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.
October 15, 2009 

Water Docket 

United States Environmental Protection Agency 

Mail Code: 2822T 

1200 Pennsylvania Avenue, NW 

Washington, DC 20460 

Subject: Federal Requirements Under the Underground Injection Control (UIC) 

Program for Carbon Dioxide (CO2) Geologic Sequestration (GS) Wells

Docket ID No. EPA–HQ–OW–2008–0390

Fed. Reg. 43492 (July 25, 2008) 

The Electric Power Research Institute (EPRI) is pleased to have the opportunity to 

provide comments on the Environmental Protection Agency’s Notice of Data 

Availability (NODA) dated August 31, 2009 for the proposed rule titled “Federal 

Requirements Under the Underground Injection Control (UIC) Program for Carbon 

Dioxide (CO2) Geologic Sequestration (GS) Wells” of July 25, 2008, (Docket ID No. EPA–

HQ–OW–2008–0390). 

EPRI conducts research on key issues facing the electric power industry on behalf of its 

members, energy stakeholders, and society. EPRI was established as an independent, nonprofit 

center for public interest energy and environmental research. Our utility members represent over 

90% of the electricity generated in the United States including substantial support from 

international energy companies. EPRI also receives funding from various federal and state 

government agencies such as the US Department of Energy. 

EPRI supports the development of a clear (unambiguous), reasonable, and flexible framework 

that enables wide deployment of geologic storage of CO2 in a safe, environmentally protective, 

and cost-effective manner. 

Sincerely, 

Michael J. Miller 

Director, Environment 

Electric Power Research Institute 

3420 Hillview Avenue 

Palo Alto, CA 94304 
EPRI Comments on EPA’s Notice of Data Availability for the Proposed UIC 

Regulations for CO2 Injection 

The Electric Power Research Institute (EPRI) is pleased to have the opportunity to 

provide comments on the Environmental Protection Agency’s Notice of Data Availability 

(NODA) dated August 31, 2009 for the proposed rule titled “Federal Requirements 

Under the Underground Injection Control (UIC) Program for Carbon Dioxide (CO2) 

Geologic Sequestration (GS) Wells” of July 25, 2008, (Docket ID No. EPA–HQ–OW–

2008–0390). 

EPRI’s comments are focused on the technical elements of the proposed rule discussed in 

this NODA. The comments are intended to assist in the development of a clear 

(unambiguous), reasonable, and flexible framework that enables wide deployment of 

geologic storage (GS) of CO2 in a safe environmentally protective, and cost-effective 

manner. 

General comment

EPRI COMMENT#1: The NODA provides a waiver process in which a project 

proponent can submit a permit application for the injection of CO2 above the lowermost 

Underground Source of Drinking Water (USDW). EPRI supports the EPA’s decision to 

create the waiver process because it provides greater flexibility in selecting injection sites 

that meet all of the proposed technical requirements of a Class VI injection permit, except 

for depth. EPRI agrees that protection of USDWs can be accomplished regardless of 

injection depth by selecting and permitting sites with competent confining units that will 

isolate the injected CO2 from the adjacent USDW(s). 

EPRI COMMENT#2: The EPA presents a number of research projects in the NODA and 

often concludes with a general statement that the research will be used to refine and 

inform the site characterization, monitoring, and remediation requirements and guidance, 

in the Agency’s final rulemaking. Many of the research methods used by the regional 

partnerships and others were performed purely for furthering our fundamental 

understanding and knowledge of GS processes and may never evolve beyond the research 

stage. A cross-well seismic survey, which has very limited depth of penetration because 

of limited source strength and therefore requires closely spaced wells, is a good example 

of a research monitoring tool that may never be deployed on a commercial scale. The 

EPA does not provide clarity on how the results will be used or the position or direction 

the Agency has already taken or will take as a result of issues raised by the research. 

EPRI urges EPA to provide this clarity to the regulated community before issuing the 

final rule. 

