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.p

. 1

P .O

. Box 200901 " Helena, MT 59620-0901 " (406) 444-2544 " www .deq .mt .gov November 12, 2008

Water Docket

Environmental Protection Agency

Mailcode : 2822T

1200 Pennsylvania Avenue

. NW Washington, DC 20460

RE : Docket EPA-HQ-OW-2008-0390 

## N u v 2 12008

The Montana Department of Environmental Quality (MDEQ offers the following comments in response to EPA's proposed rulemaking : Federal Requirements Under the Underground Injection Control (UIC) Program for Carbon Dioxide (C02) Geologic Sequestration (GS) Wells

.

GENERAL COMMENTS :

1

. MDEQ agrees with the EPA approach to designating a new UIC class

. The specific construction requirements, monitoring, modeling and analysis and nontraditional identification of the Area of Review all support a new

class definition

.

2

. MDEQ supports delegation of Class VI primacy to states as a separate and distinct delegation process, not requiring states to also be delegated any of the other classes

. Throughout this rulemaking notice and discussion, EPA points out the differences between carbon dioxide injection and other classes of injection activities

.

3

. EPA must provide adequate funding to states delegated primacy in the UIC
program

. Current levels are not adequate and a new program must not only be adequate, but allow for start up

.

4

. EPA's definition of geologic formation relies on "layers" of rock as distinguished by its properties

. Because appropriate sites may not, indeed, be layered, the term "body" of rock, as used by geologists, is more appropriate and responsive to findings that differing sites may be suitable to geologic sequestration

.

5

. EPA's definition of "mechanical integrity" including lack of "significant leakage" may leave the environment and, possibly, safety at risk due to differing interpretations of significance

. Small amounts of leakage accumulating over time may become significant

. "Significant leakage" requires a definition

.



## NOV 13 2008

Enforcement Division " Permitting & Compliance Division " Planning, Prevention & Assistance Division " Remediation Divisionp

. 2

Bonnie Lovelace Page 2 11/10/2008

Montana Department of Environmental Quality

Water Docket EPA-HQ-OW-2008-0390

6

. EPA appears to be limiting its protection of waters to only those used/potentially used for public water supplies

. It should be made clear that private use or fewer numbers of uses than those qualifying as public water supplies within the aquifer

are also to be protected

. The requirements to identify all perforations into the
USDW should also require identification of all perforations and water uses (springs) within the Area of Review

. These sites, then, should be included in all analyses and modeling

.

7

. EPA clearly identifies the risks of seismic effects from geologic sequestration and
indicates the need to only select sites that are geologically stable

. Each state has a geologic survey which monitors seismic activity

. Further, any area can surprise geologists with activity that was unexpected

. [An example in Montana would be the usually seismically quiet area near Grass Range that surprisingly had a recent

event at over 4 on the Richter scale

. In fact, no areas of Montana are seismically

at zero on the Richter scale, but may still be appropriate for sequestration .] Each geologic sequestration site should be required to add seismic monitoring that is added to the state's monitoring network

. This monitoring should be started as baseline and continued well after closure of injection activities

.

8

. EPA seeks comment on grandfathering Class II wells as Class VI wells

. This approach should be allowed with carefully tailored monitoring designed to address whatever site-specific differences may exist in construction of the wells

. Other Class VI requirements should all be met

.

9

. EPA discussed the possibility that some carbon dioxide streams may qualify as hazardous waste under 40 CFR 261 and indicates that Class I UIC would regulate

. However, this rule set contains requirements that should be applied to geologic sequestration no matter which class regulates

. Area of Review, mechanical integrity, seismic and other requirements should apply to any geologic sequestration operations, regardless of well class

. EPA should identify those requirements and add them to the Class I rules for any geologic sequestration

.

10

. EPA seeks comment on the concept of identifying and characterizing additional confining and containment zones above the primary confining zone

. MDEQ
agrees with this approach and EPA's reasoning that such information would add to predictive models, identify monitoring locations and improve public confidence and acceptance of a proposed geologic sequestration site

. Additionally, in the environmental assessment process required under NEPA and some state environmental policy acts, such information would allow for more thorough consideration of project alternatives

.

11

. EPA seeks comment on the use of models for area of review delineation

. MDEQ
agrees that such modeling is an appropriate approach

.p

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Bonnie Lovelace Page 3 11/10/2008

Montana Department of Environmental Quality

Water Docket EPA-HQ-OW-2008-0390

12

. EPA seeks comment on requiring reevaluation of the area of review on a periodic
basis, under what conditions the area of review should be reevaluated and the appropriateness of a 10 year minimum fixed frequency

. MDEQ agrees that

reevaluations are appropriate

. However, MDEQ suggests that during the first 10

year period a 2-year frequency should be used to calibrate the models to actual
conditions

. Additionally, after any seismic event a reevaluation should be automatically triggered regardless of the year

.

13

. EPA suggests deferring corrective actions to seal perforations as the plume moves toward it

. MDEQ agrees with this approach and the consideration that such an approach would allow for improved technology to be implemented over time

.

14

. EPA seeks comment on the merits of requiring down-hole shut off valves in geologic sequestration wells

. MDEQ agrees with the EPA approach to this safety
consideration

. Public health and safety issues suggest that in the case of leakage

or malfunction this is a reasonable mitigation to overcome surface shut off problems

.

15

. EPA seeks comment on whether carbon dioxide injection should be allowed
above the lowermost underground source of drinking water (USDW) under
certain conditions

. MDEQ suggests that with all the safety considerations already

described in this rule proposal and the possible environmental impacts due to migration of contaminants and mobilization of whole rock content, injections
should be limited to beneath the lowermost USDW

.

16

. EPA seeks comment on monitoring of internal mechanical integrity on injection wells

. MDEQ believes that such monitoring is appropriate

. Injection wells would be in place for a very long time and could even be used in the future to mine the
carbon dioxide and sell it as a commodity

. Further, as technology advances, such
wells may be available for reactivation even if closed

. Integrity of the structure of
the well is paramount to the ongoing and future use

.

17

. EPA seeks comment on the merits of requiring plans for monitoring, area of
review and post-injection site care as part of a permit application

. MDEQ agrees that this is necessary and appropriate

. A "cradle-to-grave" approach is wise in this instance and allows for updating the permit application materials as new technologies are forthcoming

.

