2.2

– Responses to Public Comments on AoR and Corrective Action

This file contains responses to public comments on area of review (AoR) and corrective

action (comment codes 3200 to 3700). This section includes comments on delineation

of the AoR, use of computational models, identifying and addressing wells that need

corrective action, reevaluating the AoR, phased correct ive action, and corrective action
plans.

The table below presents all of the EPA

‐ assigned comment codes that are included in

this section of the comment and response summary. Use the bookmarks in the PDF to

move among the comment codes.

Topics included in this summary an d associated comment codes

Topic Code

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

2.2.1 Delineating the AoR/Modeling CO2 movement 3300

2.2.1.1 Comments in favor of requiring computational models to delineate the AoR 3310

2.2.1.2 Comments opposed to requiring computational models to delineate the AoR 3320

2.2.1.3 Applicability /adequacy of computational models 3330

2.2.1.4 Specific delineation models 3340

2.2.1.5 Use of proprietary models for GS sites 3350

2.2.2 Corrective Action 3400

2.2.2.1 Scope of the inventory process (e.g., reliance on publicly available information,
depth of wells) 3420

2.2.2.2 Evaluation of wells in the AoR (e.g., types of data to be reviewed) 3440

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

2.2.3 Area of Review Reevaluation 3500

2.2.3.1 AoR reevaluation frequency 3530

2.2.3.2 Conditions that merit reevaluation of the AoR 3560

2.2.4 Phased Corrective Action (No comments were submitted for this topic.) 3600

2.2.4.1 Comments in favor of allowing phased corrective action 3630

2.2.4.2 Comments opposed to allowing phased corrective action 3660

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

Every comment on these topic areas and the associated response is included in this

summary; there is some repetition where multiple commenters made the same

comment.

Responses to letters from individual commenters or organizations are also available in

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



### Individual Comments

Commenter Name: John Hanger Letter ID: 0130 Commenter Organization: Pennsylvania Dept. of Env. Protection Comment ID: 21503

Comment: Proposed Area of Review and Corrective Action Requirements

-PA needs to be assured that the designated "Area of Review" is sufficient and inclusive to provide for sound analysis of the impacts and control of potential environmental impacts to groundwater, water supplies, and surface water. State complications may arise from property and mineral rights related to permitting and operations of the proposed Class VI regulations based on this definition and its application.

-Area of Review should include a "buffer zone" surrounding the Area of Review boundary that is adequate to address risk of improper assessment. The size of the boundary should be left to the applicant but should be subject to the Director’s approval.

Response: EPA agrees that the unique aspects of GS merit the use of sophisticated computational modeling for delineation of the AoR, based on site-specific features and geology, including the presence of faults, fractures, and artificial penetrations to ensure protection of USDWs. EPA believes that computational modeling of the AoR prior to injection will provide the best obtainable estimates of the extent of the CO2 plume over several years of active injection. EPA has strengthened the minimum frequency for the AoR reevaluation from ten years to 5 years (146.84(e)). 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.

EPA disagrees that incorporating a buffer zone into the definition of the AoR is necessary, because EPA believes that the AoR definition incorporates all areas that may be affected by the injection activity, and the iterative AoR reevaluation process required at 146.84(e) further accounts for uncertainty in the original modeling. The Agency has carefully considered all comments on the AoR definition at 146.84(a) and modified it to read as follows: The region surrounding the geologic sequestration project where USDWs may be endangered by the injection activity. The area of review is delineated using computational modeling that accounts for the physical and chemical properties of all phases of the injected CO2 stream and is based on available site characterization, monitoring, and operational data.

Commenter Name: Anonymous2 Letter

ID: 0133 Commenter Organization: Sierra Club National Global Warming and Energy Committee and Sierra Club California-Nevada Regional Conservation Committee on Energy and Climate Change Comment

ID: 21578

Other EPA Comment Codes and Descriptions: 1220 1.1.1.1 Terminology and definitions

Comment: I. Technical DefinitionsArea of Review and Fluid Movement: Adopt the specific language used by the adhoc CO2 workgroup in its Recommendation 3.1 for determining the parameters of each Area of Review, i.e. -- "based on generally accepted and site relevant techniques, such as modeling, that define, in three dimensions, the maximum extent of the modeled CO2 plume [inclusive of free phase and water- dissolved CO2]and associated pressure front."

Response: Based on review of all public comments on the AoR definition at 146.84(a), the Agency has modified it to read as follows: The region surrounding the geologic sequestration project where USDWs may be endangered by the injection activity. The area of review is delineated using computational modeling that accounts for the physical and chemical properties of all phases of the injected CO2 stream and is based on available site characterization, monitoring, and operational data. The definition in the proposed rule accounted for the varying physical and chemical properties of the CO2 including free-phase and water-dissolved CO2, as the commenter suggests. The definition in

the final rule will continue to do so.

The UIC regulations, including the Class VI regulations, are designed to ensure protection of USDWs from endangerment. The Agency believes that the AoR needs to incorporate not only the CO2 itself—regardless of saturation or phase—but also the area of increased pressure ahead of the CO2 plume, which can potentially displace saline, native fluids (i.e., naturally occurring salty water) into USDWs. This pressure front would typically encompass an area larger than the plume itself, including any areas of small scale fingering or heterogeneities or where CO2 saturation is less than 100 percent.

Commenter Name: Anonymous2 Letter

ID: 0133 Commenter Organization: Sierra Club National Global Warming and Energy Committee and Sierra Club California-Nevada Regional Conservation Committee on Energy and Climate Change Comment

ID: 21602

Comment: Technical Definitions

A. Area of Review and Fluid Movement

Recommendation A: Adopt the specific language used by the ad-hoc CO2 workgroup in its Recommendation 3.1 for determining the parameters of each Area of Review, i.e. -- "based on generally accepted and site relevant techniques, such as modeling, that define, in three dimensions, the maximum extent of the modeled CO2 plume [inclusive of free phase and water- dissolved CO2]and associated pressure front."

Response: Based on review of all public comments on the AoR definition at 146.84(a), the Agency has modified it to read as follows: The region surrounding the geologic sequestration project where USDWs may be endangered by the injection activity. The area of review is delineated using computational modeling that accounts for the physical and chemical properties of all phases of the injected CO2 stream and is based on available site characterization, monitoring, and operational data. The definition in the proposed rule accounted for the varying physical and chemical properties of the CO2 including free-phase and water-dissolved CO2, as the commenter suggests. The definition in

the final rule will continue to do so.The UIC regulations, including the Class VI regulations, are designed to ensure protection of USDWs from endangerment. The Agency believes that the AoR needs to incorporate not only the CO2 itself—regardless of saturation or phase—but also the area of increased pressure ahead of the CO2 plume, which can potentially displace saline, native fluids (i.e., naturally occurring salty water) into USDWs. This pressure front would typically encompass an area larger than the plume itself, including any areas of small scale fingering or heterogeneities or where CO2 saturation is less than 100 percent.

Commenter Name: Bonnie Lovelace Letter ID: 0152 Commenter Organization: Montana Department of Environmental Quality (MDEQ) Comment ID:

22106 Other EPA Comment Codes and Descriptions: 1610 1.3.1 Risks to USDWs

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.

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) non-compliance 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.

Commenter Name: Kyle Isakower Letter ID: 0170 Commenter Organization: American Petroleum Institute Comment ID: 24142 Other EPA Comment Codes and Descriptions: 1220 1.1.1.1 Terminology and definitions

Comment: Rule Provision: 146.81(d) [Definition - Area of review]

API Comments: Area of review means the region surrounding the geologic Sequestration project that may be impacted by the injection activity. The area of review is based on computational modeling that accounts for the physical and chemical properties of all phases of the injected carbon dioxide stream. SUBSURFACE THREE-DIMENSIONAL EXTENT OF THE CARBON DIOXIDE PLUME,

ASSOCIATED PRESSURE FRONT, AS WELL AS THE OVERLYING FORMATIONS AND SURFACE AREA

ABOVE THAT

DELINEATED REGION.Rationale: Defining the AOR based on the extent of the CO2 plume and its associated pressure front is a more direct approach, rather than the approach offered by the EPA. The EPA definition suggests that the computational approach defines the AOR rather than the potential risks of the injection activity.

Response: EPA disagrees that the AoR definition needs to specifically include the overlying formations and surface area above the delineated region. The intent of the AoR, a long-standing concept within the UIC Program, is to delineate the surface area and all subsurface formations below it that may potentially be impacted by injection activity. Acceptable delineation models will provide predictions of CO2 fate and transport, as well as changes in formation pressure in three dimensions as a function of time that can be used to delineate the subsurface storage site and the AoR. Although EPA disagrees with the commenter's suggested change, the Agency has carefully considered all comments on the AoR definition at 146.84(a) and modified it to read as follows: The region surrounding the geologic sequestration project where USDWs may be endangered by the injection activity. The area of review is delineated using computational modeling that accounts for the physical and chemical properties of all phases of the injected CO2 stream and is based on available site characterization, monitoring, and operational data. EPA believes that this definition is sufficiently broad and describes both the intent of the computational modeling and the relationship of the AoR to areas that are subject to the risks associated with injection.

Commenter Name: James Rower Letter ID: 0173 Commenter Organization: Utility Solid Waste Activities Group (USWAG) Comment ID: 23487 Other EPA Comment Codes and Descriptions: 1220 1.1.1.1 Terminology and definitions

Comment: Corrective action - As a threshold matter, USWAG believes that the terminology used in the Proposal is problematic; use of the phrase "corrective action" to describe well plugging and repair risks confusion with the concept of corrective action under either RCRA or CERCLA. As the GAO Report cautions, public perception is critical to the development of a commercially viable CO2 GS program. GAO Report at 49. To avoid any unintended and unwarranted negative associations with the phrase "corrective action," USWAG suggests the Final Rule abandon this phrase and instead use a phrase such as "well plugging and repair."

Response: EPA notes that the term "corrective action" at 146.84(d) has been used to describe the process of addressing improperly plugged wells in the AoR of injection wells since the inception of the UIC Program, e.g., at 146.7 and 146.64. While EPA is aware that the term has a different meaning under RCRA and CERCLA, this has not caused confusion in the past. The alternative term, "well plugging," suggested by the commenter is reserved for injection well plugging (as indicated at 146.92).

Commenter Name: Robert J. Finley Letter ID: 0180 Commenter Organization: Illinois State Geological Survey Comment ID: 23626 Other EPA Comment Codes and Descriptions: 3460 2.2.2.3 Acceptable corrective action techniques for GS sites (e.g., cements)

Comment: 146.84

(c)Who determines what corrective action is required in the area of review? If a Class II well has been plugged in conformance with Class II requirements is that presumed to be adequate? Different state agencies (in a primacy state) may be responsible for Class II and Class VI wells, potentially complicating oversight

of corrective action.

Response: The GS regulation does not specify the corrective action methods to be used on wells within the AoR to meet the requirements of §146.84(d) and instead allows flexibility to ensure that all corrective action is appropriate to the well, the CO2 injection, and other site-specific conditions. All corrective action must be appropriate to the GS site to ensure that the well does not allow CO2 or other fluids to move into or endanger USDWs and must be approved by the Director. EPA recognizes that wells plugged in accordance with Class II requirements may also be appropriately plugged for a CO2 GS project. EPA adds that all corrective action must be performed pursuant to the approved AoR and corrective action plan, which affords the Director the discretion to require any additional information needed to ensure that all necessary corrective action is performed.

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.

Commenter Name: Thomas Curtis Letter ID: 0181 Commenter Organization: American Water Works Association (AWWA) Comment ID: 23732 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Part 146.84(c)(2) AWWA recommends revising the first sentence to read:

Using methods approved by the Director, identify all penetrations, including active and abandoned wells and underground mines, in the area of review that may penetrate any portion of the confining zone.

Response: EPA clarifies that the mapping and cross sections required to be submitted under 146.82(a)(3) will define the limits of the confining zone, which would be accounted for in the AoR delineation and corrective action evaluation required at 146.84(c). EPA adds that owners or operators must also, under 146.82(a)(2), submit a map of the AoR that shows all injection wells, producing wells, abandoned wells, plugged wells or dry holes, deep stratigraphic boreholes, State or EPA approved subsurface cleanup sites, surface bodies of water, springs, mines (surface and subsurface), quarries, water wells and other pertinent surface features including structures intended for human occupancy and roads. EPA believes that these requirements address the commenter's

concerns.

EPA adds that any well that penetrates the confining zone, even if it does not extend all the way through the confining formation, is to be included in the tabulation. EPA is issuing guidance on how to identify all wells that require corrective action. 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.

Commenter Name: Robert F. Van Voorhees Letter ID: 0190 Commenter Organization: Carbon Sequestration Council Comment ID: 24400 Other EPA Comment Codes and Descriptions: 1220 1.1.1.1 Terminology and definitions

Comment: Rule Provision: 146.81(d) [Definition - Area of review]

Proposed CCS Group Recommendations: Area of review means the region surrounding the geologic sequestration project that may be impacted by the injection activity. The area of review is based on computational modeling that accounts for the physical and chemical properties of all phases of the injected

carbon dioxide stream. SUBSURFACE THREE-DIMENSIONAL EXTENT OF THE CARBON DIOXIDE PLUME, ASSOCIATED PRESSURE FRONT, AS WELL AS THE OVERLYING

FORMATIONS

AND SURFACE AREA ABOVE THAT DELINEATED REGION.

Basis for CCS Group Comments: Defining the AOR based on the extent of the CO2 plume and its associated pressure front is a more direct approach, rather than the approach offered by the EPA.

Response: EPA disagrees that the AoR definition needs to specifically include the overlying formations and surface area above the delineated region. The intent of the AoR, a long-standing concept within the UIC Program, is to delineate the surface area and all subsurface formations below it that may potentially be impacted by injection activity. Acceptable delineation models will provide predictions of CO2 fate and transport, as well as changes in formation pressure, in three dimensions, as a function of time that can be used to delineate the subsurface storage site and the AoR. Although EPA disagrees with the commenter's suggested change, the Agency has carefully considered all comments on the AoR definition at 146.84(a) and modified it to read as follows: The region surrounding the geologic sequestration project where USDWs may be endangered by the injection activity. The area of review is delineated using computational modeling that accounts for the physical and chemical properties of all phases of the injected CO2 stream and is based on available site characterization, monitoring, and operational data. EPA believes that this definition is sufficiently broad and describes both the intent of the computational modeling and the relationship of the AoR to areas that are subject to the risks associated with injection.

Commenter Name: Craig R. Walters Letter ID: 0200 Commenter Organization: Anadarko Petroleum Corporation Comment ID: 24633 Other EPA Comment Codes and Descriptions: 1220 1.1.1.1 Terminology and definitions

Comment: Rule Provision: 146.81(d) [Definition - Area of review]

Anadarko Petroleum Corporation (APC) Comments: Area of review means the region surrounding the geologic sequestration project that may be impacted by the injection activity. The area of review is based on computational modeling that accounts for the physical and chemical properties of all phases of the injected

carbon dioxide stream. SUBSURFACE THREE-DIMENSIONAL EXTENT OF THE CARBON DIOXIDE PLUME, ASSOCIATED PRESSURE FRONT, AS WELL AS THE OVERLYING

FORMATIONSAND SURFACE AREA ABOVE THAT DELINEATED REGION.

Rationale: Defining the AOR based on the extent of the CO2 plume and its associated pressure front is a more direct approach, rather than the approach offered by the EPA. The EPA definition suggests that the computational approach defines the AOR rather than the potential risks of the injection activity.

Response: EPA disagrees that the AoR definition needs to specifically include the overlying formations and surface area above the delineated region. The intent of the AoR, a long-standing concept within the UIC Program, is to delineate the surface area and all subsurface formations below it that may potentially be impacted by injection activity. Acceptable delineation models will provide predictions of CO2 fate and transport, as well as changes in formation pressure, in three dimensions as a function of time that can be used to delineate the subsurface storage site and the AoR. Although EPA disagrees with the commenter's suggested change, the Agency has carefully considered all comments on the AoR definition at 146.84(a) and modified it to read as follows: The region surrounding the geologic sequestration project where USDWs may be endangered by the injection activity. The area of review is delineated using computational modeling that accounts for the physical and chemical properties of all phases of the injected CO2 stream and is based on available site characterization, monitoring, and operational data. EPA believes that this definition is sufficiently broad and describes both the intent of the computational modeling and the relationship of the AoR to areas that are subject to the risks associated with injection.

Commenter Name: Christopher Murray Letter ID: 0207 Commenter Organization: Pacific Northwest National Laboratory Comment ID: 22432

Comment: Area of Monitoring and Area of Review . . .. . . . . .. . . . . Page 4 EPA should define two regulatory regions surrounding the geologic sequestration project and provide specific definitions for those regions: 1) Area of Monitoring (AoM) and 2) Area of Review (AoR); where the AoM is used to define the spatial distribution of monitoring wells and the AoR is used to define the

limit of corrective actions

Response: EPA believes that, while the commenter offers different terminology for the AoR and the area to be monitored, the GS rule addresses the commenter's suggestions. Notably, the owner or operator is required (under 146.90) to develop and implement a testing and monitoring plan for each GS project that must consider the delineated AoR that includes both the CO2 plume and associated pressure front and incorporates many of the attributes suggested by the commenter. EPA clarifies that delineation of the AoR, as required at 146.84(c), must account for the physical and chemical properties of all phases of the injected CO2 stream, based on available site characterization, monitoring, and operational data.

Furthermore, any changes to the AoR would necessitate a review of and potential change in the testing and monitoring plan, consistent with the commenter's assertion that the AoR may vary over time. The final GS regulation includes a requirement at 146.84(e) that the AoR be reevaluated at least every 5 years, and also requires that the owner or operator periodically review the AoR and corrective action, testing and monitoring, and emergency and remedial response plans within one year of an AoR reevaluation (as well as following significant changes to the facility, or when required by the Director). The relationship between the AoR reevaluation and the testing and monitoring plan should allow for considerations suggested by the commenter. EPA believes that by linking development and review of the testing and monitoring plan to the AoRevaluation and reevaluation process, the GS rule, in effect, incorporates many of the commenter's considerations for an area of monitoring.

Commenter Name: Richard Guinn Letter ID: 0210 Commenter Organization: Eastman Chemical Company Comment ID: 22722

Comment: §146.84 Area of review and corrective action. (c) (2) "Using methods approved by the Director, identify all penetrations, including active and abandoned wells and underground mines, in the area of review that may penetrate the confining zone. Provide a description of each well’s type, construction, date drilled, location, depth, record of plugging and/or completion, and any additional information the Director may require; and..."

We recommend striking out "approved" and replacing with "prescribed". We recommend deleting the second sentence and replacing with "Where such information is available or can be obtained, provide a description of each well’s type, construction, date drilled, location, depth, record of plugging and/or completion, and any additional information prescribed by the director, and..." Acceptable methods for identifying deep wells into confining zones within the AoR should be prescribed by the EPA as part of the regulation.

Accurate information is difficult to obtain for older wells within the AoR. Examples of other information that could be required by the Director should be clearly stated.

Response: The final rule retains the language in 146.84(c)(2) as proposed. EPA disagrees that the Director should prescribe the corrective action methods to be used. Instead, all corrective action must be performed pursuant to the approved AoR and corrective action plan, which affords the Director the discretion to review and approve planned corrective action techniques and require any additional information needed to ensure that all necessary corrective action is performed (e.g., information that is not publically available). EPA is issuing guidance on how to identify all wells that require corrective action. 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 clarifies that any well that penetrates the confining zone, even if it does not extend all the way through the confining formation, is to be included in the tabulation. EPA is issuing guidance on how to identify all wells that require corrective action. EPA adds that the Director has the discretion to require the owner or operator to supplement a data records search, including requiring ground or airborne surveys for wells, if there is reason to believe, based on knowledge of the site or of available data bases, that the incompleteness of available information could compromise USDW protection from endangerment.

Commenter Name: Olon Plunk Letter ID: 0217 Commenter Organization: Xcel Energy, Inc. Comment ID: 21558

Comment: Corrective Actions/AoR

Xcel Energy is concerned that the term "corrective action" as used broadly inthe proposed rule infers to the public that a problem has occurred. We concur with USWAG's comment that it would be better to refer specifically to "well plugging and repair" to avoid stigmatizing projects for what are in fact deliberate and proactive preventive measures. In addition, Xcel Energy advocates

Response: EPA notes that the term "corrective action" at 146.84(d) has been used to describe the process of addressing improperly plugged wells in the AoR of injection wells since the inception of the UIC Program, e.g., at 146.7 and 146.64. While EPA is aware that the term has a different meaning under RCRA and CERCLA, this has not caused confusion in the past. The alternative term, "well plugging," suggested by the commenter is reserved for injection well plugging (as indicated at 146.92).

Commenter Name: Tiffany Rau Letter ID: 0224 Commenter Organization: Hydrogen Energy International Comment ID: 21678

Comment: Existing wells within the AoR may be ideal candidates for conversion to monitoring or injection wells during the life of the project and, therefore, should not be plugged and abandoned prior to injection. Existing wells within the likely plume area that are not plugged and abandoned should have diagnostic testing to ensure there is minimal risk of vertical leakage prior to conversion to monitoring or injection status.

Response: EPA recognizes that operators may choose to convert existing wells in the AoR for use as monitoring wells or injection wells. An operator seeking to use an existing well as a monitoring well would need to describe that well in the proposed testing and monitoring plan to demonstrate that is appropriately constructed for use as a monitoring well and compatible with the GS injection operation and injectate. The Director would take the condition of the well into consideration in approving the proposed testing and monitoring plan.

Commenter Name: Brian Williams Letter ID: 0225 Commenter Organization: BP Alternative Energy North America, Inc. (BP) Comment ID: 21728

Comment: Existing wells within the AoR may be ideal candidates for conversion to monitoring or injection wells during the life of the project and, therefore, should not be plugged and abandoned prior to injection. Existing wells within the likely plume area that are not plugged and abandoned should have diagnostic testing to ensure there is minimal risk of vertical leakage prior to conversion to monitoring or injection status.

Response: EPA recognizes that operators may choose to convert existing wells in the AoR for use as monitoring wells or injection wells. An operator seeking to use an existing well as a monitoring well would need to describe that well in the proposed testing and monitoring plan to demonstrate that is appropriately constructed for use as a monitoring well and compatible with the GS injection operation and injectate. The Director would take the condition of the well into consideration in approving the proposed testing and monitoring plan.

Commenter Name: Andrew Duguid Letter ID: 0226 Commenter Organization: Schlumberger Carbon Services Comment ID: 24020 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule languageComment: §146.84 Area of review and corrective action.

Proposed Rule: (a) The area of review is the region surrounding the geologic sequestration project that may be impacted by the injection activity. The area of review is based on computational modeling that accounts for the physical and chemical properties of all phases of the injected carbon dioxide stream.

Schlumberger Suggested Revision: (a) The area of review is based on computational modeling that accounts for physical and the chemical properties of all phases of the injected carbon dioxide stream, the associated pressure front, and displaced brine.

Schlumberger Rationale: -

Response: Based on review of all public comments on the AoR definition at 146.84(a), the Agency has modified it to read as follows: The region surrounding the geologic sequestration project where USDWs may be endangered by the injection activity. The area of review is delineated using computational modeling that accounts for the physical and chemical properties of all phases of the injected CO2 stream and is based on available site characterization, monitoring, and operational data. The definition in the proposed rule accounted for the varying physical and chemical properties of the CO2 including free-phase and water-dissolved CO2, as the commenter suggests. The definition in

the final rule will continue to do so.

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.

Commenter Name: Neeraj Gupta Letter ID: 0229 Commenter Organization: Battelle Energy Technology (BET) Comment ID: 21832

Comment: Page 72, Corrective Action/Abandoned Wells - We would appreciate more clarity on whether it will be required to plug and abandon wells in zones above confining layers. At our sites, it appears the regulators have expected all inactive wells in the AOR to be plugged, even if they are not penetrating the injection

zones.

Response: EPA clarifies that wells requiring corrective action are those in the AoR and wells that may penetrate the confining zone per 146.84(c)(2). Any well that penetrates the confining zone, even if it does not extend all the way through the confining formation, is to be included in the tabulation. EPA is issuing guidance on how to identify all wells that require corrective action. 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.

Corrective action must be performed on wells determined to need corrective action in order toprevent movement of fluid into or between USDWs, therefore some wells above the confining zone may not be required to undergo corrective action; however, such a determination will be based on site-specific information.

Commenter Name: Kurt Waltzer Letter ID: 0250 Commenter Organization: Clean Air Task Force Comment ID: 22294

Comment: Class VI applicants should be required to identify all known wells penetrating formations affected by increased pressure

Response: EPA clarifies that under 146.84(c)(2)operators must identify all penetrations of the confining zone in the AoR for the GS project. This area would encompass both the CO2 plume and areas of increased pressure associated with CO2 injection, regardless of which is larger.

Commenter Name: Michel Paque Letter ID: 0259 Commenter Organization: Ground Water Protection Council Comment ID: 24854 Other EPA Comment Codes and Descriptions: 1220 1.1.1.1 Terminology and definitions

Comment: Rule Provision: 146.81(d) Definitions

EPA Proposal: (d) Definitions. The following definitions apply to this subpart. To the extent that these definitions conflict with those in § 146.3 these definitions govern:

Area of review means the region surrounding the geologic sequestration project that may be impacted by the injection activity. The area of review is based on computational modeling that accounts for the physical and chemical properties of all phases of the injected carbon dioxide stream.

GWPC Recommendations: Area of review means the subsurface three-dimensional extent of the carbon dioxide stream plume associated pressure front, and displaced brine, as well as the overlying formations and surface area above that delineated region.

Rationale: Suggest removal of the second sentence and replacement with : "It includes the subsurface three-dimensional extent of the carbon dioxide plume, associated pressure front, and displaced brine, as well as the surface area above that delineated region."

Comment on the inclusion of the word "surrounding" because the AoR should be coextensive with the area defined by the Carbon Sequestration Project. Inclusion of "surrounding" makes this definition open-ended and ambiguous.

Response: Based on review of all public comments on the AoR definition at 146.84(a), the Agency has modified it to read as follows: The region surrounding the geologic sequestration project where USDWs may be endangered by the injection activity. The area of review is delineated using computational modeling that accounts for the physical and chemical properties of all phases of the injected CO2 stream and is based on available site characterization, monitoring, and operational data. The definition in the proposed rule accounted for the varying physical and chemical properties of the CO2 including free-phase and water-dissolved CO2, as the commenter suggests. The definition inthe final rule will continue to do so. 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.

Letter ID: 0263 Commenter Organization: Interstate Oil & Gas Compact Commission Comment ID: 22796

Comment: III A. 2 Proposed Area of Review and Corrective Action Requirements

IOGCC General Comment for Section lIl. A. 2: The IOGCC believes use of traditional well specific AoR is problematic for comprehensive site characterization and licensing. The IOGCC has recommended in its report a site characterization and licensing process that includes elements such as geologic and engineering evaluation, modeling, amalgamation of property rights and other appropriate elements that we believe exceeds the capacity of the traditional AoR to accomplish.

