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.






Letter ID: 0217 

Commenter: Olon Plunk 

Organization: Xcel Energy, Inc. 

Letter ID: 0217 Comment ID: 21549 Letter Lines: 64 to 73 

Comment Code: 1330 1.1.3.1 Support use of GS in general 

Comment: As we studied the feasibility of developing an IGCC project with CCS, we learned 

a great deal about geologic storage of CO2. We learned that geologic storage is 

currently one of the most important means by which power companies can reduce 

CO2 emissions while still producing reliable and affordable energy from coal. 

International studies as well as studies here in this country attest to the 

importance of geologic storage of CO2 in any strategy to reduce increasing 

carbon concentrations in the atmosphere. The development of a rational 

regulatory framework to address geologic storage of CO2 is essential in order to 

balance the nation's need for energy security, through increased use of domestic 

energy resources, with concerns over global climate change. 

Individual Response: EPA acknowledges the comment. Please see the remainder of EPA’s 

responses to this comment for further details. For additional information on EPA’s final 

regulatory approach, please see the final rule and preamble as well as the rulemaking docket. 

Letter ID: 0217 Comment ID: 21550 Letter Lines: 75 to 85 

Comment Code: 1250 1.1.1.4 Flexibility is needed (performance-based standards) 

Comment: We also learned, however, that there are number of critical policy, legal, and 

technical issues that must be resolved before geologic storage can be 

implemented on a full-scale commercial basis. The proposed rule is a significant 

early step in helping to resolve these issues. The rule, however, must be 

designed to facilitate, not unduly hinder, progress towards commercial 

deployment of geologic storage. Large-scale underground injection and storage of 

CO2 remains an emerging technology and it is important that any rule adopted by 

EPA be flexible enough to adapt to advances in science and technology moving 

forward. We offer these comments in support of a flexible and appropriately 

tailored rule that will facilitate geologic storage technology and projects 

while protecting underground sources of drinking water. 

Individual Response: EPA clarifies that the Class VI GS requirements are designed to ensure 

that, where deployed, GS is conducted in a manner that protects USDWs from endangerment. 

Encouraging investment in CCS projects and facilitating deployment are outside the scope of the 

GS rulemaking. 

To address the comment that the rule should accommodate future technological developments 

1
related to GS, EPA adds that it is using an adaptive approach to regulating GS under the UIC 

Program. Even after finalization of the GS regulation, EPA plans, every six years, to collect and 

review project data on GS research 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: 0217 Comment ID: 21551 Letter Lines: 87 to 100 

Comment Code: 1480 1.2.2.2.2 CO2 is not a pollutant 

Comment Code: 1680 1.3.8 Don't overstate risk, don't stigmatize CO2 

Comment: CO2 Characterization 

CO2 is produced continually by natural process throughout the natural world and 

poses no significant hazard to human health when properly managed. EPA is 

correct to note in the proposed rule that a potential barrier to CCS and 

geologic storage involves how the captured CO2 is treated within existing 

regulatory frameworks. EPA is incorrect, however, to suggest or presume that 

captured CO2 is a waste, or that geologic storage via a Class VI well 

constitutes disposal. In several instances, the proposed rule refers to CO2 as a 

potential hazardous waste and suggests the need for regulatory requirements for 

Class VI wells that exceed those deemed necessary for Class I hazardous waste 

injection wells. Creating such a regulatory framework that implies an undue 

level of risk associated with geologic storage is misleading and could 

stigmatize proposed projects in the eyes of both the public and investors. 

Individual Response: EPA clarifies that the GS rule does not address the status of CO2 as either 

a pollutant or a commodity. In addition, whether or not a fluid could be sold on the market as a 

commodity does not override EPA's authority under the SDWA to protect USDWs from 

endangerment. EPA stresses that the focus of the GS rule is to ensure that, where GS is deployed, 

it is conducted in a manner that protects USDWs. 

Under the SDWA, the injection of any "fluid" is subject to the requirements of the UIC program. 

"Fluid" is defined under 40 CFR 144.3 as any material or substance which flows or moves, 

whether in a semisolid, liquid, sludge, gas or other form or state, and it includes liquids, gases, 

and semisolids (i.e., slurries) injected into the subsurface. 

