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 Division 
p. 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. 3 

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 and 
p. 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. 5 

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 

406-444-1760 
Letter 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 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. 

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 endangerment. The Class VI requirements are 

appropriate because of the unique nature and risks of CO2 injection for long-term storage (e.g., 

large injection volumes, long project duration, and reservoir pressure conditions). 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. 

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 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 

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 the 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 climate change, EPA believes that providing states the flexibility to 

obtain primacy for Class VI wells independently of other well classes can help foster effective 

management of CCS. EPA believes that allowing independent Class VI primacy may encourage 

states to take responsibility for implementation of Class VI regulations and provide for a more 

comprehensive approach to managing CCS projects by promoting the integration of GS activities 

under SDWA into a broader framework for managing CCS. Furthermore, GS operations involve 

ancillary activities (e.g., pipeline operations, pore space ownership, land use rights, and surface 

1
access) for which states can call upon other authorities that exist at the state level (but outside 

UIC authority) to provide a more comprehensive CCS management approach. 

The Agency believes that it is important for states to use their unique efficiencies to promote 

adoption of this burgeoning and important technology, while assuring that USDWs are protected 

from endangerment through the UIC regulatory framework. EPA believes 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 longstanding policy of discouraging 

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

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

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

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

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

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

requirements) 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 ensure that their GS programs 

integrate into national climate change priorities 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 program 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 acquiring 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 that 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 are required to meet a minimum of 25 percent 

matching requirement. 

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

2
Comment Code: 1220 1.1.1.1 Terminology and definitions 

Comment: 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. 

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 Class 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 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. 

Individual Response: A properly designed and operated well should have no leakage in the 

casing, tubing, or packer and no fluid movement into a USDW through channels adjacent to the 

wellbore. While the intent of MITs is to detect these types of problems as early as possible, the 

goal of the well design and construction requirements at §146.86 is the 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 context 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 approach allows states flexibility, will not interfere 

with the implementation of existing UIC programs, and maintains protection of USDWs from 

endangerment. 

The final definition of mechanical integrity is unchanged. EPA clarifies that mechanical integrity 

is defined at §146.89(a) as the absence (1) of significant leak in the casing, 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 

3
and Request for Comment, EPA has made many revisions to the Class 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 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. 

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 sources 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 supply 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 private). The applicable portion of the definition of 

USDW reads: "...an aquifer or any portion of an aquifer that contains fewer than 10,000 mg/l 

total dissolved solids 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 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 

4
network. This monitoring should be started as baseline and continued well after 

closure of injection activities. 

Individual Response: EPA acknowledges that induced seismicity 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 characterization process, owners or 

operators must submit information about the seismic history of and seismic sources near a 

proposed GS site, data on known or suspected faults in the 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). This information is evaluated by the Director, who determines the 

suitability of a potential project site for GS. 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. During injection, the pressure in the injection zone 

must not exceed 90 percent of the fracture pressure of the injection zone as specified in 

§146.88(a); this requirement is intended to prevent the opening of fractures or faults through 

over pressurization of the injection zone. 

Given the emphasis on site selection to reduce 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 monitoring 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 areas" 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 several hundred years). For this reason, EPA requires 

seismic risk to be evaluated on a site-specific basis, through an analysis of seismic history and an 

evaluation of known or suspected faults in the 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 requirements at §146.90 and emergency and remedial 

response requirements as specified in §146.94 provide additional 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 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. 

Individual Response: EPA agrees that a cautious approach to grandfathering is appropriate, 

particularly given that the converted well will be used for a substantially different process, which 

involves increased reservoir pressures associated with large volumes of stored CO2 and the 

corrosivity of CO2 in the presence of water. The final GS rule provides for the construction of 

5
these wells to be grandfathered (per 146.81(c)). EPA has included a requirement in the final GS 

rule that owners or operators seeking to convert existing wells for long term storage must 

demonstrate to the Director that the grandfathered wells were engineered and constructed meet 

the requirements at §146.86(a) and ensure protection of USDWs, in lieu of requirements at 

§146.86(b) and §146.87(a). EPA adds that, following re-permitting as Class VI wells, these 

projects must be subject to the operational, MIT, monitoring, reporting, plugging, and postinjection site care and site closure requirements in the final GS rule. 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 issues (seeking comment) 

Comment: 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. 

owever, 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. 

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

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

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

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

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

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

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

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

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

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

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

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

EPA adds that revising the requirements for other classes of wells is outside the scope of the GS 

rulemaking. 

EPA clarifies that the GS rule requires owner or operators of Class VI wells 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 streams that meet the definition of a hazardous 

waste under 40 CFR part 261, owners or operators will 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. 

