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.
 

Dedicated to protecting our nation’s ground water.

Hon. Peter S. Silva

Assistant Administrator

Office of Water

USEPA Headquarters 

Ariel Rios Building 

1200 Pennsylvania Avenue, N. W. 

Mail Code: 4101M 

Washington, DC 20460

Re: Federal Requirements Under the Underground Injection Control (UIC) Program for Carbon 

Dioxide (CO2) Geologic Sequestration (GS) Wells; Notice of Data Availability and Request 

Comment, 74 Fed. Reg. 44802 (August 31, 2009), Docket: EPA

Dear Mr. Silva:

The Ground Water Protection Council (GWPC)

following comments and recommendations

limitations, it was not possible to obtain concurrence on these comments from the full GWPC 

Board of Directors. Consequently, these commen

GWPC CO2 Committee. The GWPC and the 

us with the opportunity to comment

organizations such as the GWPC t

managed in a safe and reliable manner.

Comments

In principal, the committee does not disagree

for the purpose of allowing injection of CO

Source of Drinking Water (USDW). However, we have several concerns about the

of such a process as follows:

1. The NODA proposes that PWSS Directors play a formal role in the approval or 

disapproval of applications to inject above 

like to point out several issues related to such an approval requirement

a. PWSS Directors and their staffs 

agency are less likely

needed to perform 

need to hire additional staff and acquire appropriate training for the staff. 

Further, in order for

process states may need to revise their statutes to provide authority

nation’s ground water.

October 14, 2009

1200 Pennsylvania Avenue, N. W. 

Federal Requirements Under the Underground Injection Control (UIC) Program for Carbon 

Sequestration (GS) Wells; Notice of Data Availability and Request 

Comment, 74 Fed. Reg. 44802 (August 31, 2009), Docket: EPA–HQ–OW–2008

The Ground Water Protection Council (GWPC) CO2 Committee is pleased to provide the 

recommendations related to the NODA referenced above.

limitations, it was not possible to obtain concurrence on these comments from the full GWPC 

Board of Directors. Consequently, these comments represent the consensus opinion of the 

GWPC and the committee would like to thank you for providing 

us with the opportunity to comment. We trust EPA will continue to work with the states through 

organizations such as the GWPC to insure that geologic sequestration of carbon dioxide is 

reliable manner.

does not disagree with EPA’s proposal to establish a waiver process 

for the purpose of allowing injection of CO2 into zones above the lowermost Underground 

of Drinking Water (USDW). However, we have several concerns about the

that PWSS Directors play a formal role in the approval or 

applications to inject above the lowermost USDW. The committee

like to point out several issues related to such an approval requirement:

PWSS Directors and their staffs that are not already a part of a state UIC primacy

less likely to have the requisite UIC permitting and technical 

needed to perform such a review. Consequently, such PWSS agencies

need to hire additional staff and acquire appropriate training for the staff. 

Further, in order for such PWSS Directors to be a formal part of the review 

process states may need to revise their statutes to provide authority

Ground Water Protection Council

13308 N. MacArthur Blvd.

Oklahoma City, OK 73142

Tel: (405) 516-

Fax: (405) 516-

www.gwpc.org

Federal Requirements Under the Underground Injection Control (UIC) Program for Carbon 

Sequestration (GS) Wells; Notice of Data Availability and Request for 

2008–0390

is pleased to provide the 

related to the NODA referenced above. Due to time 

limitations, it was not possible to obtain concurrence on these comments from the full GWPC 

ts represent the consensus opinion of the 

would like to thank you for providing 

trust EPA will continue to work with the states through 

o insure that geologic sequestration of carbon dioxide is 

a waiver process 

the lowermost Underground 

of Drinking Water (USDW). However, we have several concerns about the requirements 

that PWSS Directors play a formal role in the approval or 

committee would 

that are not already a part of a state UIC primacy

ve the requisite UIC permitting and technical expertise

such PWSS agencies would 

need to hire additional staff and acquire appropriate training for the staff. 

a formal part of the review 

process states may need to revise their statutes to provide authority to the PWSS 

Ground Water Protection Council

08 N. MacArthur Blvd.

Oklahoma City, OK 73142

-4972

-4973
agency. These are additional burdens on the states that do not substantially “add 

value” to the permitting or operation of geosequestration projects;

b. No additional criteria for PWSS agency review has been suggested that would

not already be part of the state UIC primacy agency’s review process. Again 

there is no “value added” element to requiring this additional review. 

