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: 0293 

Commenter: A. Scott Anderson 

Organization: Environmental Defense Fund 

Letter ID: 0293 Comment ID: 25278 Letter Lines: 58 to 63 

Comment Code: 5280 2.8.2.4 USDW non-endangerment demonstrations 

Comment: (1). It is critical that the rule contain a "closure standard" for GS projects 

that is feasible, scientifically rigorous, and adequate for purposed of 

fostering public confidence in GS technology. Unless EPA develops an adequate 

closure standard, there is no reason to expect the public to have confidence in 

this technology. We believe that the standard ought to be based on the 

suggestions made in the December 23 letter; 

Individual Response: EPA agrees that authorization of site closure must be feasible, 

scientifically rigorous, and foster public confidence in GS technology, but disagrees that the rule 

should set specific criteria. EPA believes that many site-specific factors will influence the 

determination of when the CO2 plume and pressure front no longer pose a risk of endangerment 

to USDWs. It is for this reason that EPA believes that individual UIC Directors, in consultation 

with operators, will be in the best position to determine whether additional post-injection site 

care is needed. EPA expects this decision to be made based on relevant site data and in 

consultation with all potentially impacted parties. 

EPA is developing guidance to assist owners or operators in evaluating well plugging, postinjection site care, and site closure requirements of 146.92 and 146.93. Additionally, the 

guidance will assist Directors in evaluating proposed well plugging plans and post-injection site 

care and site closure plans under 146.92 and 146.93. The guidance describes recommended 

approaches for how an owner or operator could plug injection and monitoring wells; perform 

post-injection monitoring; demonstrate non endangerment; and perform site closure activities. 

The guidance will be available at 

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

Letter ID: 0293 Comment ID: 25279 Letter Lines: 65 to 71 

Comment Code: 4110 2.4.1.1 Injection pressure limitations 

Comment: (2). Appropriate pressure management is essential if a GS project is to perform 

properly. In highly pressured reservoirs, it is vital that EPA assure that 

regulators and operators will consider both the risks of tensile failure and 

shear failure. UIC regulation has tended, at least in practice, to focus only on 

the former. For these and other reasons, we urge you to carefully consider the 

suggestions for injection pressure limitations that the Multi-Stakeholder Group 

forwarded on December 23; 

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Individual Response: EPA agrees that pressure management is essential for a Class VI well to 

perform properly. EPA emphasizes that injection pressure limits are important to protect against 

fracturing of the confining zone, and that the requirement at §146.88(a) that the pressure in the 

injection zone not exceed 90 percent of the fracture pressure provides a margin of safety in the 

well operation and protects USDWs from endangerment. If the Director determines, based on a 

review of the information collected as part of site characterization, that a lower injection pressure 

limitation is appropriate, the Director has the authority to set a lower limit in the operating permit 

than the limit established in the rule. 

EPA notes that during the site characterization process, owners or operators must submit data 

about the geology of the site, as specified at §146.82(a), including data on known or suspected 

faults and fractures and geomechanical information on fractures, stress, ductility, rock strength, 

and in situ fluid pressures within the confining zone. The Director will use these data to 

determine appropriate limits on injection. 

In response to the concern about reopening of faults at lower pressures than 90 percent of 

fracture pressure, EPA believes that the requirement for the owner or operator to submit data on 

known or suspected faults and fractures and information on the seismic history of the site will 

inform the determination of an appropriate pressure limitation in the permit. Any sites with the 

potential for reopening or reactivation of faults or unacceptable seismic risk that could otherwise 

interfere with containment will not be permitted as GS sites. 

EPA is developing guidance on site characterization for GS projects to assist owners or operators 

in meeting the requirements of §146.82 and to assist directors in evaluating permit applications. 

