying out new technologies, such as satellite imagery, micro-seismic, so 

we can see how they perform against conventional oil fuel monitoring technology, 

such as tracers and conventional seismic. 

But as you can probably hear from my accent I'm a Scotsman, and Scotsmen don't 

like to waste money. So every technology that we use at In Salah has been 

carefully chosen to represent great value for money. Before we started the 

injection at In Salah we did a site-specific assessment of the risk of leakage, 

and then we tailored the monitoring program to address all of those risks. 

So mandating any specific monitoring technology would waste a lot of money and 

resources without contributing to the protection of USDWs. So we would caution 

against the universal mandate for any specific monitoring technology. 

Many of you will have heard of the other two monitored industrial scale CO2 

injection projects in the world at Sleipner and Weyburn. If you compare the 

monitoring activities of these sites you'll see that something which works in 

one location may not work at all in another location. So we encourage the EPA to 

use risk-based performance criteria to determine the site-specific monitoring 

programs. 

Response: EPA agrees with commenters and believes that flexibility is important in developing and

implementing a monitoring plan that is appropriately tailored for a specific GS site. The purpose of

the requirement at §146.90 to develop site-specific testing and monitoring plans is to ensure that the

monitoring performed at a site is appropriate for site operational conditions and the geologic setting.

EPA believes that this is the best approach for addressing potential risks at GS sites. These flexible

provisions in the monitoring requirements for Class VI wells enable the owner or operator to tailor

monitoring programs to the specific needs of each project in consultation with the Director.

The final regulation provides for flexibility in: 1) methodologies used to collect these data, 2) the

spatial resolution at which the data should be collected, and 3) how often the data should be

collected. The number and placement of monitoring wells will be based on site-specific information

such as the calculated AoR, injection rate and volume, site geology, baseline data, and the presence

of artificial penetrations within the AoR. In some instances, there may be a limited number of

options for complying with EPA's minimum requirements. For example, monitoring for geochemical

changes will require use of monitoring wells and collection of groundwater samples for chemical

analysis. Many options currently exist for complying with other requirements, such as tracking the

position of the plume and pressure front within the injection zone.

Flexibility is also provided regarding how to monitor for the specific data required by the final rule.

The testing and monitoring plan is developed by the owner or operator in consultation with the

Director and is designed to ensure that a detailed, Director-approved document describing how

monitoring will be conducted during the lifetime of the project exists. EPA is developing guidance

on testing and monitoring to assist owners or operators and Directors in evaluating requirements

under §146.90, including proposed monitoring plans. The guidance describes available technologies

and recommended approaches for implementing a testing and monitoring plan, including preoperational geophysical logging and testing of injection wells, MITs, injection well testing during

operation, groundwater quality monitoring, tracking the CO2 plume and pressure front, and soil gas
and surface air monitoring which may be required by the UIC Director for specific GS projects. The

guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm. In addition, in January 2009,

DOE published a best practices manual entitled "Monitoring, Verification, and Accounting of CO2

Stored in Deep Geologic Formations" (DOE/NETL-311/081508); this manual is included in the

docket for the final GS rule.

Commenter Name: Scott Anderson Letter ID: 0520

Commenter Organization: Environmental Defense Fund Comment ID: 21428

Comment: We like the fact that the rules place a lot of importance on monitoring. In 

several instances, the rules proposed using monitoring to modify the various 

aspects of the operations, but we think the rules can go further in this respect 

and we will spell that out in our final comments. 

Response: EPA agrees with commenters on the importance of monitoring at GS sites and

emphasizes that monitoring of injection activities will be an important component of every GS

project. Monitoring associated with injection wells and the movement of the CO2 plume is necessary

to verify that the injectate is confined in the target formations and does not endanger USDWs.

Commenter Name: Cynthia Lane Letter ID: 0528

Commenter Organization: American Water Works Association (AWWA) Comment ID: 21386

Other EPA Comment Codes and Descriptions: 1435 1.2.1.3 EPA should develop guidance 

Comment: EPA should provide guidance on acceptable monitoring techniques and frequency, 

provide for a consistent application of the monitoring requirements. Another 

Response: EPA is developing guidance on testing and monitoring to assist owners or operators and

Directors in evaluating requirements under §146.90, including proposed monitoring plans. The

guidance describes available technologies and recommended approaches for implementing a testing

and monitoring plan, including pre-operational geophysical logging and testing of injection wells,

MITs, injection well testing during operation, groundwater quality monitoring, tracking the CO2

plume and pressure front, and soil gas and surface air monitoring which may be required by the UIC

Director for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Mike Moore Letter ID: 0532

Commenter Organization: North American Carbon Capture and Storage

Association (NACCSA)

Comment ID:

21367

Other EPA Comment Codes and Descriptions: 4000 2.4 Proposed Injection Well Operating

Requirements (40 CFR 146.88) 

Comment: The second area of concern is the proposed rule's treatment of CCS operations 

and monitoring. The proposed rule would require CCS wells to meet or exceed the 

operating standards of industrial and hazardous waste wells in many cases. NACSA 

believes that such treatment is not justified by the attributes of carbon 

dioxide. Also the director would have discretion without any guidance to require 

Response: The Agency recognizes that while there are similarities between injection of wastes for

disposal (Class I) and GS (Class VI), there are significant differences as well. Important unique

considerations for GS include the buoyancy of CO2, its corrosivity when in contact with water, its
low viscosity (i.e., high mobility), and the very large injection volumes that are anticipated. There is

also a degree of uncertainty regarding the behavior of large volumes of CO2 in the subsurface after

injection. 

Given these characteristics of anticipated GS projects, EPA believes that the monitoring

requirements at §146.90 are justified to provide early warning of any unforeseen fluid movement or

problems with the injection well that might endanger USDWs. EPA emphasizes that monitoring of

injection activities will be an important component of every GS project. Monitoring associated with

injection wells and the movement of the CO2 plume is necessary to verify that the injectate is

confined in the target formations and does not endanger USDWs.

EPA believes the operating requirements for Class VI wells are necessary and provide multiple

safeguards to ensure that well integrity, containment of fluids within the injection zone, and that the

integrity of the confining zone is not compromised. Some of the operating requirements in the GS

regulation (e.g., pressure limitations or annulus pressure requirements) are consistent with those for

other injection well types, while other requirements (e.g., use of automatic shut-off systems or

tracers at the Director's discretion) are tailored to directly address the potential for large volumes of

CO2 to be injected, among other factors. 

The requirements for GS projects are tailored to address the unique issues associated with GS

including large injection volumes, the relative buoyancy of CO2, its corrosivity in the presence of

water, the potential presence of impurities in captured CO2, and its mobility within subsurface

geologic formations. EPA also believes these requirements are appropriate for Class VI wells given

the potential geomechanical stresses in the wellbore, and the potential for movement of the CO2 in

the event of a mechanical integrity loss.

Commenter Name: George Peridas Letter ID: 0534

Commenter Organization: Natural Resources Defense Council (NRDC) Comment ID: 21462

Other EPA Comment Codes and Descriptions: 3700 2.2.5 Comments on the requirement for an

AoR and corrective action plan 

Comment: The requirements for extensive monitoring is another example. This architectural 

design nature of having to continue to update the proposed plans, operational 

parameters, closure plans, etcetera as modeling data comes in and that is 

monitoring comes in. I think it is a very sound one which should be maintained 

Response: EPA acknowledges the commenter's support of the AoR and corrective action plan, and

retains the requirement in the final regulation §146.84(b). EPA believes that the iterative process by

which monitoring and operational data are used to validate the original AoR calculation, along with

the combined knowledge and ongoing dialogue between the owner or operator and the Director on

the local geologic conditions will be critical in developing and implementing plans that protect

USDWs from endangerment.

EPA agrees that monitoring data should be used to review model assumptions, verify computational

model projections, and, when necessary, provide input for model refinements. As data are collected

at an injection site, model parameters can be adjusted to match observations (i.e., for model

calibration or), which in turn improves the predictive capability of the model. As a GS project

proceeds, both monitoring and modeling will evolve, with monitoring results supporting effective

AoR reevaluations and leading to improved model predictions.
EPA believes that developing and following testing and monitoring plans is an important part of

assuring that a GS project is operating properly and is crucial for the early detection of potential

endangerment to USDWs. EPA also believes that periodic updates to the plan are appropriate. EPA

clarifies that the final GS regulation includes a requirement that the AoR be reevaluated at least

every 5 years, and it specifies at §146.90(j) that the operator revise the testing and monitoring plan to

incorporate the results of the most recent AoR reevaluation and recent operational and monitoring

data.

Comment Code: 4610 2.6.1 Testing and monitoring plan requirement (seeking comment) 

Individual Comments

Commenter Name: Christine Reimer Letter ID: 0142

Commenter Organization: National Ground Water Association Comment ID: 22609

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: [In the text below, text in CAPS denotes added text.] 

Proposed Rule: 146.90(h)(1) 

Proposed revision: (1) The testing and monitoring plan must be based on 

potential RISKS within the area of review; 

Rationale: Risk is more generally accepted and understood. 

Response: The final rule at §146.90(h)(1) incorporates the suggested revision. Based on its

evaluation of all public comments and input on the proposed rule and NODA and Request for

Comment EPA has made many revisions to the GS rule. See the final rule and preamble for further

discussion on EPA's final approach.

Commenter Name: Brianne Metzger Letter ID: 0151

Commenter Organization: Spectra Energy Corp Comment ID: 21841

Comment: EPA is also proposing "periodic monitoring of the ground water quality and 

geochemical changes above the confining zone(s)." § 146.90(d). It is unclear 

how many wells would be required, and whether EPA expects all zones would be 

monitored. Given the potential size of the CO2 plume and the number of 

confining zones, this could potentially require many monitoring wells, which 

could be extremely expensive and unlikely to produce useful data. It is our 

strong recommendation that EPA minimize the amount of monitoring to the zone 

immediately above the confining zone, and only to the extent that the CO2 plume 

is within close proximity. For example, there may be regional conditions where 

ground water is separated by hundred or thousands of feet of confining strata, 

and where such monitoring is unnecessary. We would recommend that the Director 

be given discretion to limit or tailor ground water monitoring, as appropriate, 

based on regional and site specific factors. 

Response: The GS rule stipulates that the monitoring frequency and spatial distribution of
monitoring wells must be based on baseline geochemical data that were collected during the initial

site characterization and the area of review evaluation, as described in §146.90(d)(2). The details of

the geochemical monitoring will be described in the Director-approved testing and monitoring plan.

Regarding monitoring locations, section §146.90(d) requires periodic monitoring of the ground water

quality and geochemical changes above the confining zone(s). Monitoring above the confining layer

will provide an indication of upward movement of CO2 that might endanger a USDW. The exact

number of formations to be tested will, however, be based on site-specific characteristics and

vulnerabilities and described in the Director-approved testing and monitoring plan. 

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil gas and surface air monitoring which may be required by the UIC Director

for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

EPA also acknowledges that complete coverage of the potential plume area or leakage in the

subsurface is not possible through the use of monitoring wells. However, data from an appropriate

number of monitoring wells sited based on site-specific information will provide direct information

that is not otherwise obtainable and, along with other monitoring data, will support a broader

understanding of fluid behavior at the site. 

EPA acknowledges the commenters' concern about the cost of monitoring. However, EPA believes

that monitoring is essential for protection of USDWs at GS sites. Although a significant cost in

absolute terms, monitoring costs are expected to be a small fraction of site operating costs, according

to EPA's cost analysis for the GS rulemaking (which is available in the docket).

Commenter Name: Bonnie Lovelace Letter ID: 0152

Commenter Organization: Montana Department of Environmental Quality

(MDEQ)

Comment ID:

22118

Other EPA Comment Codes and Descriptions: 3700 2.2.5 Comments on the requirement for an

AoR and corrective action plan; 4710 2.7.1 Proposed submissions required for permit applications

(seeking comment) 

Comment: 17. EPA seeks comment on the merits of requiring plans for monitoring, area of 

review and post-injection site care as part of a permit application. MDEQ agrees 

that this is necessary and appropriate. A"cradle-to-grave" approach is wise in 

this instance and allows for updating the permit application materials as new 

technologies are forthcoming. 

Response: EPA acknowledges the commenter’s support of the GS project plans. EPA believes that

the requirement for the plans associated with GS projects will promote an ongoing dialogue between

the owner or operator and the Director to ensure that USDWs are protected from endangerment.

EPA is developing guidances for owners or operators describing recommended approaches to

prepare the project plans. The guidances will be available on EPA's web site, at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.
On the topic of monitoring and plan revision: EPA agrees with commenters on the importance of

monitoring at GS sites and emphasizes that monitoring of injection activities will be an important

component of every GS project. EPA also believes that periodic updates to the plans are appropriate.

EPA clarifies that the final GS regulation includes a requirement that the AoR be reevaluated at least

every 5 years, and it specifies at §146.90(j) that the operator revise the testing and monitoring plan to

incorporate the results of the most recent AoR reevaluation and recent operational and monitoring

data.

EPA agrees that incorporating the plans into the permit rather than establishing specific requirements

for corrective action, monitoring, injection well plugging, and post-injection site care in the

regulation provide the appropriate flexibility to address the variety of site-specific conditions that

may be encountered at GS sites. This approach is retained in the final rule. Please see the final rule

and the discussion of the required GS project plans in the preamble for additional information.

EPA also believes that it is appropriate to require owners and operators to submit all plans, including

the injection well plugging and post-injection site care and site closure plans, at the time of permit

application. EPA believes that the Director needs a satisfactory level of assurance that the owner or

operator has planned for these events before injection commences and that the owner or operator has

ensured that appropriate financial resources are available to fund all required activities, as required at

§146.85. The final rule retains requirements for submitting these plans with the permit application at

§146.82(a). EPA believes that the requirement for this and other plans associated with GS projects

will promote an ongoing dialogue between the owner or operator and the Director to ensure USDWs

are protected from endangerment. In addition, these plans will support a demonstration that owners

and operators have adequate financial resources to meet well plugging and post-injection site care

and site closure requirements.

Commenter Name: Michael Mudd Letter ID: 0167

Commenter Organization: FutureGen Alliance (FGIA) Comment ID: 22473

Other EPA Comment Codes and Descriptions: 3700 2.2.5 Comments on the requirement for an

AoR and corrective action plan 

Comment: A-7 Record Keeping and Reporting Requirements III-A-7 We support the requirement 

for 1) a monitoring and testing plan 2) an AoR and Correction Action Plan and 

3) a Post-Injection Site Care and Site Closure plan. 

Response: EPA acknowledges the commenter’s support of the GS project plans. EPA believes that

the requirement for the plans associated with GS projects will promote an ongoing dialogue between

the owner or operator and the Director to ensure that USDWs are protected from endangerment.

EPA is developing guidance for owners or operators describing recommended approaches to prepare

the project plans. The guidance will be available on EPA's web site, at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

EPA agrees that developing, implementing, and periodically reviewing the required GS project plans

is an important part of assuring that a GS project is operating properly and is crucial for the early

detection of potential endangerment to USDWs. EPA also believes that periodic updates to the plans

are appropriate. EPA clarifies that the final GS regulation includes a requirement that the AoR be

reevaluated at least every 5 years, and it specifies at §146.90(j) that the operator revise the testing

and monitoring plan to incorporate the results of the most recent AoR reevaluation and recent

operational and monitoring data. EPA also agrees that the site-specific plans required for GS projects

will maximize protection of USDWs from endangerment.
Commenter Name: Kyle Isakower Letter ID: 0170

Commenter Organization: American Petroleum Institute Comment ID: 24196

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Rule Provision: 146.90(h)(1) 

API Comments: (1) The testing and monitoring plan must be based on potential 

vulnerabilities SITE-SPECIFIC GEOLOGIC FACTORS, MODELING, AND RISK-ASSESSMENT

within the area of review; 

Rationale: Technical clarification 

Response: Based on its evaluation of all public comments and input on the proposed rule and

NODA and Request for Comment, EPA has made many revisions to the GS rule. See the final rule

and preamble for further discussion on EPA's final approach. EPA anticipates that the testing and

monitoring plan will address site-specific geologic factors, modeling, and risk-assessment. EPA is

developing guidance on how best to develop the various required project plans, including the testing

and monitoring plan. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Kyle Isakower Letter ID: 0170

Commenter Organization: American Petroleum Institute Comment ID: 24197

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Rule Provision: 146.90(i) 

API Comments: (i) Any additional monitoring, as required by the Director, BASED 

ON SITE-SPECIFIC CONDITIONS AND RISK-BASED FACTORS, necessary to support, 

upgrade, and improve computational modeling of the area of review evaluation 

required under § 146.84(b) and to determine compliance with standards under 40 

CFR 144.12 

Rationale: Technical clarification 

Response: Based on its evaluation of all public comments and input on the proposed rule and

NODA and Request for Comment, EPA has made many revisions to the GS rule. See the final rule

and preamble for further discussion on EPA's final approach. EPA agrees that any additional

monitoring requirements would be based on site-specific geologic factors, modeling, and riskassessment. EPA is developing guidance for directors that provides recommended approaches when

exercising discretion to require additional monitoring. The guidance can be found on EPA’s website

at http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Kyle Isakower Letter ID: 0170

Commenter Organization: American Petroleum Institute Comment ID: 24251

Other EPA Comment Codes and Descriptions: 4710 2.7.1 Proposed submissions required for

permit applications (seeking comment) 
Comment: Rule Provisions: 146.90, 146.93(a), 146.94(a) 

EPA Preamble Question: 34. EPA is proposing that permit applications for GS 

sites include several plans not currently required under existing UIC 

regulations. These plans include a monitoring and testing plan, an AoR and 

corrective action plan, and a post-injection site care and site closure plan. 

EPA seeks comment on the merits of requiring plans for monitoring, AoR, and 

Post-injection site care as part of a permit application. EPA Notice 43517. 

API Response: The development of such plans is a good idea because it negates 

prescriptive regulation of the process. API is concerned that every modification 

of a plan may trigger a major permit modification. Although actual monitoring of 

injection formation is most effective, there is still the unintended consequence 

of penetrating the confining zone to gain that data. The number of monitoring 

wells should not be established in advance. It is unclear how monitoring well 

construction, operation, and closure will be regulated since these are not 

actual injection wells. 

Timing of development of plans should be linked to the actual activity being 

addressed (i.e. staged). It should not be necessary to prepare and submit a site 

closure plan or the post-closure monitoring plan at the start of the project, 

particularly considering that these activities will not occur for many years 

after the project starts. 

Response: EPA agrees with commenters that developing and following testing and monitoring plans

is an important part of assuring that a GS project is operating properly and is crucial for the early

detection of potential endangerment to USDWs. EPA expects that the number of monitoring wells

needed will be determined based on site-specific information. EPA also agrees that periodic updates

to the plan are appropriate. EPA clarifies that the final GS regulation includes a requirement that the

AoR be reevaluated at least every five years, and it specifies at §146.90(j) that the operator revise the

testing and monitoring plan to incorporate the results of the most recent AoR reevaluation and recent

operational and monitoring data.

EPA believes that monitoring using wells in the injection zone, e.g., for pressure monitoring as

required at §146.90(g)(1), can be safely performed if the wells are constructed to prevent flow

between the injection zone and USDWs or other layers above the confining zone. Such construction

technologies exist and have been used in the oil and gas industry for years. The testing and

monitoring plan must describe how the owner or operator plans to site and construct monitoring

wells. EPA is developing guidance on well construction that will include recommendations for

monitoring well construction. The guidance will be available on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

EPA clarifies that every revision to the testing and monitoring plan will not necessarily trigger a

major permit modification. The existing regulation at 40 CFR 144.39(a) identifies causes for

modification of permits that would invoke the public notification procedures at 40 CFR 124. In the

final rule, EPA added text to §144.39(a)(5) that permit modifications would be required if the

Director determines that a modification is necessary based on an AoR reevaluation, amendments to

any of the project plans, or a review of the testing and monitoring results. 

In addition, 40 CFR Part 144.41 identifies causes for minor modifications of permits (which do not

require following the procedures of Part 124). In the final rule, EPA added a subparagraph (h) to
§144.41 that would include minor amendments (e.g., to clarify, correct, or update) to the testing and

monitoring plan, plugging plan, post-injection site care and site closure plan, or emergency and

remedial response plan for a GS well (i.e., amendments that are not included under 144.39(a)(5) and

that do not require additional permit requirements). 

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm. In addition, in January 2009,

DOE published a best practices manual entitled "Monitoring, Verification, and Accounting of CO2

Stored in Deep Geologic Formations" (DOE/NETL-311/081508); this manual is included in the

docket for the final GS rule. EPA notes that closure of monitoring wells should be addressed in the

post-injection site care and site closure plan.

EPA also believes that it is appropriate to require owners and operators to submit all plans, including

the injection well plugging and post-injection site care and site closure plans, at the time of permit

application. EPA believes that the Director needs a satisfactory level of assurance that the owner or

operator has planned for these events before injection commences and that the owner or operator has

ensured that appropriate financial resources are available to fund all required activities, as required at

§146.85. The final rule retains requirements for submitting these plans with the permit application at

§146.82(a).

Commenter Name: Thomas Curtis Letter ID: 0181

Commenter Organization: American Water Works Association (AWWA) Comment ID: 23697

Comment: be considered unless this monitoring is included. All of the monitoring 

requirements should be put forth in a monitoring plan, which should be reviewed 

and approved by the Director prior to the start of the project. This plan should 

be re-evaluated every five years during the permit review, and should be updated 

by the owner/operator based on any changes in operation or performance of the 

carbon dioxide plume. 

Response: EPA agrees with commenters that developing and following testing and monitoring plans

is an important part of assuring that a GS project is operating properly and is crucial for the early

detection of potential endangerment to USDWs. EPA also agrees that periodic updates to the plan are

appropriate. EPA clarifies that the final GS regulation includes a requirement that the AoR be

reevaluated at least every 5 years, and it specifies at §146.90(j) that the operator revise the testing

and monitoring plan to incorporate the results of the most recent AoR reevaluation and recent

operational and monitoring data. EPA is developing guidance on how best to develop the various

required project plans, including the testing and monitoring plan. The guidance can be found on

EPA’s website at http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Thomas Curtis Letter ID: 0181

Commenter Organization: American Water Works Association (AWWA) Comment ID: 23700

Other EPA Comment Codes and Descriptions: 5200 2.8.2 Post injection site care (seeking

comment) (40 CFR 146.93) 

Comment: Category: Required Project Plans 

EPA Request for Comment: EPA seeks comment on the merits of requiring plans for 

monitoring, AoR, and post-injection site care as part of a permit application. 
EPA Notice 43517. 

AWWA Response: The requirement for the development of plans for monitoring, AoR, 

and post-injection site care is necessary and is a very important part of the 

permit process. The information will provide outside stakeholders with a much 

better idea of how the project will proceed and can help to assure them that the 

owner/operator has a clear vision for the life of the project. AWWA recommends 

that these plans be reviewed at the same time that the area of review is 

reevaluated. During this review, the plans should be updated based on any 

operational changes since the last project review period and submitted to the 

Director for approval. AWWA recommends that a review occur every year for the 

first ten years of the project, and then should be reviewed every five years 

until injection ceases. 

Response: EPA agrees with the commenter. Owners or operators are required to submit an AoR and

corrective action plan, a testing and monitoring plan, and a post-injection site care and site closure

plan as part of the permit application, as specified in §146.82(a), to outline how these activities will

be performed and how non-endangerment of USDWs will be demonstrated throughout the

operational and post-injection site care periods. EPA is developing guidance on how best to develop

the various required project plans, including the testing and monitoring plan. The guidance can be

found on EPA’s website at http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm. 

The GS rule also requires owners or operators to review and update the AoR and corrective action

plan and the testing and monitoring plan throughout the life of the project, as described at

§146.84(c) and §146.90(j). The rule requires at §146.90(j) that the operator revise the testing and

monitoring plan to incorporate the results of the most recent AoR reevaluation and recent

operational and monitoring data. Owners or operators must review each plan and identify necessary

amendments to the plan or demonstrate to the Director that no amendment is needed. These reviews

must be performed within one year of an AoR reevaluation, following any significant changes to the

facility (e.g., the addition of monitoring or injection wells), or when required by the Director. In no

case can reviews occur less often than once every five years. This review frequency is appropriate to

ensure that reviews of the plans are conducted on a defined schedule or when there is a change in the

AoR or significant change, while adding little burden if an AoR reevaluation confirms that the plans

are appropriate as written. See the preamble sections on the plans for additional information. 

EPA is not requiring formal periodic review and updates to the PISC and site closure plan

throughout the injection phase as with the AoR reevaluation that is required at least every 5 years.

EPA does not expect that changes to this plan would be implemented until injection operations

cease. EPA is requiring that upon the cessation of injection, the owner or operator submit an

amended post-injection site care and site closure plan or demonstrate to the Director that no changes

to the original post-injection site care and site closure plan are necessary, as specified in

§146.93(a)(3). EPA envisions that owners or operators would take into account similar

considerations that guide updates to other project plans, e.g., monitoring and operational data and

results of AoR reevaluations.

EPA has also added a new provision at §144.39(a)(5) identifying the basis for a modification,

revocation, or reissuance of a Class VI permit whenever the Director determines that a change in the

permit is necessary based on an amended AoR and corrective action plan, testing and monitoring

plan, injection well plugging plan, post-injection site care and site closure plan, or emergency and

remedial response plan is necessary.
Commenter Name: Thomas Curtis Letter ID: 0181

Commenter Organization: American Water Works Association (AWWA) Comment ID: 23743

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Part 146.90 AWWA recommends revising this part to read: 

The owner or operator of a Class VI well must prepare, maintain, and comply with 

a testing and monitoring plan to verify that the geologic sequestration project 

is operating as permitted and is not endangering USDWs. The testing and 

monitoring plan must be submitted with the permit application, for Director 

approval, and must include a description of how the owner or operator will meet 

the requirements of this section. The testing and monitoring plan must be 

reviewed and updated, as necessary, on the same schedule as the update to the 

Area of Review. 

Response: EPA agrees that periodic updates to the plan are appropriate. EPA clarifies that the final

GS regulation includes a requirement that the AoR be reevaluated at least every 5 years, and it

specifies at §146.90(j) that the operator revise the testing and monitoring plan to incorporate the

results of the most recent AoR reevaluation and recent operational and monitoring data. Based on its

evaluation of all public comments and input on the proposed rule and NODA and Request for

Comment EPA has made many revisions to the GS rule. See the final rule and preamble for further

discussion on EPA's final approach.

EPA agrees with commenters that developing and following testing and monitoring plans is an

important part of assuring that a GS project is operating properly and is crucial for the early

detection of potential endangerment to USDWs.

Commenter Name: Thomas Curtis Letter ID: 0181

Commenter Organization: American Water Works Association (AWWA) Comment ID: 23745

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Part 146.90(h)(1) AWWA recommends revising this part to read: 

The testing and monitoring plan must be based on site-specific geologic factors, 

modeling, and a risk-assessment of potential vulnerabilities within the area of 

review; 

Response: As described above, EPA agrees that periodic updates to the plan are appropriate, and the

final GS regulation includes a requirement that the AoR be reevaluated at least every 5 years, and it

specifies at §146.90(j) that the operator revise the testing and monitoring plan to incorporate the

results of the most recent AoR reevaluation and recent operational and monitoring data. Based on its

evaluation of all public comments and input on the proposed rule and NODA and Request for

Comment EPA has made many revisions to the GS rule. See the final rule and preamble for further

discussion on EPA's final approach.

Commenter Name: Bradley J. Field Letter ID: 0186

Commenter Organization: New York State Dept. of Environmental Conservation Comment ID:
Div. of Mineral Resources 25206

Comment: HH. In addition, EPA seeks comment regarding the use of a Director-approved 

monitoring plan for GS sites. 

NYSDEC-DMN Response: The Director should be given flexibility to approve sitespecific monitoring plans. 

Response: EPA agrees with commenters that developing and following testing and monitoring plans

and giving Directors flexibility to approve the plans based on site-specific criteria are important

parts of assuring that a GS project is operating properly and is crucial for the early detection of

potential endangerment to USDWs. 

The testing and monitoring plan is developed by the owner or operator in consultation with the

Director and is designed to ensure that a detailed, Director-approved document describing how

monitoring will be conducted during the lifetime of the project exists. The testing and monitoring

plan must be approved by the Director. EPA is developing guidance on testing and monitoring to

assist owners or operators and Directors in evaluating requirements under §146.90, including

proposed monitoring plans. The guidance describes available technologies and recommended

approaches for implementing a testing and monitoring plan, including pre-operational geophysical

logging and testing of injection wells, MITs, injection well testing during operation, groundwater

quality monitoring, tracking the CO2 plume and pressure front, and soil gas and surface air

monitoring which may be required by the UIC Director for specific GS projects. The guidance can

be found on EPA’s website at http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Robert F. Van Voorhees Letter ID: 0190

Commenter Organization: Carbon Sequestration Council Comment ID: 24354

Comment: G. Testing and Monitoring Requirements 

The preamble to the proposed rule indicates that "EPA considers CO2 plume and 

associated pressure front monitoring to be necessary for verification of model 

predictions." 73 Fed. Reg. at 43514. This proposal unnecessarily undermines 

confidence in the modeling demonstrations that can and should be relied upon to 

support determinations that injected CO2 will not endanger USDWs. Modeling 

provides a conservative assessment of the potential for movement of injected 

fluids in the subsurface, not a precise "prediction" of actual fate and 

transport that can or should be "verified" on the basis of elaborate, costly, 

and uncertain efforts to observe the actual movement of fluids in the 

subsurface. As experience with hazardous waste injection shows, injection well 

operational data and the results of pressure fall-off tests provide ample data 

to validate the results of modeling. The additional monitoring requirements 

proposed in the GS context go beyond what is required for Class I hazardous 

waste injection wells; these requirements are excessive and unnecessary. 

Response: EPA agrees that good site selection and modeling are crucial elements of a successful GS

project, but disagrees that this is an effective substitute for rigorous site monitoring, including

pressure monitoring. EPA believes that pressure monitoring in the injection zone is necessary to

track the development and movement of the pressure front and CO2 plume. Monitoring can also

identify needed remedial actions, provide inputs for AoR reevaluation modeling, evaluate predictions

of plume movement, and target additional geochemical and surface monitoring needs. Knowledge of
the location of the CO2 plume and the associated pressure front will also assure the public that GS

projects are proceeding according to plan, provide sufficient information to the owner or operator

and Director, or allow for appropriate actions to address any indication that USDWs may be

endangered. 

EPA disagrees that plume and pressure front monitoring are not justified for Class VI wells. The

Agency recognizes that while there are similarities between injection of wastes for disposal (Class I)

and GS (Class VI), there are significant differences as well. Important unique considerations for GS

include the buoyancy of CO2, its corrosivity when in contact with water, its low viscosity (i.e., high

mobility), and the very large injection volumes that are anticipated. There is also a degree of

uncertainty regarding the behavior of large volumes of CO2 in the subsurface after injection. Given

these characteristics of anticipated GS projects, EPA believes that plume and pressure front

monitoring at §146.90(g) are justified to provide early warning of any unforeseen fluid movement

that might endanger USDWs. 

The final rule (at §146.90(g)) requires owners or operators to perform monitoring to track the extent

of the CO2 plume and pressure front. The owner or operator must use direct methods to monitor for

pressure changes in the injection zone. 

§146.90(g)(2) requires owners or operators to track the position of the CO2 plume using indirect

methods (e.g., seismic, electrical, gravity, or electromagnetic surveys and/or down-hole CO2

detection tools), unless the Director determines based on site-specific geology that such methods are

not appropriate. For example, geophysical methods are difficult to execute in areas that are

structurally and topographically complex or where lithologies have limited contrast in density,

porosity, permeability, and other physical properties. EPA clarifies that this determination will be

made by the Director based on the site-specific geologic information submitted by the owner or

operator with their permit application.

EPA disagrees that pressure fall-off tests are an appropriate substitute for monitoring pressure

changes in the injection zone. Pressure fall-off tests provide information only in the vicinity of the

injection well(s) and measure pressure conditions within the injection zone only. Direct monitoring

of pressure changes in the injection zone can provide advance warning of movement of CO2 or brine

that might ultimately endanger a USDW. 

EPA acknowledges the commenters' concern about the cost of monitoring. However, EPA believes

that monitoring is essential for protection of USDWs at GS sites. Although a significant cost in

absolute terms, monitoring costs are expected to be a small fraction of site operating costs, according

to EPA's cost analysis for the GS rulemaking (which is available in the docket).

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Robert F. Van Voorhees Letter ID: 0190

Commenter Organization: Carbon Sequestration Council Comment ID: 24478

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule
language 

Comment: Rule Provision: 146.90 [Introductory text] 

Proposed CCS Group Recommendations: (A) BASED ON A SITE-SPECIFIC ASSESSMENT OF 

THE POTENTIAL FOR FLUID MOVEMENT FROM THE INJECTION WELL OR INJECTION

ZONE, AND 

ON THE POTENTIAL VALUE OF MONITORING WELLS TO DETECT SUCH MOVEMENT,

the owner or 

operator of a Class VI well must prepare, maintain, and comply with a testing 

and monitoring plan to verify that the geologic sequestration project is 

operating as permitted and is not endangering USDWs. THE TESTING AND 

MONITORING PLAN MUST BE SUBMITTED WITH THE PERMIT APPLICATION, FOR

DIRECTOR 

APPROVAL AND INCLUDE A DESCRIPTION OF HOW THE OWNER OR OPERATOR WILL

MEET THE 

REQUIREMENTS OF THIS SECTION; 

Basis for CCS Group Comments: Drilling monitoring wells should be carefully 

considered since each well introduces a potential pathway for fluid movement. In 

addition the cost of adding multiple wells could create a barrier to CCS 

development, while providing limited information on actual movement of the CO2 

stream. 

Response: Based on its evaluation of all public comments and input on the proposed rule and

NODA and Request for Comment, EPA has made many revisions to the GS rule. See the final rule

and preamble for further discussion on EPA's final approach.

EPA anticipates that the testing and monitoring plan will address site-specific geologic factors,

modeling, and risk-assessment. EPA is developing guidance on how best to develop the various

required project plans, including the testing and monitoring plan. The guidance can be found on

EPA’s website at http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm

EPA believes that monitoring using wells in the injection zone, e.g., for pressure monitoring as

required at §146.90(g)(1), can be safely performed if the wells are constructed to prevent flow

between the injection zone and USDWs or other layers above the confining zone. Such construction

technologies exist and have been used in the oil and gas industry for years. EPA believes that

properly constructed monitoring wells will be a safe way to obtain the data that is essential to ensure

that the injected CO2 remains confined in the injection zone and that pressure changes are not

causing movement of formation or other fluids. To mitigate the risk of fluid movement, EPA

requires owners and operators to submit a testing and monitoring plan that describes how the owner

or operator plans to site and construct monitoring wells. EPA is developing guidance on well

construction that will include recommendations for monitoring well construction. The guidance will

be available on EPA’s website at http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Robert F. Van Voorhees Letter ID: 0190

Commenter Organization: Carbon Sequestration Council Comment ID: 24485

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Rule Provision: 146.90(i) & (j) 
Proposed CCS Group Recommendations: (i) Any additional monitoring, as required 

by the Director, necessary to support, upgrade, and improve computational 

modeling of the area of review evaluation required under § 146.84(b) and to 

determine compliance with standards under 40 CFR 144.12; and 

(j) A quality assurance and surveillance plan for all testing and monitoring 

requirements.

Basis for CCS Group Comments: These issues are addressed in subsection (c)(6) 

and (b)(5) respectively. 

Response: Based on its evaluation of all public comments and input on the proposed rule and

NODA and Request for Comment, EPA has made many revisions to the GS rule. See the final rule

and preamble for further discussion on EPA's final approach.

Commenter Name: Robert F. Van Voorhees Letter ID: 0190

Commenter Organization: Carbon Sequestration Council Comment ID: 24543

Other EPA Comment Codes and Descriptions: 4710 2.7.1 Proposed submissions required for

permit applications (seeking comment) 

Comment: Rule Provisions or Federal Register Cite: 146.90, 146.93(a), 146.94(a) 

EPA Preamble Question: 34. EPA is proposing that permit applications for GS 

sites include several plans not currently required under existing UIC 

regulations. These plans include a monitoring and testing plan, an AoR and 

corrective action plan, and a post-injection site care and site closure plan. 

EPA seeks comment on the merits of requiring plans for monitoring, AoR, and 

post-injection site care as part of a permit application. EPA Notice 43517. 

CSC Response: The development of such plans is a good idea because it negates 

prescriptive regulation of the process. CSC is concerned that every modification 

of a plan may trigger a major permit modification, although it does not appear 

that current regulations would require that result. If major permit 

modifications were required, EPA would lose the adaptability desired for 

responding to experience gained from GS projects. 

It is unclear how the construction, operation, and closure of any monitor wells 

would be regulated, since these are not actual injection wells. 

Timing of development of plans should be linked to the actual activity being 

addressed (i.e. staged). It should not be necessary to prepare and submit a site 

closure plan or the post-closure monitoring plan at the start of the project, 

particularly considering that these activities will not occur for many years 

after the project starts. 

Response: EPA agrees with commenters that developing and following testing and monitoring plans

is an important part of assuring that a GS project is operating properly and is crucial for the early

detection of potential endangerment to USDWs. EPA expects that the number of monitoring wells

needed will be determined based on site-specific information. EPA also agrees that periodic updates

to the plan are appropriate. EPA clarifies that the final GS regulation includes a requirement that the
AoR be reevaluated at least every five years, and it specifies at §146.90(j) that the operator revise the

testing and monitoring plan to incorporate the results of the most recent AoR reevaluation and recent

operational and monitoring data.

EPA clarifies that every revision to the testing and monitoring plan will not necessarily trigger a

major permit modification. The existing regulation at 40 CFR 144.39(a) identifies causes for

modification of permits that would invoke the public notification procedures at 40 CFR 124. In the

final rule, EPA added text to §144.39(a)(5) that permit modifications would be required if the

Director determines that a modification is necessary based on an AoR reevaluation, amendments to

any of the project plans, or a review of the testing and monitoring results. 

In addition, 40 CFR Part 144.41 identifies causes for minor modifications of permits (which do not

require following the procedures of Part 124). In the final rule, EPA added a subparagraph (h) to

§144.41 that would include minor amendments (e.g., to clarify, correct, or update) to the testing and

monitoring plan, plugging plan, post-injection site care and site closure plan, or emergency and

remedial response plan for a GS well (i.e., amendments that are not included under 144.39(a)(5) and

that do not require additional permit requirements). 

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm. In addition, in January 2009,

DOE published a best practices manual entitled "Monitoring, Verification, and Accounting of CO2

Stored in Deep Geologic Formations" (DOE/NETL-311/081508); this manual is included in the

docket for the final GS rule. EPA notes that closure of monitoring wells should be addressed in the

post-injection site care and site closure plan.

EPA also believes that it is appropriate to require owners and operators to submit all plans, including

the injection well plugging and post-injection site care and site closure plans, at the time of permit

application. EPA believes that the Director needs a satisfactory level of assurance that the owner or

operator has planned for these events before injection commences and that the owner or operator has

ensured that appropriate financial resources are available to fund all required activities, as required at

§146.85. The final rule retains requirements for submitting these plans with the permit application at

§146.82(a).

Commenter Name: Craig R. Walters Letter ID: 0200

Commenter Organization: Anadarko Petroleum Corporation Comment ID: 24604

Other EPA Comment Codes and Descriptions: 4710 2.7.1 Proposed submissions required for

permit applications (seeking comment) 

Comment: Rule Provisions: 146.90, 146.93(a), 146.94(a) 

EPA Rule Issue: 34. EPA is proposing that permit applications for GS sites 

include several plans not currently required under existing UIC regulations. 

These plans include a monitoring and testing plan, an AoR and corrective action 

plan, and a post-injection site care and site closure plan. EPA seeks comment on 

the merits of requiring plans for monitoring, AoR, and postinjection site care 

as part of a permit application. EPA Notice 43517. 

Anadarko Petroleum Corporation (APC) Response: The development of plans is a 

good idea because it negates prescriptive regulation of the process. APC is 

concerned that every modification of a plan may trigger a major permit 
modification. Although actual monitoring of injection formation is most 

effective, there is still the unintended consequence of penetrating the 

confining zone to gain that data. The number of monitoring wells should not be 

established in advance. It is unclear how monitoring well construction, 

operation, and closure will be regulated since these are not actual injection 

wells. 

Timing of development of plans should be linked to the actual activity being 

addressed. It should not be necessary to prepare and submit a site closure plan 

or the post-closure monitoring plan at the start of the project, particularly 

considering that these activities will not occur for many years after the 

project starts. 

Response: EPA agrees with commenters that developing and following testing and monitoring plans

is an important part of assuring that a GS project is operating properly and is crucial for the early

detection of potential endangerment to USDWs. EPA expects that the number of monitoring wells

needed will be determined based on site-specific information. EPA also agrees that periodic updates

to the plan are appropriate. EPA clarifies that the final GS regulation includes a requirement that the

AoR be reevaluated at least every five years, and it specifies at §146.90(j) that the operator revise the

testing and monitoring plan to incorporate the results of the most recent AoR reevaluation and recent

operational and monitoring data.

EPA believes that monitoring using wells in the injection zone, e.g., for pressure monitoring as

required at §146.90(g)(1), can be safely performed if the wells are constructed to prevent flow

between the injection zone and USDWs or other layers above the confining zone. Such construction

technologies exist and have been used in the oil and gas industry for years. The testing and

monitoring plan must describe how the owner or operator plans to site and construct monitoring

wells. EPA is developing guidance on well construction that will include recommendations for

monitoring well construction. The guidance will be available on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

EPA clarifies that every revision to the testing and monitoring plan will not necessarily trigger a

major permit modification. The existing regulation at 40 CFR 144.39(a) identifies causes for

modification of permits that would invoke the public notification procedures at 40 CFR 124. In the

final rule, EPA added text to §144.39(a)(5) that permit modifications would be required if the

Director determines that a modification is necessary based on an AoR reevaluation, amendments to

any of the project plans, or a review of the testing and monitoring results. 

In addition, 40 CFR Part 144.41 identifies causes for minor modifications of permits (which do not

require following the procedures of Part 124). In the final rule, EPA added a subparagraph (h) to

§144.41 that would include minor amendments (e.g., to clarify, correct, or update) to the testing and

monitoring plan, plugging plan, post-injection site care and site closure plan, or emergency and

remedial response plan for a GS well (i.e., amendments that are not included under 144.39(a)(5) and

that do not require additional permit requirements). 

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm. In addition, in January 2009,

DOE published a best practices manual entitled "Monitoring, Verification, and Accounting of CO2

Stored in Deep Geologic Formations" (DOE/NETL-311/081508); this manual is included in the
docket for the final GS rule. EPA notes that closure of monitoring wells should be addressed in the

post-injection site care and site closure plan.

EPA also believes that it is appropriate to require owners and operators to submit all plans, including

the injection well plugging and post-injection site care and site closure plans, at the time of permit

application. EPA believes that the Director needs a satisfactory level of assurance that the owner or

operator has planned for these events before injection commences and that the owner or operator has

ensured that appropriate financial resources are available to fund all required activities, as required at

§146.85. The final rule retains requirements for submitting these plans with the permit application at

§146.82(a).

Commenter Name: Craig R. Walters Letter ID: 0200

Commenter Organization: Anadarko Petroleum Corporation Comment ID: 24700

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Rule Provision: 146.90 

Anadarko Petroleum Corporation (APC) Comments: The owner or operator of a 

Class VI well must prepare, maintain, and comply with a testing and monitoring 

plan to verify that the geologic sequestration project is operating as permitted 

and is not endangering USDWs. The testing and monitoring plan must be submitted 

with the permit application, for Director approval, and must include a 

description of how the owner or operator will meet the requirements of this 

section. Testing and monitoring associated with geologic sequestration projects 

must, at a minimum, include:

(A) BASED ON A SITE-SPECIFIC ASSESSMENT OF THE POTENTIAL FOR FLUID

MOVEMENT FROM 

THE INJECTION WELL OR INJECTION ZONE, AND ON THE POTENTIAL VALUE OF

MONITORING 

WELLS TO DETECT SUCH MOVEMENT, THE OWNER OR OPERATOR OF A CLASS VI

WELL MUST 

PREPARE, MAINTAIN, AND COMPLY WITH A TESTING AND MONITORING PLAN TO

VERIFY THAT 

THE GEOLOGIC SEQUESTRATION PROJECT IS OPERATING AS PERMITTED AND IS NOT

ENDANGERING USDWS. THE TESTING AND MONITORING PLAN MUST BE SUBMITTED

WITH THE 

PERMIT APPLICATION, FOR DIRECTOR APPROVAL AND INCLUDE A DESCRIPTION OF

HOW THE 

OWNER OR OPERATOR WILL MEET THE REQUIREMENTS OF THIS SECTION; 

No rationale provided 

Response: Based on its evaluation of all public comments and input on the proposed rule and

NODA and Request for Comment, EPA has made many revisions to the GS rule. See the final rule

and preamble for further discussion on EPA's final approach.

EPA anticipates that the testing and monitoring plan will address site-specific geologic factors,

modeling, and risk-assessment. EPA is developing guidance on how best to develop the various
required project plans, including the testing and monitoring plan. The guidance can be found on

EPA’s website at http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Craig R. Walters Letter ID: 0200

Commenter Organization: Anadarko Petroleum Corporation Comment ID: 24709

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Rule Provision: 146.90(i) 

Anadarko Petroleum Corporation (APC) Comments: (i) Any additional monitoring, 

as required by the Director, necessary to support, upgrade, and improve 

computational modeling of the area of review evaluation required under § 

146.84(b) and to determine compliance with standards under 40 CFR 144.12; and

Rationale: See 146.90(c)(6) 

Response: Based on its evaluation of all public comments and input on the proposed rule and

NODA and Request for Comment, EPA has made many revisions to the GS rule. See the final rule

and preamble for further discussion on EPA's final approach.

Commenter Name: Craig R. Walters Letter ID: 0200

Commenter Organization: Anadarko Petroleum Corporation Comment ID: 24710

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Rule Provision: 146.90(j) 

Anadarko Petroleum Corporation (APC) Comments: (j) A quality assurance and 

surveillance plan for all testing and monitoring requirements.

Rationale: See 146.90(b)(5) 

Response: Based on its evaluation of all public comments and input on the proposed rule and

NODA and Request for Comment, EPA has made many revisions to the GS rule. See the final rule

and preamble for further discussion on EPA's final approach.

Commenter Name: Chris M. Hobson Letter ID: 0201

Commenter Organization: Southern Company Comment ID: 22173

Comment: Finally, Southern Company urges EPA to focus operating and monitoring 

requirements on containment and preventive measures rather than to impose 

requirements that will not indicate C02 migration until potentially damaging 

migration has occurred. In particular, we encourage containment monitoring only, 

such as one or at most two above-zone monitoring wells that measure pressure to 

detect non-containment. ¡d. at 43514. The Final Rule should encourage Owners or 

Operators to invest monitoring resources towards detecting subsurface movement 

of CO2 or other substances at a point when action may be taken to address any 

potential problems and prevent further migration, whether below or to the 

surface. 
Response: EPA disagrees that pressure monitoring above the confining zone is appropriate. Instead,

the final GS regulation, at §146.90(g)(1), requires all GS project operators to monitor for pressure

changes in the injection zone. EPA believes that pressure monitoring in the injection zone is

necessary to track the development and movement of the pressure front and CO2 plume. Pressure

monitoring within the injection zone is necessary because any such monitoring above the confining

zone would not detect movement of the pressure front unless a breach of the confining zone occurs.

EPA believes that monitoring using wells in the injection zone (i.e., that penetrate the confining

zone) can be safely performed if the wells are constructed to prevent flow between the injection zone

and USDWs or other layers above the confining zone. Such construction technologies exist and have

been used in the oil and gas industry for years. EPA believes that the benefits of monitoring in the

injection formation outweigh the manageable risk of those monitoring wells serving as conduits for

fluid movement. EPA adds that owners or operators may consider performing additional pressure

monitoring in wells that are above the confining zone (e.g., in the same wells used to perform

ground water quality monitoring required at §146.90(d)) to provide additional verification that no

pressure changes are occurring above the confining zone due to CO2 leakage.

In addition, EPA believes that shallow monitoring above the confining layer is an important part of a

rigorous monitoring program. The final rule, at §146.90(d) requires periodic monitoring of the

ground water quality and geochemical changes above the confining zone(s). Monitoring in additional

formations, e.g., the injection zone, may also be necessary, and if the Director believes such

monitoring is warranted he/she has the authority to require that it be included in the testing and

monitoring plan.

Commenter Name: John Corra Letter ID: 0205

Commenter Organization: Wyoming Department of Environmental Quality

(DEQ)

Comment ID:

22204

Other EPA Comment Codes and Descriptions: 4710 2.7.1 Proposed submissions required for

permit applications (seeking comment) 

Comment: 7. Permit application content: 

a. We agree with the US EPA that permit applications for GS sites should include 

several plans not currently required under existing UIC regulations. These plans 

include a monitoring and testing plan, an AoR and corrective action plan, and a 

post-injection site care and site closure plan. 

Response: EPA agrees with commenters that developing and following testing and monitoring plans

is an important part of assuring that a GS project is operating properly and is crucial for the early

detection of potential endangerment to USDWs. The final rule retains this requirement.

EPA agrees that incorporating the plans into the permit rather than establishing specific requirements

for corrective action, monitoring, injection well plugging, and post-injection site care in the

regulation provide the appropriate flexibility to address the variety of site-specific conditions that

may be encountered at GS sites. 

EPA believes that it is appropriate and necessary to require owners and operators to submit all plans,

including the injection well plugging and post-injection site care and site closure plans, at the time of

permit application for the Director to make a proper permit decision. EPA believes that the Director

needs a satisfactory level of assurance that the owner or operator has planned for these events before

injection commences and that the owner or operator has ensured that appropriate financial resources
are available to fund all required activities, as required at §146.85. The final rule retains requirements

for submitting these plans with the permit application at §146.82(a). EPA expects that the

requirement for this and other plans associated with GS projects will promote an ongoing dialogue

between the owner or operator and the Director to ensure USDWs are protected from endangerment.

In addition, these plans will support a demonstration under §146.85 that owners and operators have

adequate financial resources to meet well plugging and post-injection site care and site closure

requirements. Please see the final rule and the discussion of the GS project plans for additional

information.

Commenter Name: Edward Steadman Letter ID: 0220

Commenter Organization: The Energy and Environmental Research Center at the

University of North Dakota

Comment ID:

21625

Other EPA Comment Codes and Descriptions: 4660 2.6.6 Geochemical monitoring 

Comment: Page 43515. Regarding monitoring wells in the Area of Review (AoR). 

Text in this section implies that monitoring wells in the injection zone within 

the AoR are desirable, which could be interpreted by some as being required. The 

first comment with respect to this issue is that it is important to note that 

monitoring wells that penetrate the plume have potential to serve as a leakage 

pathway and, therefore, their use should be minimized. Secondly, one of the 

reasons given for the placing of monitoring wells in the AoR is that studying 

the interactions between brine and CO2 may allow for the determination of 

whether precipitation and/or dissolution of minerals is occurring. It is 

important to note that such interactions are currently not well understood and 

are the topic of great debate and controversy within the published literature. 

There is no consensus in the technical community as to how such data evaluated 

in the context of a single site, as site-specific permitting and monitoring must 

be, can be applied to ensuring the protection of USDWs at that site. While such 

data would surely be interesting and possibly useful from a scientific 

standpoint when taken in the context of many sites, it is not clear how it could 

be applied to prove or disprove that USDWs at a given location are being 

protected or are in danger of contamination. This requirement comes across as a 

regulatory-mandated means of gathering data for researchers, an activity that is 

outside the scope of USDW protection and should not be forcibly paid for by 

owners/operators of GS wells. 

Response: EPA disagrees that the monitoring requirements in the GS rule do not provide sitespecific benefits for protection of USDWs or that monitoring is for the benefit of scientific research

only. EPA believes that geochemical monitoring, when compared to baseline data, can provide direct

evidence that USDWs may be endangered.

EPA believes that monitoring using wells in the injection zone (i.e., that penetrate the confining

zone) can be safely performed if the wells are constructed to prevent flow between the injection zone

and USDWs or other layers above the confining zone. Such construction technologies exist and have

been used in the oil and gas industry for years. EPA believes that the benefits of monitoring in the

injection formation outweigh the manageable risk of those monitoring wells serving as conduits for

fluid movement. EPA adds that owners or operators may consider performing additional pressure

monitoring in wells that are above the confining zone (e.g., in the same wells used to perform

ground water quality monitoring required at §146.90(d)) to provide additional verification that no
pressure changes are occurring above the confining zone due to CO2 leakage. Monitoring also

identifies needed remedial actions, provides inputs for AoR reevaluation modeling, and targets

additional geochemical and surface monitoring needs. Knowledge of the location of the CO2 plume

and the associated pressure front will assure the public that GS projects are proceeding according to

plan, provide sufficient information to the owner or operator and Director, or allow for appropriate

actions to address any indication that USDWs may be endangered.

EPA acknowledges that, at certain sites, there may be a need for more or different monitoring

schemes (which may include monitoring in the confining zone), and adds that it is important to

balance the need for adequate monitoring that ensures USDW protection from endangerment against

too many artificial penetrations which could serve as conduits for fluid migration. Site-specific

testing and monitoring plans must describe the proposed monitoring regime, which must be

approved by the Director.

Commenter Name: Tiffany Rau Letter ID: 0224

Commenter Organization: Hydrogen Energy International Comment ID: 21672

Comment: - A monitoring plan that measures the performance of the highest leakage risk 

parameters and validates or updates predictive performance models. 

The appropriate implementation of these key areas will ensure the safe and 

secure operation of a geologic sequestration project. 

Response: EPA agrees with commenters that developing and following testing and monitoring plans

is an important part of assuring that a GS project is operating properly and is crucial for the early

detection of potential endangerment to USDWs. The final rule retains this requirement.

Commenter Name: Tiffany Rau Letter ID: 0224

Commenter Organization: Hydrogen Energy International Comment ID: 21674

Comment: (2) Flexibility in Design of Monitoring Programs and Selection of Technologies 

HEI agrees with EPA that monitoring is important. For example, once a site has 

been selected, appropriate baseline surveys should be conducted and analyzed 

prior to commencing operations. During operations and at site closure, 

appropriate monitoring technologies should be applied to confirm the integrity 

and effectiveness of the storage site. However, there is a common misperception 

that, in order to achieve secure storage, a large amount of monitoring is 

required. The United Nations states that "the proportion of CO2 retained by 

appropriately selected and managed sites is likely to exceed 99% over 1,000 

years." Thus, the key to secure storage is the appropriate selection and 

management of the site and these activities should be the focus of any 

regulatory framework for CO2 geo-sequestration. If done properly, a selected 

site will be secure with a monitoring program that is designed and focused on 

the particular storage site. 

Response: EPA agrees that good site selection, modeling, and management are crucial elements of a

successful GS project, but disagrees that this is an effective substitute for rigorous site monitoring.

EPA also agrees with commenters and believes that flexibility is important in developing and

implementing a monitoring plan that is appropriately tailored for a specific GS site. The purpose of
the requirement at §146.90 to develop site-specific testing and monitoring plans is to ensure that the

monitoring performed at a site is appropriate for site operational conditions and the geologic setting.

EPA believes that this is the best approach for addressing potential risks at GS sites. These flexible

provisions in the monitoring requirements for Class VI wells enable the owner or operator to tailor

monitoring programs to the specific needs of each project in consultation with the Director.

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil gas and surface air monitoring which may be required by the UIC Director

for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Tiffany Rau Letter ID: 0224

Commenter Organization: Hydrogen Energy International Comment ID: 21679

Comment: Furthermore, in various parts of the Proposed Rule, EPA has prescribed 

particular monitoring technologies. Mandating any specific technology(ies) 

would have the adverse effect of (1) promoting particular technologies to the 

exclusion of other developed - and to be developed - technology(ies), and (2) 

substantially increasing costs without necessarily contributing to the 

protection of USDWs. This would hinder the development and deployment of CCS at 

commercial scale. Moreover, it would discourage the development of other 

technologies. HEI therefore strongly discourages EPA from promulgating 

regulations that mandate the use of any specific monitoring technology. 