c. The determination as to which elements of state government play a formal or 

authoritative role in the review and approval of activities that are part of a state 

primacy program should rest with the state alone. States are the best judge of 

which agency should perform permitting functions;

d. 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 duplicative. In Wyoming’s case, it would result in both a federal 

and state agency having the same authority, since Region 8 administers the 

PWSS rather than the state. It is also conceivable that the UIC primacy agency

may approve or disapprove an application while the PWSS Director may take an 

opposite stance. Consequently, the effect of the waiver process would be to 

create a veto authority for one state agency over the actions of another state 

agency. In such cases, one state agency could be placed in the position of 

initiating an administrative action against another state agency or at least 

testifying against another agency in any action initiated by an aggrieved party

under state administrative adjudication laws. Therefore, in the interests of “good 

government”, a single state agency should have the final authority to approve or

deny an application.

2. In many cases, a waiver may need to be accompanied by an aquifer exemption. Since no 

changes to the aquifer exemption criteria have been proposed, it appears that obtaining

an exemption for USDW’s above the lowermost USDW for the purpose of 

geosequestration would not be possible unless the injection zone happens to qualify

under one of the existing criteria in 40 CFR Part 146.4. In such circumstances this

would create a prohibition for injection above the lowermost USDW regardless of 

whether or not a waiver process exists;

3. There is some question as to how wells converted to Class VI from Class II would be 

handled under the waiver process. Would a waiver be required for such wells and under 

what circumstances? 

Recommendations

The GWPC CO2 Committee recommends the following with respect to implementation of a 

waiver process:

1. The authority for granting a waiver should rest solely with the state UIC primacy agency.

2. The waiver, permit application and aquifer exemption request (if needed) should all be 

part of the same application process such that each is not subject to separate public notice 

and participation requirements. Further, EPA should consider accepting state public 

notification as a means of satisfying federal public notice requirements for aquifer 

exemptions.

3. In those cases where the PWSS Director is not a part of the state UIC primacy agency, a 

special notification with opportunity to comment should be provided to the PWSS 

Director.

4. EPA should consider modifying 40 CFR Part 146.4 to include an additional provision for 

aquifer exemption based on the expected use of a USDW as a CO2 storage reservoir. 

However, in adding such a provision we recommend that the proposed injection zone still 

be required to meet the criteria of not being reasonably expected to supply a public 
drinking water source, whether due to location, depth, total dissolved solids content or for 

other technological or practical reasons.

5. Because injection above USDW’s may present additional questions relative to movement 

of CO2 in the subsurface, we believe EPA should consider adding a provision for 

additional regional hydrologic studies when injection above USDW’s is proposed.

Additional observations

1. Regarding the NODA summary of LBNL studies on “Basin-Scale Hydrologic Impacts of 

CO2 Storage”, we feel that a clarification of the results of this preliminary simulation and 

their implications are needed. In particular, it was noted that, a pressure increase of 0.5 

bar might be expected at the distal extent of the regional aquifer (200km from the core 

injection area). The next sentence states that “...basin-wide pressure influences can be 

large.” This implies that 0.5bar (~0.5 atm) pressure elevation at the perimeter of the 

basin is “large”. Whereas we recognize that pressure perturbations will be significant in 

the core injection area (especially where pressure fields intersect), a 0.5bar increase in 

pressure at the basin perimeter is not significant in terms of threatening containment.

2. While the SECARB study provides an example of one case where the proposed 

constructions standards were followed without apparent incident, this does not mean they

represent the minimum or exclusive standards necessary to protect USDW’s. Other 

construction standards could prove equally effective. Please refer to well construction 

standards submitted by GWPC in its December 24, 2008 comments.

3. The NODA raises a question about the mobilization of metals from CO2 injection. 

However, there is no concurrent risk analysis provided or cited. While we recognize that 

mobilization of metals in the injection zone can occur under specific circumstances, we 

believe the containment requirements of the proposed rule are adequate to prevent 

contamination of USDW’s from the movement of CO2 and associated formation fluids in 

the injection zone. Consequently, we believe mobilization of metals in the injection zone 

is not a concern provided formation fluids remain in the injection zone. 