Response: EPA agrees that the AoR for a GS project should incorporate site characterization include elements such as geologic and engineering evaluation, modeling, and other appropriate elements, EPA clarifies that the area of review must be delineated using computational modeling that is based on available site characterization, monitoring, and operational data. EPA is developing guidance on AoR and corrective action at GS Class VI sites to assist owners/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 clarifies that the purpose of the GS regulation is to ensure the safe injection of CO2 through GS wells in order to protect USDWs from endangerment. Property, water, or mineral rights possibly affected by a GS project are outside the scope of this rule and therefore are not incorporated into the AoR definition at 146.84(a).

Commenter Name: Mark Vickery Letter ID: 0280 Commenter Organization: Texas Commission on Environmental Quality Comment ID: 24100

Comment: (b) Concern exists that the proposed rules would require the operator to have surface access to large areas of land possibly under separate ownership. This concern would apply to the proposed requirements for performance of necessary corrective action on unplugged wells, data acquisition such as in seismic surveys, and location and sampling of monitor wells or other monitoring stations. In TCEQ's experience, adoption of a rule requirement for 3-D seismic surveys over the area of review in permit applications for Class I well waste disposal in engineered salt caverns illustrates this concern. Permit applicants were not able to obtain permission from surface owners to run these surveys in all areas required by the rules. Off-site access needed for compliance with the proposedCO2-GS rules may therefore be problematic.

Response: EPA clarifies that the purpose of the corrective action requirement at 146.84(d) is to ensure that all wells in the AoR that have the potential to cause the movement of CO2 or other fluids into or between USDWs receive appropriate corrective action. In general, to meet this requirement, the owner or operator will most likely need to obtain the right of access to wells that may require corrective action, and demonstrate they have done this in their proposed AoR and corrective action plan. In the AoR and corrective action plan, the owner or operator must describe how site access will be guaranteed for future corrective action.

Commenter Name: Scott Anderson Letter ID: 0510 Commenter Organization: Environmental Defense Fund Comment ID: 21221

Comment: We're pleased that 146.84 requires modeling both of the CO2 plume and of the

extent of formation fluid and movement.

Response: EPA acknowledges the comment; the final rule retains this provision.

Commenter Name: Scott Anderson Letter ID: 0510 Commenter Organization: Environmental Defense Fund Comment ID: 21228

Comment: We, three more things, we think the rule needs to assure that AoRs are calculated as intended and updated as necessary, we think a 10-year minimum is

too short.

And we think that there's just an unintentional flaw in the definition of area of review, it doesn't seem to specifically require the consideration of the pressure front and would refer you to the second sentence of the definition of geologic sequestration project for the kind of language we think needs to be imported into the AoR definition.

Response: EPA agrees that the AoR definition should account for the impact of the CO2 plume on USDWs. The Agency has carefully considered all comments on the AoR definition at 146.84(a) and modified it to read as follows: The region surrounding the geologic sequestration project where USDWs may be endangered by the injection activity. The area of review is delineated using computational modeling that accounts for the physical and chemical properties of all phases of the injected CO2 stream and is based on available site characterization, monitoring, and operational data. The computational models used for this purpose are required to predict the fate of injected CO2 and changes in formation pressure. EPA believes that the requirements at 146.84(c)(1) to delineate the AoR using computational modeling are appropriate and encompass the significant processes that could affect the location of the CO2 plume and associated pressure front.

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 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.Commenter Name: Talib Syed Letter ID: 0537

Comment ID: 21470

Comment: I just want to give a few minor, just highlight maybe two or three points that in my opinion are important. The first thing is I think we have to pay a little bit of attention to just transposing the area of review concept that they used to with the UIC program to the CO2 geologic sequestration program. And the reason is, it is not in my opinion, the same concept that we had when we were disposing of water, etcetera. So we have got buoyancy affects to regard to take into consideration and that may be a bigger impact n what the zone of endangering influence is. And I believe that has not been taken into consideration at all and just transposing the zone of endangering influence as we are used to with the water etcetera in the UIC program, without incorporating buoyancy affects, that is an issue that needs to be very carefully taken into

consideration.

Response: EPA agrees that the buoyancy of CO2 must be accounted for in delineating the AoR for GS projects. Buoyancy is one of the characteristics of CO2 injected for GS that served as a catalyst for the development of tailored UIC requirements for GS. The Agency clarifies that employing multiphase computational modeling to determine the AoR as required at 146.84(c) will result in a more accurate prediction of the fate of CO2 and changes in formation pressure. Computational models used to delineate the AoR must consider the buoyant nature and specific properties of separate phases of the injected CO2 and native fluids within the injection zone.

Comment Code: 3300 2.2.1 Delineating the AoR/Modeling CO2 movement



### Individual Comments

Commenter Name: Michael H. Cochran Letter ID:

0108 Commenter Organization: Bureau of Water, Division of Environment, Kansas Department of Health & Environment (KDHE) Comment

ID: 21961 Other EPA Comment Codes and Descriptions: 1220 1.1.1.1 Terminology and definitions

Comment: For the definition of AoR it needs to be realized that the AoR could be quite sizeable potentially covering many square miles. We suggest using the criteria for the AoR as found in existing 146.6 and for the Pressure Front definition. Otherwise, the AoR as defined could make it impractical to accomplish the work required.

For Geologic Sequestration Project definition, our comments for the AoR definition apply also.

Response: The Agency has carefully considered all comments on the AoR definition at 146.84(a) and modified it to read as follows: The region surrounding the geologic sequestration project where USDWs may be endangered by the injection activity. The area of review is delineated using computational modeling that accounts for the physical and chemical properties of all phases of the injected CO2 stream and is based on available site characterization, monitoring, and operational data.Commenter Name: Michael H. Cochran Letter ID:

0108 Commenter Organization: Bureau of Water, Division of Environment, Kansas Department of Health & Environment (KDHE) Comment

ID: 21970

Comment: 146.84 (c)(1): The CO2 plume will never cease moving. Even deep formations have a natural flow gradient. There will also likely be movement due to density gradients and diffusion.

Response: EPA agrees with the commenter that there may be cases where movement of the CO2 plume will never cease due to gradient, diffusion, and density gradients; however, EPA believes that plume movement may stabilize at a point where movement of the CO2 plume slows or pressures in the injection zone sufficiently decline to the point that they no longer pose an endangerment to USDWs. EPA believes that in all cases, these criteria will be met at some point after the cessation of injection. As discussed in the preamble to the proposed GS regulation and the associated background document, "Computational Modeling of Underground Injection of Carbon Dioxide for Determination of Area-of-Review and Potential Risk to Underground Sources of Drinking Water" (cited in the proposed rule preamble as USEPA, 2008d), research has shown that CO2 may continue to migrate for a period of time after injection ceases.

For this reason, the GS regulation does not specify a timeframe over which the AoR delineation model should run. Rather, the model should be used to predict the ultimate plume movement up to the point the plume movement ceases or pressures in the injection zone sufficiently decline to the point that they no longer pose an endangerment to USDWs.

Commenter Name: Leslie Savage Letter ID: 0122 Commenter Organization: Railroad Commission of Texas (RRC) Comment ID: 24770 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: §146.84 Area of review and corrective action.

(a) The area of review is the region surrounding the geologic sequestration project that may be impacted by the injection activity. The area of review is based on computational modeling that accounts for the physical and chemical properties of all phases of the injected carbon dioxide stream.

{Redundant - same as the definition of "area of review."}

Response: Based on review of all public comments on the AoR definition at 146.84(a), the Agency has modified it to read as follows: The region surrounding the geologic sequestration project where USDWs may be endangered by the injection activity. The area of review is delineated using computational modeling that accounts for the physical and chemical properties of all phases of the injected CO2 stream and is based on available site characterization, monitoring, and operational data.

Commenter Name: Leslie Savage Letter ID: 0122 Commenter Organization: Railroad Commission of Texas (RRC) Comment ID: 24774 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: (1) Predict, using computational modeling, the projected lateral and verticalmigration of the carbon dioxide plume and formation fluids in the subsurface from the commencement of injection activities until the plume movement ceases, pressure differentials sufficient to cause the movement of injected fluids or formation fluids into a USDW are no longer present, or FOR after a fixed time period as determined by the Director. The modelINGmust:

Response: EPA has clarified this language in the final rule. It now reads, “Predict, using existing site characterization, monitoring and operational data, and computational modeling, the projected lateral and vertical migration of the carbon dioxide plume and formation fluids in the subsurface from the commencement of injection activities until the plume movement ceases, until pressure differentials sufficient to cause the movement of injected fluids or formation fluids into a USDW are no longer present, or until the end of a fixed time period as determined by the Director.”

Commenter Name: Leslie Savage Letter ID: 0122 Commenter Organization: Railroad Commission of Texas (RRC) Comment ID: 24775 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: (i) Be based on detailed geologic data collected to characterize the injection zone AND, confining zone and any additional zones ; and anticipated operating data, including injection pressures, rates and total volumes over the proposed life of the geologic sequestration project; (ii) Take into account RELEVANT any geologic heterogeneities AND, data quality, and their possible impact on model predictions; and (iii) Consider potential migration through KNOWN faults, fractures, and artificial penetrations.

Response: The final rule retains this requirement as proposed, except that 146.84(c)(1)(ii) also requires owners or operators to take into account other discontinuities in addition to geologic heterogeneities.

EPA disagrees that only the injection and confining zones should be included in AoR modeling of GS sites. EPA believes that the modeling should also take into account the possibility of displaced fluids or brines caused by a lateral and/or vertical pressure plume, and therefore it may be necessary to include additional zones along with the confining/injection zones to ensure the integrity of the confining zone and ultimately protect a USDW from endangerment.

Commenter Name: Anonymous2 Letter

ID: 0133 Commenter Organization: Sierra Club National Global Warming and Energy Committee and Sierra Club California-Nevada Regional Conservation Committee on Energy and Climate Change Comment

ID: 21603

Comment: In contradistinction to the workgroup's Recommendation 3.1, neither the proposed definition of the Area of Review (AOR) contained in 40 CFR 146.81(d) nor the Required Class VI Permit Information for initially permitting the AOR under 40 CFR 146.82, stipulate that the AOR be determined using --among other techniques -- modeling along three dimensions. The three dimensional modeling requirement only appears in the proposed definition for the phrase Geologic Sequestration Project at 40 CFR 146.81(d). Likewise, Recommendation 3.1's inclusion of "theassociated pressure front" as a required modeling target along with the CO2 plume -- neither appears in the Area of Review definition nor its permitting language under 40 CFR 146.82 [Required Class IV Permit Information], but does appear in the definition of the Geologic Sequestration Project at 146.81(d). Conversely, the Geologic Sequestration Project is not named as the targeted area for the initial permitting information required for Class VI injection wells at section 146.82, and is only mentioned later in the protocols at section 146.84 (a) [Area of Review and Corrective Action]. These discrepancies and omissions may lead to confusion regarding the nature and extent of the modeling required at the outset for determining each AOR and its continuing viability, and could be corrected by inserting the workgroup's recommended AOR language in the Definitions and the Required Class IV Permit Information sections.

Response: EPA disagrees that the term “three dimensional” that is in the definition of the Geologic Sequestration Project must necessarily be repeated in the AoR requirement for modeling for that modeling to be implicitly three-dimensional. The intent of the AoR, a long-standing concept within the UIC Program, is to delineate the surface area and all subsurface formations below it that may potentially be impacted by injection activity. Acceptable delineation models will provide predictions of CO2 fate and transport, as well as changes in formation pressure, in three dimensions as a function of time that can be used to delineate the subsurface storage site and the AoR. Although EPA disagrees with the commenter's suggestions, the Agency has carefully considered all comments on the AoR definition at 146.84(a) and modified it to read as follows: The region surrounding the geologic sequestration project where USDWs may be endangered by the injection activity. The area of review is delineated using computational modeling that accounts for the physical and chemical properties of all phases of the injected CO2 stream and is based on available site characterization, monitoring, and operational data.

EPA believes that this definition is sufficiently broad and describes both the intent of the computational modeling and the relationship of the AoR to areas that are subject to the risks associated with injection.

Commenter Name: Christine Reimer Letter ID: 0142 Commenter Organization: National Ground Water Association Comment ID: 22551 Other EPA Comment Codes and Descriptions: 3400 2.2.2 Corrective Action

Comment: Area of Review and Corrective Action

In the context of carbon storage, NGWA thinks it is important to distinguish between the CO2 plume footprint and the zone of elevated pressure. The rationale is given in the next section, but the following conditions should be met:

- No fixed radius can be used, a zone of endangering influence (ZEI) must be determined through modeling (but cannot be smaller than 1⁄4 mile in its smallest horizontal dimension) - In the volume generated by the CO2 plume footprint (plus appropriate buffer) (this volume is defined as the "primary AOR"): all penetrations between the base of the injection formation and the base of the USDW should be reviewed and any necessary corrective action should be taken before start of project.

- In the elevated pressure area but outside of the CO2 plume footprint (definedas the "secondary AOR"), all current penetrations through the primary seal and the injection formation should be reviewed. However the applicant should be allowed to perform corrective action in a pseudo-concentric phased manner ahead of and according to the development of the pressure plume.

- Secondary AOR/zone of elevated pressure cannot be computed independently of other injection projects in the vicinity. The impact of other sequestration projects must be included in determining injection rate / period of injection.

- Primary and secondary AOR must be periodically reviewed to ensure that modeling predictions are met. If they are not, the primary and secondary AOR should be revisited. The operator should keep track of any new penetration in the primary AOR volume and secondary AOR (for example, for oil and gas industry).

"Primary AOR" - Why "Volume of Review"

Because CO2 is strongly buoyant, it is not sufficient only to investigate penetrations in the injection formation and primary seal. The whole volume potentially contacted by the CO2 plume should be reviewed. The review and corrective actions should be performed before the start of injection because there is no stopping the CO2 migration once started. The greatest degree of effort should be on the deeper wells in the injection zone and primary containment then on the secondary containment and seal (if any) and then on shallower wells but as many as possible of the shallower wells should be compiled too.

Delayed Corrective Action for "Secondary AOR"

A simple time-dependent secondary AOR that expands as the volume of injection increases and the CO2 migrates is not acceptable. The secondary AOR should be agreed upon and reviewed before injection starts but corrective action can be somewhat delayed. The secondary AOR consists of only the injection formation and seal as used in the current rules because only brine/formation water leakage is an issue in the elevated pressure area. The likely presence of a large elevated pressure area does not make realistic imposing corrective action on all wells before the start of a project. There is no need to provide corrective action to wells before the pressure significantly rises. If another problem (e.g., CO2 leakage) occurs earlier at another location and injection stops, pressure will not keep rising and will drop. In addition, delaying corrective action will allow taking advantage of technical improvements that will undoubtedly occur in

the next decades.

Response: EPA agrees that the AoR for a GS project should incorporate both the CO2 plume and the pressure front, and clarifies that the requirements for AoR delineation in the final rule incorporate both the CO2 plume and associated pressure front. This area would be modeled based on anticipated CO2 volumes to be injected and other site-specific information that would impact pressure changes in the subsurface. EPA agrees that both of these should be taken into account in determining corrective action needs and developing a testing and monitoring plan, and that the requirement to delineate the AoR at §146.84(c) addresses the potential risks raised by thecommenters. EPA believes that the final GS requirements for delineating the AoR provide sufficient protection to USDWs, without introducing an overly complex regulatory process.

EPA acknowledges the commenter’s support of phased corrective action and 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.

Commenter Name: Christine Reimer Letter ID: 0142 Commenter Organization: National Ground Water Association Comment ID: 22595 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Proposed Rule: 146.84(c)(1)(i)

Proposed revision: (i) Be based on detailed geologic data collected to characterize the injection zone, confining zone(s), transmissive monitoring zones and any additional zones; and anticipated operating data, including injection pressures, rates and total volumes over the proposed life of the geological sequestration project;

Rationale: NGWA proposes that if there are secondary confining units that they should be included in the site model along with any transmissive zones between the primary and secondary confining units.

Response: EPA agrees that additional confining and containment zones should be accounted for in the AoR delineation if site-specific circumstances indicate a need for this. 146.84 (c)(1)(i) specifies that computational modeling should be based on detailed geologic data collected to characterize the injection zone and confining zone, as well as any additional zones.

Commenter Name: Bonnie Lovelace Letter ID: 0152 Commenter Organization: Montana Department of Environmental Quality (MDEQ) Comment ID:

22122

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.

Response: The final rule leaves 144.55 unchanged; i.e., Class VI wells are not addressed in this provision.

Commenter Name: Michael Mudd Letter ID: 0167 Commenter Organization: FutureGen Alliance (FGIA) Comment ID: 22458 Other EPA Comment Codes and Descriptions: 4600 2.6 Proposed Plume and Pressure Front Monitoring Requirements (40 CFR 146.90)

Comment: Area of Review (AoR) and Area of Monitoring (AoM)p. 43493, c. 2 The Proposed Rule defines Area of Review (AoR) as "The region surrounding the geologic sequestration project that may be impacted by the injection activity". The area of review is based on computational modeling that accounts for the physical and chemical properties of all phases of the injected

carbon dioxide stream.

The proposed regulation uses the Area of Review (AoR) for defining both monitoring requirements and corrective actions:

p. 43499, c. 1 Area of Review (AoR) and Corrective Action: The Agency requires

examination of both the vertical and horizontal extent of the area that will potentially be influenced by injection and storage activities and identification of all artificial penetrations in the area that may act as conduits for fluid movement into USDWs (e.g., active and abandoned wells) and, as needed, perform corrective action to these open wells (i.e., artificial penetrations).

p. 43539, c. 3 (d)(2) The monitoring frequency and spatial distribution of monitoring wells must be based on baseline geochemical data that has been collected under §146.82(a)(6) and any modeling results in the area of review evaluation required by §146.84(b);

Comment:

- EPA should define two regulatory regions surrounding the geologic sequestration project and provide specific definitions for those regions; 1) Area of Monitoring (AoM) and 2) Area of Review; where the AoM is used to define the spatial distribution of monitoring wells and the AoR is used to define the

limit of Corrective Action:

- Area of Monitoring (AoM): The region surrounding the geologic sequestration project that contains 95% of the carbon dioxide mass. The area of monitoring is based on monitoring data and computational modeling that accounts for the physical and chemical properties of all phases of the injected carbon dioxide stream. In the absence of monitoring data, the area of monitoring is based on computational modeling.

- Area of Review (AoR): The region surrounding the geologic sequestration reservoir that has or is indicated to develop pressures that are greater than 10% different from the pre-injection formation fluid pressure, but no less than the Area of Monitoring. The area of review is based on monitoring data and computational modeling that accounts for the physical and chemical properties of all phases of the injected carbon dioxide stream. In the absence of monitoring data, the area of review is based on computational modeling.

• The proposed definitions of AoM and AoR have several important components:

- The AoM has a mass-based definition.

- The AoR has a pressure-differential-based definition.- The AoR is never smaller than the AoM.

- The AoR and AoM may be asymmetrical around the injection well(s).

- The AoR and AoM may vary over time.

- The carbon dioxide mass should be determined using a combination of monitoring data and computational modeling.

- Pressure differentials are based on equilibrium hydrostatic conditions.

Relative to existing UIC regulations governing waste disposal, EPA is introducing fundamentally new concepts for defining the area of review (AoR) for CO2 injection. The newly proposed concept is flawed and will pose an unjustifiable barrier to CO2 injection projects unless the approach for defining the AoR is addressed in the regulation. It is neither possible, nor practical, to predict where every molecule of CO2 will migrate; therefore, a threshold levels are required. In the case of large-scale injection projects, changes in formation pressures could be expected dozens to hundreds of miles from the injection well. It would not be practical for the AoR to comprise the entire area experiencing changes in formation pressure. A reasonable threshold for establishing the AoM might be where pressure changes are greater than 10% of the standard formation pressure.

The proposed regulation defines the Area of Review (AoR) as being the region that may be impacted by the injection activity, without defining or quantifying impact. To be useful the bounding areas for corrective actions and monitoring activities must have specific definitions. Under deep geologic sequestration conditions the injected fluid (i.e., supercritical CO2) has low compressibility, the displaced fluid (i.e., brine) has low compressibility, and the reservoir formation (e.g., sandstone) generally has low compressibility, all of which suggest that the impact (i.e., pressure change) of the injection activity could be detected at great distances from the injection well(s).

Injection of CO2 into deep saline formations is driven by differences between the well injection pressure and formation pressure. To avoid inducing fractures or opening existing fractures in the formation and caprock, well injection pressure will be limited to some fraction below the fracturing pressure. As CO2 migrates into the formation the formation pressure increases around the injection well. The pressure distribution in the formation around the injection well depends on the formation properties, structure, and injection rate. Injection formations will be required to be confined vertically and/or horizontally to prevent the vertical migration of injected fluids and saline

reservoir fluids into USDWs.

Confined formations (e.g., a caprock overlying a horizontally extensive formation) allow the formation fluid to be displaced laterally by the injected fluid. Injecting CO2 will result in elevated pressures both inside and beyond the CO2 plume. Elevated pressures within the CO2 plume have the potential to force CO2 and formation fluid through permeable wells, fractures, or faults thatpenetrate the formation. Elevated pressures outside the CO2 plume have the potential to force formation fluid through permeable wells, fractures or faults that penetrate the formation. The higher the formation pressure is above the ambient formation pressure, the greater the potential for CO2 and formation fluid to leak through permeable wells, fractures, and faults. The lateral pressure distribution is a function of the injection rate and the lateral distribution of formation permeability. When CO2 injection is halted, elevated pressures decay over time as the injected and formation fluids migrate away from the injection well(s).

The proposed regulations define an AoR and Corrective Action as being an area within which artificial penetrations may act as conduits for fluid movement into USDWs (e.g., active and abandoned wells) and, as needed, require the applicant to perform corrective action to seal these open wells. The potential for fluid movement into USDWs from the injection of CO2 into the injection formation is correlated with the area of elevated formation pressure, which is usually larger than the area that contains the injected CO2 mass. For confined formations, this area is defined by the lateral pressure distribution around the injection well(s).

Response: EPA believes that, while the commenter offers different terminology for the AoR and the area to be monitored, the GS rule addresses the commenter's suggestions. Notably, the owner or operator is required (under 146.90) to develop and implement a testing and monitoring plan for each GS project that must consider the delineated AoR that includes both the CO2 plume and associated pressure front and incorporates many of the attributes suggested by the commenter. EPA clarifies that delineation of the AoR, as required at 146.84(c), must account for the physical and chemical properties of all phases of the injected CO2 stream, based on available site characterization, monitoring, and operational data.

Furthermore, any changes to the AoR would necessitate a review of and potential change in the testing and monitoring plan, consistent with the commenter's assertion that the AoR may vary over time. The final GS regulation includes a requirement at 146.84(e) that the AoR be reevaluated at least every 5 years, and also requires that the owner or operator review the AoR and corrective action, testing and monitoring, and emergency and remedial response plans within one year of an AoR reevaluation (as well as following significant changes to the facility, or when required by the Director). The relationship between the AoR reevaluation and the testing and monitoring plan should allow for considerations suggested by the commenter.

EPA believes that by linking development and review of the testing and monitoring plan to the AoR evaluation and reevaluation process, the GS rule, in effect, incorporates and addresses many of the commenter's considerations for an area of monitoring.

Commenter Name: Michael J. Miller Letter ID: 0168 Commenter Organization: Electric Power Research Institute (EPRI) Comment ID: 22492 Other EPA Comment Codes and Descriptions: 4650 2.6.5 CO2 plume and pressure front tracking (seeking comment)

Comment: Preamble, page 43505: "The confining system should be of sufficient regional thickness and lateral extent to contain the entire CO2 plume and associated pressure front under the confining system following the plume’s maximum lateralexpansion."

EPRI COMMENT #2: The criteria for defining the leading edge of the plume and associated pressure front are not specified in the rule, nor is the basis for determining if these criteria are met -- physical measurement or numerical computation. In either case, what minimum change in pressure from background will EPA use to define the location of the pressure front? Will the lateral extent of the CO2 plume be defined by the leading edge of the dissolved plume or free-phase portion of the plume? Given the difficulties in defining and measuring the leading edge of the plume and pressure front, EPRI believes that the technical focus should be on demonstrating caprock containment, rather than tracking fronts.

Response: EPA agrees that demonstrating cap rock containment is an important technical focal point for permitting Class VI wells, however the Agency also believes that it is important to know the extent of the CO2 plume and pressure front to ensure cap rock integrity and protection of USDWs.

EPA clarifies that the pressure front (defined at §146.81) is the zone of elevated pressure that is created by the injection of CO2 into the subsurface. The pressure front of a CO2 plume refers to a zone where there is a pressure differential sufficient to cause the movement of injected fluids or formation fluids into a USDW. The pressure front includes all areas wherein pressure is great enough to cause fluid movement into a USDW if a conduit were to exist.

The calculation of the threshold pressure that defines the edge of the pressure front is dependent on properties of the injection and confining zones, including permeability, porosity, and compressibility, the distance between the injection zone and the lowermost USDW, and operational conditionsincluding injection pressure and rate. For these reasons, the definition of the pressure front is siteand project-specific, and a single pressure value can not be provided for all sites. 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 is also developing guidance on testing and monitoring to assist owners or operators and Directors in evaluating requirements under §146.90, which will include discussion of identifying the extent of the CO2 plume. 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. The guidance can be found on EPA’s website at http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm. In addition, in January 2009, DOE published a best practices manual entitled "Monitoring, Verification, and Accounting of CO2 Stored in Deep Geologic Formations" (DOE/NETL-311/081508); this

manual is included in the docket for the for the final GS rule.

Commenter Name: Theresa Pugh Letter ID: 0169 Commenter Organization: American Public Power Association Comment ID: 23429Comment: to use geologic sequestration in a very responsible manner. First, many states have not conducted modeling on groundwater use and availabity in decades, and the earlier modeling may have used outdated models and information. In non-oil and gas states (or perhaps some mining states) there is little known about the subsurface geology. While APPA greatly appreciates the maps and placement analysis modeling conducted by U.S. Geological Service or "USGS", Batelle, NETL/DOE and others. We do not believe that we have preliminary characterizations or pre-commercial data as to underground formations suitable for injection and long-term storage of CO2. Nor do we know what the storage

Response: EPA acknowledges that some states do not have much geological and hydrogeologic data. For this reason, it is important that owners or operators gather new site-specific data and conduct new modeling for each GS project. The Agency believes that AoR delineation using computational modeling that accounts for the multiphase flow of CO2 and native fluids (i.e., naturally occurring salty water), including density-driven flow (i.e., buoyancy), is necessary to ensure protection of USDWs from endangerment. The computational models used for this purpose are required to predict the fate of injected CO2 and changes in formation pressure. EPA believes that the requirements at 146.84(c)(1) to delineate the AoR using computational modeling are appropriate and encompass the significant processes that could affect the location of the CO2 plume and associated pressure front. 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.

EPA has evaluated technical documents regarding several computational models that may be used for GS sites. Based on this review (as documented in the AoR section of the preamble to the proposed GS regulation and the background document "Computational Modeling of Underground Injection of Carbon Dioxide for Determination of Area-of-Review and Potential Risk to Underground Sources of Drinking Water"), EPA believes that several models meet the minimum requirements for models in the GS regulation.