Response: EPA agrees that prescribing specific technologies to be used in all cases for GS would not

be appropriate given the variability in sites, and believes that the rule provides flexibility to owners

or operators to develop site-specific testing and monitoring plans that employ appropriate

technologies provided they meet the requirements at §146.90. EPA is developing guidance on testing

and monitoring to assist owners or operators and Directors in evaluating requirements under

§146.90, including proposed monitoring plans. The guidance describes available technologies and

recommended approaches for implementing a testing and monitoring plan, including pre-operational

geophysical logging and testing of injection wells, MITs, injection well testing during operation,

groundwater quality monitoring, tracking the CO2 plume and pressure front, and soil gas and

surface air monitoring which may be required by the UIC Director for specific GS projects. The

guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm. In addition, in January 2009,

DOE published a best practices manual entitled "Monitoring, Verification, and Accounting of CO2

Stored in Deep Geologic Formations" (DOE/NETL-311/081508); this manual is included in the

docket for the for the final GS rule.

Commenter Name: Brian Williams Letter ID: 0225

Commenter Organization: BP Alternative Energy North America, Inc. (BP) Comment ID: 21717

Comment: - A monitoring plan that measures the performance of the highest leakage risk 

parameters and validates or updates predictive performance models. 
The appropriate implementation of these key areas will ensure the safe and 

secure operation of a geologic sequestration project. 

Response: EPA agrees with commenters that developing and following testing and monitoring plans

is an important part of assuring that a GS project is operating properly and is crucial for the early

detection of potential endangerment to USDWs. The final rule retains this requirement.

Commenter Name: Brian Williams Letter ID: 0225

Commenter Organization: BP Alternative Energy North America, Inc. (BP) Comment ID: 21719

Comment: (2) Flexibility in Design of Monitoring Programs and Selection of Technologies 

BP agrees with EPA that monitoring is important. For example, once a site has 

been selected, appropriate baseline surveys should be conducted and analyzed 

prior to commencing operations. During operations and at site closure, 

appropriate monitoring technologies should be applied to confirm the integrity 

and effectiveness of the storage site. However, there is a common misperception 

that, in order to achieve secure storage, a large amount of monitoring is 

required. The United Nations states that "the proportion of CO2 retained by 

appropriately selected and managed sites is likely to exceed 99% over 1,000 

years." Thus, the key to secure storage is the appropriate selection and 

management of the site and these activities should be the focus of any 

regulatory framework for CO2 geo-sequestration. If done properly, a selected 

site will be secure with a monitoring program that is designed and focused on 

the particular storage site. 

Response: EPA agrees that good site selection, modeling, and management are crucial elements of a

successful GS project, but disagrees that this is an effective substitute for rigorous site monitoring.

EPA also agrees with commenters and believes that flexibility is important in developing and

implementing a monitoring plan that is appropriately tailored for a specific GS site. The purpose of

the requirement at §146.90 to develop site-specific testing and monitoring plans is to ensure that the

monitoring performed at a site is appropriate for site operational conditions and the geologic setting.

EPA believes that this is the best approach for addressing potential risks at GS sites. These flexible

provisions in the monitoring requirements for Class VI wells enable the owner or operator to tailor

monitoring programs to the specific needs of each project in consultation with the Director.

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil gas and surface air monitoring which may be required by the UIC Director

for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Brian Williams Letter ID: 0225

Commenter Organization: BP Alternative Energy North America, Inc. (BP) Comment ID: 21729

Other EPA Comment Codes and Descriptions: 1250 1.1.1.4 Flexibility is needed (performancebased standards) 
Comment: Furthermore, in various parts of the Proposed Rule, EPA has prescribed 

particular monitoring technologies. Mandating any specific technology(ies) would 

have the adverse effect of (1) promoting particular technologies to the 

exclusion of other developed - and to be developed - technology(ies), and (2) 

substantially increasing costs without necessarily contributing to the 

protection of USDWs. This would hinder the development and deployment of CCS at 

commercial scale. Moreover, it would discourage the development of other 

technologies. BP therefore strongly discourages EPA from promulgating 

regulations that mandate the use of any specific monitoring technology. 

Response: EPA agrees that prescribing specific technologies to be used in all cases for GS would not

be appropriate given the variability in sites, and believes that the rule provides flexibility to owners

or operators to develop site-specific testing and monitoring plans that employ appropriate

technologies provided they meet the requirements at §146.90. EPA is developing guidance on testing

and monitoring to assist owners or operators and Directors in evaluating requirements under

§146.90, including proposed monitoring plans. The guidance describes available technologies and

recommended approaches for implementing a testing and monitoring plan, including pre-operational

geophysical logging and testing of injection wells, MITs, injection well testing during operation,

groundwater quality monitoring, tracking the CO2 plume and pressure front, and soil gas and

surface air monitoring which may be required by the UIC Director for specific GS projects. The

guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm. In addition, in January 2009,

DOE published a best practices manual entitled "Monitoring, Verification, and Accounting of CO2

Stored in Deep Geologic Formations" (DOE/NETL-311/081508); this manual is included in the

docket for the for the final GS rule.

Commenter Name: Andrew Duguid Letter ID: 0226

Commenter Organization: Schlumberger Carbon Services Comment ID: 24004

Comment: 3. In the preamble of the draft u-tube technology is specifically called 

out as a technology available for high pressure fluid sampling. 

Schlumberger wants point out to the epa there are other techniques for 

high pressure fluid sampling the use of wireline conveyed sample 

bottles. We want to ensure that no one particular technology is adopted 

or required for high pressure sampling. The selection of a single 

sampling technique (although not in the rule language) could cause the 

best available technology to be overlooked now or in the future. We 

propose that epa either delete the reference to the u-tube samples of 

clarify that it is not the only solution available for taking high 

pressure samples 

Response: EPA recognizes that the collection of representative ground water samples from depth

poses challenges and that special methods, such as U-tubes, will be needed to preserve the integrity

of such samples. However, EPA is not requiring the use of U-tubes for sampling under the final rule.

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil gas and surface air monitoring which may be required by the UIC Director
for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Andrew Duguid Letter ID: 0226

Commenter Organization: Schlumberger Carbon Services Comment ID: 24065

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Proposed Rule: (1) The testing and monitoring plan must be based on potential 

vulnerabilities within the area of review; 

Schlumberger Suggested Revision: (1) The testing and monitoring plan must be 

based on site-specific geologic factors, modeling, and risk-assessment within 

the area of review; 

Schlumberger Rationale: - 

Response: EPA anticipates that the testing and monitoring plan will address site-specific geologic

factors, modeling, and risk-assessment. EPA is developing guidance on how best to develop the

various required project plans, including the testing and monitoring plan. The guidance can be found

on EPA’s website at http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Based on its evaluation of all public comments and input on the proposed rule and NODA and

Request for Comment EPA has made many revisions to the GS rule. See the final rule and preamble

for further discussion on EPA's final approach.

Commenter Name: Ben Yamagata Letter ID: 0227

Commenter Organization: Coal Utilization Research Council Comment ID: 21789

Other EPA Comment Codes and Descriptions: 1250 1.1.1.4 Flexibility is needed (performancebased standards) 

Comment: Plume and Pressure Front Monitoring 

EPA would require each Class VI well permit application to contain a monitoring 

plan to verify that a GS well is operating as intended and not endangering USDW. 

EPA should be aware that certain monitoring technology is currently under 

development and not available as a tool in the near term to meet the proposed 

EPA requirements. Further, the usefulness of available technology is a function 

of site-specific characterizations. The EPA should not impose a one-size-fitsall approach. CURC recommends that the EPA permit well owners and operators to 

propose the use of available technology to meet the proposed requirements and 

then to amend their tailored monitoring plans as technology evolves. 

Response: EPA agrees that prescribing specific technologies to be used in all cases for GS would not

be appropriate given the variability in sites, and believes that the rule provides flexibility to owners

or operators to develop site-specific testing and monitoring plans that employ appropriate

technologies provided they meet the requirements at §146.90. EPA is developing guidance on testing

and monitoring to assist owners or operators and Directors in evaluating requirements under

§146.90, including proposed monitoring plans. The guidance describes available technologies and

recommended approaches for implementing a testing and monitoring plan, including pre-operational
geophysical logging and testing of injection wells, MITs, injection well testing during operation,

groundwater quality monitoring, tracking the CO2 plume and pressure front, and soil gas and

surface air monitoring which may be required by the UIC Director for specific GS projects. The

guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm. In addition, in January 2009,

DOE published a best practices manual entitled "Monitoring, Verification, and Accounting of CO2

Stored in Deep Geologic Formations" (DOE/NETL-311/081508); this manual is included in the

docket for the for the final GS rule.

Commenter Name: Neeraj Gupta Letter ID: 0229

Commenter Organization: Battelle Energy Technology (BET) Comment ID: 21850

Other EPA Comment Codes and Descriptions: 4600 2.6 Proposed Plume and Pressure Front

Monitoring Requirements (40 CFR 146.90) 

Comment: Page 102, Pressure monitoring in overlying zones- Implicit in this monitoring 

requirement is that network of deep monitoring wells will be required with the 

injection well. We know of no other method to accurately measure deep 

pressures. As such, this requirement will be costly to implement and should be 

spelled out clearly for planning purposes. It may also be pertinent to make 

this optional depending on identified risks. 

Response: EPA acknowledges the commenters' concern about the cost of monitoring. However,

EPA believes that monitoring is essential for protection of USDWs at GS sites. Although a

significant cost in absolute terms, monitoring costs are expected to be a small fraction of site

operating costs, according to EPA's cost analysis for the GS rulemaking (which is available in the

docket).

EPA believes that monitoring using wells in the injection zone, e.g., for pressure monitoring as

required at §146.90(g)(1), can be safely performed if the wells are constructed to prevent flow

between the injection zone and USDWs or other layers above the confining zone. Such construction

technologies exist and have been used in the oil and gas industry for years. EPA believes that

properly constructed monitoring wells will be a safe way to obtain the data that is essential to ensure

that the injected CO2 remains confined in the injection zone and that pressure changes are not

causing movement of formation or other fluids. To mitigate the risk of fluid movement, EPA

requires owners and operators to submit a testing and monitoring plan that describes how the owner

or operator plans to site and construct monitoring wells. EPA is developing guidance on well

construction that will include recommendations for monitoring well construction. The guidance will

be available on EPA’s website at http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, and tracking the CO2 plume

and pressure front. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm. In addition, in January 2009,

DOE published a best practices manual entitled "Monitoring, Verification, and Accounting of CO2

Stored in Deep Geologic Formations" (DOE/NETL-311/081508); this manual is included in the

docket for the final GS rule.
Commenter Name: Mark Bohrer Letter ID: 0241

Commenter Organization: North Dakota Industrial Commission Comment ID: 23256

Other EPA Comment Codes and Descriptions: 4710 2.7.1 Proposed submissions required for

permit applications (seeking comment) 

Comment: 34. EPA is proposing that permit applications for GS sites include several plans 

not currently required under existing UIC regulations. These plans include a 

monitoring and testing plan, an AoR and corrective action plan, and a postinjection site care and site closure plan. EPA seeks comment on the merits of 

requiring plans for monitoring, AoR, and post-injection site care as part of a 

permit application. EPA Notice 43517. 

Allowing for different plans would be much more effective than prescriptive 

regulations; however, a plan modification should not be considered a major 

permit modification. Caution needs to be taken when monitoring the injection 

formation due to the artificial penetration of the confining zone to gain data. 

The number of monitoring wells should be decided on a case-by case basis. It is 

unclear how monitoring wells will be regulated since they are not injection 

wells. The timing of plan submittal should be linked to the activity being 

Response: EPA agrees with commenters that developing and following testing and monitoring plans

is an important part of assuring that a GS project is operating properly and is crucial for the early

detection of potential endangerment to USDWs. 

EPA expects that the number of monitoring wells needed will be determined based on site-specific

information as the testing and monitoring plan is developed. EPA believes that monitoring using

wells in the injection zone (i.e., that penetrate the confining zone) can be safely performed if the

wells are constructed to prevent flow between the injection zone and USDWs or other layers above

the confining zone. Such construction technologies exist and have been used in the oil and gas

industry for years. EPA believes that the benefits of monitoring in the injection formation outweigh

the manageable risk of those monitoring wells serving as conduits for fluid movement. 

EPA also agrees that periodic updates to the plan are appropriate. EPA clarifies that the final GS

regulation includes a requirement that the AoR be reevaluated at least every 5 years, and it specifies

at §146.90(j) that the operator revise the testing and monitoring plan to incorporate the results of the

most recent AoR reevaluation and recent operational and monitoring data. EPA clarifies that every

revision to the testing and monitoring plan will not necessarily trigger a major permit modification.

The existing regulation at 40 CFR 144.39(a) identifies causes for modification of permits that would

invoke the public notification procedures at 40 CFR 124, including: alterations or additions to the

facility; availability of additional information; new regulations; and compliance schedule

modifications. In the final rule, EPA added text to §144.39(a)(5) that permit modifications would be

required if the Director determines that a modification is necessary based on an AoR reevaluation,

amendments to any of the project plans, or a review of the testing and monitoring results. 

In addition, 40 CFR Part 144.41 identifies causes for minor modifications of permits (which do not

require following the procedures of Part 124). These include correction of typographical errors; more

frequent monitoring or reporting; changes in an interim compliance date; changes in ownership or

control of a facility; changes in the quantities or types of fluids injected which are within the

capacity of the facility; changes in construction requirements; or amendments to a plugging and

abandonment plan. In the final rule, EPA added a subparagraph (h) to §144.41 that would include

minor amendments (e.g., to clarify, correct, or update) the testing and monitoring plan, plugging
plan, post-injection site care and site closure plan, or emergency and remedial response plan for a

GS well (i.e., amendments that are not included under 144.39(a)(5) and that do not require additional

permit requirements). 

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil gas and surface air monitoring which may be required by the UIC Director

for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm. In addition, in January 2009,

DOE published a best practices manual entitled "Monitoring, Verification, and Accounting of CO2

Stored in Deep Geologic Formations" (DOE/NETL-311/081508); this manual is included in the

docket for the final GS rule. EPA notes that closure of monitoring wells should be addressed in the

post-injection site care and site closure plan.

Commenter Name: Kurt Waltzer Letter ID: 0250

Commenter Organization: Clean Air Task Force Comment ID: 22310

Comment: Perhaps inadvertently, the proposed rule does not explicitly require updating of 

several of the required plans. In most but not all cases, there is a rather 

ambiguous requirement to "maintain" a given plan. Explicit requirements to make 

updates as warranted appear to be missing from provisions relating to: 

• the testing and monitoring plan required by §146.90 (the ambiguous word 

"maintain" is used and there appears to be no requirement that estimated 

plugging costs be kept current); 

Response: EPA agrees that developing and following testing and monitoring plans is an important

part of assuring that a GS project is operating properly and is crucial for the early detection of

potential endangerment to USDWs. EPA also agrees that periodic updates to the plan are appropriate.

EPA clarifies that the final GS regulation includes a requirement that the AoR be reevaluated at least

every 5 years, and it specifies at §146.90(j) that the operator revise the testing and monitoring plan to

incorporate the results of the most recent AoR reevaluation and recent operational and monitoring

data.

Commenter Name: Kurt Waltzer Letter ID: 0250

Commenter Organization: Clean Air Task Force Comment ID: 22317

Comment: Monitoring 

In §146.90 the proposed rule outlines requirements for testing and monitoring. 

We strongly support the inclusion of such provisions. Monitoring is central to 

verifying and adapting the operational parameters of a GS project, while the 

concept of GS cannot be simply based on the premise of confinement without 

verification. We also support the provisions calling for a testing and 

monitoring plan, although we have suggested above that the requirements for 

updating this plan be strengthened. The collection of baseline data and 

information prior to the commencement of operations is also necessary for a 
number of monitoring techniques to produce useful results, and should be 

preserved. 

Response: EPA agrees with commenters that developing and following testing and monitoring plans

is an important part of assuring that a GS project is operating properly and is crucial for the early

detection of potential endangerment to USDWs. EPA also agrees that periodic updates to the plan are

appropriate. EPA clarifies that the final GS regulation includes a requirement that the AoR be

reevaluated at least every 5 years, and it specifies at §146.90(j) that the operator revise the testing

and monitoring plan to incorporate the results of the most recent AoR reevaluation and recent

operational and monitoring data. EPA adds that the final rule, at §146.82, retains the data collection

requirements that are part of the permit application.

Commenter Name: Kurt Waltzer Letter ID: 0250

Commenter Organization: Clean Air Task Force Comment ID: 25257

Other EPA Comment Codes and Descriptions: 3500 2.2.3 Area of Review Reevaluation (seeking

comment) 

Comment: Perhaps inadvertently, the proposed rule does not explicitly require updating of 

several of the required plans. In most but not all cases, there is a rather 

ambiguous requirement to "maintain" a given plan. Explicit requirements to make 

updates as warranted appear to be missing from provisions relating to: 

• the testing and monitoring plan required by §146.90 (the ambiguous word 

"maintain" is used and there appears to be no requirement that estimated 

plugging costs be kept current); 

Response: The final rule includes provisions that owners or operators review and update the AoR

and corrective action plan, the testing and monitoring plan, and the emergency and remedial

response plan throughout the life of the project, as specified in §146.84(c), §146.90(j), and

§146.94(d). Owners or operators must review each plan and identify necessary amendments to the

plan or demonstrate to the Director that no amendment is needed. These reviews must be performed

within one year of an AoR reevaluation, following any significant changes to the facility (e.g., the

addition of monitoring or injection wells), or when required by the Director.

Commenter Name: Michel Paque Letter ID: 0259

Commenter Organization: Ground Water Protection Council Comment ID: 24922

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Rule Provision: 146.90 

EPA Proposal: 10. Testing and monitoring requirements 

The owner or operator of a Class VI well must prepare, maintain, and comply with 

a testing and monitoring plan to verify that the geologic sequestration project 

is operating as permitted and is not endangering USDWs. The testing and 

monitoring plan must be submitted with the permit application, for Director 

approval, and must include a description of how the owner or operator will meet 

the requirements of this section. Testing and monitoring associated with 

geologic sequestration projects must, at a minimum, include: 
GWPC Recommendations: Support the proposed EPA language. 

Response: Based on its evaluation of all public comments and input on the proposed rule and

NODA and Request for Comment EPA has made many revisions to the GS rule. See the final rule

and preamble for further discussion on EPA's final approach.

EPA agrees with commenters that developing and following testing and monitoring plans is an

important part of assuring that a GS project is operating properly and is crucial for the early

detection of potential endangerment to USDWs.

Commenter Name: Michel Paque Letter ID: 0259

Commenter Organization: Ground Water Protection Council Comment ID: 24930

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Rule Provision: 146.90(h) 

EPA Proposal: (1) The testing and monitoring plan must be based on potential 

vulnerabilities within the area of review; 

(2) The monitoring frequency and spatial distribution of surface air monitoring 

and/or soil gas monitoring must reflect baseline data and the monitoring plan 

must include how the proposed monitoring will yield useful information on the 

area of review delineation and/or compliance with standards under 40 CFR 144.12; 

GWPC Recommendations: (1) The testing and monitoring plan must be based on sitespecific geologic factors, modeling, and risk-assessment within the area of 

review; 

(2) Agree with EPA language 

Rationale: The GWPC feels that the term "potential vulnerabilities" is too 

nebulous. We suggest replacing this term with the term "site-specific geologic 

factors, modeling, and risk-assessment." 

Response: Based on its evaluation of all public comments and input on the proposed rule and

NODA and Request for Comment EPA has made many revisions to the GS rule. See the final rule

and preamble for further discussion on EPA's final approach.

EPA anticipates that the testing and monitoring plan will address site-specific geologic factors,

modeling, and risk-assessment. EPA is developing guidance on how best to develop the various

required project plans, including the testing and monitoring plan. The guidance can be found on

EPA’s website at http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Michel Paque Letter ID: 0259

Commenter Organization: Ground Water Protection Council Comment ID: 24931

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule
language 

Comment: Rule Provision: 146.90(i) 

EPA Proposal: (i) Any additional monitoring, as required by the Director, 

necessary to support, upgrade, and improve computational modeling of the area of 

review evaluation required under § 146.84(b) and to determine compliance with 

standards under 40 CFR 144.12; and 

(j) A quality assurance and surveillance plan for all testing and monitoring 

requirements. 

GWPC Recommendations: Support the proposed EPA language. 

Rationale: Agree with EPA’s rationale. 

Response: EPA acknowledges the comment. The final rule retains these provisions as proposed.

Letter ID: 0263

Commenter Organization: Interstate Oil & Gas Compact Commission Comment ID: 22820

Comment: III A. 6 Proposed Plume andPressure Front Monitoring Requirements 

JJ. In addition, EPA seeks comment regarding the use of a Director-approved 

monitoring plan for GS sites. 

IOGCC Response: The Director should be given flexibility to approve 

site specific monitoring plans as proposed in the IOGCC model regulations. 

Response: EPA agrees with commenters that developing and following testing and monitoring plans

and giving Directors flexibility to approve the plans based on site-specific criteria are important

parts of assuring that a GS project is operating properly and is crucial for the early detection of

potential endangerment to USDWs. 

The testing and monitoring plan is developed by the owner or operator in consultation with the

Director and is designed to ensure that a detailed, Director-approved document describing how

monitoring will be conducted during the lifetime of the project exists. EPA is developing guidance

on testing and monitoring to assist owners or operators and Directors in evaluating requirements

under §146.90, including proposed monitoring plans. The guidance describes available technologies

and recommended approaches for implementing a testing and monitoring plan, including preoperational geophysical logging and testing of injection wells, MITs, injection well testing during

operation, groundwater quality monitoring, tracking the CO2 plume and pressure front, and soil gas

and surface air monitoring which may be required by the UIC Director for specific GS projects. The

guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Scott Anderson Letter ID: 0510

Commenter Organization: Environmental Defense Fund Comment ID: 21226

Comment: We also think that further steps are needed in order to assure that monitoring 

includes all aspects of projects. But right now the rule in several places does 
require monitoring to be used to drive adjustments in the project, but we feel 

strongly that we need to go further, and we also think that this was 

contemplated by the IPCC when they said that in a properly selected and managed 

site that 99 percent of this to be expected to be retained over a thousand 

years. 

Monitoring needs to be used in a reiterative process to improve site 

characterization, the definition, and the adjustment as necessary of the AoR. 

Adjustment in the risk analysis, adjustment in models, needs to be used to 

inform and create new input into the models. It needs to help determine, and 

revise, and improve the monitoring program itself. It needs to inform financial 

assurance requirements. And it needs to inform closure requirements. In short, 

monitoring is essential to an adaptive well-managed sequestration site. And 

then the rule that makes a good start at requiring that and needs to finish the 

job. 

Response: EPA agrees with commenters on the importance of monitoring at GS sites and

emphasizes that monitoring of injection activities will be an important component of every GS

project. Monitoring associated with injection wells and the movement of the CO2 plume is necessary

to verify that the injectate is confined in the target formations and does not endanger USDWs. 

EPA agrees with commenters that developing and following testing and monitoring plans is an

important part of assuring that a GS project is operating properly and is crucial for the early

detection of potential endangerment to USDWs. EPA also agrees that periodic updates to the plan are

appropriate. EPA clarifies that the final GS regulation includes a requirement that the AoR be

reevaluated at least every 5 years, and it specifies at §146.90(j) that the operator revise the testing

and monitoring plan to incorporate the results of the most recent AoR reevaluation and recent

operational and monitoring data.

EPA agrees that monitoring data should be used to review model assumptions, verify computational

model projections, and, when necessary, provide input for model refinements. As data are collected

at an injection site, model parameters can be adjusted to match observations (i.e., for model

calibration or), which in turn improves the predictive capability of the model. As a GS project

proceeds, both monitoring and modeling will evolve, with monitoring results supporting effective

AoR reevaluations and leading to improved model predictions.

EPA agrees that monitoring is a key element of ensuring that USDWs are protected from

endangerment. Tracking the plume and the position of the pressure front during injection operations

and the post-injection site care period will provide important data for determining that the injectate is

confined within the target formation, as well as for evaluating any risks within the AoR and ensuring

protection of USDWs from endangerment. EPA also agrees with the commenter that data collected

during site characterization (such as baseline geochemistry, pre-injection reservoir pressure, etc.) are

appropriate to ensure that baseline information is available to form the basis for comparison during

GS operation and post-injection. For example, the baseline geochemical information will allow the

owner or operator and permitting authority to evaluate monitoring data and identify any changes in

subsurface geochemistry that may indicate fluid movement.

Commenter Name: Cynthia Lane Letter ID: 0528

Commenter Organization: American Water Works Association (AWWA) Comment ID: 21385
Comment: We need appropriate subsurface monitoring technology identified and developed to 

prevent or respond to potential contamination of USDW's, by these and other 

chemical compounds. 

Response: EPA does not believe that prescribing specific technologies to be used in all cases for GS

would be appropriate given the variability in sites. Rather EPA is developing guidance on testing and

monitoring to assist owners or operators and Directors in evaluating requirements under §146.90,

including proposed monitoring plans. The guidance describes available technologies and

recommended approaches for implementing a testing and monitoring plan, including pre-operational

geophysical logging and testing of injection wells, MITs, injection well testing during operation,

groundwater quality monitoring, tracking the CO2 plume and pressure front, and soil gas and

surface air monitoring which may be required by the UIC Director for specific GS projects. The

guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm. In addition, in January 2009,

DOE published a best practices manual entitled "Monitoring, Verification, and Accounting of CO2

Stored in Deep Geologic Formations" (DOE/NETL-311/081508); this manual is included in the

docket for the final GS rule.

Comment Code: 4620 2.6.2 Injectate monitoring 

Individual Comments

Commenter Name: Herbert Skolnick, Ph.D. Letter ID: 0110

Commenter Organization: Group Against Smog and Pollution, Inc. (GASP) Comment ID: 22040

Comment: Conclusion 

Regardless of what specific form the CO2 sequestration program ultimately takes, 

at a minimum, the program must ensure that: 

1. the chemistry of the CO2 and its contaminants is ascertained prior to 

injection; 

Response: EPA agrees that monitoring of the injectate prior to and during injection is important to

allow for comparison of baseline data and operational-phase monitoring results to provide warning

of potential USDW endangerment. For this reason owners or operators must perform an analysis of

the chemical and physical characteristics of the CO2 stream, as required at §146.82 (a)(7)(iv). In

addition, Section §146.90(a) requires owners or operators to perform analysis of the CO2 stream

during injection operations with sufficient frequency to yield data representative of its chemical and

physical characteristics.

Commenter Name: Herbert Skolnick, Ph.D. Letter ID: 0110

Commenter Organization: Group Against Smog and Pollution, Inc. (GASP) Comment ID: 22043

Other EPA Comment Codes and Descriptions: 4630 2.6.3 Corrosion monitoring; 4660 2.6.6

Geochemical monitoring 

Comment: Regardless of what specific form the CO2 sequestration program ultimately takes, 

at a minimum, the program must ensure that: 
2. the sequestered material’s behavior in the chemical, geological, and 

hydrological environment where it is stored is anticipated and carefully 

monitored; and 

Response: EPA agrees with commenters on the importance of monitoring at GS sites and

emphasizes that monitoring of injection activities must be an important component of every GS

project. Monitoring associated with injection wells and the movement of the CO2 plume is necessary

to verify that the injectate is confined in the target formations and does not endanger USDWs. The

GS rule, at §146.90, requires injectate monitoring, mechanical integrity testing, corrosion

monitoring, tracking the CO2 plume and area of elevated pressure, monitoring geochemical changes

above the confining zone, and, at the discretion of the Director, surface air and soil gas monitoring

for CO2 fluctuations, and any additional tests necessary to ensure USDW protection from

endangerment.

Commenter Name: Dwight Lockwood, PE, QEP Letter ID: 0141

Commenter Organization: Global Energy, Inc. Comment ID: 23104

Other EPA Comment Codes and Descriptions: 1630 1.3.3 RCRA/hazardous waste issues (seeking

comment); 1640 1.3.4 CERCLA issues (seeking comment) 

Comment: CO2 as Hazardous Waste (RCRA or CERCLA) 

1.We support the EPA view that injectate should be characterized relative to 40 

CFR Part 261. We further believe that the stream can be treated to remove 

undesired contaminants to the levels that thresholds are not triggered. 

2.Characterization and certification in the permit application should be a 

sufficient basis for assurance here. Periodic sampling and analysis on some 

reasonable frequency during injection is acceptable. On the other hand, we do 

not believe that this measurement and reporting needs to be more than perhaps 

quarterly, as the adverse impact of exceedances for relatively short periods is 

not likely to be geologically significant very fast. Corrective action to 

mitigate the effects of an incorrect injection fluid (but not to remedy an 

injection already accomplished) needs to be pragmatic and not onerous. 

3.As with Class I well liability exemptions, Class VI wells, once their 

injectate is characterized and approved (as not triggering CERCLA or RCRA), and 

regular sampling of the stream for quality control is implemented then a 

similar exemption is warranted. 

Response: EPA agrees that monitoring of the injectate prior to and during injection is important to

allow for comparison of baseline data and operational-phase monitoring results to provide warning

of potential USDW endangerment. For this reason owners or operators must perform an analysis of

the chemical and physical characteristics of the CO2 stream, as required at §146.82 (a)(7)(iv). In

addition, Section §146.90(a) requires owners or operators to perform analysis of the CO2 stream

during injection operations with sufficient frequency to yield data representative of its chemical and

physical characteristics.

The necessary frequency of injectate analysis will be project-specific and will depend upon the CO2

source and the likelihood of variability in injectate composition. For example, a CO2-capture

process from a coal-fired power plant with a consistent coal source and operating parameters is
likely to produce a CO2 stream with a fairly consistent composition. A process with a changing

composition of coal may have more variability in the purity of the CO2 that is captured. In such a

setting, more frequent sampling may be appropriate. The details of the sampling should be described

in the testing and monitoring plan, which will be approved by the Director based on a review of sitespecific information, including information on the source and characteristics of the injectate.

EPA clarifies that, following an initial characterization of the injectate, EPA expects that the permit

would stipulate the acceptable composition of the injectate (e.g., as CO2 plus an acceptable range of

expected impurities). Any divergence from this would be a permit violation.

EPA notes however, that the final GS rule, which adds new regulations for Class VI wells under the

Safe Drinking Water Act (SDWA), is not making any changes to the RCRA regulations.

Accordingly, the CO2 stream characterization requirements under the GS rule would not substitute

for the obligation of a generator of RCRA solid waste to characterize its waste in accordance with

EPA’s RCRA regulations. Injection of a RCRA hazardous waste may only occur in a Class I

hazardous waste injection well.

EPA notes that CO2 itself is not listed as a hazardous substance under CERCLA, although the CO2

stream may contain a listed hazardous substance (such as mercury) or may mobilize substances in

the subsurface that could react with ground water to produce listed hazardous substances (such as

sulfuric acid). Whether such substances may result in CERCLA liability from a sequestration facility

depends entirely on the composition of the specific CO2 stream and the environmental media in

which it is stored (e.g., soil or ground water). CERCLA exempts from liability, under CERCLA

section 107, 42 U.S.C. 9607, certain “federally permitted releases” (FPR) as defined in CERCLA, 42

U.S.C. 9601(10). Class VI permits will need to be carefully structured to ensure that they prevent

potential releases from the well which are outside the scope of the Class VI permit.

The commenter’s reference to a Class I liability exemption is unclear and not legally correct.

Furthermore, after site closure an owner or operator may remain liable under tort and other remedies,

or under other federal statutes including, but not limited to, Clean Air Act, 42 U.S.C. §§7401-7671;

CERCLA, 42 U.S.C. §9601-9675; and RCRA, 42 U.S.C. §6901-6992. EPA does not have authority

to transfer SDWA or other legal liability for Class VI wells to the State or federal government or a

third-party fund. See the final rule preamble for further discussion of EPA's final approach.

Commenter Name: Ronald Evans Letter ID: 0215

Commenter Organization: Denbury Resources, Inc. (DRI) Comment ID: 24308

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: G. § 146.90 Testing and monitoring requirements. 

1. EPA Proposed §146.90(b) Installation and use, except during well 

workovers as defined in § 146.86(d), of continuous recording devices to 

monitor injection pressure, rate and volume; the pressure on the annulus 

between the tubing and the long string casing; and the annulus fluid 

volume; 

Consistent with our comment regarding proposed § 146.88(e) in Section 5 above, 

Denbury is unaware of a methodology to monitor the actual volume of annular 

fluid in the annulus on a continuous basis, and thus seeks agency clarification 
on this portion of the proposed rule. 

Response: EPA believes that knowing annulus fluid volume, as required at §146.88(e), is a

necessary component of monitoring well mechanical integrity, but believes that monitoring the

annulus fluid volume added is sufficient to meet the intent of continuous monitoring of the pressure

on the annulus. The final GS rule at §146.90 (b) requires that owners or operators use continuous

recording devices to monitor injection pressure, rate, and volume; the pressure on the annulus

between the tubing and the long string casing; and the annulus fluid volume added.

Commenter Name: Darrick Eugene Letter ID: 0223

Commenter Organization: Texas Carbon Capture and Storage Association Comment ID: 23988

Comment: 8. § 146.90 Testing and monitoring requirements. 

EPA Proposed §146.90(b) Installation and use, except during well 

workovers as defined in § 146.86(d), of continuous recording devices to 

monitor injection pressure, rate and volume; the pressure on the annulus 

between the tubing and the long string casing; and the annulus fluid 

volume; 

Consistent with our comment regarding proposed § 146.88(e) in Section 5 above, 

TxCCSA is unaware of a methodology to monitor the actual volume of annular fluid 

in the annulus on a continuous basis, and thus seeks agency clarification on 

this portion of the proposed rule. 

Response: EPA believes that knowing annulus fluid volume, as required at §146.88(e), is a

necessary component of monitoring well mechanical integrity, but believes that monitoring the

annulus fluid volume added is sufficient to meet the intent of continuous monitoring of the pressure

on the annulus. The final GS rule at §146.90 (b)) requires that owners or operators use continuous

recording devices to monitor injection pressure, rate and volume; the pressure on the annulus

between the tubing and the long string casing; and the annulus fluid volume added.

Commenter Name: Mark Bohrer Letter ID: 0241

Commenter Organization: North Dakota Industrial Commission Comment ID: 23301

Comment: 146.90(b) Is continuous recording of annular fluid volume possible or practical? 

Response: EPA believes that knowing annulus fluid volume, as required at §146.88(e), is a

necessary component of monitoring well mechanical integrity, but believes that monitoring the

annulus fluid volume added is sufficient to meet the intent of continuous monitoring of the pressure

on the annulus. The final GS rule at §146.90 (b)) requires that owners or operators use continuous

recording devices to monitor injection pressure, rate and volume; the pressure on the annulus

between the tubing and the long string casing; and the annulus fluid volume added.

Comment Code: 4630 2.6.3 Corrosion monitoring 

Individual Comments
Commenter Name: Michael H. Cochran Letter ID:

0108

Commenter Organization: Bureau of Water, Division of Environment, Kansas

Department of Health & Environment (KDHE)

Comment

ID: 21980

Other EPA Comment Codes and Descriptions: 4543 2.5.2.1 MIT procedures and methods for GS

(seeking comment) 

Comment: 146.89 (c) (3): The casing inspection log (CIL) does not detect fluid movement 

behind the casing and should not be listed here. This is an excellent log for 

detecting corrosion problems and the degree of corrosion casing inspection logs 

conducted periodically is a good method for monitoring corrosion in the well. 

Response: EPA agrees that the casing inspection log is not an appropriate test to detect fluid

movement behind the casing, but clarifies that it is appropriate for determining the presence or

absence of corrosion of the long-string casing, and is required if the Director determines that it is

necessary based on site-specific information. EPA has revised the final GS rule to require that the

frequency of the casing inspection log be specified in the approved testing and monitoring plan. See

§146.89(d). For additional information, please see the discussion of MITs in the final rule preamble.

Commenter Name: Herbert Skolnick, Ph.D. Letter ID: 0110

Commenter Organization: Group Against Smog and Pollution, Inc. (GASP) Comment ID: 22043

Other EPA Comment Codes and Descriptions: 4620 2.6.2 Injectate monitoring; 4660 2.6.6

Geochemical monitoring 

Comment: Regardless of what specific form the CO2 sequestration program ultimately takes, 

at a minimum, the program must ensure that: 

2. the sequestered material’s behavior in the chemical, geological, and 

hydrological environment where it is stored is anticipated and carefully 

monitored; and 

Response: EPA agrees with commenters on the importance of monitoring at GS sites and

emphasizes that monitoring of injection activities must be an important component of every GS

project. Monitoring associated with injection wells and the movement of the CO2 plume is necessary

to verify that the injectate is confined in the target formations and does not endanger USDWs. The

GS rule, at §146.90, requires injectate monitoring, mechanical integrity testing, corrosion

monitoring, tracking the CO2 plume and area of elevated pressure, monitoring geochemical changes

above the confining zone, and, at the discretion of the Director, surface air and soil gas monitoring

for CO2 fluctuations, and any additional tests necessary to ensure USDW protection from

endangerment.

Commenter Name: John Stormon Letter ID: 0123

Commenter Organization: Washington State Dept. of Ecology Comment ID: 23007

Other EPA Comment Codes and Descriptions: 4500 2.5 Proposed Mechanical Integrity Testing

(MIT) Requirements (40 CFR 146.89) 

Comment: Periodic corrosion and well integrity testing is important for all pollution 

prevention programs. This well testing will help operators to focus maintenance 

and repair activities on the wells that are degrading. It is far better to 

prevent leakage from a well breach than to fix the well after discovering that 

it has leaked. 
Response: EPA agrees with the commenter; the final rule requires both internal and external

mechanical integrity testing. Mechanical integrity testing is one of the cornerstones of the existing

EPA UIC program. The MIT requirements at §146.89, along with the corrosion monitoring required

at §146.90(c), ensure protection of USDWs from endangerment and provide an important early

warning of potential problems in the injection well. Routine mechanical integrity testing of injection

wells provides data that enables the identification and remediation of well integrity problems before

they lead to leakage and/or endangerment of USDWs. For additional information, please see the

discussion of MITs in the final rule preamble.

EPA also agrees that corrosion monitoring is appropriate given the potentially corrosive nature of the

CO2 stream. CO2 in the presence of water becomes acidic, potentially accelerating corrosion of well

materials. The CO2 stream for a GS project may also contain small volumes of impurities that could

contribute to corrosion. For these reasons, the final rule requires quarterly corrosion monitoring (at

§146.90(c)).

Commenter Name: Brianne Metzger Letter ID: 0151

Commenter Organization: Spectra Energy Corp Comment ID: 21837

Comment: For reasons described above, we also believe that the requirement to conduct 

corrosion monitoring on a quarterly basis is excessive and unnecessary. To 

require quarterly monitoring could negatively impact the flow rate, thus 

requiring operators to add more wells. This could limit the overall 

effectiveness of the project. In addition, quarterly corrosion monitoring 

would require the operator to remove the bottom hole configuration to perform 

necessary tests. This is both costly and time consuming and would require 

operations to be temporarily shutdown. 

Response: EPA believes that quarterly corrosion monitoring is reasonable and appropriate given the

potentially corrosive nature of the CO2 stream. CO2 in the presence of water becomes acidic,

potentially accelerating corrosion of well materials. The CO2 stream for a GS project may also

contain small volumes of impurities that could contribute to corrosion. For these reasons, the final

rule requires quarterly corrosion monitoring (at §146.90(c)).

Commenter Name: Brianne Metzger Letter ID: 0151

Commenter Organization: Spectra Energy Corp Comment ID: 21840

Comment: EPA’s proposal also calls for the use of "coupons" to monitor for corrosion. 40 

C.F.R. § 146.90(c)(1). Based on our experience with the use of coupons, we 

would recommend against this requirement, as coupons are susceptible to failure 

and can lodge deep in the injection well, thereby causing problems with flow 

rate. In addition, coupons do not identify where corrosion may or may not be 

taking place, due to the differences in temperature and pressure between 

ambient and downhole conditions. The results from the use of coupons could 

suggest that an entire casing or tubing string needs to be replaced when, in 

fact, only a portion of the well casing may need to be replaced. Therefore, 

coupons do not produce representative results and the data will generally not 

be helpful. Similarly, the concept of a "constructed loop" at the surface to 

monitor and test material integrity is also not recommended, as it does not 

replicate actual downhole conditions. 40 C.F.R. § 146.90(c)(2). We believe 

that one of the best tests for corrosion monitoring is the casing evaluation 
logs, which allow an operator to identify specific zones where corrosion may be 

occurring. 

Response: EPA believes that the use of coupons for corrosion monitoring is feasible and appropriate

for GS wells. Corrosion monitoring by various techniques, including the use of coupons, has been

performed by operators of Class I hazardous waste injection wells for many years. Use of coupons

can help provide early warning of corrosion of well materials that could compromise the well's

integrity. 

The use of well coupons for testing with CO2 for compatibility is one of three options outlined in

§146.90(c). Operators also have the option of routing the CO2 stream through a loop constructed

with the material used in the well or using an alternative method approved by the Director. 

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil gas and surface air monitoring which may be required by the UIC Director

for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Kyle Isakower Letter ID: 0170

Commenter Organization: American Petroleum Institute Comment ID: 24189

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Rule Provision: 146.90(c) 

API Comments: (c) WHERE CONDITIONS WARRANT, corrosion monitoring of the well 

materials for loss of mass, thickness, cracking, pitting and other signs of 

corrosion must be performed on a AND RECORDED AT LEAST quarterly basis

WHICH MAY BE MODIFIED TO BE LESS FREQUENT AS APPROVED BY THE DIRECTOR

BASED ON 

CONSTRUCTION MATERIALS, OPERATING CONDITIONS, AND MONITORING HISTORY

to ensure 

that the well components meet the minimum standards for material strength and 

performance set forth in §146.86(b) by: 

Rationale: Technical correction. 

API questions the need for corrosion monitoring of most injected CO2 streams 

since they will typically be nearly pure and dry thus having no corrosive 

properties. Industry experience with production, transportation, and injection 

of dry CO2 strongly illustrates the non-corrosive nature of this type of CO2 

stream. 

Response: EPA believes that corrosion monitoring is warranted and necessary for all Class VI wells

in order to protect USDWs. CO2 in the presence of water (including water with NOx, SOx, and H2S

impurities) can be corrosive to well materials and cements. Thus, although a CO2 stream may be

dry, the potential for corrosion of well materials down-hole, where the injectate can potentially mix
with water in the target formation, must be considered. 

Several laboratory studies and a limited number of field studies have investigated and characterized

the effects of carbonic acid on well materials. Laboratory studies (e.g., Kutchko et al., 2007;

Kutchko et al., 2008) consistently identify alterations (typically carbonation) of cement as the result

of interactions between cement and CO2-saturated brine. 

Currently, there are only a few analyses of cement from wells that have been in prolonged contact

with CO2 in actual field (down-hole) conditions. Evaluation of cement from a well at the Scurry

Area Canyon Reef Operators Committee (SACROC) site showed alteration, but did not show

degradation that compromised the structural integrity of the cement (Carey et al., 2007). In another

study, cement samples were collected and analyzed from a CO2 production well in a natural CO2

reservoir in Colorado exposed to a CO2-water down-hole environment for 30 years (Crow et al.,

2008). The study found evidence of reaction between the CO2-rich water and the cement. 

Oil industry research also addresses the effects of corrosion of steel tubing and pipes. Lopez et al.

(2003) noted that 60 percent of oilfield failures are related to the effects of carbonic acid from

produced brines on carbon and low alloy steels. 

Laboratory investigation of cement alteration/degradation is an ongoing research area. Few fieldbased studies have been completed to date. The laboratory and field studies currently available

suggest that corrosion problems can be managed; however, there is not a large enough body of

research to rule out potential corrosion problems of steel components of injection wells. The IPCC

(2005) report on carbon dioxide capture and storage reviewed oil and gas industry experience with

gas injection wells, close industry analogues to CO2 injection wells. The report stated that while the

design of CO2 injection wells will be very similar to gas injection wells, most down-hole

components of the CO2 injection wells will “need to be upgraded for higher pressure ratings and

corrosion resistance.” Given the pressure and corrosion considerations, anticipated long lifespan of a

GS well, and the difficulties that would be associated with a corrosion-related well failure, EPA

believes that corrosion monitoring in the down-hole environment is justified. For these reasons, the

final rule requires quarterly corrosion monitoring (at §146.90(c)).

Commenter Name: Kyle Isakower Letter ID: 0170

Commenter Organization: American Petroleum Institute Comment ID: 24190

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Rule Provision: 146.90(c) 

API Comments: (1) Placing ANALYZING coupons of the well construction 

materials PLACED in contact with the carbon dioxide stream; or 

(2) Routing the carbon dioxide stream through a loop constructed with the 

material used in the well AND INSPECTING THE MATERIALS IN THE LOOP; or 

(3) Using an alternative method, MATERIALS, OR TIME PERIOD approved by the 

Director; 

Rationale: Clarifying edits. 

Response: Based on its evaluation of all public comments and input on the proposed rule and

NODA and Request for Comment, EPA has made many revisions to the GS rule. See the final rule
and preamble for further discussion on EPA's final approach.

Commenter Name: Frederick R. Eames Letter ID: 0178

Commenter Organization: CCS Alliance Comment ID: 23868

Other EPA Comment Codes and Descriptions: 4546 2.5.2.2 MIT frequency (seeking comment) 

Comment: We do not believe there is any compelling reason to require annual integrity 

testing or quarterly corrosion monitoring. A five-year testing routine has been 

sufficient for acid gas wells in Canada. Many known injection wells are reused 

producer wells that have been in corrosive environments for over 15 years and 

remain in good condition. Annual testing and quarterly corrosion testing could 

also result in significant costs from plant shutdowns and downtime. Many 

companies already conduct periodic plant-wide shutdowns to thoroughly inspect 

piping and equipment for corrosion and make any necessary equipment upgrades. 

These shutdowns, which ordinarily occur once every three to five years, are also 

used to inspect injection wells, including pulling tubing, running cement bond 

logs, and well casing integrity logs to determine the thickness and integrity of 

the steel in the boreholes. From these tests, companies are able to assess the 

cement and casing conditions, which provide the primary "isolation" mechanism 

from the reservoir fluids. Moreover, companies can and often do run noise logs 

that can assess for "channeling" behind the casing. 

Response: EPA disagrees that a five-year external MIT is appropriate. The final GS regulation

retains the requirement that owners or operators of Class VI wells must demonstrate injection well

external mechanical integrity at least once annually under §146.89(c). While EPA acknowledges the

successful history of the Class II injection program, including injection of sour (acid) gas, the

Agency believes that CO2 injection for GS is substantially different from Class II ER operations and

believes annual MITs are justifiable for the protection of USDWs from endangerment given the

unique nature of CO2 GS relative to other injection operations, including the potential corrosive

impact of CO2 in the presence of water and impurities on well materials, the potential geomechanical

impacts to well integrity due to CO2 phase changes, the temperature and pressure effects associated

with injecting supercritical CO2, and the buoyant nature of the injected CO2. Because of the

unknown long-term effects of CO2 GS, EPA chose a more conservative initial approach in the early

stages of deployment for GS.

In addition, a comprehensive review conducted by EPA of MIT results from 1993 to 1998 found that

Class I wells injecting corrosive fluids fail MITs at rates two to three times higher than those that

inject non-corrosive fluids (USEPA 1999). Given the potential for CO2 to be corrosive (e.g., in the

presence of water or aqueous formation fluids), there is a potential risk factor for MIT failure and,

for this reason, EPA believes that the tailored MIT requirements in the final GS rule are appropriate.

Regarding concerns about disruptions of plant operations, EPA believes that, due to the expected size

of GS fields, many GS operations will have more than one injection well, and that testing of each

well can be timed to avoid complete interruption of the project. 

On the topic of corrosion monitoring, EPA disagrees with commenters' assertions that corrosion

monitoring is unnecessary or excessive. CO2 in the presence of water (including water with NOx,

SOx, and H2S impurities) can be corrosive to well materials and cements. Thus, although a CO2

stream may be dry, the potential for corrosion of well materials down-hole, where the injectate can

potentially mix with water in the target formation, must be considered.
EPA adds that it is using an adaptive approach to regulating GS. The Agency plans to collect and

review data every six years on GS projects, including MIT data, to determine whether the appropriate

amount and types of information and appropriate documentation are being collected, and to

determine if modifications to the requirements are appropriate or necessary.

Commenter Name: Robert F. Van Voorhees Letter ID: 0190

Commenter Organization: Carbon Sequestration Council Comment ID: 24480

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Rule Provision: 146.90(c) 

Proposed CCS Group Recommendations: (C) WHERE APPROPRIATE, THE TESTING AND 

MONITORING PLAN SHALL ALSO INCLUDE: 

(1) CONTINUOUS MONITORING FOR PRESSURE CHANGES IN AN APPROPRIATELY

POROUS AND 

PERMEABLE FORMATION OVERLYING THE CONFINING ZONE.; 

(2) THE USE OF INDIRECT, GEOPHYSICAL TECHNIQUES TO DETERMINE THE POSITION

OF THE 

CO2 STREAM FRONT, THE WATER QUALITY IN A DESIGNATED FORMATION, OR TO

PROVIDE 

OTHER SITE SPECIFIC DATA; 

(3) PERIODIC MONITORING OF WATER QUALITY IN AN APPROPRIATELY POROUS AND

PERMEABLE FORMATION OVERLYING THE INJECTION ZONE; 

(4) PERIODIC MONITORING OF WATER QUALITY IN ONE OR MORE USDWS; 

c (5) Corrosion monitoring of the well materials for loss of mass, 

thickness, cracking, pitting and other signs of corrosion performed and recorded 

AT LEAST on a quarterly WHICH MAY BE MODIFIED TO BE LESS FREQUENT AS 

APPROVED BY THE DIRECTOR BASED ON CONSTRUCTION MATERIALS, OPERATING

CONDITIONS, 

AND MONITORING HISTORY to ensure that the well components meet the minimum 

standards for material strength and performance set forth in §146.86(b) by: 

(1) (I) Placing ANALYZING coupons of the well construction materials 

placed in contact with the carbon dioxide stream; or 

(2) (II) Routing the carbon dioxide stream through a loop constructed with 

the material used in the well AND INSPECTING THE MATERIALS IN THE LOOP; or 

(3) (III) Using an alternative method, MATERIALS, OR TIME PERIOD approved by 

the Director; 

(6) ANY ADDITIONAL TESTING AND MONITORING NECESSARY TO SUPPORT

MODELING THE 
EXTENT OF THE CARBON DIOXIDE PLUME AND THE POSITION OF THE PRESSURE

FRONT; AND 

(7) ANY ADDITIONAL TESTING AND MONITORING NECESSARY TO DETERMINE

WHETHER FLUID 

MOVEMENT IS OCCURRING INTO OR BETWEEN USDWS THAT WOULD ENDANGER A

USDW. 

Basis for CCS Group Comments: There should be no need for corrosion monitoring 

of most injected CO2 streams because those streams will typically overwhelmingly 

CO2 and dry thus having no corrosive properties. Industry experience with 

production, transportation, and injection of dry CO2 strongly illustrates the 

non-corrosive nature of this type of CO2 stream. 

This proposal revises the provision to make it a requirement only where 

appropriate based on the materials of construction and characteristics of the 

injected CO2 stream and other factors. 

The corrosion provisions are included in subsection (c)(5). 

Response: EPA believes that quarterly corrosion monitoring of GS wells is necessary. CO2 in the

presence of water (including water with NOx, SOx, and H2S impurities) can be corrosive to well

materials and cements. Thus, although a CO2 stream may be dry, the potential for corrosion of well

materials down-hole, where the injectate can potentially mix with water in the target formation, must

be considered. 

Several laboratory studies and a limited number of field studies have investigated and characterized

the effects of carbonic acid on well materials. Laboratory studies (e.g., Kutchko et al., 2007;

Kutchko et al., 2008) consistently identify alterations (typically carbonation) of cement as the result

of interactions between cement and CO2-saturated brine. 

Currently, there are only a few analyses of cement from wells that have been in prolonged contact

with CO2 in actual field (down-hole) conditions. Evaluation of cement from a well at the Scurry

Area Canyon Reef Operators Committee (SACROC) site showed alteration, but did not show

degradation that compromised the structural integrity of the cement (Carey et al., 2007). In another

study, cement samples were collected and analyzed from a CO2 production well in a natural CO2

reservoir in Colorado exposed to a CO2-water down-hole environment for 30 years (Crow et al.,

2008). The study found evidence of reaction between the CO2-rich water and the cement. 

Oil industry research also addresses the effects of corrosion of steel tubing and pipes. Lopez et al.

(2003) noted that 60 percent of oilfield failures are related to the effects of carbonic acid from

produced brines on carbon and low alloy steels. 

Laboratory investigation of cement alteration/degradation is an ongoing research area. Few fieldbased studies have been completed to date. The laboratory and field studies currently available

suggest that corrosion problems can be managed; however, there is not a large enough body of

research to rule out potential corrosion problems of steel components of injection wells. The IPCC

(2005) report on carbon dioxide capture and storage reviewed oil and gas industry experience with

gas injection wells, close industry analogues to CO2 injection wells. The report stated that, while the

design of CO2 injection wells will be very similar to gas injection wells, most down-hole
components of the CO2 injection wells will “need to be upgraded for higher pressure ratings and

corrosion resistance.” Given the pressure and corrosion considerations, anticipated long lifespan of a

GS well and the difficulties that would be associated with a corrosion-related well failure, EPA

believes that corrosion monitoring in the down-hole environment is justified. For these reasons, the

final rule requires quarterly corrosion monitoring at §146.90(c).

EPA maintains that plume tracking and pressure monitoring are key components of monitoring at

GS sites. A rigorous plume tracking and pressure monitoring scheme, such as one that meets the

requirements at §146.90(g), is imperative for ensuring that the CO2 plume is contained within the

injection zone. Pressure monitoring in the injection zone is necessary to track the development and

movement of the pressure front and CO2 plume. When combined with information on temperature,

pressure data provide an indication of the phase (e.g., gas, supercritical) and distribution of the

injected CO2. Monitoring can also identify needed remedial actions, provide inputs for AoR

reevaluation modeling, evaluate predictions of plume movement, and target additional geochemical

and surface monitoring needs. 

EPA also believes that the ground water geochemical monitoring outlined in §146.90(d) will

maximize protection of USDWs from endangerment at GS sites. Direct geochemical sampling is an

important part of a monitoring program. See the final rule and preamble for further discussion on

EPA's final approach.

Commenter Name: Craig R. Walters Letter ID: 0200

Commenter Organization: Anadarko Petroleum Corporation Comment ID: 24702

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Rule Provision: 146.86(c) 

Anadarko Petroleum Corporation (APC) Comments: (C) WHERE APPROPRIATE, THE 

TESTING AND MONITORING PLAN SHALL ALSO INCLUDE: 

(1) CONTINUOUS MONITORING FOR PRESSURE CHANGES IN AN APPROPRIATELY

POROUS AND 

PERMEABLE FORMATION OVERLYING THE CONFINING ZONE. WHEN A WELL IS

INSTALLED TO 

ENABLE SUCH MONITORING, THE OWNER OR OPERATOR SHALL, ON A SPECIFIED

FREQUENCY OR 

AT SPECIFIED TIMES, SAMPLE THE FORMATION AND ANALYZE FOR CONSTITUENTS

SPECIFIED 

IN THE PLAN; 

(2) THE USE OF INDIRECT, GEOPHYSICAL TECHNIQUES TO DETERMINE THE POSITION

OF THE 

CO2 STREAM FRONT, THE WATER QUALITY IN A DESIGNATED FORMATION, OR TO

PROVIDE 

OTHER SITE SPECIFIC DATA; 

(3) PERIODIC MONITORING OF WATER QUALITY IN AN APPROPRIATELY POROUS AND

PERMEABLE FORMATION OVERLYING THE INJECTION ZONE; 
(4) PERIODIC MONITORING OF WATER QUALITY IN ONE OR MORE USDWS; 

(5) CORROSION MONITORING OF THE WELL MATERIALS FOR LOSS OF MASS,

THICKNESS, 

CRACKING, PITTING AND OTHER SIGNS OF CORROSION PERFORMED AND RECORDED

AT LEAST 

QUARTERLY WHICH MAY BE MODIFIED TO BE LESS FREQUENT AS APPROVED BY

THE DIRECTOR 

BASED ON CONSTRUCTION MATERIALS, OPERATING CONDITIONS, AND

MONITORING HISTORY TO 

ENSURE THAT THE WELL COMPONENTS MEET THE MINIMUM STANDARDS FOR

MATERIAL STRENGTH 

AND PERFORMANCE SET FORTH IN §146.86(B) BY: 

(I) ANALYZING COUPONS OF THE WELL CONSTRUCTION MATERIALS PLACED IN

CONTACT WITH 

THE CARBON DIOXIDE STREAM; OR 

(II) ROUTING THE CARBON DIOXIDE STREAM THROUGH A LOOP CONSTRUCTED

WITH THE 

MATERIAL USED IN THE WELL AND INSPECTING THE MATERIALS IN THE LOOP; OR 

(III) USING AN ALTERNATIVE METHOD, MATERIALS, OR TIME PERIOD APPROVED BY

THE 

DIRECTOR; 

(6) ANY ADDITIONAL TESTING AND MONITORING APPROPRIATE TO SUPPORT

MODELING THE 

EXTENT OF THE CARBON DIOXIDE PLUME AND THE POSITION OF THE PRESSURE

FRONT; AND 

(7) ANY ADDITIONAL TESTING AND MONITORING NECESSARY TO DETERMINE

WHETHER FLUID 

MOVEMENT IS OCCURRING INTO OR BETWEEN USDWS THAT WOULD ENDANGER A

USDW. 