Again, the GWPC CO2 Committee would like to thank EPA for providing the opportunity to 

comment on the NODA. We look forward to working with EPA on the implementation of a 

primacy process for CO2 geosequestration that will insure state programs receive delegation of 

this important program in a reasonable and expeditious manner.

Respectfully,

Mike Paque

GWPC Executive Director
Letter ID: 0373  

Commenter: Mike Paque  

Organization: Ground Water Protection Council (GWPC)  

Letter ID: 0373 Comment ID: 28018 Letter Lines: 45 to 48  

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

Comment: In principal, the committee does not disagree with EPA’s proposal to establish a  

waiver process for the purpose of allowing injection of CO2 into zones above the  

lowermost Underground Source of Drinking Water (USDW). However, we have several  

concerns about the requirements `of such a process as follows:  

Individual Response: EPA 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. Please see EPA's specific responses below.  

Letter ID: 0373 Comment ID: 28019 Letter Lines: 50 to 86  

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

Directors  

Comment: 1. The NODA proposes that PWSS Directors play a formal role in the approval or  

disapproval of applications to inject above the lowermost USDW. The committee  

would like to point out several issues related to such an approval requirement:  

a. PWSS Directors and their staffs that are not already a part of the state UIC  

primacy agency are less likely to have the requisite UIC permitting and  

technical expertise needed to perform such a review. Consequently, such PWSS  

agencies would need to hire additional staff and acquire appropriate training  

for the staff. Further, in order for such PWSS Directors to be a formal part of  

the review process states may need to revise their statutes to provide  

authority to the PWSS agency. These are additional burdens on the states that do  

not substantially "add value" to the permitting or operation of geosequestration  

projects;  

b. No additional criteria for PWSS agency review has been suggested that would  
not already be part of the state UIC primacy agency’s review process. Again  

there is no "value added" element to requiring this additional review.  

c. The determination as to which elements of state government play a formal or  

authoritative role in the review and approval of activities that are part of a  

state primacy program should rest with the state alone. States are the best  

judge of which agency should perform permitting functions;  

d. 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 duplicative. In Wyoming’s case, it would result in both a  

federal and state agency having the same authority, since Region 8 administers  

the PWSS rather than the state. It is also conceivable that the UIC primacy  

agency may approve or disapprove an application while the PWSS Director may take  

an opposite stance. Consequently, the effect of the waiver process would be to  

create a veto authority for one state agency over the actions of another state  

agency. In such cases, one state agency could be placed in the position of  

initiating an administrative action against another state agency or at least  

testifying against another agency in any action initiated by an aggrieved party  

under state administrative adjudication laws. Therefore, in the interests of  

"good government", a single state agency should have the final authority to  

approve or deny an application.  

Individual Response: 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.

EPA requires that this consultation be documented to ensure transparent public disclosure of all

information evaluated by the Directors and their respective recommendations. EPA clarifies that the

PWSS director does not have "veto power" over a UIC permitting decision; instead, the role of the PWSS

Director is to ensure consideration of water system and water resource issues where injection into non‐

USDW formations above the lowermost USDW is being considered. Due to the unique nature of the

injection depth waiver process and in an effort to ensure national consistency and application of the

requirements, the requirement at §146.95(d) indicates that the Regional Administrator makes the final

determination regarding waiver issuance following an evaluation of all site‐specific information, public

notice, and recommendations from the UIC Director. EPA believes that UIC Program staff is in the

appropriate position to evaluate the technical details of the waiver application, in concert with the UIC

permit application, to inform the Regional Administrator’s decision. EPA adds that adoption of the

waiver process will remain at the discretion of individual UIC programs.  

EPA disagrees that consultation with the PWSS Director would be "burdensome," "inefficient," or

"duplicative," and believes that the consultative communication between the UIC Director and PWSS
Directors will enable a comprehensive evaluation of resource concerns and increase USDW protection

EPA adds that it does not anticipate that the PWSS director would perform the same level of review as

the UIC Director and anticipates states would determine the level of PWSS review.  

EPA is developing guidance on the injection depth waiver process. The guidance describes the

recommended approach an owner or operator may follow when submitting a waiver application,

processing waiver applications by the UIC and PWSS Program Directors, and additional considerations

that may apply to projects that have been issued waivers. This guidance will be available on EPA’s

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

EPA clarifies that adoption of the waiver process remains at the discretion of individual UIC programs.

