This comment letter response contains two parts:   

(1) The original submittal from the commenter.

(2) A data base printout of EPA’s response to each point raised by the commenter.

Notes about the response letters:

• The response letters were generated by a data base used to track the content of all public

comment submittals and ensure that the Agency responds to each. Each comment letter

was assigned a Letter ID that corresponds to the last four digits of the docket number of the

original comment (as posted on www.regulations.gov).

• Each response letter includes: comment text; an EPA‐assigned comment code; and an

individual response. These are described and explained below.  

• The data base contains Comment text from the letters submitted by commenters.  

Many hard copy letters were scanned into electronic format for inclusion in the data

base. As a result, there may be some typographical errors attributable to optical

character recognition issues.  However, all original submittals were reviewed in the

process of drafting responses to ensure that the comment content was understood and

appropriately addressed.

• The content of each comment letter was divided into topic areas and assigned a unique

Comment ID.  Additionally, one or more Comment Codes (i.e., unique topic area ID) was

assigned to each discrete point raised by a commenter. This information was added to

the data base. To inform final rulemaking decisions, all comments and information

received on a given topic were reviewed by technical experts in each rule area (e.g., on

construction requirements).  

• Following decisions on the final rule requirements, Individual responses were drafted

by topic area to ensure completeness and consistency of the responses with the final

rule and other responses to similar comments.  Each discrete point made by a

commenter was given a unique response.

• Upon completion of comment responses, all information was entered into the data base.

Each letter response is a compilation of each comment and its individual response,

compiled in the order of the original comment letter.  As a result of this process, there is

repetition in the response text.  The Agency believes this approach ensures completeness

and attention to each comment letter that was submitted.   

• All comments in a topic area were reviewed, evaluated, and responded to concurrently.  

Responses on each topic area are compiled and are also available in the rulemaking docket.







Letter ID: 0188 

Commenter: Daniel Plath 

Organization: NiSource, Inc. 

Letter ID: 0188 Comment ID: 25225 Letter Lines: 50 to 55 

Comment Code: 1500 1.2.2.2.4 Some other agency should regulate GS 

Comment: We believe numerous program areas need to be developed to address the multitude 

of issues that are certain arise to make GS a commercially viable option for the 

CO2 capture and storage. In all likelihood, other regulatory authorities will be 

responsible for components of the GS regulatory framework. Close coordination 

between all parties will be needed to assure a consistent set of standards for 

effective GS. 

Individual Response: EPA clarifies that the scope of the GS regulation is limited to injection of 

CO2, and that all requirements in the GS rule are designed for the purpose of protecting USDWs 

from endangerment. The SDWA does not provide the UIC Program with the authority to develop 

regulations for all areas related to GS, such as releases to the atmosphere. 

EPA acknowledges that GS falls within the broader context of CCS and the need for regulatory 

clarity to ensure that USDWs are protected from endangerment. In developing the final GS rule, 

the Office of Water coordinated with other Agency program offices and across federal agencies 

(e.g., with the Department of Energy; United States Geological Survey; Bureau of Ocean Energy 

Management, Regulation, and Enforcement, formerly the Minerals Management Service; Bureau 

of Land Management). The Agency continues to evaluate areas of potential applicability of other 

Federal environmental statutes including, but not limited to: the Clean Air Act; the Resource 

Conservation and Recovery Act; the Comprehensive Environmental Response, Compensation, 

and Liability Act; and the Marine Protection, Research and Sanctuaries Act to various aspects of 

GS and CCS. The Agency will continue to coordinate on GS and CCS related issues to minimize 

redundancy and maximize efficiencies for owners or operators. For additional information, 

please see the discussion entitled "How Does This Rulemaking Relate to Other Federal 

Authorities and GS and CCS Activities?" in the preamble to the final GS rule. 

Regarding the need for a CCS agency to coordinate across agencies, EPA is coordinating with 

and will continue to facilitate communication among federal and state agencies during the 

implementation phase of the GS regulation. 

EPA adds that the intent of the GS rule is not to promote GS. Rather, the purpose of the GS 

regulation is to assure that, where deployed, GS is conducted in a manner that protects USDWs 

from endangerment. 