Rationale: Drilling monitoring wells should be carefully considered since each 

well introduces a potential pathway for movement. In addition the cost of adding 

multiple wells could create a barrier to CCS development, while providing 

limited information on actual movement of the CO2 stream. 

APC questions the need for corrosion monitoring of most injected CO2 streams 

since they will typically be nearly pure and dry thus having no corrosive 

properties. Industry experience with production, transportation, and injection 

of dry CO2 strongly illustrates the non-corrosive nature of this type of CO2 

stream. 

Response: EPA believes that quarterly corrosion monitoring of GS wells is necessary. CO2 in the

presence of water (including water with NOx, SOx, and H2S impurities) can be corrosive to well

materials and cements. Thus, although a CO2 stream may be dry, the potential for corrosion of well

materials down-hole, where the injectate can potentially mix with water in the target formation, must

be considered. 
Several laboratory studies and a limited number of field studies have investigated and characterized

the effects of carbonic acid on well materials. Laboratory studies (e.g., Kutchko et al., 2007;

Kutchko et al., 2008) consistently identify alterations (typically carbonation) of cement as the result

of interactions between cement and CO2-saturated brine. 

Currently, there are only a few analyses of cement from wells that have been in prolonged contact

with CO2 in actual field (down-hole) conditions. Evaluation of cement from a well at the Scurry

Area Canyon Reef Operators Committee (SACROC) site showed alteration, but did not show

degradation that compromised the structural integrity of the cement (Carey et al., 2007). In another

study, cement samples were collected and analyzed from a CO2 production well in a natural CO2

reservoir in Colorado exposed to a CO2-water down-hole environment for 30 years (Crow et al.,

2008). The study found evidence of reaction between the CO2-rich water and the cement. 

Oil industry research also addresses the effects of corrosion of steel tubing and pipes. Lopez et al.

(2003) noted that 60 percent of oilfield failures are related to the effects of carbonic acid from

produced brines on carbon and low alloy steels. 

Laboratory investigation of cement alteration/degradation is an ongoing research area. Few fieldbased studies have been completed to date. The laboratory and field studies currently available

suggest that corrosion problems can be managed; however, there is not a large enough body of

research to rule out potential corrosion problems of steel components of injection wells. The IPCC

(2005) report on carbon dioxide capture and storage reviewed oil and gas industry experience with

gas injection wells, close industry analogues to CO2 injection wells. The report stated that while the

design of CO2 injection wells will be very similar to gas injection wells, most down-hole

components of the CO2 injection wells will “need to be upgraded for higher pressure ratings and

corrosion resistance.” Given the pressure and corrosion considerations, anticipated long lifespan of a

GS well and the difficulties that would be associated with a corrosion-related well failure, EPA

believes that corrosion monitoring in the down-hole environment is justified. For these reasons, the

final rule requires quarterly corrosion monitoring at §146.90(c).

EPA maintains that plume tracking and pressure monitoring are key components of monitoring at

GS sites. A rigorous plume tracking and pressure monitoring scheme, such as one that meets the

requirements at §146.90(g), is imperative for ensuring that the CO2 plume is contained within the

injection zone. Pressure monitoring in the injection zone is necessary to track the development and

movement of the pressure front and CO2 plume. When combined with information on temperature,

pressure data provide an indication of the phase (e.g., gas, supercritical) and distribution of the

injected CO2. Monitoring can also identify needed remedial actions, provide inputs for AoR

reevaluation modeling, evaluate predictions of plume movement, and target additional geochemical

and surface monitoring needs. 

EPA also believes that the ground water geochemical monitoring outlined in §146.90(d) will

maximize protection of USDWs from endangerment at GS sites. Direct geochemical sampling is an

important part of a monitoring program. See the final rule and preamble for further discussion on

EPA's final approach.

Commenter Name: Craig R. Walters Letter ID: 0200

Commenter Organization: Anadarko Petroleum Corporation Comment ID: 24703

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule
language 

Comment: Rule Provision: 146.90(c) 

Anadarko Petroleum Corporation (APC) Comments: (c) Corrosion monitoring of the 

well materials for loss of mass, thickness, cracking, pitting and other signs of 

corrosion must be performed on a quarterly basis to ensure that the well 

components meet the minimum standards for material strength and performance set 

forth in § 146.86(b) by: 

(1) Placing coupons of the well construction materials in contact with the 

carbon dioxide stream; or 

(2) Routing the carbon dioxide stream through a loop constructed with the 

material used in the well; or 

(3) Using an alternative method approved by the Director;

Rationale: See 146.90(5)(i-iii) 

Response: EPA believes that corrosion monitoring is necessary for all Class VI wells to prevent

endangerment of USDWs. CO2 in the presence of water (including water with NOx, SOx, and H2S

impurities) can be corrosive to well materials and cements. Thus, although a CO2 stream may be

dry, the potential for corrosion of well materials down-hole, where the injectate can potentially mix

with water in the target formation, must be considered. 

Based on its evaluation of all public comments and input on the proposed rule and NODA and

Request for Comment, EPA has made many revisions to the GS rule. See the final rule and preamble

for further discussion on EPA's final approach.

Commenter Name: Ronald Evans Letter ID: 0215

Commenter Organization: Denbury Resources, Inc. (DRI) Comment ID: 24309

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: 2. EPA Proposed §146.90(c) Corrosion monitoring of the well materials 

for loss of mass, thickness, cracking, pitting and other signs of 

corrosion must be performed on a quarterly basis to ensure that the well 

components meet the minimum standards for material strength and 

performance set forth in § 146.86(b) by: 

(1) Placing coupons of the well construction materials in contact with 

the carbon dioxide stream; or 

(2) Routing the carbon dioxide stream through a loop constructed with 

the material used in the well; or 

(3) Using an alternative method approved by the Director; 

Denbury believes the requirements in EPA proposed §146.90(c) related to 

corrosion monitoring are inapplicable. In the vast majority of cases, the CO2 

will be transported to the injection site through pipelines, will be dehydrated 

prior to transportation and therefore when injected it will be noncorrosive.[FN44] In those instances, the test methods described in § 146.90(c) 

(1) and (c)(2) (except of course alternatives approved by the Director) will not 

provide meaningful information regarding the mechanical integrity of down-hole 
casing, tubing and other equipment because the CO2 will simply not be corrosive 

at the surface. Consequently, to have any relevance such requirements should be 

reserved for situations where water saturated CO2 is being injected. 

§146.90(c) Corrosion monitoring of the well materials for loss of mass, 

thickness, cracking, pitting and other signs of corrosion must be 

performed on a quarterly basis to ensure that the well components 

THAT CONTACT WATER SATURATED CARBON DIOXIDE STREAMS meet the minimum 

standards for material strength and performance set forth in § 146.86(b) 

by: 

(1) Placing coupons of the well construction materials in contact 

with the carbon dioxide stream; or 

(2) Routing the carbon dioxide stream 

through a loop constructed with the material used in the well; or 

(3) Using an alternative method approved by the Director. THE REQUIREMENTS 

OF THIS SUBPART ARE WAIVED WHEN THE CARBON DIOXIDE STREAM IS

DEHYDRATED 

TO MEET PIPELINE SPECIFICATIONS. 

[44] For evidence on CO2 corrosiveness in the absence of free water see Don 

Duttlinger, "Enhanced Recovery Intertwines Naturally With CO2 Sequestration," 

Tech Connections Column, American Oil and Gas Reporter (January 2004), available 

at http://www.pttc.org/aogr_columns_archived/aogrcojan04.htm (From the 

processing/injection standpoint, CO2 is noncorrosive as long as it is dry. 

Proving that point, Kinder Morgan has hydro-tested the 32-year-old CRC Pipeline 

built in 1971 to transport CO2. Only one minor failure occurred. After testing, 

the line was rated for 2,025 psi maximum operating pressure, which established a 

200 psi increase over most recent ratings); see also J. Layne, "Results of the 

Hydrotest of the 30-year old Canyon Reef Carriers CO2 Pipeline," 2003 CO2 

Flooding Conference, University of Texas of the Permian Basin's Center for 

Energy and Economic Diversification, Midland,Texas (December 11-12, 2003). 

Response: EPA disagrees that corrosion monitoring is unnecessary or excessive. CO2 in the

presence of water (including water with NOx, SOx, and H2S impurities) can be corrosive to well

materials and cements. Thus, although a CO2 stream may be dry, the potential for corrosion of well

materials down-hole, where the injectate can potentially mix with water in the target formation, must

be considered. EPA believes that the testing methods specified in the rule are appropriate and have

been used successfully by Class I hazardous waste injection well owners or operators.

Several laboratory studies and a limited number of field studies have investigated and characterized

the effects of carbonic acid on well materials. Laboratory studies (e.g., Kutchko et al., 2007;

Kutchko et al., 2008) consistently identify alterations (typically carbonation) of cement as the result

of interactions between cement and CO2-saturated brine. 

Currently, there are only a few analyses of cement from wells that have been in prolonged contact

with CO2 in actual field (down-hole) conditions. Evaluation of cement from a well at the Scurry

Area Canyon Reef Operators Committee (SACROC) site showed alteration, but did not show

degradation that compromised the structural integrity of the cement (Carey et al., 2007). In another

study, cement samples were collected and analyzed from a CO2 production well in a natural CO2

reservoir in Colorado exposed to a CO2-water down-hole environment for 30 years (Crow et al.,
2008). The study found evidence of reaction between the CO2-rich water and the cement. 

Oil industry research also addresses the effects of corrosion of steel tubing and pipes. Lopez et al.

(2003) noted that 60 percent of oilfield failures are related to the effects of carbonic acid from

produced brines on carbon and low alloy steels. 

Laboratory investigation of cement alteration/degradation is an ongoing research area. Few fieldbased studies have been completed to date. The laboratory and field studies currently available

suggest that corrosion problems can be managed; however, there is not a large enough body of

research to rule out potential corrosion problems of steel components of injection wells. The IPCC

(2005) report on carbon dioxide capture and storage reviewed oil and gas industry experience with

gas injection wells, close industry analogues to CO2 injection wells. The report stated that while the

design of CO2 injection wells will be very similar to gas injection wells, most down-hole

components of the CO2 injection wells will “need to be upgraded for higher pressure ratings and

corrosion resistance.” Given the pressure and corrosion considerations, anticipated long lifespan of a

GS well and the difficulties that would be associated with a corrosion-related well failure, EPA

believes that corrosion monitoring in the down-hole environment is justified. For these reasons, the

final rule requires quarterly corrosion monitoring (at §146.90(c)). See the final rule and preamble for

further discussion on EPA's final approach.

Commenter Name: Darrick Eugene Letter ID: 0223

Commenter Organization: Texas Carbon Capture and Storage Association Comment ID: 23989

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: EPA Proposed §146.90(c) Corrosion monitoring of the well materials for 

loss of mass, thickness, cracking, pitting and other signs of corrosion 

must be performed on a quarterly basis to ensure that the well 

components meet the minimum standards for material strength and 

performance set forth in § 146.86(b) by: 

(1) Placing coupons of the well construction materials in contact with 

the carbon dioxide stream; or 

(2) Routing the carbon dioxide stream through a loop constructed with 

the material used in the well; or 

(3) Using an alternative method approved by the Director; 

TxCCSA believes the requirements in EPA proposed §146.90(c) related to corrosion 

monitoring are inapplicable. In the vast majority of cases, the CO2 will be 

transported to the injection site through pipelines, will be dehydrated prior to 

transportation and therefore when injected it will be non-corrosive.[FN2] In those 

instances, the test methods described in § 146.90(c)(1) and (c)(2) (except of 

course alternatives approved by the Director) will not provide meaningful 

information regarding the mechanical integrity of down-hole casing, tubing and 

other equipment because the CO2 will simply not be corrosive at the surface. 

Consequently, to have any relevance such requirements should be reserved for 

situations where water saturated CO2 is being injected. 

[FN2: For evidence on CO2 corrosivity in the absence of free water see Don 

Duttlinger, Enhanced Recovery Intertwines Naturally With CO2 Sequestration, Tech 

Connections Column, January 2004, American Oil and Gas Reporter, available at 
http://www.pttc.org/aogr_columns_archived/aogrcojan04.htm (From the 

processing/injection standpoint, CO2 is noncorrosive as long as it is dry. 

Proving that point, Kinder Morgan has hydro-tested the 32-year-old CRC Pipeline 

built in 1971 to transport CO2. Only one minor failure occurred. After testing, 

the line was rated for 2,025 psi maximum operating pressure, which established a 

200 psi increase over most recent ratings); see J. Layne, Results of the 

Hydrotest of the 30-year old Canyon Reef Carriers CO2 Pipeline, 2003 CO2 

Flooding Conference, December 11-12, 2003, Midland,Texas (University of Texas of 

the Permian Basin’s Center for Energy and Economic Diversification).] 

§146.90(c) Corrosion monitoring of the well materials for loss of mass, 

thickness, cracking, pitting and other signs of corrosion must be 

performed on a quarterly basis to ensure that the well components 

THAT CONTACT WATER SATURATED CARBON DIOXIDE STREAMS meet the minimum 

standards for material strength and performance set forth in § 146.86(b) 

by: 

(1) Placing coupons of the well construction materials in contact with 

the carbon dioxide stream; or 

(2) Routing the carbon dioxide stream through a loop constructed with 

the material used in the well; or 

(3) Using an alternative method approved by the Director. 

THE REQUIREMENTS 

OF THIS SUBPART ARE WAIVED WHEN THE CARBON DIOXIDE STREAM IS

DEHYDRATED 

TO MEET PIPELINE SPECIFICATIONS. 

Response: Based on its evaluation of all public comments and input on the proposed rule and

NODA and Request for Comment EPA has made many revisions to the GS rule. See the final rule

and preamble for further discussion on EPA's final approach.

EPA disagrees with commenters' assertions that corrosion monitoring is unnecessary or excessive.

CO2 in the presence of water (including water with NOx, SOx, and H2S impurities) can be

corrosive to well materials and cements. Thus, although a CO2 stream may be dry, the potential for

corrosion of well materials down-hole, where the injectate can potentially mix with water in the

target formation, must be considered. 

Several laboratory studies and a limited number of field studies have investigated and characterized

the effects of carbonic acid on well materials. Laboratory studies (e.g., Kutchko et al., 2007;

Kutchko et al., 2008) consistently identify alterations (typically carbonation) of cement as the result

of interactions between cement and CO2-saturated brine. EPA believes that the testing methods

specified in the rule are appropriate and have been used successfully by Class I hazardous waste

injection well owners or operators.

Currently, there are only a few analyses of cement from wells that have been in prolonged contact

with CO2 in actual field (down-hole) conditions. Evaluation of cement from a well at the Scurry

Area Canyon Reef Operators Committee (SACROC) site showed alteration, but did not show

degradation that compromised the structural integrity of the cement (Carey et al., 2007). In another

study, cement samples were collected and analyzed from a CO2 production well in a natural CO2

reservoir in Colorado exposed to a CO2-water down-hole environment for 30 years (Crow et al.,

2008). The study found evidence of reaction between the CO2-rich water and the cement. 
Oil industry research also addresses the effects of corrosion of steel tubing and pipes. Lopez et al.

(2003) noted that 60 percent of oilfield failures are related to the effects of carbonic acid from

produced brines on carbon and low alloy steels. 

Laboratory investigation of cement alteration/degradation is an ongoing research area. Few fieldbased studies have been completed to date. The laboratory and field studies currently available

suggest that corrosion problems can be managed; however, there is not a large enough body of

research to rule out potential corrosion problems of steel components of injection wells. The IPCC

(2005) report on carbon dioxide capture and storage reviewed oil and gas industry experience with

gas injection wells, close industry analogues to CO2 injection wells. The report stated that while the

design of CO2 injection wells will be very similar to gas injection wells, most down-hole

components of the CO2 injection wells will “need to be upgraded for higher pressure ratings and

corrosion resistance.” Given the pressure and corrosion considerations, anticipated long lifespan of a

GS well and the difficulties that would be associated with a corrosion-related well failure, EPA

believes that corrosion monitoring in the down-hole environment is justified. For these reasons, the

final rule requires quarterly corrosion monitoring (at §146.90(c)).

The Agency plans to, every six years, collect and review data on GS projects to determine whether

the appropriate amount and types of information and appropriate documentation are being collected,

and to determine if modifications to the requirements are appropriate or necessary.

Commenter Name: Andrew Duguid Letter ID: 0226

Commenter Organization: Schlumberger Carbon Services Comment ID: 24054

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Proposed Rule: (c) Corrosion monitoring of the well materials for loss of mass, 

thickness, cracking, pitting and other signs of corrosion must be performed on a 

quarterly basis to ensure that the well components meet the minimum standards 

for material strength and performance set forth in §146.86(b) by: 

Schlumberger Suggested Revision: (c) Corrosion monitoring of the well materials 

for loss of mass, thickness, cracking, pitting and other signs of corrosion must 

be performed quarterly and may be modified to be less frequent as approved by 

the Director based on construction materials, operating conditions, and 

monitoring history to ensure that the well components meet the minimum standards 

for material strength and performance set forth in §146.86(b) by: 

Schlumberger Rationale: Allows application of performance based approach. 

Response: EPA believes that corrosion monitoring is appropriate given the potentially corrosive

nature of the CO2 stream. CO2 in the presence of water becomes acidic, potentially accelerating

corrosion of well materials. The CO2 stream for a GS project may also contain small volumes of

impurities that could contribute to corrosion. For these reasons, the final rule requires quarterly

corrosion monitoring at §146.90(c), as proposed.

Commenter Name: Andrew Duguid Letter ID: 0226

Commenter Organization: Schlumberger Carbon Services Comment ID: 24055
Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Proposed Rule: (1) Placing coupons of the well construction materials in contact 

with the carbon dioxide stream; or 

Schlumberger Suggested Revision: (1) Analyzing coupons of the well construction 

materials placed in contact with the carbon dioxide stream; or 

Schlumberger Rationale: - 

Response: Based on its evaluation of all public comments and input on the proposed rule and

NODA and Request for Comment EPA has made many revisions to the GS rule. See the final rule

and preamble for further discussion on EPA's final approach.

Commenter Name: Andrew Duguid Letter ID: 0226

Commenter Organization: Schlumberger Carbon Services Comment ID: 24056

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Proposed Rule: (2) Routing the carbon dioxide stream through a loop constructed 

with the material used in the well; or 

Schlumberger Suggested Revision: (2) Routing the carbon dioxide stream through a 

loop constructed with the material used in the well and inspecting the materials 

in the loop; or 

Schlumberger Rationale: - 

Response: Based on its evaluation of all public comments and input on the proposed rule and

NODA and Request for Comment EPA has made many revisions to the GS rule. See the final rule

and preamble for further discussion on EPA's final approach.

Commenter Name: Andrew Duguid Letter ID: 0226

Commenter Organization: Schlumberger Carbon Services Comment ID: 24057

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Proposed Rule: (3) Using an alternative method approved by the Director; 

Schlumberger Suggested Revision: (3) Using an alternative method, materials, or 

time period approved by the Director; 

Schlumberger Rationale: - 

Response: Based on its evaluation of all public comments and input on the proposed rule and

NODA and Request for Comment EPA has made many revisions to the GS rule. See the final rule

and preamble for further discussion on EPA's final approach.

Commenter Name: Neeraj Gupta Letter ID: 0229

Commenter Organization: Battelle Energy Technology (BET) Comment ID: 21848
Comment: Page 88, Corrosion Coupons- We would appreciate more clarity on where corrosion 

coupons would be necessary (i.e. only within the injection zone or spaced within 

the tubing). Would it be sufficient to use place coupons above-ground in the 

CO2 pipeline near the well? 

Response: EPA clarifies that the requirement to monitor corrosion by placing the coupons in the

well would provide a more accurate analogue of the conditions to which well materials are exposed

than would surface testing (i.e., in the pipeline). Please note that the use of coupons is one out three

methods that an owner or operator may use to monitor corrosion under §146.90(c). EPA adds that,

under SDWA authority, the Agency cannot prescribe any testing methods that involve the pipeline. 

Several options are available for monitoring corrosion using coupons. For example, corrosion

coupons may be placed in a side stream loop so they are exposed to the injectate. Valves on either

end of the side stream loop allow the owner or operator to shut off the injectate flow, extract the

coupons, and measure any change in thickness. Another monitoring option is to insert the coupons

through a "T" in the flowline and directly lower this into the injection flow. The coupons can then be

retracted into the side pipe, extracted, and measured. Finally, spool pieces of the construction

material can be installed either in the injectate flow line or in a side stream; flanges and valves allow

the spool pieces to be isolated from the injectate so they can be evaluated for corrosion.

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil gas and surface air monitoring which may be required by the UIC Director

for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Mark Bohrer Letter ID: 0241

Commenter Organization: North Dakota Industrial Commission Comment ID: 23302

Comment: 146.90(c) Quarterly is too onerous. Director should have discretion to require 

less frequently based upon performance. 

Response: EPA believes that quarterly corrosion monitoring is appropriate given the potentially

corrosive nature of the CO2 stream. CO2 in the presence of water becomes acidic, potentially

accelerating corrosion of well materials. The CO2 stream for a GS project may also contain small

volumes of impurities that could contribute to corrosion. For these reasons, the final rule requires

quarterly corrosion monitoring, at §146.90(c).

Commenter Name: Michel Paque Letter ID: 0259

Commenter Organization: Ground Water Protection Council Comment ID: 24924

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Rule Provision: 146.90 

EPA Proposal: (c) Corrosion monitoring of the well materials for loss of mass, 

thickness, cracking, pitting and other signs of corrosion must be performed on a 
quarterly basis to ensure that the well components meet the minimum standards 

for material strength and performance set forth in § 146.86(b) by: 

GWPC Recommendations: c) Corrosion monitoring of the well materials for loss of 

mass, thickness, cracking, pitting and other signs of corrosion must be 

performed and recorded at least quarterly and may be modified to be less 

frequent as approved by the Director based on construction materials, operating 

conditions, and monitoring history to ensure that the well components meet the 

minimum standards for material strength and performance set forth in §146.86(b) 

by: 

Rationale: Allows application of performance based approach. 

Rationale: Allows less frequent monitoring, for example, where corrosion 

resistant materials are used. 

Response: EPA believes that quarterly corrosion monitoring is appropriate given the potentially

corrosive nature of the CO2 stream. CO2 in the presence of water becomes acidic, potentially

accelerating corrosion of well materials. The CO2 stream for a GS project may also contain small

volumes of impurities that could contribute to corrosion. For these reasons, the final rule requires

quarterly corrosion monitoring, at §146.90(c).

Based on its evaluation of all public comments and input on the proposed rule and NODA and

Request for Comment EPA has made many revisions to the GS rule. See the final rule and preamble

for further discussion on EPA's final approach.

Commenter Name: Michel Paque Letter ID: 0259

Commenter Organization: Ground Water Protection Council Comment ID: 24925

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Rule Provision: 146.90(c) 

EPA Proposal: (1) Placing coupons of the well construction materials in contact 

with the carbon dioxide stream; or 

(2) Routing the carbon dioxide stream through a loop constructed with the 

material used in the well; or 

(3) Using an alternative method approved by the Director; 

GWPC Recommendations: (1) Analyzing coupons of the well construction materials 

placed in contact with the carbon dioxide stream; or 

(2) Routing the carbon dioxide stream through a loop constructed with the 

material used in the well and inspecting the materials in the loop; or 

(3) Using an alternative method, materials, or time period approved by the 

Director; 

Rationale: Clarification edits 

Response: As described above, EPA believes that quarterly corrosion monitoring is appropriate

given the potentially corrosive nature of the CO2 stream. Based on its evaluation of all public
comments and input on the proposed rule and NODA and Request for Comment EPA has made

many revisions to the GS rule. See the final rule and preamble for further discussion on EPA's final

approach.

Commenter Name: Donn Miller Letter ID: 0270

Commenter Organization: State of Oregon, Water Resources Department Comment ID: 22889

Comment: 146.90 Testing and Monitoring Requirements. 

(c) We support extensive corrosion monitoring and control, at least until 

collectively we know more about how cement will react to long-term contact with 

CO2. 

Response: EPA agrees that corrosion monitoring is appropriate given the potentially corrosive nature

of the CO2 stream. CO2 in the presence of water becomes acidic, potentially accelerating corrosion

of well materials. The CO2 stream for a GS project may also contain small volumes of impurities

that could contribute to corrosion. For these reasons, the final rule requires quarterly corrosion

monitoring at §146.90(c).

Comment Code: 4640 2.6.4 Pressure fall-off testing (seeking comment) 

Individual Comments

Commenter Name: John Hanger Letter ID: 0130

Commenter Organization: Pennsylvania Dept. of Env. Protection Comment ID: 21510

Comment: -Depending on the geology surrounding the containment formation, it is possible 

that the CO2 could be absorbed/adsorbed by some of the surrounding formations. 

This could cause a drop in pressure not directly associated with leakage. EPA 

should determine or allow for a maximum allowable pressure drop, or correction 

value, dependent on the appropriate surrounding geology. 

Response: EPA believes that pressure fall-off testing is necessary for GS wells. Pressure fall-off

tests are designed to verify that modeled projections of reservoir pressure decline agree with

measured pressure decline profiles. These tests can be useful in AoR calculations and reevaluations

and may also indicate mischaracterization of site geology and the presence of leakage pathways.

EPA therefore believes that pressure fall-off testing is necessary every five years at a minimum, and

the final GS regulation includes this requirement at §146.90(f). Pressure fall-off tests may be

conducted in conjunction with other well performance tests (i.e., mechanical integrity testing) to

ensure safe and effective operations.

EPA is developing guidance on testing and monitoring at GS sites, which will address pressure falloff testing. The guidance also describes available technologies and recommended approaches for

implementing a testing and monitoring plan, including pre-operational geophysical logging and

testing of injection wells, MITs, injection well testing during operation, groundwater quality

monitoring, tracking the CO2 plume and pressure front, and soil gas and surface air monitoring

which may be required by the UIC Director for specific GS projects. The guidance can be found on

EPA’s website at http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.
Commenter Name: Christine Reimer Letter ID: 0142

Commenter Organization: National Ground Water Association Comment ID: 22608

Comment: Proposed Rule: 146.90(f) 

Comment: What additional information does this test provide that is not 

available from other sources? The perception from some of our reviewers is that 

there may not be much information that is gathered that is not already available 

from other sources. If there is no significant additional information 

provided, running the test may not be necessary. 

Response: EPA disagrees and believes that pressure fall-off testing is necessary for GS wells.

Pressure fall-off tests are designed to verify that modeled projections of reservoir pressure decline

agree with measured pressure decline profiles. These tests can be useful in AoR calculations and

reevaluations and may also indicate mischaracterization of site geology and the presence of leakage

pathways. EPA therefore believes that pressure fall-off testing must be conducted at least once every

five years, and the final GS regulation includes this requirement at §146.90(f). Pressure fall-off tests

may be conducted in conjunction with other well performance tests (i.e., mechanical integrity testing)

to ensure safe and effective operations.

Commenter Name: Kyle Isakower Letter ID: 0170

Commenter Organization: American Petroleum Institute Comment ID: 24248

Comment: Rule Provisions: 146.90(f) 

EPA Preamble Question: 31. EPA’s proposal would require that owners or operators 

perform a pressure fall-off test at least once every five years. EPA seeks 

comment on the use and frequency of pressure fall-off testing for GS wells. EPA 

Notice 43515. 

API Response: 31. We recommend that an initial falloff test be conducted upon completion of the

well prior to any operational injection and after the first year of operational injection. Following the

first year, the frequency should be at the discretion of the Director

but the frequency should be aligned with the reevaluation of the AoR. 

Response: EPA believes that a frequency of at least once every five years, as specified at §146.90(f),

is an appropriate interval for pressure fall-off testing (particularly given the suite of tests operators

will perform on the well and the site). EPA clarifies that the Director may require more frequent

pressure fall-off tests at a specific project, if necessary based on site-specific circumstances. Pressure

fall-off tests may be conducted in conjunction with other well performance tests (i.e., mechanical

integrity testing) to ensure safe and effective operations. All monitoring data collected, including

information from pressure fall-off tests, will be incorporated in AoR reevaluations conducted at least

every five years.

Commenter Name: Thomas Curtis Letter ID: 0181

Commenter Organization: American Water Works Association (AWWA) Comment ID: 23698

Comment: 

Pressure fall-off testing should definitely be required however the five year 

length between testing is too long. This should be performed on an annual basis 

as part of the annual reporting requirements 
Response: EPA believes that a frequency of at least once every five years, as specified at §146.90(f),

is an appropriate interval for pressure fall-off testing (particularly given the suite of tests operators

will perform on the well and the site). EPA clarifies that the Director may require more frequent

pressure fall-off tests at a specific project, if necessary based on site-specific circumstances. Pressure

fall-off tests may be conducted in conjunction with other well performance tests (i.e., mechanical

integrity testing) to ensure safe and effective operations. All monitoring data collected, including

information from pressure fall-off tests, will be incorporated in AoR reevaluations conducted at least

every five years.

Commenter Name: Bradley J. Field Letter ID: 0186

Commenter Organization: New York State Dept. of Environmental Conservation

Div. of Mineral Resources

Comment ID:

25202

Comment: DD. EPA seeks comment on the use and frequency of pressure fall-off testing for 

GS wells. 

NYSDEC-DMN Response: NYSDEC-DMN is unclear as to the actual utility of pressure 

fall-off testing for operational GS wells. Instead of being mandated at least 

once every five years, the Director should have the discretion to require such 

testing as deemed appropriate. 

Response: EPA believes that pressure fall-off testing is necessary for GS wells. Pressure fall-off

tests are designed to verify that modeled projections of reservoir pressure decline agree with

measured pressure decline profiles. These tests can be useful in AoR calculations and reevaluations

and may also indicate mischaracterization of site geology and the presence of leakage pathways.

EPA therefore believes that pressure fall-off testing must be conducted at least once every five years

and the final GS regulation includes this requirement at §146.90(f). Pressure fall-off tests may be

conducted in conjunction with other well performance tests (i.e., mechanical integrity testing) to

ensure safe and effective operations.

EPA believes that a frequency of at least once every five years, as specified at §146.90(f), is an

appropriate interval for pressure fall-off testing (particularly given the suite of tests operators will

perform on the well and the site). EPA clarifies that the Director may require more frequent pressure

fall-off tests at a specific project, if necessary based on site-specific circumstances. Pressure fall-off

tests may be conducted in conjunction with other well performance tests (i.e., mechanical integrity

testing) to ensure safe and effective operations. All monitoring data collected, including information

from pressure fall-off tests, will be incorporated in AoR reevaluations conducted at least every five

years.

Commenter Name: Daniel Plath Letter ID: 0188

Commenter Organization: NiSource, Inc. Comment ID: 25237

Comment: 4. Pressure Falloff Tests (146.90(f)) 

The EPA proposes and requests comment on the requirement for operators to 

conduct a pressure falloff test once every 5 years (Preamble (73 Fed. Reg. at 

43515). Notwithstanding our comments below about the Proposed Rule having 

excessive data collection requirements, one area in which NiSource believes the 

Proposed Rule is actually too lenient is with respect to only requiring a 

pressure falloff test at least once every 5 years. NiSource recommends where 
appropriate that this be either done at an interval no greater than two years or 

at a site specific injected volume interval. NiSource notes the duration of 

shut-in will be reservoir dependent but a range of 1 to 5 days, depending on the 

reservoir circumstances, is recommended. 

The key to this being an invaluable tool with natural gas reservoir storage 

integrity monitoring isn't that the time period is long enough to actually reach 

pressure stability as it is that the testing is conducted at consistent time 

intervals and volume levels over the life of the field. This is primarily done 

by collecting and studying shut-in data at every well every spring and fall when 

the field is empty and full of working gas, respectively. Testing at a fairly 

consistent time/volume interval provides for more relevant comparisons over 

time, and enhances the usefulness for comparisons over extended periods of time, 

even when comparing test results over several decades. This in turn permits an 

efficient understanding of what the gas is doing in the vast reservoir area over 

the life of the field and the identification of even very slowly growing 

abnormal trends in the gas plume's pressure-volume behavior. An accurate 

identification of the fields, if any that are experiencing gas migration issues 

then allows the operator to focus resources to identify the root cause and to 

rectify the specific probiem. NiSource believes these testing provisions would 

be helpful if included in the proposed rule. Therefore, we suggest the rule 

language be adjusted to accommodate these factors. 

While the volume in a GS field will be continually increasing versus cycling as 

with natural gas storage, the concept of having snap shots of the shut-in 

reservoir pressure for the entire CO2 plume at consistent time/volume intervals 

should still lead to a similar understanding of the plume's overall behavior. 

These observations can then be compared with the reservoir simulation 

predictions and would help with fine tuning model assumptions. Significant 

deviations, if any, would be quickly identified and would become the 

investigative focal point for the operator's resources. 

In many instances, we recommend this shut-in pressure test and analysis coupled 

with simulation be recognized as a viable primary method for CO2 plume 

monitoring with more extensive methods (e.g. 4D seismic, etc.) only being used 

to periodically fine tune the model or in instances when questions arise. The 

appropriate testing basis, time or volume based, will likely be site and 

operator specific. Therefore, the Final Rule needs to provide for flexibility to 

utilize this method and allow the use of new testing technology that may become 

available in the future. 

Response: EPA believes that a frequency of at least once every five years, as specified at §146.90(f),

is an appropriate interval for pressure fall-off testing (particularly given the suite of tests operators

will perform on the well and the site). EPA clarifies that the Director may require more frequent

pressure fall-off tests at a specific project, if necessary based on site-specific circumstances. Pressure

fall-off tests may be conducted in conjunction with other well performance tests (i.e., mechanical

integrity testing) to ensure safe and effective operations. All monitoring data collected, including

information from pressure fall-off tests, will be incorporated in AoR reevaluations conducted at least

every five years.
EPA adds that the pressure fall-off testing will be performed in concert with other testing, including

plume monitoring, pursuant to the approved testing and monitoring plan. If any site-specific

information indicates a need for additional or more frequent testing to ensure USDWs are protected,

it is within the Director's discretion to require additional testing to ensure protection of USDWs.

Commenter Name: Robert F. Van Voorhees Letter ID: 0190

Commenter Organization: Carbon Sequestration Council Comment ID: 24540

Comment: Rule Provisions or Federal Register Cite: 146.90(f) 

EPA Preamble Question: 31. EPA’s proposal would require that owners or operators 

perform a pressure fall-off test at least once every five years. EPA seeks 

comment on the use and frequency of pressure fall-off testing for GS wells. EPA 

Notice 43515. 

CSC Response: We recommend that an initial falloff test be conducted upon 

completion of the well prior to any operational injection and after the first 

year of operational injection. Following the first year, the frequency should be 

at the discretion of the Director but the frequency should be aligned with the 

reevaluation of the AoR. 

Response: EPA believes that a frequency of at least once every five years, as specified at §146.90(f),

is an appropriate interval for pressure fall-off testing (particularly given the suite of tests operators

will perform on the well and the site). EPA clarifies that the Director may require more frequent

pressure fall-off tests at a specific project, if necessary based on site-specific circumstances. Pressure

fall-off tests may be conducted in conjunction with other well performance tests (i.e., mechanical

integrity testing) to ensure safe and effective operations. All monitoring data collected, including

information from pressure fall-off tests, will be incorporated in AoR reevaluations conducted at least

every five years.

Commenter Name: Craig R. Walters Letter ID: 0200

Commenter Organization: Anadarko Petroleum Corporation Comment ID: 24601

Comment: Rule Provisions: 146.90(f) 

EPA Rule Issue: 31. EPA’s proposal would require that owners or operators 

perform a pressure fall-off test at least once every five years. EPA seeks 

comment on the use and frequency of pressure fall-off testing for GS wells. EPA 

Notice 43515. 

Anadarko Petroleum Corporation (APC) Response: We recommend that an initial 

falloff test be conducted upon completion of the well prior to any operational 

injection and after the first year of operational injection. Following the first 

year, the frequency should be at the discretion of the Director but the 

frequency should be aligned with the reevaluation of the AoR. 

Response: EPA believes that a frequency of at least once every five years, as specified at §146.90(f),

is an appropriate interval for pressure fall-off testing (particularly given the suite of tests operators

will perform on the well and the site). EPA clarifies that the Director may require more frequent

pressure fall-off tests at a specific project, if necessary based on site-specific circumstances. Pressure

fall-off tests may be conducted in conjunction with other well performance tests (i.e., mechanical

integrity testing) to ensure safe and effective operations. All monitoring data collected, including
information from pressure fall-off tests, will be incorporated in AoR reevaluations conducted at least

every five years.

Commenter Name: Ronald Evans Letter ID: 0215

Commenter Organization: Denbury Resources, Inc. (DRI) Comment ID: 24310

Comment: 3. EPA Proposed §146.90(f) A pressure fall-off test at least once every 

five years unless more frequent testing is required by the Director 

based on site specific information; 

The scope of this proposed requirement is not clear. Does the EPA proposal 

require the submittal of the actual data, or merely an analysis of the pressure 

fall-off test? 

Response: EPA expects that the Director would request an electronic copy of the data in addition to

an analysis report completed by the owner or operator. This would afford the Director the

opportunity to review the data and verify that the analysis is accurate. EPA also expects that the

details of what information must be submitted would be described in the testing and monitoring

procedures in the Class VI permit.

Commenter Name: Darrick Eugene Letter ID: 0223

Commenter Organization: Texas Carbon Capture and Storage Association Comment ID: 23990

Comment: EPA Proposed §146.90(f) A pressure fall-off test at least once every 

five years unless more frequent testing is required by the Director 

based on site specific information; 

The scope of this proposed requirement is not clear. Does the EPA proposal 

require the submittal of the actual data, or merely an analysis of the pressure 

fall-off test? 

Response: EPA expects that the Director would request an electronic copy of the data in addition to

an analysis report completed by the owner or operator. This would afford the Director the

opportunity to review the data and verify that the analysis is accurate. EPA also expects that the

details of what information must be submitted would be described in the testing and monitoring

procedures in the Class VI permit.

Commenter Name: Andrew Duguid Letter ID: 0226

Commenter Organization: Schlumberger Carbon Services Comment ID: 24062

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Proposed Rule: (f) A pressure fall-off test at least once every five years 

unless more frequent testing is required by the Director based on site specific 

information; 

Schlumberger Suggested Revision: (f) A pressure fall-off test or other 

equivalent test that identifies reservoir conditions with respect to flow 

dynamics at least once every five years unless more frequent testing is required 

by the Director based on site specific information; 
Schlumberger Rationale: Allows more flexibility while still providing the needed 

information 

Response: EPA believes that pressure fall-off testing is necessary for GS wells. Pressure fall-off

tests are designed to verify that modeled projections of reservoir pressure decline agree with

measured pressure decline profiles. These tests can be useful in AoR calculations and reevaluations

and may also indicate mischaracterization of site geology and the presence of leakage pathways.

EPA therefore believes that pressure fall-off testing is conducted at least once every five years and

the final GS regulation includes this requirement at §146.90(f). Pressure fall-off tests may be

conducted in conjunction with other well performance tests (i.e., mechanical integrity testing) to

ensure safe and effective operations.

Commenter Name: Neeraj Gupta Letter ID: 0229

Commenter Organization: Battelle Energy Technology (BET) Comment ID: 21858

Comment: Page 103, Pressure fall-off tests- In our experience, pressure fall-off tests 

offer more information in initial injection testing. After longer term 

injection, we’ve seen basically the same, muted response. In addition, the 

fall-off response tended to take much longer after sustained injection. A 

concern may be that you need to monitor pressure fall off for several weeks, 

months, or years after 5 years of continuous injection to obtain useful data. 

This would lead to the need for standby wells or emitting CO2 to the atmosphere 

during fall-off tests. We think these should be part of the initial testing 

sequence for new injection wells, but they might be a more optional rather than 

a mandatory part of testing. 

Response: EPA believes that a frequency of at least once every five years, as specified at §146.90(f),

is an appropriate interval for pressure fall-off testing (particularly given the suite of tests operators

will perform on the well and the site). EPA clarifies that the Director may require more frequent

pressure fall-off tests at a specific project, if necessary based on site-specific circumstances. Pressure

fall-off tests may be conducted in conjunction with other well performance tests (i.e., mechanical

integrity testing) to ensure safe and effective operations. All monitoring data collected, including

information from pressure fall-off tests, will be incorporated in AoR reevaluations, at least every

five years.

Commenter Name: Philip Papadeas Letter ID: 0238

Commenter Organization: Sandia Technologies, LLC Comment ID: 23356

Comment: §146.90 (f) 

Re: Pressure Falloff testing of at least once every 5 years. 

This is of concern, since annual pressure tests are required for Class I 

operators, then why is the EPA diluting this requirement. As a consultant, I 

believe that for the first 5 years of established operation on the well, it 

should be installed as an annual requirement for Pressure Falloff testing, and 

thereafter, the operator can request from the Agency for once per 5-years. The 

behavior of buoyant carbon dioxide suggests more testing and monitoring and not 

less than Class I wells which have more safeguards present during operations. 

Response: EPA believes that a frequency of at least once every five years, as specified at §146.90(f),

is an appropriate interval for pressure fall-off testing (particularly given the suite of tests operators
will perform on the well and the site). EPA clarifies that the Director may require more frequent

pressure fall-off tests at a specific project, if necessary based on site-specific circumstances. Pressure

fall-off tests may be conducted in conjunction with other well performance tests (i.e., mechanical

integrity testing) to ensure safe and effective operations. All monitoring data collected, including

information from pressure fall-off tests, will be incorporated in AoR reevaluations, at least every

five years.

Commenter Name: Mark Bohrer Letter ID: 0241

Commenter Organization: North Dakota Industrial Commission Comment ID: 23253

Comment: 31. EPA’s proposal would require that owners or operators perform a pressure 

fall-off test at least once every five years. EPA seeks comment on the use and 

frequency of pressure fall-off testing for GS wells. EPA Notice 43515. 

An initial pressure fall-off test could be required and subsequent tests 

required at the time the AOR is reevaluated. 

Response: EPA believes that a frequency of at least once every five years, as specified at §146.90(f),

is an appropriate interval for pressure fall-off testing (particularly given the suite of tests operators

will perform on the well and the site). EPA adds that this frequency is the same as that required for

AoR reevaluations. EPA clarifies that the Director may require more frequent pressure fall-off tests

at a specific project, if necessary based on site-specific circumstances. Pressure fall-off tests may be

conducted in conjunction with other well performance tests (i.e., mechanical integrity testing) to

ensure safe and effective operations. All monitoring data collected, including information from

pressure fall-off tests, will be incorporated in AoR reevaluations, at least every five years.

Letter ID: 0263

Commenter Organization: Interstate Oil & Gas Compact Commission Comment ID: 22817

Comment: III A. 6 Proposed Plume and Pressure Front Monitoring Requirements 

FF. EPA seeks comment on the use and frequency of pressure fall-off testing for GS 

wells. 

IOGCC Response: The IOGCC does not see the necessity of pressure fall off testing 

for GS wells. It should be used as necessary but not mandated. 

Response: EPA disagrees and believes that pressure fall-off testing is necessary for GS wells to

ensure the protection of USDWs. Pressure fall-off tests are designed to verify that modeled

projections of reservoir pressure decline agree with measured pressure decline profiles. These tests

can be useful in AoR calculations and reevaluations and may also indicate mischaracterization of

site geology and the presence of leakage pathways. EPA therefore believes that pressure fall-off

testing must be conducted at least once every five years, and the final GS regulation includes this

requirement at §146.90(f). Pressure fall-off tests may be conducted in conjunction with other well

performance tests (i.e., mechanical integrity testing) to ensure safe and effective operations.

Comment Code: 4650 2.6.5 CO2 plume and pressure front tracking (seeking comment) 
Individual Comments

Commenter Name: Leslie Savage Letter ID: 0122

Commenter Organization: Railroad Commission of Texas (RRC) Comment ID: 24796

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: (g) Testing and monitoring to track the extent of the carbon dioxide plume and 

the position of the pressure front by either monitoring for pressure changes 

in the first formation overlying the confining zone or using indirect, 

geophysical techniques (e.g., seismic, electrical, gravity, or electromagnetic 

surveys and/or down-hole CO2 detection tools); 

{If there are changes in the first formation overlying the confining 

zone, the carbon dioxide stream has not been confined.} 

Response: The final rule, at §146.90(g), requires owners or operators to perform monitoring to track

the extent of the CO2 plume and pressure front. The owner or operator must use direct methods to

monitor for pressure changes in the injection zone. Indirect methods (e.g., seismic, electrical, gravity,

or electromagnetic surveys and/or down-hole CO2 detection tools) are required unless the Director

determines, based on site-specific geology that such methods are not appropriate 

EPA believes that pressure monitoring in the injection zone is necessary to track the development

and movement of the pressure front and CO2 plume. When combined with information on

temperature, pressure data provide an indication of the phase (e.g., gas, supercritical) and distribution

of the injected CO2 (73 FR 43515). Monitoring can also identify needed remedial actions, provide

inputs for AoR reevaluation modeling, evaluate predictions of plume movement, and target

additional geochemical and surface monitoring needs. 

EPA adds that owners or operators may consider (or the Director may require) performing additional

pressure monitoring in wells that are above the confining zone (e.g., in the same wells used to

perform ground water quality monitoring required at §146.90(d)) to provide additional verification

that no pressure changes are occurring above the confining zone due to CO2 leakage. The final rule,

at §146.90(d), also requires geochemical monitoring above the confining zone.

Commenter Name: John Stormon Letter ID: 0123

Commenter Organization: Washington State Dept. of Ecology Comment ID: 23005

Other EPA Comment Codes and Descriptions: 4655 2.6.5.1 Plume tracking

techniques/geophysical methods (seeking comment) 

Comment: Monitoring: Direct monitoring of the formations immediately above the confining 

layer for a geologic sequestration injection zone is an important requirement 

for the early detection of unacceptable leakage. Monitoring wells installed into 

this monitoring zone will be quite expensive but should be required for all 

projects. Geophysical methods and other indirect monitoring, while useful, 

should not be allowed to substitute for all direct monitoring above the 

confining layer. 

Response: EPA disagrees that pressure monitoring above the confining zone is appropriate. Instead,

EPA believes that pressure monitoring in the injection zone is necessary to track the development

and movement of the pressure front and CO2 plume. The final rule (at §146.90(g)) requires owners
or operators to perform monitoring to track the extent of the CO2 plume and pressure front. The

owner or operator must use direct methods to monitor for pressure changes in the injection zone.

Indirect methods (e.g., seismic, electrical, gravity, or electromagnetic surveys and/or down-hole CO2

detection tools) are also required unless the Director determines, based on site-specific geology, that

such methods are not appropriate.

EPA believes that pressure monitoring within the injection zone is necessary because any such

monitoring above the confining zone would not detect movement of the pressure front unless a

breach of the confining zone occurs. EPA believes that monitoring using wells in the injection zone

(i.e., that penetrate the confining zone) can be safely performed if the wells are constructed to

prevent flow between the injection zone and USDWs or other layers above the confining zone. Such

construction technologies exist and have been used in the oil and gas industry for years. EPA

believes that the benefits of monitoring in the injection formation outweigh the manageable risk of

those monitoring wells serving as conduits for fluid movement. EPA adds that owners or operators

may consider performing additional pressure monitoring in wells that are above the confining zone

(e.g., in the same wells used to perform ground water quality monitoring required at §146.90(d)) to

provide additional verification that no pressure changes are occurring above the confining zone due

to CO2 leakage and that the Director has the authority to require such monitoring under §146.90(i).

Monitoring also identifies needed remedial actions, provides inputs for AoR reevaluation modeling,

and targets additional geochemical and surface monitoring needs. Knowledge of the location of the

CO2 plume and the associated pressure front will assure the public that GS projects are proceeding

according to plan, provide sufficient information to the owner or operator and Director, or allow for

appropriate actions to address any indication that USDWs may be endangered.

EPA also agrees that direct monitoring for ground water quality above the confining zone is

important, and the GS rule requires this at §146.90(d). Monitoring in additional formations, e.g., the

injection zone, may also be necessary, and if the Director believes such monitoring is warranted

he/she has the authority to require that it be included in the testing and monitoring plan.

Commenter Name: John Stormon Letter ID: 0123

Commenter Organization: Washington State Dept. of Ecology Comment ID: 23006

Comment: The number of wells drilled through the confining layer into the injection zone 

should be minimized. Each well represents a risk of establishing a pathway for 

the migration of CO2 or in-situ fluids into shallower aquifers. Projects may be 

able to get sufficient monitoring data from injection wells to minimize the need 

for stand-alone injection zone monitoring wells. 

Decisions on the level of direct and indirect monitoring should be made on a 

site by site basis, based upon the geologic characteristics, but some direct 

monitoring must be required above the confining layer to confirm that indirect 

monitoring is accurate. 

Response: As described above, EPA believes that direct pressure monitoring in the injection zone is

necessary to track the development and movement of the pressure front and CO2 plume. 

EPA believes that monitoring using wells in the injection zone (i.e., that penetrate the confining

zone) can be safely performed if the wells are constructed to prevent flow between the injection zone

and USDWs or other layers above the confining zone. Such construction technologies exist and have

been used in the oil and gas industry for years. EPA believes that the benefits of monitoring in the
injection formation outweigh the manageable risk of those monitoring wells serving as conduits for

fluid movement. EPA adds that owners or operators may consider performing additional pressure

monitoring in wells that are above the confining zone (e.g., in the same wells used to perform

ground water quality monitoring required at §146.90(d)) to provide additional verification that no

pressure changes are occurring above the confining zone due to CO2 leakage and that the Director

has the authority to require such monitoring at §146.90(i). EPA adds that the final rule also requires

geochemical monitoring above the confining zone, at §146.90(d).

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil gas and surface air monitoring which may be required by the UIC Director

for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm. EPA is also developing guidance,

available on the same website, on well construction that will include recommendations for

monitoring well construction. 

In addition, in January 2009, DOE published a best practices manual entitled "Monitoring,

Verification, and Accounting of CO2 Stored in Deep Geologic Formations" (DOE/NETL311/081508); this manual is included in the docket for the final GS rule.

Commenter Name: John Hanger Letter ID: 0130

Commenter Organization: Pennsylvania Dept. of Env. Protection Comment ID: 21511

Comment: -EPA should identify specific technologies or processes that will enable 

operators or owners to verify that the CO2 is moving the way in which the models 

indicated. 

Response: EPA does not believe that prescribing specific technologies to be used in all cases for GS

would be appropriate given the variability in sites. Rather, EPA is developing guidance on testing

and monitoring to assist owners or operators and Directors in evaluating requirements under

§146.90, including proposed monitoring plans. The guidance describes available technologies and

recommended approaches for implementing a testing and monitoring plan, including pre-operational

geophysical logging and testing of injection wells, MITs, injection well testing during operation,

groundwater quality monitoring, tracking the CO2 plume and pressure front, and soil gas and

surface air monitoring which may be required by the UIC Director for specific GS projects. The

guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm. In addition, in January 2009,

DOE published a best practices manual entitled "Monitoring, Verification, and Accounting of CO2

Stored in Deep Geologic Formations" (DOE/NETL-311/081508); this manual is included in the

docket for the final GS rule.

Commenter Name: Christine Reimer Letter ID: 0142

Commenter Organization: National Ground Water Association Comment ID: 22566

Comment: In the injection zone, monitoring must identify the location of the injected CO2 

and the associated pressure front. MMV in the monitoring zone should be geared 

to ensure that any vertical migration across the cap rock is identified. 
Monitoring of USDWs should be set up to look for changes that would be 

associated with the presence of CO2 or CO2-displaced brine. While some general 

monitoring points in all of these zones will be needed, it may be more practical 

to locate monitoring points or take measurements near locations identified 

during the characterization and potential fast-paths, such as abandoned wells, 

existing wells, or faults and fractures. One location that may provide the best 

use of monitoring resources is near the injection well. This is the most likely 

location for upward fluid movement without specific knowledge of a potential 

leakage pathway. Leakage could occur either through mechanical integrity failure 

or defects, or failure or defects of the confining units. Monitoring, in the 

monitoring zone and lowest USDW in addition to the injection zone, provides a 

vertical pressure profile, measures stress on the confining units, and may 

detect water quality changes. 

Response: EPA agrees that multi-faceted monitoring is appropriate at GS sites. The final rule, at

§146.90(g), requires owners or operators to perform monitoring to track the extent of the CO2 plume

and pressure front. The owner or operator must use direct methods to monitor for pressure changes

in the injection zone. Indirect methods (e.g., seismic, electrical, gravity, or electromagnetic surveys

and/or down-hole CO2 detection tools) are also required unless the Director determines, based on

site-specific geology, that such methods are not appropriate.

EPA believes that pressure monitoring in the injection zone is necessary to track the development

and movement of the pressure front and CO2 plume. Monitoring can also identify needed remedial

actions, provide inputs for AoR reevaluation modeling, evaluate predictions of plume movement,

and target additional geochemical and surface monitoring needs. Knowledge of the location of the

CO2 plume and the associated pressure front will also assure the public that GS projects are

proceeding according to plan, provide sufficient information to the owner or operator and Director,

or allow for appropriate actions to address any indication that USDWs may be endangered. 

EPA also believes that direct monitoring for ground water quality above the confining zone is

important, and the GS rule requires this at §146.90(d). Monitoring in additional formations, e.g., the

injection zone, may also be necessary, and if the Director believes such monitoring is warranted

he/she has the authority to require that it be included in the testing and monitoring plan.

EPA believes that monitoring plans and methods need to be site-specific and believes that the

monitoring requirements for GS sites at §146.90 provide an appropriate level of flexibility in

structuring a testing and monitoring plan that protects USDWs from endangerment. 

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil gas and surface air monitoring which may be required by the UIC Director

for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Christine Reimer Letter ID: 0142

Commenter Organization: National Ground Water Association Comment ID: 22571
Other EPA Comment Codes and Descriptions: 3530 2.2.3.1 AoR reevaluation frequency (seeking

comment) 

Comment: MMV should be conducted hand-in-hand with modeling over the entire period that 

MMV is occurring, with each new round of measurements being incorporated into a 

new iteration of the appropriate site models. An iterative measurement-modeling 

approach will allow for the best understanding of the shape and size of the AoR. 

It will also help identify areas of uncertainty in the model that may be reduced 

with changes in the MMV plan. Changes identified in the size of the AoR and for 

risk of leakage will help ensure that MMV is carried out at the right frequency 

and in the right locations. The timing of the MMV operations should be flexible 

and adjustable based on the performance of the site and the site models. It is 

likely that the site data from early in the operation will probably be more 

valuable than data from later in the operation for assessing the performance of 

the site and identifying and reducing uncertainties. MMV operations that are 

not continuous should be conducted more frequently at the start of the 

operational phase and then be allowed to become less frequent if the site is 

performing safely and in concert with the model predictions. The initial, more 

frequent monitoring should be specified in the permit as an experimental phase 

of the injection project. The continuation of injection should be contingent 

upon successful containment of the injected CO2 during the experimental phase. 