18

. EPA seeks comment on frequency of all reporting requirements

. MDEQ believes

that the proposed timeframe for post-closure recordkeeping and reporting is too

short (page 43517)

. These projects are major facilities that should require a longer period of monitoring at least similar to other major industries

. A 10-year
minimum would be consistent with, for example, many surface mining operations
that allow for reclamation to meet requirements

. EPA's discussion of other
factors for post-closure site care suggests at least a 10-year period

. Seismic andp

. 4

Bonnie Lovelace Page 4 11/10/2008

Montana Department of Environmental Quality

Water Docket EPA-HQ-OW-2008-0390

surface level carbon dioxide monitoring needs to be continued

. Further, this

requirement should include the annual reporting that EPA considered, including

the content listed

.

19

. EPA is seeking comments on the proposed requirements for well plugging, postinjection site care, and site closure, including the proposed requirements for the
post-injection time period

. MDEQ agrees with EPA's approach and with the

discretion for the Director to shorten the period based upon performance

information

.

REGULATION-SPECIFIC COMMENTS

144 .36 : MDEQ believes that the life of the permit should not exceed 10 years

. Such a

limitation would allow for updating all aspects of the application, a complete review by

the regulatory agency and public comment

.

144 .55 : MDEQ suggests that this rule require that all perforations within the area of

review be identified and used in modeling

. Limiting the information only to those

perforations that penetrate the injection zone may limit the understanding of impacts of

plume movement

.

146 .82 (b) : MDEQ suggests that the information requirements not be limited to public

records only

. The area of review should be surveyed completely and all information

shown on a map

.

146 .82 (e) : MDEQ suggests that the tabulation of wells within the area of review not be

limited to only those that penetrate the injection or confining zone(s)

. Identifying all perforations will allow for complete public involvement and identification of areas of risk

should the plume move upward

.

146 .82 (g) : MDEQ suggests that this rule be more specific to include geochemical data

collection for the injection formation and the confining zone directly above the injection

zone

.

146 .83 (a) (1) : MDEQ suggests adding the same language to (1) as is found in (2) :
"without initiating or propagating fractures in the injection zone

.

146 .83 (b) : MDEQ suggests that this content be a requirement, not at the discretion of

the Director

. All possible demonstration of containment needs to be a requirement

.

146 .84(2)(i) : MDEQ suggests a change in timeframe

. See General Comment 11

.

146 .85 ( c ) : MDEQ suggests that the owner or operator follow up notification of

adverse financial conditions with a plan to resolve the deficiency in a very short

timeframe

.p

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Bonnie Lovelace Page 5 11/10/2008 Montana Department of Environmental Quality
Water Docket EPA-HQ-OW-2008-0390

146 .86(b)(3) : MDEQ supports the cementing requirement for the length of long string casing from the bottom to the surface

. This precaution protects the casing from corrosion and the impacts of such corrosion including failure of the seal that would allow migration of fluids

.

146 .88(a) : MDEQ believes that the factor of safety is too low with 90 percent of the fracture pressure allowed

. A safer level of about 75 percent should be required

.

146 .93 (f) : MDEQ supports the requirement to make known to any land owners or future purchasers the existence of the plume below their land

.

Thank you for the opportunity to comment on these important rules

.

Sincerely,



### i~~~ x~ue ~%~ac~

Bonnie Lovelace
Special Projects Manager

Director's Office

Montana Department of Environmental Quality

406-444-1760Letter ID: 0152

Commenter: Bonnie Lovelace Organization: Montana Department of Environmental Quality (MDEQ)

Letter ID: 0152 Comment ID: 22101 Letter Lines: 32 to 35

Comment Code: 2020 1.5.1 Support Class VI designation

Comment: GENERAL COMMENTS: 1 . MDEQ agrees wi th the EPA approach to designating

a new UIC class. The specific construction requirem ents, monitoring, modeling and analysis

and nontraditional identification of th e Area of Review all support a new

class definition.

Individual Response: EPA acknowledges the comment and 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 e ndangerment. The Class VI requirements are appropriate because of the unique nature and ri sks of CO2 injection for long-term storage (e.g., large injection volumes, long proj ect duration, and reservoir pressure conditions). The GS rule contains tailored requirements for the perm itting, geologic site ch aracterization, AoR and corrective action, well construc tion, operation, mechanical integr ity testing, monitoring, well plugging, post-injection site care, an d site closure of GS wells that directly address issues unique to the nature of large-scale CO2 injection for GS.

Letter ID: 0152 Comment ID: 22102 Letter Lines: 37 to 41

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

Comment: 2. MDEQ supports delegation of Class VI pr imacy to states as a separate and distinct delegation process, not requiring states to al so be delegated any of the other classes. Throughout this rule making notice and discussion, EPA points

out the differences between carbon dioxi de injection and other classes ofinjection activities.

Individual Response: EPA agrees with commenters 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 th e final GS rule. Given the potential for CCS (encompassing capture, transportation, and geologic sequestration) to be an important part of a national priority to address clim ate change, EPA believes that provi ding states the flexibility to obtain primacy for Class VI wells independently of other well cla sses 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 integrat ion of GS activities

under SDWA into a broader framework for mana ging CCS. Furthermore, GS operations involve ancillary activities (e.g., pipeline operations, pore space ownership, land use rights, and surface

1access) for which states can call upon other authorit ies that exist at the state level (but outside UIC authority) to provide a more comp rehensive CCS management approach.

The Agency believes that it is important for stat es to use their unique e fficiencies to promote adoption of this burgeoning and important tec hnology, while assuring that USDWs are protected from endangerment through the UIC regulatory framework. EPA believe s that, due to the importance of implementing an effective, comprehensive, and seamless CCS program, States should be provided the flexibility to obtain primacy for Class VI only.

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 applications for Class VI wells represents a shift in its longstandi ng 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 Cl ass under Section 1422. EPA will continue to discourage applications for pa rtial primacy for all other well types under Section 1422.

EPA clarifies that states should be able to obtain primacy for Cla ss VI wells independent of other well classes provided they devel op regulations that are at leas t as stringent as the minimum Federal requirements (e.g., permitting, inspec tion, operation, monitoring, and recordkeeping requirements) provided 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 to en sure that their GS programs integrate into national climate change priori ties and protect USDWs from endangerment.

Letter ID: 0152 Comment ID: 22103 Letter Lines: 43 to 45

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

Comment: 3. EPA must provide adequate funding to states delegated primacy in the UIC program. Current levels are not adequate and a new pr ogram must not only be adequate, but allow for start up.