Under §146.82(a)(7), owners or operators of GS wells must characterize their CO2 stream as part 

of their permit application. If the injectate is determined to meet the definition of a hazardous 

waste under RCRA, and as defined in 40 CFR Part 261, the stringent UIC Class I hazardous 

waste requirements for injection of hazardous waste apply. Thus, injection of corrosive CO2 into 

Class VI wells is prohibited. In addition, owners or operators must periodically monitor their 

injectate throughout injection operations under §146.90(a). 

EPA disagrees that the GS regulation overstates the risk of CO2 injection or implies an undue 

level of risk. EPA recognizes that injecting large volumes of CO2 for GS poses unique 

2
challenges that, if not properly managed, could endanger drinking water sources and have other 

adverse impacts. However, with proper site selection, the final, tailored, Class VI requirements 

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

water, and potential impurities in the CO2 stream. In addition, EPA expects the tailored 

permitting, siting, construction, operation, monitoring, and post-injection site care requirements 

in the GS rule to prevent leakage from injection formations and protect USDWs. 

EPA does not agree that the tailored requirements will create a negative public perception of GS. 

The Agency believes that a demonstration to the public that GS projects are meeting the GS 

rule's tailored requirements will likely improve confidence in the project and help address public 

questions and concerns. 

Regarding the ability of owners or operators to secure investment in GS projects, EPA believes 

that financing entities will have improved confidence in projects that incorporate multiple 

protective requirements. 

Letter ID: 0217 Comment ID: 21552 Letter Lines: 102 to 109 

Comment Code: 1630 1.3.3 RCRA/hazardous waste issues (seeking comment) 

Comment Code: 1640 1.3.4 CERCLA issues (seeking comment) 

Comment: In their comments regarding the proposed rule, both the Edison Electric 

Institute (EEI) and the Utility Solid Waste Activity Group (USWAG) present well 

articulated concerns regarding the legal and regulatory issues that could arise 

from the inappropriate treatment of captured CO2 within the context of the 

Resource Conservation and Recovery Act, and the Comprehensive Environmental 

Response, Compensation and Liability Act. Both groups describe potential 

solutions to this issue; Xcel Energy endorses these comments and suggested 

solutions. 

Individual Response: EPA received many comments regarding the applicability of the RCRA 

regulations and statute to CO2 streams that are geologically sequestered under the final Class VI 

UIC well requirements. As a result, EPA has decided to initiate a separate proposed rulemaking 

specifically to examine the issue of RCRA applicability to CO2 streams being geologically 

sequestered, including the possible option of a conditional exemption from the RCRA 

requirements for CO2 GS in Class VI wells. EPA will consider these comments as part of its 

development of that proposal. The Agency will consider issues particular to RCRA in the context 

of that separate rulemaking, and recommends that the commenter read that proposed rule when it 

is published. The Agency notes that commenters who wish to submit comments on the RCRA 

proposal will need to do so during the comment period for that rule. Finally, EPA also notes that 

the final GS rule, which adds new regulations for Class VI wells under the Safe Drinking Water 

Act (SDWA), is not making any changes to the RCRA regulations. 

EPA clarifies that CO2 itself is not listed as a hazardous substance under CERCLA; however, the 

CO2 stream may contain a listed hazardous substance (such as mercury) or may mobilize 

substances in the subsurface that could react with ground water to produce listed hazardous 

3
substances (such as sulfuric acid). Whether such substances may result in CERCLA liability 

from a sequestration facility depends entirely on the composition of the specific CO2 stream and 

the environmental media in which it is stored (e.g., soil or ground water). CERCLA exempts 

from liability, under CERCLA section 107, 42 U.S.C. 9607, certain “federally permitted 

releases” (FPR) as defined in CERCLA, 42 U.S.C. 9601(10). Class VI permits will need to be 

carefully structured to ensure that they prevent potential releases from the well which are outside 

the scope of the Class VI permit. 

For additional information, please see EPA's responses to specific comments by Edison Electric 

Institute and the Utility Solid Waste Activity Group. 