Specific comments

Specific EPRI comments on the EPA NODA follow. EPA draft rules, interpretations or 

requests for comments are shown in bold print and are identified by page number where 
they appear in the Federal Register / Vol. 74, No. 167 / Monday, August 31, 2009 / 

Proposed Rules. EPRI comments immediately follow the EPA citation. 

Page 44808: “The Agency seeks comment on this research and any additional 

studies related to a) mobilization of constituents and b) the likelihood or frequency 

of such leakage/risks.” 

EPRI COMMENT #3: As noted in the NODA, the Lawrence Berkeley National 

Laboratory (LBNL) project was a modeling study and, therefore, calls for experimental 

verification before reaching definitive conclusions. To this end, EPRI conducted an 

initial field study and analysis of the potential impact of CO2 on shallow groundwater, to 

be completed by the end of 2009. The field study was performed at the Zero Emission 

Research and Technology (ZERT) field site in Bozeman, Montana; ZERT was hosted by 

Montana State University and was designed to test instruments used to detect leaks of 

CO2 to the surface and not groundwater impacts. ZERT injected food-grade CO2 into 

shallow groundwater in 2008 over a thirty day period. Under the EPRI study, more than 

80 groundwater samples were collected and analyzed using very low detection levels by 

the US Geological Survey, under contract to LBNL and EPRI. We observed increases in 

the groundwater concentration of several major cations and trace elements above 

background, including arsenic and lead, after CO2 injection began, but none of the 

constituents exceeded their respective action levels or maximum contaminant levels. 

Only three of the constituents, iron, manganese and total dissolved solids, exceeded the 

standard under which they are regulated, in this case the secondary drinking water criteria. 

It is our understanding that the EPA secondary drinking water criteria are not federally 

enforceable but are intended as guidelines for the states. These regulations control 

constituents in drinking water that primarily affect the aesthetic qualities relating to the 

public acceptance of drinking water. 

However, the ZERT site conditions were not ideal for studying the effects of CO2 on 

potable groundwater for several reasons: 

1. Shallow (<6 feet) unconfined groundwater aquifers like that at the ZERT field site 

are not typically representative of USDWs because they do not have an upper 

confining unit that serves to protect the aquifer from surface contamination; 

2. Shallow aquifers respond to atmospheric conditions including recharge from 

precipitation and oxidizing conditions that influence experiment results; 

3. Deeper aquifers, which are representative of USDWs, lie below confining units 

that serve as barriers to surface contamination; 

4. Reducing conditions are more prevalent in deeper aquifers potentially resulting in 

different experimental outcomes than observed at ZERT; 

5. Results from 2008 study may underestimate impacts since a similar injection 

conducted in 2007 injection may have biased the later results. 

Therefore, EPRI and its members, recognizing the need for more definitive data, are 

about to embark on a three-year field study specifically designed to evaluate the impact 

of CO2 on potable groundwater, identify key reactive transport mechanisms, calibrate and 
validate flow and reactive transport models, and test the ability of existing models to 

predict transport behavior. These results provide an opportunity for improving models 

for commercial use; such models would be a tool for assessing CO2 GS projects. 

Page 44808: “EPA believes that the example studied by LBNL illustrates the 

importance of basin-scale evaluation of reservoir pressures and far-field pressures 

resulting from CO2 injection.” 

EPRI COMMENT#4: EPRI agrees that pressure interference from multiple projects in a 

basin may have an impact on near and far-field pressures. This suggests that basin-scale 

management where multiple projects are planned would be beneficial. 

The next set of comments apply to requirements included in the proposed waiver 

process. 

Page 44811: “(3) An injection zone and confining formations free of transmissive 

fractures and faults.” 

EPRI COMMENT#5: EPRI does not see a need to exclude injection zones containing 

transmissive fractures or faults from being considered as geologic storage targets as long 

as these transmissive features are not present in the overlying/underlying confining units. 