Individual Response: EPA acknowledges that there may be technical and administrative challenges including resource concerns , and will work closely with the states to assist them in resolving funding issues or acquiri ng the resources, personnel, and training needed to address the unique technical challenges associated with GS.

EPA will also incorporate Class VI wells into the UIC Program's grant allocation process. The

States/Tribes/Territories must also demonstrate th at they have adequate resources to implement the program through matching resources against those allocated by the UIC Program's grant allocation formula. Currently, primacy programs ar e required to meet a minimum of 25 percent matching requirement.

Letter ID: 0152 Comment ID: 22104 Letter Lines: 47 to 51

2Comment Code: 1220 1.1.1.1 Terminology and definitions

Comment: 4. EPA's definition of geologic formati on relies on "layers" of rock as distinguished by its properti es. Because appropriate sites may not, indeed, be layered, the term "body" of rock, as used by geologists, is more appropriate and responsive to findings that differing sites may be suitable to geologic sequestration.

Individual Response: EPA disagrees with the suggested edit . The final definitions of confining zone and injection zone at §146.81( d) continue to use the terms “geologic formation, group of formations, or part of a formation.”

Based on its evaluation of all public comments and input on the proposed rule and the NODA and Request for Comment, EPA has made many revisions to the Cla ss VI GS rule. Please see the final rule and preamble for additional information.

Letter ID: 0152 Comment ID: 22105 Letter Lines: 53 to 56

Comment Code: 1220 1.1.1.1 Terminology and definitions

Comment: 5. EPA's definition of"mechanical integrit y" including lack of "significant leakage" may leave the environment a nd, possibly, safety at risk due to differing interpretations of significance. Small amounts of leakage accumulating over time may become significant. "Signi ficant leakage" requires a definition.

Individual Response: A properly designed and operated we ll should have no leakage in the casing, tubing, or packer and no fluid movement into a USDW th rough channels adjacent to the

wellbore. While the intent of MITs is to detect these types of pr oblems as early as possible, the goal of the well design and constr uction requirements at §146.86 is th e complete absence of such problems. EPA clarifies that the purpose of the "significant leakage" language in this narrow context is simply to avoid triggering corrective actions for essentially de minimis situations. Determining whether a MIT result should trigger follow-up action is necessarily a case and sitespecific situation; as a result, EPA does not believe it is appropriate to define the term "significant leakage" in the c ontext of MITs. In addition, EPA has not defined this term for purposes of other injection well classes and this has not been shown to hinder permitting authorities' and owners or operators' ability to assess whether injection wells have adequate mechanical integrity. EPA believes that this appro ach allows states flexib ility, will not interfere with the implementation of existing UIC program s, and maintains protection of USDWs from endangerment.

The final definition of mechanical integrity is unchanged. EPA clarif ies that mechanical integrity is defined at §146.89(a) as the absence (1) of signif icant leak in the casin g, tubing, or packer and (2) of significant fluid movement into a USDW through channels adjacent to the injection

wellbore.

Based on its evaluation of all public comments and input on the proposed rule and the NODA

3and Request for Comment, EPA has made many revisions to the Cla ss VI GS rule. Please see the final rule and preamble for additional information.

Letter ID: 0152 Comment ID: 22106 Letter Lines: 58 to 64

Comment Code: 1610 1.3.1 Risks to USDWs

Comment Code: 3200 2.2 Proposed Area of Review and Corrective Action Requirements (40 CFR 146.84)

Comment: 6. EPA appears to be limiting its prot ection of waters to only those used/potentially used for public water s upplies. It should be made clear that private use or fewer numbers of uses than those qualifying as public water supplies within the aquifer are also to be protected. The requirements to identify all perforations into the USDW should also require identification of all perforations and water uses (springs) within the Area of Review. These sites, then, should be included in all analyses and modeling.

Individual Response: EPA disagrees that only aquifers currently providing public water supplies will be protected by the GS regulation. The UIC regulations, promulgated under Section 1421(d)(2) of the SDWA, including the Class VI regulations, require that injection operations protect against endangerment for drinking water s ources if such injection may result in 1) noncompliance with national primary drinking water regulations or 2) may otherwise adversely affect the health of persons in USDWs which supp ly or can reasonably be expected to supply any public water system. The definition of a USDW is based on the total dissolved solids content, not the users of the supply (i.e., public versus privat e). The applicable porti on of the definition of USDW reads: "...an aquifer or any portion of an aquifer that contai ns fewer than 10,000 mg/l

total dissolved solid s and is not an exempted aquifer," as defined at 144.3. Aquifers supplying private wells that may reasonably be expected to supply any public water system and meeting

these criteria are considered USDWs that warrant protection from endangerment by GS operations.

Letter ID: 0152 Comment ID: 22107 Letter Lines: 66 to 76

Comment Code: 1620 1.3.2 Induced seismicity

Comment Code: 5220 2.8.2.1 Post-injection monitoring activities

Comment: 7. EPA clearly identifies the risks of seismic effects from geologic sequestration and indicates the need to only select sites that are geologically stable. Each state has a geologic surv ey which monitors seismic activity. Further, any area can surprise geologists with activity that was unexpected. [An example in Montana would be the usually seismically quiet area near Grass Range that surprisingly had a recent event at over 4 on the Richter scale. In fact, no areas of Montana are seismically at ze ro on the Richter scal e, but may still be appropriate for sequestration.] Each ge ologic sequestration site should be required to add seismic monitoring that is added to the state's monitoring

4network. This monitoring should be starte d as baseline and c ontinued well after closure of inject ion activities.

Individual Response: EPA acknowledges that induced seismi city is a risk that may be

associated with GS but maintains that the risk is low (IPCC, 2005). The GS rule contains several requirements to address seismic risk. First, as part of the site characteriza tion process, owners or operators must submit information about the se ismic history of and seismic sources near a proposed GS site, data on known or suspected fa ults in the AoR, geomechanical information on fractures, stress, ductility, rock strength, and in si tu fluid pressures within the confining zone as specified in §146.82(a)(3). This information is evaluated by the Director, who determines the suitability of a potential project site for GS. Any sites with the poten tial for reopening or

reactivation of faults or un acceptable seismic risk that co uld otherwise interfere with containment will not be permitted as GS sites. Duri ng injection, the pressure in the injection zone must not exceed 90 percent of the fracture pre ssure of the injection zone as specified in §146.88(a); this requirement is inte nded to prevent the opening of fractures or faults through over pressurization of the injection zone.