Response: EPA agrees with commenters on the importance of monitoring at GS sites and

emphasizes that monitoring of injection activities will be an important component of every GS

project. Monitoring associated with injection wells and the movement of the CO2 plume is necessary

to verify that the injectate is confined in the target formations and does not endanger USDWs. 

EPA agrees that monitoring data should be used to review model assumptions, verify computational

model projections, and, when necessary, provide input for model refinements. As data are collected

at an injection site, model parameters can be adjusted to match observations (i.e., for model

calibration), which in turn improves the predictive capability of the model. As a GS project proceeds,

both monitoring and modeling will evolve, with monitoring results supporting effective AoR

reevaluations and leading to improved model predictions.

As described above, EPA does not agree that each GS site should have to be permitted as a Class V

experimental technology well before being authorized to operate as a full-scale Class VI well. EPA

does not consider it appropriate to permit CO2 injection wells that are testing the injectivity or

appropriateness of an individual formation (e.g., as a prelude to a commercial-scale operation) as

Class V experimental technology wells. Such wells should be permitted as Class VI wells. 

EPA clarifies that some monitoring frequencies are specified in §146.90; others will be established

in the monitoring and testing plan submitted with the permit application under §146.90. The Director

may require changes in the frequencies when the plan is updated, as is required at least every 5 years

(or when there are changes to the facility or at the request of the Director).

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil gas and surface air monitoring which may be required by the UIC Director
for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Christine Reimer Letter ID: 0142

Commenter Organization: National Ground Water Association Comment ID: 22572

Other EPA Comment Codes and Descriptions: 5460 2.9.2 Comments on transfer of liability for

long-term care 

Comment: As the pressure in the injection zone starts to stabilize it may be possible to 

lengthen the period between measurements if the reservoir is performing as 

expected based on the calibrated site models. When the location of the CO2 

either stops changing or can be predicted and validated against measurements 

over multiple measurement cycles, the ownership of the site and the 

responsibility for future MMV, if deemed necessary, may be transferred from the 

operator to the government, starting the post-closure phase. If the site is not 

behaving as expected, an iterative MMV-modeling approach will help identify 

areas of uncertainty that can be reduced by changes in the MMV plan to collect 

more or different data to determine the site’s performance. 

Regulations for the operational phase need to ensure that a licensed Carbon 

Capture and Storage (CCS) site is operated safely and should allow for 

flexibility in the monitoring schedule based on the performance of the site and 

site models. A site that is performing well probably requires less frequent 

monitoring than one that is not performing well. A long-term match between MMV 

data and site modeling results probably indicates a good understanding of the 

site and should be one of the criteria used to decide when the custodianship of 

the site should be transferred from the operator to the government. It is 

possible that iterative MMV and modeling will show that the AoR changes over 

time. The idea of a variable AoR should be included and accepted in any 

regulations. The results of the MMV and modeling including the integrity of the 

Response: EPA clarifies that once injection is complete, the owner or operator must monitor as

specified in the post-injection site care and site closure plan for at least 50 years (the Director may

require longer if necessary to ensure USDW protection) or for the duration of the alternative

timeframe approved by the Director pursuant to the requirements at §146.93(b), unless the owner or

operator can make a demonstration earlier that the geologic sequestration project no longer poses a

risk of endangerment to USDWs. 

As described above, EPA agrees that monitoring data should be used to review model assumptions,

verify computational model projections, and, when necessary, provide input for model refinements.

As data are collected at an injection site, model parameters can be adjusted to match observations

(i.e., for model calibration or), which in turn improves the predictive capability of the model. As a

GS project proceeds, both monitoring and modeling will evolve, with monitoring results supporting

effective AoR reevaluations and leading to improved model predictions.

EPA agrees with commenters and believes that flexibility is important in developing and

implementing a monitoring plan that is appropriately tailored for a specific GS site. The purpose of

the requirement at §146.90 to develop site-specific testing and monitoring plans is to ensure that the

monitoring performed at a site is appropriate for site operational conditions and the geologic setting. 
Regarding transfer of responsibility following site closure, please note that EPA does not have

authority to transfer SDWA or other legal liability for Class VI wells to the State or federal

government or a third-party fund. Under the final GS rule, once an owner or operator has met all

regulatory requirements under Part 146 for Class VI wells and the Director has approved site closure

pursuant to requirements at §146.93, the owner or operator will generally no longer be subject to

enforcement for regulatory noncompliance. Furthermore, the financial instrument required under

§146.85 will be released if it was not used. However, even if a site closure is approved under

§146.93, an owner or operator may be held liable for regulatory noncompliance (including violation

of 40 CFR 144.12) in certain circumstances. For example, an owner or operator may be held liable

for regulatory noncompliance even after site closure was approved if the Director relied on erroneous

information (e.g., erroneous modeling data) provided by the owner or operator when approving site

closure. 

Separate from EPA’s authority to enforce regulatory compliance, an owner or operator may be

subject to a §1431 response order even after proper site closure is approved under §146.93. Under

§1431 the Administrator may require an owner or operator to take necessary response measures if he

or she receives information that a contaminant is present or is likely to enter a public water system

or an USDW, which may present an imminent and substantial endangerment to the health of

persons, and the appropriate State and local authorities have not acted to protect the health of such

persons. The action may include issuing administrative orders or commencing a civil action for

appropriate relief against the owner or operator of a Class VI well. If the owner or operator fails to

comply with the order, they may be subject to a civil penalty for each day in which such violation

occurs or failure to comply continues. 

Furthermore, after site closure an owner or operator may remain liable under tort and other remedies,

or under other federal statutes including, but not limited to, Clean Air Act, 42 U.S.C. §§ 7401-7671;

CERCLA, 42 U.S.C. § 9601-9675; and RCRA, 42 U.S.C. § 6901-6992. See the final rule preamble

for further discussion of EPA's final approach.

Commenter Name: James Dooley Letter ID: 0156

Commenter Organization: Joint Global Change Research Institute, Pacific

Northwest National Laboratory

Comment ID:

22668

Comment: o What if any are the construction requirements and mechanical integrity 

requirements for monitoring wells? 

Response: Construction specifications for monitoring wells must be described in the testing and

monitoring plan submitted with the permit application. EPA is developing guidance on well

construction that will include recommendations for monitoring well construction. The guidance will

be available on EPA’s website at http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

EPA is also developing guidance on testing and monitoring to assist owners or operators and

Directors in evaluating requirements under §146.90, including proposed monitoring plans. The

guidance describes available technologies and recommended approaches for implementing a testing

and monitoring plan, including pre-operational geophysical logging and testing of injection wells,

MITs, injection well testing during operation, groundwater quality monitoring, tracking the CO2

plume and pressure front, and soil gas and surface air monitoring which may be required by the UIC

Director for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm. In addition, in January 2009,

DOE published a best practices manual entitled "Monitoring, Verification, and Accounting of CO2

Stored in Deep Geologic Formations" (DOE/NETL-311/081508); this manual is included in the
docket for the final GS rule.

Commenter Name: James Childress Letter ID: 0158

Commenter Organization: Gasification Technologies Council (GTC) Comment ID: 23775

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: §146.90 Testing and monitoring requirements. (g) "Testing and monitoring to 

track the extent of the carbon dioxide plume and the position of the pressure 

front by either monitoring for pressure changes in the first formation overlying 

the confining zone or using indirect, geophysical techniques (e.g., seismic, 

electrical, gravity, or electromagnetic surveys and/or down-hole carbon dioxide 

detection tools); - 

We recommend deletion of this requirement in its entirety and replacing with 

"Testing and monitoring to track the extent of the carbon dioxide plume." 

Tracking the precise position of a moving pressure front will require a large 

number of expensive and deeply located probes. A limited number of pressure 

monitors that can provide information on pressures affecting the confinement 

layers are more valuable. The Proposed Rule also requires well owners to monitor 

periodically groundwater quality and geochemical changes above the confining 

zone. The requirements for such deep monitor wells could be costly. Requiring 

both pressure and geochemical monitoring will be costly and provide questionable 

additional information or warning. 

Response: EPA maintains that plume tracking and pressure monitoring are key components of

monitoring at GS sites. A rigorous plume tracking and pressure monitoring scheme, such as one that

meets the requirements at §146.90(g), is imperative for ensuring that the CO2 plume is contained

within the injection zone. 

The final rule (at §146.90(g)) requires owners or operators to perform monitoring to track the extent

of the CO2 plume and pressure front. The owner or operator must use direct methods to monitor for

pressure changes in the injection zone. Indirect methods (e.g., seismic, electrical, gravity, or

electromagnetic surveys and/or down-hole CO2 detection tools) are also required unless the Director

determines, based on site-specific geology, that such methods are not appropriate 

Pressure monitoring in the injection zone is necessary to track the development and movement of the

pressure front and CO2 plume. When combined with information on temperature, pressure data

provide an indication of the phase (e.g., gas, supercritical) and distribution of the injected CO2 (73

FR 43515). Monitoring can also identify needed remedial actions, provide inputs for AoR

reevaluation modeling, evaluate predictions of plume movement, and target additional geochemical

and surface monitoring needs.

EPA recognizes that installation of monitoring wells entails additional resources. However, the

Agency believes that such monitoring is necessary to ensure that GS projects are appropriately

operated and monitored and to protect USDWs from endangerment. EPA believes that pressure

monitoring in the injection zone is necessary to track the development and movement of the pressure

front and CO2 plume. Monitoring can also identify needed remedial actions, provide inputs for AoR

reevaluation modeling, evaluate predictions of plume movement, and target additional geochemical

and surface monitoring needs. Knowledge of the location of the CO2 plume and the associated
pressure front will assure the public that GS projects are proceeding according to plan, provide

sufficient information to the owner or operator and Director, or allow for appropriate actions to

address any indication that USDWs may be endangered.

The combination of site characterization and predictive modeling will help guide the siting of

monitoring wells and enable operators to optimize the number and position of wells. The Directorapproved testing and monitoring plan will describe the use and installation of monitoring wells at the

site.

EPA acknowledges the commenters' concern about the cost of pressure monitoring. However, EPA

believes that this monitoring is essential for protection of USDWs at GS sites Although a significant

cost in absolute terms, monitoring costs are expected to be a small fraction of site operating costs,

according to EPA's cost analysis for the GS rulemaking (which is available in the docket).

Commenter Name: Michael Mudd Letter ID: 0167

Commenter Organization: FutureGen Alliance (FGIA) Comment ID: 22472

Comment: A-6 Proposed Plume and pressure Front Monitoring III-A-6 Page 102. Pressure 

gauges placed in the first formation overlying the confining zone would not be 

useful for tracking the lateral migration of the CO2 plume or pressure front. 

Would EPA require monitoring wells that penetrate through the confining zone 

and into the storage formation for this purpose? 

Fiber optic pressure and temperature sensors are likely to be prohibitively 

expensive. 

Response: EPA has revised this requirement in the final rule. Instead, the final GS regulation, at

§146.90(g)(1), requires all GS project owners or operators to monitor for pressure changes in the

injection zone. EPA believes that pressure monitoring in the injection zone is necessary to track the

development and movement of the pressure front and CO2 plume. 

Pressure monitoring within the injection zone is necessary because any such monitoring above the

confining zone would not detect movement of the pressure front unless a breach of the confining

zone occurs. EPA believes that monitoring using wells in the injection zone (i.e., that penetrate the

confining zone) can be safely performed if the wells are constructed to prevent flow between the

injection zone and USDWs or other layers above the confining zone. Such construction technologies

exist and have been used in the oil and gas industry for years. EPA believes that the benefits of

monitoring in the injection formation outweigh the manageable risk of those monitoring wells

serving as conduits for fluid movement. EPA adds that owners or operators may consider performing

additional pressure monitoring in wells that are above the confining zone (e.g., in the same wells

used to perform ground water quality monitoring required at §146.90(d)) to provide additional

verification that no pressure changes are occurring above the confining zone due to CO2 leakage.

Monitoring also identifies needed remedial actions, provides inputs for AoR reevaluation modeling,

and targets additional geochemical and surface monitoring needs. Knowledge of the location of the

CO2 plume and the associated pressure front will assure the public that GS projects are proceeding

according to plan, provide sufficient information to the owner or operator and Director, or allow for

appropriate actions to address any indication that USDWs may be endangered.

EPA acknowledges that, at certain sites, there may be a need for additional or different monitoring

schemes (which may include monitoring in the confining zone), and adds that it is important to
balance the need for adequate monitoring that ensures USDW protection from endangerment against

too many artificial penetrations which could serve as conduits for fluid migration. EPA expects sitespecific testing and monitoring plans to describe the proposed monitoring regime, which must be

approved by the Director.

EPA does not believe that prescribing specific technologies to be used in all cases for GS would be

appropriate given the variability in sites. Rather, EPA is developing guidance on testing and

monitoring to assist owners or operators and Directors in evaluating requirements under §146.90,

including proposed monitoring plans. The guidance describes available technologies and

recommended approaches for implementing a testing and monitoring plan, including pre-operational

geophysical logging and testing of injection wells, MITs, injection well testing during operation,

groundwater quality monitoring, tracking the CO2 plume and pressure front, and soil gas and

surface air monitoring which may be required by the UIC Director for specific GS projects. The

guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm. In addition, in January 2009,

DOE published a best practices manual entitled "Monitoring, Verification, and Accounting of CO2

Stored in Deep Geologic Formations" (DOE/NETL-311/081508); this manual is included in the

docket for the for the final GS rule. 

EPA acknowledges the commenters' concern about the cost of monitoring. However, EPA believes

that monitoring is essential for protection of USDWs at GS sites. Although a significant cost in

absolute terms, monitoring costs are expected to be a small fraction of site operating costs, according

to EPA's cost analysis for the GS rulemaking (which is available in the docket).

Commenter Name: Michael J. Miller Letter ID: 0168

Commenter Organization: Electric Power Research Institute (EPRI) Comment ID: 22492

Other EPA Comment Codes and Descriptions: 3300 2.2.1 Delineating the AoR/Modeling CO2

movement 

Comment: Preamble, page 43505: "The confining system should be of sufficient regional 

thickness and lateral extent to contain the entire CO2 plume and associated 

pressure front under the confining system following the plume’s maximum lateral 

expansion." 

EPRI COMMENT #2: The criteria for defining the leading edge of the plume and 

associated pressure front are not specified in the rule, nor is the basis for 

determining if these criteria are met -- physical measurement or numerical 

computation. In either case, what minimum change in pressure from background 

will EPA use to define the location of the pressure front? Will the lateral 

extent of the CO2 plume be defined by the leading edge of the dissolved plume or 

free-phase portion of the plume? Given the difficulties in defining and 

measuring the leading edge of the plume and pressure front, EPRI believes that 

the technical focus should be on demonstrating caprock containment, rather than 

tracking fronts. 

Response: EPA agrees that demonstrating cap rock containment is an important technical focal point

for permitting Class VI wells, however the Agency also believes that it is important to know the

extent of the CO2 plume and pressure front to ensure cap rock integrity and protection of USDWs. 

EPA clarifies that the pressure front (defined at §146.81) is the zone of elevated pressure that is
created by the injection of CO2 into the subsurface. The pressure front of a CO2 plume refers to a

zone where there is a pressure differential sufficient to cause the movement of injected fluids or

formation fluids into a USDW. The pressure front includes all areas wherein pressure is great

enough to cause fluid movement into a USDW if a conduit were to exist.

The calculation of the threshold pressure that defines the edge of the pressure front is dependent on

properties of the injection and confining zones, including permeability, porosity, and compressibility,

the distance between the injection zone and the lowermost USDW, and operational conditions

including injection pressure and rate. For these reasons, the definition of the pressure front is siteand project-specific, and a single pressure value can not be provided for all sites. EPA is developing

guidance on AoR and corrective action at GS Class VI sites to assist owners or operators and

Directors in evaluating requirements and proposed AoR and corrective action plans under 146.84.

The guidance describes EPA's recommended approaches for the data to be considered in an initial

AoR delineation, how to apply computational modeling to delineate the AoR, performing corrective

action at GS sites, and, when appropriate, completing AoR reevaluations. The guidance will be

available on EPA's web site, at http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

EPA is also developing guidance on testing and monitoring to assist owners or operators and

Directors in evaluating requirements under §146.90, which will include discussion of identifying the

extent of the CO2 plume. The guidance describes available technologies and recommended

approaches for implementing a testing and monitoring plan, including pre-operational geophysical

logging and testing of injection wells, MITs, injection well testing during operation, groundwater

quality monitoring, tracking the CO2 plume and pressure front, and soil gas and surface air

monitoring which may be required by the UIC Director for specific GS projects. The guidance can

be found on EPA’s website at http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm. In

addition, in January 2009, DOE published a best practices manual entitled "Monitoring, Verification,

and Accounting of CO2 Stored in Deep Geologic Formations" (DOE/NETL-311/081508); this

manual is included in the docket for the for the final GS rule.

Commenter Name: Theresa Pugh Letter ID: 0169

Commenter Organization: American Public Power Association Comment ID: 23423

Comment: Plume and pressure front monitoring- Because of APPA’s inextricable link to the 

municipal water utilities, we fully appreciate the importance of accurate 

monitoring of the plume and pressure front. Id. at 43514. APPA defers to AWWA to 

comment on monitoring and frequency of monitoring requirements. APPA believes 

that most early projects will likely monitor far more often than will be 

unnecessary as more information is gained regarding the accuracy of initial 

modeling. 

Response: EPA agrees with commenters on the importance of monitoring at GS sites and

emphasizes that monitoring of injection activities will be an important component of every GS

project. Monitoring associated with injection wells and the movement of the CO2 plume is necessary

to verify that the injectate is confined in the target formations and does not endanger USDWs. 

EPA believes that monitoring data should be used to review model assumptions, verify

computational model projections, and, when necessary, provide input for model refinements. As data

are collected at an injection site, model parameters can be adjusted to match observations (i.e., for

model calibration or), which in turn improves the predictive capability of the model. As a GS project

proceeds, both monitoring and modeling will evolve, with monitoring results supporting effective
AoR reevaluations and leading to improved model predictions and changes to an owner and

operators testing and monitoring plan.

Commenter Name: Kyle Isakower Letter ID: 0170

Commenter Organization: American Petroleum Institute Comment ID: 24194

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Rule Provision: 149.90(g) 

API Comments: (g) Testing and monitoring AS APPROPRIATE TO SUPPORT THE MODEL FOR

to trackING the extent of the carbon dioxide plume and the position of the 

pressure front. by either monitoring for pressure changes in the first 

formation overlying the confining zone or using indirect, geophysical techniques 

(e.g., seismic, electrical, gravity, or electromagnetic surveys and/or down-hole 

carbon dioxide detection tools);

Rationale: Monitoring outside of the injection zone provides little information 

of value for tracking and monitoring the injected plume. Examples of how to test 

and monitor could be included in the Preamble but need not be included in the 

rule itself. 

Response: EPA has revised this requirement in the final rule. The final GS regulation, at

§146.90(g)(1), requires all GS project owners or operators to monitor for pressure changes in the

injection zone. EPA believes that pressure monitoring in the injection zone is necessary to track the

development and movement of the pressure front and CO2 plume. 

Pressure monitoring within the injection zone is necessary because any such monitoring above the

confining zone would not detect movement of the pressure front unless a breach of the confining

zone occurs. EPA believes that monitoring using wells in the injection zone (i.e., that penetrate the

confining zone) can be safely performed if the wells are constructed to prevent flow between the

injection zone and USDWs or other layers above the confining zone. Such construction technologies

exist and have been used in the oil and gas industry for years. EPA believes that the benefits of

monitoring in the injection formation outweigh the manageable risk of those monitoring wells

serving as conduits for fluid movement. EPA adds that owners or operators may consider performing

additional pressure monitoring in wells that are above the confining zone (e.g., in the same wells

used to perform ground water quality monitoring required at §146.90(d)) to provide additional

verification that no pressure changes are occurring above the confining zone due to CO2 leakage.

Monitoring also identifies needed remedial actions, provides inputs for AoR reevaluation modeling,

and targets additional geochemical and surface monitoring needs. Knowledge of the location of the

CO2 plume and the associated pressure front will assure the public that GS projects are proceeding

according to plan, provide sufficient information to the owner or operator and Director, or allow for

appropriate actions to address any indication that USDWs may be endangered.

EPA acknowledges that, at certain sites, there may be a need for more or different monitoring

schemes (which may include monitoring in the confining zone), and adds that it is important to

balance the need for adequate monitoring that ensures USDW protection from endangerment against

too many artificial penetrations which could serve as conduits for fluid migration. EPA expects sitespecific testing and monitoring plans to describe the proposed monitoring regime, which must be
approved by the Director.

Flexibility is also provided regarding how to monitor for the specific data required by the final rule.

The testing and monitoring plan is developed by the owner or operator in consultation with the

Director and is designed to ensure that a detailed, Director-approved document describing how

monitoring will be conducted during the lifetime of the project exists. 

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil gas and surface air monitoring which may be required by the UIC Director

for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Kyle Isakower Letter ID: 0170

Commenter Organization: American Petroleum Institute Comment ID: 24247

Comment: Rule Provisions: 146.90 

EPA Preamble Question: 30. EPA seeks comment on the requirement for monitoring 

of GS sites for the purpose of tracking the location of the CO2 plume and 

associated pressure front over time. EPA Notice 43514 

API Response: The frequency of monitoring should be dictated by site-specific 

operational and geologic conditions combined with the results of monitoring with 

model predictions. The guiding principle for monitoring is to verify proper 

confinement of the CO2 and ensure protection of USDWs. EPA should recognize that 

use of modeling and other monitoring techniques are relatively qualitative 

processes that can have varying degrees of accuracy that will improve over time 

in an iterative process. 

Response: The GS rule stipulates that the monitoring frequency and spatial distribution of

monitoring wells must be based on baseline geochemical data that were collected during the initial

site characterization and the area of review evaluation (§146.90(d)(2)). The details of the

geochemical monitoring will be based on site-specific information and described in the Directorapproved testing and monitoring plan.

EPA adds that the iterative process of monitoring, modeling, and AoR reevaluation is appropriate to

verify that the CO2 plume and pressure front are moving through the subsurface as predicted, verify

the accuracy of the delineation model (or identify needed changes), and refine testing and monitoring

activities to ensure that USDWs are protected from endangerment and that there would be adequate

warning of potential problems at the site before any endangerment could occur.

Commenter Name: Kyle Isakower Letter ID: 0170

Commenter Organization: American Petroleum Institute Comment ID: 24249

Other EPA Comment Codes and Descriptions: 4655 2.6.5.1 Plume tracking

techniques/geophysical methods (seeking comment) 

Comment: Rule Provisions: 146.90(g) 

EPA Preamble Question: 32. Based on information evaluated to date, EPA believes 
that tracking the plume and pressure front is an important companion step to 

address any uncertainties associated with initial AoR modeling and requests 

comment on this approach and more efficient alternatives that may be used to 

track the plume and pressure front. EPA Notice 43516. 

API Response: Based on experience to date, CO2 plume can be monitored using 

surface or wellbore seismic and possibly some remote satellite techniques. 

Monitoring of the pressure front will be more difficult since that requires data 

from the injection formation that can only be obtained by drilling a well (which 

introduces additional artificial penetrations into the containment system). 

Modeling can estimate the movement of a pressure front. Those estimations are 

limited by the accuracy of the model and its iterative adjustments as previously 

mentioned. 

EPA should note that plume and pressure front are different concepts and should 

not be confused. They yield information on two different metrics. One tells you 

about the remaining capacity of the storage formation and the other describes 

the direction and movement of the CO2 plume. 

Response: EPA believes that direct pressure measurements are appropriate and that direct pressure

monitoring will be feasible at all GS sites. The final rule (at §146.90(g)) requires owners or operators

to perform monitoring to track the extent of the CO2 plume and pressure front. The owner or

operator must use direct methods to monitor for pressure changes in the injection zone. Indirect

methods (e.g., seismic, electrical, gravity, or electromagnetic surveys and/or down-hole CO2

detection tools) are also required unless the Director determines, based on site-specific geology, that

such methods are not appropriate. 

EPA believes that pressure monitoring in the injection zone is necessary to track the development

and movement of the pressure front and CO2 plume. Monitoring can also identify needed remedial

actions, provide inputs for AoR reevaluation modeling, evaluate predictions of plume movement,

and target additional geochemical and surface monitoring needs. Knowledge of the location of the

CO2 plume and the associated pressure front will assure the public that GS projects are proceeding

according to plan, provide sufficient information to the owner or operator and Director, or allow for

appropriate actions to address any indication that USDWs may be endangered.

EPA agrees that geophysical (e.g., seismic) methods are useful for plume tracking at GS sites.

Remote sensing methods (e.g., PSInSAR) may also prove to be useful. Such methods may be an

important component of plume tracking at some GS sites. For this reason, the final rule (at

§146.90(g)) requires the use of indirect methods (e.g., seismic, electrical, gravity, or electromagnetic

surveys and/or down-hole CO2 detection tools) unless the Director determines, based on site-specific

geology, that such methods are not appropriate.

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, which will include discussion of identifying the extent of the

CO2 plume and pressure front. The guidance describes available technologies and recommended

approaches for implementing a testing and monitoring plan, including pre-operational geophysical

logging and testing of injection wells, MITs, injection well testing during operation, groundwater

quality monitoring, tracking the CO2 plume and pressure front, and soil gas and surface air

monitoring which may be required by the UIC Director for specific GS projects. The guidance can

be found on EPA’s website at http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm. In
addition, in January 2009, DOE published a best practices manual entitled "Monitoring, Verification,

and Accounting of CO2 Stored in Deep Geologic Formations" (DOE/NETL-311/081508); this

manual is included in the docket for the for the final GS rule.

Commenter Name: Robert J. Finley Letter ID: 0180

Commenter Organization: Illinois State Geological Survey Comment ID: 23640

Comment: 146.90 

(g) 

Tracking of the pressure front needs to be further considered. What tools are 

suggested for tracking a pressure front in a saline reservoir other than direct 

measurement at a wellbore? Should the primary seal over a saline reservoir be 

further penetrated by wellbores just to obtain these data? What detection limits 

apply to the leading edge of a pressure gradient that are acceptable for 

monitoring? None of the indirect geophysical techniques listed are sensitive to 

in-zone pressure changes in a single phase reservoir. 

The monitoring option suggested in this section is a questionable option. If the 

confining zone is maintaining the desired integrity, then monitoring in the 

first formation overlying the confining zone should not show any pressure 

changes and hence will not inform as to the position of the pressure front or 

the CO2 plume (via sampling). Only if the confining zone fails will this be 

viable. Further, the "first formation" overlying the confining zone may not be 

suitable for any monitoring if it has little or no effective porosity and 

suitable permeability. The implication is that you are proposing monitoring in a 

suitable (permeable) rock interval above the confining zone, but that may not be 

in the first stratigraphically defined formation. 

Are there stress or tilt sensors that be installed in a wellbore or at the 

surface that can indirectly detect a pressure front in the receiving reservoir? 

What is their resolution and how does that apply in a regulatory context? 

Surface tiltmeters are do not work in all situations, dependent on bedrock 

rigidity and surface soil conditions/thickness. 

Also, what is the definition of the CO2 plume boundary? Is it a given saturation 

over a given thickness? Is it any detectable amplitude brightening on a 

reflection seismic image or other geophysical indication? 

Response: EPA has revised the pressure monitoring requirement for the final rule. EPA believes that

direct pressure measurements are appropriate and that direct pressure monitoring will be feasible at

all GS sites. The final rule (at §146.90(g)) requires owners or operators to perform monitoring to

track the extent of the CO2 plume and pressure front. The owner or operator must use direct

methods to monitor for pressure changes in the injection zone. Indirect methods (e.g., seismic,

electrical, gravity, or electromagnetic surveys and/or down-hole CO2 detection tools) are also

required unless the Director determines, based on site-specific geology, that such methods are not

appropriate. 

EPA believes that pressure monitoring in the injection zone is necessary to track the development
and movement of the pressure front and CO2 plume. Monitoring can also identify needed remedial

actions, provide inputs for AoR reevaluation modeling, evaluate predictions of plume movement,

and target additional geochemical and surface monitoring needs. Knowledge of the location of the

CO2 plume and the associated pressure front will assure the public that GS projects are proceeding

according to plan, provide sufficient information to the owner or operator and Director, or allow for

appropriate actions to address any indication that USDWs may be endangered.

EPA believes that geophysical (e.g., seismic) methods are useful for plume tracking at GS sites.

Remote sensing methods and tiltmeters may also prove to be useful, but are not specified in the final

regulation. Such methods may be an important component of plume tracking at some GS sites. For

this reason, the final rule at §146.90(g) requires the use of indirect methods (e.g., seismic, electrical,

gravity, or electromagnetic surveys and/or down-hole CO2 detection tools) unless the Director

determines, based on site-specific geology that such methods are not appropriate.

In response to comments regarding the pressure front at GS sites, EPA clarifies that the pressure

front (defined at §146.81) is the zone of elevated pressure that is created by the injection of CO2 into

the subsurface. The pressure front of a CO2 plume refers to a zone where there is a pressure

differential sufficient to cause the movement of injected fluids or formation fluids into a USDW.

The pressure front includes all areas wherein pressure is great enough to cause fluid movement into a

USDW if a conduit were to exist. The calculation of the threshold pressure that defines the edge of

the pressure front is dependent on properties of the injection and confining zones, including

permeability, porosity, and compressibility, the distance between the injection zone and the

lowermost USDW, and operational conditions including injection pressure and rate. For these

reasons, the definition of the pressure front is site- and project-specific, and a single pressure value

can not be provided for all sites.

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, which will include discussion of identifying the extent of the

CO2 plume and pressure front and the use of tiltmeters. The guidance describes available

technologies and recommended approaches for implementing a testing and monitoring plan,

including pre-operational geophysical logging and testing of injection wells, MITs, injection well

testing during operation, groundwater quality monitoring, tracking the CO2 plume and pressure

front, and soil gas and surface air monitoring which may be required by the UIC Director for

specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm. In addition, in January 2009,

DOE published a best practices manual entitled "Monitoring, Verification, and Accounting of CO2

Stored in Deep Geologic Formations" (DOE/NETL-311/081508); this manual is included in the

docket for the for the final GS rule.

Commenter Name: Bradley J. Field Letter ID: 0186

Commenter Organization: New York State Dept. of Environmental Conservation

Div. of Mineral Resources

Comment ID:

25201

Comment: CC. EPA seeks comment on the requirement for monitoring of GS sites for the 

purpose of tracking the location of the CO2 plume and associated pressure front 

over time. 

NYSDEC-DMN Response: NYSDEC-DMN is in favor of the EPA requiring an operator to 

conduct ongoing and sufficient monitoring to allow the tracking the CO2 plume 

and associated pressure front. In addition to any regular reporting frequency, 
an operator should be required to provide notification whenever actual 

conditions vary significantly from modeled predictions. 

Response: EPA agrees with commenters on the importance of monitoring at GS sites and

emphasizes that monitoring of injection activities will be an important component of every GS

project. Monitoring associated with injection wells and the movement of the CO2 plume is necessary

to verify that the injectate is confined in the target formations and does not endanger USDWs. 

EPA notes that the results of monitoring to track the plume and pressure front are to be incorporated

into the reevaluation of the AoR, which must be conducted at least once every 5 years under

§146.84(e). EPA expects the monitoring results to be used to refine the AoR model.

Commenter Name: Robert F. Van Voorhees Letter ID: 0190

Commenter Organization: Carbon Sequestration Council Comment ID: 24355

Comment: 1. Monitoring CO2 Movement and Reservoir Pressure 

The preamble to the proposed rule specifically states that the "[m]onitoring of 

subsurface geochemistry and the position of the CO2 plume and pressure front are 

necessary to verify predictions of plume movement, provide inputs for modeling, 

identify needed corrective actions, and target geochemical and surface 

monitoring activities." 73 Fed. Reg. at 43514. Again, this is inconsistent with 

experience with Class I hazardous waste injection, where such monitoring has not 

been necessary and is not required. 

Response: EPA disagrees that plume and pressure front monitoring are not justified for Class VI

wells. The Agency recognizes that while there are similarities between injection of wastes for

disposal (Class I) and GS (Class VI), there are significant differences as well. Important unique

considerations for GS include the buoyancy of CO2, its corrosivity when in contact with water, its

low viscosity (i.e., high mobility), and the very large injection volumes that are anticipated. There is

also a degree of uncertainty regarding the behavior of large volumes of CO2 in the subsurface after

injection. Given these characteristics of anticipated GS projects, EPA believes that plume and

pressure front monitoring at §146.90(g) are justified to provide early warning of any unforeseen

fluid movement that might endanger USDWs. 

The final rule (at §146.90(g)) requires owners or operators to perform monitoring to track the extent

of the CO2 plume and pressure front. The owner or operator must use direct methods to monitor for

pressure changes in the injection zone. Indirect methods (e.g., seismic, electrical, gravity, or

electromagnetic surveys and/or down-hole CO2 detection tools) are also required unless the Director

determines, based on site-specific geology, that such methods are not appropriate.

EPA believes that pressure monitoring in the injection zone is necessary to track the development

and movement of the pressure front and CO2 plume. Monitoring can also identify needed remedial

actions, provide inputs for AoR reevaluation modeling, evaluate predictions of plume movement,

and target additional geochemical and surface monitoring needs. Knowledge of the location of the

CO2 plume and the associated pressure front will also assure the public that GS projects are

proceeding according to plan, provide sufficient information to the owner or operator and Director,

or allow for appropriate actions to address any indication that USDWs may be endangered.
Commenter Name: Robert F. Van Voorhees Letter ID: 0190

Commenter Organization: Carbon Sequestration Council Comment ID: 24483

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Rule Provision: 146.90(g) 

Proposed CCS Group Recommendations: (g) Testing and monitoring to track the 

extent of the carbon dioxide plume and the position of the pressure front by 

either monitoring for pressure changes in the first formation overlying the 

confining zone or using indirect, geophysical techniques (e.g., seismic, 

electrical, gravity, or electromagnetic surveys and/or down-hole carbon dioxide 

detection tools);

Basis for CCS Group Comments: Monitoring outside of the injection zone provides 

little information of value for tracking and monitoring the injected plume. 

Examples of how to test and monitor could be included in the Preamble but need 

not be included in the rule itself. 

Response: EPA has revised this requirement in the final rule. The final GS regulation, at

§146.90(g)(1), requires all GS project owners or operators to monitor for pressure changes in the

injection zone. EPA believes that pressure monitoring in the injection zone is necessary to track the

development and movement of the pressure front and CO2 plume. 

Pressure monitoring within the injection zone is necessary because any such monitoring above the

confining zone would not detect movement of the pressure front unless a breach of the confining

zone occurs. EPA believes that monitoring using wells in the injection zone (i.e., that penetrate the

confining zone) can be safely performed if the wells are constructed to prevent flow between the

injection zone and USDWs or other layers above the confining zone. Such construction technologies

exist and have been used in the oil and gas industry for years. EPA believes that the benefits of

monitoring in the injection formation outweigh the manageable risk of those monitoring wells

serving as conduits for fluid movement. EPA adds that owners or operators may consider performing

additional pressure monitoring in wells that are above the confining zone (e.g., in the same wells

used to perform ground water quality monitoring required at §146.90(d)) to provide additional

verification that no pressure changes are occurring above the confining zone due to CO2 leakage.

Monitoring also identifies needed remedial actions, provides inputs for AoR reevaluation modeling,

and targets additional geochemical and surface monitoring needs. Knowledge of the location of the

CO2 plume and the associated pressure front will assure the public that GS projects are proceeding

according to plan, provide sufficient information to the owner or operator and Director, or allow for

appropriate actions to address any indication that USDWs may be endangered.

EPA acknowledges that, at certain sites, there may be a need for more or different monitoring

schemes (which may include monitoring in the confining zone), and adds that it is important to

balance the need for adequate monitoring that ensures USDW protection from endangerment against

too many artificial penetrations which could serve as conduits for fluid migration. Site-specific

testing and monitoring plans should describe the proposed monitoring regime, which must be

approved by the Director.

Flexibility is also provided regarding how to monitor for the specific data required by the final rule.

The testing and monitoring plan is developed by the owner or operator in consultation with the

Director and is designed to ensure that a detailed, Director-approved document describing how

monitoring will be conducted during the lifetime of the project exists. 
EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil gas and surface air monitoring which may be required by the UIC Director

for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Robert F. Van Voorhees Letter ID: 0190

Commenter Organization: Carbon Sequestration Council Comment ID: 24539

Comment: Rule Provisions or Federal Register Cite: 146.90 

EPA Preamble Question: 30. EPA seeks comment on the requirement for monitoring 

of GS sites for the purpose of tracking the location of the CO2 plume and 

associated pressure front over time. EPA Notice 43514 

CSC Response: The amount of monitoring required to track plumes and pressure 

fronts is not cost justified in comparison with taking the necessary steps to 

demonstrate containment. The primary focus should be on making sure that the 

plume and formation fluid are contained within the injection zone rather than 

trying to show the exact location of the plume within that containment. 

The frequency of monitoring should be dictated by site-specific operational and 

geologic conditions combined with the results of monitoring. . 

Response: EPA clarifies that all of the monitoring requirements in the GS rule are for the purpose of

ensuring containment so that USDWs are protected from endangerment. EPA believes that knowing

the extent of the CO2 plume and pressure front is necessary to make such a determination.

Monitoring can also identify needed remedial actions, provide inputs for AoR reevaluation modeling,

evaluate predictions of plume movement, and target additional geochemical and surface monitoring

needs. Knowledge of the location of the CO2 plume and the associated pressure front will assure the

public that GS projects are proceeding according to plan, provide sufficient information to the owner

or operator and Director, or allow for appropriate actions to address any indication that USDWs may

be endangered.

Pressure monitoring within the injection zone is necessary because any such monitoring above the

confining zone would not detect movement of the pressure front unless a breach of the confining

zone occurs. EPA believes that monitoring using wells in the injection zone (i.e., that penetrate the

confining zone) can be safely performed if the wells are constructed to prevent flow between the

injection zone and USDWs or other layers above the confining zone. Such construction technologies

exist and have been used in the oil and gas industry for years. EPA believes that the benefits of

monitoring in the injection formation outweigh the manageable risk of those monitoring wells

serving as conduits for fluid movement. EPA adds that owners or operators may consider performing

additional pressure monitoring in wells that are above the confining zone (e.g., in the same wells

used to perform ground water quality monitoring required at §146.90(d)) to provide additional

verification that no pressure changes are occurring above the confining zone due to CO2 leakage. 

EPA adds that all monitoring will be conducted pursuant to the approved testing and monitoring
plan, which should be based on site-specific information about the site and planned operations.

Commenter Name: Robert F. Van Voorhees Letter ID: 0190

Commenter Organization: Carbon Sequestration Council Comment ID: 24541

Other EPA Comment Codes and Descriptions: 4655 2.6.5.1 Plume tracking

techniques/geophysical methods (seeking comment) 

Comment: Rule Provisions or Federal Register Cite: 146.90(g) 

EPA Preamble Question: 32. Based on information evaluated to date, EPA believes 

that tracking the plume and pressure front is an important companion step to 

address any uncertainties associated with initial AoR modeling and requests 

comment on this approach and more efficient alternatives that may be used to 

track the plume and pressure front. EPA Notice 43516. 

CSC Response: Uncertainties associated with AoR determinations may be addressed 

through the use of a conservative modeling approach. Requirements to "track" 

plumes or pressure fronts would be extraordinarily burdensome and are not 

necessary, as extensive experience with "no migration" exemptions for hazardous 

waste injection wells has shown. 

Response: EPA disagrees that plume and pressure front monitoring are not justified for Class VI

wells. The Agency recognizes that while there are similarities between injection of hazardous wastes

for disposal (Class I) and GS (Class VI), there are significant differences as well. Important unique

considerations for GS include the buoyancy of CO2, its corrosivity when in contact with water, its

low viscosity (i.e., high mobility), and the very large injection volumes that are anticipated. There is

also a degree of uncertainty regarding the behavior of large volumes of CO2 in the subsurface after

injection. Given these characteristics of anticipated GS projects, EPA believes that plume and

pressure front monitoring at §146.90(g) are justified to provide early warning of any unforeseen

fluid movement that might endanger USDWs. 

The final rule (at §146.90(g)) requires owners or operators to perform monitoring to track the extent

of the CO2 plume and pressure front. The owner or operator must use direct methods to monitor for

pressure changes in the injection zone. Indirect methods (e.g., seismic, electrical, gravity, or

electromagnetic surveys and/or down-hole CO2 detection tools) are also required unless the Director

determines, based on site-specific geology that such methods are not appropriate.

EPA believes that pressure monitoring in the injection zone is necessary to track the development

and movement of the pressure front and CO2 plume. Monitoring can also identify needed remedial

actions, provide inputs for AoR reevaluation modeling, evaluate predictions of plume movement,

and target additional geochemical and surface monitoring needs. Knowledge of the location of the

CO2 plume and the associated pressure front will also assure the public that GS projects are

proceeding according to plan, provide sufficient information to the owner or operator and Director,

or allow for appropriate actions to address any indication that USDWs may be endangered.

Commenter Name: Craig R. Walters Letter ID: 0200

Commenter Organization: Anadarko Petroleum Corporation Comment ID: 24600

Comment: Rule Provisions: 146.90 

EPA Rule Issue: 30. EPA seeks comment on the requirement for monitoring of GS 

sites for the purpose of tracking the location of the CO2 plume and associated 
pressure front over time. EPA Notice 43514 

Anadarko Petroleum Corporation (APC) Response: The frequency of monitoring 

should be dictated by site-specific operational and geologic conditions combined 

with the results of monitoring with model predictions and should be set at the 

permit approval stage. The guiding principle for monitoring is to verify proper 

confinement of the CO2 and ensure protection of USDWs. EPA should recognize that 

use of modeling and other monitoring techniques are relatively qualitative 

processes that can have varying degrees of accuracy that will improve over time 

in an iterative process, and EPA should provide regulatory flexibility to 

account for this. 

Response: EPA clarifies that all of the monitoring requirements in the GS rule are for the purpose of

ensuring containment so that USDWs are protected from endangerment. EPA believes that knowing

the extent of the CO2 plume and pressure front is necessary to make such a determination.

Monitoring can also identify needed remedial actions, provide inputs for AoR reevaluation modeling,

evaluate predictions of plume movement, and target additional geochemical and surface monitoring

needs. Knowledge of the location of the CO2 plume and the associated pressure front will assure the

public that GS projects are proceeding according to plan, provide sufficient information to the owner

or operator and Director, or allow for appropriate actions to address any indication that USDWs may

be endangered.

Pressure monitoring within the injection zone is necessary because any such monitoring above the

confining zone would not detect movement of the pressure front unless a breach of the confining

zone occurs. EPA believes that monitoring using wells in the injection zone (i.e., that penetrate the

confining zone) can be safely performed if the wells are constructed to prevent flow between the

injection zone and USDWs or other layers above the confining zone. Such construction technologies

exist and have been used in the oil and gas industry for years. EPA believes that the benefits of

monitoring in the injection formation outweigh the manageable risk of those monitoring wells

serving as conduits for fluid movement. EPA adds that owners or operators may consider performing

additional pressure monitoring in wells that are above the confining zone (e.g., in the same wells

used to perform ground water quality monitoring required at §146.90(d)) to provide additional

verification that no pressure changes are occurring above the confining zone due to CO2 leakage. 

EPA adds that all monitoring will be conducted pursuant to the approved testing and monitoring

plan, which should be based on site-specific information about the site and planned operations.

Commenter Name: Craig R. Walters Letter ID: 0200

Commenter Organization: Anadarko Petroleum Corporation Comment ID: 24602

Other EPA Comment Codes and Descriptions: 4655 2.6.5.1 Plume tracking

techniques/geophysical methods (seeking comment) 

Comment: Rule Provisions: 146.90(g) 

EPA Rule Issue: 32. Based on information evaluated to date, EPA believes that 

tracking the plume and pressure front is an important companion step to address 

any uncertainties associated with initial AoR modeling and requests comment on 

this approach and more efficient alternatives that may be used to track the 

plume and pressure front. EPA Notice 43516. 

Anadarko Petroleum Corporation (APC) Response: Plume and pressure front are 
different concepts and should not be confused. They yield information on two 

different metrics. The former tells you about the remaining capacity of the 

storage formation and the latter describes the direction and movement of the CO2 

plume. Based on experience to date, CO2 plume can be monitored using surface or 

wellbore seismic and possibly some remote satellite techniques. Monitoring of 

the pressure front will be more difficult since that requires data from the 

injection formation which can only be obtained by drilling a well. Modeling can 

estimate the movement of a pressure front. Those estimations are limited by the 

accuracy of the model and its iterative adjustments as previously mentioned. 

Response: EPA acknowledges that monitoring the plume and pressure front are different issues and

believes that direct pressure measurements are appropriate and that direct pressure monitoring will

be feasible at all GS sites. The final rule (at §146.90(g)) requires owners or operators to perform

monitoring to track the extent of the CO2 plume and pressure front. The owner or operator must use

direct methods to monitor for pressure changes in the injection zone. Indirect methods (e.g., seismic,

electrical, gravity, or electromagnetic surveys and/or down-hole CO2 detection tools) are also

required unless the Director determines, based on site-specific geology, that such methods are not

appropriate. 

EPA believes that pressure monitoring in the injection zone is necessary to track the development

and movement of the pressure front and CO2 plume. Monitoring can also identify needed remedial

actions, provide inputs for AoR reevaluation modeling, evaluate predictions of plume movement,

and target additional geochemical and surface monitoring needs. Knowledge of the location of the

CO2 plume and the associated pressure front will assure the public that GS projects are proceeding

according to plan, provide sufficient information to the owner or operator and Director, or allow for

appropriate actions to address any indication that USDWs may be endangered.

Commenter Name: Craig R. Walters Letter ID: 0200

Commenter Organization: Anadarko Petroleum Corporation Comment ID: 24707

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Rule Provision: 146.90(g) 

Anadarko Petroleum Corporation (APC) Comments: (g) Testing and monitoring to 

track the extent of the carbon dioxide plume and the position of the pressure 

front by either monitoring for pressure changes in the first formation overlying 

the confining zone or using indirect, geophysical techniques (e.g., seismic, 

electrical, gravity, or electromagnetic surveys and/or down-hole carbon dioxide 

detection tools);

Rationale: See 146.90(c)(1 thru 4 and 7) 

Monitoring outside of the injection zone provides little information of value 

for tracking and monitoring the injected plume. Examples of how to test and 

monitor could be included in the Preamble but need not be included in the rule 

itself. 

Response: EPA believes that direct pressure measurements are appropriate and the final rule (at

§146.90(g)) requires owners or operators to perform monitoring to track the extent of the CO2 plume
and pressure front. The owner or operator must use direct methods to monitor for pressure changes

in the injection zone. Indirect methods (e.g., seismic, electrical, gravity, or electromagnetic surveys

and/or down-hole CO2 detection tools) are also required unless the Director determines, based on

site-specific geology, that such methods are not appropriate. 

EPA believes that pressure monitoring in the injection zone is necessary to track the development

and movement of the pressure front and CO2 plume. Monitoring can also identify needed remedial

actions, provide inputs for AoR reevaluation modeling, evaluate predictions of plume movement,

and target additional geochemical and surface monitoring needs. Knowledge of the location of the

CO2 plume and the associated pressure front will assure the public that GS projects are proceeding

according to plan, provide sufficient information to the owner or operator and Director, or allow for

appropriate actions to address any indication that USDWs may be endangered.

EPA acknowledges that, at certain sites, there may be a need for more or different monitoring

schemes (which may include monitoring in the confining zone), and adds that it is important to

balance the need for adequate monitoring that ensures USDW protection from endangerment against

too many artificial penetrations which could serve as conduits for fluid migration. Site-specific

testing and monitoring plans should describe the proposed monitoring regime, which must be

approved by the Director.

Flexibility is also provided regarding how to monitor for the specific data required by the final rule.

The testing and monitoring plan is developed by the owner or operator in consultation with the

Director and is designed to ensure that a detailed, Director-approved document describing how

monitoring will be conducted during the lifetime of the project exists. 

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, which will include discussion of identifying the extent of the

CO2 plume and pressure front. The guidance describes available technologies and recommended

approaches for implementing a testing and monitoring plan, including pre-operational geophysical

logging and testing of injection wells, MITs, injection well testing during operation, groundwater

quality monitoring, tracking the CO2 plume and pressure front, and soil gas and surface air

monitoring which may be required by the UIC Director for specific GS projects. The guidance can

be found on EPA’s website at http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm. In

addition, in January 2009, DOE published a best practices manual entitled "Monitoring, Verification,

and Accounting of CO2 Stored in Deep Geologic Formations" (DOE/NETL-311/081508); this

manual is included in the docket for the final GS rule.

Commenter Name: Richard Guinn Letter ID: 0210

Commenter Organization: Eastman Chemical Company Comment ID: 22725

Comment: §146.90 Testing and monitoring requirements. (g) "Testing and monitoring to 

track the extent of the carbon dioxide plume and the position of the pressure 

front by either monitoring for pressure changes in the first formation overlying 

the confining zone or using indirect, geophysical techniques (e.g., seismic, 

electrical, gravity, or electromagnetic surveys and/or down-hole carbon dioxide 

detection tools);" 

We recommend deletion of this requirement in its entirety and replacing with 

"Testing and monitoring to track the extent of the carbon dioxide plume." 

Tracking the precise position of a moving pressure front will require a large 

number of expensive and deeply located probes. A limited number of pressure 
monitors that can provide information on pressures affecting the confinement 

layers are more valuable. The Proposed Rule also requires well owners to monitor 

periodically groundwater quality and geochemical changes above the confining 

zone. The requirements for such deep monitor wells could be costly. Requiring 

both pressure and geochemical monitoring will be costly and provide questionable 

additional information or warning. 

Response: EPA maintains that plume tracking and pressure monitoring are key components of

monitoring at GS sites. A rigorous plume tracking and pressure monitoring scheme, such as one that

meets the requirements at §146.90(g), is imperative for ensuring that the CO2 plume is contained

within the injection zone. Pressure monitoring in the injection zone is necessary to track the

development and movement of the pressure front and CO2 plume. When combined with information

on temperature, pressure data provide an indication of the phase (e.g., gas, supercritical) and

distribution of the injected CO2 (73 FR 43515). Monitoring can also identify needed remedial

actions, provide inputs for AoR reevaluation modeling, evaluate predictions of plume movement,

and target additional geochemical and surface monitoring needs.

EPA recognizes that installation of monitoring wells entails additional resources. However, the

Agency believes that such monitoring is necessary to ensure that GS projects are appropriately

operated and monitored and to protect USDWs from endangerment. Knowledge of the location of

the CO2 plume and the associated pressure front will assure the public that GS projects are

proceeding according to plan, provide sufficient information to the owner or operator and Director,

or allow for appropriate actions to address any indication that USDWs may be endangered.

Commenter Name: John King Letter ID: 0211

Commenter Organization: Shell Exploration and Production Company

(SEPCo)

Comment ID:

22778

Comment: 1. Monitoring CO2 Movement and Reservoir Pressure 

The preamble to the proposed rule specifically states that the "[m]onitoring of 

subsurface geochemistry and the position of the CO2 plume and pressure front are 

necessary to verify predictions of plume movement, provide inputs for modeling, 

identify needed corrective actions, and target geochemical and surface 

monitoring activities." 73 Fed. Reg. at 43514. Again, this is an assertion that 

cannot be reconciled with experience with Class I hazardous waste injection, 

where such monitoring has never been considered necessary and is not required. 

Response: EPA disagrees that plume and pressure front monitoring are not justified for Class VI

wells. The Agency recognizes that while there are similarities between injection of wastes for

disposal (Class I) and GS (Class VI), there are significant differences as well. Important unique

considerations for GS include the buoyancy of CO2, its corrosivity when in contact with water, its

low viscosity (i.e., high mobility), and the very large injection volumes that are anticipated. There is

also a degree of uncertainty regarding the behavior of large volumes of CO2 in the subsurface after

injection. Given these characteristics of anticipated GS projects, EPA believes that plume and

pressure front monitoring at §146.90(g) are justified to provide early warning of any unforeseen

fluid movement that might endanger USDWs. 

The final rule (at §146.90(g)) requires owners or operators to perform monitoring to track the extent

of the CO2 plume and pressure front. The owner or operator must use direct methods to monitor for
pressure changes in the injection zone. Indirect methods (e.g., seismic, electrical, gravity, or

electromagnetic surveys and/or down-hole CO2 detection tools) are also required unless the Director

determines, based on site-specific geology, that such methods are not appropriate.

EPA believes that pressure monitoring in the injection zone is necessary to track the development

and movement of the pressure front and CO2 plume. Monitoring can also identify needed remedial

actions, provide inputs for AoR reevaluation modeling, evaluate predictions of plume movement,

and target additional geochemical and surface monitoring needs. Knowledge of the location of the

CO2 plume and the associated pressure front will also assure the public that GS projects are

proceeding according to plan, provide sufficient information to the owner or operator and Director,

or allow for appropriate actions to address any indication that USDWs may be endangered.

Commenter Name: Andrew Duguid Letter ID: 0226

Commenter Organization: Schlumberger Carbon Services Comment ID: 23999

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: 4. Schlumberger supports the concept of testing and monitoring to track the CO2 

plume and the associated pressure front. We feel that without this monitoring 

the validation and updating of the models used to predict the size and shape of 

the AOR cannot be properly conducted and that the use of models to predict the 

size and shape of the AOR will be ineffective. However we feel that the 

language in section 146.90(g) is too restrictive. The current language states: 

(g) Testing and monitoring to track the extent of the carbon dioxide 

plume and the position of the pressure front by either monitoring for 

pressure changes in the first formation overlying the confining zone or 

using indirect, geophysical techniques (e.g., seismic, electrical, 

gravity, or electromagnetic surveys and/or down-hole carbon dioxide 

detection tools); 

We feel that the restrictions placed in this language could adversely impact the 

efficiency of monitoring and modeling depending on site conditions. 

Schlumberger proposes the following alternate language: 

(g) Testing and monitoring to track the extent of the carbon dioxide 

plume and the position of the pressure front by either monitoring for 

pressure changes, using geophysical techniques (e.g., seismic, 

electrical, gravity, or electromagnetic surveys and/or down-hole carbon 

dioxide detection tools), other techniques that are approved by the 

director or a combination of techniques if multiple techniques are 

deemed necessary by the director; 

Response: EPA has revised this requirement in the final rule. The final GS regulation, at

§146.90(g)(1), requires all GS project owners or operators to monitor directly for pressure changes in

the injection zone. EPA believes that pressure monitoring in the injection zone is necessary to track

the development and movement of the pressure front and CO2 plume. In addition, §146.90(g)(2)

requires owners or operators to track the position of the CO2 plume using indirect methods (e.g.,

seismic, electrical, gravity, or electromagnetic surveys and/or down-hole CO2 detection tools),

unless the Director determines based on site-specific geology, that such methods are not appropriate.
EPA is affording Director's discretion regarding the use of geophysical techniques at some sites

because the Agency recognizes that geophysical methods are not appropriate in all geologic settings.

EPA clarifies that this determination will be made by the Director based on the site-specific geologic

information submitted by the owner or operator with their permit application.

EPA believes that this approach provides flexibility to develop a site-specific monitoring plan,

ensures that direct monitoring is available to track the movement of the CO2 and validate models,

and recognizes that indirect techniques are not appropriate in all situations. The owner or operator's

approved testing and monitoring plan will include the site-specific details, technologies, testing and

monitoring frequencies, and other pertinent information.

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil gas and surface air monitoring which may be required by the UIC Director

for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Andrew Duguid Letter ID: 0226

Commenter Organization: Schlumberger Carbon Services Comment ID: 24059

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Proposed Rule: (1) The location and number of monitoring wells must be based on 

specific information about the geologic sequestration project, including 

injection rate and volume, geology, the presence of artificial penetrations and 

other factors; 

Schlumberger Suggested Revision: (1) The location and number of monitoring wells 

must be based on specific information about the geologic sequestration project, 

including injection rate and volume, geology, the presence of artificial 

penetrations and other relevant factors as warranted by a risk-assessment; 

Schlumberger Rationale: The monitoring should be designed to reduce risk 

Response: EPA agrees that monitoring plans and methods need to be site-specific and believes that

the monitoring requirements for GS sites at §146.90 provide an appropriate level of flexibility in

structuring a testing and monitoring plan that protects USDWs from endangerment. EPA retains the

requirement regarding placement of monitoring wells, but adds that any additional relevant sitespecific information must be considered in the development of the testing and monitoring plan to

ensure USDW protection from endangerment.