Letter ID: 0188 Comment ID: 25226 Letter Lines: 57 to 71 

Comment Code: 1250 1.1.1.4 Flexibility is needed (performance-based standards) 

1
Comment Code: 2400 1.8 Comments on EPA's adaptive rulemaking process 

Comment: Recognizing that a great deal of this technology is currently in development and 

will not be commercially deployed for several years, it is vital that the final 

rule, if necessary, include reasonable performance based regulations that can be 

swiftly adjusted and finetuned as experience is gained in large-scale CO2 GS. 

The promulgation of this rule is only but the first step in the establishment of 

a regulatory framework to support the implementation of GS as the technology is 

scaled up from the current experimental stage to fully operational wells, 

considerable experience will be gained that would help further identify areas 

where adjustments to the rules would be necessary. Therefore, we recommend a two 

phase regulatory approach. The first phase would be to address initial projects 

where operational experience and familiarity with carbon injection and storage 

can be gained. That knowledge, including lessons learned from the both the 

technical and regulatory perspective, could then be utilized to develop a second 

phase rule that would more likely be able to provide a better balance between 

risks with regulatory requirements. 

Individual Response: EPA agrees that an adaptive approach to the UIC GS rulemaking is 

appropriate. The Agency plans to use such an approach to ensure that USDWs are protected from 

endangerment and meet the potentially fast pace of GS deployment. EPA believes that an 

adaptive approach will allow regulatory development to proceed in time to meet the current and 

future demand for Class VI permits while recognizing the need to: continue to gather data from 

pilot projects and other research as it becomes available; and to enhance understanding of the 

technical and administrative aspects of GS deployment, operation, and technology developments. 

EPA plans, every six years, to collect and review data on GS projects 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. 

EPA disagrees that the GS rulemaking needs to be based solely on large-volume projects. While 

studying the impact of injecting large volumes of CO2 is important, data on other aspects of 

GS—including the buoyancy and corrosivity of CO2 in the presence of water, the potential 

presence of impurities in captured CO2, and its mobility within subsurface formations—

informed the rulemaking. 

Letter ID: 0188 Comment ID: 25227 Letter Lines: 73 to 76 

Comment Code: 1000 1. General and Administrative Comments 

Comment: NiSource would also like to make the point that we support the comments made on 

the behalf of natural gas utility members by the American Gas Association (AGA). 

In particular, we would like to echo the AGA's concerns regarding the protection 

of geologic natural gas storage. 

Individual Response: EPA acknowledges the comment. Please see the remainder of EPA's 

2
responses to this comment and AGA’s comments for further details. For additional information 

on EPA's final regulatory approach, please see the final rule and preamble as well as the 

rulemaking docket. 

Letter ID: 0188 Comment ID: 25228 Letter Lines: 112 to 119 

Comment Code: 1310 1.1.2.4 Comments on other "out of scope" issues, e.g., pore space 

ownership 

Comment: While NiSource will readily agree that there are many differences between 

storage of natural gas and geologic sequestration of CO2, NiSource submits that 

there are a number of technical and commercial similarities in addition to 

lessons that can be applied from decades of injection and control of high 

pressure natural gas. These similarities include technical issues, securing 

mineral rights, landowner relations, coexisting with third party development of 

the surface and subsurface, and a wide range of regulatory and commercial 

aspects. The following points summarize four primary lessons learned through 

Individual Response: EPA recognizes that the oil and gas industry has decades of experience 

injecting CO2 and has demonstrated the effectiveness of many of the technologies that will be 

employed at GS sites. The Class VI GS rule builds on this expertise with requirements tailored to 

the unique issues associated with GS through proper permitting, siting, well construction, 

operation, monitoring, and closure of GS projects. However, EPA clarifies that pore space issues 

are outside the scope of the Class VI GS rulemaking. EPA clarifies that these issues are under the 

purview of states and any of these issues, as they relate to GS, will need to be addressed though 

state regulations. 