Commenter Name: Kyle Isakower Letter ID: 0170 Commenter Organization: American Petroleum Institute Comment ID: 24130 Other EPA Comment Codes and Descriptions: 1220 1.1.1.1 Terminology and definitions

Comment: Definition of Geological Sequestration Project (GSP) and Area of Review (AoR)

EPA's definitions of GSP and AoR require alignment. Currently the GSP and AoR definitions confusingly use different wording to describe similar concepts. It is API's view that these definitions should be essentially the same. API offers languages in our detailed edits that achieve

this.

Response: Based on review of all public comments on the AoR definition at 146.84(a), the Agency has modified it to read as follows: The region surrounding the geologic sequestration project where USDWs may be endangered by the injection activity. The area of review is delineated using computational modeling that accounts for the physical and chemical properties of all phases of the injected CO2 stream and is based on available site characterization, monitoring, and operational data. The definition in the proposed rule accounted for the varying physical and chemical properties of theCO2, including free-phase and water-dissolved CO2. The definition in the final rule will continue to

do so.

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.

Commenter Name: Kyle Isakower Letter ID: 0170 Commenter Organization: American Petroleum Institute Comment ID: 24158 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Rule Provision: 146.84(a)

API Comments: (a) The area of review is the region surrounding the geologic sequestration project that may be impacted by the injection activity. The area of review is based on computational modeling that accounts for the physical and chemical properties of all phases of the injected carbon dioxide stream. THE SUBSURFACE THREE-DIMENSIONAL EXTENT OF THE CARBON DIOXIDE PLUME,

ASSOCIATED PRESSURE FRONT, AS WELL AS THE OVERLYING FORMATIONS AND SURFACE AREA

ABOVE THAT

DELINEATED REGION.

Rationale: Edits make this provision consistent with the definition of "Area of Review", which was revised.

Response: EPA disagrees that the AoR definition needs to specifically include the overlying formations and surface area above the delineated region. The intent of the AoR, a long-standing concept within the UIC Program, is to delineate the surface area and all subsurface formations below it that may potentially be impacted by injection activity. Acceptable delineation models will provide predictions of CO2 fate and transport, as well as changes in formation pressure, in three dimensions as a function of time that can be used to delineate the subsurface storage site and the AoR. Although EPA disagrees with the commenter's suggested change, the Agency has carefully considered all comments on the AoR definition at 146.84(a) and modified it to read as follows: The region surrounding the geologic sequestration project where USDWs may be endangered by the injection activity. The area of review is delineated using computational modeling that accounts for the physical and chemical properties of all phases of the injected CO2 stream and is based on available site characterization, monitoring, and operational data. EPA believes that this definition is sufficiently broad and describes both the intent of the computational modeling and the relationship of the AoR to areas that are subject to the risks associated with injection.

Commenter Name: Kyle Isakower Letter ID: 0170 Commenter Organization: American Petroleum Institute Comment ID: 24161 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rulelanguage

Comment: Rule Provision: 146.84(c)(1)

API Comments: (1) Predict, using computational modeling, the projected lateral and vertical migration of the carbon dioxide plume and formation fluids in the subsurface from the commencement of injection activities until the plume movement ceases, pressure differentials sufficient to cause the movement of injected fluids or formation fluids into a USDW are no longer present, or

after FOR a fixed time period as determined by the Director. The model

MODELING must:

Rationale: Clarification.

Rule Provision: 146.84(c)(1)

API Comments: (i) Be based on detailed geologic data collected AVAILABLE to characterize the injection zone, confining zone and any additional zones ; and anticipated operating data, including injection pressures, rates and total volumes over the proposed life of the geological sequestration project THE DURATION OF INJECTION; (ii) Take into account any RELEVANT geologic heterogeneities, AND data quality, and their possible impact on model predictions; and

Rationale: Allows the use of all available data, not just data collected specifically for this permit.

Response: EPA has clarified the language in §146.84(c)(1) for the final rule. It now reads, “Predict, using existing site characterization, monitoring and operational data, and computational modeling, the projected lateral and vertical migration of the carbon dioxide plume and formation fluids in the subsurface from the commencement of injection activities until the plume movement ceases, until pressure differentials sufficient to cause the movement of injected fluids or formation fluids into a USDW are no longer present, or until the end of a fixed time period as determined by the Director.”

The final rule retains §146.84(c)(1)(ii) as proposed, except that it now requires owners or operators to take into account other discontinuities in addition to geologic heterogeneities when determining

the AoR.

EPA disagrees that only the injection and confining zones should be included in AoR modeling of GS sites. EPA believes that the modeling should also take into account the possibility of displaced fluids or brines caused by a lateral and/or vertical pressure plume, and therefore it may be necessary to include additional zones along with the confining/injection zones to ensure the integrity of the confining zone and ultimately protect a USDW from endangerment.

Commenter Name: James Rower Letter ID: 0173 Commenter Organization: Utility Solid Waste Activities Group (USWAG) Comment ID: 23465 Other EPA Comment Codes and Descriptions: 3140 2.1.4 Comments that the proposed geologic data requirements are too stringent

Comment: • The Final Rule must not make the application process overly burdensome or unrealistic by requiring detailed information that may not be available at thetime of the initial application; instead, the Final Rule should allow for submission of updated information regarding a CO2 GS well and its AoR as that

information becomes available.

Response: EPA agrees that not all of the information listed at §146.82 of the proposed regulation will be available at the time the owner or operator develops their initial permit application. In response to comments and based on an evaluation of the proposed requirements at §146.82, the Agency revised this subpart so that the final regulation specifies separate requirements for information to be submitted with the permit application and before well construction is approved (at §146.82(a)) and information to be submitted before operation of the well is authorized (at §146.82(c)).

EPA believes that this revision of §146.82 addresses commenters' concerns regarding the timing of information to be submitted. In addition, §146.82 in the final rule is similar to the permit application requirements for other injection well classes, which could help avoid confusion about how to meet the permitting requirements for Class VI wells. The requirements at §146.82(c) for information to be submitted before operation of the well is authorized are very similar to those for Class I wells, with modifications and additions that address the unique challenges and types of data collected for GS

wells.

Commenter Name: Frederick R. Eames Letter ID: 0178 Commenter Organization: CCS Alliance Comment ID: 23874 Other EPA Comment Codes and Descriptions: 1220 1.1.1.1 Terminology and definitions

Comment: EPA defines "area of review" as "the region surrounding the geologic sequestration project that may be impacted by the injection activity. The area of review is based on computational modeling that accounts for the physical and chemical properties of all phases of the injected carbon dioxide stream." The phrase "may be impacted" is too vague, The AoR delineation should be based on or limited by certain risk criteria; otherwise, an AoR could cover an inappropriately large area that could be expensive to review and characterize.

Response: EPA agrees with commenters that further clarity is needed with regard to the boundaries of the AoR. After considering the public comments on the proposed GS regulation, EPA has augmented the definition of AoR to better encompass the area that may be impacted by the injection activity (i.e., the "surrounding area" to which the commenter refers). The Agency has modified the AoR definition at 146.84(a) to read as follows: The region surrounding the geologic sequestration project where USDWs may be endangered by the injection activity. The area of review is delineated using computational modeling that accounts for the physical and chemical properties of all phases of the injected CO2 stream and is based on available site characterization, monitoring, and operational

data.

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.Commenter Name: Robert J. Finley Letter ID: 0180 Commenter Organization: Illinois State Geological Survey Comment ID: 23628

Comment: (c)(1)(iii)

What does this mean, "Consider potential migration"? Does this require modeling faults as though they were transmissive even though there may be no evidence of

such?

Response: EPA anticipates that the modeling would consider any potential fluid migration that may exist at the site. If site-specific geologic data indicate that faults at the site are non-transmissive, then

the model need not account for transmissive faults.

Commenter Name: Thomas Curtis Letter ID: 0181 Commenter Organization: American Water Works Association (AWWA) Comment ID: 23652

Comment: In its comments, AWWA makes several recommendations for the following specific items to be included in the final regulation:

- Development of a standard computation flow model to delineate the area of review;

Response: EPA believes that operators should have the flexibility to select models with which they are familiar and that are most appropriate to the site conditions and available data types and amounts. EPA also recognizes that a standardized model for AoR delineations could be effective as long as the model accounts for the expected variations in site conditions, and adds that a state or regional UIC Director has the discretion to select one standard model if it took site-specific

variations into account.

EPA does not envision that members of the public would evaluate the AoR delineation models themselves. The models and their inputs will, by necessity, entail an extensive amount of technical information that may not be easily understood by the public. EPA believes that it is the Director's responsibility, as a steward of public health and the environment, to review models, model inputs, and results and to determine whether the model is appropriate for predicting the AoR, and to distribute information that may be easily understood by the public (e.g., in the form of a fact sheet). However, the models must be made available to the public.

Commenter Name: Thomas Curtis Letter ID: 0181 Commenter Organization: American Water Works Association (AWWA) Comment ID: 23690 Other EPA Comment Codes and Descriptions: 3350 2.2.1.5 Use of proprietary models for GS sites (seeking comment)

Comment: Category: Modeling

EPA Request for Comment: EPA proposes that the owners or operators of GS wells be required to delineate the AoR for CO2 GS sites using computational fluid flow models designed for the specific site conditions and injection regime. EPA seeks comment on the use of modeling for AoR delineation. EPA Notice 43506.

When using a proprietary model, owners or operators should clearly disclose the code assumptions, relevant equations, and scientific basis. EPA seeks comment onallowing the use of proprietary models for GS sites. EPA Notice 43507.

AWWA Response: The proposed rule depends heavily on computer modeling to track the carbon dioxide plume and demonstrate that it is contained within the confining zone. As stated by EPA, some of these models are proprietary and the rule is unclear how or if confirmation of the model results will be provided. Additionally, each of the individual proprietary models can show a different answer to the problem. Owner/operators need to ensure that their basis for the model is static, and that the basis does not change once more details are known about the movement of the plume. For example, the operation of the geologic sequestration system should be adjusted based on modeling results, and the model shouldn't be revised because the plume is moving in a direction not originally predicted.

AWWA recommends that EPA standardize on one specific model that is transparent and available for outside stakeholders to review, including the public. The other option is for EPA to develop a standard model that would be used for all geologic sequestration projects. If EPA were to develop a standard model, a pilot program should be part of the model development so that the modeling results could be validated with real-life monitoring data. In either case, clearly stating the model assumptions made during model set-up is critical, and these assumptions must be made available to stakeholders when they are reviewing

the model results.

Response: The final rule does not require use of a standardized model. As described above, EPA believes that operators should have the flexibility to select models with which they are familiar and that are most appropriate to the site conditions and available data types and amounts. EPA also recognizes that a standardized model for AoR delineations could be effective as long as the model accounts for the expected variations in site conditions, and adds that a state or regional UIC Director could select one standard model if it took site-specific variations into account.

EPA does not envision that members of the public will evaluate the AoR delineation models themselves. The models and their inputs will, by necessity, entail an extensive amount of technical information that may not be easily understood by the public. EPA believes that it is the Director's responsibility, as a steward of public health and the environment, to review models, model inputs, and results and to determine whether the model is appropriate for predicting the AoR, and to distribute information that may be easily understood by the public (e.g., in the form of a fact sheet). EPA adds that its Confidential Business Information requirements at 40 CFR 144.5 will apply to the use of proprietary models.

Commenter Name: Thomas Curtis Letter ID: 0181 Commenter Organization: American Water Works Association (AWWA) Comment ID: 23730 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Part 146.84 It is important to note that the carbon dioxide plume will never cease moving. Even deep formations have a natural flow gradient, and it is likely that there will always be some movement due to changes in density gradients and diffusion. This should be considered when defining the AoR for each project.Response: EPA agrees with the commenter that there may be cases where movement of the CO2 plume will never cease due to gradient, diffusion, and density gradients, but disagrees that the AoR definition at 146.84(a) should describe a never-ending timeframe of CO2 plume movement. The GS regulation recognizes that plume movement may stabilize to a point where movement of the CO2 plume slows or pressures in the injection zone sufficiently decline to the point that they no longer pose an endangerment to USDWs, although movement does not completely cease. EPA believes that in all cases, these criteria will be met at some point after the cessation of injection. As discussed in the preamble to the proposed GS regulation and the associated background document"Computational Modeling of Underground Injection of Carbon Dioxide for Determination of Areaof-Review and Potential Risk to Underground Sources of Drinking Water" (cited in the proposed rule preamble as USEPA, 2008d), research has shown that CO2 may continue to migrate for a period of time after injection ceases.

For this reason, the GS regulation does not specify a timeframe over which the AoR delineation model should run. Rather, the model should be used to predict the ultimate plume movement up to the point the plume movement ceases or pressures in the injection zone sufficiently decline to the point that they no longer pose an endangerment to USDWs.

EPA believes that an iterative process of AoR reevaluation is appropriate to verify that the CO2 plume and pressure front are moving through the subsurface as predicted, verify the accuracy of the delineation model (or identify needed changes), and refine testing and monitoring activities to ensure that USDWs are protected from endangerment and that there would be adequate warning of potential problems at the site before any endangerment could occur. EPA adds that the requirement at 146.93(b) for post-injection site care further ensures that any continued movement of the CO2 plume and pressure front will be addressed until it can be demonstrated that the GS operation no longer poses an endangerment risk to USDWs.

Commenter Name: Thomas Curtis Letter ID: 0181 Commenter Organization: American Water Works Association (AWWA) Comment ID: 23731 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Part 146.84(c)(1)(iii) AWWA recommends revising this part to read:

Consider potential migration through faults, fractures, other discontinuities and artificial penetrations.

Response: EPA did not change 146.84(c)(1)(iii) but instead changed the text at 146.84(c)(1)(ii) to read as follows: "Take into account any geologic heterogeneities, other discontinuities, data quality, and their possible impact on model predictions" to address the water association commenter's concern regarding the potential for migration of CO2 at GS sites.

Commenter Name: Bradley J. Field Letter ID: 0186 Commenter Organization: New York State Dept. of Environmental Conservation

Div. of Mineral Resources Comment ID:

25180

Comment: III A. 2 Proposed Area of Review and Corrective Action Requirements

NYSDEC-DMN General Comment for Section III. A. 2: NYSDEC-DMN believes use oftraditional well-specific AoR is problematic for comprehensive and adequate site characterization, and that EPA’s proposed approach is appropriate.

Response: EPA agrees that the unique aspects of GS merit the use of sophisticated computational modeling for delineation of the AoR, based on site-specific features and geology, including the presence of faults, fractures, and artificial penetrations. EPA believes that computational modeling of the AoR prior to injection will provide the best obtainable estimates of the extent of the CO2 plume over several years of active injection. EPA has strengthened the minimum frequency for the AoR reevaluation from ten years to 5 years (146.84(e)). 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.

Commenter Name: Robert F. Van Voorhees Letter ID: 0190 Commenter Organization: Carbon Sequestration Council Comment ID: 24334 Other EPA Comment Codes and Descriptions: 3310 2.2.1.1 Comments in favor of requiring computational models to delineate the AoR (seeking comment)

Comment: 1. AOR Definition

The proposed rule vaguely defines the AOR as "the region surrounding" the GS project that "may be impacted by the injection activity." 72 Fed. Reg. at 43535 (proposed 40 C.F.R. 146.81(d)). The definition goes on to suggest that the AOR is to be "based on computational modeling that accounts for the physical and chemical properties of all phases of the injected carbon dioxide stream." Id.

There are three issues.

First, the proposed definition suggests the need for a more complex modeling approach than may typically be necessary or appropriate. As experience with hazardous waste injection "no migration" petitions shows, it is rarely necessary to attempt to model chemical changes in the injectate plume; instead conservative modeling of transport should typically be sufficient by itself to show that USDWs will not be endangered. Where this is the case, it is containment of the injectate plume - rather than the precise composition of the plume - that matters and there is no need to model chemical changes. This is a critical point, because it is generally far easier to model transport than chemical changes occurring in the subsurface. In fact, it would be extraordinarily burdensome to have to model "the chemical properties of all phases of the injected carbon dioxide stream" as the proposed rule suggests. Such modeling should be required only to the extent that it is truly necessary to ensure that USDWs will be protected.

Second, the preamble to the proposal suggests that the "best" (most sophisticated?) and most "accurate" modeling should be preferred or even required. 73 Fed. Reg. at 43507. However, fine precision generally isn't necessary, The appropriate goal for modeling is to ensure protection of USDWs, and conservative (i.e., less precise) modeling may be sufficient and even preferable for this purpose. A quest for greater precision would not guarantee greater confidence in modeling results, and could effectively require a less conservative - and thus potentially less protective - modeling approach.Third, the functional purpose of the AOR is to define the area within which impacts of the injection activity could cause endangerment of a USDW; specifically, the AOR defines the area within which corrective action for abandoned boreholes may be necessary to prevent endangerment of USDWs. The language of the proposed rule (i.e., "may be impacted by the injection activity") is not clearly limited to impacts of the injection activity that could cause endangerment of USDW’s. It should be.

Response: EPA believes that predicting the complex, multiphase, buoyant flow of the CO2, coinjectates, 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.

EPA acknowledges that fine precision may not always be necessary and that many factors determine ultimate confidence in modeling results. However, EPA does not believe that more precision would result in a less protective modeling approach. EPA anticipates that the owner or operator, in consultation with the Director, will choose the model that is most appropriate for a particular GS project, and that this dialogue is a key factor in assuring that the GS site is modeled (and eventually operated and tracked) in a manner that protects USDWs from endangerment. EPA encourages and expects owners or operators to use the best multiphase, computational models available.

Commenter Name: Robert F. Van Voorhees Letter ID: 0190 Commenter Organization: Carbon Sequestration Council Comment ID: 24424 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Rule Provision: 146.84(a)

Proposed CCS Group Recommendations: (a) The area of review is the region surrounding the geologic sequestration project that may be impacted by the injection activity. The area of review is based on computational modeling that accounts for the physical and chemical properties of all phases of the injected

carbon dioxide stream. THE SUBSURFACE THREE-DIMENSIONAL EXTENT OF THE

CARBON DIOXIDE PLUME, ASSOCIATED PRESSURE FRONT, AS WELL AS THE OVERLYING

FORMATIONS

AND SURFACE AREA ABOVE THAT DELINEATED REGION.

Basis for CCS Group Comments: Edits make this provision consistent with the definition of "Area of Review", which was revised.

Response: EPA disagrees that the AoR definition needs to specifically include the overlying formations and surface area above the delineated region. The intent of the AoR, a long-standing concept within the UIC Program, is to delineate the surface area and all subsurface formations below it that may potentially be impacted by injection activity. Acceptable delineation models will provide predictions of CO2 fate and transport, as well as changes in formation pressure, in three dimensions,as a function of time that can be used to delineate the subsurface storage site and the AoR. Although EPA disagrees with the commenter's suggested change, the Agency has carefully considered all comments on the AoR definition at 146.84(a) and modified it to read as follows: The region surrounding the geologic sequestration project where USDWs may be endangered by the injection activity. The area of review is delineated using computational modeling that accounts for the physical and chemical properties of all phases of the injected CO2 stream and is based on available site characterization, monitoring, and operational data. EPA believes that this definition is sufficiently broad and describes both the intent of the computational modeling and the relationship of the AoR to areas that are subject to the risks associated with injection.

Commenter Name: Robert F. Van Voorhees Letter ID: 0190 Commenter Organization: Carbon Sequestration Council Comment ID: 24429 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Rule Provision: 146.84(c)(1)

Proposed CCS Group Recommendations: (1) Predict, using computational modeling, the projected lateral and vertical migration of the carbon dioxide plume and formation fluids in the subsurface from the commencement of injection activities until INJECTION INDUCED plume movement ceases, pressure differentials sufficient to cause the movement of injected fluids or formation fluids into a USDW are no longer present, or after FOR a fixed time period as determined by the

Director. The model MODELING must:

Basis for CCS Group Comments: Clarification

Response: Based on an evaluation of all comments received, EPA has clarified this language in the final rule at 146.84(c)(1). It now reads, “Predict, using existing site characterization, monitoring and operational data, and computational modeling, the projected lateral and vertical migration of the carbon dioxide plume and formation fluids in the subsurface from the commencement of injection activities until the plume movement ceases, until pressure differentials sufficient to cause the movement of injected fluids or formation fluids into a USDW are no longer present, or until the end of a fixed time period as determined by the Director.”

Commenter Name: Robert F. Van Voorhees Letter ID: 0190 Commenter Organization: Carbon Sequestration Council Comment ID: 24430 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Rule Provision: 146.84(c)(1)(i) & (ii)

Proposed CCS Group Recommendations: (i) Be based on detailed geologic data

collected AVAILABLE to characterize the injection zone, confining zone and any additional zones ; and anticipated operating data, including injection pressures, rates and total volumes over the proposed life of the geological sequestration project THE DURATION OF INJECTION;

(ii) Take into account any RELEVANT geologic heterogeneities, AND data quality, and their possible impact on model predictions; andBasis for CCS Group Comments: Allows the use of all available data, not just data collected specifically for this permit.

Response: EPA agrees that detailed geologic data is invaluable to modeling an accurate AoR. EPA clarifies that owners or operators may use existing data as well as data collected during site characterization to predict the AoR. The final rule retains the language in §146.84(c)(1)(i) as proposed, and modifies §146.84(c)(1)(ii) slightly to require owners or operators to take into account “other discontinuities” in addition to geologic heterogeneities when predicting the AoR.

EPA disagrees that only the injection and confining zones should be included in AoR modeling of GS sites. EPA believes that the modeling should also take into account the possibility of displaced fluids or brines caused by a lateral and/or vertical pressure plume, and therefore it may be necessary to include additional zones along with the confining/injection zones to ensure the integrity of the confining zone and ultimately protect a USDW from endangerment.

Commenter Name: Robert F. Van Voorhees Letter ID: 0190 Commenter Organization: Carbon Sequestration Council Comment ID: 24431 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Rule Provision: 146.84(c)(1)(iii)

Proposed CCS Group Recommendations: Support the proposed language.

Basis for CCS Group Comments: Agree with EPA’s rationale.

Response: EPA acknowledges the commenter’s support; the final GS rule retains the provision in §146.84(c)(1)(iii) as proposed.

Commenter Name: Robert F. Van Voorhees Letter ID: 0190 Commenter Organization: Carbon Sequestration Council Comment ID: 24438 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Rule Provision: 146.84(g)

Proposed CCS Group Recommendations: (g) The emergency and remedial response plan (as required by § 146.94) and a demonstration of financial responsibility (as described by § 146.85) must account for the entire area of review AS MODIFIED PURSUANT TO § 146.94(F), regardless of whether or not corrective action in the area of review is phased.

Basis for CCS Group Comments: Need to add phrase to account for the periodic reevaluations and possible revisions that will be occurring.

Response: EPA agrees with the commenter and has modified the final rule at §146.84(f) to require the emergency and remedial response plan and the demonstration of financial responsibility to take into account the most recently evaluated AoR.Commenter Name: John R. Baza Letter ID: 0193 Commenter Organization: Utah Division of Oil, Gas, and Mining Comment ID: 23912

Comment: Area of Review ("AOR") Determination, Monitoring and Verification

The EPA seeks comment on the use of modeling for AOR delineation, the use of proprietary models for GS sites, and the frequency of AOR reevaluation. By letter dated December 23, 2008, the Interstate Oil and Gas Compact Commission ("IOGCC") has submitted several comments to the EPA on these issues with respect to the proposed rule. As a regulatory agency within a member state of IOGCC, the

Division concurs with the IOGCC comments and recommendations related to AOR.

Response: Based on its evaluation of all public comments and input on the proposed rule and NODA and Request for Comment, EPA has made many revisions to the GS Rule. See the final rule and preamble for further discussion on EPA’s final approach.

Commenter Name: Andy Horn Letter ID: 0196 Commenter Organization: Colorado Ground Water Association (CGWA) Comment ID: 23929

Comment: Issue 9. Use of models to assess area of review is only briefly discussed in the proposed regulation.

The regulation specifies the use of mathematical models to assess the AoR and potential impacts. Prior to beginning modeling to evaluate the suitability of a potential reservoir, applicants should be required to collect sufficient field data from the reservoir and over-and underlying formations to evaluate the effects of the project on not only the area of review but also nearby locations where groundwater resources are present, even if not used widely. In modeling of proposed GS projects, multi-phase geologic models should be used coupled with solute transport modeling to evaluate the anticipated impacts. Additionally, models which can evaluate the geomechanical stresses upon the geologic materials within the AoR should be used to determine the potential for induced seismicity. Prior to modeling, site characterization should be performed with an adequate number test boreholes and wells to allow a statistically-valid characterization of issues within the AoR. In addition, the models should simulate the entire project lifespan and a substantial amount of time in the post-closure phase to provide insight into, support mitigation of, potential failure mechanisms.

Issues to be evaluated in reservoir modeling should include but not be limited

to:

* Rock mechanics and susceptibility to fracture/failure, * Water quality within the AoR including strata above and lateral to the proposed GS reservoir, * Reservoir and aquifer properties, * Potential for CO2 migration into overlying strata via faults and improperly sealed boreholes, * Potential water quality impacts on USDWs due to the pressure field developed under project scale injection, * Mechanical and hydraulic properties of low-permeability units anticipated to serve as barriers to migration of the CO2 and,* The effects of fluids that will be displaced from zones between the GS

reservoir and USDWs.

Ongoing collection of verification data for these models is important and should be performed on an interval that will be sufficient to allow identification and mitigation of potential failure mechanisms. Use of any model must be combined with calibration, where field observations should be replicated in the model. Any models that are used must be fully documented, with assumptions and methodology provided. A 5-year review interval is suggested over the course of the project life. Models alone, without sufficient field data collected prior to and during operation, are not protective of the public safety or resources.

Response: EPA agrees that detailed geologic data, including the types of data to which the commenter refers, is invaluable to modeling an accurate AoR. The Agency believes that the AoR delineation requirements in 146.84 (c)(1)(i), which specify using "detailed geologic data collected to characterize the injection zone, confining zone and any additional zones; and anticipated operating data...," and (c)(iii) to "consider potential migration through faults, fractures and artificial penetrations," provide the necessary information needed for appropriate site modeling, subsequent site evaluation, and protection of USDWs from endangerment. EPA adds that the extensive requirements for data that is to be included in the permit application at 146.82 incorporate these same types of information. The Director will review the AoR models in the context of the extensive site data submitted with the permit application. EPA recognizes that in some instances, the Director may require additional types of data to be included in the AoR delineation (146.84(c)(1)).

Commenter Name: Craig R. Walters Letter ID: 0200 Commenter Organization: Anadarko Petroleum Corporation Comment ID: 24654 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Rule Provision: 146.84(a)

Anadarko Petroleum Corporation (APC) Comments: (a) The area of review is the region surrounding the geologic sequestration project that may be impacted by the injection activity. The area of review is based on computational modeling that accounts for the physical and chemical properties of all phases of the injected carbon dioxide stream. SUBSURFACE THREE-DIMENSIONAL EXTENT OF THE CARBON DIOXIDE PLUME, ASSOCIATED PRESSURE FRONT, AS WELL AS THE

OVERLYING

FORMATIONS AND SURFACE AREA ABOVE THAT DELINEATED REGION.

