### This comment letter response contains two parts:

(1) The original submittal from the commenter.

(2) A data base printout of EPA’s response to each point raised by the commenter.

Notes about the response letters:

• The response letters were generated by a data base used to track the content of all public

comment submittals and ensure that the Agency responds to each. Each comment letter

was assigned a Letter ID that corresponds to the last four digits of the docket number of the

original comment (as posted on www.regulations.gov).

• Each response letter includes: comment text; an EPA

‐ assigned comment code; and an

individual response. These are described and explained below.

• The data base contains Comment text from the letters submitted by commenters.

Many hard copy letters were scanned into electronic format for inclusion in the data

base. As a result, there may be some typographical errors attributable to optical

character recognition issues. However, all original submittals were reviewed in the

process of drafting responses to ensure that the comment content was understood and

appropriately addressed.

• The content of each comment letter was divided into topic areas and assigned a unique

Comment ID. Additionally, one or more Comment Codes (i.e., unique topic area ID) was

assigned to each discrete point raised by a commenter. This information was added to

the data base. To inform final rulemaking decisions, all comments and information

received on a given topic were reviewed by technical experts in each rule area (e.g., on

construction requirements).

• Following decisions on the final rule requirements, Individual responses were drafted

by topic area to ensure completeness and consistency of the responses with the final

rule and other responses to similar comments. Each discrete point made by a

commenter was given a unique response.

• Upon completion of comment responses, all information was entered into the data base.

Each letter response is a compilation of each comment and its individual response,

compiled in the order of the original comment letter. As a result of this process, there is

repetition in the response text. The Agency believes this approach ensures completeness

and attention to each comment letter that was submitted.

• All comments in a topic area were reviewed, evaluated, and responded to concurrently.

Responses on each topic area are compiled and are also available in the rulemaking docket.

### Attention: Docket ID No. EPA-HQ-OW-2008-0390

Comments on the EPA’s Proposed Fe deral Requirements under the Underground

Injection Control (UIC) Pr ogram for Carbon Dioxide (C O2) Geologic Sequestration

(GS) wells; Notice of Data Availability.

The Notice of Data Availability (NODA) references useful new studies that can help to inform

EPA’s proposed rule-making for geologic storage of CO 2 

### . However, Anadarko Petroleum

Corporation (APC) sees nothing in the new info rmation that suggests that EPA should depart

from the adaptive approach to regulation that EPA has discussed as th e basic objective for the

geologic sequestration (GS) rule. Adherence to an adaptive approach for regulations will

facilitate new information being implemented in a responsible way. The proven success of 30+

years of CO 2 

### enhanced oil recovery, 70+ years of natural gas storag e, and 150 years of oil and

gas production, demonstrates the industry knows how to safely and effectiv ely drill wells, inject

and store fluids, and monitor fo r containment. In addition, CO 2 

### injection for purposes of

enhanced oil or gas recovery (“ EOR/EGR”) has been successfully regulated as Class II injection

for decades, and we agree with EPA that there is nothing to justify any disruption of the existing

regulatory regime for the thousa nds of injection wells already in use in these operations.

Injection Depth for GS Projects

APC is supportive of EPA’s effort to introduce flex ibility on the depth of in jection relative to the

location of USDWs. APC holds that CO2 can be injected above a USDW while protecting the

USDW and maintaining access to th e USDW for future use. An adarko’s Salt Creek EOR project

in Wyoming, which has a USDW below the inject ion zone, is an excellent example of how

industry can operate CO2 injection wells in an EOR context without endangering or limiting

access to USDWs that are located below the in jection zone. Accessing USDWs below a CCS

site does not present significant technological hurdles. Industry has the technology to drill

through over-pressured gas reservoi rs which are analogous to CCS sites. There are some

excellent examples of off-shore technologies for drilli ng through salt formations and shallow gas

pockets that involve the same type of pressure issues that would be encountered in drilling

through a CCS site.

The EPA’s stated basis for requiring sequestra tion above a USDW, that “placing distance

between the injection formation and USDWs decreases risks to USDWs” (NODA p.44809) is

too simplistic. Distance will undoubtedly help, but distance does not deserve to be singled out

like this; it will not make up for otherwise poor si te characteristics nor does the lack of depth

defeat a good site. The nature and characteristics of the confining material is paramount and

must be considered along with distance in dete rmining the sufficiency of containment at any

particular site. Site selecti on and characterization must focu s on the trapping and containment

mechanisms themselves without giving undue weight to distance, which pl ays a role but is not

always determinative.

APC supports the concept of allowing injectio n above a USDW; however, we are concerned

about the waiver process as currently designe d. First, the EPA has not demonstrated how

injection above a USDW presents an additional risk that would warrant a significant increase in

the permitting requirements. If the proposed re gulations are adopted, then a properly sited

project will not pose any greate r danger sited above a USDW as below one. Characterization of

the confining zones will still be necessary wh ether they prevent against upward movement or

downward movement. The regulations as proposed have been written broadly enough to require

### the site characterization to en compass both above and below a proposed injection zone, where

appropriate.