Therefore, States, Territories, and Tribes seeking primacy for Class VI wells are not required to provide

for injection depth waivers in their UIC regulations and may choose not to make this process available to

Class VI wells under their jurisdiction. Although some commenters asked EPA to require that waivers be

applied nationally, the Agency believes that the decision about whether a waiver program is appropriate

in a specific State, Tribe, or Territory should be made by each program.  

Letter ID: 0373 Comment ID: 28020 Letter Lines: 88 to 94  

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

Comment: 2. In many cases, a waiver may need to be accompanied by an aquifer exemption.  

Since no changes to the aquifer exemption criteria have been proposed, it appears  

that obtaining an exemption for USDW’s above the lowermost USDW for the purpose  

of geosequestration would not be possible unless the injection zone happens to  

qualify under one of the existing criteria in 40 CFR Part 146.4. In such  

circumstances this would create a prohibition for injection above the lowermost  

USDW regardless of whether or not a waiver process exists;  

Individual Response: EPA believes that there are limited circumstances where aquifer exemptions for

GS may be warranted. The final rule allows for the expansion of the areal extent of existing aquifer

exemptions for Class II EOR/EGR wells transitioning to Class VI injection for GS pursuant to requirements

at §§146.4 and 144.7(d).  

The aquifer exemption requirements in the final rule provide flexibility and afford owners or operators

an opportunity to assess and select a suitable GS site while also preserving USDWs (i.e.,

formations/aquifers afforded SDWA protection). Class VI owners or operators granted expansions of

existing Class II EOR/EGR aquifer exemptions for GS projects must meet all of the tailored requirements

for GS wells in the final GS rule.
The Agency clarifies that the aquifer exemption requirements and the injection depth waiver

requirements serve different purposes. Class VI owners or operators granted expansions of existing

Class II EOR/EGR aquifer exemptions for GS projects must meet all of the tailored requirements for GS

wells in the final GS rule, including the site criteria at §146.83. EPA believes that, in most cases, the

injection depth waiver is a more appropriate option than aquifer exemptions for Class VI injection, and

believes that aquifer exemption expansions for GS should be granted in limited circumstances.  

Letter ID: 0373 Comment ID: 28021 Letter Lines: 96 to 98  

Comment Code: 3400 3.4 Additional Information Regarding the Waiver Approach  

Comment: 3. There is some question as to how wells converted to Class VI from Class II  

would be handled under the waiver process. Would a waiver be required for such  

wells and under what circumstances?  

Individual Response: If an owner or operator is transitioning a well from Class II to Class VI that injects

above the lowermost USDW, they must apply for a waiver from the injection depth requirements

pursuant to §146.95. EPA clarifies that the final GS rule contains risk‐based criteria at §144.19 to inform

a Director’s determination to apply Class VI requirements to wells transitioning from an ER project to a

project for which the primary purpose is long‐term storage of CO2. For additional information on

transitioning of Class II wells for GS, see the preamble to the final rule and the responses to comments

on the proposed GS rule.

EPA is developing guidance on transitioning from Class II to Class VI. The guidance will assist Directors

and owner or operators in evaluating where a project may fit within a Class II to Class VI transition. The

guidance describes the methods available for the Director to determine the risk posed to USDWs from a

GS/ER project, and how the Director may determine if a project should be regulated within the Class II

or Class VI UIC program. This guidance will be available on EPA’s website at

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

Letter ID: 0373 Comment ID: 28022 Letter Lines: 102 to 106  

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

Directors  

Comment: The GWPC CO2 Committee recommends the following with respect to implementation of  

a waiver process:  

1. The authority for granting a waiver should rest solely with the state UIC  
primacy agency.  

Individual Response: EPA clarifies that the final determination regarding waiver issuance will be made

by the Director, following evaluation of all site‐specific information, public notice, and receipt of written

concurrence or non‐concurrence from the Regional Administrator. The role of the PWSS Director is to

ensure consideration of water system and water resource issues where injection into non‐USDW

formations above the lowermost USDW is being considered.  

EPA clarifies that, pursuant to §146.95(d), the Regional Administrator will make the final determination

whether to issue an injection depth waiver. However, prior to a final decision, the Director must provide

the Regional Administrator with the information collected during the waiver application and the public

notice processes. Based on this information and pursuant to requirements at §146.95(d), the Regional

Administrator will provide written concurrence or non‐concurrence regarding waiver issuance. The

Agency clarifies that these requirements are within the authority of the Safe Drinking Water Act.  