Fractured formations often have excellent permeability promoting high injection rates at 

relatively low injection pressures. Lower injection pressures will lead to lower risk of 

fracturing the adjacent confining unit(s). 

Page 44811, “(4) A characterization of regional fracture properties and a 

demonstration that such fractures will not interfere with injection, serve as conduits, 

or endanger USDWs.” 

ERPI COMMENT#6: EPRI does not understand the need for this requirement given the 

EPA’s position that the waiver should only be granted for confining units free of 

transmissive faults and fracture as quoted above. Why would a regional characterization 

of the properties of these features be required if transmissive members of the population 

can’t be present in the confining unit in order to receive the waiver? 

EPRI believes a regional characterization of fracture properties should not be required for 

injection zones too. A regional assessment of fracture properties is somewhat academic 

and may not aid the project proponent and regulator in assessing local project safety. 

Local rock properties and stresses (past and present) control evolution of local fracture 

patterns and their corresponding hydraulic properties. Regional stresses and rock 

properties may be significantly different than local conditions leading to erroneous 

conclusions. Therefore, fracture characterization, if required at all, should be limited to 

the Area of Review where local features would potentially be present and serve as 

conduits. 
Page 44811: “The potential capacity of the geologic formation to sequester CO2, 

accounting for the availability of alternative injection sites;” 

EPRI COMMENT#7: Presumably the project proponent will have screened numerous 

sites (if available) before selecting an optimum location that meets the requirements of 

the EPA rule as finally promulgated (including capacity) and the economic, technical and 

non-technical needs of the project. However, numerous factors enter into the decision to 

develop a GS project and submit a permit application, not just “capacity” and 

“availability of alternative injection sites.” Therefore, the need for this requirement is not 

clear. 

EPRI’s next comment is based on (a) the following EPA assumption: “The basis of 

these requirements is the principle that placing distance between the injection 

formation and USDWs decreases risks to USDWs” (Page 44809), and (b) the 

statement that “The owner/operator may be required to comply with additional 

requirements that apply as a result of receipt of the waiver, designed to ensure the 

protection of USDWs both above and below the injection zone.” (Page 44811). 

EPRI COMMENT#8: EPA’s technical rationale for wanting to include additional 

requirements in the permit waiver beyond those already required for an injection into a 

zone located below the lowermost USDW is unclear. EPA’s justification appears to be 

based on vertical position of the injection zone relative to the adjacent USDWs and 

intervening distance between the two. Injection below the lowermost USDW appears to 

be viewed by EPA as being less risky than injection above the lowermost USDW, even 

though the upper boundary condition could be identical in both cases. For example, one 

could propose a GS project with injection immediately below the lowermost USDW with 

only one intervening confining unit of given thickness (i.e., distance) between it and the 

lowermost USDW above to prevent CO2 migration. Likewise, one could propose a GS 

project above the lowermost USDW with the same identical upper boundary condition 

(i.e. one intervening confining unit with same thickness) relative to the next USDW 

above. The risk of impact from CO2 migration into the overlying USDW is identical. See 

figure below for illustration of this concept. 
This figure illustrates that injection of CO2 into the center zone below identical confining 

units having identical properties (including thickness) will result in identical risks to the 

overlying USDW regardless whether injection is occurring above or below the lowermost 

USDW. 

The EPA draft standard published in July 2008 for injection below the lowermost USDW 

appears to be deemed adequately protective of USDWs above by EPA. EPRI sees no 

physical reason why the same standards would not be equally protective of USDWs if 

injection occurs into a zone above the lowermost USDW, when the boundary conditions 

and risks are essentially identical. Therefore, EPRI questions the need for additional well 

construction, operational or monitoring, as required by the proposed waiver process, 

regardless of vertical position; it appears that the Agency has already taken this scenario 

into account in the July 2008 draft rule. 