Second, for the waiver system to work effectiv ely, the final decision making authority for a

waiver should be with the agen cy holding primacy for the propos ed Class VI UIC program. Any

requirement that would provide fo r two separate agencies of stat e government to have the same

authority over a single permitting process is in efficient and unnecessarily duplicative creating a

risk of inconsistent permitting decisions. EPA’ s current proposal would appear to give the

Public Water Supply Supervision (PWSS) Program Director essentiall y veto power over the

waiver. APC feels this is not a ppropriate due to the fact that the PWSS Program Director (and

the Director’s staff) is not as knowledgeable regarding underground injection as the UIC

Program Director (and the Director ’s staff). In addition, APC que stions what authority the EPA

has to dictate to those states with primacy whic h agencies must approve a permit. Instead, APC

recommends that the PWSS, like all other interested agencies, be included in the comment period

making sure that they have the oppor tunity to raise any concerns they may have with the project.

Comments on Research, Data Analysis, and Findings

Class VI well construction, operational, and monitoring requirements

EPA has noted in the NODA that the SECARB pr oject “employs, demons trates, and validates

the EPA’s proposed Class VI well constructio n, operational, and monitoring requirements”

(NODA, p. 44806). However, APC notes that no one project “validates” a given construction,

operation, or monitoring technique in a general se nse. The well involved in this project, by

requirement of the Mississippi Department of Environmental Quality, me ets Class I hazardous

waste injection well design standards which were applied in an abundance of caution.

Construction to these Class IH standards wa s not proposed voluntarily by the SECARB project

team. The construction of this well and the resulting protectiveness only demonstrate that the

design level is sufficient to be protective of USDWs not that it is the only design level sufficient

to be protective. A rich database of successful well construction is also offered by the CO2-EOR

and underground gas storage experience. APC conti nues to urge EPA to reconsider its proposed

well construction and operation requirements which while protective, are mu ch more prescriptive

and rigorous than necessary for commercial-scal e implementation of CCS and do not reflect

industry’s 35-plus years of success in injecting CO 2 

### under the Class II UIC program. The Class

II EOR wells constructed for these projects - and their operating practices - have an excellent

record of mechanical in tegrity and of protectin g USDWs. Some of the proposed requirements,

such as cementing the long string casing to surfa ce, are not only unnecessarily burdensome, but

might also interfere with operations a nd could introduce unintended risks.

Monitoring: Tracers & Soil and Air Monitoring

There are many monitoring tools that could be s hown to have some utility, but it does not follow

that every tool – or any particular tool – shoul d be used for any given geological storage project,

especially as the scaling-up to commercial proj ects would be cost-prohibi tive for some of the

tested monitoring techniques. The testing of pa rticular monitoring tech nologies does not show

the necessity of these techniques or the inadequacy of alternativ es that were not tested.

The Pump Canyon Project represents just one test of traces; the outcome should not be

generalized. Use of tracers should be a site specific decision. Mo re specifically, the

perfluorocarbon (PFT) tracers used in the Escatawpa pilot projec t are of concern, as they are

### greenhouse gases much more potent than CO 2 

### . In addition, PFTs have a high-risk of

contamination which makes them very impractical when utilizing beyond a pilot-scale project.

Tracers may be useful for CO 2 

### storage in some circumstan ces, but potential unintended

consequences should be considered both when sele cting whether tracers ar e an appropriate tool,

and if so, what kind of tracer is most appropriate for the project.

Soil and air monitoring, used at both the Es catawpa and Aneth Fiel d pilot proj ects, are

unnecessary under most foreseeable circumstances. Natural CO 2 

### concentration in soil can have

high spatial and temporal variation resultin g from complex environmental interactions,

particularly in wet, warm e nvironments. In the air, CO 2 

### has a high detection limit; a leak would

have to be significant and sustained to detect it with air monitoring technologies. Leakage

detection would be particularly difficult in industrial areas or near population centers, where CO 2



### concentration in the air is already high and variable. Though having knowledge of CO 2 

### flux in

the soil and air at a given site location may prove useful for si te characterization, soil and air

monitoring will not be effective in most places. The general strategy of monitoring programs

will be to detect leakage long before it reaches the surface, rendering limited utility to these

techniques. The benefit of these near surface strategies is unlikel y to outweigh the cost in most

situations.

Risk to Groundwater from Trace Element Mobilization

APC urges EPA to not take the results of the LB NL study out of context or as more conclusive

than they are. The NODA even states that the model results were based on “several assumptions

and parameter values with a large degree of uncertainty” (NODA, p.44807). It must also be

noted that the LBNL study goal was not , contrary to EPA’s asserti on, to model a “representative

groundwater” (NODA p. 44807).

The probability of trace element contaminating groundwater requires the multiplied probabilities

of CO 2 

### movement out of the intende d storage zone, finding a migration path to a USDW, passing

through or ending up in a zone with minera ls that contain heavy metal assemblages,

environmental conditions favorable to dissolutio n, and an undetected, unremediated leak that

mobilizes these elements into a USDW as opposed to imm obilizing them through mineral

precipitation or adsorption onto clays/organics. The probability of USDW contamination, based

on the probabilities of each of these individual events, will be different for every site. The risk of

trace metal contamination of gr oundwater will typically be sma ll, knowable, and manageable at

well selected and managed geologic storage sites as noted in the text “the majority of results did

not show mobilization at levels exceedi ng the MCL or AL” (NODA, p. 44807).

Also, actual field results – as opposed to the modeling exercise - have shown the risk of

contamination is low. For example, at SACROC oilfield in Scurry County, TX, CO 2 

### has been

injected for EOR since 1972, and acc ording to recent publications they have not seen evidence of

certain elements mobilized from injection zones at SACROC into overlying USDWs (reports

referenced in detail in both the API’s NODA response as well as the CSC’s NODA response).