Given the emphasis on site selection to reduc e the potential for induced seismicity, EPA disagrees that seismic monitoring is necessary at all GS sites. However, EPA adds that the Director has the authority to require such mon itoring under §146.90(i) if he or she believes this to be appropriate based on site-specific information.

EPA does not believe that limiting GS to "stable ar eas" will provide certainty that seismic events will not occur. The Agency acknowledges that some regions of the country are at risk for infrequent, damage-causing seismic events even if such events have not been recorded in the recent historical record (i.e., in the past seve ral hundred years). For this reason, EPA requires seismic risk to be evaluated on a site-specific basi s, through an analysis of seismic history and an evaluation of known or suspected faults in th e AoR, geomechanical information on fractures, stress, ductility, rock strength, and in situ fluid pressures within the confining zone as specified in §146.82(a)(3). In addition, if an adverse event, such as a well failure or evidence of fluid movement were to occur, the monitoring requ irements at §146.90 and emergency and remedial response requirements as specified in §146.94 provide addi tional protection.

Letter ID: 0152 Comment ID: 22108 Letter Lines: 78 to 81

Comment Code: 2064 1.5.3.2 Grandfathering construction of Class II wells (seeking comment)

Comment: 8. EPA seeks comment on grandfathering Cla ss II wells as Class VI wells. This approach should be allowed with care fully tailored monitoring designed to address whatever site-specific differen ces may exist in construction of the wells. Other Class VI requirements should all be met.

Individual Response: EPA agrees that a cautious approach to grandfathering is appropriate, particularly given that the convert ed well will be used for a substa ntially different process, which involves increased reservoir pre ssures associated with large volumes of stored CO2 and the corrosivity of CO2 in the presence of water. Th e final GS rule provides for the construction of

5these wells to be grandfathered (per 146.81(c)). EPA has included a requirement in the final GS rule that owners or operators seeking to c onvert existing wells for long term storage must demonstrate to the Director that the grandfathe red wells were engineered and constructed meet the requirements at §146.86(a) and ensure prot ection of USDWs, in lieu of requirements at §146.86(b) and §146.87(a). EPA adds that, followi ng re-permitting as Class VI wells, these projects must be subject to the operationa l, MIT, monitoring, reporting, plugging, and postinjection site care and site closur e requirements in the final GS ru le. See the discussion of EPA's final regulatory approach in the preamble to the GS rule for additional detail on these requirements.

Letter ID: 0152 Comment ID: 22109 Letter Lines: 83 to 89

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

Comment: 9. EPA discussed the possibility that some carbon dioxide streams may qualify as

hazardous waste under 40 CFR 261 and indicate s that Class I UIC would regulate. owever, this rule set cont ains requirements that shoul d be applied to geologic sequestration no matter which class regul ates. Area of Review, mechanical integrity, seismic and other requirem ents should apply to any geologic sequestration operations, regardless of we ll class. EPA should identify those requirements and add them to the Class I rules for any geologic sequestration.

Individual Response: EPA received many comments regardi ng the applicability of the RCRA regulations and statute to CO2 st reams that are geologically seque stered under the final Class VI UIC well requirements. As a result, EPA has deci ded to initiate a sepa rate proposed rulemaking specifically to examine the issue of RCRA appl icability 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 pa rticular 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 comment ers who wish to submit comments on the RCRA proposal will need to do so during the comment pe riod for that rule. Finall y, EPA also notes that the final GS rule, which adds ne w regulations for Class VI wells under the Safe Drinking Water Act (SDWA), is not making any changes to the RCRA regulations.

EPA adds that revising the requirements for other cl asses of wells is outside the scope of the GS rulemaking.

EPA clarifies that the GS rule requires owner or operators of Class VI we lls to characterize their injection stream prior to injection, and throughout the operational life of the injection facility. Since the GS rule, at §146.81(d), prohibits CO2 st reams that meet the definition of a hazardous waste under 40 CFR part 261, owners or operators w ill need to characterize their CO2 stream as part of their permit application to determine if the injectate is a RCRA hazardous waste. If so, injection may only occur in a Class I hazardous waste injection well.

6Letter ID: 0152 Comment ID: 22110 Letter Lines: 91 to 98

Comment Code: 3120 2.1.2 Need to identify additional confining and containment zones (seeking comment)

Comment: 10. EPA seeks comment on the concept of identifying and characterizing additional confining and containment zones above the primary confining zone. MDEQ agrees with this approach and EPA's reasoning that such information would add to predictive models, identify monitoring lo cations and improve public confidence and acceptance of a proposed geologic sequestration site. Additionally, in the environmental assessment process required unde r NEPA and some state environmental policy acts, such information would a llow for more thorough consideration of project alternatives.

Individual Response: EPA agrees with the commenter that, in some situations, the presence of additional confining and containment zones above the primary (i.e., lowermost) confining zone can improve USDW protection from endangerment. The final regulation re tains the requirement at §146.83(b) which affords the Director discretion to require owners or op erators to identify and

characterize additional zones.

Letter ID: 0152 Comment ID: 22111 Letter Lines: 100 to 101

Comment Code: 3310 2.2.1.1 Comments in favor of requiring computational models to delineate the AoR (seeking comment)

Comment: 11. EPA seeks comment on the use of models for area of review delineation. MDEQ agrees that such modeling is an appropriate approach.

Individual Response: EPA acknowledges the commenter’s s upport and agrees that predicting the complex multiphase, buoyant flow of the CO 2, co-injectates, and compounds that may be mobilized due to injection requires the sophistica tion of computational models, as required at §146.84(c)(1). Models can predict CO2 fate and tr ansport, as well as changes in formation pressure, in three dimensions, as a function of ti me in order to delineate the subsurface storage site and the AoR. Models can account for site-specific and predicted operating conditions as well as geologic heterogeneities a nd potential migration through fau lts, fractures, and artificial penetrations.