One could argue that the lower boundary doubles the risk for a GS project injecting 

above the lowermost USDW increases the risk of a project because contamination of this 

lower USDW could occur from above (refer to figure). However, it is the transmissivity 

and lateral continuity of the upper and lower seals that control CO2 migration across the 

boundary that defines the risk, not the number of boundaries. (i.e, one or two) across 

which CO2 could migrate to adjacent USDWs. In addition, it is far less likely that free 

CO2 will migrate across the lower boundary because CO2 is buoyant. Saline groundwater 

(and CO2 dissolved in the same) could potentially be displaced below the lower seal, but 

the requirements in the draft standards published by EPA in July 2008 already affords 

adequate USDW protection against these mechanisms – i.e., EPA’s current draft rule 

already accounts for the worst case scenario (displaced water containing dissolved CO2

and free CO2). 

In summary, EPRI believes that the above additional requirements proposed for the 

waiver process, as well as those for enhanced construction and operational requirements 

and type of monitoring technology to be deployed, address concerns that are already 
covered by the July 2008 draft rule, with one exception. We agree with EPA’s proposed 

requirement for monitoring in the USDW below the injection zone when injecting CO2

above the lowermost USDW. 
Letter ID: 0355  

Commenter: Michael J. Miller  

Organization: Electric Power Research Institute (EPRI)  

Letter ID: 0355 Comment ID: 28078 Letter Lines: 34 to 42  

Comment Code: 3210 3.2.1. Comments Generally in Support of the Approach  

Comment: EPRI COMMENT#1: The NODA provides a waiver process in which a project proponent  

can submit a permit application for the injection of CO2 above the lowermost  

Underground Source of Drinking Water (USDW). EPRI supports the EPA’s decision to  

create the waiver process because it provides greater flexibility in selecting  

injection sites that meet all of the proposed technical requirements of a Class  

VI injection permit, except for depth. EPRI agrees that protection of USDWs can  

be accomplished regardless of injection depth by selecting and permitting sites  

with competent confining units that will isolate the injected CO2 from the  

adjacent USDW(s).  

Individual Response: EPA acknowledges the commenter's support of the waiver approach and site‐

specific flexibility in regulatory development and permitting as described in the NODA and Request for

Comment. The Agency acknowledges that there are some situations where injection into non‐USDW

formations above the lowermost USDW can be performed in a manner that protects USDWs. The final

GS rule at §146.95 establishes a process by which owners and operators can seek a waiver of the Class

VI injection depth requirements. The Agency believes the waiver approach: 1) responds to concerns

about local and regional geologic storage capacity limitations imposed by the proposed injection depth

requirements; 2) allows for a more site‐specific assessment of injection depth for GS projects; 3)

accommodates injection into different formation types; 4) allows for injection of CO2 for GS into non‐

USDWs above and/or between USDWs when appropriate and where it can be demonstrated that

USDWs will be protected; and 5) responds to concerns about the use of aquifer exemptions for GS.

Finally, EPA's approach to addressing injection depth variability through a waiver process responds to

concerns about future drinking water resource availability and the need to ensure that high quality

water remains available in sufficient quantities to supply drinking water needs.  

Letter ID: 0355 Comment ID: 28079 Letter Lines: 44 to 57  

Comment Code: 2000 2. Comments on Research, Data Analysis, and Findings presented in the NODA

(seeking comment)  
Comment: EPRI COMMENT#2: The EPA presents a number of research projects in the NODA and  

often concludes with a general statement that the research will be used to  

refine and inform the site characterization, monitoring, and remediation  

requirements and guidance, in the Agency’s final rulemaking. Many of the  

research methods used by the regional partnerships and others were performed  

purely for furthering our fundamental understanding and knowledge of GS  

processes and may never evolve beyond the research stage. A cross‐well seismic  

survey, which has very limited depth of penetration because of limited source  

strength and therefore requires closely spaced wells, is a good example of a  

research monitoring tool that may never be deployed on a commercial scale. The  

EPA does not provide clarity on how the results will be used or the position or  

direction the Agency has already taken or will take as a result of issues raised  

by the research. EPRI urges EPA to provide this clarity to the regulated  

community before issuing the final rule.  