The LBNL report’s authors realize the limitations to their models and EPA should also. Despite

having set up the simulation so that trace elemen t mobilization would likely result, the authors

conclude that “. . . model uncertainties, kineti c factors, and post-wit hdrawal water treatment

methods all suggest diligence rather than alarm.”

### Basin Scale Impacts of CO 2 

### Injection

EPA states that the LBNL study of Basin-Scale imp acts “illustrates the importance of basin-scale

evaluation of reservoir pressures and far-field pressures resulting from CO2 injection” (NODA,

p. 44808). APC would caution EPA from basing regulations or permit requirements on the

outcomes of the study due to the co nstraints of the model and assu mptions. In addition the state

of understanding the modeling of basin-scale CO2 se questration impacts is in its early stages and

thus is not appropriate for use in rulemaking at this time. Conclusions based on the modeled

brine flow out of the basin and fa r field pressure effects should be considered tentative at best

given the significant (and potentially incorrect) assumptions made in the model. This is

particularly true given that the modeled brine out-flow and far field pressure effects are very

small, and would not likely have been observed if the model had included lateral heterogeneities

in permeability and porosity and higher compressibility.

Under the proposed rule, basin-wide model resu lts are not applicable to Area of Review

decisions for individual site selection. The multi-stakeholder group recommendations dated May

14, 2009, provide an approach for handling multi- project basins where pressures fronts may

intersect and influence. Adaptive rule-making could allow for adjustments to encompass multiproject scenarios in the same basin if needed in the future. However, it raises the question of

who would be responsible for doing basin-wide analysis and at wh at point should it be

conducted.

CO 2 

### Modeling

EPA states that “modeling the injection and se questration of CO2 po ses unique challenges”

(NODA p. 44808). While on its face true, the statem ent exaggerates the challenges. Industry is

constantly being faced with new situations that pose “unique challenges”. For example in the

Canadian oil sands, industry routinely simulate s heavy oil thermal recovery operations which

require steam injection into shallow reservoirs at high temperature, causing thermal alteration of

the oil, reactivity of mineral species, and overpressure. These operations are more complicated

and more chemically reactive than CO 2 

### storage operations. Industr y has extensive experience in

these types of simulations, and though not a perfect analog for CO 2 

### storage, it shows that we can

model highly complex and dynamic subsurface processes.

The fact is that the state of modeling for CO 2 

### storage is more than ade quate to proceed with EPA

rule promulgation. Additional research is of c ourse encouraged, but there are no major technical

breakthroughs in the realm of modeling that need to occur before beginning commercial-scale

CO 2 

### storage operations in the United States. Adap tive regulations will facilitate new information

being implemented in a responsible way.

APC takes exception to EPA’s assertion that there is a “. . . need to couple multiphase flow,

reactive transport, and geomechanical processe s” (NODA p.44808). Such a model is certainly

possible but will likely be intractable, expensive, and it will still be at the mercy of the quality of

the input. It is more important to correctly capture the range of processes and possible outcomes

at a given location than to use a particular softwa re package or type of mo deling. Robust yet less

complex models capturing the most important p hysical and chemical processes can accomplish

the modeling goals necessary for safe storage.Letter ID: 0380

Commenter: Rebecca Thingelstad

Organization: Anadarko Petroleum Corporation (APC)

Letter ID: 0380 Comment ID: 28090 Letter Lines: 22 to 36

Comment Code: 1000 1. General Comments on the Notice of Data Availability

Comment: The Notice of Data Availability (NODA) references useful new studies that can

help to inform EPA’s proposed rule

‐ making for geologic storage of CO2. However,

Anadarko Petroleum Corporation (APC) sees nothing in the new information that

suggests that EPA should depart from the adaptive approach to regulation that

EPA has discussed as the basic objective for the geologic sequestration (GS)

rule. Adherence to an adaptive approach for regulations will facilitate new

information being implemented in a responsible way. The proven success of 30+

years of CO2 enhanced oil recovery, 70+ years of natural gas storage, and 150

years of oil and gas production, demonstrates the industry knows how to safely

and effectively drill wells, inject and store fluids, and monitor for

containment. In addition, CO2 injection for purposes of enhanced oil or gas

recovery ("EOR/EGR") has been successfully regulated as Class II injection for

decades, and we agree with EPA that there is nothing to justify any disruption

of the existing regulatory regime for the thousands of injection wells already

in use in these operations.

Individual Response: EPA is following an adaptive approach to the GS rulemaking to incorporate new

research, data, and information about GS. EPA intends to continue to collect data on GS and to

incorporate such data as it implements its adaptive approach to GS rulemaking to incorporate new

research, data, and information about GS. The Agency believes that an adaptive approach provides Class

VI owners or operators the flexibility to use and apply newly developed technologies for GS as they

become available in the future. For additional information on the adaptive approach, see the responses

to comments on the proposed rule in the rulemaking docket.

EPA recognizes that the oil and gas industry has decades of experience injecting CO2 for the purpose of

ER. The GS rulemaking builds upon existing experience and knowledge about safe injection practices in

ER and other injection industries, with tailored requirements that address the unique nature of CO2

injection for GS.

The final rule does not preclude CO2 injection for ER under Class II permits. However, the rule requires

re

‐ permitting of Class II wells (as Class VI) if the primary purpose of the injection transitions from ER tolong

‐ term storage, and establishes specific, risk

‐ based criteria to be considered by the Director in

making this determination (§144.19). For more information on the transition from Class II to Class VI,

see the responses to comments on the proposed rule in the rulemaking docket.