Letter ID: 0217 Comment ID: 21553 Letter Lines: 111 to 143 

Comment Code: 1250 1.1.1.4 Flexibility is needed (performance-based standards) 

Comment: Default Provisions 

Although underground injection of CO2 is well established for enhanced oil and 

gas recovery, it remains in it nascent stages with respect to large-scale 

geologic storage. Throughout the proposed rule, EPA suggests the need for 

blanket prohibitions, limitations and default provisions that are overly 

conservative and not supported by established facts. Such examples include: 

- 50-year default post closure period 

- Mandatory 10-year reevaluation of the Area of Review (AoR) 

- Categorical exclusion of specific formations (e.g,. coal seams) 

- Prohibitions on types of well drilling (e.g., horizontal, angled) 

- Mandate to always inject below the lowermost USDW 

- Prohibition on use of exempt aquifers 

- Prohibition on hydraulic fracturing 

- Mandatory use of tracers 

- Mandatory annual and electronic reporting 

At this early stage, EPA should avoid establishing arbitrary limits or 

prohibitions that might stifle research and development, or that are so 

excessively conservative as to close the door on geologic storage projects that 

are otherwise safe and economically sound. The final rule must recognize that 

the potential risks, as well as the approaches to mitigate or eliminate that 

risk, will vary greatly from project to project. The broad imposition of 

administrative and technical requirements designed to be protective of the 

highest risk projects unnecessarily burden low to moderate risk projects. Viable 

projects might not be proposed or move forward due to excessive economic burdens 

or regulatory uncertainty. EPA should avoid a "one size fits all" approach and 

instead develop a framework that provides the flexibility for projects to be 

successfully permitted, based on each project's unique characteristics and 

circumstances. 

4
Long-Term Liability 

Individual Response: The Agency believes that the Class VI requirements balance site-specific 

flexibility with USDW protection. Rather than setting performance or technology-based 

standards for GS projects, EPA is adopting a flexible approach, where operators of GS projects 

would develop and implement site-specific plans for delineating the AoR, testing and monitoring 

the site, performing corrective action, and post-injection site care. EPA believes that the plans—

which would be reviewed and approved by the Director and periodically updated throughout the 

life of the project—promote an ongoing dialogue between the operator and the Director that will 

encourage use of the most appropriate technologies for a particular project. 

EPA clarifies that the Class VI GS requirements are designed to ensure that, where deployed, GS 

is conducted in a manner that protects USDWs from endangerment. Encouraging investment in 

CCS projects and facilitating deployment are outside the scope of the GS rulemaking. 

Letter ID: 0217 Comment ID: 21554 Letter Lines: 145 to 155 

Comment Code: 5460 2.9.2 Comments on transfer of liability for long-term care 

Comment: Owners and operators must have a means to bound and quantify the potential longterm liabilities associated with a geologic storage project, otherwise, it could 

be impossible to secure the necessary insurance and financing. As a matter of 

national policy, the success of geologic storage is essential to our future 

energy security and climate mitigation strategies. These projects provide a 

public benefit. As such, the regulatory framework should provide a mechanism 

whereby the long-term liability for a properly sited, permitted, operated and 

closed project can be capped or quantified, and then later transferred or 

shared. Unless the potential open-ended and long-term liability imposed by the 

proposed rule is resolved, it is questionable whether geologic storage can be 

implemented on a large-scale basis. 

Individual Response: EPA acknowledges the commenter’s concern regarding the applicability 

of multiple statutes to GS projects and the need for a single clear liability regime for owners or 

operators. EPA is working to create a nationally consistent financial responsibility regime within 

its authority to ensure that financial resources are available to protect USDWs throughout the life 

of the GS project. However, the authority under the SDWA does not extend to release owners or 

operators from long-term responsibility for the potential economic costs of impacts unrelated to 

USDWs. EPA does not have authority to transfer liability from one entity to another and SDWA 

does not provide for the creation of a third party financial instrument where EPA is the trustee. In 

the UIC program, liability under SDWA §1423 remains with the owner or operator for all well 

classes until all regulatory requirements have been met. EPA understands that Congress is 

considering legislation that may address the liability issue. EPA clarifies that the GS regulation 

does not promote or encourage the use of GS; rather it is designed to ensure consistency in 

permitting underground injection of CO2 at GS operations across the United States and provide 

requirements to prevent endangerment of USDWs in anticipation of the eventual use of GS to 

5
reduce CO2 emissions. 