Letter ID: 0188 Comment ID: 25229 Letter Lines: 119 to 137 

Comment Code: 1610 1.3.1 Risks to USDWs 

Comment Code: 3400 2.2.2 Corrective Action 

Comment Code: 3800 2.3 Proposed Injection Well Construction Requirements (40 CFR 

146.86) 

Comment Code: 5100 2.8.1 Injection well plugging activities (seeking comment) (40 CFR 

146.92) 

Comment: aspects. The following points summarize four primary lessons learned through 

operation of natural gas storage that would be applicable to GS: 

1. History has shown that the one component in the system that has caused the 

most safety issues is the wells; specifically the operator's wells, plugged and 

abandoned (P&A) wells and third party operating wells (e.g. oil and gas 

production wells). The casing and cement in the storage well is the "first line 

of defense" in the containment of high pressure gas and a properly designed, 

constructed and maintained well is critical. Even after several decades of 

3
operations over a four State area, NiSource subsidiaries have never experienced 

loss of containment from cap rock leakage, migration up faults, re-activation of 

faults, earthquakes, or the other potential leakage pathways that EPA discusses 

in the Proposed Rule. While history will ultimately reveal the root causes of 

future problems, if any, with GS, NiSource submits that the predominant cause 

will likely be identified as being related to an active well, abandoned well or 

third party well if not properly addressed in the Final Rule. This is based on 

the belief that the rigorous site selection process will preclude the other 

sites that would have had other issues, e.g. cap rock leakage, from even being 

activated in the first place. 

Individual Response: EPA agrees that proper site characterization should minimize leakage 

through faults, breaks in the seal of the confining layer, and other geologic pathways. EPA 

believes that the construction, operating, and monitoring requirements in the GS rule will prevent 

leakage from occurring through active wells. Appropriately designed and constructed wells are 

necessary to prevent endangerment to USDWs and maintain integrity of the well throughout the 

lifetime of a GS project. This is the foundation of the requirements for construction and preoperational testing of Class VI wells at §§146.86 and 146.87. 

EPA also agrees that the AoR and corrective action process should identify both abandoned 

wells and third party wells that could serve as leakage pathways. The UIC Program's longstanding approach to corrective action, tailored to the potential corrosivity of and impurities in 

the CO2 stream, can address the potential risk associated with improperly plugged wells in the 

AoR. 

EPA notes that the final rule, at 40 CFR §124.10(c)(1)(xi), requires the notification of state oil 

and gas agencies, state mineral exploration agencies, and state public water supply supervision 

directors about the availability of the draft permit . EPA expects that such notification can help 

with further identifying wells in the area of review. 

Letter ID: 0188 Comment ID: 25230 Letter Lines: 119 to 120 ; 139 to 148 

Comment Code: 4600 2.6 Proposed Plume and Pressure Front Monitoring Requirements (40 

CFR 146.90) 

Comment: aspects. The following points summarize four primary lessons learned through 

operation of natural gas storage that would be applicable to GS: 

2. NiSource's Columbia subsidiary has performed many of the pre-activation and 

monitoring, measuring and verification (MMV) activities EPA discusses. While 

these technologies are useful, a number are primarily applicable to the initial 

development of a new field or as niche diagnostic tools for specific problems. 

Applying a large number of MMV techniques is appropriate for pilot projects 

though it is rarely a best practice for an established commercial application 

where the historical risks are well known and where there are practical limits 

on staff's time, budgets and other resources. Ultimately, the cost of GS will be 

4
passed on to electric customers and government regulations need to provide a 

balanced perspective. 

Individual Response: EPA agrees with commenters and believes that flexibility is important in 

developing and implementing a monitoring plan that is appropriately tailored for a specific GS 

site. The purpose of the requirement at §146.90 to develop site-specific testing and monitoring 

plans is to ensure that the monitoring performed at a site is appropriate for site operational 

conditions and the geologic setting. EPA believes that this is the best approach for addressing 

potential risks at GS sites. These flexible provisions in the monitoring requirements for Class VI 

wells enable the owner or operator to tailor monitoring programs to the specific needs of each 

project in consultation with the Director. 