Letter ID: 0380 Comment ID: 28091 Letter Lines: 38 to 52

Comment Code: 3210 3.2.1. Comments Generally in Support of the Approach

Comment Code: 3420 3.4.2. Request for Information on Areas Where Injection Depth and USDWs Are a

Concern (seeking comment)

Comment: Injection Depth for GS Projects

APC is supportive of EPA’s effort to introduce flexibility on the depth of

injection relative to the location of USDWs. APC holds that CO2 can be injected

above a USDW while protecting the USDW and maintaining access to the USDW for

future use. Anadarko’s Salt Creek EOR project in Wyoming, which has a USDW below

the injection zone, is an excellent example of how industry can operate CO2

injection wells in an EOR context without endangering or limiting access to

USDWs that are located below the injection zone. Accessing USDWs below a CCS

site does not present significant technological hurdles. Industry has the

technology to drill through over

‐ pressured gas reservoirs which are analogous to

CCS sites. There are some excellent examples of off

‐ shore technologies for

drilling through salt formations and shallow gas pockets that involve the same

type of pressure issues that would be encountered in drilling through a CCS

site.

Individual Response: EPA acknowledges the commenter's support of the waiver approach and site

‐

specific flexibility in regulatory development and permitting as described in the NODA and Request for

Comment. The Agency acknowledges that there are some situations where injection into non

‐ USDW

formations above the lowermost USDW can be performed in a manner that protects USDWs. The final

GS rule at §146.95 establishes a process by which owners and operators can seek a waiver of the Class

VI injection depth requirements. The Agency believes the waiver approach: 1) responds to concerns

about local and regional geologic storage capacity limitations imposed by the proposed injection depth

requirements; 2) allows for a more site

‐ specific assessment of injection depth for GS projects; 3)

accommodates injection into different formation types; 4) allows for injection of CO2 for GS into non

‐

USDWs above and/or between USDWs when appropriate and where it can be demonstrated that

USDWs will be protected; and 5) responds to concerns about the use of aquifer exemptions for GS.

Finally, EPA's approach to addressing injection depth variability through a waiver process responds to

concerns about future drinking water resource availability and the need to ensure that high quality

water remains available in sufficient quantities to supply drinking water needs.EPA acknowledges that technologies and past experience exist to inject through over

‐ pressured

formations while maintaining zonal isolation (e.g., oil and gas industry experience in drilling through

shallow pockets of gas or other zones that have higher pressures). EPA has reviewed information on

these types of projects and has determined that, if properly constructed, wells can be drilled through

pressurized zones without causing fluid movement. However, to provide additional USDW protection

and ensure that any planned drilling is conducted appropriately, the final GS rule requires the Director

to consider planned or permitted water, hydrocarbon, or mineral resource exploitation potential of the

proposed injection formation and other formations both above and below the injection zone to

determine if there are any plans to drill through the formation to access resources in or beneath the

proposed injection zone/formation as specified in §146.95(b)(1)(vii). EPA believes that these additional

considerations are necessary when permitting such wells to ensure protection of all USDWs and that the

additional requirements that apply to owners or operators of Class VI wells granted a waiver of the

injection depth requirements at §146.95 will provide this protection.

Letter ID: 0380 Comment ID: 28092 Letter Lines: 65 to 74

Comment Code: 3200 3.2. Comments on Alternative Injection Depth Waiver Approach

Comment: APC supports the concept of allowing injection above a USDW; however, we are

concerned about the waiver process as currently designed. First, the EPA has not

demonstrated how injection above a USDW presents an additional risk that would

warrant a significant increase in the permitting requirements. If the proposed

regulations are adopted, then a properly sited project will not pose any greater

danger sited above a USDW as below one. Characterization of the confining zones

will still be necessary whether they prevent against upward movement or downward

movement. The regulations as proposed have been written broadly enough to

require the site characterization to encompass both above and below a proposed

injection zone, where appropriate.

Individual Response: EPA believes that that injection for the purpose of GS into non

‐ USDW formations

above the lowermost USDW warrants tailored requirements to address the unique challenges and risks

relative to injection below the lowermost USDW. For example, there is a risk of downward migration of

fluids if there is no lower confining layer or inadequate confinement. In addition, there is potential that

wells will be drilled through the injection zone in the future to reach USDWs. EPA believes that the

additional requirements that apply to owners or operators of Class VI wells granted a waiver of the

injection depth requirements at §146.95 will provide additional considerations for the owner or

operator and Director when permitting such wells to ensure protection of all USDWs.Letter ID: 0380 Comment ID: 28093 Letter Lines: 76 to 90

Comment Code: 3350 3.3.5. Requirement to Submit Waiver Application to UIC and PWSS Program

Directors

Comment: Second, for the waiver system to work effectively, the final decision making

authority for a waiver should be with the agency holding primacy for the

proposed Class VI UIC program. Any requirement that would provide for two

separate agencies of state government to have the same authority over a single

permitting process is inefficient and unnecessarily duplicative creating a risk

of inconsistent permitting decisions. EPA’s current proposal would appear to

give the Public Water Supply Supervision (PWSS) Program Director essentially

veto power over the waiver. APC feels this is not appropriate due to the fact

that the PWSS Program Director (and the Director’s staff) is not as

knowledgeable regarding underground injection as the UIC Program Director (and

the Director’s staff). In addition, APC questions what authority the EPA has to

dictate to those states with primacy which agencies must approve a permit.