EPA disagrees that caps should be placed on financial responsibility requirements in the 

proposed rule. A cap may result in the endangerment of a USDW if the appropriate amount of 

money provided under the financial instrument is less then what is needed to protect the USDW. 

EPA believes that the instruments chosen for financial responsibility must cover the complete 

costs of these activities. 

Letter ID: 0217 Comment ID: 21555 Letter Lines: 157 to 164 

Comment Code: 5430 2.9.1 Comments on proposed financial responsibility requirements (40 

CFR 146.85) 

Comment Code: 5432 2.9.1.1 Need to adjust financial responsibility mechanisms (seeking 

comment) 

Comment Code: 5434 2.9.1.2 Need for additional instruments (seeking comment) 

Comment: Financial Assurance 

Xcel Energy agrees that some method of financial assurance is appropriate for 

geologic storage projects. However, it is important to retain the concepts of 

both self-assurance and phased-assurance. The amount of financial assurance 

required should be limited to what is known, or can be estimated with reasonable 

accuracy, today. Financial assurance should be periodically adjusted as new 

information becomes available. 

Individual Response: EPA will allow owners or operators to use one or more or multiple 

financial responsibility instruments for well plugging and site closure. However, EPA will not 

allow for a separate financial responsibility demonstration for well plugging and PISC; this must 

be done at the time of permit application. This will ensure that resources are available to prevent 

the endangerment of USDWs in the event that the owner or operator experiences financial 

difficulties at any time during the life of the GS project. 

EPA agrees that it is important to periodically update cost estimates that support financial 

responsibility determinations. EPA clarifies that the GS rule, at §146.85(c), requires the owner or 

operator to provide annual updates to the cost estimate to account for any amendments to the 

AoR and corrective action plan, the injection well plugging plan, the PISC and site closure plan, 

and the emergency and remedial response plan. The owner or operator must also update the cost 

estimate annually for inflation. EPA adds that the Director can also require the owner or operator 

to provide an adjustment of the cost estimate if the Director determines that the original 

demonstration is no longer adequate, as specified at §146.85(e). 

EPA will retain the use of self-insurance as an instrument for financial responsibility for Class 

VI wells. Owner or operators may self insure through a financial test provided certain conditions 

are met such as demonstration of profitability and stability. Furthermore, EPA is developing 

guidance that describes the types of financial instruments, including self insurance, which 

owners or operators can use to meet financial responsibility requirements for GS wells. The 

6
financial responsibility guidance will include considerations for Directors regarding how to 

evaluate the appropriateness of a specific financial responsibility instrument for a specific 

project. This guidance is available on EPA's website at 

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm. EPA notes that Directors 

may disallow certain instruments. 

Letter ID: 0217 Comment ID: 21556 Letter Lines: 166 to 176 

Comment Code: 5600 2.11 Comments related to UIC Program primacy for Class VI wells 

Comment Code: 5610 2.11.1 Allowing partial primacy for Class VI wells (seeking comment) 

Comment: State Primacy 

Xcel Energy supports the concept of state primacy. States should have the 

ability to obtain delegated authority for Class VI wells only, as opposed to 

being required to develop delegable programs for all classes of wells. As noted 

by EEI and USWAG, permitting decisions are best made at the state level where 

knowledge of local conditions and public concerns is the greatest. In addition, 

it is essential that the final rule establish a "lead state" concept for 

projects where the AoR may cross state boundaries. Xcel Energy supports 

assigning the project permitting lead role to the state where the Class VI 

wellhead is located. 

Individual Response: EPA agrees that states should be allowed to obtain primacy for Class VI 

wells independently of other well classes, and will allow independent primacy for Class VI wells 

under §145.1(i) of the final GS rule. In the past, EPA has not accepted UIC primacy applications 

for individual well classes under Section 1422 of SDWA. In other words, if a State wanted 

primacy for Class I wells, the State would also need to accept responsibility for Class III, IV, and 

V wells. This policy has been in place since the initiation of the UIC Program in the early 1980s 

and was intended to encourage states to take full responsibility for UIC programs, avoid 

duplication of efforts, and provide for administrative efficiencies. 