The final regulation provides for flexibility in: 1) methodologies used to collect these data, 2) the 

spatial resolution at which the data should be collected, and 3) how often the data should be 

collected. The number and placement of monitoring wells will be based on site-specific 

information such as the calculated AoR, injection rate and volume, site geology, baseline data, 

and the presence of artificial penetrations within the AoR. In some instances, there may be a 

limited number of options for complying with EPA's minimum requirements. For example, 

monitoring for geochemical changes will require use of monitoring wells and collection of 

groundwater samples for chemical analysis. Many options currently exist for complying with 

other requirements, such as tracking the position of the plume and pressure front within the 

injection zone. 

Flexibility is also provided regarding how to monitor for the specific data required by the final 

rule. The testing and monitoring plan is developed by the owner or operator in consultation with 

the Director and is designed to ensure that a detailed, Director-approved document describing 

how monitoring will be conducted during the lifetime of the project exists. EPA is developing 

guidance on testing and monitoring to assist owners or operators and Directors in evaluating 

requirements under §146.90, including proposed monitoring plans. The guidance describes 

available technologies and recommended approaches for implementing a testing and monitoring 

plan, including pre-operational geophysical logging and testing of injection wells, MITs, 

injection well testing during operation, groundwater quality monitoring, tracking the CO2 plume 

and pressure front, and soil gas and surface air monitoring which may be required by the UIC 

Director for specific GS projects. 

Letter ID: 0188 Comment ID: 25231 Letter Lines: 119 to 120 ; 150 to 159 

Comment Code: 1310 1.1.2.4 Comments on other "out of scope" issues, e.g., pore space 

ownership 

Comment: aspects. The following points summarize four primary lessons learned through 

operation of natural gas storage that would be applicable to GS: 

3. NiSource subsidiaries' experience is that it is impossible to obtain 100% 

agreement from thousands of landowners on the development of their subsurface 

for virtually any activity even with numerous public meeting, private 

5
discussions, newsletters, etc. For GS to be utilized beyond the pilot project 

scale, this issue must be addressed. While this topic is not directly within the 

scope of EPA and this Proposed Rule, EPA's requirements can have an impact on 

the degree and extent to which a potential operator will have to interfere with 

a landowner. That will directly impact a landowner's willingness to accept GS on 

their property. Excessive MMV regulations can cause the landowner to have an 

incorrect perception as to the safety of GS under their property. 

Individual Response: As described above, pore space issues are outside the scope of the Class 

VI GS rulemaking. EPA clarifies that these issues are under the purview of states and any of 

these issues, as they relate to GS, will need to be addressed though state regulations. 

EPA acknowledges that CO2 plumes may cross state or even international boundaries and 

encourages cooperation and coordination among permitting authorities. The final Class VI GS 

rule, at §146.82(a)(2), requires the owner or operator to identify all State, Tribal, and Territorial 

boundaries within the AoR. Based on this information, the Director must provide written 

notification to all States, Tribes, and Territories to inform them of the permit application and 

ensure that they are involved in any necessary processes; this new requirement was added to the 

final rule at §146.82(b). The Agency encourages transparency in the permitting process and 

anticipates that State-State/State-Tribal communication on Class VI permitting will facilitate 

information sharing and encourage safe, protective projects. 

Letter ID: 0188 Comment ID: 25232 Letter Lines: 161 to 168 

Comment Code: 1250 1.1.1.4 Flexibility is needed (performance-based standards) 

Comment Code: 1260 1.1.1.5 More certainty/stringency is needed 

Comment: 4. For an activity covering such a diverse geographic, geologic, and commercial 

spectrum as GS, NiSource believes it is essential to incorporate considerable 

regulatory flexibility. However, some relatively high minimum standards of 

technical requirements should be established in key areas. While this may sound 

contradictory, NiSource's observation is that firmly addressing those few real 

risks will ultimately pay significant dividends by preventing a few "bad" 

projects from being developed that ultimately lead to an avoidable incident that 

taints the entire industry. These issues are addressed below. 

Individual Response: The Agency believes that the Class VI requirements balance site-specific 

flexibility with USDW protection. Rather than setting performance or technology-based 

standards for GS projects, EPA is adopting a flexible approach, where operators of GS projects 

would develop and implement site-specific plans for delineating the AoR, testing and monitoring 

the site, performing corrective action, and post-injection site care. EPA believes that the plans—

which would be reviewed and approved by the Director and periodically updated throughout the 

life of the project—promote an ongoing dialogue between the operator and the Director that will 

encourage use of the most appropriate technologies for a particular project. 