Letter ID: 0152 Comment ID: 22112 Letter Lines: 103 to 108

Comment Code: 3530 2.2.3.1 AoR reevaluation fre quency (seeking comment)

Comment: 12. EPA seeks comment on requiring reevaluation of the area of review on a periodic basis, under what conditions the area of review should be reevaluated and the appropriateness of a 10 year minimum fixed frequency. MDEQ agrees that reevaluations are appropriate. However, MDEQ suggests that during the first 10

7year period a 2-year frequency should be us ed to calibrate the models to actual conditions. Additionally, after any seis mic event a reevaluation should be

Individual Response: EPA agrees with commenters that reevaluations of the AoR every ten years may not be sufficient to appropriately model plume and pressure front movement, establish conditions for corrective action, and ensure prot ection of USDWs from endangerment. For these reasons, the Agency changed the minimum freq uency for the AoR reevaluation at §146.84(e) from 10 years to at least every 5 years in the final GS rule. EPA belie ves that this revised frequency addresses commenters' concerns about the inherent uncertainties in modeling CO2 movement, the emerging nature of GS technology, risk-based targeting of monitoring activities, and the unique nature of CO2 GS. In addition, the Director has discre tion to require more frequent AoR reevaluation if he or she has reason to believe, based on site-specific information, that a five-year reevaluation schedule is not sufficiently protective of USDWs.

Letter ID: 0152 Comment ID: 22113 Letter Lines: 108 to 109

Comment Code: 3560 2.2.3.2 Conditions that merit reevalua tion of the AoR (seeking comment)

Comment: conditions. Additionally, after any seis mic event a reevaluation should be automatically triggered regardless of the year.

Individual Response: EPA thanks the commenter for their i nput on the types of conditions that could warrant reevaluation of the AoR at §146.84(e). EPA agrees that site-specific information is an important factor in determining when AoR r eevaluations are appropriate , and expects that the owner or operator's and Director's combined know ledge of the local geolog ic conditions will be a critical element in developing plans th at protect USDWs from endangerment.

EPA is developing guidance on AoR and corrective act ion at GS Class VI s ites to assist owners or operators and Directors in evaluating requi rements and proposed AoR and corrective action plans under §146.84. The guidance describes EPA's reco mmended approaches for the data to be

considered in an initial AoR delineation, how to apply computat ional modeling to delineate the AoR, performing corrective action at GS sites, and, when appropriate, completing AoR reevaluations. The guidance will be available on EPA's web site, at http://water.epa.gov/type/groundwat er/uic/wells_se questration.cfm.

EPA emphasizes that, while a seismic event woul d certainly warrant an AoR reevaluation, it is anticipated that the extensive geologic characte rization of a proposed GS site (including its seismic history) collected pursuant to §146.82(a) (3)(v) would reduce the likelihood of such an event. EPA is developing guidance on site charac terization for GS projects to assist owners or operators and Directors in evaluating permit requirements and app lications under §146.82. The guidance describes how best to characte rize the regional geology and hydrogeology of a proposed GS site as well as how best to perf orm the necessary geochemical, geomechanical, and geophysical analyses of the injection and confining zone.

8Letter ID: 0152 Comment ID: 22114 Letter Lines: 111 to 113

Comment Code: 3460 2.2.2.3 Acceptable corrective action techniques for GS sites (e.g., cements)

Comment: 13 . EPA suggests deferring corrective actions to seal perforati ons as the plume moves toward it. MDEQ agrees with this ap proach and the consideration that such an approach would allow for improved technology to be implemented over time.

Individual Response: EPA agrees that phased corrective ac tion may provide many benefits to a project including, but not limited to, spreading th e burden of cost, avoidi ng delays in project start-up, allowing for use of future, improved corrective action techni ques and addressing unanticipated changes in the movement of the CO 2 plume or pressure front. EPA believes that the phased corrective action approach is approp riate for GS projects, and retained it at §146.84(b)(2)(iv) in the fi nal GS regulation.

Letter ID: 0152 Comment ID: 22115 Letter Lines: 115 to 119

Comment Code: 4200 2.4.2 Down-hole shut-off valves in GS wells (seeking comment)

Comment: 14. EPA seeks comment on the merits of re quiring down-hole shut off valves in geologic sequestration wells. MDEQ agrees wi th the EPA approach to this safety

consideration. Public hea lth and safety issues suggest that in the case of leakage or malfunction this is a re asonable mitigation to overcome surface shut off problems.

Individual Response: After evaluating the risks and benefi ts of down-hole shut-off systems and considering additional research, EPA will not re quire automatic down-hole shut-off devices for onshore Class VI wells since it is not necessary in all cases to ensure protection of USDWs from endangerment. Instead, the final rule, at §146.88(e)(2 ), requires that owne rs or operators of

onshore Class VI wells install automatic surface shut-off devices. The rule affords Director's

discretion to mandate automatic down-hole shut -off devices in onshore situations that may warrant their use. However, the Agency believ es that offshore Class VI wells present unique construction and operational conditi ons, including isolation from shorelines and the need to construct wells through the water column and the subsurface, which may delay response time in

the event of well difficulties. Th e rule requires, at §146.88(e)(3), that owners or operators of

offshore wells within State territorial waters install automatic down-hole shut-off systems. EPA believes that these requirements at §146.88(e) ensure that proper precautions are taken to prevent subsurface fluid movement and ensure protection of USDWs.

Letter ID: 0152 Comment ID: 22116 Letter Lines: 121 to 126

Comment Code: 4322 2.4.4.1.1 Comments in favor of requiri ng injection below the lowermost

USDW

9Comment: 15. EPA seeks comment on whether carbon di oxide injection should be allowed

above the lowermost underground source of dr inking water (USDW) under certain conditions. MDEQ suggests that with a ll the safety consid erations already described in this rule proposal and th e possible environmental impacts due to migration of contaminants and mobilizati on of whole rock content, injections

should be limited to beneath the lowermost USDW.

Individual Response: EPA believes that there are limited circumstances where injection above the lowermost USDW can be performed in a manner that protects USDWs, as long as appropriate protections are in place. The final GS rule at §146.95 establishes a process by which owners or operators can seek a waiver of the Cl ass VI injection depth requirements for injection

into non-USDW formations above and/or between USDWs. The waiver approach requires the submission of extensive, site-specific informa tion (in conjunction with the permit application submission) to demonstrate that injection of CO2 into a non-USDW that is above or between USDWs can be done in a manner that is protectiv e of USDWs. It establ ishes: 1) requirements specifying information that owners or operators must submit, and Directors must consider, in consultation with PWSS Directors; 2) procedures for public noti ce of a waiver application and for Director-Regional Administra tor communication; 3) the waiv er issuance process; and, 4) additional requirements that apply to owners or operators of Cla ss VI wells granted a waiver of the injection depth requirements to ensure USDW protection above and below the injection zone.

