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.
United States Department ofthe Interior

U. S. GEOLOGICAL SURVEY

Reston, VA 20192

In Reply Refer To:

Mail Stop 423

Water Docket

U.S. Environmental Protection Agency

Mail Code: 2822T

1200 Pennsylvania Ave., NW

Washington, DC 20460

NOV 2 6 2008

-

Subject: Proposed Rule, Federal Requirements under the Underground Injection Control

Program for Carbon Dioxide (C02) Geologic Sequestration Wells

The U.S. Geological Survey (USGS) has reviewed the proposed regulations published in the

Federal Register (FR) on July 25, 2008, and offers the following comments.

Section 146.87 (e), Logging, Sampling, and Testing Prior to Injection Well Operation, FR

page 43538

It is stated that, "Upon completion, but prior to operation, the owner or operator must conduct

the following tests to verify hydrogeologic characteristics ofthe injection zone:

(I) A pump test; or

(2) Injectivity tests."

A 'pump' test can be either injecting or withdrawing fluid. The following suggested rewrite

reduces redundancy:

"Upon completion, but prior to operation, the owner or operator must conduct pumping tests to

verify the hydraulic properties ofthe injection zone. These tests can take the form of:

(l) withdrawal tests; or

(2) injectivity tests."

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

This section requires the owner or 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 ifsurface 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 aI., 2008, abstract, Detection ofsurface deformation related with CO2

injection by DInSAR at In Salah, Algeria, Proceedings of 33rd International Geological

NOV 1 ;~ 2008
p.2

2

Congress, Oslo, Norway). It is suggested that the proposed regulations allow for techniques

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

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 of drinking water)." In §146.90 (h)(l) 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 ofthe samples and interference from other natural and manmade 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 ofsuch 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 USDW is 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 ofinjection, while the monitoring results are investigated and

interpreted.

Thank you for the opportunity to review and comment on the proposed rule. If you have any

questions concerning our comments, please contact Lloyd Woosley, Chief ofthe USGS

Environmental Affairs Program, at (703) 350-8797 or at lwoosley@usgs.gov.

Sincerely,

(~.. . . !JL--"-"~J/!. Ue...-v-.--........

J es F. Devine

S nior Advisor for Science Applications
Letter ID: 0166 

Commenter: James Devine 

Organization: United States Geological Survey (USGS) 

Letter ID: 0166 Comment ID: 21350 Letter Lines: 36 to 54 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment Code: 3100 2.1 Proposed Geologic Siting Requirements (40 CFR 146.83) 

Comment: Section 146.87 (e), Logging, Sampling, and Testing Prior to Injection Well 

Operation, FR page 43538 

It is stated that, "Upon completion, but prior to operation, the owner or operator 

must conduct the following tests to verify hydrogeologic characteristics of the 

injection zone: 

(1) A pump test; or 

(2) Injectivity tests." 

A`pump' test can be either injecting or withdrawing fluid. The following 

suggested rewrite reduces redundancy: "Upon completion, but prior to operation, 

the owner or operator must conduct pumping tests to verify the hydraulic 

properties of the injection zone. These tests can take the form of : 

(1) withdrawal tests; or 

(2) injectivity tests." 

Individual Response: EPA retained the requirements in the final rule as proposed because 

existing UIC program requirements use similar language and the tests and their purposes are 

understood by the regulated community. Additionally, the Agency believes that verification of 

hydrogeologic characterization will generate the same information as the suggested alternative 

language. 

Letter ID: 0166 Comment ID: 21351 Letter Lines: 56 to 69 

Comment Code: 4600 2.6 Proposed Plume and Pressure Front Monitoring Requirements (40 

CFR 146.90) 

Comment Code: 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 

1
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. 

Individual 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. 

2
Letter ID: 0166 Comment ID: 21352 Letter Lines: 71 to 93 

Comment Code: 4670 2.6.7 Surface air monitoring and/or soil gas monitoring (seeking 

comment) 

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. 

Individual Response: EPA acknowledges that air and soil gas monitoring are subject to sitespecific 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. 

3
4

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 will increase USDW protection, enable immediate notification of the UIC Director in 

the case of potential USDW endangerment, and facilitate remedial action.