6
Letter ID: 0188 Comment ID: 25233 Letter Lines: 179 to 183 

Comment Code: 3400 2.2.2 Corrective Action 

Comment Code: 3800 2.3 Proposed Injection Well Construction Requirements (40 CFR 

146.86) 

Comment: The Proposed Rule adequately addresses the issues of well construction 

requirements and the review of existing plugged and abandoned wells. 

Specifically, Section 146.86 would have sufficient number of cemented strings of 

pipe in the well while Section 146.84 would ensure that abandoned wells are 

properly plugged. 

Individual Response: EPA acknowledges the comment and 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. 

EPA agrees that corrective action as required at §146.84(d) is an important part of preventing 

endangerment of USDWs from CO2 or associated fluids. EPA believes that the UIC Program's 

long-standing approach to corrective action, tailored to the potential corrosivity, and impurities 

in the CO2 stream, can address the potential risk associated with improperly plugged wells in the 

AoR. 

Letter ID: 0188 Comment ID: 25234 Letter Lines: 185 to 202 

Comment Code: 2060 1.5.3 Comments on grandfathering of existing wells (seeking comment) 

Comment: As discussed above, addressing these two issues aggressively as proposed by EPA 

will significantly ensure the confinement of the CO2. The corollary is that it 

would not be in the interest of USDW protection or GS's acceptance by the public 

for EPA to grandfather well construction practices that are significantly below 

the standard set forth in the Proposed Rule so as to permit the conversion of a 

different UIC Class well to Class VI. Simply put, if the operator can not 

recondition the wells to substantially meet the rigorous standards as set forth 

in the Final Rule for technical, financial or other reasons, then the wells 

should not be used for GS. While Section 146.81(c) does not specifically 

indicate an automatic grandfathering of Class I, II, or V wells for Class VI, it 

should be clear that the phrase "...at the Director's discretion ..." means that 

the wells will have to substantially or virtually meet the "Injection Well 

Construction Requirements" in Section 146.86 and not simply meet some limited 

portion of those requirements. 

7
While NiSource will be advocating for greater flexibility in other sections in 

its comments, NiSource recommends caution on the issue of grandfathering well 

construction practices. 

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 allows provides for the 

construction of 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 clarifies that only the construction requirements 

are grandfathered and that all other Class VI requirements (reporting, monitoring, mechnical 

integrity testing, etc.) must be met following a determination under §146.81(c). EPA disagrees 

that this requirement "lowers the standard" for GS wells. Conversion of the well would be at the 

Director's discretion following an evaluation of all other site-specific information about the well 

and the project, e.g., modeling, monitoring, and other data. Any wells that have deteriorated due 

to contact with incompatible injected or formation fluids may not be approved for conversion. 

Letter ID: 0188 Comment ID: 25235 Letter Lines: 204 to 224 

Comment Code: 3840 2.3.2 Horizontal well drilling techniques (seeking comment) 

Comment Code: 4120 2.4.1.2 Allowing hydraulic fracturing during GS (seeking comment) 

Comment: 2. Horizontal Well Construction and Injection Parameter Limitations (73 Fed. 

Reg. at 43509 and 43510) 

The EPA is inclined to permit hydraulic fracturing (frac jobs) and horizontal 

wells and asks for comments on permitting these technologies. NiSource strongly 

believes they should be permitted in addition to similar new technologies that 

will be developed sometime in the future. 

Columbia has successfully performed thousands of fracs and refracs in addition 

to drilling numerous horizontal and other non-vertical types of wells. One of 

the keys to ensure gas confinement is to have the fewest number of penetrations 

of the cap rock. Both frac jobs and horizontal wells permit significantly 

greater injectability from a single well. Our experience is that this type of 

work can increase injectability by 2 to 8 times or to phrase it differently, 

only one- eighth to one-half the number of wells would be required to match the 

equivalent performance of vertical wells or non-stimulated wells. 