For additional information on the waiver approa ch, please see the final rule and preamble, as well as EPA's responses to comments on the No tice of Data Availability and Request for

Comment.

Letter ID: 0152 Comment ID: 22117 Letter Lines: 128 to 133

Comment Code: 4520 2.5.1 Continuous internal mechani cal integrity monitoring (seeking comment)

Comment: 16. EPA seeks comment on monitoring of intern al mechanical integrity on injection wells. MDEQ believes that such monitoring is appropriate. Inj ection wells would be in place for a very long time and could even be used in the future to mine the carbon dioxide and sell it as a commodity. Further, as technology advances, such wells maybe available for reactiva tion even if closed. Integrity ofthe structure of the well is paramount to the ongoing and future use.

Individual Response: EPA acknowledges the comment and be lieves that continuous pressure monitoring to demonstrate internal mechanical integrity of Cla ss VI wells required at §146.89(b), instead of periodic testing, which is required for most other types of deep injection wells is important given the potential corrosive impact of CO2 and impurities on well materials, the potential geomechanical impacts to well inte grity due to CO2 phase changes, and the temperature and pressure effects associated w ith injecting supercritical CO2. For additional information, please see the discussion of MITs in the final rule preamble.

10Letter ID: 0152 Comment ID: 22118 Letter Lines: 135 to 139

Comment Code: 3700 2.2.5 Comments on the requirement for an AoR and corrective action plan

Comment Code: 4610 2.6.1 Testing and monitoring plan requirement (seeking comment)

Comment Code: 4710 2.7.1 Proposed submissions required for permit applications (seeking comment)

Comment: 17. EPA seeks comment on the merits of re quiring plans for monitoring, area of review and post-injec tion site care as part of a pe rmit application. MDEQ agrees that this is necessary and appropriate. A" cradle-to-grave" approach is wise in this instance and allows for updating th e permit application materials as new technologies are forthcoming.

Individual Response: EPA acknowledges the commenter’s s upport of the GS project plans. EPA believes that the requirement for the plans a ssociated with GS projects will promote an ongoing dialogue between the owner or operator and the Director to ensure that USDWs are protected from endangerment. EPA is developing guidances for ow ners or operators describing recommended approaches to prepare the project plans. The guidances will be available on EPA's web site, at http://water.epa.gov/type/g roundwater/uic/wells _sequestration.cfm.

On the topic of monitoring and plan revision: EPA agrees with commenters on the importance of monitoring at GS sites and emphasizes that monito ring of injection activities will be an important component of every GS project. EPA also be lieves that periodic updates to the plans are appropriate. EPA clarifies that the final GS re gulation includes a require ment that the AoR be reevaluated at least every 5 years, and it specifies at §146.90(j) that the operator revise the testing and monitoring plan to incorporate the results of the most recent AoR reevaluation and recent operational and monitoring data.

EPA agrees that incorporating the plans into the permit rather than establishing specific requirements for corrective action, monitoring, in jection well plugging, and post-injection site care in the regulation provide the appropriate flexibility to address the variety of site-specific conditions that may be encountered at GS sites. This approach is retained in the final rule. Please

see the final rule and the discussion of the required GS project plan s in the preamble for

additional information.

EPA also believes that it is appropriate to re quire owners and operators to submit all plans, including the injection well pluggin g and post-injection site care a nd site closure plans, at the time of permit application. EPA belie ves that the Director needs a satisfactory level of assurance that the owner or operator has pl anned for these events before injection commences and that the owner or operator has ensured that appropriate financial reso urces are available to fund all required activities, as required at §146.85. The final rule retains requirements for submitting these plans with the permit application at §146.82( a). EPA believes that the requirement for this and other plans associated with GS projec ts will promote an ongoing dialogue between the owner or operator and the Director to ensure USDWs are protected from endangerment. In

11addition, these plans will support a demonstratio n that owners and operators have adequate financial resources to meet well plugging and post-injection site ca re and site closure requirements.

Letter ID: 0152 Comment ID: 22119 Letter Lines: 141 to 150

Comment Code: 4720 2.7.2 Operational record keeping and reporting

Comment Code: 4730 2.7.3 Reporting associated with closur e and post-injection site care

Comment: 18. EPA seeks comment on frequency of all reporting requirement s. MDEQ believes that the proposed timeframe for post-clos ure recordkeeping and reporting is too short (page 43517). These projects are ma jor facilities that should require a longer period of monitoring at least simila r to other major industries. A 10-year minimum would be consistent with, for example, many surface mining operations that allow for reclamation to meet requirements. EPA's discussion of other factors for post-closure site care sugg ests at least a 10-year period. Seismic

and surface level carbon dioxide monitori ng needs to be continued. Further, this requirement should include the a nnual reporting that EPA considered, including the c ontent listed.

Individual Response: EPA agrees and believes that data collected during the post-injection phase should be retained throughout the post-inj ection site care timeframe and for ten years following site closure. EPA agrees with commente rs who suggested that well plugging reports be retained for longer than one year. EPA has clarif ied the recordkeeping requirements in the final GS rule, which includes requirements that well plugging reports, as re quired at §146.92(d), postinjection site care data, as re quired at §146.93(f), and site clos ure reports, as required at §146.93(h), be kept for ten y ears after site closure.

EPA believes that longer record retention requirements for Class VI wells are appropriate and necessary for the post-inj ection and site closure period to ensure that data are available to support non-endangerment demonstrations and to address any concerns that may arise following site closure. This data will also support EPA's review of project data as part of the adaptive rulemaking approach.

See the final rule and preamble for further disc ussion on EPA's final approach to post-injection

site care.

Letter ID: 0152 Comment ID: 22120 Letter Lines: 152 to 156

Comment Code: 5000 2.8 Proposed Well Plugging and Post-In jection Site Care Requirements

Comment: 19. EPA is seeking comments on the proposedrequirements for well plugging, postinjection site care, and site closure, including the proposed requirements for the post-injection time period. MDEQ agrees with EPA's approach and with the

discretion for the Director to shor ten the period based upon performance

12information.