Rationale: Edits make this provision consistent with the definition of "Area of Review", which was revised.

Response: EPA disagrees that the AoR definition needs to specifically include the overlying formations and surface area above the delineated region. The intent of the AoR, a long-standing concept within the UIC Program, is to delineate the surface area and all subsurface formations below it that may potentially be impacted by injection activity. Acceptable delineation models will provide predictions of CO2 fate and transport, as well as changes in formation pressure, in three dimensions as a function of time that can be used to delineate the subsurface storage site and the AoR. Although EPA disagrees with the commenter's suggested change, the Agency has carefully considered allcomments on the AoR definition at 146.84(a) and modified it to read as follows: The region surrounding the geologic sequestration project where USDWs may be endangered by the injection activity. The area of review is delineated using computational modeling that accounts for the physical and chemical properties of all phases of the injected CO2 stream and is based on available site characterization, monitoring, and operational data. EPA believes that this definition is sufficiently broad and describes both the intent of the computational modeling and the relationship of the AoR to areas that are subject to the risks associated with injection.

Commenter Name: Craig R. Walters Letter ID: 0200 Commenter Organization: Anadarko Petroleum Corporation Comment ID: 24658 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Rule Provision: 146.84(c)(1)

Anadarko Petroleum Corporation (APC) Comments: (1) Predict, using computational modeling, the projected lateral and vertical migration of the carbon dioxide plume and formation fluids in the subsurface from the commencement of injection activities until the plume movement ceases, pressure differentials sufficient to cause the movement of injected fluids or formation fluids into a USDW are no longer present, or after FOR a fixed time period as determined by the

Director. The model MODELING must:

Rationale: Clarification

Response: Based on an evaluation of all comments received, EPA has clarified this language in the final rule at 146.84(c)(1). It now reads, “Predict, using existing site characterization, monitoring and operational data, and computational modeling, the projected lateral and vertical migration of the carbon dioxide plume and formation fluids in the subsurface from the commencement of injection activities until the plume movement ceases, until pressure differentials sufficient to cause the movement of injected fluids or formation fluids into a USDW are no longer present, or until the end of a fixed time period as determined by the Director.”

Commenter Name: Craig R. Walters Letter ID: 0200 Commenter Organization: Anadarko Petroleum Corporation Comment ID: 24659 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Rule Provision: 146.84(c)(1)(i) & (ii)

Anadarko Petroleum Corporation (APC) Comments: (i) Be based on detailed geologic data collected to characterize the injection zone, confining zone and any

additional zones ; and anticipated operating data, including injection pressures, rates and total volumes over the proposed life of the geological sequestration project THE DURATION OF INJECTION;

(ii) Take into account any RELEVANT geologic heterogeneities, AND data quality, and their possible impact on model predictions; and

Rationale: Clarification.Response: EPA agrees that detailed geologic data is invaluable to modeling an accurate AoR. EPA clarifies that owners or operators may use existing data as well as data collected during site characterization to predict the AoR. The final rule retains the language in §146.84(c)(1)(i) as proposed, and modifies §146.84(c)(1)(ii) slightly to require owners or operators to take into account “other discontinuities” in addition to geologic heterogeneities when predicting the AoR.

EPA disagrees that only the injection and confining zones should be included in AoR modeling of GS sites. EPA believes that the modeling should also take into account the possibility of displaced fluids or brines caused by a lateral and/or vertical pressure plume, and therefore it may be necessary to include additional zones along with the confining/injection zones to ensure the integrity of the confining zone and ultimately protect a USDW from endangerment.

Commenter Name: Christopher Murray Letter ID: 0207 Commenter Organization: Pacific Northwest National Laboratory Comment ID: 22435

Comment: Uncertainty Associated with Modeling COZ Movement and Reservoir Pressure . . . . . . . Page 8 A formal process for uncertainty assessment of the C02 plume footprint should be incorporated in the Proposed Rule. This uncertainty assessment could be based on a bounding approach, a sensitivity analysis, Monte Carlo simulation or other method, provided the range of probable circumstances are considered.

Response: EPA acknowledges that there will be some uncertainty involved in AoR modeling. An EPA-prepared technical background document, "Computational Modeling of Underground Injection of Carbon Dioxide for Determination of Area-of-Review and Potential Risk to Underground Sources of Drinking Water" (cited as USEPA, 2008d) was provided in the regulatory docket for the proposed GS rule. This document discusses, for example, uncertainty analysis in detail. This document was provided as a background to clarify what information EPA analyzed in order to draft the modeling requirements at 146.84(c)(1), as well as what actions EPA expects owners or operators and Directors to take in this area. For example, the document states: "The requirement for an a-priori AoR delineation based on modeling predictions stresses the need for uncertainty and sensitivity analyses for the initial prediction. Sensitivity analysis is recommended as the principal evaluation tool for characterizing the most and least important sources of uncertainty in environmental models."

Commenter Name: Christopher Murray Letter ID: 0207 Commenter Organization: Pacific Northwest National Laboratory Comment ID: 22440

Comment: AREA OF MONITORING (AoM) AND AREA OF REVIEW (AoR)

PROPOSED REGULATION

p. 43493, c. 2 Area of Review (AoR): The region surrounding the geologic sequestration project that may be impacted by the injection activity. The area of review is based on computational modeling that accounts for the physical and chemical properties of all phases of the injected carbon dioxide stream.

The proposed regulation uses the Area of Review (AoR) for defining both corrective actions and monitoring requirements:p. 43499, c. 1 Area of Review (AoR) and Corrective Action: The Agency requires

examination of both the vertical and horizontal extent of the area that will potentially be influenced by injection and storage activities and identification of all artificial penetrations in the area that may act as conduits for fluid movement into USDWs (e.g., active and abandoned wells) and, as needed, perform corrective action to these open wells (i.e., artificial penetrations).

p. 43539, c. 3 (2) The monitoring frequency and spatial distribution of monitoring wells must be based on baseline geochemical data that has been collected under §146.82(a)(6) and any modeling results in the area of review evaluation required by § 146.84(b);

We agree with the concept of defining bounding areas for corrective actions and monitoring activities, but the proposed regulation uses a single area, Area of Review (AoR), for both and fails to address how to quantify this area. The proposed regulation defines the Area of Review (AoR) as being the region that may be impacted by the injection activity, without defining or quantifying impact. To be useful the bounding areas for corrective actions and monitoring activities must have specific definitions. Under deep geologic sequestration conditions the injected fluid (i.e., supercritical CO2) has low compressibility, the displaced fluid (i.e., brine) has low compressibility, and the reservoir formation (e.g., sandstone) generally has low compressibility, all of which suggest that the impact (i.e., pressure change) of the injection activity could be detected at great distances from the injection well(s).

Response: EPA believes that, while the commenter offers different terminology for the AoR and the area to be monitored, the GS rule addresses the commenter's suggestions. Notably, the owner or operator is required (under 146.90) to develop and implement a testing and monitoring plan for each GS project that must consider the delineated AoR that includes both the CO2 plume and associated pressure front and incorporates many of the attributes suggested by the commenter. EPA clarifies that delineation of the AoR, as required at 146.84(c), must account for the physical and chemical properties of all phases of the injected CO2 stream, based on available site characterization, monitoring, and operational data.

Furthermore, any changes to the AoR would necessitate a review of and potential change in the testing and monitoring plan, consistent with the commenter's assertion that the AoR may vary over time. The final GS regulation includes a requirement at 146.84(e) that the AoR be reevaluated at least every 5 years, and also requires that the owner or operator periodically review the AoR and corrective action, testing and monitoring, and emergency and remedial response plans within one year of an AoR reevaluation (as well as following significant changes to the facility, or when required by the Director). The relationship between the AoR reevaluation and the testing and monitoring plan should allow for considerations suggested by the commenter.

EPA believes that by linking development and review of the testing and monitoring plan to the AoR evaluation and reevaluation process, the GS rule, in effect, incorporates many of the commenter's considerations for an area of monitoring.

EPA did not specifically define the term "impacted" in this context because of the wide range of potential geologic and other site-specific conditions that may be vary from site to site. EPA believes that each GS site will be unique and that the affected area where USDWs may be at risk should bedefined based on computational modeling that accounts for available site characterization, monitoring, and operational data.

EPA anticipates that the delineated AoR will serve as the foundation for identifying areas in which corrective action and monitoring associated with the site would occur, and that the AoR and corrective action plan and the testing and monitoring plan would be based on the delineated AoR. EPA is developing guidance for owners or operators on developing project-specific plans; the guidance will be available on EPA's web site, at http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

EPA believes it is appropriate to allow the owner or operator the flexibility to develop a site-specific AoR and corrective action plan that takes into account the unique conditions of the site, subject to the approval of the Director. Within the UIC Program, impacts associated with injection would include anything that could endanger a USDW, including, but not limited to, the CO2 plume and pressure front, displaced saline fluids, co-contaminants, and mobilized minerals.

Commenter Name: Christopher Murray Letter ID: 0207 Commenter Organization: Pacific Northwest National Laboratory Comment ID: 22443 Other EPA Comment Codes and Descriptions: 4600 2.6 Proposed Plume and Pressure Front Monitoring Requirements (40 CFR 146.90)

Comment: Injection of CO2 into deep saline formations is driven by differences between the well injection pressure and formation pressure. To avoid inducing fractures or opening existing fractures in the formation and caprock, well injection pressure will be limited to some fraction below the fracturing pressure. As CO2 migrates into the formation the formation pressure increases around the injection well. The pressure distribution in the formation around the injection well depends on the formation properties, structure, and injection rate. Injection formations will be required to be confined vertically and/or horizontally to prevent the vertical migration of injected fluids and saline

reservoir fluids into USDWs.

Confined formations (e.g., a caprock overlying a horizontally extensive formation) allow the formation fluid to be displaced laterally by the injected fluid. Injecting CO2 results in elevated pressures both inside and beyond the CO2 plume. Elevated pressures within the CO2 plume have the potential to force CO2 and formation fluid through permeable wells, fractures, or faults that penetrate the formation. Elevated pressures outside the CO2 plume have the potential to force formation fluid through permeable wells, fractures or faults that penetrate the formation. The higher the formation pressure is above the ambient formation pressure, the greater the potential for CO2 and formation fluid to leak through permeable wells, fractures, and faults. The lateral pressure distribution is a function of the injection rate and the lateral distribution of formation permeability. When CO2 injection is halted, elevated pressures decay over time as the injected and formation fluids migrate away from the injection well(s).

The proposed regulations define an AoR and Corrective Action as being an area within which artificial penetrations may act as conduits for fluid movement into USDWs (e.g., active and abandoned wells) and, as needed, require the applicantto perform corrective action to seal these open wells. The potential for fluid movement into USDWs from the injection of CO2 into the injection formation is correlated with the area of elevated formation pressure, which is usually larger than the area that contains the injected CO2 mass. For confined formations, this area is defined by the lateral pressure distribution around the injection well(s).

PNNL RECOMMENDATION

EPA should define two regulatory regions surrounding the geologic sequestration project and provide specific definitions for those regions; 1) Area of Monitoring (AoM) and 2) Area of Review; where the AoM is used to define the spatial distribution of monitoring wells and the AoR is used to define the limit

of corrective actions:

Area of Monitoring (AoM): The region surrounding the geologic sequestration project that The area of monitoring is based on monitoring data contains 95% of the carbon dioxide mass. and computational modeling that accounts for the physical and chemical properties of all phases of the injected carbon dioxide stream. In the absence of monitoring data, the area of monitoring is based on computational modeling.

Area of Review (AoR): The region surrounding the geologic sequestration reservoir that has or is indicated to develop pressures that are greater than 10% different from the original hydrostatic formation fluid pressure, but no less than the Area of Monitoring. The area of review is based on monitoring data and computational modeling that accounts for the physical and chemical properties of all phases of the injected carbon dioxide stream. In the absence of monitoring data, the area of review is based on computational modeling.

The proposed definitions of AoM and AoR have several important components:

- The AoMhas a mass-based definition. - The AoR has a pressure-differential-based definition. - The AoR is never smaller than the AoM. - The AoR and AoM may be asymmetrical around the injection well(s). - The AoR and AoM may vary over time. - The carbon dioxide mass should be determined using a combination of monitoring data and computational modeling. - Pressure differentials are based on equilibrium hydrostatic conditions.

Response: EPA believes that, while the commenter offers different terminology for the AoR and the area to be monitored, the GS rule addresses the commenter's suggestions. Notably, the owner or operator is required (under 146.90) to develop and implement a testing and monitoring plan for each GS project that must consider the delineated AoR that includes both the CO2 plume and associated pressure front and incorporates many of the attributes suggested by the commenter. EPA clarifies that delineation of the AoR, as required at 146.84(c), must account for the physical and chemical properties of all phases of the injected CO2 stream, based on available site characterization, monitoring, and operational data.

Furthermore, any changes to the AoR would necessitate a review of and potential change in the testing and monitoring plan, consistent with the commenter's assertion that the AoR may vary overtime. The final GS regulation includes a requirement at 146.84(e) that the AoR be reevaluated at least every 5 years, and also requires that the owner or operator periodically review the AoR and corrective action, testing and monitoring, and emergency and remedial response plans within one year of an AoR reevaluation (as well as following significant changes to the facility, or when required by the Director). The relationship between the AoR reevaluation and the testing and monitoring plan should allow for considerations suggested by the commenter.

EPA believes that by linking development and review of the testing and monitoring plan to the AoR evaluation and reevaluation process, the GS rule, in effect, incorporates many of the commenter's considerations for an area of monitoring.

Commenter Name: Michael Stroben Letter ID: 0209 Commenter Organization: Duke Energy Comment ID: 22684 Other EPA Comment Codes and Descriptions: 3530 2.2.3.1 AoR reevaluation frequency (seeking comment)

Comment: REEVALUATION OF AREA OF REVIEW ("AoR")

Current UIC regulations require the owner/operator of a proposed injection site to determine the AoR based on the area necessary to include the calculated cone of pressure influence. The amount of CO2 that will be injected at a GS site over the life of a project will be tens if not hundreds of millions of tons. This quantity of CO2 along with uncertain dispersion characteristics makes it next to impossible to determine the correct AoR utilizing a fixed radius or simple

mathematical method.

Acceptable methods for determining the AoR should include but not be limited to multiphase fluid flow models. It is anticipated that modeling will improve over time as experience with CO2 sequestration increases. Demonstration projects should not be constrained by allowing only the use of current models. Any model based on accepted science that has been validated should be acceptable. Models should be calibrated using actual site data once it becomes available.

The AoR for a GS site for CO2 will be dynamic and in all probability irregular in shape. Based on the quantity of CO2 to be sequestered at a site, the AoR could be hundreds of square miles. A significant amount of time and money would be needed to complete an up-front evaluation of the life of a project AoR. A large portion of this effort could be wasted since the injection plumb may not travel as anticipated. As a result of this uncertainty, Duke Energy recommends a phased evaluation for the AoR. The AoR should be reviewed periodically (every ten years or as agreed upon by the Director). This would allow any necessary corrective actions to be focused where needed. This approach would allow projects to proceed more expeditiously, reduce start-up costs and because of the periodic review, provide greater protection to USDW.

Response: EPA clarifies that the AoR must be delineated as part of the permit application, as required at §§146.82(a)(2) and 146.82(c)(1). The Agency believes that AoR delineation using computational modeling that accounts for the multiphase flow of CO2 and native fluids (i.e., naturally occurring salty water), including density-driven flow (i.e., buoyancy), is necessary to ensure protection of USDWs from endangerment. The computational models used for this purposeare required to predict the fate of injected CO2 and changes in formation pressure. EPA believes that the requirements at 146.84(c)(1) to delineate the AoR using computational modeling are appropriate and encompass the significant processes that could affect the location of the CO2 plume and associated pressure front.

EPA agrees that modeling technology is likely to improve over time, and EPA believes that future AoR reevaluations, as required at 146.84(e), should incorporate the best modeling available. Periodic reevaluations also ensure that a deliberative effort is made to verify, based on monitoring and operational data, that the CO2 plume is moving within the subsurface as predicted. However, EPA clarifies that the AoR delineation process will not be phased. Owners or operators must delineate the entire AoR of the project prior to receiving an operating permit. This evaluation must include the entire region surrounding the geologic sequestration project where USDWs may be endangered by the injection activity.

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.

Commenter Name: John King Letter ID: 0211 Commenter Organization: Shell Exploration and Production Company (SEPCo) Comment ID:

22767 Other EPA Comment Codes and Descriptions: 1220 1.1.1.1 Terminology and definitions

Comment: 1. AOR Definition

The proposed rule vaguely defines the AOR as "the region surrounding" the GS project that "may be impacted by the injection activity." 72 Fed. Reg. at 43535 (proposed 40 C.F.R. 146.81(d)). The definition goes on to suggest that the AOR is to be "based on computation modeling that accounts for the physical and chemical properties of all phases of the injected carbon dioxide stream." Id.

There are two issues.

First, the proposed definition suggests the need for a more complex modeling approach than may typically be necessary or appropriate. As experience with hazardous waste injection shows, it is rarely necessary to attempt to model chemical changes in the injectate plume. Indeed, it is typically far easier to model transport than chemical fate, and conservative modeling of transport should typically be sufficient by itself to show that USDWs will not be endangered. Where this is the case, it is containment of the plume -- rather than the precise composition of the plume -- that matters, and modeling of chemical changes would be unnecessary. Similarly, the preamble suggests that the "most sophisticated" and most "accurate" modeling should be preferred or even required. 73 Fed. Reg. at 43507. Again, however, the appropriate goal is to ensure protection of USDWs, and simpler, more conservative modeling may often be sufficient (and even preferable) for this purpose.

Second, the functional purpose of the AOR is to define the area within which impacts of the injection activity could cause endangerment of a USDW; specifically, the AOR defines the area within which corrective action forabandoned boreholes may be necessary to prevent endangerment of USDWs. The language of the proposed rule (i.e., "may be impacted by the injection activity") is not clearly limited to impacts of the injection activity that could cause endangerment of USDW’s, and it should be.

Response: EPA believes that predicting the complex multiphase, buoyant flow of the CO2, coinjectates, 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.

EPA acknowledges that fine precision may not always be necessary and that many factors determine ultimate confidence in modeling results. However, EPA does not believe that more precision would result in a less protective modeling approach. EPA anticipates that the owner or operator, in consultation with the Director, will choose the model that is most appropriate for a particular GS project, and that this dialogue is a key factor in assuring that the GS site is modeled (and eventually operated and tracked) in a manner that protects USDWs from endangerment. EPA encourages and expects owners or operators to use the best multiphase, computational models available.

Commenter Name: Diane VanDe Hei Letter ID: 0213 Commenter Organization: Association of Metropolitan Water Agencies (AMWA) Comment ID:

22935

Comment: o Groundwater modeling is improving and variable density flow models for deeper aquifers can be used with reasonable accuracy for understanding subsurface flow and quality. However these models must take variables such as heat transport into account to better translate to a CO2 geosequestration scenario.

Response: EPA agrees that heat transport may be an important process in modeling of the AoR. The GS regulation stipulates, at 146.84(a), that the physical and chemical properties of all phases of the injected CO2 stream must be accounted for in the model. Heat transport is one of several processes that describe the geologic site, the injection scenario, and the fluids present, all of which are the foundation for the multiphase, AoR model development.

Commenter Name: Edward Steadman Letter ID: 0220 Commenter Organization: The Energy and Environmental Research Center at the University of North Dakota Comment ID:

21590 Other EPA Comment Codes and Descriptions: 1810 1.4.1 Research on identifying risks to

USDWs

Comment: Page 43499. One would caution rule makers on putting too much faith into any one institution or any one method when studying potential impacts. Should not such information be provided by various technical sources? While the utility of models and laboratory data is recognized, their results should not supersede real-world experience, field-based data, and local knowledge.

Response: EPA considered a wide range of information from laboratory, modeling, and field research as it developed the requirements for GS wells. In addition to laboratory studies andmodeling research that provide relevant information on GS, the Agency is also involved in collecting and analyzing GS project data and permit information from a variety of sources. Most notably, EPA has evaluated UIC permits and reviewed operational data and information associated with the seven regional carbon sequestration partnerships funded by the U.S. Department of Energy and coordinated through the National Energy Technology Laboratory (NETL), and several international projects. In addition to the information cited in the preamble to the proposed rule, EPA published a Notice of Data Availability and Request for Comment (NODA) on August 31, 2009 (74 FR 44802), in which the Agency described the preliminary results of research at three DOE partnership sites: the Escatawpa, Mississippi project; the Aneth Field project in Paradox Basin, Southeast Utah; and the Pump Canyon Site, New Mexico.

Regarding the suggestion that EPA give more weight to field data and experiential knowledge, EPA notes that it continues to track ongoing field and laboratory research into all aspects of GS. Forexample, EPA is tracking the operations and technical developments of more than three dozen smalland large-scale GS injection projects in the US and abroad. Also, since field experience and well construction, injection, and monitoring information relevant to GS comes from operations that inject acid gas or inject CO2 for ER, the Agency has conducted evaluations regarding these commercial field operations and continues to track GS-relevant developments in these commercial operations.

The Agency will continue to track GS project developments and evaluate new and ongoing research and information to ensure USDW protection. EPA is using an adaptive approach to regulating GS under the UIC Program. Even after finalization of the GS regulation, the Agency plans to collect and review data every six years 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 finalized requirements are appropriate or necessary.

EPA agrees that AoR modeling should be based on actual data collected on the site, including detailed geologic data collected to characterize the injection zone, confining zone and any additional zones, as required at 146.84(c)(1)(i). The Agency believes that the integration of site specific information into a predictive multiphase computational model will ensure the best possible AoR delineation. EPA also recognizes that modeling technology will continue to improve, and encourages and expects owners or operators to use the best available multiphase computational models to determine the AoR. Reliance on improved models will likely increase the accuracy and quality of the AoR characterization, resulting in increased protection of USDWs from endangerment.

Commenter Name: Edward Steadman Letter ID: 0220 Commenter Organization: The Energy and Environmental Research Center at the University of North Dakota Comment ID:

21592 Other EPA Comment Codes and Descriptions: 1810 1.4.1 Research on identifying risks to

USDWs

Comment: Page 43500. Regarding the basis of some of the rules related to modeling Much has happened in the world of modeling CO2 injection and long-term storage since 2005. Many of the key messages from the workshop upon which some of the statements on this topic are based may be long out of date.

Response: EPA continues to review new and ongoing modeling studies, including those conducted at national research laboratories, such as Lawrence Berkeley National Laboratories as well as data from the DOE Partnership GS pilot projects where some of the most current models are being developed and/or used. EPA published a Notice of Data Availability and Request for Comment onAugust 31, 2009 (74 FR 44802), in which the Agency described two recent modeling studies by the Lawrence Berkeley National Laboratory on the potential effects of CO2 injection on USDWs and human health in the event that a GS project is not properly sited, operated, or managed. These studies are in the rulemaking docket and on LBNL's website at http://esd.lbl.gov/GCS/projects/CO2/index_CO2.html. Additionally, EPA continues to fund research on ground water that will integrate experimental and modeling efforts with the objective of evaluating the potential consequences of CO2 leaks from GS operations into ground water resources.

EPA is using an adaptive approach to regulating GS under the UIC Program. Even after finalization of the GS regulation, EPA plans to collect and review data every six years 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.

As described above, EPA recognizes that modeling technology will continue to improve, and encourages and expects owners or operators to use the best available multiphase computational models to determine the AoR. Reliance on improved models will likely increase the accuracy and quality of the AoR characterization, resulting in increased protection of USDWs from endangerment.

Commenter Name: Edward Mehnert Letter ID: 0221 Commenter Organization: Illinois State Geological Survey Comment ID: 21637 Other EPA Comment Codes and Descriptions: 4600 2.6 Proposed Plume and Pressure Front Monitoring Requirements (40 CFR 146.90)

Comment: p.43506, IIIA2 Proposed Area of Review: Does the area of review need to be one contiguous area? For a deep saline aquifer with no structural trap, it may be beneficial to have two separate areas of review--one for the CO2 plume and another for the pressure front at a distant USDW boundary. In this setting, the pressure front may move brine upgradient into a portion of the aquifer that contains fresher water (<10,000 mg/L TDS). The distance between the injection well and the "freshwater" section of the aquifer may be more than 100 miles.

Response: EPA clarifies that the requirements for AoR delineation incorporate both the CO2 plume and associated pressure front. EPA agrees that both of these should be taken into account in determining corrective action needs and developing a testing and monitoring plan, and that the requirement to delineate the AoR at 146.84(c) addresses the potential risks raised by the commenters. EPA believes that the final GS requirements for delineating the AoR provide sufficient protection to USDWs, without introducing an overly complex regulatory process.

Commenter Name: Edward Mehnert Letter ID: 0221 Commenter Organization: Illinois State Geological Survey Comment ID: 21638

Comment: p.43506, IIIA2 Proposed Area of Review: I agree that models offer the best approach to predict the potential effect of CO2 injection into an aquifer. What happens when multiple injection wells are operated in the same aquifer such that well interference is an issue? How do you manage this situation if different models are utilized? As an alternative to many stand-alone models, can a regional model with common boundary and initial conditions be developed and then a local model with detailed site data would be added to this regional model?The Twin Cities Metropolitian Groundwater Flow model (http://www.pca.state.mn.us/water/groundwater/metromodel.html) is an example of this concept.

Response: EPA agrees that the impacts of multiple operators injecting into hydraulically connected formations must be accounted for in the AoR modeling. EPA adds that the owner or operator must demonstrate in the proposed AoR and corrective action plan to the satisfaction of the Director that the modeled AoR will be based on detailed site-specific geologic data collected during the site characterization process including consideration of existing conditions (e.g., current injection activities). 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 in a formation or a series of hydraulically connected formations. EPA acknowledges the commenter's reference to the Twin Cities Metropolitan Groundwater Flow model. The Agency anticipates that many such examples will be developed as GS projects are deployed and new modeling products are developed to address this new application.

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.

Commenter Name: Ben Yamagata Letter ID: 0227 Commenter Organization: Coal Utilization Research Council Comment ID: 21787 Other EPA Comment Codes and Descriptions: 3330 2.2.1.3 Applicability /adequacy of computational models (seeking comment)

Comment: Area of Review (AoR)

The proposed regulation does not actually define the AoR, it merely states that the area will be determined by mathematical models. One of the concerns with the use of such complex models is that the site may not be fully characterized with respect to hydro-geologic properties. There may be significant uncertainty in one or more hydraulic process/parameters. Therefore, it is possible to obtain a wide-range of model outcomes from different model parameters. The treatment of uncertainty in model parameters and sensitivity of model results to parameter selection should be addressed. Given that the AoR will be periodically revisited, we recommend that the final rule make a pragmatic determination of what will be necessary to protect groundwater, given the requirement for reevaluation over time, and that the Agency focus the requirements to rely upon the mathematical models with the inherent differences

noted above.