Whatever technologies that can be employed, whether existing or new, to reduce 

the number of penetrations are valuable from a surface environmental impact, 

landowner acceptance, and cost management perspective and should be allowed by 

8
this regulation. 

Individual Response: In the final rule, EPA allows the use of horizontal wells at GS projects. In 

the proposed rule, EPA sought comment on the appropriateness of horizontal drilling techniques 

for Class VI wells, and commenters representing energy companies, electric utilities, the oil and 

gas industry, CCS associations, states, and the public, unanimously supported the concept and 

provided many reasons why horizontal wells could be beneficial at GS sites. Based on an 

evaluation of these comments and additional research by EPA, the Agency has concluded that 

horizontal wells that are properly constructed, logged, and tested for mechanical integrity (i.e., to 

meet the requirements of the GS rule) can ensure the protection of USDWs from endangerment. 

The final rule allows the use of hydraulic fracturing for purposes of Class VI injection, where 

approved by the Director. Hydraulic fracturing is one of several stimulation technologies 

available to improve wellbore and formation injectivity. 

EPA clarifies that all stimulation, including hydraulic fracturing, must be approved by the 

Director and that §146.88(a) permits injection pressure to exceed 90 percent of the fracture 

pressure only during well stimulation. Owners or operators must submit a proposed stimulation 

program as part of the permit application under §146.82(a)(9); the plan must demonstrate that 

any stimulation activities will not compromise the integrity of the confining zone. The Director 

will evaluate the owner or operator's proposed stimulation plan in the context of all information 

about the site, and the owner or operator must perform stimulation only as approved. 

The final rule at §146.91(d)(2) also requires that the owner or operator notify the Director 30 

days before performing stimulation during the operational phase of a GS project; this will 

provide an additional opportunity for the Director to review the owner or operator's plans for 

stimulation and add other requirements as needed. EPA clarifies that UIC regulations prohibit 

fracturing of the confining zone at any time during injection or stimulation. 

Letter ID: 0188 Comment ID: 25236 Letter Lines: 226 to 238 

Comment Code: 4490 2.4.5 Use of tracers and potential impact on human health or ecosystems 

(seeking comment) 

Comment: 3. Proposed Injection Well Operating Requirements (73 Fed. Reg. at 43512-13) 

The Proposed Rule states that tracers are not mandated to be used but are at the 

Director's discretion to require. Columbia has utilized tracers in several 

fields over the years and has found them to be a useful tool for specific 

applications. It is not, however, a tool that is useful all the time for every 

field. While it is not overly expensive relative to the rest of the facility 

cost, it is a very labor and data intensive application and would represent a 

resource misallocation if mandated by the Final Rule. NiSource believes it would 

be inappropriate to grant the Director the ability to exercise discretion to 

require their use. Instead, we believe it would be much more beneficial to 

simply allow the operator the ability to use tracers at his or her discretion 

9
when appropriate to address specific situations. 

Individual Response: EPA agrees that tracer use is not appropriate in all situations. For this 

reason, EPA does not require the use of tracers at all GS sites; however, the Director has 

discretion to require their use if he/she determines that the use of tracers could improve 

monitoring of the site and enhance USDW protection from endangerment. The rule will also 

allow their use if proposed by the owner or operator and approved by the Director. 

EPA has been following new and ongoing research on the safety and efficacy of tracers, 

including their efficiency and cost-effectiveness. The Agency plans to, every six years, collect 

and review data on GS projects 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: 0188 Comment ID: 25237 Letter Lines: 240 to 287 

Comment Code: 4640 2.6.4 Pressure fall-off testing (seeking comment) 

Comment: 4. Pressure Falloff Tests (146.90(f)) 

The EPA proposes and requests comment on the requirement for operators to 

conduct a pressure falloff test once every 5 years (Preamble (73 Fed. Reg. at 

43515). Notwithstanding our comments below about the Proposed Rule having 

excessive data collection requirements, one area in which NiSource believes the 

Proposed Rule is actually too lenient is with respect to only requiring a 

pressure falloff test at least once every 5 years. NiSource recommends where 

appropriate that this be either done at an interval no greater than two years or 

at a site specific injected volume interval. NiSource notes the duration of 

shut-in will be reservoir dependent but a range of 1 to 5 days, depending on the 

reservoir circumstances, is recommended. 