Individual Response: EPA acknowledges the commenter’s suppor t and agrees that there will be

circumstances where it can be demonstrated in less than 50 years that the plume and pressure front no longer pose a risk of endangerment to USDWs. For this reason, the GS rule offers owners or operators flexibility regarding the du ration of the PISC timeframe by: (1) allowing the

Director discretion to shorten or lengthen the PISC timeframe during the PISC period based on site-specific data, pursuant to requirements at §146.93(b); or (2) a ffording the Director discretion

to allow a Class VI well owner or operator to demonstrate, ba sed on substantial data during the permitting process, that an alternative PISC timeframe may be appropriate if it ensures nonendangerment of USDWs pursuant to requirements at §146.93(c). EPA believes that a default post-injection site car e timeframe of 50 years, with flexibility to adjust the timeframe for a limited number of GS projects during the permitting process where

substantial data exists to demonstrate that an alternative timeframe would be protective of USDWs, or based on data collected during the PISC period, is appropriate to address the range of sites where GS is anticipated to occur, to ac commodate site-specific circumstances and various geologic conditions, and addre sses commenters’ concerns, wh ile ensuring USDW protection. Both approaches will utilize si te-specific data, and be based on pressure monitoring and USDW impacts.

Letter ID: 0152 Comment ID: 22121 Letter Lines: 158 to 162

Comment Code: 5700 2.12 Comments on the proposed durati on of Class VI permits (seeking comment)

Comment: REGULATION-SPECIFIC COMMENTS

144.36: MDEQ believes that the life ofthe permit should not exceed 10 years. Such a limitation would allow for updating all asp ects of the application, a complete review by the regulatory ag ency and public comment.

Individual Response: The final rule maintains the lifetime permit provision and clarifies that the permit extends through the post-injection site car e period (144.36(a)). However, it also adds a requirement that the Director review each Class VI permit at least once every 5 years. The Director’s review will be informed by the owners ’ or operators’ iterative reevaluation of the GS project. Specifically, the final rule includes a requirement that the AoR be reevaluated at least every five years, and also requires owners or operators to review and update the AoR and corrective action plan, the testi ng and monitoring plan, and the emergency and remedial response plan throughout the lif e of the project (146.84(e), 146.90(j), and 146.94(d)). Owners or operators must review each plan and identify necessary am endments to the plan or demonstrate to the Director that no amendment is needed. In no case can reviews occur less often than once every five years. The iterative process and subseque nt plan reevaluations ensure that time and resources are committed to the most critical aspects of the permit in preventing endangerment to

USDWs.

13EPA adds that, in addition to the requirement th at the Director review the permit every 5 years, as part of existing requ irements at 40 CFR 144.39, the Director has the authorit y to revise the permit if project operations change or if the director believes based on monitoring or operational data that the project may endanger USDWs. EPA has also added text to 144.39(a)(5) that says permit modifications may be require d if the Director determines th at a modification is necessary based on an AoR reevaluation, amendments to any of the project plans, or a review of the testing and monitoring results. The Director may also choose to require minor permit modifications under 40 CFR 144.41 depending on the extent of the plan amendment. All permit modifications, except minor modifications under 40 CFR 144.41, require an opportunity for public comment on the portion of the permit that is being reopened.

EPA believes that the iterative process of develo ping and executing the va rious plans required of GS well operators in the final rule (e.g., for AoR and corrective action, testing and monitoring, injection well plugging, pos t-injection site care, and emergency and remedial response) is tailored to the unique aspects of —and is more appropriate for– GS than establishing a finite permit duration (e.g., ten years as suggested by some commenters).

The Agency plans to collect and review data on GS projects every six years 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 appr opriate or necessary.

Letter ID: 0152 Comment ID: 22122 Letter Lines: 164 to 167

Comment Code: 3300 2.2.1 Delineating the AoR/M odeling CO2 movement

Comment: 144.55: MDEQ suggests that this rule require that all perforations within the area of review be identified and used in modeling. Limiting the information only to those perforations that penetrat e the injection zone may limit the understanding of impacts of plume movement.

Individual Response: The final rule leaves 144.55 unchanged; i.e., Class VI wells are not

addressed in th is provision.

Letter ID: 0152 Comment ID: 22123 Letter Lines: 169 to 171

Comment Code: 3150 2.1.5 Comments on required permit information (40 CFR 146.82)

Comment: 146.82 (b): MDEQ suggests that the inform ation requirements not be limited to public records only. The area ofreview shoul d be surveyed completely and all information shown on a map.

Individual Response: EPA believes that a determination a bout whether or what information may be necessary (for a specific GS project) is outside of the public record will be site-specific and based on knowledge of the site, data availab ility, and data quality. Fo r instance, in meeting the requirement to tabulate information on wells in the AoR, the Director has the discretion to

14require the owner or operator to supplement a data records search if ther e is reason to believe that the incompleteness of available informa tion could compromise USDW protection from endangerment. EPA acknowledges that maps ar e probably the most appropriate method for presenting the required information. EPA is deve loping guidance on site characterization for GS projects to assist owners or operators and Directors in ev aluating permit requirements and applications under §146.82. The gui dance provides recommendati ons regarding characterizing the regional geology and hydrogeology of a propos ed GS site as well as performing the necessary geochemical, geomechanical, and geophysic al analyses of the injection and confining zone. The guidance can be found on EPA’s website at http://water.epa.gov/type/groundwater /uic/wells_sequestration.cfm.

Letter ID: 0152 Comment ID: 22124 Letter Lines: 173 to 176

Comment Code: 3150 2.1.5 Comments on required permit information (40 CFR 146.82)

Comment: 146.82 (e): MDEQ suggests that the tabulation of wells w ithin the area of review not be limited to only those that penetrat e the injection or c onfining zone(s). Identifying all perforations will allow for complete public involvement and

identification of areas of risk should the plume move upward.

Individual Response: EPA believes that a determination a bout whether or what information may be necessary (for a specific GS project) is outside of the public record will be site-specific and based on knowledge of the site, data availab ility, and data quality. Fo r instance, in meeting the requirement to tabulate information on wells in the AoR, the Director has the discretion to require the owner or operator to supplement a data records search if ther e is reason to believe that the incompleteness of available informa tion could compromise USDW protection from endangerment.

EPA believes that limiting this inventory effort to those wells that penetrate the confining zone is appropriate, because the confining zone, by defini tion, acts as a barrier to the fluid movement that could endanger a USDW.