Instead, APC recommends that the PWSS, like all other interested agencies, be

included in the comment period making sure that they have the opportunity to

raise any concerns they may have with the project.

Individual Response: EPA disagrees that consultation with the PWSS Director is duplicative: the

communication with the PWSS Director is consultative and does not constitute a final decision making.

The final GS rule includes a requirement that the UIC Program Director consult with the PWSS Directors

of all states, Territories, and Tribes having jurisdiction within the AoR of a well for which a waiver is

sought as specified in §146.95(b)(2). EPA believes this process is necessary and appropriate to ensure

that water system concerns are considered when evaluating a waiver application.

Letter ID: 0380 Comment ID: 28094 Letter Lines: 92 to 117

Comment Code: 2110 2.1.1. SECARB (Escatawpa, MS)

Comment: Comments on Research, Data Analysis, and Findings

Class VI well construction, operational, and monitoring requirements

EPA has noted in the NODA that the SECARB project "employs, demonstrates, and

validates the EPA’s proposed Class VI well construction, operational, and

monitoring requirements" (NODA, p. 44806). However, APC notes that no one

project "validates" a given construction, operation, or monitoring technique ina general sense. The well involved in this project, by requirement of the

Mississippi Department of Environmental Quality, meets Class I hazardous waste

injection well design standards which were applied in an abundance of caution.

Construction to these Class IH standards was not proposed voluntarily by the

SECARB project team. The construction of this well and the resulting

protectiveness only demonstrate that the design level is sufficient to be

protective of USDWs not that it is the only design level sufficient to be

protective. A rich database of successful well construction is also offered by

the CO2

‐ EOR and underground gas storage experience. APC continues to urge EPA to

reconsider its proposed well construction and operation requirements which while

protective, are much more prescriptive and rigorous than necessary for

commercial

‐ scale implementation of CCS and do not reflect industry’s 35

‐ plus

years of success in injecting CO2 under the Class II UIC program. The Class II

EOR wells constructed for these projects

‐ and their operating practices

‐ have

an excellent record of mechanical integrity and of protecting USDWs. Some of the

proposed requirements, such as cementing the long string casing to surface, are

not only unnecessarily burdensome, but might also interfere with operations and

could introduce unintended risks.

Individual Response: EPA acknowledges that a single project does not prove that a given design is

effective in all cases or is the only design that would be effective, and disagrees that the proposed rule

requirements are more prescriptive than necessary. The results of the SECARB project, however, do

show that the proposed requirements are effective in the studied case and can provide for safe injection

of carbon dioxide that protects USDWs. For more information on the construction requirements for GS

wells, see the responses to comments on the proposed rule in the rulemaking docket.

EPA believes that GS is sufficiently different from Class II ER operations to warrant the tailored

construction requirements for GS wells at §146.86. For example, the volume of CO2 anticipated to be

injected in Class VI wells is significantly greater than for Class II wells. Reservoir pressure conditions will

be different, with Class VI injection operations involving large volumes of CO2 and likely having higher

pressures within their storage formations than Class II ER projects. The Class VI regulations also address

the unique physical characteristics of CO2 including its buoyancy and potential corrosivity. See the

response to comments document for the proposed rule for additional information on EPA’s final

approach to construction of GS wells.

EPA intends to use an adaptive approach to the GS regulation. EPA 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.Letter ID: 0380 Comment ID: 28095 Letter Lines: 119 to 136

Comment Code: 2130 2.1.3. SWP (Pump Canyon, NM)

Comment: Monitoring: Tracers & Soil and Air Monitoring

There are many monitoring tools that could be shown to have some utility, but it

does not follow that every tool

‐ or any particular tool

‐ should be used for

any given geological storage project, especially as the scaling

‐ up to commercial

projects would be cost

‐ prohibitive for some of the tested monitoring techniques.

The testing of particular monitoring technologies does not show the necessity of

these techniques or the inadequacy of alternatives that were not tested.

The Pump Canyon Project represents just one test of traces; the outcome should

not be generalized. Use of tracers should be a site specific decision. More

specifically, the perfluorocarbon (PFT) tracers used in the Escatawpa pilot

project are of concern, as they are greenhouse gases much more potent than CO2.

In addition, PFTs have a high

‐ risk of contamination which makes them very

impractical when utilizing beyond a pilot

‐ scale project. Tracers may be useful

for CO2 storage in some circumstances, but potential unintended consequences

should be considered both when selecting whether tracers are an appropriate

tool, and if so, what kind of tracer is most appropriate for the project.

Individual Response: EPA acknowledges that the pilot sites studied involved extensive monitoring that

may not necessarily be appropriate for all GS sites. However, a robust monitoring program is critical to

ensuring protection of USDWs at GS projects from endangerment, and EPA clarifies that the use of any

monitoring technique in the pilot projects does not amount to an endorsement by EPA or an intent by

EPA to require that particular method. By testing multiple technologies, the pilot sites provide valuable

data that demonstrate whether or not these technologies are viable and informed the final GS rule

about the appropriate use of monitoring technologies.

EPA acknowledges that the appropriate monitoring methods and technologies will be determined on a

site

‐ specific basis. Data from the projects presented supports the need for a site

‐ specific monitoring

plan that will allow use of a range of monitoring technologies suitable for each unique GS site.

EPA recognizes that certain monitoring technologies, such as tracers are subject to variability and may

not be appropriate or necessary in all settings. The GS rule at §146.90 gives the Director discretion to

determine what methods are appropriate. All monitoring must be performed according to the Director

‐

approved testing and monitoring plan. See the response to comments document for the proposed rule

for additional information on EPA’s final approach to monitoring at GS sites.