The key to this being an invaluable tool with natural gas reservoir storage 

integrity monitoring isn't that the time period is long enough to actually reach 

pressure stability as it is that the testing is conducted at consistent time 

intervals and volume levels over the life of the field. This is primarily done 

by collecting and studying shut-in data at every well every spring and fall when 

the field is empty and full of working gas, respectively. Testing at a fairly 

consistent time/volume interval provides for more relevant comparisons over 

time, and enhances the usefulness for comparisons over extended periods of time, 

even when comparing test results over several decades. This in turn permits an 

efficient understanding of what the gas is doing in the vast reservoir area over 

the life of the field and the identification of even very slowly growing 

abnormal trends in the gas plume's pressure-volume behavior. An accurate 

identification of the fields, if any that are experiencing gas migration issues 

then allows the operator to focus resources to identify the root cause and to 

rectify the specific probiem. NiSource believes these testing provisions would 

10
be helpful if included in the proposed rule. Therefore, we suggest the rule 

language be adjusted to accommodate these factors. 

While the volume in a GS field will be continually increasing versus cycling as 

with natural gas storage, the concept of having snap shots of the shut-in 

reservoir pressure for the entire CO2 plume at consistent time/volume intervals 

should still lead to a similar understanding of the plume's overall behavior. 

These observations can then be compared with the reservoir simulation 

predictions and would help with fine tuning model assumptions. Significant 

deviations, if any, would be quickly identified and would become the 

investigative focal point for the operator's resources. 

In many instances, we recommend this shut-in pressure test and analysis coupled 

with simulation be recognized as a viable primary method for CO2 plume 

monitoring with more extensive methods (e.g. 4D seismic, etc.) only being used 

to periodically fine tune the model or in instances when questions arise. The 

appropriate testing basis, time or volume based, will likely be site and 

operator specific. Therefore, the Final Rule needs to provide for flexibility to 

utilize this method and allow the use of new testing technology that may become 

available in the future. 

Individual Response: EPA believes that a frequency of at least once every five years, as 

specified at §146.90(f), is an appropriate interval for pressure fall-off testing (particularly given 

the suite of tests operators will perform on the well and the site). EPA clarifies that the Director 

may require more frequent pressure fall-off tests at a specific project, if necessary based on sitespecific circumstances. Pressure fall-off tests may be conducted in conjunction with other well 

performance tests (i.e., mechanical integrity testing) to ensure safe and effective operations. All 

monitoring data collected, including information from pressure fall-off tests, will be incorporated 

in AoR reevaluations conducted at least every five years. 

EPA adds that the pressure fall-off testing will be performed in concert with other testing, 

including plume monitoring, pursuant to the approved testing and monitoring plan. If any sitespecific information indicates a need for additional or more frequent testing to ensure USDWs 

are protected, it is within the Director's discretion to require additional testing to ensure 

protection of USDWs. 

Letter ID: 0188 Comment ID: 25238 Letter Lines: 289 to 303 

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

Comment: 5. Data and MMV Requirements (146.82 and 146.90) 

The Proposed Rule has potentially very extensive data and monitoring, measuring 

and verification (MMV) requirements, particularly once this is an established 

and proven technology. The required data to prudently develop a GS site and to 

monitor the gas plume is extremely site specific and industry knowledge base 

11
dependent. A pilot project will inherently require more frequent and diverse 

data collection and modeling than the nth project in the same formation. The 

Final Rule needs to recognize the clear differences in data requirements for 

first of its kind projects, where the primary driver is risk mitigation due to 

the multitude of unknowns, versus the application of a well developed technology 

for which cost effectiveness is the primary consideration because the experience 

and knowledge exists to effectively identify and manage the risks. NiSource does 

not see any recognition of this significant difference in the Proposed Rule and 

respectfully submit that EPA incorporate language accordingly. 