Letter ID: 0152 Comment ID: 22125 Letter Lines: 178 to 180

Comment Code: 3150 2.1.5 Comments on required permit information (40 CFR 146.82)

Comment: 146.82 (g) : MDEQ suggests th at this rule be more specific to include geochemical data collection for the inject ion formation and the confining zone directly above the injection zone.

Individual Response: The Agency believes that the re quirement at §146.82(a)(6) to submit baseline geochemical data on subsurface geologic formations, including all USDWs in the AoR is appropriate and protective of USDWs. EPA believes that this data will support monitoring plan development, inform injectate fate a nd transport model development (e.g., by providing appropriate input parameters), a nd provide information needed to respond to any unexpected and

15unpermitted leaks outside of the injection zone. Th e baseline geochemical information will allow the owner or operator and permitting authority to evaluate monitoring data and identify any changes in subsurface geochemistry that may indicate fluid movement.

The rule requires geochemical analysis of, at a minimum, the injection zone, confining zone, and all USDWs (§146.82(a)(6)). These geochemical tests ar e necessary to ensure the adequacy of the confining system and to serve as a baseline for future monitoring. The Director has the discretion to require geochemical analysis of additional s ubsurface zones if in the Director's opinion they are necessary for the protection of USDWs from endangerment.

Letter ID: 0152 Comment ID: 22126 Letter Lines: 182 to 183

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

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

Comment: 146.83 (a) (1): MDEQ suggests adding the sa me language to (1) as is found in (2): "without initiating or propagating fractures in the injection zone.

Individual Response: EPA did not make the suggested edit to the injection zone requirement but retained similar language in the restri ction on injection pr essure at §146.88(a).

Letter ID: 0152 Comment ID: 22127 Letter Lines: 185 to 187

Comment Code: 3120 2.1.2 Need to identify additional confining and containment zones (seeking comment)

Comment: 146.83 (b): MDEQ suggests th at this content be a re quirement, not at the discretion of the Director. All possible dem onstration of containment needs to be a requirement.

Individual Response: EPA agrees with the commenter that, in some situations, the presence of additional confining and containment zones above the primary (i.e., lowermost) confining zone can improve USDW protection from endangerment. EPA disagrees with the commenter that the requirement should be mandatory. The final re gulation retains the requirement at §146.83(b) which affords the Director discretion to require owners or operat ors to identify and characterize

additional zones.

Letter ID: 0152 Comment ID: 22128 Letter Lines: 189 to 189

Comment Code: 3310 2.2.1.1 Comments in favor of requiring computational models to delineate the AoR (seeking comment)

Comment: 146.84(2)(i): MDEQ suggests a change in timeframe. See General Comment 11 .

16Individual Response: EPA agrees that reevaluations of the AoR every ten years may not be sufficient to appropriately model plume and pre ssure front movement, establish conditions for corrective action, and ensure pr otection of USDWs from endange rment. For these reasons, the Agency changed the minimum frequency for the AoR reevaluation at 146.84(e) from 10 years to at least every 5 years in the fi nal GS rule. EPA believes that th is revised frequency addresses

commenters' concerns about the inherent uncertainties in modeling CO2 movement, the emerging nature of GS technology, risk-based targeting of monitoring activities, and the unique

nature of CO2 GS.

Letter ID: 0152 Comment ID: 22129 Letter Lines: 191 to 193

Comment Code: 5430 2.9.1 Comments on proposed financia l responsibility requirements (40 CFR 146.85)

Comment: 146.85(c) : MDEQ suggests that the owner or operator follow up notification of adverse financial conditions with a plan to resolve the deficiency in a very

short timeframe.

Individual Response: The goal of financial responsibility is to ensure that financial resources are available to prevent the endangerment of USDWs from improper plugging, remediation, and management of wells in the event that the owner or operator experiences fi nancial difficulties. In the event of bankruptcy, the owne r or operator must notify the Director with 10 days after commencement of the proceeding, as specified in §146.85(d)(1). EPA anticipates that upon

notification of these adverse fina ncial conditions, the Di rector will initiate discussions with the owner or operator about how to make use of fi nancial resources, as neces sary, to ensure that USDWs are protected. See the final rule and pr eamble for further disc ussion of EPA's final approach to financial responsibility.

Letter ID: 0152 Comment ID: 22130 Letter Lines: 195 to 198

Comment Code: 3824 2.3.1.2 Cementing of long-string casing (seeking comment)

Comment: 146.86(b)(3): MDEQ supports the cementing requirement for the length of long string casing from the bottom to the surf ace. This precaution protects the casing from corrosion and the impacts of such corro sion including failure of the seal that would allow migration of fluids.

Individual Response: EPA agrees that the requirement for long-string casing of Class VI wells at §146.86(b) will offer the best protection agai nst fluid movement behind the casing, between formations, and above the injec tion zone and will ensure competency of Class VI wells and protect USDWs from endangerment. The buoyant na ture of CO2 dictates deep well construction procedures that address movement of fluid be hind the casing and provide necessary barriers to CO2 leakage outside of the injection zone. In developing the constructio n requirements for Class VI wells, EPA reviewed the work cited by Care y et al. (2007) and Cr ow et al. (2008). EPA believes that they offer important justification fo r the establishment of tailored requirements.

17Letter ID: 0152 Comment ID: 22131 Letter Lines: 200 to 202

Comment Code: 4110 2.4.1.1 Injection pressure limitations

Comment: 146.88(a) : MDEQ believes that the factor of safety is too lo w with 90 percent of the fracture pressure allowed. A safe r level ofabout 75 percent should be required.

Individual Response: EPA disagrees with the s uggestion that injection pressure be set at 75 percent of fracture pressure. EPA believes that this limitation may not allow for sufficient volumes of CO2 to be transmitted away from the well and into the injection formation. EPA acknowledges that there may be circumstances where a lower pressure limitation may be appropriate; in such cases, the Director has the aut hority set a lower pressure limit in the operating permit.

Letter ID: 0152 Comment ID: 22132 Letter Lines: 204 to 205

Comment Code: 5300 2.8.3 Site closure activities (40 CFR 146.93)

Comment: 146.93(f): MDEQ supports the requirement to make known to any land owners or future purchasers the existence of the plume below their land.

Individual Response: The GS regulation at §146.93(g) requires the owner or ope rator to record a notation that the land has been used to sequester CO2 on the deed to the facility property at the

time of site closure.

18