6
Letter 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 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. 

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 retains the requirement 

at §146.83(b) which affords the Director discretion to require owners or operators 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 support and agrees that predicting 

the complex multiphase, buoyant flow of the CO2, co-injectates, and compounds that may be 

mobilized due to injection requires the sophistication of computational models, as required at 

§146.84(c)(1). Models can predict CO2 fate and transport, as well as changes in formation 

pressure, in three dimensions, as a function of time 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 and potential migration through faults, fractures, and artificial 

penetrations. 

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

Comment Code: 3530 2.2.3.1 AoR reevaluation frequency (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 

7
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 

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 protection of USDWs from endangerment. 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 final GS rule. EPA believes 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 discretion 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 reevaluation of the AoR (seeking comment) 

Comment: conditions. Additionally, after any seismic event a reevaluation should be 

automatically triggered regardless of the year. 

Individual Response: EPA thanks the commenter for their input 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 reevaluations are appropriate, and expects that the 

owner or operator's and Director's combined knowledge of the local geologic conditions will be a 

critical element in developing plans that protect USDWs from endangerment. 

EPA is developing guidance on AoR and corrective action at GS Class VI sites to assist owners 

or operators and Directors in evaluating requirements and proposed AoR and corrective action 

plans under §146.84. The guidance describes EPA's recommended approaches for the data to be 

considered in an initial AoR delineation, how to apply computational 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/groundwater/uic/wells_sequestration.cfm. 

EPA emphasizes that, while a seismic event would certainly warrant an AoR reevaluation, it is 

anticipated that the extensive geologic characterization 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 characterization for GS projects to assist owners or 

operators and Directors in evaluating permit requirements and applications under §146.82. The 

guidance describes how best to characterize the regional geology and hydrogeology of a 

proposed GS site as well as how best to perform the necessary geochemical, geomechanical, and 

geophysical analyses of the injection and confining zone. 

8
Letter 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 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. 

Individual Response: EPA agrees that phased corrective action may provide many benefits to a 

project including, but not limited to, spreading the burden of cost, avoiding delays in project 

start-up, allowing for use of future, improved corrective action techniques and addressing 

unanticipated changes in the movement of the CO2 plume or pressure front. EPA believes that 

the phased corrective action approach is appropriate for GS projects, and retained it at 

§146.84(b)(2)(iv) in the final 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 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. 

Individual Response: After evaluating the risks and benefits of down-hole shut-off systems and 

considering additional research, EPA will not require 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 owners 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 believes that offshore Class VI wells present unique 

construction and operational conditions, 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. The 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 requiring injection below the lowermost 

USDW 

9
Comment: 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. 

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 Class 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 information (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 protective of USDWs. It establishes: 1) requirements 

specifying information that owners or operators must submit, and Directors must consider, in 

consultation with PWSS Directors; 2) procedures for public notice of a waiver application and 

for Director-Regional Administrator communication; 3) the waiver issuance process; and, 4) 

additional requirements that apply to owners or operators of Class 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 approach, please see the final rule and preamble, as 

well as EPA's responses to comments on the Notice 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 mechanical integrity monitoring (seeking 

comment) 

Comment: 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 maybe available for reactivation even if closed. Integrity ofthe 

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

Individual Response: EPA acknowledges the comment and believes that continuous pressure 

monitoring to demonstrate internal mechanical integrity of Class 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 integrity due to CO2 phase changes, and the 

temperature and pressure effects associated with injecting supercritical CO2. For additional 

information, please see the discussion of MITs in the final rule preamble. 

10
Letter 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 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. 

Individual Response: EPA acknowledges the commenter’s support of the GS project plans. 

EPA believes that the requirement for the plans associated 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 owners 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/groundwater/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 monitoring of injection activities will be an important 

component of every GS project. EPA also believes that periodic updates to the plans are 

appropriate. EPA clarifies that the final GS regulation includes a requirement 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, injection 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 plans in the preamble for 

additional information. 

EPA also believes that it is appropriate to require owners and operators to submit all plans, 

including the injection well plugging and post-injection site care and site closure plans, at the 

time of permit application. EPA believes that the Director needs a satisfactory level of assurance 

that the owner or operator has planned for these events before injection commences and that the 

owner or operator has ensured that appropriate financial resources 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 projects will promote an ongoing dialogue between the 

owner or operator and the Director to ensure USDWs are protected from endangerment. In 

11
addition, these plans will support a demonstration that owners and operators have adequate 

financial resources to meet well plugging and post-injection site care and site closure 

requirements. 

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

Comment Code: 4720 2.7.2 Operational recordkeeping and reporting 

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

Comment: 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 

and surface level carbon dioxide monitoring needs to be continued. Further, 

this requirement should include the annual reporting that EPA considered, 

including the content listed. 