Response: EPA agrees that modeling results are prone to varied degrees of uncertainty. As discussed in the preamble to the proposed GS regulation and the associated background document"Computational Modeling of Underground Injection of Carbon Dioxide for Determination of Areaof-Review and Potential Risk to Underground Sources of Drinking Water" (cited in the proposed rule preamble as USEPA, 2008d), model predictions depend largely on the values of key parameters.Often these parameter values are estimated or averaged from several data sources. EPA also agrees that sensitivity analyses and "worst case scenario" modeling runs should be presented by the owner or operator and evaluated by the Director. If during the permit review, the Director determines that modeling results are too wide-ranging, further information will be required of the owner or operator.

EPA clarifies that models are tools to help predict the movement of a CO2 plume over long time frames. However, EPA recognizes that it cannot be expected that modeling something as complex as a CO2 plume can be done with complete certainty; therefore EPA is also requiring that the AoR be reevaluated to verify the CO2 plume is moving as predicted and to allow for model calibration and necessary revisions to the required GS project plans (e.g., AoR and corrective action, testing and monitoring, injection well plugging, post-injection site care and site closure, and emergency and remedial response). EPA believes that near-term predictions (e.g., over the subsequent 5 years) would have the highest degree of certainty. Periodic model calibration would allow refinement to the AoR delineation based on real-world conditions and operating data and monitoring results, and thus increase confidence in the modeled predictions. EPA adds that the final GS regulation includes a requirement at 146.84(e) that the AoR be reevaluated every 5 years (an adjustment from the ten year interval in the proposal), which should further address the commenter’s concerns regarding model uncertainty.

Commenter Name: Neeraj Gupta Letter ID: 0229 Commenter Organization: Battelle Energy Technology (BET) Comment ID: 21831

Comment: Page 64, Area of Review Determination -More clarity on determining the AOR is requested. Currently it is not clear whether AOR will be based on CO2 phase spreading, dissolved CO2 plume, or pressure footprint. Models provide a large amount of information such as CO2 gas saturation, pressure, and aqueous concentrations. They also involve a fair amount of uncertainty. Our experience is that small portion of the CO2 may extend or "finger" much further than the bulk of the injected CO2. For example would EPA accept an AOR with a radius containing 90% of the CO2 as supercritical gas saturation, so that the applicants do not have to account for small-scale fingering or heterogeneities?

Response: EPA disagrees with defining the AoR relative to the percentage of CO2 saturation. The UIC regulations, including the Class VI regulations, are designed to ensure protection of USDWs from endangerment. The Agency believes that the AoR needs to incorporate not only the CO2 itself —regardless of saturation or phase—but also the area of increased pressure ahead of the CO2 plume, which can potentially displace saline, native fluids (i.e., naturally occurring salty water) into USDWs. This pressure front would typically encompass an area larger than the plume itself, including any areas of small scale fingering or heterogeneities or where CO2 saturation is less than 100 percent. The Agency has carefully considered all comments on the AoR definition at 146.84(a) and modified it to read as follows: The region surrounding the geologic sequestration project where USDWs may be endangered by the injection activity. The area of review is delineated using computational modeling that accounts for the physical and chemical properties of all phases of the injected CO2 stream and is based on available site characterization, monitoring, and operational data.

EPA clarifies that the definition of AoR includes all areas that may potentially be endangered by the injection activity. EPA recognizes that modeled AoRs may involve some uncertainty or “fingering,” as the commenter mentions. Any needed corrective action must be done on wells in the modeled AoR, which would include these areas to ensure that they address any area that would be impacted by the CO2 plume and pressure front.Commenter Name: Kristin Henry Letter ID: 0242 Commenter Organization: Sierra Environmental Law Program, Sierra Club Comment ID: 23328

Comment: VIII. The Definition of the Area of Review Should Include Monitoring and Modeling.

The definition of Area of Review (AOR), Fed. Reg 43536, CFR §146.84, Part (a) states that the Area of Review is "based on computational modeling". It is not appropriate for the Area of Review to be based solely on computational modeling. Instead, it should be based on computational modeling, monitoring and operational data and updated until closure is approved. All references to computational modeling in relation to the Area of Review in this section, as well as in the definition of Area of Review in §146.81 should be amended as appropriate to read "based on computational modeling, monitoring and operational data and updated until closure is approved".

Response: Based on review of all public comments on the AoR definition at 146.84(a), the Agency has modified it to read as follows: The region surrounding the geologic sequestration project where USDWs may be endangered by the injection activity. The area of review is delineated using computational modeling that accounts for the physical and chemical properties of all phases of the injected CO2 stream and is based on available site characterization, monitoring, and operational data. The definition in the proposed rule accounted for the varying physical and chemical properties of the CO2 including free-phase and water-dissolved CO2, as the commenter suggests. The definition in

the final rule will continue to do so.

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 clarifies that the initial AoR delineation required under 146.84(c) is performed prior to injection, and therefore no monitoring or operational data would yet exist. The AoR delineation models will incorporate all available site data and anticipated operating procedures (e.g., injection rates and volumes).

The AoR reevaluation process required at 146.84(e) requires owners or operators to incorporate monitoring or operational data and make any needed adjustments to corrective action or monitoring at the site. EPA believes that the iterative process of AoR reevaluation is appropriate to verify that the CO2 plume and pressure front are moving through the subsurface as predicted, verify the accuracy of the delineation model (or identify needed changes), and refine testing and monitoring activities to ensure that USDWs are protected from endangerment and that there would be adequate warning of potential problems at the site before any endangerment could occur.

Commenter Name: Kurt Waltzer Letter ID: 0250 Commenter Organization: Clean Air Task Force Comment ID: 22306 Other EPA Comment Codes and Descriptions: 1220 1.1.1.1 Terminology and definitionsComment: The area of review provisions should be revised in several respects

Surprisingly, the definition of "area of review" (AOR) in §146.81(d) fails to mention that elevated pressure a critical aspect of what it means for an area to be "impacted" by injection activity. Our Environmental NGO Group recommends borrowing language from the proposed definition of "geologic sequestration project" and reworking the "area of review" definition.

Response: Although EPA disagrees with the commenter's suggested change, the Agency has carefully considered all comments on the AoR definition at 146.84(a) and modified it to read as follows: The region surrounding the geologic sequestration project where USDWs may be endangered by the injection activity. The area of review is delineated using computational modeling that accounts for the physical and chemical properties of all phases of the injected CO2 stream and is based on available site characterization, monitoring, and operational data. EPA believes that this definition is sufficiently broad and describes both the intent of the computational modeling and the relationship of the AoR to areas that are subject to the risks associated with injection.

Commenter Name: Kurt Waltzer Letter ID: 0250 Commenter Organization: Clean Air Task Force Comment ID: 22307 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: An additional concern is that both §146.81 and §146.84(a) state that the AOR is "based on computational modeling". This could imply that the Area of Review could be based solely on computational modeling. Instead, the AOR should be based on computational modeling, monitoring and operational data (and kept updated until closure is approved). All references to computational modeling in relation to the Area of Review in this section, as well as in the definition of Area of Review in §146.81 should be amended as appropriate to read "based on computational modeling, as well as monitoring and other operational data." We urge that the definition be revised as follows:

[In the paragraph below the text in all CAPS denotes added text. See also EPA-HQ-OW-0390-0250.pdf to see the original formatting.]

"Area of review means the AREA that may be impacted by the injection activity. The area of review is based on computational modeling, as well as MONITORING AND OTHER OPERATIONAL DATA, that account for the physical and chemical properties of all phases of the injected carbon dioxide stream. IT INCLUDES THE SUBSURFACE THREE-DIMENSIONAL EXTENT, THROUGHOUT THE OPERATING LIFE OF THE FACILITY, OF THE CARBON DIOXIDE STREAM PLUME, ASSOCIATED PRESSURE FRONT, AND DISPLACED

FORMATION FLUIDS, AS WELL AS THE OVERLYING FORMATIONS AND SURFACE AREA ABOVE

THAT

DELINEATED REGION."

Response: Based on review of all public comments on the AoR definition at 146.84(a), the Agency has modified it to read as follows: "The region surrounding the geologic sequestration project whereUSDWs may be endangered by the injection activity. The area of review is delineated using computational modeling that accounts for the physical and chemical properties of all phases of the injected CO2 stream and is based on available site characterization, monitoring, and operational data." The definition in the proposed rule accounted for the varying physical and chemical properties of the CO2 including free-phase and water-dissolved CO2, as the commenter suggests. The

definition in the final rule will continue to do so.

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 clarifies that the initial AoR delineation required under 146.84(c) is performed prior to injection, and therefore no monitoring or operational data would yet exist. The AoR delineation models will incorporate all available site data and anticipated operating procedures (e.g., injection rates and volumes).

The AoR reevaluation process required at 146.84(e) requires owners or operators to incorporate monitoring or operational data and make any needed adjustments to corrective action or monitoring at the site. EPA believes that the iterative process of AoR reevaluation is appropriate to verify that the CO2 plume and pressure front are moving through the subsurface as predicted, verify the accuracy of the delineation model (or identify needed changes), and refine testing and monitoring activities to ensure that USDWs are protected from endangerment and that there would be adequate warning of potential problems at the site before any endangerment could occur.

Commenter Name: Michel Paque Letter ID: 0259 Commenter Organization: Ground Water Protection Council Comment ID: 24856 Other EPA Comment Codes and Descriptions: 1220 1.1.1.1 Terminology and definitions

Comment: Rationale: Insert the definition "Computational modeling means a mathematical model that is appropriate to the site geometry and takes into account the differences between the formation and injection fluids."

Response: The final rule does not define computational modeling. The preamble to the proposed GS regulation and the modeling background document "Computational Modeling of Underground Injection of Carbon Dioxide for Determination of Area-of-Review and Potential Risk to Underground Sources of Drinking Water" (cited in the proposed rule preamble as USEPA, 2008d include FR citation) discuss, in detail, what EPA believes constitutes a computational model. Appropriate models may incorporate numerical, analytical, or semi-analytical approaches. These models solve a series of governing equations to predict the composition and volumetric fraction of each phase state, as well as fluid pressures, as a function of location and time for a particular set of conditions. 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 the data that EPA recommends 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, athttp://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Michel Paque Letter ID: 0259 Commenter Organization: Ground Water Protection Council Comment ID: 24881 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Rule Provision: 146.84

EPA Proposal: 146.84. Area of review and corrective action

(a) The area of review is the region surrounding the geologic sequestration project that may be impacted by the injection activity. The area of review is based on computational modeling that accounts for the physical and chemical properties of all phases of the injected carbon dioxide stream.

GWPC Recommendations: (a) The area of review is based on computational modeling that accounts for the physical and chemical properties of all phases of the injected carbon dioxide stream.

Rationale: This is the same as the definition of "Area of review" that was revised by the GWPC .to delete the first sentence.

Comments on many provisions are predicated on proposed changes in definitions

Response: The Agency has carefully considered all comments on the AoR definition at 146.84(a) and modified it to read as follows: The region surrounding the geologic sequestration project where USDWs may be endangered by the injection activity. The area of review is delineated using computational modeling that accounts for the physical and chemical properties of all phases of the injected CO2 stream and is based on available site characterization, monitoring, and operational data.

Commenter Name: Michel Paque Letter ID: 0259 Commenter Organization: Ground Water Protection Council Comment ID: 24885 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Rule Provision: 146.84(c)

(c) Owners or operators of Class VI wells must perform the following actions to delineate the area of review, identify all wells that require corrective action, and perform corrective action on those wells:

(1) Predict, using computational modeling, the projected lateral and vertical migration of the carbon dioxide plume and formation fluids in the subsurface from the commencement of injection activities until the plume movement ceases, pressure differentials sufficient to cause the movement of injected fluids or formation fluids into a USDW are no longer present, or after a fixed time period as determined by the Director. The model must:

GWPC Recommendations: (c) Owners or operators of Class VI wells must perform thefollowing actions to delineate the area of review, identify all wells that require corrective action, and perform corrective action on those wells:

(1) Predict, using computational modeling, the projected lateral and vertical migration of the carbon dioxide plume and formation fluids in the subsurface from the commencement of injection activities until the plume movement ceases, pressure differentials sufficient to cause the movement of injected fluids or formation fluids into a USDW are no longer present, or for a fixed time period as determined by the Director. The model must:

Rationale: Should say "for" not "after."

Response: Based on its evaluation of all public comments and input on the proposed rule, EPA has clarified this language in the final rule. It now reads, “Predict, using existing site characterization, monitoring and operational data, and computational modeling, the projected lateral and vertical migration of the carbon dioxide plume and formation fluids in the subsurface from the commencement of injection activities until the plume movement ceases, until pressure differentials sufficient to cause the movement of injected fluids or formation fluids into a USDW are no longer present, or until the end of a fixed time period as determined by the Director.”

Commenter Name: Michel Paque Letter ID: 0259 Commenter Organization: Ground Water Protection Council Comment ID: 24886 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Rule Provision: 146.84(c)(i)

EPA Proposal: (i) Be based on detailed geologic data collected to characterize the injection zone, confining zone and any additional zones; and anticipated operating data, including injection pressures, rates and total volumes over the proposed life of the geological sequestration project;

(ii) Take into account any geologic heterogeneities, data quality, and their possible impact on model predictions; and

(iii) Consider potential migration through faults, fractures, and artificial penetrations.

GWPC Recommendations: (i) Be based on detailed geologic data collected to characterize the injection zone, confining zone; and anticipated operating data, including injection pressures, rates and total volumes over the duration of injection;

(ii) Take into account relevant geologic heterogeneities, and data quality, and their possible impact on model predictions; and

(iii) Consider potential migration through faults, fractures, and artificial penetrations.

Rationale: Suggest deletion of "any additional zones". You do not need toinclude any additional zones if you use the current CFR definition of confining zone since it includes multiple zones.

Should be geologic not geological for consistency with other provisions because geologic sequestration project is defined.

Suggest "duration of injection" instead of "life of the geological sequestration project"

Suggest "relevant" instead of any in (ii)

Insert "and" between "heterogeneities" and "data"

Response: EPA agrees that detailed geologic data is invaluable to modeling an accurate AoR. The Agency believes that the AoR delineation requirements in 146.84 (c)(1)(i), which specify using "detailed geologic data collected to characterize the injection zone, confining zone and any additional zones; and anticipated operating data...," and (c)(iii) to "consider potential migration through faults, fractures and artificial penetrations," provide the necessary information needed for appropriate site modeling, subsequent site evaluation, and protection of USDWs from endangerment. EPA adds that the extensive requirements for data that is to be included in the permit application at 146.82 incorporate these same types of information. The Director will review the AoR models in the context of the extensive site data submitted with the permit application. EPA recognizes that in some instances, the Director may require additional types of data to be included in the AoR delineation (146.84(c)(1)). Based on its evaluation of all public comments and input on the proposed rule and NODA and Request for Comment EPA has made many revisions to the GS Rule. See the final rule and preamble for further discussion on EPA's final approach.

EPA disagrees that only the injection and confining zones should be included in AoR modeling of GS sites. EPA believes that the modeling should also take into account the possibility of displaced fluids or brines caused by a lateral and/or vertical pressure plume, and therefore it may be necessary to include additional zones along with the confining/injection zones to ensure the integrity of the confining zone and ultimately protect a USDW from endangerment.

Commenter Name: Michel Paque Letter ID: 0259 Commenter Organization: Ground Water Protection Council Comment ID: 24892 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Rule Provision: 146.84(g)

(g) The emergency and remedial response plan (as required by § 146.94) and a demonstration of financial responsibility (as described by § 146.85) must account for the entire area of review, regardless of whether or not corrective action in the area of review is phased.

GWPC Recommendations: (g) The emergency and remedial response plan (as required by § 146.94) and a demonstration of financial responsibility (as described by § 146.85) must account for the entire area of review [as modified], regardless of whether or not corrective action in the area of review is phased.Rationale: Need to add phrase to account for the periodic reevaluations and possible revisions that will be occurring. Addition of the term [as modified]

addresses this concern.

Response: EPA agrees with the commenter and has modified the final rule at §146.84(f) to require the owner or operator to periodically review the emergency and remedial response plan to take into account the most recent AoR. Owners or operators must also periodically update the demonstration of financial responsibility to account for any such changes.

Commenter Name: John McManus Letter ID: 0294 Commenter Organization: American Electric Power Comment ID: 25313 Other EPA Comment Codes and Descriptions: 1220 1.1.1.1 Terminology and definitions

Comment: 5. Area of review definition and basis

We also suggest that the second sentence of the proposed definition of GS project be transferred to the definition of area of review as recommended below. This language also reflects a change from "brine" to "formation fluids."

"Area of review means the subsurface three-dimensional extent of the carbon dioxide stream plume and the associated pressure front, as well as the overlying formations, [any USDWs underlying an injection zone along with any intervening formations,] [FN2] and the surface area above that delineated region."

[FN2] The bracketed language should be included to the extent that the regulations authorize GS above USDWs, an issue on which the signatories have expressed differing views in our respective comments on the proposed rule. See

footnote 1 above.

In addition, we recommend that the second sentence included both in EPA’s proposed definition of area of review and in section 146.84(a) be dropped from the definition and retained in section 146.84(a) but modified to read as

follows:

"(a) The area of review is based on computational modeling, as well as monitoring and other operational data, that account for the physical and chemical properties of all phases of the injected carbon dioxide stream."

The first sentence of section 146.84(a), which duplicates the definition of area of review, should be deleted from section 146.84(a) and retained in the definition with the modifications presented above.

Response: EPA disagrees that the AoR definition needs to specifically include the overlying formations and surface area above the delineated region. The intent of the AoR, a long-standing concept within the UIC Program, is to delineate the surface area and all subsurface formations below it that may potentially be impacted by injection activity. Acceptable delineation models will provide predictions of CO2 fate and transport, as well as changes in formation pressure, in three dimensions as a function of time that can be used to delineate the subsurface storage site and the AoR.

Although EPA disagrees with the commenter's suggested change, the Agency has carefullyconsidered all comments on the AoR definition at 146.84(a) and modified it to read as follows: The region surrounding the geologic sequestration project where USDWs may be endangered by the injection activity. The area of review is delineated using computational modeling that accounts for the physical and chemical properties of all phases of the injected CO2 stream and is based on available site characterization, monitoring, and operational data. EPA believes that this definition is sufficiently broad and describes both the intent of the computational modeling and the relationship of the AoR to areas that are subject to the risks associated with injection.

Commenter Name: Scott Anderson Letter ID: 0520 Commenter Organization: Environmental Defense Fund Comment ID: 21430 Other EPA Comment Codes and Descriptions: 3530 2.2.3.1 AoR reevaluation frequency (seeking comment)

Comment: We think the AOR's area of reviews need to be calculated as intended and updated as necessary. We think ten year updates is far too infrequent and we think that there are some technical problems with the way the AOR is defined in the rule. We believe the EPA's intention is to use elevated pressure as the main guide to AOR delineation, but in our judgment the definition just does not say that.

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 theinherent uncertainties in modeling CO2 movement, the emerging nature of GS technology, riskbased targeting of monitoring activities, and the unique nature of CO2 GS.

EPA agrees that the AoR definition should account for the impact of the CO2 plume on USDWs. The Agency has carefully considered all comments on the AoR definition at 146.84(a) and modified it to read as follows: The region surrounding the geologic sequestration project where USDWs may be endangered by the injection activity. The area of review is delineated using computational modeling that accounts for the physical and chemical properties of all phases of the injected CO2 stream and is based on available site characterization, monitoring, and operational data.

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



### Individual Comments

Commenter Name: Doug Louis Letter ID: 0121 Commenter Organization: Kansas Corporation Commission Comment ID: 22078

Comment: KCC Staff agrees the most accurate and realistic method of determining AOR uses computational models, which are updated regularly in conjunction with monitoring of physical parameters. A prescribed fixed radius surrounding individual wells would not be an appropriate determination of AOR for a complex dynamic CO2 storage facility.Response: EPA agrees that predicting the complex multiphase, buoyant flow of the CO2, coinjectates, 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.

Commenter Name: John Stormon Letter ID: 0123 Commenter Organization: Washington State Dept. of Ecology Comment ID: 23002 Other EPA Comment Codes and Descriptions: 4600 2.6 Proposed Plume and Pressure Front Monitoring Requirements (40 CFR 146.90)

Comment: Area of Review: The proposed standards correctly require not just modeling, but tracking of the actual CO2 plume and pressure front, with periodic reevaluation of the modeled behavior as additional experience is gained at a sequestration project. Modeling is a good method of predicting the behavior of injected CO2 but should not be relied upon without monitoring to verify the accuracy of the modeled predictions. The model will be continually refined throughout the life a sequestration project.

Response: EPA acknowledges the commenter’s support of the modeling approach, and agrees that reevaluation of the AoR as required at 146.84(e) must incorporate monitoring and operational data gathered since the last model run.

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. Monitoring associated with injection wells and the movement of the CO2 plume is necessary to verify that the injectate is confined in the target formations and does not endanger USDWs.

EPA agrees that monitoring data should be used to review model assumptions, verify computational model projections, and, when necessary, provide input for model refinements. As data are collected at an injection site, model parameters can be adjusted to match observations (i.e., for model calibration), which in turn improves the predictive capability of the model. As a GS project proceeds, both monitoring and modeling will evolve, with monitoring results supporting effective AoR reevaluations and leading to improved model predictions.

Commenter Name: Dwight Lockwood, PE, QEP Letter ID: 0141 Commenter Organization: Global Energy, Inc. Comment ID: 23107

Comment: Modeling

1.We support computational fluid flow modeling during injection well site selection, as well as conformational modeling to confirm performance from time to time. This is related to the periodic re-evaluation of the Area of Review.

Response: EPA acknowledges the commenter’s support of the modeling approach, and agrees that reevaluation of the AoR as required at 146.84(e) must incorporate monitoring and operational data gathered since the last model run. This will serve to verify that the CO2 plume and pressure front are moving through the subsurface as predicted, that the delineation model is accurate (or identify needed changes), and refine testing and monitoring activities to ensure that USDWs are protectedfrom endangerment and that there would be adequate warning of potential problems at the site before any endangerment could occur.

Commenter Name: Dwight Lockwood, PE, QEP Letter ID: 0141 Commenter Organization: Global Energy, Inc. Comment ID: 23109

Comment: 2.There is an increasing body of knowledge that computational fluid flow modeling is feasible and can inform an injection operation about performance, and point toward changes that may be appropriate. We are familiar with those involved with the Weyburn Field in Canada, mentioned by EPA.

Response: EPA also agrees that numerical computation, as required at 146.84(c)(1), may be necessary to calculate the complex AoR for a GS project. EPA believes 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 and in some cases may specifically require certain numerical models. EPA also agrees that physical measurement, (i.e. monitoring) is an important component to protecting USDWs from endangerment and will serve to calibrate computational model predictions during the AoR reevaluation to ensure that the AoR adequately represents the extent of the CO2 plume and pressure front.

Commenter Name: Brianne Metzger Letter ID: 0151 Commenter Organization: Spectra Energy Corp Comment ID: 21819

Comment: B. The Area of Review Should Be Determined Based On Computational Fluid Flow Models And Reevaluation Should Occur At A Fixed Frequency Not To Exceed 10

Years.

We agree with the Agency’s current position that the application of computational fluid flow models to predict the complex multi-phase buoyant flow of CO2, co-injectates, and compounds is an acceptable and appropriate approach to mapping out the Area of Review (AoR). Such computational models are currently being used by industry with success. Further, industry continues to refine the accuracy of these models as the data and science are improved.

Response: EPA acknowledges the commenter’s support and believes 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.

Commenter Name: Bonnie Lovelace Letter ID: 0152 Commenter Organization: Montana Department of Environmental Quality (MDEQ) Comment ID:

22111

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

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 toinjection 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.

Commenter Name: Bonnie Lovelace Letter ID: 0152 Commenter Organization: Montana Department of Environmental Quality (MDEQ) Comment ID:

22128

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

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 theinherent uncertainties in modeling CO2 movement, the emerging nature of GS technology, riskbased targeting of monitoring activities, and the unique nature of CO2 GS.

Commenter Name: James Dooley Letter ID: 0156 Commenter Organization: Joint Global Change Research Institute, Pacific Northwest National Laboratory Comment ID:

22616

Comment: Proposed Requirement of Computational Models to Support Permit Is Extremely Appropriate Requirement

The USEPA should be commended for requiring the use of computational models as a part of the permitting process and for the renewal of permits as well as a means of demonstrating compliance with the permit. These computational models are sufficiently well developed at this point in time that they can provide a robust set of technical information that will be needed for issuing Class VI permits. While the use of these models is a highly technical enterprise and will most likely be something that permitees will contract out, the cost of using these models is trivial compared to the capital cost of a complete end to end CCS system or the cost of purchasing enough emissions offsets to cover the CO2 emissions from something like a large power plant over its multidecade lifetime if that facility chose not to implement CCS. It is extremely appropriate to require the use of these sophisticated state of the art modeling tools.

Page 43506. The USEPA should also be commended for explicitly ruling out the use of simple "fixed radius or simple mathematical computations" to compute the AOR for large scale GS projects. Sophisticated computational tools exists which can do AOR calculations while taking into account a large number of key variable and processes. These tools and not a back of the envelope calculation should be required. It is appropriate for EPA to explicitly forbid the use of these simple methodologies for Class VI AOR. By disallowing these simple methods, the USEPA is not materially increasing the cost of employing CCS. While this argument might be put forward by others as a reason to keep these simple AOR tools, it is extremely hard to imagine a private sector firm risking billions totens of billions of dollars of capital needed to construct and operate a CCSenabled power plant or industrial facility without employing sophisticated geochemical/geomechanical tools to assess a prospective GS reservoir. So the USEPA is simply asking for access to data that will most likely already exists with the applicant and is therefore not creating a new cost for CCS deployment.

Response: EPA acknowledges the commenter’s support and believes 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.

Commenter Name: Michael J. Miller Letter ID: 0168 Commenter Organization: Electric Power Research Institute (EPRI) Comment ID: 22499

Comment: Preamble, page 43507: "EPA seeks comment on the applicability of computational fluid flow models for delineating the AoR of GS sites."

EPRI COMMENT #6: We believe that the use of computer models as a tool to predict the size of the area of review (AoR) is appropriate and provides a flexible, phased approach to assessing the number of abandoned wells requiring mitigation.

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.

Commenter Name: Frederick R. Eames Letter ID: 0178 Commenter Organization: CCS Alliance Comment ID: 23854

Comment: 1. Area of Review

The CCS Alliance agrees that traditional AoR delineation methods such as a fixed radius or simple mathematical computations would not he sufficient to predict the extent of CO2 plume movement. The CCS Alliance therefore supports the use of computational fluid flow modeling designed for the specific site conditions and injection regime to delineate the AoR for CO2 GS sites. Such modeling will provide the level of sophistication necessary to predict the complex multi-phase buoyant flow of the CO2, injectates, and mobilizing compounds.

Response: EPA acknowledges the commenter’s support and believes 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 accountfor site-specific and predicted operating conditions as well as geologic heterogeneities and potential migration through faults, fractures, and artificial penetrations.

