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 of the 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 of the 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 of the 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 of the carbon dioxide plume and

the position of the 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 aI., 2008, abstract, Detection of surface deformation related with CO 2 injection by DInSAR at In Salah, Algeria, Proceedings of 33rd International Geological



## NOV 1**;~** 

## 2008p.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 of the 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 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 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 of injection, 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 of the USGS

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

Sincerely,

## (~ J/!.

.. . .**!JL--"-"~** 

### Ue...-v-.--........

J es F. Devine

S nior Advisor for Science ApplicationsLetter ID: 0166

Commenter: James Devine Organization: United States Ge ological Survey (USGS)

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

Comment Code: 1240 1.1.1.3 Suggested changes/ed its to rule language

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

Comment: Section 146.87 (e), Logging, Sampling, a nd Testing Prior to Injection Well Operation, FR page 43538

It is stated that, "Upon completion, but prio r to operation, the owner or operator must conduct the following tests to verify hydrogeologic charact eristics of the injection zone:

(1) A pump test; or

(2) Injectivity tests."

A`pump' test can be either injecti ng or withdrawing fluid. The following suggested rewrite reduces redundancy: "U pon completion, but prio r to operation, the owner or operator must conduct pump ing tests to verify the hydraulic properties of the injection zone. Thes e 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. Additionall y, 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

1dioxide plume and the position ofthe pre ssure front" by direct or indirect monitoring. Indirect, geophys ical techniques include, for example, seismic, electrical, gravity, or electromagnetic su rveys.. ." It is unclear if surface deformation measurement techniques, such as repeat topographic surveys,satellite-based elevation measurem ents, and tiltmeters, are included as acceptable indirect monitoring techniques. Surface deformation techniques are in use, for example, at In Salah, Algeri a (Onuma et al., 2008, abstract, Detection

of surface deformation related with CO 2 injection by DInSAR at In Salah, Algeria, Proceedings of 33rd Internationa l Geological Congress, Oslo, Norway). It is suggested that the proposed regu lations 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 fr ont. The owner or operator must use direct methods to monitor for pressure chan ges in the injection zone. Indirect methods (e.g., seismic, electrical, gravity, or electromagnetic surveys and/or down-hol e CO2 detection tools) are required unless the Director de termines, based on site-specific geology that such methods are not appropriate. EPA is afford ing Director's discretion rega rding the use of geophysical techniques at some sites because the Agency recognizes that geophysical methods are not appropriate in all geologic settings. EPA clarifie s 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 defo rmation 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. Like wise, if the Director had reas on to believe such methods are necessary to ensure protection of USDWs, he/she is afforded discretion to require the use of additional monitoring t echniques 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 pl an will include the site-specific details, technologies, testing and monitoring freque ncies, and other pertinent information.

EPA is developing guidance on testing and mon itoring to assist owne rs or operators and Directors in evaluating requi rements under §146.90, including pr oposed monitoring plans. The guidance describes available technologies a nd recommended approaches for implementing a testing and monitoring plan, including pre-ope rational geophysical l ogging and testing of injection wells, MITs, injecti on well testing during operation, groundwater quality monitoring, tracking the CO2 plume and pressure front, a nd soil gas and surface air monitoring which may be required by the UIC Director for specific GS projects. Th e guidance can be found on EPA’s website at http://water.epa.gov/type/groundwater/u ic/wells_sequestration.cfm. In addition, in January 2009, DOE published a best practices ma nual entitled "Monitoring, Verification, and Accounting of CO2 Stored in Deep Geol ogic Formations" (DOE /NETL-311/081508); this

manual is included in the docke t for the final GS rule.

2Letter 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, "surf ace air monitoring and/or soil gas monitoring to detect movement of carbon dioxide that could endanger a USDW (underground source ofdr inking 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 car bon dioxide in air or soil gas are adequate for the measurement of carb on dioxide; that is, the analytical methodologies are well-developed. However, the representativene ss of the samples

and interference from other natural and man- made sour ces of carbon dioxide can make for problematic correlation of carbon dioxide in the air or soil to carbon dioxide from deep subsurface storage leak s. The efficacy of such correlation techniques are not well-demonstrated by re search to date, as evidenced by the paucity of literature on the subject. Co rrelation with potential endangerment to

an USDWis even less understood. As a resu lt, requiring such m onitoring at this point amounts to requiring the owner or operator to conduct research into a technique that is not ye t well established. Poorly understood detections of elevated carbon dioxide may cause opera tional disruptions, such as short or long-term cessation of injection, while th e monitoring results are investigated and interpreted.

Individual Response: EPA acknowledges that air and soil ga s monitoring are subject to sitespecific limitations and may not be suitable in all settings as a me thod 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 ensu re USDW protection, direct

correlation of CO2 at the surface with CO2 in th e subsurface might be difficult; however, when combined with information gathered through othe r monitoring techniques required of GS well owners and operators (e.g., monitoring wells, geophysical te chniques), 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 identif ying leaks that may pose a risk to USDWs and informing emergency notification of a Class VI ow ner or operator and UIC Director in the event of a USDW endangerment, pursuan t to requirements at §146.91(c) . The decision to use surface monitoring and the selection of monitoring methods will be site-s pecific (e.g., may be influenced by geology, injection depth, and operational conditions ) and must be based on potential risks to

USDWs within the AoR.

34 Used in conjunction with deep subsurface monitoring, as required at §146.90, and as part of a multi-barrier approach to protecting USDWs fr om endangerment, surface air and soil gas monitoring will increase USDW protection, enable immediate no tification of the UIC Director in the case of potential USDW endangerme nt, and facilitate remedial action.