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil gas and surface air monitoring which may be required by the UIC Director
for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Andrew Duguid Letter ID: 0226

Commenter Organization: Schlumberger Carbon Services Comment ID: 24063

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Proposed Rule: (g) Testing and monitoring to track the extent of the carbon 

dioxide plume and the position of the pressure front by either monitoring for 

pressure changes in the first formation overlying the confining zone or using 

indirect, geophysical techniques (e.g., seismic, electrical, gravity, or 

electromagnetic surveys and/or down-hole carbon dioxide detection tools); 

Schlumberger Suggested Revision: (g) Testing and monitoring to track the extent 

of the carbon dioxide plume and the position of the pressure front. 

Schlumberger Rationale:Monitoring outside of the injection zone provides little 

information of value for tracking and monitoring the injected plume. Examples of 

how to test and monitor could be included in the Preamble. 

Response: As described above, EPA has revised this requirement in the final rule. The final GS

regulation, at §146.90(g)(1), requires all GS project owners or operators to monitor directly for

pressure changes in the injection zone. EPA believes that pressure monitoring in the injection zone is

necessary to track the development and movement of the pressure front and CO2 plume. In addition,

§146.90(g)(2) requires owners or operators to track the position of the CO2 plume using indirect

methods (e.g., seismic, electrical, gravity, or electromagnetic surveys and/or down-hole CO2

detection tools), unless the Director determines based on site-specific geology, that such methods are

not appropriate.

Commenter Name: Steven B. Corneli Letter ID: 0234

Commenter Organization: NRG Energy, Inc. Comment ID: 23170

Comment: data would be needed to verify the model predictions. In particular, it is 

impractical and cost prohibitive to measure the exact location of the CO2 plume 

and pressure front using monitor wells. The monitor wells would be very 

expensive to install and may create a potential pathway for migration of CO2. In 

addition, plume or pressure front monitoring have never been necessary or 

required under the Class I hazardous waste injection well program because 

experience has shown that it is not necessary to verify the model predictions. 

Response: EPA believes that pressure monitoring in the injection zone is necessary to track the

development and movement of the pressure front and CO2 plume. Monitoring can also identify

needed remedial actions, provide inputs for AoR reevaluation modeling, evaluate predictions of

plume movement, and target additional geochemical and surface monitoring needs. Knowledge of

the location of the CO2 plume and the associated pressure front will also assure the public that GS

projects are proceeding according to plan, provide sufficient information to the owner or operator

and Director, or allow for appropriate actions to address any indication that USDWs may be

endangered. 
EPA believes that monitoring using wells in the injection zone, e.g., for pressure monitoring as

required at §146.90(g)(1), can be safely performed if the wells are constructed to prevent flow

between the injection zone and USDWs or other layers above the confining zone. Such construction

technologies exist and have been used in the oil and gas industry for years. EPA believes that

properly constructed monitoring wells will be a safe way to obtain the data that is essential to ensure

that the injected CO2 remains confined in the injection zone and that pressure changes are not

causing movement of formation or other fluids. EPA is developing guidance on well construction

that will include recommendations for monitoring well construction. The guidance will be available

on EPA’s website at http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

To mitigate the risk of fluid movement, EPA requires owners and operators to submit a testing and

monitoring plan that describes how the owner or operator plans to site and construct monitoring

wells. 

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil gas and surface air monitoring which may be required by the UIC Director

for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm. 

EPA acknowledges the commenters' concern about the cost of monitoring. However, EPA believes

that monitoring is essential for protection of USDWs at GS sites. Although a significant cost in

absolute terms, monitoring costs are expected to be a small fraction of site operating costs, according

to EPA's cost analysis for the GS rulemaking (which is available in the docket).

Commenter Name: Philip Papadeas Letter ID: 0238

Commenter Organization: Sandia Technologies, LLC Comment ID: 23357

Comment: §146.90 (g) 

Re: Monitoring saline intervals above the Confining Zone. 

This monitoring approach may provide risk to USDWs, if monitor wells are drilled 

and installed, and adds significant burden, cost to the operator and 

uncertainties to the geologic system. One key question is however, what if no 

permeable intervals are present to monitor? Does one monitor saline intervals, 

or shallow fresh water wells? The UIC program has worked well for many years 

with a stringent continuous cemented wellbore, and no migration of fluid as 

determined from annual testing, and operational pressure monitoring of the 

injection interval. 

Close monitoring of injection pressure, and annual pressure falloff data will 

supercede a dedicated monitor well where pressure anomalies may exist due to 

pressure or some distant fluid injection or withdrawal in the shallow 

subsurface. In areas of depleted reservoirs or drawn down aquifers the pressure 

effects monitoring may not indicate anything significant. 

Calibrated reservoir and flow and containment models can predict the current and 

future pressure front as a result of the injectate. As with Class I modeling, a 
proper formation pressure gradient is required to assess a baseline, which can 

determine all future storage capacity of the reservoir in the subsurface. By 

bounding the injectate via conservative assumptions offers the best chance to 

define the pressure front, and assess how large the potential area of review may 

be necessary. 

The CO2 plume is likely to be highly variable in saturation and depends on the 

distance, location and depth considerations as well as original salinity and 

residual hydrocarbon saturation. Seismic and or vertical seismic profiling may 

offer the best approach to identifying where the highest saturation is present. 

Pressure remains the better indicator, distance from the wellbore. 

Response: EPA agrees that good site selection, modeling, and management are crucial elements of a

successful GS project, but disagrees that this is an effective substitute for rigorous site monitoring.

EPA disagrees that pressure fall-off tests are an appropriate substitute for monitoring pressure

changes in the injection zone. Pressure fall-off tests provide information in the vicinity of the

injection well(s) and measure pressure conditions within the injection zone. Direct monitoring of

pressure changes in the injection zone can provide advance warning of movement of CO2 or brine

that might ultimately endanger a USDW. 

The Agency recognizes that while there are similarities between injection of wastes for disposal

(Class I) and GS (Class VI), there are significant differences as well. Important unique

considerations for GS include the buoyancy of CO2, its corrosivity when in contact with water, its

low viscosity (i.e., high mobility), and the very large injection volumes that are anticipated. There is

also a degree of uncertainty regarding the behavior of large volumes of CO2 in the subsurface after

injection. Given these characteristics of anticipated GS projects, EPA believes that plume and

pressure front monitoring at §146.90(g) are justified to provide early warning of any unforeseen

fluid movement that might endanger USDWs. 

The final rule (at §146.90(g)) requires owners or operators to perform monitoring to track the extent

of the CO2 plume and pressure front. The owner or operator must use direct methods to monitor for

pressure changes in the injection zone. Indirect methods (e.g., seismic, electrical, gravity, or

electromagnetic surveys and/or down-hole CO2 detection tools) are also required unless the Director

determines, based on site-specific geology, that such methods are not appropriate. 

EPA believes that pressure monitoring is necessary and for this reason, all GS well owners or

operators must monitor pressure in the injection zone using direct methods (§146.90(g)(1)) to track

the development and movement of the pressure front and CO2 plume. Monitoring can also identify

needed remedial actions, provide inputs for AoR reevaluation modeling, evaluate predictions of

plume movement, and target additional geochemical and surface monitoring needs.

Commenter Name: Mark Bohrer Letter ID: 0241

Commenter Organization: North Dakota Industrial Commission Comment ID: 23252

Comment: 30. EPA seeks comment on the requirement for monitoring of GS sites for the 

purpose of tracking the location of the CO2 plume and associated pressure front 

over time. EPA Notice 43514. 

Monitoring of the carbon dioxide plume is appropriate however caution is advised 

with respect to requiring monitoring wells since these may provide a conduit for 
unwanted migration. 4D seismic and predictive models will improve over time due 

to iterative processes. 

Response: To mitigate the risk of fluid movement, EPA requires owners and operators to submit a

testing and monitoring plan that describes how the owner or operator plans to site and construct

monitoring wells. 

EPA believes, however, that monitoring using wells in the injection zone, e.g., for pressure

monitoring as required at §146.90(g)(1), can be safely performed if the wells are constructed to

prevent flow between the injection zone and USDWs or other layers above the confining zone. Such

construction technologies exist and have been used in the oil and gas industry for years. EPA

believes that properly constructed monitoring wells will be a safe way to obtain the data that is

essential to ensure that the injected CO2 remains confined in the injection zone and that pressure

changes are not causing movement of formation or other fluids. EPA is developing guidance on well

construction that will include recommendations for monitoring well construction. The guidance will

be available on EPA’s website at http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil gas and surface air monitoring which may be required by the UIC Director

for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Mark Bohrer Letter ID: 0241

Commenter Organization: North Dakota Industrial Commission Comment ID: 23254

Comment: 32. Based on information evaluated to date, EPA believes that tracking the plume 

and pressure front is an important companion step to address any uncertainties 

associated with initial AoR modeling and requests comment on this approach and 

more efficient alternatives that may be used to track the plume and pressure 

front. EPA Notice 43516. 

Tracking the plume and pressure front will allow for verification of the 

reservoir model. Pressure transient testing and seismic techniques may be 

useful alternatives. 

Response: The final rule (at §146.90(g)) requires owners or operators to perform monitoring to track

the extent of the CO2 plume and pressure front. The owner or operator must use direct methods to

monitor for pressure changes in the injection zone. Indirect methods (e.g., seismic, electrical, gravity,

or electromagnetic surveys and/or down-hole CO2 detection tools) are also required unless the

Director determines, based on site-specific geology, that such methods are not appropriate. EPA is

affording Director's discretion regarding the use of geophysical techniques at some sites because the

Agency recognizes that geophysical methods are not appropriate in all geologic settings. EPA

clarifies that this determination will be made by the Director based on the site-specific geologic

information submitted by the owner or operator with their permit application. 

EPA believes that this approach provides flexibility to develop a site-specific monitoring plan,
ensures that direct monitoring is available to track the movement of the CO2 and validate models,

and recognizes that indirect techniques are not appropriate in all situations. The owner or operator's

approved testing and monitoring plan will include the site-specific details, technologies, testing and

monitoring frequencies, and other pertinent information.

Commenter Name: Kurt Waltzer Letter ID: 0250

Commenter Organization: Clean Air Task Force Comment ID: 22321

Comment: The "position of the pressure front" is not something that is as straightforward 

to establish as the extent of the CO2 plume. As we have commented above, there 

is no distinct "front", or discontinuity, but rather a gradient in pressure that 

dissipates with distance away from the injection zone. Estimating the total 

injection footprint therefore will require appropriate thresholds to be defined 

in order to estimate the area of elevated pressure. Additionally, methods such 

as seismic surveys do not work in the same way for compressed brine as they do 

for CO2rich brine. Tracking the extent of the CO2 plume is generally possible 

and must be part of a comprehensive and credible monitoring plan and a GS 

project. The extent of the area of elevated pressure will likely be estimated 

with a combination of measurements, inferences and modeling, but it is presently 

essential to have monitoring wells penetrating the confining zone to do this. 

Where the CO2 plume itself is concerned, rather than the area of elevated 

pressure, the role of measurements (including indirect measurements such as 

seismic surveys) will and should be far greater than that of modeling. 

Response: EPA agrees with commenter that plume tracking must be part of a comprehensive and

credible monitoring plan for GS wells. For this reason, EPA believes that direct pressure

measurements are appropriate and that direct pressure monitoring will be feasible at all GS sites. The

final rule, at §146.90(g), requires owners or operators to perform monitoring to track the extent of

the CO2 plume and pressure front. The owner or operator must use direct methods to monitor for

pressure changes in the injection zone. Indirect methods (e.g., seismic, electrical, gravity, or

electromagnetic surveys and/or down-hole CO2 detection tools) are also required unless the Director

determines, based on site-specific geology, that such methods are not appropriate. 

EPA believes that pressure monitoring in the injection zone is necessary to track the development

and movement of the pressure front and CO2 plume. Monitoring can also identify needed remedial

actions, provide inputs for AoR reevaluation modeling, evaluate predictions of plume movement,

and target additional geochemical and surface monitoring needs. Knowledge of the location of the

CO2 plume and the associated pressure front will assure the public that GS projects are proceeding

according to plan, provide sufficient information to the owner or operator and Director, or allow for

appropriate actions to address any indication that USDWs may be endangered.

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, which will include discussion of identifying the extent of the

CO2 plume and pressure front. The guidance describes available technologies and recommended

approaches for implementing a testing and monitoring plan, including pre-operational geophysical

logging and testing of injection wells, MITs, injection well testing during operation, groundwater

quality monitoring, tracking the CO2 plume and pressure front, and soil gas and surface air

monitoring which may be required by the UIC Director for specific GS projects. The guidance can

be found on EPA’s website at http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm. In

addition, in January 2009, DOE published a best practices manual entitled "Monitoring, Verification,
and Accounting of CO2 Stored in Deep Geologic Formations" (DOE/NETL-311/081508); this

manual is included in the docket for the for the final GS rule.

Commenter Name: Kurt Waltzer Letter ID: 0250

Commenter Organization: Clean Air Task Force Comment ID: 22324

Comment: variability or from baseline data is hard). Current scientific thinking also 

dictates that the CO2 plume and confinement are best monitored near the 

injection zone or right above the caprock. This implies far greater depths, and 

a much larger distance between CO2 and displaced fluids from USDWs. The Director 

should have the discretion to require such techniques, but we do not believe 

that they should be made mandatory for all permits nor should the rule be 

limited to listing specific techniques (which might be superseded or have 

preferable alternatives). 

Response: EPA has changed this requirement in the final rule. The final GS regulation, at

§146.90(g)(1), requires all GS project owners or operators to monitor for pressure changes in the

injection zone. EPA believes that pressure monitoring in the injection zone is necessary to track the

development and movement of the pressure front and CO2 plume. 

Pressure monitoring within the injection zone is necessary because any such monitoring above the

confining zone would not detect movement of the pressure front unless a breach of the confining

zone occurs. EPA believes that monitoring using wells in the injection zone (i.e., that penetrate the

confining zone) can be safely performed if the wells are constructed to prevent flow between the

injection zone and USDWs or other layers above the confining zone. Such construction technologies

exist and have been used in the oil and gas industry for years. EPA believes that the benefits of

monitoring in the injection formation outweigh the manageable risk of those monitoring wells

serving as conduits for fluid movement. EPA adds that owners or operators may consider performing

additional pressure monitoring in wells that are above the confining zone (e.g., in the same wells

used to perform ground water quality monitoring required at §146.90(d)) to provide additional

verification that no pressure changes are occurring above the confining zone due to CO2 leakage.

Monitoring also identifies needed remedial actions, provides inputs for AoR reevaluation modeling,

and targets additional geochemical and surface monitoring needs. Knowledge of the location of the

CO2 plume and the associated pressure front will assure the public that GS projects are proceeding

according to plan, provide sufficient information to the owner or operator and Director, or allow for

appropriate actions to address any indication that USDWs may be endangered.

Flexibility is also provided regarding how to monitor for the specific data required by the final rule.

The testing and monitoring plan is developed by the owner or operator in consultation with the

Director and is designed to ensure that a detailed, Director-approved document describing how

monitoring will be conducted during the lifetime of the project exists. EPA is developing guidance

on testing and monitoring to assist owners or operators and Directors in evaluating requirements

under §146.90, including proposed monitoring plans. The guidance describes available technologies

and recommended approaches for implementing a testing and monitoring plan, including preoperational geophysical logging and testing of injection wells, MITs, injection well testing during

operation, groundwater quality monitoring, tracking the CO2 plume and pressure front, and soil gas

and surface air monitoring which may be required by the UIC Director for specific GS projects. The

guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.
Commenter Name: Kurt Waltzer Letter ID: 0250

Commenter Organization: Clean Air Task Force Comment ID: 22325

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: To capture the points made above and resolve current inaccuracies or limitations 

in the proposed language, we recommend the following additional changes in 

§146.90(g): 

[In the paragraph below the text 

in all CAPS denotes added text. See also EPA-HQ-OW-0390-0250.pdf, to see the 

original formatting.] 

"(1) Testing and monitoring to track ESTABLISH the extent of the carbon 

dioxide plume and the position of the pressure front WITHIN DEFINED 

THRESHOLDS, WITH THE ASSISTANCE OF MODELING TOOLS WHERE APPROPRIATE

AND THROUGH 

DIRECT MEASUREMENTS OR INDIRECT, GEOPHYSICAL OR OTHER TECHNIQUES by

either 

monitoring for pressure changes in the first formation overlying the confining 

zone or using indirect, geophysical techniques (e.g., seismic, electrical, 

gravity, or electromagnetic surveys and/or down-hole carbon dioxide detection 

tools);

(2) TESTING AND MONITORING TO ESTABLISH THE EXTENT OF THE AREA OF

ELEVATED 

PRESSURE THROUGH DIRECT MEASUREMENTS AND THE ASSISTANCE OF MODELING

TOOLS." 

and in §146.90(h): 

[In the paragraph below the text 

in all CAPS denotes added text. See also EPA-HQ-OW-0390-0250.pdf, to see the 

original formatting.] 

"At the Director’s discretion, surface air monitoring METHODS and/or soil 

gas monitoring to detect movement of carbon dioxide that could SIGNAL 

endangerMENT OF a USDW. 

(1) The testing and monitoring plan must be based on potential vulnerabilities 

within the area of review; 

(2) The monitoring frequency and spatial distribution of surface air

monitoring and/or soil gas monitoring must reflect baseline data and the 

monitoring plan must include how the proposed monitoring will yield useful 

information on the area of review delineation and/or compliance with standards 

under 40 CFR 144.12" 

Response: As described above, EPA believes that direct pressure measurements are appropriate and

that direct pressure monitoring will be feasible at all GS sites and retains this provision in the final

GS rule, at §146.90(g). 

EPA acknowledges that air and soil gas monitoring to ensure USDW protection is not necessary at

all GS sites and agrees that the decision to use surface monitoring and the selection of monitoring
methods for the purpose of USDW protection will be site-specific.

The Agency believes that surface air and soil gas monitoring, when coupled with subsurface

monitoring, may be appropriate at some GS projects to ensure USDW protection. EPA also

acknowledges that surface air and soil gas measurements are subject to variability and may not be

suitable in all settings as a method to ensure USDW protection. However, EPA does not believe that

this should entirely preclude their use. The decision to use surface monitoring and the selection of

monitoring methods will be site-specific (e.g., may be influenced by geology, injection depth, and

operational conditions) and must be based on potential risks to USDWs within the AoR. 

In the final rule, at §146.90(h), the decision to require such monitoring as an additional measure to

ensure USDW protection rests with the Director as a means of identifying leaks that may pose a risk

to USDWs and informing emergency notification of a Class VI owner or operator and UIC Director

in the event of a USDW endangerment, pursuant to requirements at §146.91(c).

Based on its evaluation of all public comments and input on the proposed rule and NODA and

Request for Comment EPA has made many revisions to the GS rule. See the final rule and preamble

for further discussion on EPA's final approach.

Commenter Name: Michel Paque Letter ID: 0259

Commenter Organization: Ground Water Protection Council Comment ID: 24928

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: EPA Proposal: (g) Testing and monitoring to track the extent of the carbon 

dioxide plume and the position of the pressure front by either monitoring for 

pressure changes in the first formation overlying the confining zone or using 

indirect, geophysical techniques (e.g., seismic, electrical, gravity, or 

electromagnetic surveys and/or down-hole carbon dioxide detection tools); 

GWPC Recommendations: (g) Testing and monitoring to track the extent of the 

carbon dioxide plume and the position of the pressure front. 

Rationale: Monitoring outside of the injection zone provides little information 

of value for tracking and monitoring the injected plume. Examples of how to 

test and monitor could be included in the Preamble but need not be included in 

the rule itself. 

Response: EPA has revised this requirement in the final rule. The final GS regulation, at

§146.90(g)(1), requires all GS project owners or operators to monitor for pressure changes in the

injection zone. EPA believes that pressure monitoring in the injection zone is necessary to track the

development and movement of the pressure front and CO2 plume. 

Pressure monitoring within the injection zone is necessary because any such monitoring above the

confining zone would not detect movement of the pressure front unless a breach of the confining

zone occurs. EPA believes that monitoring using wells in the injection zone (i.e., that penetrate the

confining zone) can be safely performed if the wells are constructed to prevent flow between the

injection zone and USDWs or other layers above the confining zone. Such construction technologies

exist and have been used in the oil and gas industry for years. EPA believes that the benefits of

monitoring in the injection formation outweigh the manageable risk of those monitoring wells
serving as conduits for fluid movement. EPA adds that owners or operators may consider performing

additional pressure monitoring in wells that are above the confining zone (e.g., in the same wells

used to perform ground water quality monitoring required at §146.90(d)) to provide additional

verification that no pressure changes are occurring above the confining zone due to CO2 leakage.

Monitoring also identifies needed remedial actions, provides inputs for AoR reevaluation modeling,

and targets additional geochemical and surface monitoring needs. Knowledge of the location of the

CO2 plume and the associated pressure front will assure the public that GS projects are proceeding

according to plan, provide sufficient information to the owner or operator and Director, or allow for

appropriate actions to address any indication that USDWs may be endangered.

EPA acknowledges that, at certain sites, there may be a need for more or different monitoring

schemes (which may include monitoring in the confining zone), and adds that it is important to

balance the need for adequate monitoring that ensures USDW protection from endangerment against

too many artificial penetrations which could serve as conduits for fluid migration. Site-specific

testing and monitoring plans should describe the proposed monitoring regime, which must be

approved by the Director.

Flexibility is also provided regarding how to monitor for the specific data required by the final rule.

The testing and monitoring plan is developed by the owner or operator in consultation with the

Director and is designed to ensure that a detailed, Director-approved document describing how

monitoring will be conducted during the lifetime of the project exists. EPA is developing guidance

on testing and monitoring to assist owners or operators and Directors in evaluating requirements

under §146.90, including proposed monitoring plans. The guidance describes available technologies

and recommended approaches for implementing a testing and monitoring plan, including preoperational geophysical logging and testing of injection wells, MITs, injection well testing during

operation, groundwater quality monitoring, tracking the CO2 plume and pressure front, and soil gas

and surface air monitoring which may be required by the UIC Director for specific GS projects. The

guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Letter ID: 0263

Commenter Organization: Interstate Oil & Gas Compact Commission Comment ID: 22816

Comment: III A. 6 Proposed Plume and Pressure Front Monitoring Requirements 

EE. EPA seeks comment on the requirement for monitoring of GS sites for the purpose 

of tracking the location of the CO2 plume and associated pressure front over time. 

IOGCC Response: The IOGCC suggests that the operator be required to conduct 

ongoing monitoring. The frequency of reporting to the regulatory agency should be 

flexible depending upon site characteristics. 

Response: The final rule (at §146.90(g)) requires owners or operators to perform monitoring to track

the extent of the CO2 plume and pressure front. The owner or operator must use direct methods to

monitor for pressure changes in the injection zone. Indirect methods (e.g., seismic, electrical, gravity,

or electromagnetic surveys and/or down-hole CO2 detection tools) are required unless the Director

determines, based on site-specific geology that such methods are not appropriate. 

EPA clarifies that the specifics of this monitoring must be described in the site-specific testing and

monitoring plan, which must be approved by the Director. EPA believes that this approach provides

flexibility to develop a site-specific monitoring plan, ensures that direct monitoring is available to
track the movement of the CO2 and validate models, and recognizes that indirect techniques are not

appropriate in all situations. The owner or operator's approved testing and monitoring plan will

include the site-specific details, technologies, testing and monitoring frequencies, and other pertinent

information.

Letter ID: 0263

Commenter Organization: Interstate Oil & Gas Compact Commission Comment ID: 22818

Other EPA Comment Codes and Descriptions: 4655 2.6.5.1 Plume tracking

techniques/geophysical methods (seeking comment) 

Comment: III A. 6 Proposed Plume andPressure Front Monitoring Requirements 

GG. Based on information evaluated to date, EPA believes that tracking the plume 

and pressure front is an important companion step to address any uncertainties 

associated with initial AoR modeling and requests comment on this approach 

and more efficient alternatives that maybe used to track the plume and pressure 

front. 

IOGCC Response: Tracking of the CO2 plume and pressure front should be required. 

The methodology, however, should not be specified but determined on a site 

specific basis. The IOGCC agrees with the following EPA statement: "As such, 

allowing flexibility in choosing the plume tracking methods and other monitoring 

technologies may provide an appropriate balance between the protective nature 

of indirect monitoring and cost considerations, as well as allowing for the 

adoption of continuously advancing technology." 

Response: EPA agrees with the comment and the final rule (at §146.90(g)) requires owners or

operators to perform monitoring to track the extent of the CO2 plume and pressure front. The owner

or operator must use direct methods to monitor for pressure changes in the injection zone. Indirect

methods (e.g., seismic, electrical, gravity, or electromagnetic surveys and/or down-hole CO2

detection tools) are also required unless the Director determines, based on site-specific geology, that

such methods are not appropriate. EPA clarifies that the specifics of this monitoring must be

described in the site-specific testing and monitoring plan, which must be approved by the Director. 

EPA believes that this approach provides flexibility to develop a site-specific monitoring plan,

ensures that direct monitoring is available to track the movement of the CO2 and validate models,

and recognizes that indirect techniques are not appropriate in all situations. The owner or operator's

approved testing and monitoring plan will include the site-specific details, technologies, testing and

monitoring frequencies, and other pertinent information.

Commenter Name: Mark Vickery Letter ID: 0280

Commenter Organization: Texas Commission on Environmental Quality Comment ID: 24103

Other EPA Comment Codes and Descriptions: 6220 3.2.2 Assumptions about the number of

monitoring wells (seeking comment) 

Comment: (d) Concern exists on the practical implementation of the proposed requirements 

for monitoring the CO2 plume and pressure front. Noting that the actual 

monitoring plan would be left to director approval, EPA's cost analysis for a 

CO2-GS project assumes the presence of three monitor wells. This would not seem 

to be sufficient for identification/confirmation of the position of the plume or 
pressure front, and leads to speculation whether under the proposed rules, the 

cost of the geosequestration portion of a carbon capture and sequestration 

project would be a significantly greater part of the overall cost of the project 

than represented. In this regard, monitor wells in any reasonable numbers could 

confirm or rule out the presence of CO2 or its pressure effects at the monitor 

well location, but would not be expected to identify or confirm the full extent 

of the plume or pressure front. Computer modeling informed by monitoring data 

should however be able to bound the reasonable extent of the plume and pressure 

front. 

Response: EPA clarifies that the specifics of monitoring, including the number of monitoring wells,

must be described in the site-specific testing and monitoring plan, which must be approved by the

Director.

EPA recognizes that the number of monitoring wells associated with GS projects will be site-specific

and vary based on many factors, including the local geologic characteristics, the presence of other

injection wells, the size of the AoR, and volumes of CO2 injected. The proposed rule Cost Analysis

described the number of monitoring wells as a ratio to the number of injection wells; EPA clarifies

that the number of injection wells was based on the size of the AoR and the type of project.

Therefore, the number of monitoring wells was indirectly based on the size of the AoR. Because ER

project sites have injection wells that are more clustered than those in saline formations, the AoR and

the number of monitoring wells were anticipated to be smaller at an ER project site compared to a

saline formation project. EPA retained this assumption regarding the density of injection wells for

the final rule analysis, but it changed its assumption on the number of monitoring wells at each site.

For the final rule, the Agency assumes one monitoring well above the injection zone per two square

miles of AoR; for monitoring wells into the injection zone, the Agency assumes one monitoring well

per four square miles. EPA assumes monitoring wells into the injection zone will also be used to

sample above the injection zone. The number of monitoring wells assumed for each project type is

presented in Exhibit 5.2 of the Cost Analysis. 

Because the actual number of monitoring wells that will be necessary for a given project site is

uncertain, EPA tested the sensitivity of overall cost estimates to the number of monitoring wells by

applying a 25 percent decrease and increase in monitoring wells per project type to the original

assumptions. This change results in annualized incremental rule costs approximately 16 percent less

and 16 percent greater than costs estimated for the primary analysis (as shown in Exhibit 5.26 of the

Cost Analysis). For additional information on EPA's final regulatory approach, including testing and

monitoring requirements, please see the final rule and preamble. 

EPA is developing guidance on monitoring and testing to assist owners/operators and Directors in

evaluating requirements under §146.90, including developing determining the appropriate number of

monitoring wells for a GS site. This guidance will be available on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Comment Code: 4655 2.6.5.1 Plume tracking techniques/geophysical methods (seeking comment) 

Individual Comments
Commenter Name: Michael H. Cochran Letter ID:

0108

Commenter Organization: Bureau of Water, Division of Environment, Kansas

Department of Health & Environment (KDHE)

Comment

ID: 21983

Comment: 146.90 (g): We believe there are few, if any indirect methods that will work or 

that can feasibly be used to monitor the plume location. This is based on our 

experience with some of these methods on other projects. For example, with 

micro-gravity the difference in values or readings would most likely be so small 

that these would probably be less than the measurement error of the equipment. 

There has to be a significant difference in density to measure the difference in 

gravity. 

Response: EPA has revised the final rule at §146.90(g)(2) to require owners or operators to track the

position of the CO2 plume using indirect methods (e.g., seismic, electrical, gravity, or

electromagnetic surveys and/or down-hole CO2 detection tools), unless the Director determines

based on site-specific geology, that such methods are not appropriate. EPA is affording Director's

discretion regarding the use of geophysical techniques at some sites because the Agency recognizes

that geophysical methods are not appropriate in all geologic settings. For example, geophysical

methods are difficult to execute in areas that are structurally and topographically complex or where

lithologies have limited contrast in density, porosity, permeability, and other physical properties.

EPA clarifies that this determination will be made by the Director based on the site-specific geologic

information submitted by the owner or operator with the permit application. 

EPA believes that this approach provides flexibility to develop a site-specific monitoring plan and

recognizes that indirect techniques are not appropriate in all situations. The owner or operator's

approved testing and monitoring plan will include the site-specific details, technologies, testing and

monitoring frequencies, and other pertinent information.

Commenter Name: Iain Wright Letter ID: 0118

Commenter Organization: BP Alternative Energy Comment ID: 22067

Other EPA Comment Codes and Descriptions: 4600 2.6 Proposed Plume and Pressure Front

Monitoring Requirements (40 CFR 146.90) 

Comment: MONITORING 

Moving on to my second point: Monitoring. Monitoring is important, but there is 

a common mis-perception that if you want secure storage, you need to do lots of 

monitoring. Well, the UN says that "the proportion of CO2 retained by 

appropriately selected and managed sites is likely to exceed 99% over 1,000 

years". SO THE KEY TO SECURE STORAGE IS THE APPROPRIATE SELECTION AND

MANAGEMENT 

OF THE SITE. If that is done properly, the site will be very secure and the need 

for monitoring can be appropriately reduced. Monitoring is like the speedometer 

on your car. It does contribute to your safety, but more important is the design 

of the car, the road and how you drive the car. 

Having said that, at In Salah, we are doing a big research project into 

monitoring, so the program is much more extensive than would be appropriate for 

a commercial project. We are trying out new technologies (such as satellite 

imagery, micro-seismic), so that we can see how they perform against 

conventional oilfield monitoring technologies (such as tracers and conventional 
seismic). 

But as you can probably hear from my accent, I’m a Scotsman, and Scotsmen don’t 

like to waste money, so every technology that we use at in Salah has been 

carefully chosen to represent good value for money. Before we started injection 

at In Salah, we did a site-specific assessment of leakage risk and then we 

tailored the monitoring program to address those risks. Mandating any specific 

monitoring technology could waste a great deal of money and resources without 

contributing to the protection of USDWs. SO WE WOULD CAUTION AGAINST A UNIVERSAL 

MANDATE FOR ANY SPECIFIC MONITORING TECHNOLOGY. 

Many of you will have heard of the other two monitored, industrial-scale CO2 

injection projects in the world, at Sleipner and Weyburn. If you compare the 

monitoring activities at these sites, you can see that something which works 

well in one location, may not work at all in another location. WE ENCOURAGE EPA 

TO USE RISK-ASSESSED, PERFORMANCE-BASED CRITERIA TO DETERMINE SITESPECIFIC 

MONITORING PROGRAMS. 

Response: EPA agrees with commenters and believes that flexibility is important in developing and

implementing a monitoring plan that is appropriately tailored for a specific GS site. The purpose of

the requirement at §146.90 to develop site-specific testing and monitoring plans is to ensure that the

monitoring performed at a site is appropriate for site operational conditions and the geologic setting.

EPA believes that this is the best approach for addressing potential risks at GS sites. These flexible

provisions in the monitoring requirements for Class VI wells enable the owner or operator to tailor

monitoring programs to the specific needs of each project in consultation with the Director.

The final regulation provides for flexibility in: 1) methodologies used to collect these data, 2) the

spatial resolution at which the data should be collected, and 3) how often the data should be

collected. The number and placement of monitoring wells will be based on site-specific information

such as the calculated AoR, injection rate and volume, site geology, baseline data, and the presence

of artificial penetrations within the AoR. In some instances, there may be a limited number of

options for complying with EPA's minimum requirements. For example, monitoring for geochemical

changes will require use of monitoring wells and collection of groundwater samples for chemical

analysis. Many options currently exist for complying with other requirements, such as tracking the

position of the plume and pressure front within the injection zone.

Flexibility is also provided regarding how to monitor for the specific data required by the final rule.

The testing and monitoring plan is developed by the owner or operator in consultation with the

Director and is designed to ensure that a detailed, Director-approved document describing how

monitoring will be conducted during the lifetime of the project exists. 

EPA also agrees that good site selection and management are crucial elements of a successful GS

project, but disagrees that this is an effective substitute for rigorous site monitoring. 

EPA does not believe that prescribing specific technologies to be used in all cases for GS would be

appropriate given the variability in sites. Rather EPA is developing guidance on testing and

monitoring to assist owners or operators and Directors in evaluating requirements under §146.90,

including proposed monitoring plans. The guidance describes available technologies and

recommended approaches for implementing a testing and monitoring plan, including pre-operational
geophysical logging and testing of injection wells, MITs, injection well testing during operation,

groundwater quality monitoring, tracking the CO2 plume and pressure front, and soil gas and

surface air monitoring which may be required by the UIC Director for specific GS projects. The

guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm. In addition, in January 2009,

DOE published a best practices manual entitled "Monitoring, Verification, and Accounting of CO2

Stored in Deep Geologic Formations" (DOE/NETL-311/081508); this manual is included in the

docket for the final GS rule.

Commenter Name: John Stormon Letter ID: 0123

Commenter Organization: Washington State Dept. of Ecology Comment ID: 23005

Other EPA Comment Codes and Descriptions: 4650 2.6.5 CO2 plume and pressure front tracking

(seeking comment) 

Comment: Monitoring: Direct monitoring of the formations immediately above the confining 

layer for a geologic sequestration injection zone is an important requirement 

for the early detection of unacceptable leakage. Monitoring wells installed into 

this monitoring zone will be quite expensive but should be required for all 

projects. Geophysical methods and other indirect monitoring, while useful, 

should not be allowed to substitute for all direct monitoring above the 

confining layer. 

Response: EPA disagrees that pressure monitoring above the confining zone is appropriate. Instead,

EPA believes that pressure monitoring in the injection zone is necessary to track the development

and movement of the pressure front and CO2 plume. The final rule (at §146.90(g)) requires owners

or operators to perform monitoring to track the extent of the CO2 plume and pressure front. The

owner or operator must use direct methods to monitor for pressure changes in the injection zone.

Indirect methods (e.g., seismic, electrical, gravity, or electromagnetic surveys and/or down-hole CO2

detection tools) are also required unless the Director determines, based on site-specific geology, that

such methods are not appropriate.

EPA believes that pressure monitoring within the injection zone is necessary because any such

monitoring above the confining zone would not detect movement of the pressure front unless a

breach of the confining zone occurs. EPA believes that monitoring using wells in the injection zone

(i.e., that penetrate the confining zone) can be safely performed if the wells are constructed to

prevent flow between the injection zone and USDWs or other layers above the confining zone. Such

construction technologies exist and have been used in the oil and gas industry for years. EPA

believes that the benefits of monitoring in the injection formation outweigh the manageable risk of

those monitoring wells serving as conduits for fluid movement. EPA adds that owners or operators

may consider performing additional pressure monitoring in wells that are above the confining zone

(e.g., in the same wells used to perform ground water quality monitoring required at §146.90(d)) to

provide additional verification that no pressure changes are occurring above the confining zone due

to CO2 leakage and that the Director has the authority to require such monitoring under §146.90(i).

Monitoring also identifies needed remedial actions, provides inputs for AoR reevaluation modeling,

and targets additional geochemical and surface monitoring needs. Knowledge of the location of the

CO2 plume and the associated pressure front will assure the public that GS projects are proceeding

according to plan, provide sufficient information to the owner or operator and Director, or allow for

appropriate actions to address any indication that USDWs may be endangered.

EPA also agrees that direct monitoring for ground water quality above the confining zone is
important, and the GS rule requires this at §146.90(d). Monitoring in additional formations, e.g., the

injection zone, may also be necessary, and if the Director believes such monitoring is warranted

he/she has the authority to require that it be included in the testing and monitoring plan.

Commenter Name: Christine Reimer Letter ID: 0142

Commenter Organization: National Ground Water Association Comment ID: 22568

Comment: The methods used for monitoring on projects to date have included time-lapse 

seismic, passive seismic, pressure logging, temperature logging, neutron 

saturation logging, fluid sampling, air sampling [IPCC, 2005]. While it is 

probably not appropriate to specify the suite of MMV tools to be used at every 

site, because not all tools will work at all sites, it is important to emphasize 

that multiple MMV technologies will be required at every site in order to 

completely monitor and collect the necessary data to verify that the site is 

operating within the bounds of its permit. Although it seems unreasonable to 

specify all MMV technologies, it does seem reasonable to specify that monitoring 

wells be installed to collect the necessary fluid samples, pH, resistivity, and 

pressure data. Also, although seismic monitoring may not work everywhere, in 

locations where it is expected to work it should be incorporated into the 

monitoring scheme. Seismic monitoring for CO2 plume location has been 

successfully employed in early projects including Sliepner storage project, 

Weyburn storage project, and Frio brine project [IPCC, 2005, Wilson and Monea, 

2005, Daley et al., 2007]. The data collected from monitoring should be used to 

update and verify the site’s performance and risk models. 

In addition, to aid in selecting other MMV technologies, the International 

Energy Agency has developed a comprehensive database that can be accessed at: 

http://www.co2captureandstorage.info/co2tool_v2.1beta/index.php 

Daley, T.M., Solbau, R.D., Ajo-Franklin, J.B., and Benson, S.M., 2007, 

"Continuous active-source seismic monitoring of CO2 in a brine aquifer," 

Geophysics, Vol. 72, No. 5, pp. A57-A61. 

Intergovernmental Panel on Climate Change, 2005, IPCC special report on carbon 

capture and storage, United Nations Framework Convention on Climate Change, ISBN 

92-9169-119-4. 

Wilson, M. and Monea, M., 2005, IEA GHG Weyburn Monitoring and Storage Project, 

Summary Report, 2000-2004, Petroleum Technology Research Center, Regina SK, 

Canada, Proceedings of the 7th International Conference on Greenhouse Gas 

Control Technologies (GHGT-7), Vol. III, September 5-9, Vancouver, Canada 

Response: EPA clarifies that the specifics of monitoring, including the number of monitoring wells,

must be described in the site-specific testing and monitoring plan, which must be approved by the

Director. EPA is developing guidance on testing and monitoring to assist owners or operators and

Directors in evaluating requirements under §146.90, including proposed monitoring plans. The

guidance describes available technologies and recommended approaches for implementing a testing

and monitoring plan, including pre-operational geophysical logging and testing of injection wells,

MITs, injection well testing during operation, groundwater quality monitoring, tracking the CO2

plume and pressure front, and soil gas and surface air monitoring which may be required by the UIC
Director for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: James Dooley Letter ID: 0156

Commenter Organization: Joint Global Change Research Institute, Pacific

Northwest National Laboratory

Comment ID:

22663

Comment: - Page 43515. It strikes this reviewer as odd to cite only one study (Burton et 

al, 2007) to support the statement that "current monitoring technologies are 

more than adequate for monitoring pressure in a GS project." It is not clear if 

by including this in the preamble to the draft rule whether EPA shares this 

assessment or not. This seems like an awfully broad and sweeping statement. 

Consider rewording. Consider being explicit as to whether EPA shares this view 

or if part of any NODA associated with this rule making should try to collect 

information that goes beyond this one study to confirm or refute this assertion 

that pressure monitoring technologies which exist today are sufficient to meet 

any GS need in any kind of formation anywhere and at any time across all regions 

of the USA. 

Response: EPA clarifies that the GS rule, at §146.90(g), requires owners or operators to perform

monitoring to track the extent of the CO2 plume and pressure front. The owner or operator must use

direct methods to monitor for pressure changes in the injection zone. Indirect methods (e.g., seismic,

electrical, gravity, or electromagnetic surveys and/or down-hole CO2 detection tools) are required

unless the Director determines, based on site-specific geology that such methods are not appropriate.

EPA recognizes that monitoring technologies will evolve and improve over time, and for these

reasons, the Agency is using an adaptive approach to regulate GS injection. The Agency plans, every

six years, to collect and review data on GS projects to determine whether the appropriate amount and

types of information and appropriate documentation are being collected, and to determine if

modifications to the requirements are appropriate or necessary.

Commenter Name: James Dooley Letter ID: 0156

Commenter Organization: Joint Global Change Research Institute, Pacific

Northwest National Laboratory

Comment ID:

22664

Comment: - Page 43516. It is not clear if the USEPA is asserting that using "seismic 

crosswell methods" are "costly and time consuming" or if that is a finding of 

the GEO-SEQ (2004) report mentioned at the start of this paragraph. If it is 

the latter then it is important to clearly attribute that statement to the 

authors of the GEO-SEQ report. Otherwise, it appears that the USEPA is calling 

into question the cost effectiveness and utility of a technique that has yet to 

be robustly tested with respect to GS. That would seem to be a premature 

assumption based only on the results of the GEO-SEQ project, since crosswell 

seismic could be a preferred option for some sites where alternative options are 

impractical or economically infeasible. This section contains a number of 

implicit references to cost/benefit calculations for monitoring technologies. If 

the USEPA believes that these techniques are needed to discharge its 

responsibilities under the SDWA, then that should be stated and these techniques 

should be required. The text could say something about encouraging 

technological progress in the hopes of coming up with less costly but equally 

effective monitoring technologies, but it does not seem appropriate to try and 
justify some actions by alluding to cost benefit analyses as the basis for 

decision making. 

Response: EPA does not believe that prescribing specific technologies to be used in all cases for GS

would be appropriate given the variability in sites. Rather, EPA is developing guidance on testing

and monitoring to assist owners or operators and Directors in evaluating requirements under

§146.90, including proposed monitoring plans. The guidance describes available technologies and

recommended approaches for implementing a testing and monitoring plan, including pre-operational

geophysical logging and testing of injection wells, MITs, injection well testing during operation,

groundwater quality monitoring, tracking the CO2 plume and pressure front, and soil gas and

surface air monitoring which may be required by the UIC Director for specific GS projects. The

guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

EPA clarifies that cost-benefit analyses are not required to be done under the SDWA to determine

the most appropriate monitoring technologies, location, or frequency. Instead, the Agency believes

that the flexibility afforded the owner or operator at §146.90 to develop a testing and monitoring

plan tailored to site-specific characteristics is appropriate for GS. EPA estimated the costs of

monitoring GS sites as part of the GS rulemaking effort, and estimates that the Class VI

requirements will result in additional costs. The cost analysis for the final GS rulemaking (which is

available in the docket) shows an approximate increase of 30 percent in comparison to Class I wells.

Commenter Name: James Devine Letter ID: 0166

Commenter Organization: United States Geological Survey (USGS) Comment ID: 21351

Other EPA Comment Codes and Descriptions: 4600 2.6 Proposed Plume and Pressure Front

Monitoring Requirements (40 CFR 146.90) 

Comment: Section 146.90 (g), Testing and Monitoring Requirements, FR page 43540 

This section requires the owneror operator "to track the extent ofthe carbon 

dioxide plume and the position ofthe pressure front" by direct or indirect 

monitoring. Indirect, geophysical techniques include, for example, seismic, 

electrical, gravity, or electromagnetic surveys.. ." It is unclear if surface 

deformation measurement techniques, such as repeat topographic 

surveys,satellite-based elevation measurements, and tiltmeters, are included as 

acceptable indirect monitoring techniques. Surface deformation techniques are in 

use, for example, at In Salah, Algeria (Onuma et al., 2008, abstract, Detection 

of surface deformation related with CO2 injection by DInSAR at In Salah, 

Algeria, Proceedings of 33rd International Geological Congress, Oslo, Norway). 

It is suggested that the proposed regulations allow for techniques beyond the 

realm of"traditional" geophysics and techniques not yet developed. 

Response: The final rule, at §146.90(g), requires owners or operators to perform monitoring to track

the extent of the CO2 plume and pressure front. The owner or operator must use direct methods to

monitor for pressure changes in the injection zone. Indirect methods (e.g., seismic, electrical, gravity,

or electromagnetic surveys and/or down-hole CO2 detection tools) are required unless the Director

determines, based on site-specific geology that such methods are not appropriate. EPA is affording

Director's discretion regarding the use of geophysical techniques at some sites because the Agency

recognizes that geophysical methods are not appropriate in all geologic settings. EPA clarifies that

this determination will be made by the Director based on the site-specific geologic information
submitted by the owner or operator with the permit application. 

EPA is not prescribing that deformation measurement techniques be used. However, if the owner or

operator believes they would enhance the monitoring regime, they may be proposed in the testing

and monitoring plan. Likewise, if the Director had reason to believe such methods are necessary to

ensure protection of USDWs, he/she is afforded discretion to require the use of additional

monitoring techniques at §146.90(i). 

EPA believes that this approach provides flexibility to develop a site-specific monitoring plan,

ensures that direct monitoring is available to track the movement of the CO2 and validate models,

and recognizes that indirect techniques are not appropriate in all situations. The owner or operator's

approved testing and monitoring plan will include the site-specific details, technologies, testing and

monitoring frequencies, and other pertinent information.

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil gas and surface air monitoring which may be required by the UIC Director

for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm. In addition, in January 2009,

DOE published a best practices manual entitled "Monitoring, Verification, and Accounting of CO2

Stored in Deep Geologic Formations" (DOE/NETL-311/081508); this manual is included in the

docket for the final GS rule.

Commenter Name: Michael J. Miller Letter ID: 0168

Commenter Organization: Electric Power Research Institute (EPRI) Comment ID: 22507

Comment: Preamble, page 43514 & 43515: "Under today’s proposal, owners or operators 

would be required to track the subsurface extent of the CO2 plume and pressure 

front using pressure gauges in the first formation overlying the confining zone 

or using indirect geophysical techniques (e.g., seismic, electrical, gravity, or 

electromagnetic surveys) or other down-hole CO2 detection tools, monitor for 

geochemical changes in subsurface formations, and if directed, monitor at the 

surface. Today’s proposal would also require owners or operators to monitor 

ground water quality and geochemical changes above the confining system." 

EPRI COMMENT #13: Refer to EPRI comment #2 for questions regarding how EPA 

intends to define each front and the need to demonstrate containment instead. 

Also, EPRI comments #3B and #14 for representative geochemical sampling and 

sampling of low-yield formations, respectively. 

EPRI is not aware of any remote field measurements, including seismic 

techniques, that can be used to determine the position of the dissolved CO2 

front. Therefore, definition of the CO2 front should be limited to the leading 

edge of the free-CO2 plume if remote monitoring techniques are used. Remote 

monitoring techniques may not work in all geologic settings. Very small pressure 

changes measured in the first formation overlying the confining zone may be 

masked by other pressure effects. For example, relatively large barometric 
pressure fluctuations translated down the well to the monitoring zone, changes 

in fluid pressure caused by nearby pumping wells, or limited transducer 

resolution, accuracy and electronic noise may interfere with or distort the 

pressure signal, making it difficult to measure the pressure front. 

Appropriateness of detection tools will need to be evaluated on a site-by-site 

basis, and the proposed rule recognizes this need. However, EPRI believes the 

emphasis should be on demonstrating containment through careful characterization 

of the storage reservoir and caprock, coupled with predictive CO2 fate and 

transport models of reservoir and caprock performance, rather than on plume and 

pressure front tracking, as the latter may not be practical or possible. 

Response: In response to comments regarding the pressure front at GS sites, EPA clarifies that the

pressure front (defined at §146.81) is the zone of elevated pressure that is created by the injection of

CO2 into the subsurface. The pressure front of a CO2 plume refers to a zone where there is a

pressure differential sufficient to cause the movement of injected fluids or formation fluids into a

USDW. The pressure front includes all areas wherein pressure is great enough to cause fluid

movement into a USDW if a conduit were to exist. The calculation of the threshold pressure that

defines the edge of the pressure front is dependent on properties of the injection and confining zones,

including permeability, porosity, and compressibility, the distance between the injection zone and the

lowermost USDW, and operational conditions including injection pressure and rate. For these

reasons, the definition of the pressure front is site- and project-specific, and a single pressure value

can not be provided for all sites.

EPA has revised the final rule, at §146.90(g), to require owners or operators to perform monitoring

to track the extent of the CO2 plume and pressure front. The owner or operator must use direct

methods to monitor for pressure changes in the injection zone. Indirect methods (e.g., seismic,

electrical, gravity, or electromagnetic surveys and/or down-hole CO2 detection tools) are required

unless the Director determines, based on site-specific geology that such methods are not appropriate. 

EPA believes that pressure monitoring in the injection zone is necessary to track the development

and movement of the pressure front and CO2 plume. Monitoring can also identify needed remedial

actions, provide inputs for AoR reevaluation modeling, evaluate predictions of plume movement,

and target additional geochemical and surface monitoring needs. Knowledge of the location of the

CO2 plume and the associated pressure front will assure the public that GS projects are proceeding

according to plan, provide sufficient information to the owner or operator and Director, or allow for

appropriate actions to address any indication that USDWs may be endangered. 

EPA is affording Director's discretion regarding the use of geophysical techniques at some sites

because the Agency recognizes that geophysical methods are not appropriate in all geologic settings.

For example, geophysical methods are difficult to execute in areas that are structurally and

topographically complex or where lithologies have limited contrast in density, porosity,

permeability, and other physical properties. EPA clarifies that this determination will be made by the

Director based on the site-specific geologic information submitted by the owner or operator with

their permit application.

Commenter Name: Kyle Isakower Letter ID: 0170

Commenter Organization: American Petroleum Institute Comment ID: 24249

Other EPA Comment Codes and Descriptions: 4650 2.6.5 CO2 plume and pressure front tracking

(seeking comment) 
Comment: Rule Provisions: 146.90(g) 

EPA Preamble Question: 32. Based on information evaluated to date, EPA believes 

that tracking the plume and pressure front is an important companion step to 

address any uncertainties associated with initial AoR modeling and requests 

comment on this approach and more efficient alternatives that may be used to 

track the plume and pressure front. EPA Notice 43516. 

API Response: Based on experience to date, CO2 plume can be monitored using 

surface or wellbore seismic and possibly some remote satellite techniques. 

Monitoring of the pressure front will be more difficult since that requires data 

from the injection formation that can only be obtained by drilling a well (which 

introduces additional artificial penetrations into the containment system). 

Modeling can estimate the movement of a pressure front. Those estimations are 

limited by the accuracy of the model and its iterative adjustments as previously 

mentioned. 

EPA should note that plume and pressure front are different concepts and should 

not be confused. They yield information on two different metrics. One tells you 

about the remaining capacity of the storage formation and the other describes 

the direction and movement of the CO2 plume. 

Response: EPA believes that direct pressure measurements are appropriate and that direct pressure

monitoring will be feasible at all GS sites. The final rule (at §146.90(g)) requires owners or operators

to perform monitoring to track the extent of the CO2 plume and pressure front. The owner or

operator must use direct methods to monitor for pressure changes in the injection zone. Indirect

methods (e.g., seismic, electrical, gravity, or electromagnetic surveys and/or down-hole CO2

detection tools) are also required unless the Director determines, based on site-specific geology, that

such methods are not appropriate. 

EPA believes that pressure monitoring in the injection zone is necessary to track the development

and movement of the pressure front and CO2 plume. Monitoring can also identify needed remedial

actions, provide inputs for AoR reevaluation modeling, evaluate predictions of plume movement,

and target additional geochemical and surface monitoring needs. Knowledge of the location of the

CO2 plume and the associated pressure front will assure the public that GS projects are proceeding

according to plan, provide sufficient information to the owner or operator and Director, or allow for

appropriate actions to address any indication that USDWs may be endangered.

EPA agrees that geophysical (e.g., seismic) methods are useful for plume tracking at GS sites.

Remote sensing methods (e.g., PSInSAR) may also prove to be useful. Such methods may be an

important component of plume tracking at some GS sites. For this reason, the final rule (at

§146.90(g)) requires the use of indirect methods (e.g., seismic, electrical, gravity, or electromagnetic

surveys and/or down-hole CO2 detection tools) unless the Director determines, based on site-specific

geology, that such methods are not appropriate.

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, which will include discussion of identifying the extent of the

CO2 plume and pressure front. The guidance describes available technologies and recommended

approaches for implementing a testing and monitoring plan, including pre-operational geophysical

logging and testing of injection wells, MITs, injection well testing during operation, groundwater

quality monitoring, tracking the CO2 plume and pressure front, and soil gas and surface air
monitoring which may be required by the UIC Director for specific GS projects. The guidance can

be found on EPA’s website at http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm. In

addition, in January 2009, DOE published a best practices manual entitled "Monitoring, Verification,

and Accounting of CO2 Stored in Deep Geologic Formations" (DOE/NETL-311/081508); this

manual is included in the docket for the for the final GS rule.

Commenter Name: Thomas Curtis Letter ID: 0181

Commenter Organization: American Water Works Association (AWWA) Comment ID: 23744

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Part 146.90(g) AWWA recommends revising this part to read: 

Testing and monitoring to track the extent of the carbon dioxide plume and the 

position of the pressure front by either monitoring for pressure changes in the 

confining zone, in the first formation overlying the confining zone or using 

indirect, geophysical techniques (e.g., seismic, electrical, gravity, or 

electromagnetic surveys and/or down-hole carbon dioxide detection tools); 

Response: EPA has revised the final GS regulation, at §146.90(g)(1), to require all GS project

owners or operators to monitor for pressure changes in the injection zone. EPA believes that pressure

monitoring in the injection zone is necessary to track the development and movement of the pressure

front and CO2 plume. Pressure monitoring within the injection zone is necessary because any such

monitoring above the confining zone would not detect movement of the pressure front unless a

breach of the confining zone occurs. EPA believes that monitoring using wells in the injection zone

(i.e., that penetrate the confining zone) can be safely performed if the wells are constructed to

prevent flow between the injection zone and USDWs or other layers above the confining zone. Such

construction technologies exist and have been used in the oil and gas industry for years. EPA

believes that the benefits of monitoring in the injection formation outweigh the manageable risk of

those monitoring wells serving as conduits for fluid movement. EPA adds that owners or operators

may consider and Directors may require performing additional pressure monitoring in wells that are

above the confining zone (e.g., in the same wells used to perform ground water quality monitoring

required at §146.90(d)) to provide additional verification that no pressure changes are occurring

above the confining zone due to CO2 leakage. Monitoring also identifies needed remedial actions,

provides inputs for AoR reevaluation modeling, and targets additional geochemical and surface

monitoring needs. Knowledge of the location of the CO2 plume and the associated pressure front

will assure the public that GS projects are proceeding according to plan, provide sufficient

information to the owner or operator and Director, or allow for appropriate actions to address any

indication that USDWs may be endangered.

In addition, §146.90(g)(2) requires owners or operators to track the position of the CO2 plume using

indirect methods (e.g., seismic, electrical, gravity, or electromagnetic surveys and/or down-hole CO2

detection tools), unless the Director determines based on site-specific geology, that such methods are

not appropriate. 