Commenter Name: Robert F. Van Voorhees Letter ID: 0190 Commenter Organization: Carbon Sequestration Council Comment ID: 24333

Comment: B. Area of Review and Corrective Action Requirements

We support the use of computational models for determination of the appropriate area of review ("AOR") for GS purposes. Modeling of the pressure effects associated with injection - together with conservative modeling to bound the potential extent of CO2 plume movement - are appropriate aids to the evaluation of geologic siting and corrective action to address risks presented by artificial penetrations such as abandoned boreholes. The use of such modeling is already well-established in the context of oil and gas exploration and production and has been used in the UIC program for "no-migration" petitions for hazardous waste injection. Similar modeling can reasonably be adopted for use in

the GS context as well.

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). that may be mobilized due to injection requires the sophistication of computational models. 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.

Commenter Name: Robert F. Van Voorhees Letter ID: 0190 Commenter Organization: Carbon Sequestration Council Comment ID: 24334 Other EPA Comment Codes and Descriptions: 3300 2.2.1 Delineating the AoR/Modeling CO2

movement
Comment: 1. AOR Definition

The proposed rule vaguely defines the AOR as "the region surrounding" the GS project that "may be impacted by the injection activity." 72 Fed. Reg. at 43535 (proposed 40 C.F.R. 146.81(d)). The definition goes on to suggest that the AOR is to be "based on computational modeling that accounts for the physical and chemical properties of all phases of the injected carbon dioxide stream." Id.

There are three issues.

First, the proposed definition suggests the need for a more complex modeling approach than may typically be necessary or appropriate. As experience with hazardous waste injection "no migration" petitions shows, it is rarely necessary to attempt to model chemical changes in the injectate plume; instead conservative modeling of transport should typically be sufficient by itself to show that USDWs will not be endangered. Where this is the case, it is containment of the injectate plume - rather than the precise composition of the plume - that matters and there is no need to model chemical changes. This is acritical point, because it is generally far easier to model transport than chemical changes occurring in the subsurface. In fact, it would be extraordinarily burdensome to have to model "the chemical properties of all phases of the injected carbon dioxide stream" as the proposed rule suggests. Such modeling should be required only to the extent that it is truly necessary to ensure that USDWs will be protected.

Second, the preamble to the proposal suggests that the "best" (most sophisticated?) and most "accurate" modeling should be preferred or even required. 73 Fed. Reg. at 43507. However, fine precision generally isn't necessary, The appropriate goal for modeling is to ensure protection of USDWs, and conservative (i.e., less precise) modeling may be sufficient and even preferable for this purpose. A quest for greater precision would not guarantee greater confidence in modeling results, and could effectively require a less conservative - and thus potentially less protective - modeling approach.

Third, the functional purpose of the AOR is to define the area within which impacts of the injection activity could cause endangerment of a USDW; specifically, the AOR defines the area within which corrective action for abandoned boreholes may be necessary to prevent endangerment of USDWs. The language of the proposed rule (i.e., "may be impacted by the injection activity") is not clearly limited to impacts of the injection activity that could cause endangerment of USDW’s. It should be.

Response: EPA believes that predicting the complex, multiphase, buoyant flow of the CO2, coinjectates, 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.

EPA acknowledges that fine precision may not always be necessary and that many factors determine ultimate confidence in modeling results. However, EPA does not believe that more precision would result in a less protective modeling approach. EPA anticipates that the owner or operator, in consultation with the Director, will choose the model that is most appropriate for a particular GS project, and that this dialogue is a key factor in assuring that the GS site is modeled (and eventually operated and tracked) in a manner that protects USDWs from endangerment. EPA encourages and expects owners or operators to use the best multiphase, computational models available.

Commenter Name: Christopher Murray Letter ID: 0207 Commenter Organization: Pacific Northwest National Laboratory Comment ID: 22434

Comment: Using Multiphase Computational Models to Delineate the AoR. . . . . . . Page 7 We support the use of sophisticated, multiphase, computational models designed for site-specific conditions for AoR delineation, as specified by EPA in the proposed regulations.

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 toinjection 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.

Commenter Name: Christopher Murray Letter ID: 0207 Commenter Organization: Pacific Northwest National Laboratory Comment ID: 22445

Comment: USING MULTIPHASE COMPUTATIONAL MODELS TO DELINEATE THE AoR

PROPOSED REGULATION

p. 43506, c. 1 Current UIC regulations require that the owner or operator define the Area of Review (AoR), within which the owner or operator must identify all penetrations (regardless of property ownership) in the confining zone and the injection zone and determine whether they have been properly completed or plugged.

p. 43506, c. 2 EPA believes that predicting the complex multi-phase buoyant flow of the CO2, coinjectates, and compounds that may be mobilized due to injection requires the sophistication of multiphase computational models. EPA proposes that the owners or operators of GS wells delineate the AoR for CO2 GS sites using computational fluid flow models designed for the specific site conditions and injection regime.

DISCUSSION

The use of multiphase computational models for prediction of plume areas has been supported by several groups, including the Intergovernmental Panel on Climate Change (IPCC, (2005), which suggested the use of modeling for evaluation of the long-term distribution of CO2 in the subsurface. This modeling could be used as the basis for identification of the AoR for a given site. The IPCC report makes clear that the models used for these efforts should be multiphase models that incorporate the important physical, chemical, and geomechanical processes present at a given site (IPCC 2005).

Whereas a prescribed radius or simple mathematical computation, as included in the current UIC regulations, may be adequate for some UIC sites, research and experience in modeling CO2 sequestration leads us to conclude that these simplified approaches are clearly not sufficient to predict the extent of an injected CO2 plume. EPA should be commended for requiring the use of multiphase computational models for delineating the AoR. We know that initial models of the Sleipner site suggested relatively simple and predictable migration of CO2. However, time lapse seismic monitoring of the injected plume revealed the importance of an internal shale formation within the injection reservoir that has significantly altered the direction and extent of CO2 migration from those early predictions (Chadwick et al. 2004). This finding emphasizes the importance of computational fluid flow modeling capable of handling complex internal heterogeneity for prediction of CO2 plume geometries, which areunlikely to be cylindrical or closely predicted using the approaches that have been previously used in UIC applications.

PNNL RECOMMENDATION

We support the use of sophisticated, multiphase, computational models designed for site-specific conditions for AoRdelineation, as specified by EPA in the proposed regulations.

REFERENCES

R.A. Chadwick, P. Zweigel, U. Gregersen, G.A. Kirby, S. Holloway and P.N. Johannessen. 2004. Geological reservoir characterization of a CO2 storage site : the Utsira Sand, Sleipner, Northern North Sea, Energy 29:1371-1381.

IPCC. 2005. IPCC Special Report: Carbon Dioxide Capture and Storage. Summary for Policy Makers and Technical Summary, B. Metz, O. Davidson, H. de Coninck, M. Loos, and L. Meyer (eds.). CambridgeUniversity Press, NewYork.

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.

Commenter Name: John King Letter ID: 0211 Commenter Organization: Shell Exploration and Production Company (SEPCo) Comment ID:

22766

Comment: B. Area of Review and Corrective Action Requirements

We support the use of computational models for determination of the appropriate area of review ("AOR") for GS purposes. Modeling of the pressure effects associated with injection -- together with conservative modeling to bound the potential extent of CO2 plume movement -- are appropriate aids to the evaluation of geologic siting and corrective action to address risks presented by penetrations such as abandoned boreholes. The use of such modeling is already well established in the context of oil and gas exploration and production and has been used in the UIC program for "no-migration" petitions for hazardous waste injection. Similar modeling can reasonably be adopted for use in the GS

context as well.

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 potentialmigration through faults, fractures, and artificial penetrations.

Commenter Name: Andrew Duguid Letter ID: 0226 Commenter Organization: Schlumberger Carbon Services Comment ID: 24024

Comment: Proposed Rule: (1) Predict, using computational modeling, the projected lateral and vertical migration of the carbon dioxide plume and formation fluids in the subsurface from the commencement of injection activities until the plume movement ceases, pressure differentials sufficient to cause the movement of injected fluids or formation fluids into a USDW are no longer present,

Schlumberger Suggested Revision: -

Schlumberger Rationale: We support this as written

Response: EPA acknowledges the commenter’s support; the final GS rule retains the provision with minor modifications to require the use of existing data in predicting the AoR.

Commenter Name: Neeraj Gupta Letter ID: 0229 Commenter Organization: Battelle Energy Technology (BET) Comment ID: 21830

Comment: Page 64, Area of Review Determination/Modeling - We agree that multiphase numerical models are the best option for determining area of review (AOR) for complex, full-scale injection sites. Simpler analytical models may be used for smaller-scale, short-term tests. Multiphase computer simulations, supported with field data, should be primary tool for managing the storage sites through out the life cycle from site selection, permitting, characterization, operations, to post operational monitoring and closure. However, modeling should not be restricted to a single code or type of code. This will stifle innovation, because many more modeling codes are likely to be developed and existing commercial, academic, and national laboratory codes are incorporating new processes and improvements based on lessons learned from field projects. The incorporation of multiphase processes is likely to be a key requirement for models. However, we do not believe that fully coupled model with CO2 flow, transport, geochemical, geomechanical, and other processes in a single simulation for the entire facility and life cycle is currently feasible. Such fully-coupled codes require extensive computational power and are more applicable to evaluating basic science questions.

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.

EPA agrees that operators should have the flexibility to select models with which they are familiar and that are most appropriate to the site conditions and available data types and amounts. EPA has evaluated technical documents regarding several computational models that may be used for GSsites. Based on this review (as documented in the preamble to the proposed GS regulation and the background document "Computational Modeling of Underground Injection of Carbon Dioxide for Determination of Area-of-Review and Potential Risk to Underground Sources of Drinking Water"), EPA believes that several models meet the minimum requirements for models in the GS regulation.

Commenter Name: Steven B. Corneli Letter ID: 0234 Commenter Organization: NRG Energy, Inc. Comment ID: 23162

Comment: 1. Use of Computational Models for Area of Review

The EPA requested comment on the proposed rule regarding the use of modeling for area of review (AoR). NRG supports the use of computational models for determination of the AoR for geologic sequestration projects. The use of such models is already being used in the UIC program for "no-migration" petitions for Class I injection wells. We believe the use of modeling for determining the pressure effects associated with the underground injection process is an appropriate confirming process for safe site selection and corrective action to address potential risk presented by GS.

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.

Commenter Name: Mark E. Fesmire Letter ID: 0237 Commenter Organization: New Mexico Oil Conservation Division (NMOCD) Comment ID: 23209

Comment: B. The OCD applauds the inclusion of computational modeling to establish the Area of Review (AOR) as much more representative of reservoir conditions than fixed radius AOR’s currently in use in the UIC program.

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.

Commenter Name: Walter L. Baker Letter ID: 0253 Commenter Organization: Utah Division of Water Quality Comment ID: 22347

Comment: COMPUTATIONAL MODELING

We support the use of multiphase models in predicting the movement of the CO2 plume and injection zone fluids given the multiphase nature of the injectate particularly in the early stage of the CCGS project. However, we also emphasisthe importance of the use of geochemical modeling in addressing the reactivity of CO2 in the presence of water and other reactive components in the matrix and fluids of the injection and confining zones.

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.

EPA disagrees that geochemical modeling (i.e., reactive transport modeling) will be necessary for delineation of the AoR in all cases. EPA clarifies that the GS regulation requires that AoR modeling consider the chemical and physical properties of the injected stream and native fluids, but does not specifically require reactive transport modeling (146.84(c)(1)). As discussed in the preamble to the proposed GS regulation, EPA expects that AoR modeling will account for multiphase fluid flow processes, including density-driven flow (e.g., buoyancy). EPA believes that the purpose of AoR modeling is to predict the regions wherein fluid pressures increase and/or to which CO2 may be transported. Based on a review of the technical literature, EPA believes that, in many cases, reactive transport modeling will not be necessary to determine whether USDWs would be endangered. Any areas of geochemical disturbance would be within the modeled AoR as defined at 146.84(c). EPA adds that the Director has discretion to require additional modeling, including geochemical modeling, if he or she determines this to be necessary. EPA adds that the purpose of modeling is to target areas where geochemical monitoring should be performed.

Commenter Name: Scott Anderson Letter ID: 0520 Commenter Organization: Environmental Defense Fund Comment ID: 21420 Other EPA Comment Codes and Descriptions: 1420 1.2.1.1 Support the GS rulemaking; 4660 2.6.6 Geochemical monitoring

Comment: We think the rule, the proposed rule has done a very good job of keeping the focus on both CO2 leakage risks and also the risk of problems from displaced brine. The confining zone in the rule is required to contain both CO2 and displaced formation fluids. The zone of elevated pressure as defined in the rule focuses on both CO2 and formation fluids that might be driven out of a US -- into a USDW. The modeling requirements are modeling both of the CO2 plume extent and formation fluid movement. There is the requirement for periodic monitoring of groundwater quality and geochemical changes above the confining zone which would help detail whether either CO2 or brine is leaking and there are adequate response provisions.

Response: EPA acknowledges the commenter’s support and believes 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.EPA believes that the creation of a new injection well class (VI) under the existing UIC Program is necessary to enable the use of GS as a climate change mitigation technology in a manner that protects USDWs from endangerment. EPA agrees that the UIC Program, under the authority of the SDWA, provides a strong framework for regulating injection of CO2 for GS and adds that the GS regulation tailors the UIC requirements to address the unique issues associated with large-scale GS including large injection volumes, the relative buoyancy of CO2, its corrosivity in the presence of water, the potential presence of impurities in captured CO2, and its mobility within subsurface geologic formations. For additional information on well construction, siting, and testing and monitoring requirements, please also see the discussion of EPA’s Final Regulatory Approach in the preamble to the final GS rule.

Commenter Name: Doug Louis Letter ID: 0530 Commenter Organization: Kansas Corporation Commission Comment ID: 21341

Comment: KCC staff agrees that the most accurate and realistic method of determining AOR is computational models which are updated regularly in conjunction with modeling monitoring of physical trailers. A prescribed fixed radius surrounding individual wells would not be an appropriate determination of AOR for a complex dynamic CO2 storage facility.

Response: EPA acknowledges the commenter’s support and agrees that the unique aspects of GSmerit the use of sophisticated computational modeling for delineation of the AoR, based on sitespecific features and geology, including the presence of faults, fractures, and artificial penetrations. EPA believes that computational modeling of the AoR prior to injection will provide the best obtainable estimates of the extent of the CO2 plume over several years of active injection. EPA has strengthened the minimum frequency for the AoR reevaluation from ten years to at least every 5 years (146.84(e)). EPA believes that this revised frequency addresses commenters' concerns aboutthe inherent uncertainties in modeling CO2 movement, the emerging nature of GS technology, riskbased targeting of monitoring activities, and the unique nature of CO2 GS.

Comment Code: 3320 2.2.1.2 Comments opposed to requiring computational models to delineate

the AoR



### Individual Comments

Commenter Name: James Rower Letter ID: 0173 Commenter Organization: Utility Solid Waste Activities Group (USWAG) Comment ID: 23485 Other EPA Comment Codes and Descriptions: 3350 2.2.1.5 Use of proprietary models for GS sites (seeking comment)

Comment: 8. Modeling

As most models now are proprietary, USWAG supports the use of proprietary models for use with CO2 GS sites. As EPA recognizes, many popular proprietary codes in the petroleum-reservoir engineering discipline have been used in peer-reviewed studies to model CO2 sequestration. 73 Fed. Reg. at 43507. These and other proprietary models should be available for use in modeling for Class VI CO2 GS wells, provided that they are based on accepted science and have been validated,and as long as the Owners or Operators using proprietary models disclose, as necessary, the code assumptions, relevant equations, and scientific basis of each model. USWAG believes that the use of computational fluid flow models for delineating the AoR of GS sites is acceptable but should not be required. Id.

Response: EPA agrees that some of the available proprietary models may meet the needs for calculating the AoRs of GS sites and will allow their use for GS projects. EPA acknowledges that several proprietary models have been used by petroleum-reservoir engineering professionals as well as in peer-reviewed studies to model CO2 sequestration. EPA plans to allow their use in meeting the requirements for the GS regulation, but clarifies that GS well operators using proprietary models are required to disclose, to the Director's satisfaction, the code assumptions, relevant equations, and scientific basis. EPA adds that its Confidential Business Information requirements at 40 CFR 144.5 will apply to the use of proprietary models.

EPA clarifies that the final rule will require the use of computational models. EPA believes that the unique aspects of GS merit the use of sophisticated computational modeling for delineation of the AoR, based on site-specific features and geology, including the presence of faults, fractures, and artificial penetrations. EPA believes that computational modeling of the AoR prior to injection will provide the best obtainable estimates of the extent of the CO2 plume over several years of active injection.

Commenter Name: Chris M. Hobson Letter ID: 0201 Commenter Organization: Southern Company Comment ID: 22168

Comment: model. Id. at 43507. Based on the valuable experience Southern Company has gained through our C02 GS pilot project, we also support the use of computational fluid flow models for AoR delineation, provided that these models are available for use at the option of the Owner or Operator and are not required for all CO2 GS projects. See id.

Response: EPA clarifies that the final rule requires the use of computational modeling at 146.84(c)(1). EPA believes that the use of computational modeling, rather than reliance on a fixed radius or simple computation, is necessary to account for the complexity of GS projects. EPA believes 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. 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.

Commenter Name: Mark Bohrer Letter ID: 0241 Commenter Organization: North Dakota Industrial Commission Comment ID: 23231 Other EPA Comment Codes and Descriptions: 3330 2.2.1.3 Applicability /adequacy of computational models (seeking comment)

Comment: 11. EPA believes that predicting the complex multi-phase buoyant flow of the CO2, "co-injectates," and compounds that may be mobilized due to injection requires the sophistication of computational models. EPA proposes that the owners or operators of GS wells be required to delineate the AoR for CO2 GS sites using computational fluid flow models designed for the specific site conditions and injection regime. EPA seeks comment on the use of modeling forAoR delineation. EPA Notice 43506.

There is concern about the lack of information necessary to construct a valid model in areas where the sequestration zone has not been extensively studied. This lack of information may make modeling difficult or not very useful. Any modeling used should be re-examined and recalibrated over time with additional data gathered. Modeling should not be solely relied upon where real data offers a different view. Seismic and offset well data can help delineate the AOR.

Response: The Agency believes that AoR delineation using computational modeling that accounts for the multiphase flow of CO2 and native fluids (i.e., naturally occurring salty water), including density-driven flow (i.e., buoyancy), is necessary to ensure protection of USDWs from endangerment. The computational models used for this purpose are required to predict the fate of injected CO2 and changes in formation pressure. EPA believes that the requirements at 146.84(c)(1) to delineate the AoR using computational modeling are appropriate and encompass the significant processes that could affect the location of the CO2 plume and associated pressure front and has

retained this in the final rule.

EPA agrees that the modeling should be re-examined and recalibrated over time. The GS regulation at 146.84(e) also requires owners or operators to periodically reevaluate the AoR to incorporate monitoring and operational data. This process provides additional opportunities to verify that the models have accurately predicted movement of the CO2 plume and to make any needed adjustments to corrective action or monitoring at the site.

Letter ID: 0263 Commenter Organization: Interstate Oil & Gas Compact Commission Comment ID: 22797

Comment: III A. 2 Proposed Area of Review and Corrective Action Requirements

L. EPA seeks comment on the use of modeling for AoR delineation.

IOGCC Response: See General Comment for Section III. A. 2 above. The collection of physical data (i.e. well bore data) maybe necessary to fully utilize modeling to determine the ultimate extent of the proposed CO2 storage volume. Models should only be used when they are appropriate. The Director needs the flexibility to be able to supplement or substitute other data elements as appropriate.

Response: EPA agrees that it is appropriate to allow operators the flexibility to select modeling, site characterization, and monitoring techniques that are most appropriate to site conditions and available types and amounts of data. However, EPA believes that modeling is necessary to delineate the AoR for GS projects, and the final rule retains this requirement. EPA notes that the final rule at 146.84(c)(1) requires the AoR to be predicted using existing site characterization, monitoring, and operational data, along with computational modeling, but that it does not specify the particular data inputs. EPA adds that the final rule at 146.82(c)(1) requires the owner or operator to revise the proposed AoR submitted under 146.82(a)(2) as necessary to address new data collected during logging and testing.

Comment Code: 3330 2.2.1.3 Applicability /adequacy of computational models (seeking comment)

### Individual Comments

Commenter Name: John Hanger Letter ID: 0130 Commenter Organization: Pennsylvania Dept. of Env. Protection Comment ID: 21504

Comment: -The proposed rule discusses multiphase modeling and considers them appropriate for hydraulically connected formations being used by different operators. Where there are multiple operators injecting into a formation that is hydraulically connected, rules should require an evaluation of the chemical reaction of the different injections, unless they are chemically the same, as well as their

interaction with native fluids.

Response: EPA agrees that the impacts of multiple operators injecting into hydraulically connected formations should be accounted for in the AoR modeling. EPA adds that the owner or operator must demonstrate in the proposed AoR and corrective action plan to the satisfaction of the Director that the modeled AoR will be based on detailed site-specific geologic data collected during the site characterization process including consideration of existing conditions (e.g., current injection activities). 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 in a formation or a series of hydraulically connected formations. 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.

Commenter Name: Christine Reimer Letter ID: 0142 Commenter Organization: National Ground Water Association Comment ID: 22548

Comment: General Comments on the Use of Modeling for Ground-Water Protection Related to CO2 Sequestration

Quantitative modeling must play an important role in the assessment of groundwater protection related to CO2 sequestration projects. A ‘quantitative model’ is defined here as a quantitative mathematical analog of the real subsurface

system.

Three overall purposes for quantitative modeling are generally recognized:

1. Generic: Model used in a hypothetical sense 2. Interpretive: Model used to understand system dynamics 3. Predictive: Model used to predict future behavior of the subsurface

system.

All three purposes are generally needed for a CO2 sequestration project. For example, generic models are used to determine the important physical or geochemical mechanisms that dominate transport or trapping of CO2. An interpretive model is applied to test specific hypotheses regarding these behaviors. Predictive modeling provides the basis for design of the finalinjection scheme and establishment of potential risk to drinking water.

Quantitative models may range from simple analytic calculations to complex multi-component multi-phase coupled three-dimensional numerical simulations. The choice of quantitative model (analytic or numerical) depends in large part on the ultimate objective of the modeling study, and on practical constraints including availability of data and computational limitations. Which type of model or combination of models is most appropriate for a specific situation depends on many factors. In general, using a combination of modeling and analysis techniques is recommended, because different levels of complexity are needed at various stages of a project and for different objectives, and application of multiple modeling techniques can be used for "cross-checking" and overall quality assurance.

Numerical models are widely available and usually represent a relatively wide range of physical and chemical processes, spatial heterogeneity of material properties, and nonlinear interactions among different processes. While these kinds of models allow for substantial flexibility and can provide detailed predictions of system behavior, they also require large amounts of data, much of which may be difficult to obtain or estimate. As such, specific choices of models must be made with care, and some situations may most effectively be addressed by a combination of different kinds of models.

Quantitative modeling, whether conducted with analytical or numerical modeling tools, provides significant insights into system behavior. The advantages of such models are that they:

1. provide a framework for data collection centered about a specific set of transport and geochemical behaviors. 2. allow communication and the interpretation of these data in the context of scientific principles and facilitate collaboration among engineers, scientists, and regulators. 3. may be extended far into the future using multiple design scenarios 4. can be compared to measured data which allow hydraulic and geochemical parameters to be estimated. 5. Can be used to access the performance of the system in a long performance period for which field and laboratory data are not

available.

It is important to recognize that all quantitative mathematical models are based upon a "conceptual model" which defines the important fluid and chemical interactions as well as the spatial and temporal extent of the model. Because the conceptualization is a critical part of the modeling activity, it is important to explore multiple conceptual models during the modeling process to assure that important scenarios are not excluded from the analysis.

The selection of which quantitative model to use relies on the identification of the physical/chemical parameters and functions that must be represented. Because the injection and migration of CO2 into the subsurface is hydraulically and chemically complex, comprehensive quantitative modeling would have to includemany parameters and factors -- including the flow of miscible and immiscible phases in all potential states as well as chemical reactions among fluids and with the geologic media and necessary heat transfer. The geologic medium may also deform or be chemically altered in response to the presence of CO2. The complexity of these coupled processes, in the presence of complex hydrostratigraphy, lead to models that are at the limit of the current capabilities of available computer hardware and software. It is likely, therefore, that multiple models may be required to provide the necessary insights into the important physical and chemical processes. Ultimately, sound scientific and engineering judgments should be applied to determine which physical or chemical processes are most important for a given analysis, and to make assumptions that are consistent with those judgments. For example, during the injection phase of a CO2 operation, multi-phase flow physics tend to dominate other processes such as interphase mass transfer and geochemical reactions. This separation of time scales can lead to important simplifications for the purpose of risk assessment. Similar analysis of spatial scales can provide additional simplifications, leading to practical modeling tools for the purpose of risk assessment. It is, therefore. imperative that modeling experts participate and manage all phases of the modeling process, in concert and constant communication with the project team and the appropriate regulatory reviewers, to ensure that appropriate and comprehensive quantitative modeling tools are applied successfully."

The process of comparing simulated and measured predictions for the purpose of developing a more accurate depiction of a subsurface flow system is generally referred to as "model calibration" in the ground-water literature. (This same process is referred to as "inverse modeling" in exploration geophysics and "history matching" in petroleum reservoir simulation.) Model calibration involves varying the parameters of the quantitative model to achieve the minimum difference between measured and predicted responses. This is usually achieved through an automated process using non-linear regression or a heuristic algorithm to optimize the problem (e.g. as implemented in the PEST or UCODE software). In the case of ground-water modeling, the predicted and measured data are usually pressures, discharge rates, or concentrations of fluids or dissolved species. These data may not be available during the design stage of a CO2 project unless wells already exist in the target formation. As wells are drilled and geologic and fluid information are collected, however, the model should be refined and calibrated. Most automated calibration procedures allow for statistical estimation of confidence in the estimated parameters, providing a basis for quantifying the sensitivity of the model to changes in its parameters, and for performing quality control of model predictions.

The design, construction, and calibration of analytic or numerical models should follow a quality assurance and quality control procedure. These procedures should include benchmarking of the mathematical predictions against known results, a method for assuring input data quality and lineage, and a statistical analysis of the predictive results against available data and/or sensitivity analyses. ASTM guides are available for ground-water modeling and code benchmarking (e.g. Guides D 6025, D 5447, D 5490, D 5611, D 5609, D 5610, and D 5718).Response: EPA agrees that complex modeling techniques are necessary to calculate the AoR while adequately accounting for the complexities of a GS site and all phases of a CO2 plume. EPA believes, based on the research that supported the modeling requirements in the GS regulation (as described in the background document, "Computational Modeling of Underground Injection of Carbon Dioxide for Determination of Area-of-Review and Potential Risk to Underground Sources of Drinking Water" cited in the proposed rule preamble as USEPA, 2008d), that technology has advanced to the point that a CO2 injection project can be appropriately modeled to predict and track a CO2 plume (and pressure front). Each AoR calculation will be reviewed based on site-specific geologic conditions, planned operating conditions, and available modeling and computational technology. EPA agrees that appropriate data quality review should be conducted during AoR modeling. Methods for assuring input data quality and lineage, as well as statistical analysis of predictive results may be used during evaluation of a permit application, at the discretion of the

Director.