EPA acknowledges comments regarding the costs associated with monitoring. The Agency believes therequirements for comprehensive monitoring are necessary to protect USDWs. A discussion of the costs

attributed to monitoring technologies (used during injection and the post

‐ injection site care timeframes)

is available in the Technology and Cost Document for the GS rule, which is in the federal docket for this

rulemaking.

Letter ID: 0380 Comment ID: 28096 Letter Lines: 153 to 185

Comment Code: 2210 2.2.1. Groundwater Quality and Mobilization of Trace Elements (seeking

comment)

Comment: Risk to Groundwater from Trace Element Mobilization

APC urges EPA to not take the results of the LBNL study out of context or as

more conclusive than they are. The NODA even states that the model results were

based on "several assumptions and parameter values with a large degree of

uncertainty" (NODA, p.44807). It must also be noted that the LBNL study goal was

not, contrary to EPA’s assertion, to model a 'representative groundwater" (NODA

p. 44807).

The probability of trace element contaminating groundwater requires the

multiplied probabilities of CO2 movement out of the intended storage zone,

finding a migration path to a USDW, passing through or ending up in a zone with

minerals that contain heavy metal assemblages, environmental conditions

favorable to dissolution, and an undetected, unremediated leak that mobilizes

these elements into a USDW as opposed to immobilizing them through mineral

precipitation or adsorption onto clays/organics. The probability of USDW

contamination, based on the probabilities of each of these individual events,

will be different for every site. The risk of trace metal contamination of

groundwater will typically be small, knowable, and manageable at well selected

and managed geologic storage sites as noted in the text "the majority of results

did not show mobilization at levels exceeding the MCL or AL" (NODA, p. 44807).

Also, actual field results

‐ as opposed to the modeling exercise

‐ have shown

the risk of contamination is low. For example, at SACROC oilfield in Scurry

County, TX, CO2 has been injected for EOR since 1972, and according to recent

publications they have not seen evidence of certain elements mobilized from

injection zones at SACROC into overlying USDWs (reports referenced in detail in

both the API’s NODA response as well as the CSC’s NODA response). The LBNL

report’s authors realize the limitations to their models and EPA should also.

Despite having set up the simulation so that trace element mobilization wouldlikely result, the authors conclude that ".

. . model uncertainties, kinetic

factors, and post

‐ withdrawal water treatment methods all suggest diligence

rather than alarm."

Individual Response: EPA clarifies that the LBNL study was conducted to study the potential

vulnerability of a wide range of aquifer types in the unlikely case of CO2 intrusion to provide a

foundation for further studies on ground water quality concerns, such as site

‐ specific studies including

laboratory and field experiments and associated modeling with the objective of reducing uncertainty of

assumptions and parameters.

EPA notes that all of the cited elements (and others not cited here) are generally present in natural

ground waters regardless of location, albeit typically at very small (i.e., trace) concentrations. However,

it is true that analyses for many potentially hazardous trace elements are not made routinely, and that

the analytical methods used have often been insufficiently sensitive to quantify the concentrations

actually present. Regarding the presence or absence of minerals hosting the potentially hazardous trace

elements, very few studies have been conducted on the mineralogy of potable water aquifer host rocks

in which the modes of occurrence of trace elements have been characterized. Birkholzer et al. (2008)

evaluated concentrations in soils and sediments from USGS’ National Geochemistry Database andlooked

at evidence from crustal abundances and abundances in domestic coals. They concluded that many

trace elements occur ubiqui¬tously in soils, sediments, and aquifer rocks throughout the world.

EPA agrees (and mentioned in the NODA) that the risk of CO2 leaking from deep storage is low for

properly managed GS projects, but the leakage probability is not necessarily zero (i.e., pre

‐ injection site

characterization may fail to detect leakage pathways or monitoring during and after injection may miss

small

‐ scale signals of local leaks). Therefore, the potential consequences of unlikely leakage events need

to be understood and predictive capabilities need to be developed as a basis for risk and vulnerability

assessment.

EPA agrees that risk assessment studies, as well as additional geochemical investigations on ground

water vulnerability, should be site specific. For this reason, all GS project owner or operators must

submit detailed, site

‐ specific information about a proposed GS site, including information on the

porosity, permeability, mineralogy, and geochemistry of the targeted injection and confining zones as

well as all USDWs within the AoR. Operators must also present information on the compatibility of the

CO2 stream with fluids in the injection zone and minerals in the injection and confining zones

(§146.82(c)(3)). The data can help the Director determine the potential for geochemical reactions

between the injectate and the host geologic formations. For additional information on EPA’s approach

to site characterization for GS wells, see the responses to comments on the proposed rule in the

rulemaking docket.

EPA notes the cited paper by Smyth et al. (2009) suggests that no contamination of an overlying aquifer

has occurred at the SACROC oil field. However, the paper does not establish (1) if this is because no CO2

leakage occurred, (2) if leakage occurred but the leaking CO2 has not yet reached the aquifer, or (3) ifCO2 has migrated into the aquifer but has not caused noticeable geochemical response. The latter is

unlikely, as other studies clearly suggested mobilization of metals in response to increased CO2 levels in

the water. For example, the same cited paper by Smyth et al. (2009) reports on laboratory experiments

with exposure of diverse aquifer rocks to CO2, showing geochemical response within hours to days after

introduction of CO2. Kharaka et al. (2009) report on a field experiment with injection of CO2 into

shallow groundwater, also showing a rapid and systematic geochemical response in the aquifer, with

concentration increases observed for several trace metals. These studies support the LBNL findings that

CO2 intrusion into USDW, however unlikely, can lead to mobilization of trace elements.