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: 0373 Comment ID: 28023 Letter Lines: 108 to 112  

Comment Code: 3360 3.3.6. Requirement to Apply for Waiver Separately from UIC Permit Application

(seeking comment)  

Comment: 2. The waiver, permit application and aquifer exemption request (if needed)  

should all be part of the same application process such that each is not subject  

to separate public notice and participation requirements. Further, EPA should  

consider accepting state public notification as a means of satisfying federal  

public notice requirements for aquifer exemptions.  

Individual Response: EPA agrees that it is appropriate to consider and evaluate the waiver application in

concert with the UIC permit application, and not under a separate process. For this reason, the final

requirements at §146.95 create an application and review process for GS injection depth waivers that is

integrated with the UIC permit application process while ensuring that the proposed project is

considered in the context of the presence of USDWs above and below the injection zone and potential

impacts on water systems.

For example, rather than submit a separate waiver application, owners or operators seeking waivers

must provide a supplemental report (the GS Class VI injection depth waiver application report)
referenced at §146.82(d) and outlined at §146.95(a) with additional, site‐specific information relevant to

operation under an injection depth waiver. This report, suggested by commenters, is designed to ensure

that all waiver information is discrete (from the permit application) and can be made available to the

Director, PWSS Directors, and the public when the waiver is publicly noticed. The UIC permit application

and waiver application would be reviewed together. If the permitting authority receives comments on

the injection depth waiver during the public comment period for both the waiver and the permit

application, the Director in consultation with the Regional Administrator, must evaluate comments prior

to providing a recommendation to the Regional Administrator regarding a waiver and issuing the Class

VI permit.

In addition, the public notification process for the waiver must occur concurrently with the UIC permit

notification to ensure that all necessary information is disclosed to the public for notice and comment

and that the public understands that the site, if permitted, would be operating under a waiver from the

injection depth requirements as specified in §146.95(c). EPA believes these requirements balance USDW

protection and disclosure of PWSS information with the GS permit application process requirements.  

Letter ID: 0373 Comment ID: 28112 Letter Lines: 114 to 116  

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

Directors  

Comment: 3. In those cases where the PWSS Director is not a part of the state UIC primacy  

agency, a special notification with opportunity to comment should be provided to  

the PWSS Director.  

Individual Response: 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.

EPA requires that this information be documented to ensure that this consultation will enable

transparent public disclosure of all information evaluated by the Directors and their respective

recommendations.  

EPA believes this process is necessary and appropriate to ensure that water system concerns are

considered when evaluating a waiver application. EPA clarifies that the final determination regarding

waiver issuance will be made by the Director, following evaluation of all site‐specific information, public

notice, and receipt of written concurrence or non‐concurrence from the Regional Administrator. EPA

believes that UIC Program staff are in the appropriate position to evaluate the technical details of the

waiver application, in concert with the UIC permit application, and the final requirements retain decision

making authority with the UIC Program.  
Letter ID: 0373 Comment ID: 28113 Letter Lines: 118 to 124  

Comment Code: 3230 3.2.3. Comments that Additional Submissions are Needed (seeking comment)  

Comment: 4. EPA should consider modifying 40 CFR Part 146.4 to include an additional  

provision for aquifer exemption based on the expected use of a USDW as a CO2  

storage reservoir. However, in adding such a provision we recommend that the  

proposed injection zone still be required to meet the criteria of not  

being reasonably expected to supply a public drinking water source, whether due  

to location, depth, total dissolved solids content or for other technological or  

practical reasons.  

Individual Response: EPA believes that there are limited circumstances where aquifer exemptions for

GS may be warranted. The final rule allows for the expansion of the areal extent of existing aquifer

exemptions for Class II EOR/EGR wells transitioning to Class VI injection for GS pursuant to requirements

at §§146.4 and 144.7(d). However, the final rule precludes the issuance of new aquifer exemptions for

Class VI GS wells; that is, aquifer exemptions will only be granted for projects that are transitioning from

Class II EOR/EGR wells to Class VI.  

The aquifer exemption requirements in the final rule provide flexibility and afford owners or operators

an opportunity to assess and select a suitable GS site while also preserving USDWs (i.e.,

formations/aquifers afforded SDWA protection). Class VI owners or operators granted expansions of

existing Class II EOR/EGR aquifer exemptions for GS projects must meet all of the tailored requirements

for GS wells in the final GS rule.