Individual Response: EPA agrees and believes that data collected during the post-injection 

phase should be retained throughout the post-injection site care timeframe and for ten years 

following site closure. EPA agrees with commenters who suggested that well plugging reports be 

retained for longer than one year. EPA has clarified the recordkeeping requirements in the final 

GS rule, which includes requirements that well plugging reports, as required at §146.92(d), postinjection site care data, as required at §146.93(f), and site closure reports, as required at 

§146.93(h), be kept for ten years after site closure. 

EPA believes that longer record retention requirements for Class VI wells are appropriate and 

necessary for the post-injection 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 discussion 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-Injection Site Care Requirements 

Comment: 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 

12
information. 

Individual Response: EPA acknowledges the commenter’s support 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 duration 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) affording the Director discretion 

to allow a Class VI well owner or operator to demonstrate, based 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 care 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 accommodate site-specific circumstances and various 

geologic conditions, and addresses commenters’ concerns, while ensuring USDW protection. 

Both approaches will utilize site-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 duration 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 aspects of the application, a complete 

review by the regulatory agency and public comment. 

Individual Response: The final rule maintains the lifetime permit provision and clarifies that the 

permit extends through the post-injection site care 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 testing and monitoring plan, and the emergency and remedial response 

plan throughout the life of the project (146.84(e), 146.90(j), and 146.94(d)). Owners or operators 

must review each plan and identify necessary amendments 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 subsequent plan reevaluations ensure that time and 

resources are committed to the most critical aspects of the permit in preventing endangerment to 

USDWs. 

13
EPA adds that, in addition to the requirement that the Director review the permit every 5 years, 

as part of existing requirements at 40 CFR 144.39, the Director has the authority 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 required if the Director determines that 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 developing and executing the various plans required of 

GS well operators in the final rule (e.g., for AoR and corrective action, testing and monitoring, 

injection well plugging, post-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 appropriate or necessary. 

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

Comment Code: 3300 2.2.1 Delineating the AoR/Modeling 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 penetrate 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 this 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 information requirements not be limited to 

public records only. The area ofreview should be surveyed completely and all 

information shown on a map. 

Individual Response: EPA believes that a determination about 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 availability, and data quality. For instance, in meeting 

the requirement to tabulate information on wells in the AoR, the Director has the discretion to 

14
require the owner or operator to supplement a data records search if there is reason to believe 

that the incompleteness of available information could compromise USDW protection from 

endangerment. EPA acknowledges that maps are probably the most appropriate method for 

presenting the required information. EPA is developing guidance on site characterization for GS 

projects to assist owners or operators and Directors in evaluating permit requirements and 

applications under §146.82. The guidance provides recommendations regarding characterizing 

the regional geology and hydrogeology of a proposed GS site as well as performing the 

necessary geochemical, geomechanical, and geophysical 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 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. 

Individual Response: EPA believes that a determination about 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 availability, and data quality. For 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 there is reason to believe 

that the incompleteness of available information 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 definition, 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 that this rule be more specific to include 

geochemical data collection for the injection formation and the confining zone 

directly above the injection zone. 

Individual Response: The Agency believes that the requirement 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 and transport model development (e.g., by providing 

appropriate input parameters), and provide information needed to respond to any unexpected and 

15
unpermitted leaks outside of the injection zone. The 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 are 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 subsurface 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/edits 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 same 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 restriction on injection pressure 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 that this content be a requirement, not at the 

discretion of the Director. All possible demonstration 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 regulation retains the requirement at §146.83(b) 

which affords the Director discretion to require owners or operators 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 . 

16
Individual Response: EPA agrees 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 protection of USDWs from endangerment. 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 final GS rule. EPA believes 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. 

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

Comment Code: 5430 2.9.1 Comments on proposed financial 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 financial difficulties. In 

the event of bankruptcy, the owner 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 financial conditions, the Director will initiate discussions with the 

owner or operator about how to make use of financial resources, as necessary, to ensure that 

USDWs are protected. See the final rule and preamble for further discussion 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 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. 

Individual Response: EPA agrees that the requirement for long-string casing of Class VI wells 

at §146.86(b) will offer the best protection against fluid movement behind the casing, between 

formations, and above the injection zone and will ensure competency of Class VI wells and 

protect USDWs from endangerment. The buoyant nature of CO2 dictates deep well construction 

procedures that address movement of fluid behind the casing and provide necessary barriers to 

CO2 leakage outside of the injection zone. In developing the construction requirements for Class 

VI wells, EPA reviewed the work cited by Carey et al. (2007) and Crow et al. (2008). EPA 

believes that they offer important justification for the establishment of tailored requirements. 

17
Letter 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 low with 90 percent 

of the fracture pressure allowed. A safer level ofabout 75 percent should be 

required. 

Individual Response: EPA disagrees with the suggestion 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 authority 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 operator 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