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 contai n a "closure standard " for GS projects

that is feasible, scientifically rigor ous, and adequate for purposed of

fostering public confidence in GS tec hnology. Unless EPA develops an adequate

closure standard, there is no reason to e xpect the public to ha ve confidence in

this technology. We believe that the st andard 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 technol ogy, 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 pressu re front no longer pose a risk of endangerment

to USDWs. It is for this reason that EPA believe s that individual UIC Dir ectors, 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 potentia lly 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 propo sed well plugging plans a nd post-injection site

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

approaches for how an owner or operator coul d plug injection and m onitoring wells; perform

post-injection monitoring; dem onstrate non endangerment; and perf orm 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 ma nagement 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 bot h the risks of tensile failure and

shear failure. UIC regulati on 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 limita tions that the Mult i-Stakeholder Group

forwarded on December 23;

1Individual Response: EPA agrees that pressure management is essential for a Class VI well to

perform properly. EPA emphasizes that injection pr essure 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 fractur e pressure provides a margin of safety in the

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

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

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

than the limit established in the rule.

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

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

faults and fractures and geomechanical informati on on fractures, stress, du ctility, rock strength,

and in situ fluid pressures w ithin the confining zone. The Di rector 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 requireme nt for the owner or operator to submit data on

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

inform the determination of an appropriate pressu re 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 approach es for characterizing the regional geology and

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

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

primacy agencies that will include recommended a pproaches for evaluating owner or operatorsubmitted data in setting permit conditions. The gu idance 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 in jection 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 allo w some projects (i.e., projects in

oilfield that produce incident al amounts of oil in conj unction 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" oilfie lds. Moreover, it

should also be expected that reservoi r pressures in such projects will

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

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

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

2fixed simply by providing that all pr ojects that produce any oil shall be

regulated under existing Class II regulati ons or the Class VI will apply to

projects that are "exclusive ly" or "primarily" or "specifically" for the purpose

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

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

activities present three different risk profiles and that th erefore 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 stor age in brine formations. While the

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

regulation of sequestration in highly pre ssured 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 Cl ass 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 ex ceed those limits, they will be considered to be

in violation of the Class II UIC re gulations. 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 an ticipated to be injected for long term

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

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

higher pressures within thei r storage formations than Class II ER projects.

The final Class VI regulations re quire that any owner or operato r injecting CO2 for the primary

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

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

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

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

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

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

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

while allowing for site-specific flexibility.

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

34 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 change s in risk to USDWs from projects, and how the

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

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

http://water.epa.gov/type/groundwat er/uic/wells_sequest ration.cfm. For more information, please

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

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

nature of injecting la rge 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 correc tive action, well construction, ope ration, mechanical integrity

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

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