The Agency clarifies that the aquifer exemption requirements and the injection depth waiver

requirements serve different purposes. Class VI owners or operators granted expansions of existing

Class II EOR/EGR aquifer exemptions for GS projects must meet all of the tailored requirements for GS

wells in the final GS rule, including the site criteria at §146.83. EPA believes that, in most cases, the

injection depth waiver is a more appropriate option than aquifer exemptions for Class VI injection, and

believes that aquifer exemption expansions for GS should be granted in limited circumstances.  

Letter ID: 0373 Comment ID: 28114 Letter Lines: 133 to 143  

Comment Code: 2220 2.2.2. Basin‐Scale Hydrologic Impacts of CO2 Storage (seeking comment)  

Comment: 1. Regarding the NODA summary of LBNL studies on "Basin‐Scale Hydrologic Impacts  

of CO2 Storage', we feel that a clarification of the results of this preliminary  

simulation and their implications are needed. In particular, it was noted that, a  
pressure increase of 0.5 bar might be expected at the distal extent of the  

regional aquifer (200km from the core injection area). The next sentence states  

that "...basin‐wide pressure influences can be large." This implies that 0.5‐bar  

(~0.5 atm) pressure elevation at the perimeter of the basin is "large". Whereas  

we recognize that pressure perturbations will be significant in the core  

injection area (especially where pressure fields intersect), a 0.5‐bar increase  

in pressure at the basin perimeter is not significant in terms of threatening  

containment.  

Individual Response: EPA clarifies that in the study the 0.5‐bar pressure threshold was used as an

example illustrating the enormous size of the region affected by some pressure perturbation; it was not

meant to imply that a 0.5‐bar pressure increase is a significant threat. However, even a more significant

5‐bar threshold would still result in a large pressure‐affected region. The concern about pressure

perturbation is that deep saline water could be pushed upward into overlying freshwater aquifers via

potentially existing localized pathways.  

Letter ID: 0373 Comment ID: 28115 Letter Lines: 145 to 150  

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

Comment: 2. While the SECARB study provides an example of one case where the proposed  

constructions standards were followed without apparent incident, this does not  

mean they represent the minimum or exclusive standards necessary to protect  

USDW’s. Other construction standards could prove equally effective. Please  

refer to well construction standards submitted by GWPC in its December 24, 2008  

comments.  

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 from endangerment.  

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.

For more information on the construction requirements for GS wells, see the responses to comments on

the proposed rule in the rulemaking docket.  
Letter ID: 0373 Comment ID: 28116 Letter Lines: 152 to 159  

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

comment)  

Comment: 3. The NODA raises a question about the mobilization of metals from CO2  

injection. However, there is no concurrent risk analysis provided or cited.  

While we recognize that mobilization of metals in the injection zone can occur  

under specific circumstances, we believe the containment requirements of the  

proposed rule are adequate to prevent contamination of USDW’s from the movement  

of CO2 and associated formation fluids in the injection zone. Consequently, we  

believe mobilization of metals in the injection zone is not a concern provided  

formation fluids remain in the injection zone.  

Individual Response: EPA agrees that contamination of USDWs would not be a concern provided

formation fluids remain in the injection zone. It is mentioned in the NODA that the risk of fluids leaking

from deep storage is low for properly managed GS projects, but it may not be completely ruled out.

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.

Site specific risk analyses should be undertaken in order to determine the probability of CO2 (and

associated formation fluids) leaking from the storage reservoir. EPA clarifies that 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 Area of Review. 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 (CO2) 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.  

Letter ID: 0373 Comment ID: 29336 Letter Lines: 126 to 129  

Comment Code: 3230 3.2.3. Comments that Additional Submissions are Needed (seeking comment)  

Comment: 5. Because injection above USDW’s may present additional questions relative to  

movement of CO2 in the subsurface, we believe EPA should consider adding a  

provision for additional regional hydrologic studies when injection above USDW’s  

is proposed.  
Individual Response: EPA agrees that protecting drinking water resources is vital and is the purpose of

the UIC requirements. The waiver approach establishes extensive site‐specific geologic and

hydrogeologic information related to injecting above or between USDWs that the owner or operator

must submit and the Director must consider, in consultation with PWSS Directors, to ensure that water

supplies in the area and all USDWs are protected.