Letter ID: 0380 Comment ID: 28097 Letter Lines: 187 to 210

Comment Code: 2220 2.2.2. Basin

‐ Scale Hydrologic Impacts of CO2 Storage (seeking comment)

Comment: Basin Scale Impacts of CO2 Injection

EPA states that the LBNL study of Basin

‐ Scale impacts "illustrates the

importance of basin

‐ scale evaluation of reservoir pressures and far

‐ field

pressures resulting from CO2 injection" (NODA, p. 44808). APC would caution EPA

from basing regulations or permit requirements on the outcomes of the study due

to the constraints of the model and assumptions. In addition the state of

understanding the modeling of basin

‐ scale CO2 sequestration impacts is in its

early stages and thus is not appropriate for use in rulemaking at this time.

Conclusions based on the modeled brine flow out of the basin and far field

pressure effects should be considered tentative at best given the significant

(and potentially incorrect) assumptions made in the model. This is particularly

true given that the modeled brine out

‐ flow and far field pressure effects are

very small, and would not likely have been observed if the model had included

lateral heterogeneities in permeability and porosity and higher compressibility.

Under the proposed rule, basin

‐ wide model results are not applicable to Area of

Review decisions for individual site selection. The multi

‐ stakeholder group

recommendations dated May 14, 2009, provide an approach for handling multi

‐

project basins where pressures fronts may intersect and influence. Adaptive

rule

‐ making could allow for adjustments to encompass multiproject scenarios in

the same basin if needed in the future. However, it raises the question of who

would be responsible for doing basin

‐ wide analysis and at what point should it

be conducted.

Individual Response: The results of the modeling study did not cause EPA to change any aspects of the

site characterization or AoR delineation requirements for GS projects. The final GS rule focuses onpermitting of individual GS wells and therefore does not include requirements for basin

‐ scale

evaluations. However, EPA agrees that proactive management of basin scale concerns to maintain

pressures within acceptable ranges is important, and encourages owners or operators and permitting

authorities to communicate planned GS activities to maximize coordination and minimize pressure

interference. If a permit applicant (or the permitting authority) is aware of pending GS projects near a

proposed well, the AoR delineation performed pursuant to §146.84 should account for the impacts of

multiple owners and operators injecting within a single basin. EPA anticipates that, where multiple

operators are involved, the Director would not approve modeling that does not account for changes that

may result from all injection operations. The proximity of injection sites to each other and the relative

timing of each injection operation might indicate a possible increase in risk for the containment of the

total CO2 and/or the effects of hydraulic perturbations and brine displacement. For additional

information regarding EPA’s requirements for AoR delineation for GS projects, see the responses to

comments on the proposed rule in the rulemaking docket.

Regarding the model assumptions, EPA acknowledges that basin

‐ scale predictions are uncertain due to

the limited information generally available for large subsurface volumes. While the example modeling

study cited in the NODA and Request for Comment, and its underlying assumptions, are based on the

best information available, significant prediction uncertainty remains and results should be viewed as

illustrative, as acknowledged in Birkholzer and Zhou (2009). EPA clarifies, however, that the model

choice for pore compressibility is discussed in detail in Zhou et al. (2009), and is believed to be well

constrained. The pore compressibility used in the model was obtained through a pumping test in central

Illinois, at a depth of 2000 m just north of the assumed injection area. Additional pumping tests available

in shallower parts of the storage reservoir corroborate the chosen value. These values used in the model

are within the range of pore compressibility reported for well

‐ consolidated sandstones at in situ

effective stresses representative of Mt. Simon. The model assumption made about lateral homogeneity

in permeability and porosity is important for determining brine flow and far

‐ field pressure, but it is not

clear without better knowledge about lateral variability whether inclusion of heterogeneity would

increase or decrease far

‐ field effects.

Letter ID: 0380 Comment ID: 28098 Letter Lines: 212 to 241

Comment Code: 2310 2.3.1. Review of Modeling Studies (seeking comment)

Comment: CO2 Modeling

EPA states that "modeling the injection and sequestration of CO2 poses unique

challenges" (NODA p. 44808). While on its face true, the statement exaggerates

the challenges. Industry is constantly being faced with new situations that pose

'unique challenges". For example in the Canadian oil sands, industry routinely

simulates heavy oil thermal recovery operations which require steam injectioninto shallow reservoirs at high temperature, causing thermal alteration of the

oil, reactivity of mineral species, and overpressure. These operations are more

complicated and more chemically reactive than CO2 storage operations. Industry

has extensive experience in these types of simulations, and though not a perfect

analog for CO2 storage, it shows that we can model highly complex and dynamic

subsurface processes.

The fact is that the state of modeling for CO2 storage is more than adequate to

proceed with EPA rule promulgation. Additional research is of course encouraged,

but there are no major technical breakthroughs in the realm of modeling that

need to occur before beginning commercial

‐ scale CO2 storage operations in the

United States. Adaptive regulations will facilitate new information being

implemented in a responsible way.

APC takes exception to EPA’s assertion that there is a ".