EPA anticipates that modeling technology will continue to improve, and encourages and expects owners or operators to use the best available multiphase computational models to determine the AoR. Reliance on improved models will likely increase the accuracy and quality of the AoR characterization, resulting in increased protection of USDWs from endangerment.

EPA adds that, to address uncertainty in modeled results, particularly over the long term, it is requiring that the AoR be reevaluated (under 146.84(e)) to verify the CO2 plume is behaving as predicted and to allow for necessary revisions to corrective action or monitoring. The final GS regulation includes a requirement that the AoR be reevaluated at least every 5 years (an adjustment from the ten year interval in the proposal), which should further address the commenters' concerns. This frequency will provide the Agency with information on AoR reevaluations to support subsequent regulatory evaluations that are part of the Agency's adaptive approach. The Agency 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.

Commenter Name: Christine Reimer Letter ID: 0142 Commenter Organization: National Ground Water Association Comment ID: 22552

Comment: Modeling is Needed: When considering tens of miles, trying to use conservatively the analytical solution as provided in 40 CFR §146.06 will likely generate unrealistically large AORs. Parameters such as formation thickness and heterogeneity, storativity and permeability values will likely vary in the zone of elevated pressure suggesting that model results should be accepted as valid.

How to define the edge of the AOR? If the CO2 plume is relatively easy to define in terms of modeling, this is much less true for the pressure plume. Limits to the secondary AOR can be defined more or less as it is currently done by the contour line of the additional pressure that would push the injection formation brine beyond some elevation threshold (for example, 100 ft below the base of the USDW). Time-varying area where corrective action needs to take place as injection progresses can be defined in a similar fashion.

AORs can be initially defined solely on the basis of modeling. However, NGWA strongly supports that a satisfactory match between prediction and actual fieldmeasurements needs to be assessed as the project progresses.

Response: EPA agrees that monitoring and operational data should be used to verify that the CO2 plume and pressure front are moving as predicted in AoR calculation models (146.84(e)). EPA believes that the requirements for periodic AoR reevaluation can also help address uncertainties inherent in predictive modeling and allow for refinement of model predictions based on monitoring, operational, and other site-specific data.

Commenter Name: Christine Reimer Letter ID: 0142 Commenter Organization: National Ground Water Association Comment ID: 22581

Comment: Preamble Questions: EPA seeks comment on the applicability of computational fluid flow models for delineating the AoR of GS sites. EPA Notice 69.

NGWA Response: See NGWA General Comment Document Section titled "General Comments on Use of Modeling for Ground-Water Protection Related to CO2 Sequestration".

Response: As described above, EPA agrees that complex modeling techniques may be required to calculate the AoR while adequately accounting for the complexities of a GS site and all phases of a CO2 plume.

Commenter Name: James Childress Letter ID: 0158 Commenter Organization: Gasification Technologies Council (GTC) Comment ID: 23771 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: §146.84 Area of review and corrective action. (c) (1) "Predict, using computational modeling, the projected lateral and vertical migration of the carbon dioxide plume and formation fluids in the subsurface from the commencement of injection activities until the plume movement ceases, pressure differentials sufficient to cause the movement of injected fluids or formation fluids into a USDW are no longer present, or after a fixed time period as determined by the Director."

We recommend striking out "Predict, using computational modeling, the protected lateral and vertical migration of the carbon dioxide plume" and replacing with "Using computational modeling, provide protected potential ranges of lateral and vertical migration of the carbon dioxide plume" The use of multiphase groundwater flow and transport models is to predict the composition and movement of each phase state (e.g., liquid, gas ,supercritical fluid) of CO2 in the subsurface, as well as fluid pressures, to define the AoR. One of the concerns with the use of such complex models is that the site may not be fully characterized with respect to hydro-geologic properties. There may be significant uncertainty in one or more hydraulic processes/parameters. Therefore, it is possible to obtain a wide-range of model outcomes from different model parameters. The uncertainty in model parameters and sensitivity of model results to parameter selection should be addressed.

Response: EPA has clarified this language in the final rule. It now reads, “Predict, using existingsite characterization, monitoring and operational data, and computational modeling, the projected lateral and vertical migration of the carbon dioxide plume and formation fluids in the subsurface from the commencement of injection activities until the plume movement ceases, until pressure differentials sufficient to cause the movement of injected fluids or formation fluids into a USDW are no longer present, or until the end of a fixed time period as determined by the Director.”

EPA agrees that modeling results are prone to varied degrees of uncertainty. As discussed in the preamble to the proposed GS regulation and the associated background document "Computational Modeling of Underground Injection of Carbon Dioxide for Determination of Area-of-Review and Potential Risk to Underground Sources of Drinking Water" (cited in the proposed rule preamble as USEPA, 2008d), model predictions depend largely on the values of key parameters. Often these parameter values are estimated or averaged from several data sources. EPA also agrees that sensitivity analyses and "worst case scenario" modeling runs should be presented by the owner or operator and evaluated by the Director. If during the permit review, the Director determines that modeling results are too wide-ranging, further information will be required of the owner or operator.

EPA clarifies that models are tools to help predict the movement of a CO2 plume over long time frames. However, EPA recognizes that it cannot be expected that modeling something as complex as a CO2 plume can be done with complete certainty; therefore EPA is also requiring that the AoR be reevaluated to verify the CO2 plume is moving as predicted and to allow for model calibration and necessary revisions to the required GS project plans (e.g., AoR and corrective action, testing and monitoring, injection well plugging, post-injection site care and site closure, and emergency and remedial response). EPA believes that near-term predictions (e.g., over the subsequent 5 years) will have the highest degree of certainty. Periodic model calibration will allow refinement to the AoR delineation based on real-world conditions and operating data and monitoring results, and thus increase confidence in the modeled predictions. EPA adds that the final GS regulation includes a requirement at §146.84(e) that the AoR be reevaluated at least every 5 years (an adjustment from the ten year interval in the proposal), which should further address the commenters' concerns regarding model uncertainty.

Commenter Name: James Childress Letter ID: 0158 Commenter Organization: Gasification Technologies Council (GTC) Comment ID: 23779

Comment: EPA seeks comment on the applicability of computational fluid flow models for delineating the AoR of GS sites. EPA Notice 69.

Computational fluid flow models should be permitted for delineating the AoR of GS sites provided also that data are provided supporting their validation in similar complex structures and flow regimes

Response: EPA agrees that a detailed geologic assessment is essential to evaluating the presence and adequacy of a proposed site to receive and confine the CO2. EPA encourages owners and operators to submit (and Directors to review) any available data on the site, such as seismic or off-set well data. The AoR and corrective action plan required at §146.84(b)must describe the site characterization data on which the model will be based. The Director has discretion to require the use of existing data if it is not initially included. Furthermore, the owner or operator's testing and monitoring plan required at §146.90 should provide for site-specific data (which may include seismic and direct measurements) that can be used to inform updates to the model and support AoR

reevaluations.The Agency believes 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. 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.

EPA clarifies that the model inputs must include actual geologic information, data collected during the site characterization process (e.g., information about artificial penetrations), and anticipated operating parameters (e.g., injection rates) submitted with the permit application under §146.82. Models will be revised and recalibrated during subsequent AoR reevaluations, which must account for all available monitoring and operational data, as required at §146.84(e).

Commenter Name: Kyle Isakower Letter ID: 0170 Commenter Organization: American Petroleum Institute Comment ID: 24223

Comment: Rule Provisions: 146.82(c), 146.84, 146.90(d)(2) EPA Preamble Question: 11. EPA believes that predicting the complex multi-phase buoyant flow of the CO2, "co-injectates," and compounds that may be mobilized due to injection requires the sophistication of computational models. EPA proposes that the owners or operators of GS wells be required to delineate the AoR for CO2 GS sites using computational fluid flow models designed for the specific site conditions and injection regime. EPA seeks comment on the use of modeling for AoR delineation. EPA Notice 43506.

API Response: Modeling is well developed technology that can readily simulate complex behavior of injected CO2. It should be one of the techniques used to delineate the AoR. Modeling alone though should not be the sole basis for determining the AoR. Other technologies such as seismic, use of off-set wells, should also be considered when delineating the proposed AoR.

The oil and gas industry has a great deal of experience that can be generally applied in the delineation of the AoR.

The most complex model is not always necessary to adequately delineate the AoR. Some CO2 EOR projects have successfully operated for decades using only production data and pressure mapping, which has in effect defined AoR.

Response: EPA agrees that the AoR should not be based exclusively on modeling. EPA has clarified the AoR modeling requirement in §146.84(c)(1) for the final rule. It now reads, “Predict, using existing site characterization, monitoring and operational data, and computational modeling, the projected lateral and vertical migration of the carbon dioxide plume and formation fluids in the subsurface from the commencement of injection activities until the plume movement ceases, until pressure differentials sufficient to cause the movement of injected fluids or formation fluids into a USDW are no longer present, or until the end of a fixed time period as determined by the Director.”

EPA clarifies that the model inputs must include actual geologic information, data collected during the site characterization process (e.g., information about artificial penetrations), and anticipated operating parameters (e.g., injection rates) submitted with the permit application under §146.82. This would include any seismic or off-set well data collected to meet the requirements of §146.82(a).Models will be revised and recalibrated during subsequent AoR reevaluations, which must account for all available monitoring and operational data, as required at §146.84(e).

Commenter Name: Kyle Isakower Letter ID: 0170 Commenter Organization: American Petroleum Institute Comment ID: 24225

Comment: Rule Provisions: 146.84 EPA Preamble Question: 13. EPA seeks comment on the applicability of computational fluid flow models for delineating the AoR of GS sites. EPA Notice

43507.

API Response: While computational fluid flow models can inform the delineation of the AoR, modeling shouldn’t be the sole criteria for determining AoR. (See Comment # above also.)

Response: As described above, EPA agrees that the AoR should not be based exclusively on modeling. EPA has clarified the AoR modeling requirement in §146.84(c)(1) for the final rule, specifying that site characterization, monitoring, and operational data must be used along with modeling.

Commenter Name: Robert J. Finley Letter ID: 0180 Commenter Organization: Illinois State Geological Survey Comment ID: 23627

Comment: (c)(1)

It is unclear to this reviewer whether computational modeling can address the

lateral and vertical movement of all "formation fluids in the subsurface". This needs to be restricted to the receiving reservoir. Further, it is unclear if current modeling can adequately address both pressure driven fluid flow and density driven flow at plume boundaries that carries saturated brine away from free phase supercritical CO2 at the plume margins. Also, in a fully equilibrated column of reservoir rock at hydrostatic pressure, a 1 psi differential in a receiving reservoir could potentially be sufficient to cause fluids to migrate. However, the capillary entry pressure of the confining layer may prevent this. As stated here, however, there is no accounting for capillary entry pressure and its role in confining the injectate.

Response: EPA disagrees that modeling of only the receiving reservoir (i.e., the injection zone) is adequate in all cases to predict the potential movement of the CO2 plume and pressure front and ensure that USDWs will not be endangered. EPA believes, based on research and technical expert consultations, that available complex computational models can effectively simulate CO2 transport, fate, and changes in formation pressure in three dimensions. The Agency believes that these multiphase models will be able to incorporate factors such as pressure driven fluid flow, density driven flow, hydrostatic pressure and capillary entry pressure.

Multiphase models have been used by States and industry for predicting the movement of water and solutes in soil, the behavior of non-aqueous phase liquid contaminants (e.g., trichloroethene) at hazardous waste sites, the recovery of oil and gas from petroleum-bearing formations, and more recently, CO2 in the subsurface.Commenter Name: Bradley J. Field Letter ID: 0186 Commenter Organization: New York State Dept. of Environmental Conservation

Div. of Mineral Resources Comment ID:

25181

Comment: J. EPA seeks comment on the use of modeling for AoR delineation.

NYSDEC-DMN Response: See General Comment for Section III. A. 2 above. AoR delineation should be based on best available technology and available data. The collection of physical data (i.e., well bore data) may be necessary to fully use modeling to determine the ultimate extent of the proposed CO2 storage volume and reservoir pressures. The Director should have the flexibility to be able to supplement or substitute other data elements as appropriate ahead of such drilling and data gathering with confirmation of the model once additional

information is available.

Response: EPA agrees that it is appropriate to allow operators the flexibility to select modeling, site characterization, and monitoring techniques that are most appropriate to site conditions and available types and amounts of data. The owner or operator must demonstrate, in the proposed AoR and corrective action plan required at §146.84(b), to the satisfaction of the Director, that the modeled AoR will be based on detailed geologic data collected on the site. EPA anticipates that any model that does this in a satisfactory manner will be approved by the Director. EPA acknowledges that modeling technology is expected to continuously improve, and encourages and expects owners or operators to use the best available multiphase computational models to determine the AoR. Reliance on improved models will likely increase the accuracy and quality of the AoR characterization, resulting in better protection of USDWs from endangerment.

Commenter Name: Bradley J. Field Letter ID: 0186 Commenter Organization: New York State Dept. of Environmental Conservation

Div. of Mineral Resources Comment ID:

25183

Comment: L. EPA seeks comment on the applicability of computational fluid flow models for delineating the AoR of GS sites.

NYSDEC-DMN Response: See General Comment for Section III. A. 2 above. AoR delineation should be based on best available technology and available data. The collection of physical data (i.e., well bore data) may be necessary to fully use modeling to determine the ultimate extent of the proposed CO2 storage volume and reservoir pressures. The Director should have the flexibility to be able to supplement or substitute other data elements as appropriate ahead of such drilling and data gathering with confirmation of the model once additional

information is available.

Response: As described above, EPA agrees that it is appropriate to allow operators the flexibility to select modeling, site characterization, and monitoring techniques that are most appropriate to site conditions and available types and amounts of data. The owner or operator must demonstrate, in the proposed AoR and corrective action plan required at §146.84(b), to the satisfaction of the Director, that the modeled AoR will be based on detailed geologic data collected on the site. EPA adds that the Director has authority to request supplemental information if needed to ensure that the site will be protective of USDWs.Commenter Name: Robert F. Van Voorhees Letter ID: 0190 Commenter Organization: Carbon Sequestration Council Comment ID: 24515

Comment: Rule Provisions or Federal Register Cite: 146.82(c), 146.84, 146.90(d)(2) EPA Preamble Question: 11. EPA proposes that the owners or operators of GS wells be required to delineate the AoR for CO2 GS sites using computational fluid flow models designed for the specific site conditions and injection regime. EPA seeks comment on the use of modeling for AoR delineation. EPA Notice 43506.

CSC Response: Modeling is well developed technology that can readily simulate complex behavior of injected CO2. It should be one of the techniques used to

delineate the AoR.

The oil and gas industry has a great deal of experience that can be generally applied in the delineation of the AoR.

The most complex model is not always necessary to adequately delineate the AoR. Some CO2 EOR projects have successfully operated for decades using only production data and pressure mapping, which has in effect defined AoR.

Response: EPA agrees that the oil and gas industry has contributed to the state of modeling science, and anticipates that some industry-developed modeling products will be acceptable for models in the AoR for GS sites, as long as GS well operators clearly disclose, to the Director's satisfaction, the code assumptions, relevant equations, and scientific basis.

EPA clarifies that the model inputs must include actual geologic information, data collected during the site characterization process (e.g., information about artificial penetrations), and anticipated operating parameters (e.g., injection rates) submitted with the permit application under §146.82. Models will be revised and recalibrated during subsequent AoR reevaluations, which must account for all available monitoring and operational data, as required at §146.84(e).

EPA encourages and expects owners or operators to use the most appropriate multiphase computational models available to determine the AoR. However, EPA does not believe that the most "complex" model will, in all cases, be the best available AoR delineation model. The requirements at §146.84(c)(1) are designed to allow the owner or operator to choose, in consultation with the Director, the modeling platform that is most appropriate for a particular GS project.

EPA anticipates that modeling technology will continue to improve, and encourages and expects owners or operators to use the best available multiphase computational models to determine the AoR. Reliance on improved models will likely increase the accuracy and quality of the AoR characterization, resulting in increased protection of USDWs from endangerment.

Commenter Name: Robert F. Van Voorhees Letter ID: 0190 Commenter Organization: Carbon Sequestration Council Comment ID: 24517

Comment: Rule Provisions or Federal Register Cite: 146.84 EPA Preamble Question: 13. EPA seeks comment on the applicability of computational fluid flow models for delineating the AoR of GS sites. EPA Notice

43507.

CSC Response: Computational fluid flow models can inform the delineation of theAoR. (See also Comment on Question 11 above.)

Response: EPA encourages and expects owners or operators to use the most appropriate multiphase computational models available to determine the AoR. The requirements at §146.84(c)(1) are designed to allow the owner or operator to choose, in consultation with the Director, the modeling platform that is most appropriate for a particular GS project. EPA adds that its Confidential Business Information requirements at 40 CFR 144.5 will apply to the use of proprietary models.

EPA anticipates that modeling technology will continue to improve, and encourages and expects owners or operators to use the best available multiphase computational models to determine the AoR. Reliance on improved models will likely increase the accuracy and quality of the AoR characterization, resulting in increased protection of USDWs from endangerment.

Commenter Name: Craig R. Walters Letter ID: 0200 Commenter Organization: Anadarko Petroleum Corporation Comment ID: 24578

Comment: Rule Provisions: 146.82(c), 146.84, 146.90(d)(2) EPA Rule Issue: 11. EPA believes that predicting the complex multi-phase buoyant flow of the CO2, "co-injectates," and compounds that may be mobilized due to injection requires the sophistication of computational models. EPA proposes that the owners or operators of GS wells be required to delineate the AoR for CO2 GS sites using computational fluid flow models designed for the specific site conditions and injection regime. EPA seeks comment on the use of modeling for

AoR delineation. EPA Notice 43506.

Anadarko Petroleum Corporation (APC) Response: Modeling is a well developed technology that can readily simulate complex behavior of injected CO2. It should be one of the techniques used to delineate the AoR. Modeling alone though should not be the sole basis for determining the AoR. Other technologies such as seismic and/or use of off-set wells, should also be considered when delineating the proposed AoR.

The oil and gas industry has a great deal of experience that can be generally applied in the delineation of the AoR.

The most complex model is not always necessary to adequately delineate the AoR. Nor is it necessary to specify only one model as this would hinder the development of future models and techniques. Therefore, APC recommends that EPA provide flexibility in the rule to accommodate the use of future technologies and refrain from unnecessarily prescriptive measures.

Response: EPA agrees that the oil and gas industry has contributed to the state of modeling science, and anticipates that some industry-developed modeling products will be acceptable for models in the AoR for GS sites, as long as GS well operators clearly disclose, to the Director's satisfaction, the code assumptions, relevant equations, and scientific basis.

EPA clarifies that the model inputs must include actual geologic information, data collected during the site characterization process (e.g., information about artificial penetrations), and anticipated operating parameters (e.g., injection rates) submitted with the permit application under §146.82. Models will be revised and recalibrated during subsequent AoR reevaluations, which must accountfor all available monitoring and operational data, as required at §146.84(e).

EPA encourages and expects owners or operators to use the most appropriate multiphase computational models available to determine the AoR. However, EPA does not believe that the most "complex" model will, in all cases, be the best available AoR delineation model. The requirements at §146.84(c)(1) are designed to allow the owner or operator to choose, in consultation with the Director, the modeling platform that is most appropriate for a particular GS project.

EPA anticipates that modeling technology will continue to improve, and encourages and expects owners or operators to use the best available multiphase computational models to determine the AoR. Reliance on improved models will likely increase the accuracy and quality of the AoR characterization, resulting in increased protection of USDWs from endangerment.

Commenter Name: Craig R. Walters Letter ID: 0200 Commenter Organization: Anadarko Petroleum Corporation Comment ID: 24580

Comment: Rule Provisions: 146.84 EPA Rule Issue: 13. EPA seeks comment on the applicability of computational fluid flow models for delineating the AoR of GS sites. EPA Notice 43507.

Anadarko Petroleum Corporation (APC) Response: While computational fluid flow models can inform the delineation of the AoR, modeling shouldn’t be the sole criteria for determining AoR. (See Comments to EPA Notice 43506 and 43507 above also.)

Response: EPA agrees that the AoR should not be based exclusively on modeling. EPA has clarified the AoR modeling requirement in §146.84(c)(1) for the final rule. It now reads, “Predict, using existing site characterization, monitoring and operational data, and computational modeling, the projected lateral and vertical migration of the carbon dioxide plume and formation fluids in the subsurface from the commencement of injection activities until the plume movement ceases, until pressure differentials sufficient to cause the movement of injected fluids or formation fluids into a USDW are no longer present, or until the end of a fixed time period as determined by the Director.”

EPA clarifies that the model inputs must include actual geologic information, data collected during the site characterization process (e.g., information about artificial penetrations), and anticipated operating parameters (e.g., injection rates) submitted with the permit application under §146.82. This would include any seismic or off-set well data collected to meet the requirements of §146.82(a). Models will be revised and recalibrated during subsequent AoR reevaluations, which must account for all available monitoring and operational data, as required at §146.84(e).

Commenter Name: Christopher Murray Letter ID: 0207 Commenter Organization: Pacific Northwest National Laboratory Comment ID: 22436

Comment: Validation of Multiphase Computational Models . . . . . Page 10 EPA should establish a suite of test problems with specified parameters that could be used by the applicant to demonstrate the suitability of the computational code to be used for analysis of the proposed site.

Response: EPA notes that the Agency will not perform independent "tests" or validation of individual modeling products. EPA believes that operators should have the flexibility to selectmodels with which they are familiar and that are most appropriate to site conditions and available data types and amounts.

EPA clarifies that an EPA-prepared technical background document, "Computational Modeling of Underground Injection of Carbon Dioxide for Determination of Area-of-Review and Potential Risk to Underground Sources of Drinking Water" (cited as USEPA, 2008d) was provided in the regulatory docket for the proposed GS rule. This document discusses, for example, uncertainty analysis in detail. This document was provided as a background to clarify what information EPA analyzed in order to draft the modeling requirements at §146.84(c)(1), as well as what actions EPA expects owners or operators and Directors to take in this area. For example, the document states: "The requirement for an a-priori AoR delineation based on modeling predictions stresses the need for uncertainty and sensitivity analyses for the initial prediction. Sensitivity analysis is recommended as the principal evaluation tool for characterizing the most and least important sources of uncertainty

in environmental models."

EPA based this background document in part on guidance drafted by the National Research Council and on EPA's Council on Regulatory Environmental Modeling (CREM) document. EPA refers interested commenters to the document "Guidance on the Development, Evaluation and Application of Environmental Models," (74 FR 14551, March 31, 2009).

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.

Commenter Name: Christopher Murray Letter ID: 0207 Commenter Organization: Pacific Northwest National Laboratory Comment ID: 22446

Comment: Uncertainty Associated with Modeling CO2 Movement and Reservoir Pressure

PROPOSED REGULATION

p. 43506, c. 3 In suggesting the use of computational flow models for delineating the AoR of GS sites, EPA notes their potential "to predict CO2 movement in response to varying conditions or scenarios, such as changing injection rates, or the presence or absence of fractures or faults in confining layers." However, the Proposed Rule does not explicitly discuss uncertainty assessment in the use of modeling for AoR delineation.

DISCUSSION

Although we agree with the EPA that computational multiphase fluid flow models are appropriate for delineating the AoR of GS sites, the Proposed Rule does not adequately address how uncertainty should be managed in regards to modeling GS sites, and we consider this to be an important aspect. By not explicitly addressing uncertainty, the Proposed Rule infers that a single deterministicmodel result would be appropriate for determining the AoR and/or for site review and reevaluation. This ignores the fact that there is always a certain level of ncertainty in model results due to the cumulative variability in input data and uncertainty in model parameters.

The carbon sequestration roadmap produced by the National Energy Technology Laboratory (DOE 2007) notes that one of the goals of field tests conducted during

the Validation Phase is to "Validate and refine current CO2 reservoir models for various geologic sequestration sites." Validation does not prove that a given model is correct, but it does provide additional constraints on the model parameters. However, in the case of saline formation storage, history matching is generally not feasible for constraining uncertainties, due to a lack of underground data for comparison (IPCC 2005). Therefore the IPCC (2005) recommended that systematic parameter variation Routines and statistical functions should be included in future coupled simulators to allow uncertainty

estimates for numerical reservoir simulation results.

Uncertainty analysis is a valuable analytical tool and is critical for providing confidence in model results. Several approaches can be taken to capture the uncertainty present in any site modeling exercise (e.g., Neuman and Wierenga 2003). Three commonly used alternatives are Monte Carlo simulation, the bounding approach, and sensitivity analysis. The type of uncertainty analysis appropriate to a particular problem depends on the complexity of the problem and the

available data.

Probabilistic approaches like those suggested by the IPCC (2005) and Neuman and Wierenga(2003) would provide useful assessments of the uncertainty associated with the predicted CO2 plume footprint, and could be used to evaluate the risk

associated with various choices of theAoR.

PNNL RECOMMENDATION

A formal process for uncertainty assessment of the CO2 plume footprint should be incorporated in the Proposed Rule. This uncertainty assessment could be based on a bounding approach, a sensitivity analysis, Monte Carlo simulation or other method, provided the range of probable circumstances are considered. This would allow for a better assessment of the AoR that addresses the inherent uncertainty in computational fluid flow modeling of the injection process.

REFERENCES

IPCC. 2005. IPCC Special Report: Carbon Dioxide Capture and Storage. Summary for PolicyMakers and Technical Summary, B. Metz, O. Davidson, H. de Coninck, M. Loos, and L. Meyer (eds.). Cambridge University Press, NewYork.

Neuman, SP, and PJ Wierenga. 2003, A Comprehensive Strategy of Hydrogeologic Modeling and Uncertainty Analysis for Nuclear Facilities and Sites. Technical Rpt. NUREG/CR-6805, U. S. Nuclear Regulatory Commission, Washington DC.

U.S . DOE. 2007. Carbon Sequestration Technology and Program Plan Roadmap.NationalEnergy Technology Laboratory.

Response: EPA acknowledges that there will be some uncertainty involved in AoR modeling. An EPA-prepared technical background document, "Computational Modeling of Underground Injection of Carbon Dioxide for Determination of Area-of-Review and Potential Risk to Underground Sources of Drinking Water" (cited as USEPA, 2008d) was provided in the regulatory docket for the proposed GS rule. This document discusses, for example, uncertainty analysis in detail. This document was provided as a background to clarify what information EPA analyzed in order to draft the modeling requirements at 146.84(c)(1), as well as what actions EPA expects owners or operators and Directors to take in this area. For example, the document states: "The requirement for an a-priori AoR delineation based on modeling predictions stresses the need for uncertainty and sensitivity analyses for the initial prediction. Sensitivity analysis is recommended as the principal evaluation tool for characterizing the most and least important sources of uncertainty in environmental models."

EPA based this background document in part on guidance drafted by the National Research Council and on EPA's Council on Regulatory Environmental Modeling (CREM) document. EPA refers interested commenters to the document "Guidance on the Development, Evaluation and Application of Environmental Models," (74 FR 14551, March 31, 2009).