EPA acknowledges that, at certain sites, there may be a need for more or different monitoring

schemes (which may include monitoring in the confining zone), and adds that it is important to

balance the need for adequate monitoring that ensures USDW protection from endangerment against

too many artificial penetrations which could serve as conduits for fluid migration. Site-specific

testing and monitoring plans must describe the proposed monitoring regime, which must be
approved by the Director.

Flexibility is also provided regarding how to monitor for the specific data required by the final rule.

The testing and monitoring plan is developed by the owner or operator in consultation with the

Director and is designed to ensure that a detailed, Director-approved document describing how

monitoring will be conducted during the lifetime of the project exists. 

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil gas and surface air monitoring which may be required by the UIC Director

for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Bradley J. Field Letter ID: 0186

Commenter Organization: New York State Dept. of Environmental Conservation

Div. of Mineral Resources

Comment ID:

25203

Comment: EE. Based on information evaluated to date, EPA believes that tracking the plume 

and pressure front is an important companion step to address any uncertainties 

associated with initial AoR modeling and requests comment on this approach and 

more efficient alternatives that may be used to track the plume and pressure 

front. 

NYSDEC-DMN Response: NYSDEC-DMN agrees that tracking of the CO2 plume and 

pressure front is important and should be required. However, the exact 

methodology should not be specified but determined on a site-specific basis. 

NYSDEC-DMN also agrees with EPA’s statement "As such, allowing flexibility in 

choosing the plume tracking methods and other monitoring technologies may 

provide an appropriate balance between the protective nature of indirect 

monitoring and cost considerations, as well as allowing for the adoption of 

continuously advancing technology." 

Response: EPA agrees with commenters that an effective monitoring plan will need to consider sitespecific conditions. The final rule (at §146.90(g)) requires owners or operators to perform monitoring

to track the extent of the CO2 plume and pressure front. The owner or operator must use direct

methods to monitor for pressure changes in the injection zone. Indirect methods (e.g., seismic,

electrical, gravity, or electromagnetic surveys and/or down-hole CO2 detection tools) are required

unless the Director determines, based on site-specific geology that such methods are not appropriate. 

EPA believes that this approach provides flexibility to develop a site-specific monitoring plan,

ensures that direct monitoring is available to track movement of the CO2 and validate models, and

recognizes that indirect techniques are not appropriate in all situations. The owner or operator's

approved testing and monitoring plan will include the site-specific details, technologies, testing and

monitoring frequencies, and other pertinent information.

EPA believes that pressure monitoring in the injection zone is necessary to track the development

and movement of the pressure front and CO2 plume, and, for this reason, all GS well owners or

operators must use direct methods to monitor for pressure changes in the injection zone, as required
at §146.90(g)(1). 

EPA is affording Director's discretion regarding the use of geophysical techniques at some sites

because the Agency recognizes that geophysical methods are not appropriate in all geologic settings.

For example, geophysical methods are difficult to execute in areas that are structurally and

topographically complex or where lithologies have limited contrast in density, porosity,

permeability, and other physical properties. EPA clarifies that this determination will be made by the

Director based on the site-specific geologic information submitted by the owner or operator with the

permit application.

Commenter Name: Bradley J. Field Letter ID: 0186

Commenter Organization: New York State Dept. of Environmental Conservation

Div. of Mineral Resources

Comment ID:

25205

Other EPA Comment Codes and Descriptions: 4760 2.7.6 Proposed reporting frequency (seeking

comment) 

Comment: GG. Specifically, EPA seeks comment regarding the usefulness of indirect 

geophysical monitoring and surface air and soil gas monitoring. 

NYSDEC-DMN Response: NYSDEC-DMN agrees with EPA’s proposal to require operators 

to report semi- annually on the characteristics of injection fluids, injection 

pressure, flow rate, temperature, volume and annular pressure, and on the 

results of MITs, ground water monitoring, and any required atmospheric/soil gas 

monitoring. However, the amount and types of monitoring that are required should 

be site specific. Certain geophysical monitoring techniques that successfully 

monitor plume migration in the southern states may not have any monitoring 

capability in northern Paleozoic basins. 

Response: EPA agrees with commenters and believes that flexibility is important in developing and

implementing a monitoring plan that is appropriately tailored for a specific GS site. The purpose of

the requirement at §146.90 to develop site-specific testing and monitoring plans is to ensure that the

monitoring performed at a site is appropriate for site operational conditions and the geologic setting.

EPA believes that this is the best approach for addressing potential risks at GS sites. These flexible

provisions in the monitoring requirements for Class VI wells enable the owner or operator to tailor

monitoring programs to the specific needs of each project in consultation with the Director.

EPA clarifies that the final rule, at §146.90(g)(2), requires owners or operators to track the position

of the CO2 plume using indirect methods (e.g., seismic, electrical, gravity, or electromagnetic

surveys and/or down-hole CO2 detection tools), unless the Director determines based on site-specific

geology, that such methods are not appropriate. EPA is affording Director's discretion regarding the

use of geophysical techniques at some sites because the Agency recognizes that geophysical methods

are not appropriate in all geologic settings. For example, geophysical methods are difficult to execute

in areas that are structurally and topographically complex or where lithologies have limited contrast

in density, porosity, permeability, and other physical properties. EPA clarifies that this determination

will be made by the Director based on the site-specific geologic information submitted by the owner

or operator with their permit application. 

EPA believes that this approach provides flexibility to develop a site-specific monitoring plan,

ensures that direct monitoring is available to track the movement of the CO2 and validate models,

and recognizes that indirect techniques are not appropriate in all situations. The owner or operator's
approved testing and monitoring plan must include the site-specific details, technologies, testing and

monitoring frequencies, and other pertinent information.

As described above EPA is retaining the requirement at §146.91(a) for semi-annual reporting of

monitoring and operational data. For additional information, please see the final rule and the

preamble for a discussion of EPA's final approach to recordkeeping and reporting.

Commenter Name: Robert F. Van Voorhees Letter ID: 0190

Commenter Organization: Carbon Sequestration Council Comment ID: 24357

Comment: b. Geophysical Methods for Plume Tracking 

As an alternative to monitor wells, the proposed rule suggests that it may be 

possible to use remote geophysical techniques for "plume tracking." 73 Fed. Reg. 

at 43515. Unfortunately, the technologies available would be very expensive to 

employ on the scale required. Seeking to achieve greater precision can lead to 

an expensive and unnecessary quest. 

Response: The final rule at §146.90(g) requires owners or operators to perform monitoring to track

the extent of the CO2 plume and pressure front. The owner or operator must use direct methods to

monitor for pressure changes in the injection zone. Indirect methods (e.g., seismic, electrical, gravity,

or electromagnetic surveys and/or down-hole CO2 detection tools) are required unless the Director

determines, based on site-specific geology, that such methods are not appropriate.

EPA believes that pressure monitoring in the injection zone is necessary to track the development

and movement of the pressure front and CO2 plume. Monitoring can also identify needed remedial

actions, provide inputs for AoR reevaluation modeling, evaluate predictions of plume movement,

and target additional geochemical and surface monitoring needs. Knowledge of the location of the

CO2 plume and the associated pressure front will also assure the public that GS projects are

proceeding according to plan, provide sufficient information to the owner or operator and Director,

or allow for appropriate actions to address any indication that USDWs may be endangered. 

EPA is affording Director's discretion regarding the use of geophysical techniques at some sites

because the Agency recognizes that geophysical methods are not appropriate in all geologic settings.

For example, geophysical methods are difficult to execute in areas that are structurally and

topographically complex or where lithologies have limited contrast in density, porosity,

permeability, and other physical properties. EPA clarifies that this determination must be made by

the Director based on the site-specific geologic information submitted by the owner or operator with

their permit application. 

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil, gas, and surface air monitoring which may be required by the UIC Director

for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.
Commenter Name: Robert F. Van Voorhees Letter ID: 0190

Commenter Organization: Carbon Sequestration Council Comment ID: 24541

Other EPA Comment Codes and Descriptions: 4650 2.6.5 CO2 plume and pressure front tracking

(seeking comment) 

Comment: Rule Provisions or Federal Register Cite: 146.90(g) 

EPA Preamble Question: 32. Based on information evaluated to date, EPA believes 

that tracking the plume and pressure front is an important companion step to 

address any uncertainties associated with initial AoR modeling and requests 

comment on this approach and more efficient alternatives that may be used to 

track the plume and pressure front. EPA Notice 43516. 

CSC Response: Uncertainties associated with AoR determinations may be addressed 

through the use of a conservative modeling approach. Requirements to "track" 

plumes or pressure fronts would be extraordinarily burdensome and are not 

necessary, as extensive experience with "no migration" exemptions for hazardous 

waste injection wells has shown. 

Response: EPA disagrees that plume and pressure front monitoring are not justified for Class VI

wells. The Agency recognizes that while there are similarities between injection of hazardous wastes

for disposal (Class I) and GS (Class VI), there are significant differences as well. Important unique

considerations for GS include the buoyancy of CO2, its corrosivity when in contact with water, its

low viscosity (i.e., high mobility), and the very large injection volumes that are anticipated. There is

also a degree of uncertainty regarding the behavior of large volumes of CO2 in the subsurface after

injection. Given these characteristics of anticipated GS projects, EPA believes that plume and

pressure front monitoring at §146.90(g) are justified to provide early warning of any unforeseen

fluid movement that might endanger USDWs. 

The final rule (at §146.90(g)) requires owners or operators to perform monitoring to track the extent

of the CO2 plume and pressure front. The owner or operator must use direct methods to monitor for

pressure changes in the injection zone. Indirect methods (e.g., seismic, electrical, gravity, or

electromagnetic surveys and/or down-hole CO2 detection tools) are also required unless the Director

determines, based on site-specific geology that such methods are not appropriate.

EPA believes that pressure monitoring in the injection zone is necessary to track the development

and movement of the pressure front and CO2 plume. Monitoring can also identify needed remedial

actions, provide inputs for AoR reevaluation modeling, evaluate predictions of plume movement,

and target additional geochemical and surface monitoring needs. Knowledge of the location of the

CO2 plume and the associated pressure front will also assure the public that GS projects are

proceeding according to plan, provide sufficient information to the owner or operator and Director,

or allow for appropriate actions to address any indication that USDWs may be endangered.

Commenter Name: Craig R. Walters Letter ID: 0200

Commenter Organization: Anadarko Petroleum Corporation Comment ID: 24602

Other EPA Comment Codes and Descriptions: 4650 2.6.5 CO2 plume and pressure front tracking

(seeking comment) 

Comment: Rule Provisions: 146.90(g) 

EPA Rule Issue: 32. Based on information evaluated to date, EPA believes that 

tracking the plume and pressure front is an important companion step to address 

any uncertainties associated with initial AoR modeling and requests comment on 
this approach and more efficient alternatives that may be used to track the 

plume and pressure front. EPA Notice 43516. 

Anadarko Petroleum Corporation (APC) Response: Plume and pressure front are 

different concepts and should not be confused. They yield information on two 

different metrics. The former tells you about the remaining capacity of the 

storage formation and the latter describes the direction and movement of the CO2 

plume. Based on experience to date, CO2 plume can be monitored using surface or 

wellbore seismic and possibly some remote satellite techniques. Monitoring of 

the pressure front will be more difficult since that requires data from the 

injection formation which can only be obtained by drilling a well. Modeling can 

estimate the movement of a pressure front. Those estimations are limited by the 

accuracy of the model and its iterative adjustments as previously mentioned. 

Response: EPA acknowledges that monitoring the plume and pressure front are different issues and

believes that direct pressure measurements are appropriate and that direct pressure monitoring will

be feasible at all GS sites. The final rule (at §146.90(g)) requires owners or operators to perform

monitoring to track the extent of the CO2 plume and pressure front. The owner or operator must use

direct methods to monitor for pressure changes in the injection zone. Indirect methods (e.g., seismic,

electrical, gravity, or electromagnetic surveys and/or down-hole CO2 detection tools) are also

required unless the Director determines, based on site-specific geology, that such methods are not

appropriate. 

EPA believes that pressure monitoring in the injection zone is necessary to track the development

and movement of the pressure front and CO2 plume. Monitoring can also identify needed remedial

actions, provide inputs for AoR reevaluation modeling, evaluate predictions of plume movement,

and target additional geochemical and surface monitoring needs. Knowledge of the location of the

CO2 plume and the associated pressure front will assure the public that GS projects are proceeding

according to plan, provide sufficient information to the owner or operator and Director, or allow for

appropriate actions to address any indication that USDWs may be endangered.

Commenter Name: John King Letter ID: 0211

Commenter Organization: Shell Exploration and Production Company

(SEPCo)

Comment ID:

22780

Comment: b. Geophysical Methods for Plume Tracking 

As an alternative to monitor wells, the proposed rule suggests that it may be 

possible to use remote geophysical techniques for "plume tracking." 73 Fed. Reg. 

at 43515. Unfortunately, it is not clear that there are established technologies 

available that are sufficiently reliable and mature in their development for 

application in a regulatory context. In general, the technologies available 

would be very expensive to employ on the scale required, and provide inferential 

data that is subject to considerable interpretation. Such techniques are 

unsuitable for required use in a regulatory context. 

The problem with interpretive tests is that they are interpretive and therefore 

inherently subject to uncertainties. The suggestion that such techniques could 

be used for "plume tracking" to "verify" the results of modeling is optimistic 

at best, and creates unrealistic expectations for the technologies involved. In 
fact, the use of such techniques may do more to amplify residual uncertainties 

and thereby undermine public confidence in GS. 

Response: The final rule (at §146.90(g)) requires owners or operators to perform monitoring to track

the extent of the CO2 plume and pressure front. The owner or operator must use direct methods to

monitor for pressure changes in the injection zone. Indirect methods (e.g., seismic, electrical, gravity,

or electromagnetic surveys and/or down-hole CO2 detection tools) are also required unless the

Director determines, based on site-specific geology, that such methods are not appropriate.

EPA is affording Director's discretion regarding the use of geophysical techniques at some sites

because the Agency recognizes that geophysical methods are not appropriate in all geologic settings.

For example, geophysical methods are difficult to execute in areas that are structurally and

topographically complex or where lithologies have limited contrast in density, porosity,

permeability, and other physical properties. EPA clarifies that this determination must be made by

the Director based on the site-specific geologic information submitted by the owner or operator with

their permit application. 

There may also be interference from urban and residential infrastructure, and sites with loose

materials such as glacial deposits may produce poor or inaccurate seismic images. But the laterally

continuous, confined formations that make many sites appropriate for GS will also render many of

them suitable for seismic surveying. In fact, seismic and other geophysical and remote sensing

methods have been used with success at GS pilot projects and are likely to be useful for plume

tracking at many GS sites. StatOilHydro has used both time-lapse seismic and gravity methods to

track the CO2 plume at the Sleipner site. Seismic surveys have also been used successfully at the

Weyburn pilot project site in Saskatchewan. Although resolution on seismic surveys is generally

accepted to be the best of the geophysical methods, gravity monitoring at Sleipner has also imaged

the plume, and results have agreed with seismic surveys. At InSalah, PSInSAR satellite monitoring

has been used in combination with tiltmeter data and was able to detect otherwise imperceptible

ground displacement (i.e., at the millimeter scale) that indicates the presence of CO2.

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil gas and surface air monitoring which may be required by the UIC Director

for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

EPA disagrees that monitoring at GS sites will undermine public confidence in GS and the UIC

Program. EPA believes that appropriately designed and implemented monitoring plans will increase

public confidence in the safety of GS, helping to assure the public that any problems are detected

early and that appropriate measures are taken to protect USDWs from endangerment. Knowledge of

the location of the CO2 plume and the associated pressure front will enable EPA to assure the public

that GS projects are proceeding according to plan, provide sufficient information to the owner or

operator and Director, or allow for appropriate actions to address any indication that USDWs may be

endangered.

Commenter Name: Tiffany Rau Letter ID: 0224
Commenter Organization: Hydrogen Energy International Comment ID: 21675

Other EPA Comment Codes and Descriptions: 1840 1.4.1.3 Other research 

Comment: HEI and its affiliated companies in BP have significant and highly relevant 

experience around monitoring of the subsurface and the surface. For many 

decades, BP has been effectively employing a number of monitoring technologies 

to ensure the safety and integrity of its customary oil and gas operations, 

including CO2 EOR-related operations since the 1970’s in West Texas and Alaska. 

Notably, since 2004 BP has been operating the In Salah, Algeria, CO2 storage 

project where BP (and partners) has been storing around 1 million tones CO2 per 

year in a deep saline formation close to a producing gas field. The In Salah CO2 

Storage project also incorporates a research project to test CO2 storage 

monitoring technologies with a program that is much more extensive than would be 

appropriate for a commercial project. At In Salah, BP is testing new 

technologies (such as satellite imagery and micro-seismic) and conventional 

oilfield technologies (such as tracers and conventional 3D seismic) to compare 

and contrast results as the partnership endeavors to design and develop 

monitoring technologies and methodologies that are reliable and cost-effective, 

given the expectation of future commercial application. 

Before initiating injection at In Salah, BP conducted a thorough assessment of 

potential leakage paths at the site; BP then tailored the monitoring program to 

address those site-specific risks. There are two other monitored, industrialscale CO2 injection projects in the world (at Sleipner and Weyburn) and the 

site-specific nature of monitoring requirements is demonstrated by comparing 

these three CO2 storage projects - monitoring that works well at one location 

may not work at all in another location. 

Response: EPA continues to track ongoing field and laboratory research into all aspects of GS,

including subsurface CO2 monitoring. The Agency is tracking the operations and technical

developments of more than three dozen small- and large-scale GS injection projects in the US and

abroad. Also, since field experience and well construction, injection, and monitoring information

relevant to GS comes from operations that inject acid gas or inject CO2 for ER, the Agency has

conducted evaluations regarding these commercial field operations and continues to track GSrelevant developments in these commercial operations.

Additionally, EPA ORD's National Center for Environmental Research (NCER) awarded six Science

To Achieve Results (STAR) grants in the Fall of 2009 to recipients from major universities and

institutions within the scope of "Integrated Design, Modeling and Monitoring of Geologic

Sequestration of Anthropogenic Carbon Dioxide to Safeguard Sources of Drinking Water." In one

project, the University of Texas at Austin will assess appropriate monitoring approaches at geologic

sequestration sites.

Regarding the development of monitoring and testing plans, EPA believes that testing and

monitoring plans should be based on site-specific information, similar to the examples described by

the commenter, and believes that flexibility is important in developing and implementing a

monitoring plan that is appropriately tailored for a specific GS site. The purpose of the requirement

at §146.90 to develop site-specific testing and monitoring plans is to ensure that the monitoring

performed at a site is appropriate for site operational conditions and the geologic setting. EPA

believes that this is the best approach for addressing potential risks at GS sites. These flexible

provisions in the monitoring requirements for Class VI wells enable the owner or operator to tailor
monitoring programs to the specific needs of each project in consultation with the Director.

The final regulation provides for flexibility in: 1) methodologies used to collect these data, 2) the

spatial resolution at which the data should be collected, and 3) how often the data should be

collected. The number and placement of monitoring wells will be based on site-specific information

such as the calculated AoR, injection rate and volume, site geology, baseline data, and the presence

of artificial penetrations within the AoR. In some instances, there may be a limited number of

options for complying with EPA's minimum requirements. For example, monitoring for geochemical

changes will require use of monitoring wells and collection of groundwater samples for chemical

analysis. Many options currently exist for complying with other requirements, such as tracking the

position of the plume and pressure front within the injection zone.

Flexibility is also provided regarding how to monitor for the specific data required by the final rule.

The testing and monitoring plan is developed by the owner or operator in consultation with the

Director and is designed to ensure that a detailed, Director-approved document describing how

monitoring will be conducted during the lifetime of the project exists. EPA is developing guidance

on testing and monitoring to assist owners or operators and Directors in evaluating requirements

under §146.90, including proposed monitoring plans. The guidance describes available technologies

and recommended approaches for implementing a testing and monitoring plan, including preoperational geophysical logging and testing of injection wells, MITs, injection well testing during

operation, groundwater quality monitoring, tracking the CO2 plume and pressure front, and soil gas

and surface air monitoring which may be required by the UIC Director for specific GS projects. The

guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Brian Williams Letter ID: 0225

Commenter Organization: BP Alternative Energy North America, Inc. (BP) Comment ID: 21720

Other EPA Comment Codes and Descriptions: 1840 1.4.1.3 Other research 

Comment: BP has significant and highly relevant experience around monitoring of the 

subsurface and the surface. For many decades, BP has been effectively employing 

a number of monitoring technologies to ensure the safety and integrity of its 

customary oil and gas operations, including CO2 EOR-related operations since the 

1970’s in West Texas and Alaska. Notably, since 2004 BP has been operating the 

In Salah, Algeria, CO2 storage project where BP (and partners) has been storing 

around 1 million tones CO2 per year in a deep saline formation close to a 

producing gas field. The In Salah CO2 Storage project also incorporates a 

research project to test CO2 storage monitoring technologies with a program that 

is much more extensive than would be appropriate for a commercial project. At In 

Salah, BP is testing new technologies (such as satellite imagery and microseismic) and conventional oilfield technologies (such as tracers and 

conventional 3D seismic) to compare and contrast results as the partnership 

endeavors to design and develop monitoring technologies and methodologies that 

are reliable and cost-effective, given the expectation of future commercial 

application. 

Before initiating injection at In Salah, BP conducted a thorough assessment of 

potential leakage paths at the site; BP then tailored the monitoring program to 

address those site-specific risks. There are two other monitored, industrialscale CO2 injection projects in the world (at Sleipner and Weyburn) and the 
site-specific nature of monitoring requirements is demonstrated by comparing 

these three CO2 storage projects - monitoring that works well at one location 

may not work at all in another location. 

Response: EPA continues to track ongoing field and laboratory research into all aspects of GS,

including subsurface CO2 monitoring. The Agency is tracking the operations and technical

developments of more than three dozen small- and large-scale GS injection projects in the US and

abroad. Also, since field experience and well construction, injection, and monitoring information

relevant to GS comes from operations that inject acid gas or inject CO2 for ER, the Agency has

conducted evaluations regarding these commercial field operations and continues to track GSrelevant developments in these commercial operations.

Additionally, EPA ORD's National Center for Environmental Research (NCER) awarded six Science

To Achieve Results (STAR) grants in the Fall of 2009 to recipients from major universities and

institutions within the scope of "Integrated Design, Modeling and Monitoring of Geologic

Sequestration of Anthropogenic Carbon Dioxide to Safeguard Sources of Drinking Water." In one

project, the University of Texas at Austin will assess appropriate monitoring approaches at geologic

sequestration sites.

Regarding the development of monitoring and testing plans, EPA believes that testing and

monitoring plans should be based on site-specific information, and believes that flexibility is

important in developing and implementing a monitoring plan that is appropriately tailored for a

specific GS site. The purpose of the requirement at §146.90 to develop site-specific testing and

monitoring plans is to ensure that the monitoring performed at a site is appropriate for site

operational conditions and the geologic setting. EPA believes that this is the best approach for

addressing potential risks at GS sites. These flexible provisions in the monitoring requirements for

Class VI wells enable the owner or operator to tailor monitoring programs to the specific needs of

each project in consultation with the Director.

The final regulation provides for flexibility in: 1) methodologies used to collect these data, 2) the

spatial resolution at which the data should be collected, and 3) how often the data should be

collected. The number and placement of monitoring wells will be based on site-specific information

such as the calculated AoR, injection rate and volume, site geology, baseline data, and the presence

of artificial penetrations within the AoR. In some instances, there may be a limited number of

options for complying with EPA's minimum requirements. For example, monitoring for geochemical

changes will require use of monitoring wells and collection of groundwater samples for chemical

analysis. Many options currently exist for complying with other requirements, such as tracking the

position of the plume and pressure front within the injection zone.

Flexibility is also provided regarding how to monitor for the specific data required by the final rule.

The testing and monitoring plan is developed by the owner or operator in consultation with the

Director and is designed to ensure that a detailed, Director-approved document describing how

monitoring will be conducted during the lifetime of the project exists. EPA is developing guidance

on testing and monitoring to assist owners or operators and Directors in evaluating requirements

under §146.90, including proposed monitoring plans. The guidance describes available technologies

and recommended approaches for implementing a testing and monitoring plan, including preoperational geophysical logging and testing of injection wells, MITs, injection well testing during

operation, groundwater quality monitoring, tracking the CO2 plume and pressure front, and soil gas

and surface air monitoring which may be required by the UIC Director for specific GS projects. The

guidance can be found on EPA’s website at
http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Neeraj Gupta Letter ID: 0229

Commenter Organization: Battelle Energy Technology (BET) Comment ID: 21860

Comment: Page 108, Seismic Monitoring- Seismic and other indirect geophysical monitoring 

has been used to evaluate CO2 movement at some sites. However, it is also well 

known that all of these options (threedimensional, cross well, vertical seismic 

profile etc) may not work in every settings where rocks are too thin, have 

unsuitable sonic properties, and/or there is too much surface infrastructure or 

overburden present. Therefore, these options should be required only based on 

their feasibility at individual locations. In addition, these technologies may 

be fairly cost prohibitive on a routine basis. Finally, it must be recognized 

that none of these technologies can provide a complete mass balance or 

accounting to CO2 movement in subsurface. 

Response: EPA agrees that seismic monitoring may not be applicable or appropriate for all sites.

The final rule (at §146.90(g)) requires owners or operators to perform monitoring to track the extent

of the CO2 plume and pressure front. The owner or operator must use direct methods to monitor for

pressure changes in the injection zone. Indirect methods (e.g., seismic, electrical, gravity, or

electromagnetic surveys and/or down-hole CO2 detection tools) are also required unless the Director

determines, based on site-specific geology, that such methods are not appropriate.

EPA is affording Director's discretion regarding the use of geophysical techniques at some sites

because the Agency recognizes that geophysical methods are not appropriate in all geologic settings.

For example, geophysical methods are difficult to execute in areas that are structurally and

topographically complex or where lithologies have limited contrast in density, porosity,

permeability, and other physical properties. EPA clarifies that this determination will be made by the

Director based on the site-specific geologic information submitted by the owner or operator with

their permit application. 

There may also be interference from urban and residential infrastructure, and sites with loose

materials such as glacial deposits may produce poor or inaccurate seismic images. But the laterally

continuous, confined formations that that make many sites appropriate for GS will also render many

of them suitable for seismic surveying. In fact, seismic and other geophysical and remote sensing

methods have been used with success at GS pilot projects and are likely to be useful for plume

tracking at many GS sites. StatOilHydro has used both time-lapse seismic and gravity methods to

track the CO2 plume at the Sleipner site. Seismic surveys have also been used successfully at the

Weyburn pilot project site in Saskatchewan. Although resolution on seismic surveys is generally

accepted to be the best of the geophysical methods, gravity monitoring at Sleipner has also imaged

the plume, and results have agreed with seismic surveys. At InSalah, PSInSAR satellite monitoring

has been used in combination with tiltmeter data and was able to detect otherwise imperceptible

ground displacement (i.e., at the millimeter scale) that indicates the presence of CO2.

EPA acknowledges the commenters' concern about the cost of geophysical techniques. However,

EPA believes that tracking of the plume is essential for protection of USDWs from endangerment at

GS sites and that geophysical methods are necessary for such tracking. 

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance
describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil gas and surface air monitoring which may be required by the UIC Director

for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Kurt Waltzer Letter ID: 0250

Commenter Organization: Clean Air Task Force Comment ID: 22320

Comment: We also strongly support monitoring to track the CO2 plume. There is no unique 

method for doing this, and we do not believe that 4D-seismic techniques are 

appropriate or effective in all geologic settings, or that they should be made 

mandatory. However, tracking the extent of the CO2 plume is generally possible 

and must be part of a comprehensive and credible monitoring plan and a GS 

project. Appropriate limits of accuracy will be needed, as neither tracking 

individual CO2 molecules, nor to the nearest inch are feasible or desirable. 

However, the monitoring resolution must be such so as to enable confinement to 

be established, to give regulators confidence that the CO2 and displaced fluids 

are not near potential leakage pathways, and to warn in advance of any remedial 

action that might be needed. 

Response: EPA agrees that seismic monitoring may not be applicable or appropriate for all sites.

The final rule (at §146.90(g)) requires owners or operators to perform monitoring to track the extent

of the CO2 plume and pressure front. The owner or operator must use direct methods to monitor for

pressure changes in the injection zone. Indirect methods (e.g., seismic, electrical, gravity, or

electromagnetic surveys and/or down-hole CO2 detection tools) are also required unless the Director

determines, based on site-specific geology, that such methods are not appropriate.

EPA is affording Director's discretion regarding the use of geophysical techniques at some sites

because the Agency recognizes that geophysical methods are not appropriate in all geologic settings.

For example, geophysical methods are difficult to execute in areas that are structurally and

topographically complex or where lithologies have limited contrast in density, porosity,

permeability, and other physical properties. EPA clarifies that this determination will be made by the

Director based on the site-specific geologic information submitted by the owner or operator with

their permit application. 

There may also be interference from urban and residential infrastructure, and sites with loose

materials such as glacial deposits may produce poor or inaccurate seismic images. But the laterally

continuous, confined formations that that make many sites appropriate for GS will also render many

of them suitable for seismic surveying. In fact, seismic and other geophysical and remote sensing

methods have been used with success at GS pilot projects and are likely to be useful for plume

tracking at many GS sites. StatOilHydro has used both time-lapse seismic and gravity methods to

track the CO2 plume at the Sleipner site. Seismic surveys have also been used successfully at the

Weyburn pilot project site in Saskatchewan. Although resolution on seismic surveys is generally

accepted to be the best of the geophysical methods, gravity monitoring at Sleipner has also imaged

the plume, and results have agreed with seismic surveys. At InSalah, PSInSAR satellite monitoring

has been used in combination with tiltmeter data and was able to detect otherwise imperceptible

ground displacement (i.e., at the millimeter scale) that indicates the presence of CO2.
EPA acknowledges the commenters' concern about the cost of geophysical techniques. However,

EPA believes that tracking of the plume is essential for protection of USDWs from endangerment at

GS sites and that geophysical methods are necessary for such tracking. 

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil gas and surface air monitoring which may be required by the UIC Director

for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Michel Paque Letter ID: 0259

Commenter Organization: Ground Water Protection Council Comment ID: 24818

Comment: EPA Notice Questions: 73 FR 43517 

EPA Rule Issue: 33. EPA seeks comment on the appropriate amount and types of 

monitoring that should be conducted at a GS site. Specifically, EPA seeks 

comment regarding the usefulness of indirect geophysical monitoring and surface 

air and soil gas monitoring. In addition, EPA seeks comment regarding the use of 

a Director-approved monitoring plan for GS sites. EPA Notice 43517. 

GWPC CO2 Committee Response: Although actual monitoring of injection formation 

might be considered most effective you still have the potential problem of 

putting holes in the confining formation. Perhaps the use of seismic to place 

monitoring wells into the injection zone would be an appropriate approach. The 

number of monitoring wells should not be established in advance. Obviously the 

UIC program does not have complete control over monitoring well construction or 

operation or closure. With respect to soil and air monitoring there is a 

Response: The final rule (at §146.90(g)) requires owners or operators to perform monitoring to track

the extent of the CO2 plume and pressure front. The owner or operator must use direct methods to

monitor for pressure changes in the injection zone. Indirect methods (e.g., seismic, electrical, gravity,

or electromagnetic surveys and/or down-hole CO2 detection tools) are also required unless the

Director determines, based on site-specific geology, that such methods are not appropriate.

Pressure monitoring within the injection zone is necessary because any such monitoring above the

confining zone would not detect movement of the pressure front unless a breach of the confining

zone occurs. EPA believes that monitoring using wells in the injection zone (i.e., that penetrate the

confining zone) can be safely performed if the wells are constructed to prevent flow between the

injection zone and USDWs or other layers above the confining zone. Such construction technologies

exist and have been used in the oil and gas industry for years. EPA believes that the benefits of

monitoring in the injection formation outweigh the manageable risk of those monitoring wells

serving as conduits for fluid movement. EPA adds that owners or operators may consider performing

additional pressure monitoring in wells that are above the confining zone (e.g., in the same wells

used to perform ground water quality monitoring required at §146.90(d)) to provide additional

verification that no pressure changes are occurring above the confining zone due to CO2 leakage.

Monitoring also identifies needed remedial actions, provides inputs for AoR reevaluation modeling,
and targets additional geochemical and surface monitoring needs. Knowledge of the location of the

CO2 plume and the associated pressure front will assure the public that GS projects are proceeding

according to plan, provide sufficient information to the owner or operator and Director, or allow for

appropriate actions to address any indication that USDWs may be endangered.

EPA notes that plugging of monitoring wells must be addressed as part of the post-injection site care

and site closure plan required under §146.93. EPA is developing guidance on well construction that

will include recommendations for monitoring well construction. The guidance will be available on

EPA’s website at http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

EPA acknowledges that, at certain sites, there may be a need for more or different monitoring

schemes (which may include monitoring in the confining zone), and adds that it is important to

balance the need for adequate monitoring that ensures USDW protection from endangerment against

too many artificial penetrations which could serve as conduits for fluid migration. Site-specific

testing and monitoring plans should describe the proposed monitoring regime, including the number

and location of monitoring wells, which must be approved by the Director. 

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil gas and surface air monitoring which may be required by the UIC Director

for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm. In addition, in January 2009,

DOE published a best practices manual entitled "Monitoring, Verification, and Accounting of CO2

Stored in Deep Geologic Formations" (DOE/NETL-311/081508); this manual is included in the

docket for the final GS rule.

Commenter Name: Claire Olson Letter ID: 0260

Commenter Organization: Basin Electric Power Cooperative Comment ID: 22388

Comment: "3. Tracking the Results of CO2 GS Research Projects" 

The EPA states,"4-D seismic monitoring may be a valuable tool for CO2 plume 

tracking." The emphasis on "may be" reflects the fact that there are a variety 

of monitoring tools available and also a variety of site-specific geologic 

conditions thus the tools used to track the location of the CO2 plume should be 

flexible, and the regulations should reflect this flexibility in choosing 

methods. "4-D seismic monitoring" has been demonstrated as a research tool but 

may not be needed as a minimum operating tool. "4-D seismic monitoring" is an 

extremely expensive option. However, geochemical sampling methods and monitoring 

wells can be used to determine the distribution of CO2 within a reservoir and 

monitor for leakage. 

Response: EPA agrees that seismic monitoring is not applicable or appropriate for all sites. The final

rule (at §146.90(g)) requires owners or operators to perform monitoring to track the extent of the

CO2 plume and pressure front. The owner or operator must use direct methods to monitor for

pressure changes in the injection zone. Indirect methods (e.g., seismic, electrical, gravity, or

electromagnetic surveys and/or down-hole CO2 detection tools) are also required unless the Director
determines, based on site-specific geology, that such methods are not appropriate.

EPA is affording Director's discretion regarding the use of geophysical techniques at some sites

because the Agency recognizes that geophysical methods are not appropriate in all geologic settings.

For example, geophysical methods are difficult to execute in areas that are structurally and

topographically complex or where lithologies have limited contrast in density, porosity,

permeability, and other physical properties. EPA clarifies that this determination will be made by the

Director based on the site-specific geologic information submitted by the owner or operator with the

permit application. 

EPA acknowledges the commenters' concern about the cost of geophysical techniques. However,

EPA believes that tracking of the plume is essential for protection of USDWs from endangerment at

GS sites and that geophysical methods are necessary for such tracking. 

EPA also agrees that other data may be useful for tracking the CO2 plume. For example,

geochemical data collected above the confining layer, as required under §146.90(d), will allow the

owner or operator and permitting authority to identify any changes in subsurface geochemistry that

may indicate fluid movement when compared to baseline geochemistry data collected during site

characterization.

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil gas and surface air monitoring which may be required by the UIC Director

for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Letter ID: 0263

Commenter Organization: Interstate Oil & Gas Compact Commission Comment ID: 22818

Other EPA Comment Codes and Descriptions: 4650 2.6.5 CO2 plume and pressure front tracking

(seeking comment) 

Comment: III A. 6 Proposed Plume andPressure Front Monitoring Requirements 

GG. Based on information evaluated to date, EPA believes that tracking the plume 

and pressure front is an important companion step to address any uncertainties 

associated with initial AoR modeling and requests comment on this approach 

and more efficient alternatives that maybe used to track the plume and pressure 

front. 

IOGCC Response: Tracking of the CO2 plume and pressure front should be required. 

The methodology, however, should not be specified but determined on a site 

specific basis. The IOGCC agrees with the following EPA statement: "As such, 

allowing flexibility in choosing the plume tracking methods and other monitoring 

technologies may provide an appropriate balance between the protective nature 

of indirect monitoring and cost considerations, as well as allowing for the 

adoption of continuously advancing technology." 
Response: EPA agrees with the comment and the final rule (at §146.90(g)) requires owners or

operators to perform monitoring to track the extent of the CO2 plume and pressure front. The owner

or operator must use direct methods to monitor for pressure changes in the injection zone. Indirect

methods (e.g., seismic, electrical, gravity, or electromagnetic surveys and/or down-hole CO2

detection tools) are also required unless the Director determines, based on site-specific geology, that

such methods are not appropriate. EPA clarifies that the specifics of this monitoring must be

described in the site-specific testing and monitoring plan, which must be approved by the Director. 

EPA believes that this approach provides flexibility to develop a site-specific monitoring plan,

ensures that direct monitoring is available to track the movement of the CO2 and validate models,

and recognizes that indirect techniques are not appropriate in all situations. The owner or operator's

approved testing and monitoring plan will include the site-specific details, technologies, testing and

monitoring frequencies, and other pertinent information.

Comment Code: 4660 2.6.6 Geochemical monitoring 

Individual Comments

Commenter Name: Herbert Skolnick, Ph.D. Letter ID: 0110

Commenter Organization: Group Against Smog and Pollution, Inc. (GASP) Comment ID: 22043

Other EPA Comment Codes and Descriptions: 4620 2.6.2 Injectate monitoring; 4630 2.6.3

Corrosion monitoring 

Comment: Regardless of what specific form the CO2 sequestration program ultimately takes, 

at a minimum, the program must ensure that: 

2. the sequestered material’s behavior in the chemical, geological, and 

hydrological environment where it is stored is anticipated and carefully 

monitored; and 

Response: EPA agrees with commenters on the importance of monitoring at GS sites and

emphasizes that monitoring of injection activities must be an important component of every GS

project. Monitoring associated with injection wells and the movement of the CO2 plume is necessary

to verify that the injectate is confined in the target formations and does not endanger USDWs. The

GS rule, at §146.90, requires injectate monitoring, mechanical integrity testing, corrosion

monitoring, tracking the CO2 plume and area of elevated pressure, monitoring geochemical changes

above the confining zone, and, at the discretion of the Director, surface air and soil gas monitoring

for CO2 fluctuations, and any additional tests necessary to ensure USDW protection from

endangerment.

Commenter Name: Doug Louis Letter ID: 0121

Commenter Organization: Kansas Corporation Commission Comment ID: 22076

Comment: The rule should be more specific as to what geochemical data needs to collected 

(i.e. from the injection formation, the confining layer or from the USDW?) 

Response: Section §146.90(d) requires periodic monitoring of the ground water quality and

geochemical changes above the confining zone(s). Monitoring above the confining layer will provide

an indication of upward movement of CO2 that might endanger a USDW. The exact number of
formations to be tested will, however, be based on site-specific characteristics and vulnerabilities

and described in the Director-approved testing and monitoring plan.

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil gas and surface air monitoring which may be required by the UIC Director

for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Leslie Savage Letter ID: 0122

Commenter Organization: Railroad Commission of Texas (RRC) Comment ID: 24794

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: (d) Periodic monitoring of the ground water quality and geochemical changes 

above the confining zone(s) that may be a result of carbon dioxide movement 

through the confining zone or additional identified zones: 

Response: Regarding monitoring locations, section §146.90(d) requires periodic monitoring of the

ground water quality and geochemical changes above the confining zone(s). EPA clarifies that this

monitoring requirement does not include the confining layer itself. Monitoring above the confining

layer will provide an indication of upward movement of CO2 that might endanger a USDW. The

exact number of formations to be tested must, however, be based on site-specific characteristics and

vulnerabilities and described in the Director-approved testing and monitoring plan.

Commenter Name: Christine Reimer Letter ID: 0142

Commenter Organization: National Ground Water Association Comment ID: 22567

Comment: In the monitored zones, geochemical and fluid chemical information should be 

based on constituents identified in the characterization as likely indicators of 

leakage. These indicators will likely include the pH and also be identified in 

the major and minor chemical constituents of the formation and ionic 

constituents of the formation-fluid. 

Response: While each monitoring plan must be site-specific based on data collected during the

initial site characterization and baseline geochemical monitoring, it is likely that geochemical

sampling might include basic water quality parameters such as pH, specific conductivity,

temperature, CO2, alkalinity, major ions, and select heavy metals. Additional parameters may be

monitored based on the potential for leaching of minerals or the geochemistry of native fluids. 

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil gas and surface air monitoring which may be required by the UIC Director

for specific GS projects. The guidance can be found on EPA’s website at
http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Christine Reimer Letter ID: 0142

Commenter Organization: National Ground Water Association Comment ID: 22607

Comment: Proposed Rule: 146.90(d) 

Comment: The monitoring should be site specific and include particular analytes 

at risk to the aquifer from the existing geologic environment. 

Response: While each monitoring plan must be site-specific based on data collected during the

initial site characterization and baseline geochemical monitoring, it is likely that geochemical

sampling might include basic water quality parameters such as pH, specific conductivity,

temperature, CO2, alkalinity, major ions, and select heavy metals. Additional parameters may be

monitored based on the potential for leaching of minerals or the geochemistry of native fluids. 

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil gas and surface air monitoring which may be required by the UIC Director

for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: James Childress Letter ID: 0158

Commenter Organization: Gasification Technologies Council (GTC) Comment ID: 23774

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language; 4400 2.4.4.3 Allowing injection above or between USDWs (seeking comment) 

Comment: §146.90 Testing and monitoring requirements. (d) Periodic monitoring of the 

ground water quality and geochemical changes above the confining zone(s) that 

may be a result of carbon dioxide movement through the confining zone or 

additional identified zones: 

We recommend changing to "Periodic monitoring of the ground water quality and 

geochemical changes between the confining zone(s) and the USDW that may be a 

result of carbon dioxide movement through the confining zone or additional 

identified zones:" This rewording is consistent with allowing for injection 

either above or below USDWs 

Response: EPA disagrees that the GS rule should specify the zones to be monitored. EPA clarifies

that §146.90(d) requires periodic monitoring of the ground water quality and geochemical changes

above the confining zone(s). EPA clarifies that this monitoring requirement does not include the

confining layer itself. Monitoring above the confining layer will provide an indication of upward

movement of CO2 that might endanger a USDW. The exact number of formations to be tested will,

however, be based on site-specific characteristics and vulnerabilities and described in the Directorapproved testing and monitoring plan. 

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in
evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil gas and surface air monitoring which may be required by the UIC Director

for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

In the final GS rule, owners or operators granted injection depth waivers are subject to additional

requirements at §146.95(f)(3) to monitor above and below the injection zone in order to ensure

protection of USDWs underlying and overlying the injection zone during both well operation and the

post-injection site care period. 

For additional information on the waiver approach, please see the final rule and preamble, as well as

EPA's responses to comments on the Notice of Data Availability and Request for Comment.

Commenter Name: Michael J. Miller Letter ID: 0168

Commenter Organization: Electric Power Research Institute (EPRI) Comment ID: 22493

Other EPA Comment Codes and Descriptions: 3150 2.1.5 Comments on required permit

information (40 CFR 146.82) 

Comment: Preamble, page 43505, §146.82(g), and § 146.90(d): "Today’s proposal would 

require owners or operators to submit geochemical data on a) the injection zone, 

b) the confining zones, c) containment zones above the confining zones in which 

any potentially migrating CO2 could be trapped, d) all USDWs, and e) any other 

geologic zone or formation that is important to the proposed monitoring 

program." 

EPRI COMMENT #3A: EPA does not provide the technical justification for 

collecting geochemical data from all zones, geologic formations and USDWs. We 

believe the collection of data should be limited to zones needed to demonstrate 

system performance defined by the minimum siting criteria specified in 

§146.83(a)(1) and (a)(2). EPRI believes that system performance with the end 

goal of protecting USDW can be achieved by collecting geochemical data from a 

maximum of four zones for the reasons provided below: 

1) Injection zone -- during site characterization, check for conditions that 

could lead to CO2-induced rock dissolution, potentially resulting in formation 

and injection well collapse (well integrity); 

2) Primary confining zone -- during site characterization, check for conditions 

that could lead to caprock dissolution and degradation, potentially resulting in 

loss of CO2 containment with subsequent CO2 movement through the primary barrier 

(caprock integrity); 

3) Monitoring zone -- a zone proposed by the applicant and approved by the EPA 

where performance monitoring is required to take place in accordance with 

§146.90(d). The monitoring zone would lie between the primary confining zone and 

the USDW. It would be the only zone sampled on a routine schedule during CO2 

injection operations and closure to detect the leakage of CO2 through the 
primary confining zone (performance monitoring) as noted ; and 

4) USDW zone -- during site characterization, collect optional samples at or 

near the closest USDW boundary to the injection zone to establish baseline water 

quality. 

EPRI COMMENT #3B: Before promulgating the rule, a comprehensive study of deep 

well fluid sampling techniques needs to be performed to ensure that the 

techniques cited by EPA consistently produce samples that are representative of 

deep reservoir conditions. Otherwise, interpretation of geochemical data derived 

from methods producing inconsistent or non-representative sample data could 

result in erroneous conclusions, including unnecessary or inappropriate 

corrective action. Collecting representative deep well samples from confining 

zones is especially challenging (see EPRI comment #14). 

Response: The GS regulation, at §146.82(a)(6), requires the owner or operator to submit baseline

geochemical data on subsurface geologic formations. EPA is not specifying for which formations

this information should be submitted to allow flexibility, but examples may include the following

formations: a) the injection zone, b) the confining zones, c) containment zones above the confining

zones in which any potentially migrating CO2 could be trapped, d) all USDWs, and e) any other

geologic zone or formation that is important to the proposed monitoring program. The Director has

the authority to request additional geochemical data as well. 

EPA believes that the necessary sampling techniques are available, and is developing guidance on

site characterization for GS projects to assist owners or operators and Directors in evaluating permit

requirements and applications under §146.82. The guidance provides recommendations regarding

characterizing the regional geology and hydrogeology of a proposed GS site as well as performing

the necessary geochemical, geomechanical, and geophysical analyses of the injection and confining

zone. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

On the topic of sampling, EPA recognizes that the collection of representative ground water samples

from depth poses challenges and that special methods, such as U-tubes, will be needed to preserve

the integrity of such samples. EPA is developing guidance on testing and monitoring to assist

owners or operators and Directors in evaluating requirements under §146.90, including proposed

monitoring plans. The guidance describes available technologies and recommended approaches for

implementing a testing and monitoring plan, including pre-operational geophysical logging and

testing of injection wells, MITs, injection well testing during operation, groundwater quality

monitoring, tracking the CO2 plume and pressure front, and soil gas and surface air monitoring

which may be required by the UIC Director for specific GS projects. The guidance can be found on

EPA’s website at http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Regarding the comment about the technical justifications and difficulty of sampling within the

confining zone, EPA clarifies that §146.90(d) requires owners and operators to monitor ground water

quality and geochemical changes above the confining zone(s), rather than within the confining zone.

Commenter Name: Michael J. Miller Letter ID: 0168

Commenter Organization: Electric Power Research Institute (EPRI) Comment ID: 22508

Comment: Preamble, page 43515: "Monitoring within the confining zone for pressure, pH, 
salinity, or the presence of dissolved minerals, heavy metals, or organic 

contaminants requires direct access to the subsurface via monitoring wells." 

EPRI COMMENT #14: See EPRI comment #3B. We believe that measuring pressure in a 

deep confining zone is possible, but collecting representative deep well samples 

from confining zones for geochemical characterization may not be technically 

possible (with emphasis on representative). This could lead to erroneous 

results and conclusions. EPA currently requires that all monitoring wells be 

purged of "stagnant" groundwater in the well prior to sampling to produce a 

"fresh" sample from the adjacent formation that is representative of the 

formation fluid. Low-yield confining units are typically purged dry prior to 

sampling or pumped at a very slow rate to prevent the formation from being 

dewatered. In either case, this typically results in significant sample 

depressurization when sampling deep wells. Important geochemical parameters 

including pH, alkalinity, and dissolved metals (which are dependent on 

groundwater pH) will change when depressurization occurs, producing erroneous 

analytical results. The u-tube sample method described by Friefeld et al (2005) 

cannot be used to overcome this limitation for low-yield confining zones. 

Freifeld B.M., R.C. Trautz, Y.K. Kharaka, T.J. Phelps, L.R. Myer, S.D. Hovorka, 

D.J. Collins (2005) The U-tube: a novel system for acquiring borehole fluid 

samples from a deep geologic CO2 sequestration experiment. Journal of 

Geophysical Research, 110, B10203, doi:10.1029/2005JB003735. 

Response: As described above, EPA recognizes that the collection of representative ground water

samples from depth poses challenges and that special methods, such as U-tubes, will be needed to

preserve the integrity of such samples. EPA is developing guidance on testing and monitoring to

assist owners or operators and Directors in evaluating requirements under §146.90, including

proposed monitoring plans.

Commenter Name: Kyle Isakower Letter ID: 0170

Commenter Organization: American Petroleum Institute Comment ID: 24191

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Rule Provision: 149.90(d) 

API Comments: (d) Periodic monitoring of the ground water FORMATION FLUID 

quality and geochemical changes above IN A PERMEABLE AND POROUS FORMATION AS 

NEAR AS PRACTICABLE TO the confining zone(s) FOR GEOCHEMICAL CHANGES that may

be 

a result of carbon dioxide OR DISPLACED FORMATION FLUID movement through the 

confining zone or additional identified zones:

(1) The location and number of monitoring wells must be based on specific 

information about the geologic sequestration project, including injection rate 

and volume, geology, the presence of artificial penetrations and other RELEVANT 

factors AS WARRANTED BY A RISK-ASSESSMENT; 

(2) The monitoring frequency and spatial distribution of monitoring wells must 

be based on GEOLOGICAL, geochemical AND GEOPHYSICAL data that has been collected 

under § 146.82(a)(6) §146.82(D) and any modeling results in the area of 
review evaluation required by §146.84(b); 

Rationale: Drilling monitoring wells should be carefully considered since each 

well introduces a potential pathway for movement. In addition the cost of adding 

multiple wells could create a barrier to CCS development, while providing 

limited information on actual movement of the CO2 stream. 

Response: EPA agrees that monitoring plans and methods need to be site-specific and believes that

the monitoring requirements for GS sites at §146.90 provide an appropriate level of flexibility in

structuring a testing and monitoring plan that protects USDWs from endangerment, while addressing

the needs suggested in the commenter’s proposed edits. 

Regarding monitoring locations, section §146.90(d) requires periodic monitoring of the ground water

quality and geochemical changes above the confining zone(s). EPA clarifies that this monitoring

requirement does not include the confining layer itself. Monitoring above the confining layer will

provide an indication of upward movement of CO2 that might endanger a USDW. The exact number

of formations to be tested must, however, be based on site-specific characteristics and vulnerabilities

and described in the Director-approved testing and monitoring plan.

To mitigate the risk of fluid movement, EPA requires owners and operators to submit a testing and

monitoring plan that describes how the owner or operator plans to site and construct monitoring

wells. 

EPA believes, however, that monitoring using wells in the injection zone, e.g., for pressure

monitoring as required at §146.90(g)(1), can be safely performed if the wells are constructed to

prevent flow between the injection zone and USDWs or other layers above the confining zone. Such

construction technologies exist and have been used in the oil and gas industry for years. EPA

believes that properly constructed monitoring wells will be a safe way to obtain the data that is

essential to ensure that the injected CO2 remains confined in the injection zone and that pressure

changes are not causing movement or formation of other fluids. To mitigate the risk of fluid

movement, EPA requires owners and operators to submit a testing and monitoring plan that

describes how the owner or operator plans to site and construct monitoring wells. EPA is developing

guidance on well construction that will include recommendations for monitoring well construction.

The guidance will be available on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil gas and surface air monitoring which may be required by the UIC Director

for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

EPA acknowledges the commenters' concern about the cost of monitoring. However, EPA believes

that monitoring is essential for protection of USDWs at GS sites. Although a significant cost in

absolute terms, monitoring costs are expected to be a small fraction of site operating costs, according

to EPA's cost analysis for the GS rulemaking (which is available in the docket).
Commenter Name: Frederick R. Eames Letter ID: 0178

Commenter Organization: CCS Alliance Comment ID: 23872

Comment: EPA proposes in section 146.90(d) "periodic monitoring of the ground water 

quality and geochemical changes above the confining zone(s)." It is unclear how 

many wells would be required, and whether EPA expects that all zones would be 

monitored. Given the potential size of the CO2 plume and the number of confining 

zones, this could potentially require many monitoring wells, which could be 

extremely expensive and may not produce useful data. We strongly recommend that 

EPA limit monitoring to the zone immediately above the confining zone, and only 

to the extent that the CO2 plume is within close proximity. There may be 

regional conditions where ground water is separated by hundreds or thousands of 

feet of confining strata, and where such monitoring is completely unnecessary. 

Directors should have discretion to limit or tailor ground water monitoring, as 

appropriate, based on regional and site specific factors. 

Response: Regarding monitoring locations, section §146.90(d) requires periodic monitoring of the

ground water quality and geochemical changes above the confining zone(s). EPA clarifies that this

monitoring requirement does not include the confining layer itself. Monitoring above the confining

layer will provide an indication of upward movement of CO2 that might endanger a USDW. The

exact number of formations to be tested will, however, be based on site-specific characteristics and

vulnerabilities and described in the Director-approved testing and monitoring plan.

EPA believes that monitoring above the confining layer is an important part of a rigorous monitoring

program. The final rule, at §146.90(d) requires periodic monitoring of the ground water quality and

geochemical changes above the confining zone(s). Monitoring in additional formations, e.g., the

injection zone, may also be necessary, and if the Director believes such monitoring is warranted

he/she has the authority to require that it be included in the testing and monitoring plan.

EPA agrees that geochemical monitoring in the injection zone may not be warranted in all cases, and

that it is important to install an appropriate number of monitoring wells based on site-specific

information and the planned monitoring regime. However, the Agency believes that the data gained

from monitoring wells in carefully selected locations will be invaluable. 

EPA disagrees that such monitoring should be restricted to areas near the plume. Research, both

EPA-funded and external, has shown that the zone of elevated pressure may be much larger than the

plume (e.g., Birkholzer et al., 2008). This area of elevated pressure may cause migration of native

brines from the target formation into overlying formations. Careful placement of monitoring wells

within the delineated AoR (which includes areas beyond the extent of the CO2 plume) would allow

for detection of changes in water quality related to GS activities. EPA acknowledges that very thick

confining zones would reduce the chance that CO2 or other fluids will move from the injection zone;

however, to increase protectiveness, a multiple-barrier approach to protecting USDWs from

endangerment that includes both proper site characterization and a detailed monitoring regime is

warranted.

Commenter Name: Thomas Curtis Letter ID: 0181

Commenter Organization: American Water Works Association (AWWA) Comment ID: 24332

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Part 146.90(d) AWWA recommends revising this part to read: 
Periodic monitoring of the ground water quality and geochemical changes within 

(if wells can be installed without adversely affecting the integrity of the 

confining zone) and above the confining zone(s) that may be a result of carbon 

dioxide movement through the confining zone or additional identified zones: 

Response: EPA clarifies that §146.90(d) requires geochemical monitoring above the confining zone.

To mitigate the risk of fluid movement, EPA requires owners and operators to submit a testing and

monitoring plan that describes how the owner or operator plans to site and construct monitoring

wells. 