However, given the potential for CCS (encompassing capture, transportation, and geologic 

sequestration) to be an important part of a national priority to address climate change, EPA 

believes that providing states the flexibility to obtain primacy for Class VI wells independently 

of other well classes can help foster effective management of CCS. EPA believes that allowing 

independent Class VI primacy may encourage states to take responsibility for implementation of 

Class VI regulations and provide for a more comprehensive approach to managing CCS projects 

by promoting the integration of GS activities under SDWA into a broader framework for 

managing CCS. Furthermore, GS operations involve ancillary activities (e.g., pipeline 

operations, pore space ownership, land use rights, and surface access) for which states can call 

upon other authorities that exist at the state level (but outside UIC authority) to provide a more 

comprehensive CCS management approach. 

EPA also believes that allowing states to apply only for Class VI primacy will shorten the 

primacy approval process for states. EPA's willingness to accept independent primacy 

7
applications for Class VI wells represents a shift in its longstanding policy of discouraging 

"partial primacy." It is very important to note that this shift in policy allowing for Class VI 

primacy does not apply to any other well Class under Section 1422. EPA will continue to 

discourage applications for partial primacy for all other well types under Section 1422. 

EPA clarifies that states should be able to obtain primacy for Class VI wells independent of other 

well classes provided they develop regulations that are at least as stringent as the minimum 

Federal requirements (e.g., permitting, inspection, operation, monitoring, and recordkeeping 

requirements) in the final GS rule. EPA believes that existing programs can adapt their expertise 

to the new requirements for Class VI wells and will be able to develop a primacy application for 

Class VI wells under section 1422 of SDWA and ensure that their GS programs integrate into 

national climate change priorities and protect USDWs from endangerment. 

EPA clarifies that issuance and oversight of a GS permit, including any associated AoR 

boundary related coordination, is the responsibility of the primacy (State, Tribal or Territorial) or 

regional DI program in the state where the injection well is located. EPA understands that the 

CO2 plumes for large GS projects may cross State, Tribal, Territorial, EPA Regional, or national 

boundaries. The final GS rule, at 146.82(a)(2), requires the owner or operator to identify all 

State, Tribal, and Territorial boundaries within the AoR. Based on this information, the Director 

must provide written notification to all States, Tribes, and Territories to inform them of the 

permit application 146.82(b) and ensure that they are involved in any necessary processes (e.g., 

development of the emergency and remedial response plan (146.94)). The Agency encourages 

transparency in the permitting process and anticipates that State-State/State-Tribal 

communication on GS permitting will facilitate information sharing and encourage safe, 

protective projects. 

Letter ID: 0217 Comment ID: 21557 Letter Lines: 178 to 191 

Comment Code: 3120 2.1.2 Need to identify additional confining and containment zones 

(seeking comment) 

Comment: Secondary Containment 

Requiring secondary containment as a matter of standard practice is unnecessary 

and will likely significantly decrease the number of geologic storage sites 

available. Such a requirement exceeds the standard for Class I hazardous waste 

injection wells, creating the logical, yet erroneous inference that CO2 

injection in a Class VI well poses a greater risk than Class I injection of a 

hazardous waste. Given the proposed rule's basic premise that the design of a 

Class VI well and the designated receiving formation must be protective of USDWs 

in order to be permitted in the first instance, the need for secondary 

containment is redundant and unnecessary. Secondary containment should remain 

only as an option to be proposed by the project applicant in instances where 

legitimate concerns over the primary containment capabilities of the receiving 

formation preclude permitting in the normal manner. 

8
Individual Response: EPA clarifies that secondary confining zones are not required for all GS 

sites. Rather, secondary confining zones are required when the Director determines that these 

zones are needed to maximize the protection of USDWs from endangerment. EPA retains the 

requirement to identify additional containment/confining zones, if required by the Director, as 

proposed (e.g., §146.83(b)). EPA believes that, in some situations, the presence of additional 

confining and containment zones above the primary (i.e., lowermost) confining zone can 

improve USDW protection. The Agency acknowledges that the additional confining formations 

may also, in site-specific circumstances, further impede vertical fluid movement, provide 

additional sites for monitoring, mitigation, and remediation, and allow for pressure dissipation. 