Individual Response: EPA believes that the regional partnerships provide important information on GS,

but recognizes that use of a technology in a RCSP project does not necessarily make the technology valid

for all applications. Each project will be unique and the final rule provides for site‐specific approaches to

ensure that appropriate construction, operation, and monitoring is performed at each site. However, by

testing multiple technologies, the pilot sites provide valuable data that demonstrate whether or not

these technologies are viable and informed the final GS rule. Please see the discussion of EPA's final

regulatory approach in the preamble to the final GS rule for additional detail on the final requirements

for GS wells.  

Letter ID: 0355 Comment ID: 28080 Letter Lines: 67 to 119  

Comment Code: 2400 2.4. Other Research Offered by Commenters (seeking comment)  

Comment: Page 44808: "The Agency seeks comment on this research and any additional  

studies related to a) mobilization of constituents and b) the likelihood or  

frequency of such leakage/risks."  

EPRI COMMENT #3: As noted in the NODA, the Lawrence Berkeley National Laboratory  

(LBNL) project was a modeling study and, therefore, calls for experimental  

verification before reaching definitive conclusions. To this end, EPRI  

conducted an initial field study and analysis of the potential impact of CO2 on  

shallow groundwater, to be completed by the end of 2009. The field study was  

performed at the Zero Emission Research and Technology (ZERT) field site in  

Bozeman, Montana; ZERT was hosted by Montana State University and was designed  

to test instruments used to detect leaks of CO2 to the surface and not  
groundwater impacts. ZERT injected food‐grade CO2 into shallow groundwater in  

2008 over a thirty day period. Under the EPRI study, more than 80 groundwater  

samples were collected and analyzed using very low detection levels by the US  

Geological Survey, under contract to LBNL and EPRI. We observed increases in the  

groundwater concentration of several major cations and trace elements above  

background, including arsenic and lead, after CO2 injection began, but none of  

the constituents exceeded their respective action levels or maximum contaminant  

levels. Only three of the constituents, iron, manganese and total dissolved  

solids, exceeded the standard under which they are regulated, in this case the  

secondary drinking water criteria. It is our understanding that the EPA  

secondary drinking water criteria are not federally enforceable but are intended  

as guidelines for the states. These regulations control constituents in drinking  

water that primarily affect the aesthetic qualities relating to the public  

acceptance of drinking water.  

However, the ZERT site conditions were not ideal for studying the effects of CO2  

on potable groundwater for several reasons:  

1. Shallow (

site are not typically representative of USDWs because they do not have an upper  

confining unit that serves to protect the aquifer from surface contamination;  

2. Shallow aquifers respond to atmospheric conditions including recharge from  

precipitation and oxidizing conditions that influence experiment results;  

3. Deeper aquifers, which are representative of USDWs, lie below confining units  

that serve as barriers to surface contamination;  

4. Reducing conditions are more prevalent in deeper aquifers potentially  

resulting in different experimental outcomes than observed at ZERT;  

5. Results from 2008 study may underestimate impacts since a similar injection  

conducted in 2007 injection may have biased the later results.  

Therefore, EPRI and its members, recognizing the need for more definitive data,  

are about to embark on a three‐year field study specifically designed to  

evaluate the impact of CO2 on potable groundwater, identify key reactive  

transport mechanisms, calibrate and validate flow and reactive transport models,  

and test the ability of existing models to predict transport behavior. These  

results provide an opportunity for improving models for commercial use; such  

models would be a tool for assessing CO2 GS projects.  
Individual Response: EPA has reviewed the information on the Zero Emission Research and Technology

(ZERT) field site. EPA acknowledges the submittal and will continue to review studies related to

modeling verification, comparisons with field results of CO2 injection, and the study of the effects of

CO2 on shallow ground water. EPA intends to continue to collect data on GS and to incorporate such

data and information as it implements its adaptive approach to the GS rulemaking to incorporate new

research, data, and information about GS. For more information on the adaptive approach, see the

responses to comments on the proposed rule in the rulemaking docket.  