EPA believes that monitoring using wells in the injection zone, e.g., for pressure monitoring as

required at §146.90(g)(1), can be safely performed if the wells are constructed to prevent flow

between the injection zone and USDWs or other layers above the confining zone. Such construction

technologies exist and have been used in the oil and gas industry for years. EPA believes that

properly constructed monitoring wells will be a safe way to obtain the data that is essential to ensure

that the injected CO2 remains confined in the injection zone and that pressure changes are not

causing movement of formation or other fluids. To mitigate the risk of fluid movement, EPA

requires owners and operators to submit a testing and monitoring plan that describes how the owner

or operator plans to site and construct monitoring wells. EPA is developing guidance on well

construction that will include recommendations for monitoring well construction. The guidance will

be available on EPA’s website at http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil gas and surface air monitoring which may be required by the UIC Director

for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Robert F. Van Voorhees Letter ID: 0190

Commenter Organization: Carbon Sequestration Council Comment ID: 24356

Comment: a. Monitor Wells 

Monitor wells reaching the deep subsurface are problematic in a variety of 

respects. They are expensive to install, create potential pathways for vertical 

fluid migration, and - in the deep subsurface where natural fluid movement may 

be very slow or effectively non-existent - they have little potential to provide 

more than an isolated "point measurements." Monitor wells also have built-in 

confounding factors that include both the potential for well construction to 

impact fluid quality in the target sampling interval and the fact that sampling 

may itself cause fluid movement that might not otherwise occur. Because pressure 

fronts extend much further than injected fluid plume fronts during injection, 

pressure monitoring is more likely to be useful than fluid sampling, but costs 

would still be very high and the ability to detect relevant changes would still 

be difficult. For these reasons, EPA chose not to impose monitor well 

requirements on other classes of injection wells, though it did allow monitor 

wells to be used for Class I hazardous waste injection wells at the discretion 
of the Director to address particular circumstances at the site. See 52 Fed. 

Reg. 32446 at 32463-64 (August 27, 1987), 53 Fed. Reg. 28118 at 28141, 28144-45 

(July 26, 1988). Experience with hazardous waste injection does not commend the 

use of monitor wells even in that context, and there is no justification to 

impose a more stringent an approach for the injection of CO2. Accordingly, we 

recommend that the potential for gaining useful information from monitor wells 

be carefully considered in developing an appropriate monitoring plan and that 

such wells be used only as justified by specific circumstances. (See Attachment 

A, 146.90(a).) 

Response: EPA believes that monitoring using wells in the injection zone, e.g., for pressure

monitoring as required at §146.90(g)(1), can be safely performed if the wells are constructed to

prevent flow between the injection zone and USDWs or other layers above the confining zone. Such

construction technologies exist and have been used in the oil and gas industry for years. EPA

believes that properly constructed monitoring wells will be a safe way to obtain the data that is

essential to ensure that the injected CO2 remains confined in the injection zone and that pressure

changes are not causing movement of formation or other fluids. To mitigate the risk of fluid

movement, EPA requires owners and operators to submit a testing and monitoring plan that

describes how the owner or operator plans to site and construct monitoring wells. EPA is developing

guidance on well construction that will include recommendations for monitoring well construction.

The guidance will be available on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

While EPA chose not to impose similar monitoring requirements on other classes of injection wells

(except for Class I hazardous waste injection wells), the Agency believes that a conservative,

protective approach is appropriate, given the large volumes of CO2 being injected. 

EPA also acknowledges that complete coverage of the potential plume area or leakage in the

subsurface is not possible through the use of monitoring wells. However, data from an appropriate

number of monitoring wells sited based on site-specific information will provide direct information

that is not otherwise obtainable and, along with other monitoring data, will support a broader

understanding of fluid behavior at the site. 

EPA adds that the iterative process of monitoring, modeling, and AoR reevaluation is appropriate to

verify that the CO2 plume and pressure front are moving through the subsurface as predicted, verify

the accuracy of the delineation model (or identify needed changes), and refine testing and monitoring

activities to ensure that USDWs are protected from endangerment and that there would be adequate

warning of potential problems at the site before any endangerment could occur. 

EPA acknowledges the commenters' concern about the cost of monitoring. However, EPA believes

that monitoring is essential for protection of USDWs at GS sites. Although a significant cost in

absolute terms, monitoring costs are expected to be a small fraction of site operating costs, according

to EPA's cost analysis for the GS rulemaking (which is available in the docket). 

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil, gas, and surface-air monitoring which may be required by the UIC Director
for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Robert F. Van Voorhees Letter ID: 0190

Commenter Organization: Carbon Sequestration Council Comment ID: 24481

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Rule Provision: 146.90(d) 

Proposed CCS Group Recommendations: (d) Periodic monitoring of the ground 

water quality and geochemical changes above the confining zone(s) that may be a 

result of carbon dioxide movement through the confining zone or additional 

identified zones: 

(1) The location and number of monitoring wells must be based on specific 

information about the geologic sequestration project, including injection 

rate and volume, geology, the presence of artificial penetrations and other 

factors; 

(2) The monitoring frequency and spatial distribution of monitoring wells must 

be based on baseline geochemical data that has been collected under § 146.82(a) 

(6) and any modeling results in the area of review evaluation required by § 

146.84(b);

Response: EPA did not make the suggested changes, but agrees that monitoring plans and methods

need to be site-specific and based on baseline data and data collected throughout operations. EPA

believes that the monitoring requirements for GS sites at §146.90 provide an appropriate level of

flexibility in structuring a testing and monitoring plan that protects USDWs from endangerment. 

The final regulation provides for flexibility in: 1) methodologies used to collect these data, 2) the

spatial resolution at which the data should be collected, and 3) how often the data should be

collected. The number and placement of monitoring wells will be based on site-specific information

such as the calculated AoR, injection rate and volume, site geology, baseline data, and the presence

of artificial penetrations within the AoR. In some instances, there may be a limited number of

options for complying with EPA's minimum requirements. For example, monitoring for geochemical

changes will require use of monitoring wells and collection of groundwater samples for chemical

analysis. Many options currently exist for complying with other requirements, such as tracking the

position of the plume and pressure front within the injection zone.

Flexibility is also provided regarding how to monitor for the specific data required by the final rule.

The testing and monitoring plan is developed by the owner or operator in consultation with the

Director and is designed to ensure that a detailed, Director-approved document describing how

monitoring will be conducted during the lifetime of the project exists. EPA is developing guidance

on testing and monitoring to assist owners or operators and Directors in evaluating requirements

under §146.90, including proposed monitoring plans. The guidance describes available technologies

and recommended approaches for implementing a testing and monitoring plan, including preoperational geophysical logging and testing of injection wells, MITs, injection well testing during

operation, groundwater quality monitoring, tracking the CO2 plume and pressure front, and soil gas

and surface air monitoring which may be required by the UIC Director for specific GS projects. The
guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Craig R. Walters Letter ID: 0200

Commenter Organization: Anadarko Petroleum Corporation Comment ID: 24704

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Rule Provision: 146.90(d) 

Anadarko Petroleum Corporation (APC) Comments: (d) Periodic monitoring of the 

ground water quality and geochemical changes above the confining zone(s) that 

may be a result of carbon dioxide movement through the confining zone or 

additional identified zones: 

(1) The location and number of monitoring wells must be based on specific 

information about the geologic sequestration project, including injection rate 

and volume, geology, the presence of artificial penetrations and other factors; 

(2) The monitoring frequency and spatial distribution of monitoring wells must 

be based on baseline geochemical data that has been collected under § 146.82(a) 

(6) and any modeling results in the area of review evaluation required by § 

146.84(b);

Rationale: See 146.90(c)(1 thru 4 and 7) 

Response: EPA did not make the suggested changes, but agrees that monitoring plans and methods

need to be site-specific and based on baseline data and data collected throughout operations. EPA

believes that the monitoring requirements for GS sites at §146.90 provide an appropriate level of

flexibility in structuring a testing and monitoring plan that protects USDWs from endangerment. 

The final regulation provides for flexibility in: 1) methodologies used to collect these data, 2) the

spatial resolution at which the data should be collected, and 3) how often the data should be

collected. The number and placement of monitoring wells will be based on site-specific information

such as the calculated AoR, injection rate and volume, site geology, baseline data, and the presence

of artificial penetrations within the AoR. In some instances, there may be a limited number of

options for complying with EPA's minimum requirements. For example, monitoring for geochemical

changes will require use of monitoring wells and collection of groundwater samples for chemical

analysis. Many options currently exist for complying with other requirements, such as tracking the

position of the plume and pressure front within the injection zone.

Flexibility is also provided regarding how to monitor for the specific data required by the final rule.

The testing and monitoring plan is developed by the owner or operator in consultation with the

Director and is designed to ensure that a detailed, Director-approved document describing how

monitoring will be conducted during the lifetime of the project exists. EPA is developing guidance

on testing and monitoring to assist owners or operators and Directors in evaluating requirements

under §146.90, including proposed monitoring plans. The guidance describes available technologies

and recommended approaches for implementing a testing and monitoring plan, including preoperational geophysical logging and testing of injection wells, MITs, injection well testing during

operation, groundwater quality monitoring, tracking the CO2 plume and pressure front, and soil gas
and surface air monitoring which may be required by the UIC Director for specific GS projects. The

guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Richard Guinn Letter ID: 0210

Commenter Organization: Eastman Chemical Company Comment ID: 22724

Comment: §146.90 Testing and monitoring requirements. (d) Periodic monitoring of the 

ground water quality and geochemical changes above the confining zone(s) that 

may be a result of carbon dioxide movement through the confining zone or 

additional identified zones: 

We recommend changing to " Periodic monitoring of the ground water quality and 

geochemical changes between the confining zone(s) and the USDW that may be a 

result of carbon dioxide movement through the confining zone or additional 

identified zones: " 

This rewording is consistent with allowing for injection either above or below 

USDWs 

Response: Regarding monitoring locations, section §146.90(d) requires periodic monitoring of the

ground water quality and geochemical changes above the confining zone(s). EPA clarifies that this

monitoring requirement does not include the confining layer itself. Monitoring above the confining

layer will provide an indication of upward movement of CO2 that might endanger a USDW. The

exact number of formations to be tested must, however, be based on site-specific characteristics and

vulnerabilities and described in the Director-approved testing and monitoring plan.

Commenter Name: John King Letter ID: 0211

Commenter Organization: Shell Exploration and Production Company

(SEPCo)

Comment ID:

22777

Comment: Suggestions that it should be necessary to monitor geochemical changes or to 

study interactions between brine and CO2 in the injection zone are particularly 

troubling, because detailed information concerning such interactions should 

rarely if ever be relevant from a regulatory standpoint. In particular, USDWs 

are generally protected by ensuring that injected fluids will remain isolated 

from them, and experience with hazardous waste injection " where the injection 

of highly corrosive waste is not uncommon " has shown that geochemical 

interactions that could actually compromise containment cannot reasonably be 

expected in the absence of truly unusual circumstances. Accordingly, any general 

requirement to monitor geochemical changes in the subsurface would be 

unreasonable. 

Response: EPA disagrees with the commenter. While contamination is unlikely at properly selected,

constructed, and operated sites, EPA believes that robust monitoring is necessary to ensure that

USDWs are protected. 

EPA also acknowledges that complete coverage of the potential plume area or leakage in the

subsurface is not possible through the use of monitoring wells. However, data from an appropriate

number of monitoring wells sited based on site-specific information will provide direct information
that is not otherwise obtainable and, along with other monitoring data, will support a broader

understanding of fluid behavior at the site. 

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil gas and surface air monitoring which may be required by the UIC Director

for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

EPA adds that the iterative process of monitoring, modeling, and AoR reevaluation is appropriate to

verify that the CO2 plume and pressure front are moving through the subsurface as predicted, verify

the accuracy of the delineation model (or identify needed changes), and refine testing and monitoring

activities to ensure that USDWs are protected from endangerment and that there would be adequate

warning of potential problems at the site before any endangerment could occur.

Commenter Name: Diane VanDe Hei Letter ID: 0213

Commenter Organization: Association of Metropolitan Water Agencies

(AMWA)

Comment ID:

22937

Comment: o Rock cores and thorough geochemical analysis of geosequestration should happen 

even before the AoR. Advances in research and subsurface modeling make it 

possible to analyze the interaction between rock formations and CO2. Performing 

these analyses early on could potentially prevent unintended consequences. 

Response: EPA agrees and believes that the baseline geochemical data required at §146.82(a)(6) will

provide information on predicting potential interactions between rocks and CO2 as the commenter

suggests, and also expects that this information will inform the development and approval of a sitespecific testing and monitoring plan.

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil gas and surface air monitoring which may be required by the UIC Director

for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm. In addition, in January 2009,

DOE published a best practices manual entitled "Monitoring, Verification, and Accounting of CO2

Stored in Deep Geologic Formations" (DOE/NETL-311/081508); this manual is included in the

docket for the final GS rule.

Commenter Name: Edward Steadman Letter ID: 0220

Commenter Organization: The Energy and Environmental Research Center at the

University of North Dakota

Comment ID:

21625

Other EPA Comment Codes and Descriptions: 4610 2.6.1 Testing and monitoring plan

requirement (seeking comment) 
Comment: Page 43515. Regarding monitoring wells in the Area of Review (AoR). 

Text in this section implies that monitoring wells in the injection zone within 

the AoR are desirable, which could be interpreted by some as being required. The 

first comment with respect to this issue is that it is important to note that 

monitoring wells that penetrate the plume have potential to serve as a leakage 

pathway and, therefore, their use should be minimized. Secondly, one of the 

reasons given for the placing of monitoring wells in the AoR is that studying 

the interactions between brine and CO2 may allow for the determination of 

whether precipitation and/or dissolution of minerals is occurring. It is 

important to note that such interactions are currently not well understood and 

are the topic of great debate and controversy within the published literature. 

There is no consensus in the technical community as to how such data evaluated 

in the context of a single site, as site-specific permitting and monitoring must 

be, can be applied to ensuring the protection of USDWs at that site. While such 

data would surely be interesting and possibly useful from a scientific 

standpoint when taken in the context of many sites, it is not clear how it could 

be applied to prove or disprove that USDWs at a given location are being 

protected or are in danger of contamination. This requirement comes across as a 

regulatory-mandated means of gathering data for researchers, an activity that is 

outside the scope of USDW protection and should not be forcibly paid for by 

owners/operators of GS wells. 

Response: EPA disagrees that the monitoring requirements in the GS rule do not provide sitespecific benefits for protection of USDWs or that monitoring is for the benefit of scientific research

only. EPA believes that geochemical monitoring, when compared to baseline data, can provide direct

evidence that USDWs may be endangered.

EPA believes that monitoring using wells in the injection zone (i.e., that penetrate the confining

zone) can be safely performed if the wells are constructed to prevent flow between the injection zone

and USDWs or other layers above the confining zone. Such construction technologies exist and have

been used in the oil and gas industry for years. EPA believes that the benefits of monitoring in the

injection formation outweigh the manageable risk of those monitoring wells serving as conduits for

fluid movement. EPA adds that owners or operators may consider performing additional pressure

monitoring in wells that are above the confining zone (e.g., in the same wells used to perform

ground water quality monitoring required at §146.90(d)) to provide additional verification that no

pressure changes are occurring above the confining zone due to CO2 leakage. Monitoring also

identifies needed remedial actions, provides inputs for AoR reevaluation modeling, and targets

additional geochemical and surface monitoring needs. Knowledge of the location of the CO2 plume

and the associated pressure front will assure the public that GS projects are proceeding according to

plan, provide sufficient information to the owner or operator and Director, or allow for appropriate

actions to address any indication that USDWs may be endangered.

EPA acknowledges that, at certain sites, there may be a need for more or different monitoring

schemes (which may include monitoring in the confining zone), and adds that it is important to

balance the need for adequate monitoring that ensures USDW protection from endangerment against

too many artificial penetrations which could serve as conduits for fluid migration. Site-specific

testing and monitoring plans must describe the proposed monitoring regime, which must be

approved by the Director.
Commenter Name: Andrew Duguid Letter ID: 0226

Commenter Organization: Schlumberger Carbon Services Comment ID: 24058

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Proposed Rule: (d) Periodic monitoring of the ground water quality and 

geochemical changes above the confining zone(s) that may be a result of carbon 

dioxide movement through the confining zone or additional identified zones: 

Schlumberger Suggested Revision: (d) Periodic monitoring of the ground water 

quality for geochemical changes above the confining zone(s) that may be a result 

of carbon dioxide movement through the confining zone or additional identified 

zones: 

Schlumberger Rationale: - 

Response: EPA did not make the suggested change. Based on its evaluation of all public comments

and input on the proposed rule and NODA and Request for Comment EPA has made many revisions

to the GS rule. See the final rule and preamble for further discussion on EPA's final approach.

Commenter Name: Andrew Duguid Letter ID: 0226

Commenter Organization: Schlumberger Carbon Services Comment ID: 24060

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Proposed Rule: (2) The monitoring frequency and spatial distribution of 

monitoring wells must be based on baseline geochemical data that has been 

collected under §146.82(a) (6) and any modeling results in the area of review 

evaluation required by §146.84(b); 

Schlumberger Suggested Revision: (2) The monitoring frequency and spatial 

distribution of monitoring wells must be based on geological and geophysical 

data that has been collected under §146.82(d) and any modeling results in the 

area of review evaluation required by §146.84(b); 

Schlumberger Rationale:Geochemical data does not seem have a high degree of 

relevance in selecting monitoring well sites. 

Response: EPA believes that baseline characterization of the site, including the geochemical data

and initial modeling, will be highly valuable in selection of monitoring well locations and in refining

plans for monitoring frequency. The GS rule stipulates that the monitoring frequency and spatial

distribution of monitoring wells must be based on baseline geochemical data that were collected

during the initial site characterization and the area of review evaluation at §146.90(d)(2). The details

of the geochemical monitoring will be based on site-specific information and described in the

Director-approved testing and monitoring plan.

Commenter Name: Steven B. Corneli Letter ID: 0234

Commenter Organization: NRG Energy, Inc. Comment ID: 23169

Other EPA Comment Codes and Descriptions: 4600 2.6 Proposed Plume and Pressure Front

Monitoring Requirements (40 CFR 146.90) 
Comment: Monitoring Requirements 

The preamble of the proposed rule states that the "monitoring of subsurface 

geochemistry and the position of the CO2 plume and pressure front are necessary 

to verify predictions of plume movement, provide inputs for modeling, identify 

needed corrective actions, and target geochemical and surface monitoring 

activities." 73 Fed. Reg. at 43514. NRG believes that the proposed monitoring 

requirements are excessive and unjustified. The use of monitor wells or seismic 

data would be needed to verify the model predictions. In particular, it is 

Response: EPA disagrees that the monitoring requirements in the GS rule are excessive or

unjustified. In addition to monitoring to track the movement of the CO2 plume and pressure front,

EPA believes that monitoring above the confining layer is an important part of a rigorous monitoring

program. Such monitoring can provide an early warning that the plume may be approaching a

USDW. The final rule, at §146.90(d), requires periodic monitoring of the ground water quality and

geochemical changes above the confining zone(s). EPA also believes that geophysical (e.g., seismic)

methods are useful for plume tracking at GS sites. For this reason, the final rule at §146.90(g)

requires the use of indirect methods (e.g., seismic, electrical, gravity, or electromagnetic surveys

and/or down-hole CO2 detection tools) unless the Director determines, based on site-specific

geology that such methods are not appropriate

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil gas and surface air monitoring which may be required by the UIC Director

for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

EPA also acknowledges that complete coverage of the potential plume area or leakage in the

subsurface is not possible through the use of monitoring wells. However, data from an appropriate

number of monitoring wells sited based on site-specific information will provide direct information

that is not otherwise obtainable and, along with other monitoring data, will support a broader

understanding of fluid behavior at the site. 

EPA adds that the iterative process of monitoring, modeling, and AoR reevaluation is appropriate to

verify that the CO2 plume and pressure front are moving through the subsurface as predicted, verify

the accuracy of the delineation model (or identify needed changes), and refine testing and monitoring

activities to ensure that USDWs are protected from endangerment and that there would be adequate

warning of potential problems at the site before any endangerment could occur.

Commenter Name: Michel Paque Letter ID: 0259

Commenter Organization: Ground Water Protection Council Comment ID: 24926

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Rule Provision: 146.90(d) 

EPA Proposal: (d) Periodic monitoring of the ground water quality and 
geochemical changes above the confining zone(s) that may be a result of carbon 

dioxide movement through the confining zone or additional identified zones: 

(1) The location and number of monitoring wells must be based on specific 

information about the geologic sequestration project, including injection rate 

and volume, geology, the presence of artificial penetrations and other factors; 

(2) The monitoring frequency and spatial distribution of monitoring wells must 

be based on baseline geochemical data that has been collected under § 146.82(a) 

(6) and any modeling results in the area of review evaluation required by § 

146.84(b); 

GWPC Recommendations: (d) Periodic monitoring of reservoir formation fluid 

quality in a permeable and porous formation as near as practicable to the 

confining zone(s) for geochemical changes that may be a result of carbon dioxide 

or displaced formation fluid movement: 

(1) The location and number of monitoring wells must be based on specific 

information about the geologic sequestration project, including injection rate 

and volume, geology, the presence of artificial penetrations and other relevant 

factors as warranted by a risk-assessment; 

(2) The monitoring frequency and spatial distribution of monitoring wells must 

be based on geological, geochemical and geophysical data that has been collected 

under §146.82(d) and any modeling results in the area of review evaluation 

required by §146.84(b); 

Rationale: Drilling monitoring wells should be carefully considered since each 

well introduces a potential pathway for movement. 

[Geochemical data do not have a high degree of relevance in selecting monitoring 

well sites.] 

Response: EPA believes that monitoring using wells in the injection zone, e.g., for pressure

monitoring as required at §146.90(g)(1), can be safely performed if the wells are constructed to

prevent flow between the injection zone and USDWs or other layers above the confining zone. Such

construction technologies exist and have been used in the oil and gas industry for years. EPA

believes that properly constructed monitoring wells will be a safe way to obtain the data that is

essential to ensure that the injected CO2 remains confined in the injection zone and that pressure

changes are not causing movement of formation or other fluids. To mitigate the risk of fluid

movement, EPA requires owners and operators to submit a testing and monitoring plan that

describes how the owner or operator plans to site and construct monitoring wells. EPA has

developed a brief technical paper on construction of monitoring wells that perforate the confining

zone; this paper can be found in the rulemaking docket. EPA is also developing guidance on well

construction that will include recommendations for monitoring well construction. The guidance will

be available on EPA’s website at http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Baseline characterization of the site, including the geochemical data and initial modeling, will be

highly valuable in selection of monitoring well locations and in refining plans for monitoring

frequency. The GS rule stipulates that the monitoring frequency and spatial distribution of

monitoring wells must be based on baseline geochemical data that were collected during the initial
site characterization and the area of review evaluation (§146.90(d)(2)). The details of the

geochemical monitoring must be based on site-specific information and described in the Directorapproved testing and monitoring plan.

Letter ID: 0263

Commenter Organization: Interstate Oil & Gas Compact Commission Comment ID: 22819

Comment: III A. 6 Proposed Plume and Pressure Front Monitoring Requirements 

HH. EPA seeks comment on the appropriate amount and types of monitoring that 

should be conducted at a GS site. 

IOGCC Response: The IOGCC agrees that owners and operators should report semiannually on the characteristics of injection fluids, injection pressure, flow 

rate, temperature, volume and annular pressure, and on the results of MITs, 

ground water monitoring, and any required atmospheric/soil gas monitoring. The 

amount and types of monitoring to be required, however, should be site specific. 

Response: EPA agrees that monitoring plans and methods need to be site-specific and believes that

the monitoring requirements for GS sites at §146.90 provide an appropriate level of flexibility in

structuring a testing and monitoring plan that protects USDWs from endangerment. The final

regulation provides for flexibility in: 1) methodologies used to collect these data, 2) the spatial

resolution at which the data should be collected, and 3) how often the data should be collected. The

number and placement of monitoring wells will be based on site-specific information such as the

calculated AoR, injection rate and volume, site geology, baseline data, and the presence of artificial

penetrations within the AoR. 

EPA adds that the final rule, at §146.91(a) requires that owners and operators report semi-annually

on operating data and some monitoring data. See the preamble to the final rule for additional

information. 

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil gas and surface air monitoring which may be required by the UIC Director

for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Steven Chester Letter ID: 0264

Commenter Organization: Michigan Department of Environmental Quality

(MDEQ)

Comment ID:

22844

Other EPA Comment Codes and Descriptions: 4670 2.6.7 Surface air monitoring and/or soil gas

monitoring (seeking comment) 

Comment: EPA (III . A. 6.) seeks comment on the amount and types of monitoring to be 

conducted at GS sites. 

- Staff is not certain that the monitoring parameters listed will yield any 
information that relates to endangerment of USDW by leakage from the sequestration 

zone with the exception of the determination of the position of the CO2 plume and 

area of elevated pressure. Staff believes, however, that the surface casing and 

tubing pressures, injection rates, and volumes should be measured daily and 

reported on a monthly basis. It is not clear that surface monitoring will 

provide unambiguous information regarding the position of the injected CO2 

plume, particularly in view of the uncertainty associated with the movement of the 

plume. It is also not clear that wells in the confining zone will be of any value 

since there may be no fluid movement into any particular well, and there is much 

uncertainty as to appropriate or optimum placement of confining zone monitoring 

wells. 

Response: EPA agrees that pressure monitoring in the confining zone may not provide the data

needed to evaluate plume movement. Instead, the final GS regulation, at §146.90(g)(1), requires all

GS project owners or operators to monitor for pressure changes in the injection zone. EPA believes

that pressure monitoring in the injection zone is necessary to track the development and movement

of the pressure front and CO2 plume which provides valuable information in determining whether

there is a potential for USDW endangerment. 

Pressure monitoring within the injection zone is necessary because any such monitoring above the

confining zone would not detect movement of the pressure front unless a breach of the confining

zone occurs. EPA believes that monitoring using wells in the injection zone (i.e., that penetrate the

confining zone) can be safely performed if the wells are constructed to prevent flow between the

injection zone and USDWs or other layers above the confining zone. Such construction technologies

exist and have been used in the oil and gas industry for years. 

EPA acknowledges that air and soil gas monitoring are subject to variability and may not be suitable

in all settings as a method to ensure USDW protection. However, EPA does not believe that this

should entirely preclude their use. For example, if a leak to the surface is suspected, surface

monitoring could provide vital information on its location and magnitude to assist owners and

operators in identifying what USDWs may have been impacted by a leak. EPA clarifies that the

various air and soil gas monitoring methods (e.g., chambers, eddy covariance, hyperspectral

imaging) all have different capabilities that may prove useful in specific GS projects (Miles, et al.

2005; Pickles and Cover, 2005; IPCC, 2005; Menzies, et al. 2001). The final rule at §146.90(h)

retains the allowance for surface air and soil gas monitoring at the discretion of the Director as a

means of identifying leaks that may pose a risk to USDWs and informing emergency notification of

a Class VI owner or operator and UIC Director in the event of a USDW endangerment, pursuant to

requirements at §146.91(c). EPA clarifies that the decision to use surface monitoring and the

selection of monitoring methods will be site-specific (e.g., may be influenced by geology, injection

depth, and operational conditions) and must be based on potential risks to USDWs within the AoR.

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil gas and surface air monitoring which may be required by the UIC Director

for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.
Commenter Name: Scott Anderson Letter ID: 0510

Commenter Organization: Environmental Defense Fund Comment ID: 21222

Comment: And we're pleased that 146.90 requires periodic monitoring both the ground water 

quality and geo-chemical changes above the confining zone. That is really 

critical to making sure that there's no leaking of fluids or CO2 through the 

confining zone. 

Response: EPA acknowledges the comment; the final rule retains this approach. EPA believes that

the ground water geochemical monitoring outlined in §146.90(d) will maximize protection of

USDWs from endangerment at GS sites. Direct geochemical sampling is an important part of a

monitoring program. EPA agrees that direct monitoring for ground water quality above the confining

zone is important, and the GS rule requires this at §146.90(d). Monitoring in additional formations,

e.g., the injection zone, may also be necessary, and if the Director believes such monitoring is

warranted he/she has the authority to require that it be included in the testing and monitoring plan.

Commenter Name: Scott Anderson Letter ID: 0520

Commenter Organization: Environmental Defense Fund Comment ID: 21420

Other EPA Comment Codes and Descriptions: 1420 1.2.1.1 Support the GS rulemaking; 3310

2.2.1.1 Comments in favor of requiring computational models to delineate the AoR (seeking

comment) 

Comment: We think the rule, the proposed rule has done a very good job of keeping the 

focus on both CO2 leakage risks and also the risk of problems from displaced 

brine. The confining zone in the rule is required to contain both CO2 and 

displaced formation fluids. The zone of elevated pressure as defined in the rule 

focuses on both CO2 and formation fluids that might be driven out of a US -- 

into a USDW. The modeling requirements are modeling both of the CO2 plume extent 

and formation fluid movement. There is the requirement for periodic monitoring 

of groundwater quality and geochemical changes above the confining zone which 

would help detail whether either CO2 or brine is leaking and there are adequate 

response provisions. 

Response: EPA acknowledges the commenter’s support and believes that predicting the complex

multiphase, buoyant flow of the CO2, co-injectates, and compounds that may be mobilized due to

injection requires the sophistication of computational models, as required at §146.84(c)(1). Models

can predict CO2 fate and transport, as well as changes in formation pressure, in three dimensions, as

a function of time in order to delineate the subsurface storage site and the AoR. Models can account

for site-specific and predicted operating conditions as well as geologic heterogeneities and potential

migration through faults, fractures, and artificial penetrations.

EPA believes that the creation of a new injection well class (VI) under the existing UIC Program is

necessary to enable the use of GS as a climate change mitigation technology in a manner that

protects USDWs from endangerment. EPA agrees that the UIC Program, under the authority of the

SDWA, provides a strong framework for regulating injection of CO2 for GS and adds that the GS

regulation tailors the UIC requirements to address the unique issues associated with large-scale GS

including large injection volumes, the relative buoyancy of CO2, its corrosivity in the presence of

water, the potential presence of impurities in captured CO2, and its mobility within subsurface

geologic formations. For additional information on well construction, siting, and testing and

monitoring requirements, please also see the discussion of EPA’s Final Regulatory Approach in the

preamble to the final GS rule.
Commenter Name: Doug Louis Letter ID: 0530

Commenter Organization: Kansas Corporation Commission Comment ID: 21339

Comment: determined and defined for regulatory certainty. The rules should be more 

specific as to what geochemical data needs to be collected; that is from the 

injection formation, the confining layer or from the USDW. 

Response: Section §146.90(d) requires periodic monitoring of the ground water quality and

geochemical changes above the confining zone(s). Monitoring above the confining layer will provide

an indication of upward movement of CO2 that might endanger a USDW. The exact number of

formations to be tested must, however, be based on site-specific characteristics and vulnerabilities

and described in the Director-approved testing and monitoring plan.

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil gas and surface air monitoring which may be required by the UIC Director

for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Comment Code: 4670 2.6.7 Surface air monitoring and/or soil gas monitoring (seeking comment) 

Individual Comments

Commenter Name: Karl R. Moor Letter ID: 0109

Commenter Organization: Southern Company, on behalf of Edison Electric

Institute (EEI)

Comment ID:

22000

Other EPA Comment Codes and Descriptions: 4490 2.4.5 Use of tracers and potential impact on

human health or ecosystems (seeking comment) 

Comment: Similarly, EPA should not require the use of tracers or soil flux to monitor for 

possible carbon dioxide leaks. Not only are tracers relatively untested when it 

comes to their ability to monitor such leaks - and, in fact, the best tracer for 

monitoring carbon dioxide leaks would be CO2 itself - but they also will not 

transmit information sufficiently early to provide any sort of real protection 

to underground sources of drinking water. Soil flux monitoring is problematic 

because it can result in false positives based on natural variability in the 

earth flux rate. What these requirements would do, however, is signal to the 

public that carbon capture and storage is unsafe because it might be leaking 

CO2, despite the fact that this is very unlikely to happen. The United Nations’ 

Intergovernmental Panel on Climate Change has found that the amount of carbon 

dioxide retained in appropriately sited storage sites is very likely to exceed 

99 percent over 100 years. 

Response: EPA acknowledges that air and soil gas monitoring are subject to variability and may not

be suitable in all settings as a method to ensure USDW protection. However, EPA does not believe
that this should entirely preclude their use. For example, if a leak to the surface is suspected, surface

monitoring could provide vital information on its location and magnitude to assist owners and

operators in identifying what USDWs may have been impacted by a leak. EPA clarifies that the

various air and soil gas monitoring methods (e.g., chambers, eddy covariance, hyperspectral

imaging) all have different capabilities that may prove useful in specific GS projects (Miles et al.,

2005; Pickles and Cover, 2005; IPCC, 2005; Menzies et al., 2001). The occurrence of false positives

will be reduced by comparing monitoring data to baseline data collected prior to injection or from a

nearby area away from the GS project.

The final rule at §146.90(h) retains the allowance for surface air and soil gas monitoring at the

discretion of the Director as a means of identifying leaks that may pose a risk to USDWs and

informing emergency notification of a Class VI owner or operator and UIC Director in the event of a

USDW endangerment, pursuant to requirements at §146.91(c). EPA clarifies that the decision to use

surface monitoring and the selection of monitoring methods will be site-specific (e.g., may be

influenced by geology, injection depth, and operational conditions) and must be based on potential

risks to USDWs within the AoR. 

EPA agrees that the use of tracers should not be required at all GS sites, but should be available as

an option. For this reason, EPA does not require the use of tracers at all GS sites; however, the

Director has discretion to require their use if he/she determines that the use of tracers could improve

monitoring of the site and enhance USDW protection from endangerment. The rule will also allow

their use if proposed by the owner or operator and approved by the Director. 

EPA agrees that the CO2 itself may serve as a tracer in the form of stable isotopes of carbon. For

example, anthropogenic CO2 is depleted in 13C compared to naturally occurring CO2. If tracers are

determined to be necessary at a GS site, this may be an appropriate option.

EPA disagrees that the use of tracers, if needed, would signal to the public that GS is unsafe. EPA

believes that tracers can be useful tools for monitoring, plume tracking, and verification at GS sites

and may help improve public confidence in certain projects. EPA believes that providing the public

with important information about the project, including how tracers would be an integral part of the

site monitoring plan, will be a key part of improving public acceptance of specific projects and GS

technology in general.

Commenter Name: Leslie Savage Letter ID: 0122

Commenter Organization: Railroad Commission of Texas (RRC) Comment ID: 24752

Comment: c. delete references to air and soil gas monitoring, since such monitoring is a 

case of too little too late - and can result in false positives due to ambient 

variability; and 

Response: EPA acknowledges that air and soil gas monitoring are subject to variability and may not

be suitable in all settings as a method to ensure USDW protection. However, EPA does not believe

that this should entirely preclude their use. For example, if a leak to the surface is suspected, surface

monitoring could provide vital information on its location and magnitude to assist owners and

operators in identifying what USDWs may have been impacted by a leak. EPA clarifies that the

various air and soil gas monitoring methods (e.g., chambers, eddy covariance, hyperspectral

imaging) all have different capabilities that may prove useful in specific GS projects (Miles et al.,

2005; Pickles and Cover, 2005; IPCC, 2005; Menzies et al., 2001). The occurrence of false positives

will be reduced by comparing monitoring data to baseline data collected prior to injection or from a

nearby area away from the GS project.
The final rule at §146.90(h) retains the allowance for surface air and soil gas monitoring at the

discretion of the Director as a means of identifying leaks that may pose a risk to USDWs and

informing emergency notification of a Class VI owner or operator and UIC Director in the event of a

USDW endangerment, pursuant to requirements at §146.91(c). EPA clarifies that the decision to use

surface monitoring and the selection of monitoring methods will be site-specific (e.g., may be

influenced by geology, injection depth, and operational conditions) and must be based on potential

risks to USDWs within the AoR.

Commenter Name: Leslie Savage Letter ID: 0122

Commenter Organization: Railroad Commission of Texas (RRC) Comment ID: 24797

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: (h) At the Director's discretion, surface air monitoring and/or soil gas 

monitoring to detect movement of carbon dioxide that could endanger a USDW. (1) 

The testing and monitoring plan must be based on potential vulnerabilities 

within the area of review; (2) The monitoring frequency and spatial distribution 

of surface air monitoring and/or soil gas monitoring must reflect baseline data 

and the monitoring plan must include how the proposed monitoring will yield 

useful information on the area of review delineation and/or compliance with 

standards under 40 CFR 144.12;

{Any requirement for surface air monitoring and/or soil gas monitoring is not 

warranted. If the purpose is to detect "movement of carbon dioxide that could 

endanger a USDW, it would be too late if carbon dioxide were detected in the air 

or soil. In addition, levels of ambient carbon dioxide are too variable for 

this to be useful. RRC suggests eliminating any potential requirement for 

surface air or soil gas monitoring, because formation monitoring should catch 

whatever condition might reasonably be expected to be caught by surface or soil 

gas monitoring. } 

Response: EPA acknowledges that air and soil gas monitoring to ensure USDW protection is not

necessary at all GS sites and believes that the decision to use surface monitoring and the selection of

monitoring methods for the purpose of USDW protection will be site-specific. In the final rule, at

§146.90(h), the decision to require such monitoring as an additional measure to ensure USDW

protection rests with the Director as a means of identifying leaks that may pose a risk to USDWs and

informing emergency notification of a Class VI owner or operator and UIC Director in the event of a

USDW endangerment, pursuant to requirements at §146.91(c).

EPA clarifies that subsurface geochemical and pressure monitoring in the subsurface formations are

the first line of monitoring that would allow detection of potential endangerment to USDWs from GS

activities (this is required at all GS sites, as described at §146.90(d)). The Agency also believes that

surface air and soil gas monitoring, when coupled with subsurface monitoring, may be appropriate at

some GS projects to ensure USDW protection. EPA acknowledges that surface air and soil gas

monitoring may not be suitable in all settings as a method to ensure USDW protection. However,

EPA does not believe that this should entirely preclude their use. The decision to use surface

monitoring and the selection of monitoring methods will be site-specific (e.g., may be influenced by

geology, injection depth, and operational conditions) and must be based on potential risks to USDWs

within the AoR.
Commenter Name: Christine Reimer Letter ID: 0142

Commenter Organization: National Ground Water Association Comment ID: 22569

Other EPA Comment Codes and Descriptions: 4490 2.4.5 Use of tracers and potential impact on

human health or ecosystems (seeking comment) 

Comment: Although surface monitoring may be needed from a community outreach and 

environmental safety point of view, it is important to note that by the time any 

leakage is detected at the surface it will have already passed by and possibly 

impacted underground drinking waters. Projects like the Frio brine project 

[McCallum et al, 2005] have incorporated tracers as a way to identify CO2 

leakage. The use of non-isotopic tracers, tracers other than C13, C14, and O18 

that occur naturally in CO2, should be studied very carefully for unintended 

environmental effects prior to implementation. 

McCallum, S.D., Riestenberg, D.E., Cole, D.R., Freifeld, B.M., Trautz, R.C., 

Havorka, S.D., and Phelps, T.J., 2005, "Monitoring geologically sequestered CO2 

during the Frio brine pilot test using perfluorocarbon tracers," Proceedings of 

the 4th Annual Conference on Carbon Capture and Sequestration, May 2-5, 2005, 

Monitor and Exchange Publications and Forum, Washington, D.C. 

Response: EPA clarifies that subsurface geochemical and pressure monitoring in the subsurface

formations are the first line of monitoring that would allow detection of potential endangerment to

USDWs from GS activities (this is required at all GS sites, as described at §146.90(d)). The Agency

also believes that surface air and soil gas monitoring, when coupled with subsurface monitoring,

may be appropriate at some GS projects to ensure USDW protection. EPA acknowledges that surface

air and soil gas monitoring may not be suitable in all settings as a method to ensure USDW

protection. However, EPA does not believe that this should entirely preclude their use. The decision

to use surface monitoring and the selection of monitoring methods will be site-specific (e.g., may be

influenced by geology, injection depth, and operational conditions) and must be based on potential

risks to USDWs within the AoR.

If surface monitoring were the only monitoring method employed to ensure USDW protection, direct

correlation of CO2 at the surface with CO2 in the subsurface might be difficult; however, when

combined with information gathered through other monitoring techniques required of GS well

owners and operators (e.g., monitoring wells, geophysical techniques), air and soil gas monitoring

may provide valuable data on the magnitude and location of a leak. The CO2 itself may serve as a

tracer in the form of stable isotopes of carbon. For example, anthropogenic CO2 is depleted in 13C

compared to naturally occurring CO2.

The final rule at §146.90(h) retains the allowance for surface air and soil gas monitoring at the

discretion of the Director as a means of identifying leaks that may pose a risk to USDWs and

informing emergency notification of a Class VI owner or operator and UIC Director in the event of a

USDW endangerment, pursuant to requirements at §146.91(c).

EPA believes that, in some circumstances, tracers can be an important component of a multifaceted

approach to monitoring GS projects. However, the Agency recognizes that tracers may not be

appropriate in all GS projects. For this reason, EPA does not require the use of tracers at all GS sites;

however, the Director has discretion to require their use if he/she determines that the use of tracers

could improve monitoring of the site and enhance USDW protection from endangerment.
Commenter Name: Brianne Metzger Letter ID: 0151

Commenter Organization: Spectra Energy Corp Comment ID: 21843

Comment: H. The Requirement To Perform Ambient Monitoring Exceeds EPA’s Authority Under 

SDWA. 

EPA is also proposing that the Director be given discretion to require surface 

air monitoring and/or soil gas monitoring to detect movement of carbon dioxide 

that could endanger a USDW. 40 C.F.R. § 146.90(h). We would recommend that 

this provision be deleted. It is not clear how ambient air or soil gas 

monitoring is related to or supports the protection of USDWs. Based on our 

experience, the use of surface air monitoring can frequently result in false 

positives, which could prompt unnecessary and costly response actions and 

needlessly alarm the public. We believe that targeted ground water monitoring 

and other wellhead testing and monitoring requirements are sufficient to detect 

any movement of CO2 that could endanger a USDW. Given the narrow scope of SDWA 

authority, we question the Agency’s authority to directly or indirectly require 

such monitoring where it does not naturally bear on the protection of USDWs. If 

EPA should decide to retain this provision in the final rule, we would ask the 

Agency to clarify that any requirement for ambient air or soil gas monitoring 

would be purely discretionary on the part of the State, would be pursuant only 

to state law and not the federal UIC program, and thus would not be federally 

enforceable. Bath Petroleum Storage, Inc. v. Sovas, 309 F.Supp. 2d 357 (N.D. 

N.Y. 2004) (state law requiring sonar survey for UIC injection not federally 

enforceable). 

Response: The final rule at §146.90(h) retains the allowance for surface air and soil gas monitoring

at the discretion of the Director as a means of identifying leaks that may pose a risk to USDWs and

informing emergency notification of a Class VI owner or operator and UIC Director in the event of a

USDW endangerment, pursuant to requirements at §146.91(c). EPA clarifies that the decision to use

surface monitoring and the selection of monitoring methods will be site-specific (e.g., may be

influenced by geology, injection depth, and operational conditions) and must be based on potential

risks to USDWs within the AoR. 

EPA believes that surface air and soil gas monitoring are within the scope of the SDWA in that they

can provide additional data to pinpoint the location and magnitude (or absence) of leaks that could

endanger USDWs. Used in conjunction with deep subsurface monitoring, as required at §146.90, and

as part of a multi-barrier approach to protecting USDWs from endangerment, surface air and soil gas

monitoring are within the scope of SDWA’s general authority (SDWA sections 1421 et al). 

The Agency believes that surface air and soil gas monitoring, when coupled with subsurface

monitoring, may be appropriate at some GS projects to ensure USDW protection. EPA also

acknowledges that surface air and soil gas measurements are subject to variability and may not be

suitable in all settings as a method to ensure USDW protection. However, EPA does not believe that

this should entirely preclude their use. The decision to use surface monitoring and the selection of

monitoring methods will be site-specific (e.g., may be influenced by geology, injection depth, and

operational conditions) and must be based on potential risks to USDWs within the AoR.

Commenter Name: James Childress Letter ID: 0158

Commenter Organization: Gasification Technologies Council (GTC) Comment ID: 23776
Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: §146.90 Testing and monitoring requirements. (71) "At the Director's discretion, 

surface air monitoring and/or soil gas monitoring to detect movement of carbon 

dioxide that could endanger a USDW. " 

We recommend deletion of this requirement in its entirety. While this 

requirement may be suitable for determining potential air leakage relevant to 

monitoring of CO2 in a greenhouse gas policy context, this requirement does not 

provide any additional protection to migration to USDW as surface breakthrough 

will only occur well after the deep-surface migration of CO2 to a USDW. Surface 

monitoring to detect CO2 has high uncertainty and seasonal variability that is 

likely to result in many false positives and operational distractions. Seismic 

methods of tracking the CO2 plume are more effective than soil gas monitoring of 

CO2, which is affected by many other factors and thus is highly variable. 

Response: EPA acknowledges that surface air and soil gas measurements are subject to variability

and may not be suitable in all settings as a method to ensure USDW protection. However, EPA does

not believe that this should entirely preclude their use. The decision to use surface monitoring and

the selection of monitoring methods will be site-specific (e.g., may be influenced by geology,

injection depth, and operational conditions) and must be based on potential risks to USDWs within

the AoR. The Agency believes that surface air and soil gas monitoring, when coupled with

subsurface monitoring, may be appropriate at some GS projects to ensure USDW protection.

The final rule at §146.90(h) retains the allowance for surface air and soil gas monitoring at the

discretion of the Director as a means of identifying leaks that may pose a risk to USDWs and

informing emergency notification of a Class VI owner or operator and UIC Director in the event of a

USDW endangerment, pursuant to requirements at §146.91(c). EPA clarifies that the decision to use

surface monitoring and the selection of monitoring methods will be site-specific (e.g., may be

influenced by geology, injection depth, and operational conditions) and must be based on potential

risks to USDWs within the AoR.

Commenter Name: James Childress Letter ID: 0158

Commenter Organization: Gasification Technologies Council (GTC) Comment ID: 23786

Comment: EPA seeks comment on the appropriate amount and types of monitoring that should 

be conducted at a GS site. Specifically. EPA seeks comment regarding the 

usefulness of indirect geophysical monitoring and surface air and soil gas 

monitoring. In addition, EPA seeks comment regarding the use of a Directorapproved monitoring plan for GS sites. EPA Notice 111 

Surface air and soil gas monitoring are not useful. Seismic methods of tracking 

the CO2 plume are more effective than soil gas monitoring of CO2, which is 

affected by many other factors and thus is highly variable. Surface breakthrough 

represents an "after-the-fact" event. While this requirement may be suitable for 

determining potential air CO2 leakage relevant to monitoring of CO2 in a GHG 

context, this requirement does not provide any additional protection to 

migration to USDW as surface CO2 breakthrough will only occur well after the 

deep-surface migration of CO2 to a USDW. Surface monitoring to detect CO2 has 
high uncertainty and seasonal variability that is likely to result in many false 

positives, operational distractions and unduly raise public concern. 

Response: EPA clarifies that subsurface geochemical and pressure monitoring in the subsurface

formations are the first line of monitoring that would allow detection of potential endangerment to

USDWs from GS activities (this is required at all GS sites, as described at §146.90(d)). The Agency

also believes that surface air and soil gas monitoring, when coupled with subsurface monitoring,

may be appropriate at some GS projects to ensure USDW protection. 

EPA clarifies that surface air and soil gas monitoring are not required at all GS sites. However, the

GS rule at §146.90(h) gives the Director discretion to require surface air and/or soil gas monitoring

as a means of identifying leaks that may pose a risk to USDWs and informing emergency

notification of a Class VI owner or operator and UIC Director in the event of a USDW

endangerment, pursuant to requirements at §146.91(c). EPA clarifies that the decision to use surface

monitoring and the selection of monitoring methods will be site-specific (e.g., may be influenced by

geology, injection depth, and operational conditions) and must be based on potential risks to USDWs

within the AoR.

EPA acknowledges that air and soil gas monitoring are subject to variability and may not be suitable

in all settings as a method to ensure USDW protection. However, EPA does not believe that this

should entirely preclude their use. The decision to use surface monitoring and the selection of

monitoring methods will be site-specific (e.g., may be influenced by geology, injection depth, and

operational conditions) and must be based on potential risks to USDWs within the AoR.

Commenter Name: James Devine Letter ID: 0166

Commenter Organization: United States Geological Survey (USGS) Comment ID: 21352

Comment: Section 146.90 (h), Testing and Monitoring Requirements, FR page 43540 

This section requires, at the Director's discretion, "surface air monitoring 

and/or soil gas monitoring to detect movement of carbon dioxide that could 

endanger a USDW (underground source ofdrinking water)." In § 146.90 (h)(1) and 

(h)(2), the proposed regulations qualify the application of gas monitoring to 

sites with suitable conditions and adequate baseline data, that is, sites amenable 

to the technique. 

Current methods for measurement of carbon dioxide in air or soil gas are 

adequate for the measurement of carbon dioxide; that is, the analytical 

methodologies are well-developed. However, the representativeness of the samples 

and interference from other natural and man- made sources of carbon dioxide can 

make for problematic correlation of carbon dioxide in the air or soil to carbon 

dioxide from deep subsurface storage leaks. The efficacy of such correlation 

techniques are not well-demonstrated by research to date, as evidenced by the 

paucity of literature on the subject. Correlation with potential endangerment to 

an USDWis even less understood. As a result, requiring such monitoring at this 

point amounts to requiring the owner or operator to conduct research into a 

technique that is not yet well established. Poorly understood detections 

of elevated carbon dioxide may cause operational disruptions, such as short or 

long-term cessation of injection, while the monitoring results are investigated 

and interpreted. 
Response: EPA acknowledges that air and soil gas monitoring are subject to site-specific limitations

and may not be suitable in all settings as a method to ensure USDW protection. However, EPA does

not believe that this should entirely preclude their use. If surface monitoring were the only

monitoring method employed to ensure USDW protection, direct correlation of CO2 at the surface

with CO2 in the subsurface might be difficult; however, when combined with information gathered

through other monitoring techniques required of GS well owners and operators (e.g., monitoring

wells, geophysical techniques), air and soil gas monitoring may provide valuable data on the

magnitude and location of a leak. 

The final rule at §146.90(h) retains the allowance for surface air and soil gas monitoring at the

discretion of the Director as a means of identifying leaks that may pose a risk to USDWs and

informing emergency notification of a Class VI owner or operator and UIC Director in the event of a

USDW endangerment, pursuant to requirements at §146.91(c). The decision to use surface

monitoring and the selection of monitoring methods will be site-specific (e.g., may be influenced by

geology, injection depth, and operational conditions) and must be based on potential risks to USDWs

within the AoR. 

Used in conjunction with deep subsurface monitoring, as required at §146.90, and as part of a multibarrier approach to protecting USDWs from endangerment, surface air and soil gas monitoring will

increase USDW protection, enable immediate notification of the UIC Director in the case of

potential USDW endangerment, and facilitate remedial action.

Commenter Name: Kyle Isakower Letter ID: 0170

Commenter Organization: American Petroleum Institute Comment ID: 24195

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Rule Provision: 146.90(h) 

API Comments: (h) At the Director’s discretion BASED ON SITE-SPECIFIC CONDITIONS 

AND RISK-BASED FACTORS, surface air monitoring and/or soil gas monitoring to 

detect movement of carbon dioxide that could endanger a USDW. 

Rationale: In most situations soil and air monitoring does not provide an 

effective method of protecting USDWs. 

Response: EPA clarifies that subsurface geochemical and pressure monitoring in the subsurface

formations are the first line of monitoring that would allow detection of potential endangerment to

USDWs from GS activities (this is required at all GS sites, as described at §146.90(d)). The Agency

also believes that surface air and soil gas monitoring, when coupled with subsurface monitoring,

may be appropriate at some GS projects to ensure USDW protection. 

The final rule at §146.90(h) retains the allowance for surface air and soil gas monitoring at the

discretion of the Director as a means of identifying leaks that may pose a risk to USDWs and

informing emergency notification of a Class VI owner or operator and UIC Director in the event of a

USDW endangerment, pursuant to requirements at §146.91(c).

The selection of monitoring methods will be site-specific (e.g., may be influenced by geology,

injection depth, and operational conditions) and must be based on potential risks to USDWs within
the AoR.

Commenter Name: Kyle Isakower Letter ID: 0170

Commenter Organization: American Petroleum Institute Comment ID: 24250

Comment: EPA Preamble Question: 33. EPA seeks comment on the appropriate amount and types 

of monitoring that should be conducted at a GS site. Specifically, EPA seeks 

comment regarding the usefulness of indirect geophysical monitoring and surface 

air and soil gas monitoring. In addition, EPA seeks comment regarding the use of 

a Director-approved monitoring plan for GS sites. EPA Notice 43517. 

API Response: Monitoring techniques and frequency should be determined on a 

site-specific basis. Selection of monitoring types and frequency should balance 

the potential risks posed by the project with the cost of monitoring. Surface 

and soil gas monitoring does not add value to the protection of USDWs. Many of 

the surface and soil gas monitoring techniques currently being evaluated lack 

the track record necessary for use in a regulatory compliance setting. Moreover, 

the potential for false-positives could undermine public confidence in GS 

technologies. EPA should defer on using surface and soil gas monitoring 

technologies until the DOE Regional Partnerships can demonstrate their 

effectiveness. 

Response: As described above, EPA acknowledges that air and soil gas monitoring to ensure

USDW protection is not necessary at all GS sites and agrees that the decision to use surface

monitoring and the selection of monitoring methods for the purpose of USDW protection will be

site-specific. 

EPA acknowledges that air and soil gas monitoring are subject to variability and may not be suitable

in all settings as a method to ensure USDW protection. However, EPA does not believe that this

should entirely preclude their use. For example, if a leak to the surface is suspected, surface

monitoring could provide vital information on its location and magnitude to assist owners and

operators in identifying what USDWs may have been impacted by a leak. EPA clarifies that the

various air and soil gas monitoring methods (e.g., chambers, eddy covariance, hyperspectral

imaging) all have different capabilities that may prove useful in specific GS projects (Miles et al.,

2005; Pickles and Cover, 2005; IPCC, 2005; Menzies et al., 2001). The occurrence of false positives

will be reduced by comparing monitoring data to baseline data collected prior to injection or from a

nearby area away from the GS project.

Commenter Name: James Rower Letter ID: 0173

Commenter Organization: Utility Solid Waste Activities Group (USWAG) Comment ID: 23490

Other EPA Comment Codes and Descriptions: 1400 1.2 Comments on EPA's Authority to

Regulate Injection of CO2 

Comment: It also is important to clarify in the Final Rule that well plugging is only 

necessary and appropriate for those wells that are potential conduits of 

contamination to USDWs. USWAG raises this point because EPA suggests that the 

Final Rule may give the Director discretion to require Owners or Operators to 

conduct surface air monitoring and/or soil gas monitoring in the AoR. Id. at 

43516. Such a requirement would be appropriate only to the extent that this 

monitoring would be done with the goal of identifying potential endangerment of 
USDWs as a result of CO2 injection and sequestration activities. Id. To the 

extent that such monitoring would be required simply to guard against potential 

atmospheric releases or to trigger a corrective action requirement to terminate 

such atmospheric releases, it would be outside of the scope of EPA's authority 

under this rulemaking. See id. at 43498 ("preventing releases of CO2 to the 

atmosphere is not within the scope of this proposal"). 

Response: EPA believes that surface air and soil gas monitoring are within the scope of the SDWA

in that they can provide additional data to pinpoint the location and magnitude (or absence) of leaks

that could endanger USDWs. Used in conjunction with deep subsurface monitoring, as required at

§146.90, and as part of a multi-barrier approach to protecting USDWs from endangerment, surface

air and soil gas monitoring are within the scope of SDWA’s general authority (SDWA sections 1421

et al.).

EPA clarifies that use of surface air and soil gas monitoring as specified in the final GS rule at

§146.90(h), as a means of identifying leaks that may pose a risk to USDWs and informing

emergency notification of a Class VI owner or operator and UIC Director in the event of a USDW

endangerment, pursuant to requirements at §146.91(c), is at the Director's discretion.

Regarding corrective action for wells in the AoR, EPA clarifies that the rule, at §146.84(d), requires

owners or operators to perform corrective action on all deficient wells in the AoR. This requirement

is independent of the testing and monitoring requirements at §146.90.