The guidance will describe recommended approaches for characterizing the regional geology and 

hydrogeology of a proposed site and performing the necessary geochemical, geomechanical, and 

geophysical analyses of the injection and confining zone. EPA is also developing guidance for 

primacy agencies that will include recommended approaches for evaluating owner or operatorsubmitted data in setting permit conditions. The guidance will be available on EPA's web site, at 

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

Letter ID: 0293 Comment ID: 25280 Letter Lines: 73 to 104 

Comment Code: 2046 1.5.2.3 Continuing to classify CO2 injection for EOR/EGR as Class II/ 

dividing line between Class II and Class VI (seeking comment) 

Comment: (3). EDF believes that the Agency should take a different approach to regulating 

sequestration in the oilfield context than the approach embodied in the proposed 

rule. As proposed, the rule would allow some projects (i.e., projects in 

oilfield that produce incidental amounts of oil in conjunction with CO2 storage) 

to be regulated less stringently than is needed. Small amounts of oil production 

should be expected where CO2 is stored in "depleted" oilfields. Moreover, it 

should also be expected that reservoir pressures in such projects will 

materially exceed the pressures generally encountered in business-as-usual 

enhanced oil recovery projects. We believe that the risk profile presented by 

such projects should be addressed head-on - we do not believe the problem can be 

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fixed simply by providing that all projects that produce any oil shall be 

regulated under existing Class II regulations or the Class VI will apply to 

projects that are "exclusively" or "primarily" or "specifically" for the purpose 

of sequestration. Instead, we believe that EPA should recognize, for Safe 

Drinking Water Act purposes, that three types of CO2 injection/storage 

activities present three different risk profiles and that therefore they ought 

to be regulated in three different ways. The three project types as we see it 

are: (a) injection/storage that takes place in conjunction with traditional 

Class II enhanced oil recovery operations; (b) CO2 storage in oilfields where in 

all probability there will continue to be some oil production but where the goal 

will be to pressure up the reservoir as high as possible in order to store as 

much CO2 as possible; and (c) CO2 storage in brine formations. While the 

December 23 Multi-Stakeholder Group letter does not suggest in detail how the 

regulation of sequestration in highly pressured oilfields might differ from both 

the existing Class II regulations and from the Class VI regulations as proposed, 

the December 23 submission does provide a suggested "bright line" that can be 

used to distinguish between the two types of oilfield activity. It is important, 

in our judgment, that the Agency consider modifying the proposed rule so that 

UIC regulation will be tailored to each of the three contexts outlined above. It 

will be important to solicit another round of public comment on this idea before 

adopting final regulations - something we hope can be done in conjunction with a 

NODA process. 

Individual Response: EPA agrees that injection of CO2 for the primary purpose of enhancing 

oil and gas recovery should remain under the Class II Program. EPA clarifies that owners and 

operators of traditional EOR projects are subject to limits on injection, including pressure limits, 

established under their Class II permits. If they exceed those limits, they will be considered to be 

in violation of the Class II UIC regulations. The Agency also agrees that the nature and risks of 

CO2 injection for the primary purpose of long term storage poses different risks than injection 

for the primary purpose of ER, and therefore has developed new Class VI regulations to address 

these unique risks. For example, the volume of CO2 anticipated to be injected for long term 

storage is significantly greater than for ER operations. Reservoir pressure conditions will also be 

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

higher pressures within their storage formations than Class II ER projects. 

The final Class VI regulations require that any owner or operator injecting CO2 for the primary 

purpose of long term storage obtain a Class VI permit with some special consideration for the 

fact that they are transitioning from a well not originally designed to meet Class VI requirements. 

The Director has the authority to determine at what point a Class VI permit is required for those 

projects that are transitioning from the primary purpose of EOR to long term storage of CO2. 

The final regulation provides a set of technical factors for the Director to evaluate in making this 

determination, at §144.19. EPA believes that this approach provides sufficient protection of 

USDWs when there is an increased risk to USDWs as compared to traditional Class II operations 

while allowing for site-specific flexibility. 

EPA is developing guidance on transitioning permits from Class II to Class VI. The guidance 

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will assist Directors in determining whether an injection project should be transitioned from 

Class II where the primary purpose is oil and gas production to Class VI where the primary 

purpose is long-term storage of large volumes of CO2. The guidance describes recommended 

methods the Director may use to evaluate changes in risk to USDWs from projects, and how the 

Director may determine whether a project should be regulated within the Class II or Class VI 

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

http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm. For more information, please 

see the discussion on transition of Class II wells in the preamble to the final GS rule. 

EPA agrees that tailored requirements for Class VI wells are necessary to address the unique 

nature of injecting large volumes of CO2 and to ensure that USDWs are protected from 

endangerment. The GS rule contains tailored requirements for the permitting, geologic site 

characterization, AoR and corrective action, well construction, operation, mechanical integrity 

testing, monitoring, well plugging, post-injection site care, and site closure of GS wells that 

directly address issues unique to the nature of large-scale CO2 injection for GS.