Letter ID: 0355 Comment ID: 28081 Letter Lines: 121 to 128  

Comment Code: 2220 2.2.2. Basin‐Scale Hydrologic Impacts of CO2 Storage (seeking comment)  

Comment: Page 44808: "EPA believes that the example studied by LBNL illustrates the  

importance of basin‐scale evaluation of reservoir pressures and far‐field  

pressures resulting from CO2 injection."  

EPRI COMMENT#4: EPRI agrees that pressure interference from multiple projects in  

a basin may have an impact on near and far‐field pressures. This suggests that  

basin‐scale management where multiple projects are planned would be beneficial.  

Individual Response: The final GS rule focuses on permitting of individual GS wells and therefore does

not include requirements for basin‐scale evaluations. However, EPA agrees that proactive management

of basin scale concerns to maintain pressures within acceptable ranges is important, and encourages

owners or operators and permitting authorities to communicate planned GS activities to maximize

coordination and minimize pressure interference. If a permit applicant (or the permitting authority) is

aware of pending GS projects near a proposed well, the AoR delineation performed pursuant to §146.84

should account for the impacts of multiple owners and operators injecting within a single basin. EPA

anticipates that, where multiple operators are involved, the Director would not approve modeling that

does not account for changes that may result from all injection operations. The proximity of injection

sites to each other and the relative timing of each injection operation might indicate a possible increase

in risk for the containment of the total CO2 and/or the effects of hydraulic perturbations and brine

displacement.  

EPA adds that if any new GS projects are permitted within the AoR of a GS project between AoR

evaluations, the AoR reevaluation would need to address such projects. EPA also expects that the

permitting of the newer GS project would have considered the presence of an existing project. For

additional information regarding EPA’s requirements for AoR delineation for GS projects, see the

responses to comments on the proposed rule in the rulemaking docket.  
Letter ID: 0355 Comment ID: 28082 Letter Lines: 130 to 141  

Comment Code: 3310 3.3.1. Site Characterization  

Comment: process.  

Page 44811: "(3) An injection zone and confining formations free of transmissible  

fractures and faults."  

EPRI COMMENT#5: EPRI does not see a need to exclude injection zones containing  

transmissible fractures or faults from being considered as geologic storage  

targets as long as these transmissible features are not present in the  

overlying/underlying confining units. Fractured formations often have excellent  

permeability promoting high injection rates at relatively low injection  

pressures. Lower injection pressures will lead to lower risk of fracturing the  

adjacent confining unit(s).  

Individual Response: EPA clarifies that the requirement refers to the confining zone. The final GS rule

requires a demonstration that the confining units are free of transmissive faults and fractures per

§146.95(a)(2). For additional information on site characterization for GS projects, see the preamble to

the final rule and the responses to comments on the proposed GS rule.  

Letter ID: 0355 Comment ID: 28083 Letter Lines: 143 to 162  

Comment Code: 3310 3.3.1. Site Characterization  

Comment: Page 44811, "(4) A characterization of regional fracture properties and a  

demonstration that such fractures will not interfere with injection, serve as  

conduits, or endanger USDWs."  

ERPI COMMENT#6: EPRI does not understand the need for this requirement given the  

EPA’s position that the waiver should only be granted for confining units free  

of transmissible faults and fracture as quoted above. Why would a regional  

characterization of the properties of these features be required if transmissible  

members of the population can't be present in the confining unit in order to  

receive the waiver?  