. . need to couple

multiphase flow, reactive transport, and geomechanical processes" (NODA

p.44808). Such a model is certainly possible but will likely be intractable,

expensive, and it will still be at the mercy of the quality of the input. It is

more important to correctly capture the range of processes and possible outcomes

at a given location than to use a particular software package or type of

modeling. Robust yet less complex models capturing the most important physical

and chemical processes can accomplish the modeling goals necessary for safe

storage.

Individual Response: EPA believes that modeling of CO2 injection for GS does pose several unique

challenges, based on review of relevant technical literature, and participation in several technical

symposia and workshops related to computational modeling in this area. While this type of multiphase,

non

‐ isothermal, multi

‐ component computational modeling may be familiar in certain advanced

industries, it is certainly novel to the UIC community, and is more sophisticated than modeling typically

required in U.S. EPA regulations. However, EPA agrees with the commenter that advanced

computational modeling of GS sites is feasible, and trusts that experts in industry will meet the

challenges posed by GS modeling. For this reason, EPA has required computational modeling for

delineation of the AoR in a Class VI permit application.

EPA also agrees with the commenter that coupling of multiphase flow, reactive transport, and

geomechanical processes may not be necessary in all cases for modeling to delineate the AoR in a Class

VI permit application. EPA clarifies that today’s federal regulation requires that models used for AoR

delineation be able to account for multiphase flow and the buoyancy of CO2. However, the Director has

the discretion to require more advanced models be used for AoR delineation, including additional

coupling of reactive transport and geomechanical processes. EPA agrees with the commenter that these

types of fully coupled models are possible, and believes that in certain cases they will be necessary for

accurate delineation of the AoR. For many projects, however, simpler models, as advocated by thecommenter, may be suitable for AoR delineation. EPA believes that the Director of individual projects is

in the best position to determine the specific technical requirements of the model(s) used.

Letter ID: 0380 Comment ID: 28571 Letter Lines: 54 to 63

Comment Code: 3100 3.1. Comments on Concerns About Injection Depth for Class VI Wells

Comment: The EPA’s stated basis for requiring sequestration above a USDW, that "placing

distance between the injection formation and USDWs decreases risks to USDWs"

(NODA p.44809) is too simplistic. Distance will undoubtedly help, but distance

does not deserve to be singled out like this; it will not make up for otherwise

poor site characteristics nor does the lack of depth defeat a good site. The

nature and characteristics of the confining material is paramount and must be

considered along with distance in determining the sufficiency of containment at

any particular site. Site selection and characterization must focus on the

trapping and containment mechanisms themselves without giving undue weight to

distance, which plays a role but is not always determinative.

Individual Response: EPA believes that suitable confining layers (e.g., low

‐ permeability, low

‐ porosity

formations identified through proper site characterization process) along with proper well construction,

operation, monitoring, and post

‐ injection site care are key to protecting USDWs from endangerment.

Additionally, the Agency believes that distance between the injection zone and USDWs can impede

vertical fluid movement, allow for pressure dissipation, and provide additional sites for monitoring,

mitigation, and remediation if conditions warrant.

However, EPA acknowledges that there are situations where injection into non

‐ USDW formations above

the lowermost USDW can be performed in a manner that protects USDWs, as long as appropriate

protections are in place. The final GS rule at §146.95 establishes a process by which owners and

operators can seek a waiver of the Class VI injection depth requirements.

Letter ID: 0380 Comment ID: 28658 Letter Lines: 138 to 151

Comment Code: 2110 2.1.1. SECARB (Escatawpa, MS)

Comment Code: 2120 2.1.2. SWP (Aneth Field, UT)

Comment: Soil and air monitoring, used at both the Escatawpa and Aneth Field pilot

projects, are unnecessary under most foreseeable circumstances. Natural CO2

concentration in soil can have high spatial and temporal variation resultingfrom complex environmental interactions, particularly in wet, warm environments.

In the air, CO2 has a high detection limit; a leak would have to be significant

and sustained to detect it with air monitoring technologies. Leakage detection

would be particularly difficult in industrial areas or near population centers,

where CO2 concentration in the air is already high and variable. Though having

knowledge of CO2 flux in the soil and air at a given site location may prove

useful for site characterization, soil and air monitoring will not be effective

in most places. The general strategy of monitoring programs will be to detect

leakage long before it reaches the surface, rendering limited utility to these

techniques. The benefit of these near surface strategies is unlikely to outweigh

the cost in most situations.

Individual Response: EPA acknowledges that the pilot sites studied involved extensive monitoring that

may not necessarily be appropriate for all GS sites. However, EPA believes that a robust monitoring

program is critical to ensuring protection of USDWs at GS projects from endangerment, but clarifies that

the use of any monitoring technique in the pilot projects does not amount to an endorsement by EPA or

an intent by EPA to require that particular method. By testing multiple technologies, the pilot sites

provide valuable data that demonstrate whether or not these technologies are viable and informed the

final GS rule about the appropriate use of monitoring technologies.

EPA acknowledges that the appropriate monitoring methods and technologies will be determined on a

site

‐ specific basis. Data from the projects presented supports the need for a site

‐ specific monitoring

plan that will allow use of a range of monitoring technologies suitable for each unique GS site.

EPA recognizes that certain monitoring technologies, particularly surface air and soil gas monitoring are

subject to variability and may not be appropriate or necessary in all settings. The GS rule at §146.90

gives the Director discretion to determine what methods are appropriate. All monitoring must be

performed according to the Director

‐ approved testing and monitoring plan. See the response to

comments document for the proposed rule for additional information on EPA’s final approach to

monitoring at GS sites.