Individual Response: EPA acknowledges that early pilot projects may focus on gathering data 

to inform GS technology. However, EPA believes that a detailed geological site characterization 

of every GS site (as required under §146.82) is essential to evaluating the presence and adequacy 

of the various geologic features necessary to receive and confine injected CO2 for GS. The 

requirements for geologic site characterization are based on a long standing UIC regulatory 

framework developed to address specific risks to USDWs posed by injection. The Class VI GS 

requirements are tailored so that they are appropriate for the unique nature of injecting large 

volumes of CO2 into a variety of geological formations for long-term storage. EPA adds that, if 

data on a formation or site collected in connection with an earlier project can support a geologic 

characterization, the Director has discretion to accept this data, provided it is sufficient to 

demonstrate site suitability. 

The mission of the UIC program and the goal of the GS regulation is to protect USDWs from 

endangerment, and every aspect of the GS rule is designed toward that end. Therefore, EPA 

disagrees that any of these protective requirements are unnecessary, and clarifies that waiving 

any of the requirements would not be acceptable. The GS regulation allows flexibility where 

appropriate. 

Letter ID: 0188 Comment ID: 25239 Letter Lines: 305 to 320 

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

Comment: 6. Automatic Downhole Shut-off Systems (146.88) 

The Rule proposes to require automatic downhole shut-off subsurface safety 

valves. Experience by multiple natural gas storage operators, including Columbia 

is that subsurface safety valves actually increase the safety risks to the 

public and company personnel. Some operators, including ours, have even realized 

that the theoretical benefit does not out weigh the real world risks and have 

removed them from most of their wells. The safety valves have been relegated to 

the role of a niche application where additional safety features are necessary, 

e.g. a very high flow rate well in the midst of suburban housing because the 

product being stored has a high flammability characteristic. 

The Final Rule should not require the application of every safety feature in 

every instance as much as it should provide regulatory flexibility in 

12
recognition that the risks posed by all wells are not equal and that the best 

way is to tailor the design for the specific situation. 

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: 0188 Comment ID: 25240 Letter Lines: 322 to 344 

Comment Code: 5240 2.8.2.2 Post injection timeframe (seeking comment) 

Comment: 7. Post Site Care and Site Closure (146.93) 

A fixed time period of 50 years of post injection site monitoring before site 

closure can occur is highly speculative as noted by EPA in the Preamble. 

NiSource believes that the appropriate method is a performance-based standard 

which is site specific. While we recognize the potential flexibility granted in 

146.92(b)(2) for the Director to permit a shorter time period if supported by 

the data, the reality is that when a potential operator is evaluating 

development of a site, the 50 year monitoring period will be used. This may have 

the chilling effect of discouraging would-be developers from undertaking a GS 

project in the first place. On the other hand, if while collecting site 

evaluation data a potential operator has the ability to model the potential 

closure period based on the expected performance of the reservoir, then they are 

likely to be more willing to undertake the project if the initial data indicates 

a more reasonable site closure time frame. This would also encourage the 

development of new technologies to more efficiently manage the closure period. 

Based on many of the other discussions taking place on the GS topic, such as the 

Interstate Oil and Gas Compact Commission's recommendations, this is a topic 

that may likely have a legislative solution as opposed to a regulatory solution. 

The primary outcome of EPA's inclusion of this feature in the Final Rule has the 

potential of encumbering efforts to develop GS as a viable means of long-term 

storage of CO2. 

Individual Response: EPA agrees with commenters that there will be circumstances where it 

13
14

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 post-injection 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, during the permitting process based on substantial 

data, that an alternative PISC timeframe may be appropriate if it ensures non-endangerment of 

USDWs pursuant to requirements at §146.93(c). 

EPA believes however, that to ensure USDW protection from endangerment, a default timeframe 

for post-injection site care will be necessary in all but a limited number of cases. This default 50 

year post-injection site care timeframe represents a reasonable and protective monitoring period 

based on a review of research studies, industry reports, and existing environmental programs, 

and evaluation of public comments. 

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. 

EPA adds that the purpose of the GS rule is not to incentivize the use of GS; rather, the purpose 

of the GS rule is to ensure that, where GS is deployed, it is conducted in a manner that protects 

USDWs from endangerment.