EPRI believes a regional characterization of fracture properties should not be  

required for injection zones too. A regional assessment of fracture properties  
is somewhat academic and may not aid the project proponent and regulator in  

assessing local project safety. Local rock properties and stresses (past and  

present) control evolution of local fracture patterns and their corresponding  

hydraulic properties. Regional stresses and rock properties may be significantly  

different than local conditions leading to erroneous conclusions. Therefore,  

fracture characterization, if required at all, should be limited to the Area of  

Review where local features would potentially be present and serve as conduits.  

Individual Response: EPA clarifies that the requirement for regional characterization of fracture

properties applies to the confining zone. The final GS rule requires a demonstration that the confining

units are free of transmissive faults and fractures and requires regional characterization of fracture

properties as specified in §146.95(a)(2) to support a determination that no fractures will interfere with

injection, serve as conduits, or endanger USDWs. This requirement applies to all GS projects as specified

in §146.82(a), and the requirements at §146.95 for owners and operators seeking injection depth

waivers are intended to add to and modify the requirements that all GS well owners or operators must

meet, including those for site‐specific geologic characterization of faults and fractures, to ensure that

the proposed site is evaluated in the context of the presence of USDWs above and below the injection

zone. EPA anticipates that issuance of waivers will be limited to circumstances where there are deep

USDWs and/or where the lack of a waiver of injection depth requirements would result in impractical or

technically infeasible well construction, and where USDW protection is demonstrated and maintained

through the life of the GS project. For additional information on site characterization for GS projects, see

the preamble to the final rule and the responses to comments on the proposed GS rule.  

Letter ID: 0355 Comment ID: 28084 Letter Lines: 164 to 173  

Comment Code: 3310 3.3.1. Site Characterization  

Comment: Page 44811: "The potential capacity of the geologic formation to sequester CO2,  

accounting for the availability of alternative injection sites;"  

EPRI COMMENT#7: Presumably the project proponent will have screened numerous  

sites (if available) before selecting an optimum location that meets the  

requirements of the EPA rule as finally promulgated (including capacity) and the  

economic, technical and non‐technical needs of the project. However, numerous  

factors enter into the decision to develop a GS project and submit a permit  

application, not just "capacity" and "availability of alternative injection  

sites." Therefore, the need for this requirement is not clear.  

Individual Response: EPA clarifies that the intent of the requirement to consider alternative injection

sites ensures the waiver approach is applied only when needed. EPA anticipates that issuance of waivers
will be limited to circumstances where there are deep USDWs and/or where the lack of a waiver of

injection depth requirements would result in impractical or technically infeasible well construction, and

where USDW protection is demonstrated and maintained through the life of the GS project.  

Letter ID: 0355 Comment ID: 28085 Letter Lines: 175 to 223  

Comment Code: 3380 3.3.8. Additional Requirements Established by the UIC Director  

Comment: EPRI’s next comment is based on (a) the following EPA assumption: "The basis of  

these requirements is the principle that placing distance between the injection  

formation and USDWs decreases risks to USDWs" (Page 44809), and (b) the  

statement that "The owner/operator may be required to comply with additional  

requirements that apply as a result of receipt of the waiver, designed to ensure  

the protection of USDWs both above and below the injection zone." (Page 44811).  

EPRI COMMENT#8: EPA’s technical rationale for wanting to include additional  

requirements in the permit waiver beyond those already required for an injection  

into a zone located below the lowermost USDW is unclear. EPA’s justification  

appears to be based on vertical position of the injection zone relative to the  

adjacent USDWs and intervening distance between the two. Injection below the  

lowermost USDW appears to be viewed by EPA as being less risky than injection  

above the lowermost USDW, even though the upper boundary condition could be  

identical in both cases. For example, one could propose a GS project with  

injection immediately below the lowermost USDW with only one intervening  

confining unit of given thickness (i.e., distance) between it and the lowermost  

USDW above to prevent CO2 migration. Likewise, one could propose a GS project  

above the lowermost USDW with the same identical upper boundary condition (i.e.  

one intervening confining unit with same thickness) relative to the next USDW  

above. The risk of impact from CO2 migration into the overlying USDW is  

identical. See figure below for illustration of this concept.  