Commenter Name: James Rower Letter ID: 0173

Commenter Organization: Utility Solid Waste Activities Group (USWAG) Comment ID: 23499

Comment: With respect to the Proposal's suggestion for surface monitoring requirements, 

USWAG believes that such requirements will come at significant cost with little 

benefit. While surface monitoring may reveal CO2 migration, these data will be 

of limited use since, by that point, CO2 has already been released to the 

surface. Moreover, data from surface air and soil gas monitoring are complicated 

by a number of factors, including natural and anthropogenic impacts from fires, 

development, and population growth. Rather than spending significant resources 

on gathering data that are of limited reliability and of little practical use in 

preventing surface releases, the Final Rule should direct that these resources 

will be put towards detection of subsurface CO2 movement. This would prove a far 

more effective use of monitoring resources as it would enable Owners or 

Operators to correct any problems before CO2 reaches the surface. 

Response: EPA acknowledges that air and soil gas monitoring are subject to variability and may not

be suitable in all settings as a method to ensure USDW protection. However, the Agency believes

that surface air and soil gas monitoring, when coupled with subsurface monitoring, may be

appropriate at some GS projects to ensure USDW protection. However, EPA does not believe that

this should entirely preclude their use. For example, if a leak to the surface is suspected, surface

monitoring could provide vital information on its location and magnitude to assist owners and

operators in identifying what USDWs may have been impacted by a leak. EPA clarifies that the

various air and soil gas monitoring methods (e.g., chambers, eddy covariance, hyperspectral

imaging) all have different capabilities that may prove useful in specific GS projects (Miles et al.,

2005; Pickles and Cover, 2005; IPCC, 2005; Menzies et al., 2001). The occurrence of false positives
will be reduced by comparing monitoring data to baseline data collected prior to injection or from a

nearby area away from the GS project.

Commenter Name: Kenneth Nemeth Letter ID: 0176

Commenter Organization: Southern States Energy Board Comment ID: 23543

Other EPA Comment Codes and Descriptions: 4490 2.4.5 Use of tracers and potential impact on

human health or ecosystems (seeking comment) 

Comment: pressure front. CO2 monitoring should be fit for purpose. Air and soil gas 

monitoring is unlikely to be beneficial, and the use of tracers should be at the 

discretion of the owner/operator. 

Response: EPA acknowledges that air and soil gas monitoring to ensure USDW protection is not

necessary at all GS sites and agrees that the decision to use surface monitoring and the selection of

monitoring methods for the purpose of USDW protection will be site-specific.

The Agency believes that surface air and soil gas monitoring, when coupled with subsurface

monitoring, may be appropriate at some GS projects to ensure USDW protection. EPA also

acknowledges that surface air and soil gas measurements are subject to variability and may not be

suitable in all settings as a method to ensure USDW protection. However, EPA does not believe that

this should entirely preclude their use. The decision to use surface monitoring and the selection of

monitoring methods will be site-specific (e.g., may be influenced by geology, injection depth, and

operational conditions) and must be based on potential risks to USDWs within the AoR. 

If surface monitoring were the only monitoring method employed to ensure USDW protection, direct

correlation of CO2 at the surface with CO2 in the subsurface might be difficult; however, when

combined with information gathered through other monitoring techniques required of GS well

owners and operators (e.g., monitoring wells, geophysical techniques), air and soil gas monitoring

may provide valuable data on the magnitude and location of a leak. The CO2 itself may serve as a

tracer in the form of stable isotopes of carbon. For example, anthropogenic CO2 is depleted in 13C

compared to naturally occurring CO2.

In the final rule, at §146.90(h), the decision to require such monitoring as an additional measure to

ensure USDW protection rests with the Director as a means of identifying leaks that may pose a risk

to USDWs and informing emergency notification of a Class VI owner or operator and UIC Director

in the event of a USDW endangerment, pursuant to requirements at §146.91(c).

EPA agrees that the use of tracers may not be appropriate for all GS sites, but should be available as

an option. For this reason, EPA does not require the use of tracers at all GS sites; however, the

Director has discretion to require their use if he/she determines that the use of tracers could improve

monitoring of the site and enhance USDW protection from endangerment. The rule will also allow

their use if proposed by the owner or operator and approved by the Director.

Commenter Name: Quinlan J. Shea Letter ID: 0177

Commenter Organization: Edison Electric Institute Comment ID: 23553

Other EPA Comment Codes and Descriptions: 4490 2.4.5 Use of tracers and potential impact on

human health or ecosystems (seeking comment) 

Comment: EEI is also concerned about proposed requirements related to monitoring for 

potential CO2 movement and the use of tracers. Under the proposed regulations, 
the UIC program director would have discretion to require the use of tracers or 

surface air/soil gas monitoring "to detect movement of CO2 that could endanger a 

USDW." Tracers and surface air/soil gas monitoring should not be required, and 

may create an overly negative and unwarranted public perception regarding the 

safety of GS projects or tracers. 

Response: EPA believes that monitoring at a GS site is of critical importance to ensuring protection

of USDWs from endangerment. Appropriately selected monitoring technologies, including surface

air and soil-gas monitoring will also serve to increase public confidence in the safety of GS and to

assure the public that GS projects are being appropriately operated and monitored. The information

gained through such monitoring will also enable permitting authorities to take appropriate steps to

address any indication that USDWs may be endangered. 

If surface monitoring were the only monitoring method employed to ensure USDW protection, direct

correlation of CO2 at the surface with CO2 in the subsurface might be difficult; however, when

combined with information gathered through other monitoring techniques required of GS well

owners and operators (e.g., monitoring wells, geophysical techniques), air and soil gas monitoring

may provide valuable data on the magnitude and location of a leak. The CO2 itself may serve as a

tracer in the form of stable isotopes of carbon. For example, anthropogenic CO2 is depleted in 13C

compared to naturally occurring CO2. 

EPA clarifies that surface air and soil gas monitoring are not required at all GS sites. However, the

GS rule at §146.90(h) gives the Director discretion to require surface air and/or soil gas monitoring

as a means of identifying leaks that may pose a risk to USDWs and informing emergency

notification of a Class VI owner or operator and UIC Director in the event of a USDW

endangerment, pursuant to requirements at §146.91(c).

Regarding the use of tracers, EPA agrees that tracers may not be appropriate for all GS sites, but

should be available as an option. For this reason, EPA does not require the use of tracers at all GS

sites; however, the Director has discretion to require their use if he/she determines that the use of

tracers could improve monitoring of the site and enhance USDW protection from endangerment. The

rule will also allow their use if proposed by the owner or operator and approved by the Director.

Commenter Name: Quinlan J. Shea Letter ID: 0177

Commenter Organization: Edison Electric Institute Comment ID: 23589

Other EPA Comment Codes and Descriptions: 4490 2.4.5 Use of tracers and potential impact on

human health or ecosystems (seeking comment) 

Comment: D. Monitoring Provisions and Use of Tracers 

EEI is also concerned about proposed requirements related to monitoring for 

potential CO2 movement and the use of tracers. Under the proposed regulations, 

the UIC program director would have discretion to require the use of tracers or 

surface air/soil gas monitoring "to detect movement of CO2 that could endanger a 

USDW." For the reasons set forth below, EEI is opposed to such a requirement, 

even where, as proposed, it is left to the discretion of the program director. 

- Functionality, usefulness and cost: Tracers are relatively untested in terms 

of workability as a leak-detecting mechanism. Of greater concern, however, is 

the fact that using tracers or surface air or soil gas monitoring would likely 
provide too little information, too late, in terms of providing protection for 

USDW, in the sense that USDW would likely be affected by the time the results of 

such methods revealed any concerns. Moreover, by their very nature, tracers can 

be detected at ultra-low concentrations. If the tracer is spilled or a small 

amount leaked, or if a pipe downstream from the tracer injection point leaked, 

the surface air would become contaminated. Minute amounts of tracer might be 

detectable for quite a distance, making the likelihood of a false positive for 

the tracer much greater without any real benefit to the overall protection of 

USDW. In sum, if employed for purposes of long-term monitoring of underground 

waters, tracers would be unlikely to yield significant useful data and would 

prove extremely expensive. 

- Safety: Tracers may present their own safety concerns depending on the 

precise nature of the tracer at issue. Further, the use of tracers may pose 

independent risks for project operators. There may be potential health effects 

from some tracers if workers are accidentally exposed. 

Response: EPA clarifies that subsurface geochemical and pressure monitoring in the subsurface

formations are the first line of monitoring that would allow detection of potential endangerment to

USDWs from GS activities (this is required at all GS sites, as described at §146.90(d)). The Agency

also believes that surface air and soil gas monitoring, when coupled with subsurface monitoring,

may be appropriate at some GS projects to ensure USDW protection. EPA acknowledges that surface

air and soil gas monitoring may not be suitable in all settings as a method to ensure USDW

protection. However, EPA does not believe that this should entirely preclude their use. The decision

to use surface monitoring and the selection of monitoring methods will be site-specific (e.g., may be

influenced by geology, injection depth, and operational conditions) and must be based on potential

risks to USDWs within the AoR.

The final rule at §146.90(h) retains the allowance for surface air and soil gas monitoring at the

discretion of the Director as a means of identifying leaks that may pose a risk to USDWs and

informing emergency notification of a Class VI owner or operator and UIC Director in the event of a

USDW endangerment, pursuant to requirements at §146.91(c). 

As described above, EPA agrees that tracer use is not appropriate in all situations. EPA

acknowledges that some tracers may have the potential to cause harm to people or the environment.

For this reason, EPA does not require the use of tracers at all GS sites. Nevertheless, there are many

different types of tracers and not all are problematic; research is being done to overcome problems

with existing tracers. EPA believes that tracers have been used safely and successfully in other

applications. Therefore the Director has discretion to require their use if he/she determines that the

use of tracers could improve monitoring of the site and enhance USDW protection from

endangerment. The rule will also allow their use if proposed by the owner or operator and approved

by the Director.

EPA has been following new and ongoing research on the safety and efficacy of tracers, and

believes that, in some circumstances, tracers can be an effective part of monitoring GS projects. EPA

will continue to track research related to tracer use and plans to, every six years, collect and review

data on GS projects to determine whether the appropriate amount and types of information and

appropriate documentation are being collected, and to determine if modifications to the requirements

are appropriate or necessary.
Commenter Name: Quinlan J. Shea Letter ID: 0177

Commenter Organization: Edison Electric Institute Comment ID: 23591

Other EPA Comment Codes and Descriptions: 1400 1.2 Comments on EPA's Authority to

Regulate Injection of CO2 

Comment: - Potential issues of EPA authority: As noted above, EEI views the development 

and implementation of legally defensible regulations as a key to commercial 

deployment of CCS. To that end, EEI encourages the Agency to consider carefully 

the link between each proposed provision and its authority to regulate under 

SDWA. Where the link is more tenuous, the proposed provision may be subject to 

greater risk of legal challenge, posing uncertainty for those who desire to move 

ahead with projects. While, as the Agency points out, the use of tracers or 

surface air/soil gas monitoring could indicate that some threat to USDW may be 

posed, it seems more likely that by the time the results of such methods 

revealed any concerns, such sources would already be affected. Thus, the nexus 

between those methods and protection of USDW may be subject to challenge by 

opponents of the proposed provisions. And the nexus between surface air/soil 

gas monitoring and protection of USDW may be at greater risk of challenge, as 

the detection of a CO2 leak to surface air conceivably provides no useful 

information that would serve to protect USDW. Indeed, while EPA notes in the 

preamble that detection of leakage to the surface "would indicate potential 

endangerment" to USDW as a last line of defense, the Agency also acknowledges 

that regulation of surface or atmospheric releases of CO2 are outside the scope 

of the proposed rules and the Agency‘s SDWA authority. 

While the proposed rules would leave these requirements to the discretion of the 

UIC program director, again the proposal sets no clear parameters for the 

exercise of such discretion. EEI does not believe that any provisions related 

to the use of tracers are required or warranted for the protection of USDW, but 

should EPA choose to impose a discretionary requirement, any such requirement 

should be bounded by appropriate parameters for its use. 

Response: As described above, subsurface geochemical and pressure monitoring in the subsurface

formations are the first line of monitoring that would allow detection of potential endangerment to

USDWs from GS activities (this is required at all GS sites, as described at §146.90(d)). 

EPA agrees that the implementation of the GS rule in a manner that ensures protection of USDWs

from endangerment is important to establishing a foundation for further advances in the field of CO2

GS. EPA acknowledges the need for regulatory certainty: the final GS requirements provide a level

of certainty by setting forth unique requirements for GS. These requirements include: the tailored

AoR delineation process under §146.84, the types of monitoring appropriate to GS projects under

§146.90, and the post-injection site care process under §146.93. 

While EPA agrees with commenters that a stable, predictable, nationally consistent, and workable

regulatory framework is important, EPA stresses that the focus of the GS rule is to ensure that, where

GS is deployed, it is conducted in a manner that protects USDWs from endangerment.

EPA disagrees with the comment with respect to its authority under the SDWA and believes it

within the Agency’s authority to provide the Director with discretion to require surface air

monitoring and/or soil gas monitoring in the AoR at §146.90(h). This discretion is limited to

potential risks to USDWs within the AoR. EPA believes that monitoring for the injected fluid at the
surface for the purposes of protecting USDWs is within the jurisdiction of the SDWA. If the injected

CO2 were to migrate through fractures, abandoned well bore holes or other means, it would be

released in a gaseous form at the surface, and therefore must be monitored as such. EPA believes

that having this information can be critical to allow the Director to determine whether injected CO2

has migrated from the injection zone and endangered a USDW(s). 

EPA is developing guidance for permitting authorities that will include recommendations for how

Directors may exercise discretion in implementing the requirements of the GS rule, including the

testing and monitoring requirements. This guidance will be available on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

The final rule at §146.90(h) retains the allowance for surface air and soil gas monitoring at the

discretion of the Director as a means of identifying leaks that may pose a risk to USDWs and

informing emergency notification of a Class VI owner or operator and UIC Director in the event of a

USDW endangerment, pursuant to requirements at §146.91(c).

Commenter Name: Frederick R. Eames Letter ID: 0178

Commenter Organization: CCS Alliance Comment ID: 23873

Comment: Proposed section 146.90(h) gives Directors discretion to require surface air 

monitoring and/or soil gas monitoring to detect movement of CO2 that could 

endanger a USDW. The Alliance recommends deleting this provision. It is not 

clear how ambient air or soil gas monitoring is related to or supports the 

protection of USDWs. Surface air monitoring can result in false positives, which 

could prompt unnecessary and costly response actions and needlessly alarm the 

public Any requirement for ambient air or soil gas monitoring would be a matter 

of state discretion pursuant to state law and not the federal UIC program, and 

would not be federally enforceable. [FN51] 

[FN51] Bath Petroleum Storage , Inc. v. Sows, 309 F.Supp. 2d 357 (N.D.N.Y 2004) 

(state law requiring sonar survey for UIC injection not federally enforceable). 

Response: EPA acknowledges that air and soil gas monitoring are subject to variability and may not

be suitable in all settings as a method to ensure USDW protection. However, EPA does not believe

that this should entirely preclude their use. EPA believes that surface air and soil gas monitoring in

conjunction with deep subsurface monitoring as required at §146.90, can provide additional data to

pinpoint the location and magnitude (or absence) of leaks that could endanger USDWs. 

The final rule at §146.90(h) retains the allowance for surface air and soil gas monitoring at the

discretion of the Director as a means of identifying leaks that may pose a risk to USDWs and

informing emergency notification of a Class VI owner or operator and UIC Director in the event of a

USDW endangerment, pursuant to requirements at §146.91(c). EPA clarifies that the decision to use

surface monitoring and the selection of monitoring methods will be site-specific (e.g., may be

influenced by geology, injection depth, and operational conditions) and must be based on potential

risks to USDWs within the AoR. 

EPA clarifies that use of surface air and soil gas monitoring as specified in the final GS rule at

§146.90(h), as a means of identifying leaks that may pose a risk to USDWs and informing

emergency notification of a Class VI owner or operator and UIC Director in the event of a USDW

endangerment, pursuant to requirements at §146.91(c) is at the Director's discretion.
Commenter Name: Thomas Curtis Letter ID: 0181

Commenter Organization: American Water Works Association (AWWA) Comment ID: 23699

Comment: Surface air and soil gas monitoring should be required however, baseline soil 

carbon dioxide levels should be determined prior to the start of monitoring. 

Testing for other compounds such as tracers that may included as part of the 

carbon dioxide injectate stream should also be considered in the development of 

the monitoring plan. 

Response: EPA agrees that surface air and soil gas monitoring, when coupled with subsurface

monitoring, may be appropriate at some GS projects to ensure USDW protection. In the final rule, at

§146.90(h), the decision to require such monitoring rests with the Director as a means of identifying

leaks that may pose a risk to USDWs and informing emergency notification of a Class VI owner or

operator and UIC Director in the event of a USDW endangerment, pursuant to requirements at

§146.91(c). 

The Agency agrees with the commenter that, if air and soil gas monitoring is performed, baseline

soil CO2 levels need to be determined before monitoring. This would be considered and described in

the site-specific testing and monitoring plan.

Commenter Name: Robert F. Van Voorhees Letter ID: 0190

Commenter Organization: Carbon Sequestration Council Comment ID: 24358

Comment: 2. Surface Air and Soil Gas Monitoring 

The goal of any UIC program regulations for GS should be to ensure that injected 

CO2 streams remain confined in the subsurface and do not endanger underground 

sources of drinking water. We are recommending sufficient requirements to ensure 

that this goal is achieved. As EPA seems to recognize, surface air or soil gas 

monitoring would impose substantial costs and the results of such monitoring 

would be subject to a host of confounding factors. Worst of all, such monitoring 

would be aimed at leakage of CO2 all the way to the surface, which - in the case 

of any properly-permitted GS project - would by definition be an extraordinarily 

low probability scenario. Accordingly, such requirements should not be imposed, 

nor should regulators have discretion to impose them. If there is any serious 

concern that injected CO2 might actually vent to the surface in a particular 

location, injection should not be permitted at that site in the first place. The 

regulations should not suggest otherwise. 

Response: EPA acknowledges that air and soil gas monitoring are subject to site-specific limitations

and may not be suitable in all settings as a method to ensure USDW protection. However, EPA does

not believe that this should entirely preclude their use. If surface monitoring were the only

monitoring method employed to ensure USDW protection, direct correlation of CO2 at the surface

with CO2 in the subsurface might be difficult; however, when combined with information gathered

through other monitoring techniques required of GS well owners and operators (e.g., monitoring

wells, geophysical techniques), air and soil gas monitoring may provide valuable data on the

magnitude and location of a leak. 

The decision to use surface monitoring and the selection of monitoring methods will be site-specific

(e.g., may be influenced by geology, injection depth, and operational conditions) and must be based

on potential risks to USDWs within the AoR. The final rule at §146.90(h) retains the allowance for
surface air and soil gas monitoring at the discretion of the Director as a means of identifying leaks

that may pose a risk to USDWs and informing emergency notification of a Class VI owner or

operator and UIC Director in the event of a USDW endangerment, pursuant to requirements at

§146.91(c).

Used in conjunction with deep subsurface monitoring, as required at §146.90, and as part of a multibarrier approach to protecting USDWs from endangerment, surface air and soil gas monitoring will

increase USDW protection, enable immediate notification of the UIC Director in the case of

potential USDW endangerment, and facilitate remedial action.

Commenter Name: Robert F. Van Voorhees Letter ID: 0190

Commenter Organization: Carbon Sequestration Council Comment ID: 24484

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Rule Provision: 146.90(h) 

Proposed CCS Group Recommendations: (h) At the Director’s discretion, surface 

air monitoring and/or soil gas monitoring to detect movement of carbon dioxide 

that could endanger a USDW. 

(1) The testing and monitoring plan must be based on potential vulnerabilities 

within the area of review; 

(2) The monitoring frequency and spatial distribution of surface air monitoring 

and/or soil gas monitoring must reflect baseline data and the monitoring plan 

must include how the proposed monitoring will yield useful information on the 

area of review delineation and/or compliance with standards under 40 CFR 

144.12;

Basis for CCS Group Comments: In most situations soil and air monitoring does 

not provide an effective method of protecting USDWs. 

Response: EPA acknowledges that air and soil gas monitoring to ensure USDW protection is not

necessary at all GS sites and agrees that the decision to use surface monitoring and the selection of

monitoring methods for the purpose of USDW protection will be site-specific.

The Agency believes that surface air and soil gas monitoring, when coupled with subsurface

monitoring, may be appropriate at some GS projects to ensure USDW protection. EPA also

acknowledges that surface air and soil gas measurements are subject to variability and may not be

suitable in all settings as a method to ensure USDW protection. However, EPA does not believe that

this should entirely preclude their use. The decision to use surface monitoring and the selection of

monitoring methods will be site-specific (e.g., may be influenced by geology, injection depth, and

operational conditions) and must be based on potential risks to USDWs within the AoR. 

In the final rule, at §146.90(h), the decision to require such monitoring as an additional measure to

ensure USDW protection rests with the Director as a means of identifying leaks that may pose a risk

to USDWs and informing emergency notification of a Class VI owner or operator and UIC Director

in the event of a USDW endangerment, pursuant to requirements at §146.91(c).
Commenter Name: Robert F. Van Voorhees Letter ID: 0190

Commenter Organization: Carbon Sequestration Council Comment ID: 24542

Comment: Rule Provisions or Federal Register Cite: 73 FR 43517 

EPA Preamble Question: 33. EPA seeks comment on the appropriate amount and types 

of monitoring that should be conducted at a GS site. Specifically, EPA seeks 

comment regarding the usefulness of indirect geophysical monitoring and surface 

air and soil gas monitoring. In addition, EPA seeks comment regarding the use of 

a Director-approved monitoring plan for GS sites. EPA Notice 43517. 

CSC Response: Monitoring techniques and frequency should be determined on a 

site-specific basis. Selection of monitoring types and frequency should balance 

the potential risks posed by the project with the cost and potential utility of 

monitoring. 

Surface and soil gas monitoring does not add value to the protection of USDWs. 

Many of the surface and soil gas monitoring techniques currently being evaluated 

lack the track record necessary for use in a regulatory compliance setting. 

Moreover, the potential for false-positives could undermine public confidence in 

GS technologies. 

Response: EPA acknowledges that air and soil gas monitoring to ensure USDW protection is not

necessary at all GS sites and agrees that the decision to use surface monitoring and the selection of

monitoring methods for the purpose of USDW protection will be site-specific.

The Agency believes that surface air and soil gas monitoring, when coupled with subsurface

monitoring, may be appropriate at some GS projects to ensure USDW protection. EPA also

acknowledges that surface air and soil gas measurements are subject to variability and may not be

suitable in all settings as a method to ensure USDW protection. However, EPA does not believe that

this should entirely preclude their use. The decision to use surface monitoring and the selection of

monitoring methods will be site-specific (e.g., may be influenced by geology, injection depth, and

operational conditions) and must be based on potential risks to USDWs within the AoR. 

In the final rule, at §146.90(h), the decision to require such monitoring as an additional measure to

ensure USDW protection rests with the Director as a means of identifying leaks that may pose a risk

to USDWs and informing emergency notification of a Class VI owner or operator and UIC Director

in the event of a USDW endangerment, pursuant to requirements at §146.91(c).

Commenter Name: Craig R. Walters Letter ID: 0200

Commenter Organization: Anadarko Petroleum Corporation Comment ID: 24603

Comment: Rule Provisions: 73 FR 43517 

EPA Rule Issue: 33. EPA seeks comment on the appropriate amount and types of 

monitoring that should be conducted at a GS site. Specifically, EPA seeks 

comment regarding the usefulness of indirect geophysical monitoring and surface 

air and soil gas monitoring. In addition, EPA seeks comment regarding the use of 

a Directorapproved monitoring plan for GS sites. EPA Notice 43517. 

Anadarko Petroleum Corporation (APC) Response: Monitoring techniques and 

frequency should be determined on a site-specific basis. Selection of monitoring 

types and frequency should balance the potential risks posed by the project with 
the cost of monitoring. 

Surface and soil gas monitoring does not add value to the protection of USDWs. 

Many of the surface and soil gas monitoring techniques currently being evaluated 

lack the track record necessary for use in a regulatory compliance setting. 

Moreover, the potential for false-positives could undermine public confidence in 

GS technologies. EPA should defer on using surface and soil gas monitoring 

technologies until their effectiveness can be demonstrated. 

Response: EPA acknowledges that air and soil gas monitoring to ensure USDW protection is not

necessary at all GS sites and agrees that the decision to use surface monitoring and the selection of

monitoring methods for the purpose of USDW protection will be site-specific.

The Agency believes that surface air and soil gas monitoring, when coupled with subsurface

monitoring, may be appropriate at some GS projects to ensure USDW protection. EPA also

acknowledges that surface air and soil gas measurements are subject to variability and may not be

suitable in all settings as a method to ensure USDW protection. However, EPA does not believe that

this should entirely preclude their use. The decision to use surface monitoring and the selection of

monitoring methods will be site-specific (e.g., may be influenced by geology, injection depth, and

operational conditions) and must be based on potential risks to USDWs within the AoR. 

In the final rule, at §146.90(h), the decision to require such monitoring as an additional measure to

ensure USDW protection rests with the Director as a means of identifying leaks that may pose a risk

to USDWs and informing emergency notification of a Class VI owner or operator and UIC Director

in the event of a USDW endangerment, pursuant to requirements at §146.91(c).

Commenter Name: Craig R. Walters Letter ID: 0200

Commenter Organization: Anadarko Petroleum Corporation Comment ID: 24708

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Rule Provision: 146.90(h) 

Anadarko Petroleum Corporation (APC) Comments: (h) At the Director’s 

discretion, surface air monitoring and/or soil gas monitoring to detect movement 

of carbon dioxide that could endanger a USDW. 

(1) The testing and monitoring plan must be based on potential vulnerabilities 

within the area of review; 

(2) The monitoring frequency and spatial distribution of surface air monitoring 

and/or soil gas monitoring must reflect baseline data and the monitoring plan 

must include how the proposed monitoring will yield useful information on the 

area of review delineation and/or compliance with standards under 40 CFR 

144.12;

Rationale: In most situations soil and air monitoring does not provide an 

effective method of protecting USDWs. 

Response: As described above, EPA acknowledges that air and soil gas monitoring to ensure
USDW protection is not necessary at all GS sites and agrees that the decision to use surface

monitoring and the selection of monitoring methods for the purpose of USDW protection will be

site-specific.

In the final rule, at §146.90(h), the decision to require such monitoring as an additional measure to

ensure USDW protection rests with the Director as a means of identifying leaks that may pose a risk

to USDWs and informing emergency notification of a Class VI owner or operator and UIC Director

in the event of a USDW endangerment, pursuant to requirements at §146.91(c).

The Agency agrees with the commenter that, if air and soil gas monitoring is performed, baseline

soil CO2 levels need to be determined before monitoring. This would be considered and described in

the site-specific testing and monitoring plan.

Commenter Name: Richard Guinn Letter ID: 0210

Commenter Organization: Eastman Chemical Company Comment ID: 22726

Comment: §146.90 Testing and monitoring requirements. (h) "At the Director’s discretion, 

surface air monitoring and/or soil gas monitoring to detect movement of carbon 

dioxide that could endanger a USDW." 

We recommend deletion of this requirement in its entirety. While this 

requirement may be suitable for determining potential air leakage relevant to 

monitoring of CO2 in a greenhouse gas policy context, this requirement does not 

provide any additional protection to migration to USDW as surface breakthrough 

will only occur well after the deep-surface migration of CO2 to a USDW. Surface 

monitoring to detect CO2 has high uncertainty and seasonal variability that is 

likely to result in many false positives and operational distractions. Seismic 

methods of tracking the CO2 plume are more effective than soil gas monitoring of 

CO2, which is affected by many other factors and thus is highly variable. 

Response: EPA acknowledges that surface air and soil gas measurements are subject to variability

and may not be suitable in all settings as a method to ensure USDW protection. However, EPA does

not believe that this should entirely preclude their use. The decision to use surface monitoring and

the selection of monitoring methods will be site-specific (e.g., may be influenced by geology,

injection depth, and operational conditions) and must be based on potential risks to USDWs within

the AoR. The Agency believes that surface air and soil gas monitoring, when coupled with

subsurface monitoring, may be appropriate at some GS projects to ensure USDW protection.

The final rule at §146.90(h) retains the allowance for surface air and soil gas monitoring at the

discretion of the Director as a means of identifying leaks that may pose a risk to USDWs and

informing emergency notification of a Class VI owner or operator and UIC Director in the event of a

USDW endangerment, pursuant to requirements at §146.91(c). EPA clarifies that the decision to use

surface monitoring and the selection of monitoring methods will be site-specific (e.g., may be

influenced by geology, injection depth, and operational conditions) and must be based on potential

risks to USDWs within the AoR.

Commenter Name: Richard Guinn Letter ID: 0210

Commenter Organization: Eastman Chemical Company Comment ID: 22736

Comment: EPA seeks comment on the appropriate amount and types of monitoring that should 
be conducted at a GS site. Specifically, EPA seeks comment regarding the 

usefulness of indirect geophysical monitoring and surface air and soil gas 

monitoring. In addition, EPA seeks comment regarding the use of a Directorapproved monitoring plan for GS sites. EPA Notice 111 

Surface air and soil gas monitoring are not useful. Seismic methods of tracking 

the CO2 plume are more effective than soil gas monitoring of CO2, which is 

affected by many other factors and thus is highly variable. Surface breakthrough 

represents an "after-the-fact" event. While this requirement may be suitable for 

determining potential air CO2 leakage relevant to monitoring of CO2 in a GHG 

context, this requirement does not provide any additional protection to 

migration to USDW as surface CO2 breakthrough will only occur well after the 

deep-surface migration of CO2 to a USDW. Surface monitoring to detect CO2 has 

high uncertainty and seasonal variability that is likely to result in many false 

positives, operational distractions and unduly raise public concern. 

Response: EPA agrees that subsurface geochemical and pressure monitoring in the subsurface

formations are the first line of monitoring that would allow detection of potential endangerment to

USDWs from GS activities (this is required at all GS sites, as described at §146.90(d)). The Agency

also believes that surface air and soil gas monitoring, when coupled with subsurface monitoring,

may be appropriate at some GS projects to ensure USDW protection. 

EPA clarifies that surface air and soil gas monitoring are not required at all GS sites. However, the

GS rule at §146.90(h) gives the Director discretion to require surface air and/or soil gas monitoring

as a means of identifying leaks that may pose a risk to USDWs and informing emergency

notification of a Class VI owner or operator and UIC Director in the event of a USDW

endangerment, pursuant to requirements at §146.91(c). EPA clarifies that the decision to use surface

monitoring and the selection of monitoring methods will be site-specific (e.g., may be influenced by

geology, injection depth, and operational conditions) and must be based on potential risks to USDWs

within the AoR.

Commenter Name: John King Letter ID: 0211

Commenter Organization: Shell Exploration and Production Company

(SEPCo)

Comment ID:

22781

Comment: 2. Surface Air and Soil Gas Monitoring 

The goal of any UIC program regulations for GS should be to ensure that injected 

CO2 streams remain confined in the subsurface and do not endanger underground 

sources of drinking water. EPA has proposed elaborate -- and in many cases 

overly-elaborate -- requirements to ensure that this goal is achieved. 

Consequently, it is difficult to imagine how requirements for surface air or 

soil gas monitoring could be justified. 

As EPA seems to recognize, surface air or soil gas monitoring would impose 

substantial costs and the results of such monitoring would be subject to a host 

of confounding factors. Worst of all, such monitoring would be aimed at leakage 

of CO2 all the way to the surface, which -- in the case of any properlypermitted GS project -- would by definition be an extraordinarily low 

probability scenario. 
Recommendation: 

Surface Air and Soil Gas Monitoring should not be imposed, nor should regulators 

have discretion to impose them. The potential for possible leakage pathways 

should be demonstrated and managed during the permitting process. 

Response: EPA clarifies that subsurface geochemical and pressure monitoring in the subsurface

formations are the first line of monitoring that would allow detection of potential endangerment to

USDWs from GS activities (this is required at all GS sites, as described at §146.90(d)). 

The Agency also believes that surface air and soil gas monitoring, when coupled with subsurface

monitoring, may be appropriate at some GS projects to ensure USDW protection. EPA

acknowledges that surface air and soil gas monitoring may not be suitable in all settings as a method

to ensure USDW protection. However, EPA does not believe that this should entirely preclude their

use. The decision to use surface monitoring and the selection of monitoring methods will be sitespecific (e.g., may be influenced by geology, injection depth, and operational conditions) and must

be based on potential risks to USDWs within the AoR.

The final rule at §146.90(h) retains the allowance for surface air and soil gas monitoring at the

discretion of the Director as a means of identifying leaks that may pose a risk to USDWs and

informing emergency notification of a Class VI owner or operator and UIC Director in the event of a

USDW endangerment, pursuant to requirements at §146.91(c).

Commenter Name: Andrew Duguid Letter ID: 0226

Commenter Organization: Schlumberger Carbon Services Comment ID: 24064

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Proposed Rule: (h) At the Director’s discretion, surface air monitoring and/or 

soil gas monitoring to detect movement of carbon dioxide that could endanger a 

USDW. 

Schlumberger Suggested Revision: (h) At the Director’s discretion based on sitespecific conditions and risk- based factors, surface air monitoring and/or soil 

gas monitoring to detect movement of carbon dioxide that could endanger a USDW. 

Schlumberger Rationale: In most situations soil and air monitoring does not 

provide an effective method of protecting USDWs. 

Response: EPA acknowledges that air and soil gas monitoring to ensure USDW protection is not

necessary at all GS sites and agrees that the decision to use surface monitoring and the selection of

monitoring methods for the purpose of USDW protection will be site-specific.

In the final rule, at §146.90(h), the decision to require such monitoring as an additional measure to

ensure USDW protection rests with the Director as a means of identifying leaks that may pose a risk

to USDWs and informing emergency notification of a Class VI owner or operator and UIC Director

in the event of a USDW endangerment, pursuant to requirements at §146.91(c).

The Agency believes that surface air and soil gas monitoring, when coupled with subsurface
monitoring, may be appropriate at some GS projects to ensure USDW protection. EPA also

acknowledges that surface air and soil gas measurements are subject to variability and may not be

suitable in all settings as a method to ensure USDW protection. However, EPA does not believe that

this should entirely preclude their use. The decision to use surface monitoring and the selection of

monitoring methods will be site-specific (e.g., may be influenced by geology, injection depth, and

operational conditions) and must be based on potential risks to USDWs within the AoR.

Commenter Name: Mark Bohrer Letter ID: 0241

Commenter Organization: North Dakota Industrial Commission Comment ID: 23255

Comment: 33. EPA seeks comment on the appropriate amount and types of monitoring that 

should be conducted at a GS site. Specifically, EPA seeks comment regarding the 

usefulness of indirect geophysical monitoring and surface air and soil gas 

monitoring. In addition, EPA seeks comment regarding the use of a Directorapproved monitoring plan for GS sites. EPA Notice 43517. 

Monitoring techniques should be determined on a site-specific basis and be based 

upon potential risks posed by the project and the cost versus benefit of 

monitoring. 

Response: EPA agrees that monitoring plans and methods need to be site-specific and believes that

the monitoring requirements for GS sites at §146.90 provide an appropriate level of flexibility in

structuring a testing and monitoring plan that protects USDWs from endangerment. The final

regulation provides for flexibility in: 1) methodologies used to collect these data, 2) the spatial

resolution at which the data should be collected, and 3) how often the data should be collected. The

number and placement of monitoring wells will be based on site-specific information such as the

calculated AoR, injection rate and volume, site geology, baseline data, and the presence of artificial

penetrations within the AoR. EPA believes that this is the best approach for addressing potential

risks at GS sites. 

EPA recognizes that installation of monitoring wells entails additional resources. However, the

Agency believes that such monitoring is necessary to ensure that GS projects are appropriately

operated and monitored and to protect USDWs from endangerment. 

Although a significant cost in absolute terms, monitoring costs are expected to be a small fraction of

site operating costs, according to EPA's cost analysis for the GS rulemaking (which is available in

the docket). While the rule requirements will necessitate additional costs, the requirements are guided

by the necessity to address the unique challenges posed by CO2 injection (including large injection

volumes, the relative buoyancy of CO2, its corrosivity in the presence of water, the potential

presence of impurities in captured CO2, and its mobility within subsurface geologic formations) as

they protect USDWs from endangerment. 

The UIC requirements are designed to ensure that where GS is employed, it is done in a manner that

protects USDWs from endangerment, consistent with the UIC Program's authority under SDWA.

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and
pressure front, and soil gas and surface air monitoring which may be required by the UIC Director

for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm. 

Commenter Name: Kurt Waltzer Letter ID: 0250

Commenter Organization: Clean Air Task Force Comment ID: 22322

Comment: Finally, surface air monitoring techniques will not always be necessary for GS 

projects. As with other monitoring methods, they may work well in particular 

settings but not in others (for example where distinguishing from natural 

variability or from baseline data is hard). Current scientific thinking also 

Response: EPA acknowledges that air and soil gas monitoring are subject to site-specific limitations

and may not be suitable in all settings as a method to ensure USDW protection. However, EPA does

not believe that this should entirely preclude their use. If surface monitoring were the only

monitoring method employed to ensure USDW protection, direct correlation of CO2 at the surface

with CO2 in the subsurface might be difficult; however, when combined with information gathered

through other monitoring techniques required of GS well owners and operators (e.g., monitoring

wells, geophysical techniques), air and soil gas monitoring may provide valuable data on the

magnitude and location of a leak. 

The final rule at §146.90(h) retains the allowance for surface air and soil gas monitoring at the

discretion of the Director as a means of identifying leaks that may pose a risk to USDWs and

informing emergency notification of a Class VI owner or operator and UIC Director in the event of a

USDW endangerment, pursuant to requirements at §146.91(c). EPA clarifies that the decision to use

surface monitoring and the selection of monitoring methods will be site-specific (e.g., may be

influenced by geology, injection depth, and operational conditions) and must be based on potential

risks to USDWs within the AoR.

Commenter Name: Michel Paque Letter ID: 0259

Commenter Organization: Ground Water Protection Council Comment ID: 24819

Comment: operation or closure. With respect to soil and air monitoring there is a 

question as to the efficacy of these as a means of protecting USDWs. 

Response: EPA acknowledges that air and soil gas monitoring are subject to site-specific limitations

and may not be suitable in all settings as a method to ensure USDW protection. However, EPA does

not believe that this should entirely preclude their use. If surface monitoring were the only

monitoring method employed to ensure USDW protection, direct correlation of CO2 at the surface

with CO2 in the subsurface might be difficult; however, when combined with information gathered

through other monitoring techniques required of GS well owners and operators (e.g., monitoring

wells, geophysical techniques), air and soil gas monitoring may provide valuable data on the

magnitude and location of a leak. 

Used in conjunction with deep subsurface monitoring, as required at §146.90, and as part of a multibarrier approach to protecting USDWs from endangerment, surface air and soil gas monitoring will

increase USDW protection, enable immediate notification of the UIC Director in the case of

potential USDW endangerment, and facilitate remedial action.

The decision to use surface monitoring and the selection of monitoring methods will be site-specific
(e.g., may be influenced by geology, injection depth, and operational conditions) and must be based

on potential risks to USDWs within the AoR. The final rule at §146.90(h) retains the allowance for

surface air and soil gas monitoring at the discretion of the Director as a means of identifying leaks

that may pose a risk to USDWs and informing emergency notification of a Class VI owner or

operator and UIC Director in the event of a USDW endangerment, pursuant to requirements at

§146.91(c).

Commenter Name: Michel Paque Letter ID: 0259

Commenter Organization: Ground Water Protection Council Comment ID: 24929

Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule

language 

Comment: Rule Provision: 146.90 

EPA Proposal: (h) At the Director’s discretion, surface air monitoring and/or 

soil gas monitoring to detect movement of carbon dioxide that could endanger a 

USDW. 

GWPC Recommendations: (h) At the Director’s discretion based on site-specific 

conditions and risk-based factors, surface air monitoring and/or soil gas 

monitoring to detect movement of carbon dioxide that could endanger a USDW. 

Rationale: In most situations soil and air monitoring does not provide an 

effective method of protecting USDWs. 

Response: As described above, EPA acknowledges that air and soil gas monitoring are subject to

site-specific limitations and may not be suitable in all settings as a method to ensure USDW

protection. However, EPA does not believe that this should entirely preclude their use. The final rule

at §146.90(h) retains the allowance for surface air and soil gas monitoring at the discretion of the

Director as a means of identifying leaks that may pose a risk to USDWs and informing emergency

notification of a Class VI owner or operator and UIC Director in the event of a USDW

endangerment, pursuant to requirements at §146.91(c).

Letter ID: 0263

Commenter Organization: Interstate Oil & Gas Compact Commission Comment ID: 24962

Comment: III A. 6 Proposed Plume and Pressure Front Monitoring Requirements 

11. Specifically, EPA seeks comment regarding the usefulness of indirect 

geophysical monitoring and surface air and soil gas monitoring. 

IOGCC Response: The IOGCC agrees that owners and operators should report semiannually on the characteristics of injection fluids, injection pressure, flow 

rate, temperature, volume and annular pressure, and on the results of MITs, ground 

water monitoring, and any required atmospheric/soil gas monitoring. The amount 

and types of monitoring to be required, however, should be site specific. 

Response: EPA agrees that monitoring plans and methods need to be site-specific and believes that

the monitoring requirements for GS sites at §146.90 provide an appropriate level of flexibility in

structuring a testing and monitoring plan that protects USDWs from endangerment. The final
regulation provides for flexibility in: 1) methodologies used to collect these data, 2) the spatial

resolution at which the data should be collected, and 3) how often the data should be collected. The

number and placement of monitoring wells will be based on site-specific information such as the

calculated AoR, injection rate and volume, site geology, baseline data, and the presence of artificial

penetrations within the AoR. 

EPA adds that the final rule, at §146.91(a) requires that owners and operators report semi-annually

on operating data and some monitoring data. See the preamble to the final rule for additional

information. 

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil gas and surface air monitoring which may be required by the UIC Director

for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm. 

Commenter Name: Steven Chester Letter ID: 0264

Commenter Organization: Michigan Department of Environmental Quality

(MDEQ)

Comment ID:

22844

Other EPA Comment Codes and Descriptions: 4660 2.6.6 Geochemical monitoring 

Comment: EPA (III . A. 6.) seeks comment on the amount and types of monitoring to be 

conducted at GS sites. 

- Staff is not certain that the monitoring parameters listed will yield any 

information that relates to endangerment of USDW by leakage from the sequestration 

zone with the exception of the determination of the position of the CO2 plume and 

area of elevated pressure. Staff believes, however, that the surface casing and 

tubing pressures, injection rates, and volumes should be measured daily and 

reported on a monthly basis. It is not clear that surface monitoring will 

provide unambiguous information regarding the position of the injected CO2 

plume, particularly in view of the uncertainty associated with the movement of the 

plume. It is also not clear that wells in the confining zone will be of any value 

since there may be no fluid movement into any particular well, and there is much 

uncertainty as to appropriate or optimum placement of confining zone monitoring 

wells. 

Response: EPA agrees that pressure monitoring in the confining zone may not provide the data

needed to evaluate plume movement. Instead, the final GS regulation, at §146.90(g)(1), requires all

GS project owners or operators to monitor for pressure changes in the injection zone. EPA believes

that pressure monitoring in the injection zone is necessary to track the development and movement

of the pressure front and CO2 plume which provides valuable information in determining whether

there is a potential for USDW endangerment. 

Pressure monitoring within the injection zone is necessary because any such monitoring above the

confining zone would not detect movement of the pressure front unless a breach of the confining

zone occurs. EPA believes that monitoring using wells in the injection zone (i.e., that penetrate the
confining zone) can be safely performed if the wells are constructed to prevent flow between the

injection zone and USDWs or other layers above the confining zone. Such construction technologies

exist and have been used in the oil and gas industry for years. 

EPA acknowledges that air and soil gas monitoring are subject to variability and may not be suitable

in all settings as a method to ensure USDW protection. However, EPA does not believe that this

should entirely preclude their use. For example, if a leak to the surface is suspected, surface

monitoring could provide vital information on its location and magnitude to assist owners and

operators in identifying what USDWs may have been impacted by a leak. EPA clarifies that the

various air and soil gas monitoring methods (e.g., chambers, eddy covariance, hyperspectral

imaging) all have different capabilities that may prove useful in specific GS projects (Miles, et al.

2005; Pickles and Cover, 2005; IPCC, 2005; Menzies, et al. 2001). The final rule at §146.90(h)

retains the allowance for surface air and soil gas monitoring at the discretion of the Director as a

means of identifying leaks that may pose a risk to USDWs and informing emergency notification of

a Class VI owner or operator and UIC Director in the event of a USDW endangerment, pursuant to

requirements at §146.91(c). EPA clarifies that the decision to use surface monitoring and the

selection of monitoring methods will be site-specific (e.g., may be influenced by geology, injection

depth, and operational conditions) and must be based on potential risks to USDWs within the AoR.

EPA is developing guidance on testing and monitoring to assist owners or operators and Directors in

evaluating requirements under §146.90, including proposed monitoring plans. The guidance

describes available technologies and recommended approaches for implementing a testing and

monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs,

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume and

pressure front, and soil gas and surface air monitoring which may be required by the UIC Director

for specific GS projects. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Michael Moore Letter ID: 0265

Commenter Organization: North American Carbon Capture & Storage

Association (NACCSA)

Comment ID:

22853

Other EPA Comment Codes and Descriptions: 4490 2.4.5 Use of tracers and potential impact on

human health or ecosystems (seeking comment) 

Comment: - Monitoring Provisions/Use of Tracers/Use ofDown-Hole Shut-off Valves: 

NACCSA is opposed to imposition of mandatory requirements to use tracers; conduct 

surface air/soil gas monitoring. 

Response: EPA believes that surface air and soil gas monitoring, when coupled with subsurface

monitoring, may be appropriate at some GS projects to ensure USDW protection. EPA

acknowledges that surface air and soil gas monitoring may not be suitable in all settings as a method

to ensure USDW protection. However, EPA does not believe that this should entirely preclude their

use. The decision to use surface monitoring and the selection of monitoring methods will be sitespecific (e.g., may be influenced by geology, injection depth, and operational conditions) and must

be based on potential risks to USDWs within the AoR.

If surface monitoring were the only monitoring method employed to ensure USDW protection, direct

correlation of CO2 at the surface with CO2 in the subsurface might be difficult; however, when

combined with information gathered through other monitoring techniques required of GS well

owners and operators (e.g., monitoring wells, geophysical techniques), air and soil gas monitoring
may provide valuable data on the magnitude and location of a leak. The CO2 itself may serve as a

tracer in the form of stable isotopes of carbon. For example, anthropogenic CO2 is depleted in 13C

compared to naturally occurring CO2. 

In the final rule, at §146.90(h), the decision to require such monitoring rests with the Director as a

means of identifying leaks that may pose a risk to USDWs and informing emergency notification of

a Class VI owner or operator and UIC Director in the event of a USDW endangerment, pursuant to

requirements at §146.91(c).

EPA believes that, in some circumstances, tracers can be an important component of a multifaceted

approach to monitoring GS projects. However, the Agency recognizes that tracers may not be

appropriate in all GS projects. For this reason, EPA does not require the use of tracers at all GS sites;

however, the Director has discretion to require their use if he/she determines that the use of tracers

could improve monitoring of the site and enhance USDW protection from endangerment.

Commenter Name: Michael Moore Letter ID: 0265

Commenter Organization: North American Carbon Capture & Storage

Association (NACCSA)

Comment ID:

22865

Other EPA Comment Codes and Descriptions: 4490 2.4.5 Use of tracers and potential impact on

human health or ecosystems (seeking comment) 

Comment: 4. Monitoring Provisions/Use ofTracers/Use of Down-Hole Shut-off Valves 

The proposed regulations would vest discretion in the program director to 

require the use of tracers and/or surface air/soil gas monitoring "to detect 

movement of CO2 that could endanger a USDW." NACCSA is opposed to this proposed 

requirement for the reasons outlined below. 

The proposal raises potential issues regarding the scope ofEPA's authority. The 

Preamble acknowledges that regulation of surface/atmospheric releases of CO2 is 

outside the scope of the proposed rule and the Agency's jurisdiction under SDWA. 

The UIC program is designed to protect USDW`s from endangerment due to subsurface 

injection. The use of tracers combined with surface or soil monitoring is 

unlikely to be protective because by the time any tracers or CO2 is detected in 

these zones it may have passed through all USDWs between the injection zone and 

the surface. 

NACCSA is also concerned that tracers are relatively untested in terms of leak 

detection capabilities and transport properties. Because there have been limited 

tests of tracers it is not clear how they interact with the subsurface and if they 

are conservatively transported with CO2. Further, tracers may also pose 

independent safety concerns for project operators, workers, and other potentially 

affected individuals and the environment. 

Response: EPA clarifies that use of surface air and soil gas monitoring as specified in the final GS

rule at §146.90(h), as a means of identifying leaks that may pose a risk to USDWs and informing

emergency notification of a Class VI owner or operator and UIC Director in the event of a USDW

endangerment, pursuant to requirements at §146.91(c), is at the Director's discretion.

If surface monitoring were the only monitoring method employed to ensure USDW protection, direct
correlation of CO2 at the surface with CO2 in the subsurface might be difficult; however, when

combined with information gathered through other monitoring techniques required of GS well

owners and operators (e.g., monitoring wells, geophysical techniques), air and soil gas monitoring

may provide valuable data on the magnitude and location of a leak. The CO2 itself may serve as a

tracer in the form of stable isotopes of carbon. For example, anthropogenic CO2 is depleted in 13C

compared to naturally occurring CO2. 

EPA believes that surface air and soil gas monitoring are within the scope of the SDWA in that they

can provide additional data to pinpoint the location and magnitude (or absence) of leaks that could

endanger USDWs. Used in conjunction with deep subsurface monitoring, as required at §146.90, and

as part of a multi-barrier approach to protecting USDWs from endangerment, surface air and soil gas

monitoring are within the scope of SDWA’s general authority (SDWA sections 1421 et al).

Regarding the use of tracers, EPA believes that, in some circumstances, tracers can be an important

component of a multifaceted approach to monitoring GS projects. However, the Agency recognizes

that tracers may not be appropriate in all GS projects. For this reason, EPA does not require the use

of tracers at all GS sites; however, the Director has discretion to require their use if he/she

determines that the use of tracers could improve monitoring of the site and enhance USDW

protection from endangerment. 

While the intent of the GS regulations is to prevent leaks of CO2 to USDWs, EPA clarifies that all

of the protective components of the regulation, including a comprehensive monitoring program per

§146.90 (which includes testing of the well, ground water quality monitoring, and tracking of the

CO2 plume and pressure front) support a multi-barrier approach to protecting USDWs. Additionally,

some studies (e.g., Phelps and Cole, 2008; Hovorka et al., 2004; McCallum et al., 2005) found that

tracers can provide useful CO2 monitoring information at injection wells both at depth and at nearsurface locations. At Frio, tracers enabled quantification of CO2 plume behavior and provided a

technique for model validity testing (McCallum et al., 2005). EPA will continue to track research

related to tracer use. The Agency plans to, every six years, collect and review data on GS projects to

determine whether the appropriate amount and types of information and appropriate documentation

are being collected, and to determine if modifications to the requirements are appropriate or

necessary.

The provision allowing the Director to require the use of tracers and surface air and soil gas

monitoring is within EPA's authority under the SDWA because these methods can provide additional

data to pinpoint the location and magnitude (or absence) of leaks that could endanger USDWs. Used

in conjunction with deep subsurface monitoring, as required at §146.90, and as part of a multibarrier approach to protecting USDWs from endangerment, tracers and surface air and soil gas

monitoring are within the scope of SDWA's general authority (SDWA sections 1421 et al).

Commenter Name: Karl R. Moor Letter ID: 0501

Commenter Organization: Southern Company Comment ID: 21161

Comment: I'm told that soil flux monitoring is also problematic because it can result in 

false positives based on natural variability in flux. 

What these requirements do is, by way of example, is signal to the public that 

carbon capture and storage is unsafe because it could lead to a leak in CO2, 

despite the fact that this is very unlikely to happen. The United Nations 

Intergovernmental Panel on Climate Change has found that the amount of carbon 
dioxide retained in the appropriately sited storage site was very likely to 

exceed 99 percent of over one hundred years. 

Response: EPA believes that monitoring at a GS site is of critical importance to ensuring protection

of USDWs from endangerment. Appropriately selected monitoring technologies, including surface

air and soil-gas monitoring will also serve to increase public confidence in the safety of GS and to

assure the public that GS projects are being appropriately operated and monitored. The information

gained through such monitoring will also enable permitting authorities to take appropriate steps to

address any indication that USDWs may be endangered. 

EPA clarifies that surface air and soil gas monitoring are not required at all GS sites. However, the

GS rule at §146.90(h) gives the Director discretion to require surface air and/or soil gas monitoring

as a means of identifying leaks that may pose a risk to USDWs and informing emergency

notification of a Class VI owner or operator and UIC Director in the event of a USDW

endangerment, pursuant to requirements at §146.91(c).

Commenter Name: Mike Moore Letter ID: 0532

Commenter Organization: North American Carbon Capture and Storage

Association (NACCSA)

Comment ID:

21368

Other EPA Comment Codes and Descriptions: 4490 2.4.5 Use of tracers and potential impact on

human health or ecosystems (seeking comment) 

Comment: dioxide. Also the director would have discretion without any guidance to require 

tracers and/or gas monitoring to detect movement of carbon dioxide that could 

endanger a USDW. NACSA believes that these methods should not be required 

because there are too many questions about their efficacy and the potential risk 

posed by tracers. 

Response: EPA acknowledges that air and soil gas monitoring are subject to site-specific limitations

and may not be suitable in all settings as a method to ensure USDW protection. However, EPA does

not believe that this should entirely preclude their use. If surface monitoring were the only

monitoring method employed to ensure USDW protection, direct correlation of CO2 at the surface

with CO2 in the subsurface might be difficult; however, when combined with information gathered

through other monitoring techniques required of GS well owners and operators (e.g., monitoring

wells, geophysical techniques), air and soil gas monitoring may provide valuable data on the

magnitude and location of a leak. The CO2 itself may serve as a tracer in the form of stable isotopes

of carbon. For example, anthropogenic CO2 is depleted in 13C compared to naturally occurring

CO2. 

Used in conjunction with deep subsurface monitoring, as required at §146.90, and as part of a multibarrier approach to protecting USDWs from endangerment, surface air and soil gas monitoring will

increase USDW protection, enable immediate notification of the UIC Director in the case of

potential USDW endangerment, and facilitate remedial action.

The decision to use surface monitoring and the selection of monitoring methods will be site-specific

(e.g., may be influenced by geology, injection depth, and operational conditions) and must be based

on potential risks to USDWs within the AoR. The final rule at §146.90(h) retains the allowance for

surface air and soil gas monitoring at the discretion of the Director as a means of identifying leaks

that may pose a risk to USDWs and informing emergency notification of a Class VI owner or

operator and UIC Director in the event of a USDW endangerment, pursuant to requirements at
§146.91(c).

EPA agrees that tracer use is not appropriate in all situations. Some tracers may have the potential to

cause harm to people or the environment. For this reason, EPA does not require the use of tracers at

all GS sites. Nevertheless there are many different types of tracers and not all are problematic;

research is being done to overcome problems with existing tracers. EPA believes that tracers have

been used safely and successfully in other applications. Therefore the Director has discretion to

require their use if he/she determines that the use of tracers could improve monitoring of the site and

enhance USDW protection from endangerment. The rule will also allow their use if proposed by the

owner or operator and approved by the Director.

EPA continues to follow new and ongoing research on the safety and efficacy of tracers. For

example, studies at the Frio Brine Pilot Experiment site (Dayton, TX) used various types of tracers,

including perfluorocarbon tracers (PFTs), sulfur hexafluoride, and the noble gases krypton, neon,

and xenon. These studies (e.g., Phelps and Cole, 2008; Hovorka et al., 2004; McCallum et al., 2005)

found that tracers can provide useful CO2 monitoring information at injection wells at depth and at

near-surface locations. At Frio, tracers enabled quantification of CO2 plume behavior and provided a

technique for model validity testing (McCallum et al., 2005). EPA will continue to track research

related to tracer use. The Agency plans to, every six years, collect and review data on GS projects to

determine whether the appropriate amount and types of information and appropriate documentation

are being collected, and to determine if modifications to the requirements are appropriate or

necessary.