EPA disagrees that the requirement would reduce the number of sites available for GS or that the 

requirement implies that CO2 poses a greater threat than Class I hazardous wells. The intent of 

this requirement is to ensure that a proposed site provides adequate protection of USDWs from 

endangerment; if this protection cannot be demonstrated, the Director would not issue a permit 

for GS at the site. 

Letter ID: 0217 Comment ID: 21558 Letter Lines: 193 to 199 

Comment Code: 3200 2.2 Proposed Area of Review and Corrective Action Requirements (40 

CFR 146.84) 

Comment: Corrective Actions/AoR 

Xcel Energy is concerned that the term "corrective action" as used broadly in 

the proposed rule infers to the public that a problem has occurred. We concur 

with USWAG's comment that it would be better to refer specifically to "well 

plugging and repair" to avoid stigmatizing projects for what are in fact 

deliberate and proactive preventive measures. In addition, Xcel Energy advocates 

Individual Response: EPA notes that the term "corrective action" at 146.84(d) has been used to 

describe the process of addressing improperly plugged wells in the AoR of injection wells since 

the inception of the UIC Program, e.g., at 146.7 and 146.64. While EPA is aware that the term 

has a different meaning under RCRA and CERCLA, this has not caused confusion in the past. 

The alternative term, "well plugging," suggested by the commenter is reserved for injection well 

plugging (as indicated at 146.92). 

Letter ID: 0217 Comment ID: 21559 Letter Lines: 199 to 210 

Comment Code: 3630 2.2.4.1 Comments in favor of allowing phased corrective action 

Comment: deliberate and proactive preventive measures. In addition, Xcel Energy advocates 

a phased approach to well plugging and repair, allowing expansion of the scope 

of wells within the AoR over time on an iterative basis as dictated by actual 

project progress and/or new information. As noted in the proposed rule, the AoR 

can also include pre-existing wells owned by other owners or operators. Geologic 

storage project owners and operators should not be held responsible to close, 

9
repair, or replace these pre-existing wells or take other corrective action 

where the pre-existing well owner or responsible party has an existing 

obligation to do so under the law. Current or past owners or operators of preexisting wells should not be rewarded for ignoring their responsibilities under 

the law, and should be penalized for failure to implement already required 

corrective action in a timely manner. Finally, the rule should explicitly allow 

Individual Response: EPA clarifies that the purpose of the requirement to perform corrective 

action at §146.84(d) is to ensure that all wells in the AoR that have the potential to cause 

movement of CO2 or other fluids into or between USDWs receive appropriate corrective action. 

All needed corrective action must be performed by the owner or operator as described in the 

approved AoR and corrective action plan, regardless of ownership. Failure to do so would either 

preclude authorization to inject or, in the case of phased corrective action, be considered a 

violation of the permit and subject to applicable civil, criminal, or administrative penalties. 

EPA clarifies that, if monitoring or modeling data indicate a change in the AoR, the owner or 

operator would need to review and amend the AoR and corrective action plan and follow the 

amended plan. 

Letter ID: 0217 Comment ID: 21560 Letter Lines: 210 to 212 

Comment Code: 3500 2.2.3 Area of Review Reevaluation (seeking comment) 

Comment: corrective action in a timely manner. Finally, the rule should explicitly allow 

for future expansion of the AoR if necessary, provided the objective to protect 

USDWs continues to be met. 

Individual Response: EPA acknowledges that the AoR for a GS project may change over time, 

and for this reason, the rule requires owner or operator to periodically review the AoR. EPA 

believes that periodic reevaluation of the AoR as required at §146.84(e) is appropriate to address 

the unique conditions posed by GS, including the anticipated injection volumes and associated 

size of CO2 plumes, as well as to address potential uncertainty in AoR modeling. 

EPA clarifies that the purpose of the requirement to perform an initial AoR delineation at 

§46.84(c)(1) is to predict as closely as possible, the ultimate extent of the CO2 plume and 

pressure front. The reevaluation should be considered adjustments to address changes that could 

not have been anticipated before injection commences. 

10