This figure illustrates that injection of CO2 into the center zone below identical  

confining units having identical properties (including thickness) will result in identical risks to the

overlying USDW regardless whether injection is occurring above or below the lowermost USDW. [SEE P.

6 of EPA‐HQ‐OW‐2008‐0390‐0355.PDF FOR FIGURE.]  

The EPA draft standard published in July 2008 for injection below the lowermost  

USDW appears to be deemed adequately protective of USDWs above by EPA. EPRI  

sees no physical reason why the same standards would not be equally protective  

of USDWs if injection occurs into a zone above the lowermost USDW, when the  
boundary conditions and risks are essentially identical. Therefore, EPRI  

questions the need for additional well construction, operational or monitoring,  

as required by the proposed waiver process, regardless of vertical position; it  

appears that the Agency has already taken this scenario into account in the July  

2008 draft rule.  

One could argue that the lower boundary doubles the risk for a GS project  

injecting above the lowermost USDW increases the risk of a project because  

contamination of this lower USDW could occur from above (refer to figure).  

However, it is the transmissivity and lateral continuity of the upper and lower  

seals that control CO2 migration across the boundary that defines the risk, not  

the number of boundaries. (i.e., one or two) across which CO2 could migrate to  

adjacent USDWs. In addition, it is far less likely that free CO2 will migrate  

across the lower boundary because CO2 is buoyant. Saline groundwater (and CO2  

dissolved in the same) could potentially be displaced below the lower seal, but  

the requirements in the draft standards published by EPA in July 2008 already  

affords adequate USDW protection against these mechanisms ‐ i.e., EPA’s current  

draft rule already accounts for the worst case scenario (displaced water  

containing dissolved CO2 and free CO2).  

Individual Response: EPA believes that that injection for the purpose of GS into non‐USDW formations

above the lowermost USDW warrants tailored requirements to address the unique challenges and risks

relative to injection below the lowermost USDW. For example, there is a risk of downward migration of

fluids if there is no lower confining layer or inadequate confinement. In addition, there is potential that

wells will be drilled through the injection zone in the future to reach USDWs. EPA believes that the

additional requirements that apply to owners or operators of Class VI wells granted a waiver of the

injection depth requirements at §146.95 will provide additional considerations for the owner or

operator and Director when permitting such wells to ensure protection of all USDWs.  

Letter ID: 0355 Comment ID: 28086 Letter Lines: 225 to 230  

Comment Code: 3210 3.2.1. Comments Generally in Support of the Approach  

Comment: In summary, EPRI believes that the above additional requirements proposed for  

the waiver process, as well as those for enhanced construction and operational  

requirements and type of monitoring technology to be deployed, address concerns  

that are already covered by the July 2008 draft rule, with one exception. We  

agree with EPA’s proposed requirement for monitoring in the USDW below the  

injection zone when injecting CO2 above the lowermost USDW.  
Individual Response: EPA agrees that site specific demonstrations of injection zone integrity along with

proper well construction, operation, monitoring, and post‐injection site care as required in the GS rule,

are appropriate to ensure USDW protection while allowing GS.  

EPA acknowledges the commenter's support of the waiver approach and site‐specific flexibility in

regulatory development and permitting as described in the NODA and Request for Comment. The

Agency acknowledges that there are some situations where injection into non‐USDW formations above

the lowermost USDW can be performed in a manner that protects USDWs.  

The final GS rule at §146.95 establishes a process by which owners and operators can seek a waiver of

the Class VI injection depth requirements and includes additional requirements, such as monitoring

above and below the injection zone, to ensure USDWs are protected from endangerment.