EPA agrees that in some cases, results from test-cases may be appropriate. In the technical background document (USEPA, 2008d), EPA provided several questions that should be raised during evaluation of models. One of these questions was "If using an independently developed or unverified code, are results from test-problems and comparisons to widely used codes presented?" Another was "Was relevant site characterization data gathered at a sufficiently high spatial resolution to inform model development? Was this data used in the model in a way that considers uncertainty?"

Regarding the suggestion that EPA establish a suite of test problems to demonstrate the suitability of the computational code, EPA notes that the Agency will not perform independent "tests" or validation of individual modeling products. EPA believes that operators should have the flexibility to select models with which they are familiar and that are most appropriate to site conditions and available data types and amounts.

EPA based this background document in part on guidance drafted by the National Research Council and on EPA's Council on Regulatory Environmental Modeling (CREM) document. EPA refers interested commenters to the document "Guidance on the Development, Evaluation and Application of Environmental Models," (74 FR 14551, March 31, 2009).

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.

Commenter Name: Christopher Murray Letter ID: 0207 Commenter Organization: Pacific Northwest National Laboratory Comment ID: 22447 Other EPA Comment Codes and Descriptions: 3350 2.2.1.5 Use of proprietary models for GS sites (seeking comment)Comment: VALIDATION OF MULTIPHASE COMPUTATIONAL MODELS

PROPOSED REGULATION

p. 43507, c. 1 Models used for GS sites should be based on accepted science and should be validated. In some cases, owners or operators may choose to use proprietary models (i.e., not available for free to the general public). EPA is aware that the use of proprietary codes may prevent full evaluation of model results (e.g ., NRC, 2007). Several popular codes in the petroleum-reservoir engineering discipline are proprietary and owners or operators of particular sites may prefer to use these codes as they have previous experience with them, and they have been used in peer-reviewed studies to model CO2 sequestration. When using a proprietary model, owners or operators should clearly disclose the code assumptions, relevant equations, and scientific basis.

DISCUSSION

We agree that computational models used for GS sites should be based on accepted science and should be validated. However, the proposed rule does not define

validation. We believe that these models must be validated in terms of their appropriateness for simulating the complexities of CO2 sequestration under the conditions present at the specific site being evaluated. The fact that a codehas been validated and previously used to model CO2 sequestration (even if peerreviewed) does not ensure that it is appropriate for use at all sites and under all conditions. For example, it is possible that, for a specific site, certain physical and/or geochemical processes must be considered that are not available in a given computational code. Whereas that code may have reasonably and successfully modeled CO2 sequestration at a dissimilar site, it may not be appropriate for the site being considered.

It may be appropriate for EPA to establish a suite of test problems that span the breadth of GS reservoir types (i.e., deep saline formations, depleted oil and gas reservoirs, faulted or fractured reservoirs, unmineable coal seams, basalts, salt domes, reactive carbonates, and shales), injection surface climatic extremes, injectate composition, single versus multiple wells, conditions (i.e., pressure reduction wells, and horizontal versus vertical injection wells), and physical/ geochemical processes deemed important in modeling CO2 sequestration (i.e. ., changes of state and chemical reactions). We suggest that this suite of problems be defined by experts in the field of CO2 sequestration modeling and code development, and that a variety of computational codes used in modeling GS sites be benchmarked using this suite. A subset of the suite of problems may be sufficient to validate a code for use at a particular site, however this subset must be rigorously defined (by EPA or the State, if it has established primacy for UIC regulation) based on the conditions specific to the site in question to ensure that the model being validated is appropriate for use at the site. Efforts are already underway to evaluate and compare computational codes being used to model GS sites. For example, several code intercomparison studies have been conducted to evaluate the capabilities and accuracy of numerical simulators for geological storage of green house gases (Pruess et al., 2004 and Law et al., 2003). In addition, the Inter-PartnershipSimulation and Risk Working Group within the DOE Regional Partnerships is embarking on an effort to compare overall modeling methodologies on a jointly accessible data set. This will be more inclusive than a code intercomparison effort as the methodologies and conceptual models used may vary widely.

Model results that should be used to determine if a code is valid for solving a specified problem include plume area and maximum plume radius (as defined by 95% of the CO2 mass) at particular time planes, injected mass over the time period of simulation, pressure distribution, and CO2 phase). Based on the code benchmarks and expert knowledge, a tolerance must be defined that determines what constitutes acceptable results. This suite of test problems could be modified or augmented as the state-of -the-science progresses in modeling, ensuring that any computational code being used at a particular site is current with regard to accepted scientific principles and rigor.

In addition to validating particular computational codes using a set of standard benchmarks, the implementation of the conceptual model should also be validated by comparing model results to observed data, and by using model calibration and history matching to improve the model results. EPA understands the importance of history-matching of model simulations with monitoring as stated on p. 43507, c.

1.

PNNL RECOMMENDATION

EPA should establish a suite of test problems with specified parameters that could be used by the applicant to demonstrate the suitability of the computational code to be used for analysis of the proposed site. As computational approaches and methods improve, this suite of problems should be modified and/or updated to incorporate the state-of -the-knowledge in GS modeling.

We agree that proprietary models can be used, provided they can demonstrate they produce results within the defined acceptable tolerance, in addition to disclosing the code assumptions, relevant equations, and scientific basis. These same requirements must, of course, be met by all computational codes being used

at GS sites.

REFERENCES:

Law, D.H.-S., L.G.H. vander Meer andW.D. Gunter, 2003: Comparison of numerical simulators for greenhouse gas storage in coal beds, Part II: Flue gas injection. Proceedings of the 6th International Conference on Greenhouse Gas Control Technologies (GHGT-6), J. Gale and Y. Kaya (eds.), 1-4 October 2002, Kyoto, Japan, Pergamon, v.I, 563-568. Geologischen Gesellschaft,149,3,449-464.

Pruess K, J Garcia, TKovscek, C Oldenburg, J Rutqvist, C Steefel, and TXu. 2002. Intercomparison of Numerical Simulation Codes for Geologic Disposal of CO2. LBNL-51813, Lawrence Berkeley National Laboratory, Berkeley, California.

Response: EPA clarifies that an EPA-prepared technical background document, "ComputationalModeling of Underground Injection of Carbon Dioxide for Determination of Area-of-Review and Potential Risk to Underground Sources of Drinking Water" (cited as USEPA, 2008d) was provided in the regulatory docket for the proposed GS rule. This document discusses, for example, uncertainty analysis in detail. This document was provided as a background to clarify what information EPA analyzed in order to draft the modeling requirements at §146.84(c)(1), as well as what actions EPA expects owners or operators and Directors to take in this area. For example, the document states: "The requirement for an a-priori AoR delineation based on modeling predictions stresses the need for uncertainty and sensitivity analyses for the initial prediction. Sensitivity analysis is recommended as the principal evaluation tool for characterizing the most and least important sources of uncertainty

in environmental models."

EPA agrees that in some cases, results from test-cases may be appropriate. In the technical background document (USEPA, 2008d), EPA provided several questions that should be raised during evaluation of models. One of these questions was "If using an independently developed or unverified code, are results from test-problems and comparisons to widely used codes presented?" Another was "Was relevant site characterization data gathered at a sufficiently high spatial resolution to inform model development? Was this data used in the model in a way that considers uncertainty?"

Regarding the suggestion that EPA establish a suite of test problems to demonstrate the suitability of the computational code, EPA notes that the Agency will not perform independent "tests" or validation of individual modeling products. EPA believes that operators should have the flexibility to select models with which they are familiar and that are most appropriate to site conditions and available data types and amounts.

EPA based this background document in part on guidance drafted by the National Research Council and on EPA's Council on Regulatory Environmental Modeling (CREM) document. EPA refers interested commenters to the document "Guidance on the Development, Evaluation and Application of Environmental Models," (74 FR 14551, March 31, 2009).

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.

Commenter Name: Richard Guinn Letter ID: 0210 Commenter Organization: Eastman Chemical Company Comment ID: 22721

Comment: §146.84 Area of review and corrective action. (c) (1) "Predict, using computational modeling, the projected lateral and vertical migration of the carbon dioxide plume and formation fluids in the subsurface from the commencement of injection activities until the plume movement ceases, pressure differentials sufficient to cause the movement of injected fluids or formation fluids into a USDW are no longer present, or after a fixed time period as determined by the Director."

We recommend striking out "Predict, using computational modeling, the projected lateral and vertical migration of the carbon dioxide plume" and replacing with"Using computational modeling, provide projected potential ranges of lateral and vertical migration of the carbon dioxide plume" The use of multiphase groundwater flow and transport models is to predict the composition and movement of each phase state (e.g., liquid, gas ,supercritical fluid) of CO2 in the subsurface, as well as fluid pressures, to define the AoR. One of the concerns with the use of such complex models is that the site may not be fully characterized with respect to hydro-geologic properties. There may be significant uncertainty in one or more hydraulic processes/parameters. Therefore, it is possible to obtain a wide-range of model outcomes from different model parameters. The uncertainty in model parameters and sensitivity of model results to parameter selection should be addressed.

Response: EPA has clarified this language in the final rule. It now reads, “Predict, using existing site characterization, monitoring and operational data, and computational modeling, the projected lateral and vertical migration of the carbon dioxide plume and formation fluids in the subsurface from the commencement of injection activities until the plume movement ceases, until pressure differentials sufficient to cause the movement of injected fluids or formation fluids into a USDW are no longer present, or until the end of a fixed time period as determined by the Director.”

EPA agrees that modeling results are prone to varied degrees of uncertainty. As discussed in the preamble to the proposed GS regulation and the associated background document "Computational Modeling of Underground Injection of Carbon Dioxide for Determination of Area-of-Review and Potential Risk to Underground Sources of Drinking Water" (cited in the proposed rule preamble as USEPA, 2008d), model predictions depend largely on the values of key parameters. Often these parameter values are estimated or averaged from several data sources. EPA also agrees that sensitivity analyses and "worst case scenario" modeling runs should be presented by the owner or operator and evaluated by the Director. If during the permit review, the Director determines that modeling results are too wide-ranging, further information will be required of the owner or operator.

EPA clarifies that models are tools to help predict the movement of a CO2 plume over long time frames. However, EPA recognizes that it cannot be expected that modeling something as complex as a CO2 plume can be done with complete certainty; therefore EPA is also requiring that the AoR be reevaluated to verify the CO2 plume is moving as predicted and to allow for model calibration and necessary revisions to the required GS project plans (e.g., AoR and corrective action, testing and monitoring, injection well plugging, post-injection site care and site closure, and emergency and remedial response). EPA believes that near-term predictions (e.g., over the subsequent 5 years) will have the highest degree of certainty. Periodic model calibration will allow refinement to the AoR delineation based on real-world conditions and operating data and monitoring results, and thus increase confidence in the modeled predictions. EPA adds that the final GS regulation includes a requirement at §146.84(e) that the AoR be reevaluated at least every 5 years (an adjustment from the ten year interval in the proposal), which should further address the commenters' concerns regarding model uncertainty.

Commenter Name: Richard Guinn Letter ID: 0210 Commenter Organization: Eastman Chemical Company Comment ID: 22729

Comment: EPA seeks comment on the applicability of computational fluid flow models for delineating the AoR of GS sites. EPA Notice 69.Computational fluid flow models should be permitted for delineating the AoR of GS sites provided also that data are provided supporting their validation in similar complex structures and flow regimes

Response: EPA agrees that a detailed geologic assessment is essential to evaluating the presence and adequacy of a proposed site to receive and confine the CO2. The AoR and corrective action plan required at §146.84(b) must describe the site characterization data on which the model will be based. The Director has discretion to require the use of existing data if it is not initially included.

The Agency believes 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. 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.

EPA clarifies that the model inputs must include actual geologic information, data collected during the site characterization process (e.g., information about artificial penetrations), and anticipated operating parameters (e.g., injection rates) submitted with the permit application under §146.82. Models will be revised and recalibrated during subsequent AoR reevaluations, which must account for all available monitoring and operational data, as required at §146.84(e).

Commenter Name: Ronald Evans Letter ID: 0215 Commenter Organization: Denbury Resources, Inc. (DRI) Comment ID: 24291 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: B. §146.84 Area of review and corrective action.

EPA’s proposed rule allows each applicant to define the Area of Review ("AoR") associated with the sequestration project. Denbury has no objection to this flexible approach as it allows the size and shape of the AoR to reflect the unique geology of each CO2 sequestration project. However, under §146.84 (a), to define the AoR, an applicant must use a model capable of considering the physical and chemical properties of all phases of the injected carbon dioxide stream. Denbury is uncertain that there is a model that can satisfy this requirement. Accordingly, Denbury suggests that the proposed rule be amended as

follows:

§146.84 Area of review and corrective action. (a) The area of review is the region surrounding the geologic sequestration project that may be impacted by the injection activity. The area of review is based on computational modeling that, TO THE

EXTENT PRACTICABLE AND TO THE EXTENT DETERMINED TO BE NECESSARY BY

THE DIRECTOR, accounts for the MATERIAL physical and chemical properties of

all CRITICAL phases of the injected carbon dioxide stream. Response: EPA disagrees that available multiphase models cannot consider the physical and chemical properties of all phases of the injected CO2 stream. Research, as discussed in the preamble to the proposed GS regulation and the associated background document "Computational Modeling ofUnderground Injection of Carbon Dioxide for Determination of Area-of-Review and Potential Risk to Underground Sources of Drinking Water" (cited in the proposed rule preamble as USEPA, 2008d), substantiates the modeling requirements in the GS regulation and indicates that technology has advanced to the point that a CO2 injection project can be adequately modeled to support both prediction and tracking the movement of the CO2 plume and pressure front. EPA believes the Director should have discretion to evaluate each plan based on current, state of the art modeling science because there are large numbers and types of available models and because advances in the field of geologic modeling continue.

Based on review of all public comments on the AoR definition at 146.84(a), the Agency has modified it to read as follows: The region surrounding the geologic sequestration project where USDWs may be endangered by the injection activity. The area of review is delineated using computational modeling that accounts for the physical and chemical properties of all phases of the injected CO2 stream and is based on available site characterization, monitoring, and operational data.

Commenter Name: Darrick Eugene Letter ID: 0223 Commenter Organization: Texas Carbon Capture and Storage Association Comment ID: 23970 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: 3. §146.84 Area of review and corrective action.

EPA’s proposed rule allows each applicant to define the Area of Review ("AoR") associated with the sequestration project. TxCCSA has no objection to this flexible approach as it allows the size and shape of the AoR to reflect the unique geology of each CO2 sequestration project. However, under §146.84 (a), to define the AoR, an applicant must use a model capable of considering the physical and chemical properties of all phases of the injected carbon dioxide stream. TxCCSA is uncertain that there is a model that can satisfy this requirement. Accordingly, TxCCSA suggests that the proposed rule be amended as

follows:

§146.84 Area of review and corrective action. (a) The area of review is the region surrounding the geologic sequestration project that may be impacted by the injection activity. The area of review is based on computational modeling that, TO THE EXTENT PRACTICABLE AND TO THE EXTENT DETERMINED TO BE NECESSARY BY THE DIRECTOR, accounts for the MATERIAL physical and chemical properties of all CRITICAL phases of the injected carbon dioxide stream.

Response: EPA disagrees that available multiphase models cannot consider the physical and chemical properties of all phases of the injected CO2 stream. Research, as discussed in the preamble to the proposed GS regulation and the associated background document "Computational Modeling of Underground Injection of Carbon Dioxide for Determination of Area-of-Review and Potential Risk to Underground Sources of Drinking Water" (cited in the proposed rule preamble as USEPA, 2008d), substantiates the modeling requirements in the GS regulation and indicates that technology has advanced to the point that a CO2 injection project can be adequately modeled to support both prediction and tracking the movement of the CO2 plume and pressure front. EPA believes the Director should have discretion to evaluate each plan based on current, state of the art modelingscience because there are large numbers and types of available models and because advances in the field of geologic modeling continue.

Based on review of all public comments on the AoR definition at 146.84(a), the Agency has modified it to read as follows: The region surrounding the geologic sequestration project where USDWs may be endangered by the injection activity. The area of review is delineated using computational modeling that accounts for the physical and chemical properties of all phases of the injected CO2 stream and is based on available site characterization, monitoring, and operational data.

Commenter Name: Ben Yamagata Letter ID: 0227 Commenter Organization: Coal Utilization Research Council Comment ID: 21787 Other EPA Comment Codes and Descriptions: 3300 2.2.1 Delineating the AoR/Modeling CO2

movement
Comment: Area of Review (AoR)

The proposed regulation does not actually define the AoR, it merely states that the area will be determined by mathematical models. One of the concerns with the use of such complex models is that the site may not be fully characterized with respect to hydro-geologic properties. There may be significant uncertainty in one or more hydraulic process/parameters. Therefore, it is possible to obtain a wide-range of model outcomes from different model parameters. The treatment of uncertainty in model parameters and sensitivity of model results to parameter selection should be addressed. Given that the AoR will be periodically revisited, we recommend that the final rule make a pragmatic determination of what will be necessary to protect groundwater, given the requirement for reevaluation over time, and that the Agency focus the requirements to rely upon the mathematical models with the inherent differences

noted above.

Response: EPA agrees that modeling results are prone to varied degrees of uncertainty. As discussed in the preamble to the proposed GS regulation and the associated background document"Computational Modeling of Underground Injection of Carbon Dioxide for Determination of Areaof-Review and Potential Risk to Underground Sources of Drinking Water" (cited in the proposed rule preamble as USEPA, 2008d), model predictions depend largely on the values of key parameters. Often these parameter values are estimated or averaged from several data sources. EPA also agrees that sensitivity analyses and "worst case scenario" modeling runs should be presented by the owner or operator and evaluated by the Director. If during the permit review, the Director determines that modeling results are too wide-ranging, further information will be required of the owner or operator.

EPA clarifies that models are tools to help predict the movement of a CO2 plume over long time frames. However, EPA recognizes that it cannot be expected that modeling something as complex as a CO2 plume can be done with complete certainty; therefore EPA is also requiring that the AoR be reevaluated to verify the CO2 plume is moving as predicted and to allow for model calibration and necessary revisions to the required GS project plans (e.g., AoR and corrective action, testing and monitoring, injection well plugging, post-injection site care and site closure, and emergency and remedial response). EPA believes that near-term predictions (e.g., over the subsequent 5 years) would have the highest degree of certainty. Periodic model calibration would allow refinement to the AoR delineation based on real-world conditions and operating data and monitoring results, and thusincrease confidence in the modeled predictions. EPA adds that the final GS regulation includes a requirement at 146.84(e) that the AoR be reevaluated every 5 years (an adjustment from the ten year interval in the proposal), which should further address the commenter’s concerns regarding model uncertainty.

Commenter Name: Mark Bohrer Letter ID: 0241 Commenter Organization: North Dakota Industrial Commission Comment ID: 23231 Other EPA Comment Codes and Descriptions: 3320 2.2.1.2 Comments opposed to requiring computational models to delineate the AoR

Comment: 11. EPA believes that predicting the complex multi-phase buoyant flow of the CO2, "co-injectates," and compounds that may be mobilized due to injection requires the sophistication of computational models. EPA proposes that the owners or operators of GS wells be required to delineate the AoR for CO2 GS sites using computational fluid flow models designed for the specific site conditions and injection regime. EPA seeks comment on the use of modeling for

AoR delineation. EPA Notice 43506.

There is concern about the lack of information necessary to construct a valid model in areas where the sequestration zone has not been extensively studied. This lack of information may make modeling difficult or not very useful. Any modeling used should be re-examined and recalibrated over time with additional data gathered. Modeling should not be solely relied upon where real data offers a different view. Seismic and offset well data can help delineate the AOR.

Response: The Agency believes that AoR delineation using computational modeling that accounts for the multiphase flow of CO2 and native fluids (i.e., naturally occurring salty water), including density-driven flow (i.e., buoyancy), is necessary to ensure protection of USDWs from endangerment. The computational models used for this purpose are required to predict the fate of injected CO2 and changes in formation pressure. EPA believes that the requirements at 146.84(c)(1) to delineate the AoR using computational modeling are appropriate and encompass the significant processes that could affect the location of the CO2 plume and associated pressure front and has

retained this in the final rule.

EPA agrees that the modeling should be re-examined and recalibrated over time. The GS regulation at 146.84(e) also requires owners or operators to periodically reevaluate the AoR to incorporate monitoring and operational data. This process provides additional opportunities to verify that the models have accurately predicted movement of the CO2 plume and to make any needed adjustments to corrective action or monitoring at the site.

Commenter Name: Mark Bohrer Letter ID: 0241 Commenter Organization: North Dakota Industrial Commission Comment ID: 23233

Comment: 13. EPA seeks comment on the applicability of computational fluid flow models for delineating the AoR of GS sites. EPA Notice 43507.

The use of computational flow models is appropriate, however; modeling should

not be the sole criteria to determine the AOR if actual measured data exists.

Response: EPA agrees that a detailed geologic assessment is essential to evaluating the presence andadequacy of a proposed site to receive and confine the CO2. The AoR and corrective action plan required at §146.84(b) must describe the site characterization data on which the model will be based. The Director has discretion to require the use of existing data if it is not initially included.

EPA clarifies that the model inputs must include actual geologic information, data collected during the site characterization process (e.g., information about artificial penetrations), and anticipated operating parameters (e.g., injection rates) submitted with the permit application under §146.82. Models will be revised and recalibrated during subsequent AoR reevaluations, which must account for all available monitoring and operational data, as required at §146.84(e).

The Agency believes 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. 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: 0263 Commenter Organization: Interstate Oil & Gas Compact Commission Comment ID: 22799

Comment: III A. 2 Proposed Area of Review and Corrective Action Requirements

N. EPA seeks comment on the applicability of computational fluid flow models for delineating the AoR ofGS sites.

IOGCC Response: See General Comment for Section III. A. 2 above. The collection of physical data (i.e. well bore data) maybe necessary to fully utilize modeling to determine the ultimate extent of the proposed CO2 storage volume. Models should only be used when they are appropriate. The regulator of a GS project should not be required to rely fully on models. As noted above, states need the flexibility to be able to go beyond models.

Response: EPA agrees that a detailed geologic assessment is essential to evaluating the presence and adequacy of a proposed site to receive and confine the CO2. The AoR and corrective action plan required at §146.84(b) must describe the site characterization data on which the model will be based. The Director has discretion to require the use of existing data if it is not initially included.

EPA clarifies that the model inputs must include actual geologic information, data collected during the site characterization process (e.g., information about artificial penetrations), and anticipated operating parameters (e.g., injection rates) submitted with the permit application under §146.82. Models will be revised and recalibrated during subsequent AoR reevaluations, which must account for all available monitoring and operational data, as required at §146.84(e).

The Agency believes 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. 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.EPA agrees that it is appropriate to allow operators the flexibility to select modeling, site characterization, and monitoring techniques that are most appropriate to site conditions and available types and amounts of data. The owner or operator must demonstrate, in the proposed AoR and corrective action plan at §146.84(b), to the satisfaction of the Director that the modeled AoR will be based on detailed geologic data collected on the site.

Comment Code: 3340 2.2.1.4 Specific delineation models



### Individual Comments

Commenter Name: Dag Nummedal Letter ID: 0533 Commenter Organization: Colorado Energy Resource Institute Comment ID: 21478

Comment: California and the Lawrence Berkeley lab on the Berkeley campus. These labs have over the last five to ten years developed some codes called NUFT and Tough-react numerical codes worry about those things. That really have advanced our ability as scientists to model ahead of time what will happen to minerals and precipitation and dissolution when this CO2 charge fluids go through the rocks.

Then the model predictions and the American Model Predictions will then be tested against lab experiments. One of the things that we are very proud of at the Colorado School of Mines is how dedicated the university is to laboratory work. There is only so much you can do in the area of modeling. You have to test the models in laboratory before you can feel comfortable using the models afterwards to predict what would happen in the subsurface.

Response: EPA acknowledges the range and capabilities of numerical modeling codes available to GS operators and other modelers and acknowledges the comment.

Comment Code: 3350 2.2.1.5 Use of proprietary models for GS sites (seeking comment)



### Individual Comments

Commenter Name: John Hanger Letter ID: 0130 Commenter Organization: Pennsylvania Dept. of Env. Protection Comment ID: 21505

Comment: -Proprietary models should not be acceptable for use because of the complex nature of the activity and the many unknowns. Through a transparent process, EPA should maintain minimum modeling standards and assumptions required for approval.

Response: EPA disagrees that the use of proprietary models should be disallowed. EPA acknowledges that several proprietary models are currently, successfully used by petroleum-reservoir engineering professionals as well as in peer-reviewed studies to model CO2 sequestration.EPA does not believe that the Agency should develop a standards and assumptions for modeling the AoR for GS sites. Instead, EPA believes that operators should have the flexibility to select the most appropriate models for the conditions at the GS site and based on the types and amount of data available given the wide range of site-specific conditions present at GS sites. 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 adds that its Confidential Business Information requirements at 40 CFR 144.5 will apply to the use of proprietary models.

To ensure that all predictive models used for AoR calculations are meeting the Agency's expectations, 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.

Commenter Name: Carl Carlsson Letter ID: 0131 Commenter Organization: SUEZ Energy Generation NA, LLC Comment ID: 21529

Comment: Use of Proprietary Models to Delineate the Area of Review SEGNA agrees with EPA that models used for GS analysis should be based on accepted science and should be validated. In addition to requiring operators to disclose code assumptions, relevant equations and the scientific basis for proprietary models, SEGNA suggests that EPA consider establishing a validation process for such models using empirical data to ensure such models are sound.

Response: EPA agrees with commenters that available proprietary models may meet the complex needs for calculating the AoRs of GS sites, and shares their concern about the need to evaluate the inputs and assumptions used. EPA plans to allow the use of proprietary models in meeting the requirements for the GS regulation, as long as GS well operators using a proprietary model clearly disclose, to the Director's satisfaction, the code assumptions, relevant equations, and scientific basis. EPA adds that its Confidential Business Information requirements at 40 CFR 144.5 will apply to the use of proprietary models.

In response to comments suggesting that history matching or validation of these models is needed, EPA believes this is true for any model. EPA notes that the GS rule requires at §146.84(e) that the AoR be reevaluated to verify that the CO2 plume is moving as predicted and to allow for necessaryrevisions to the AoR and corrective action, testing and monitoring, injection well plugging, postinjection site care and site closure, and emergency and remedial response plans. EPA clarifies, however, that the Agency will not perform independent validation of individual modeling products.

The Agency 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.

Commenter Name: Christine Reimer Letter ID: 0142 Commenter Organization: National Ground Water Association Comment ID: 22550Comment: Use of commercial proprietary codes should be authorized. Proprietary doesn't mean secret. A proprietary code largely vetted by the industry can be the best application in many circumstances. To promote peer review and benchmarking, the assumptions and theories for all numerical models should be publicly available and the solution of any analytic equations used in the predictive process should be fully elaborated.

Response: EPA agrees that available proprietary models may meet the complex needs for calculating the AoRs of GS sites, and shares their concern about the need to evaluate the inputs and assumptions used. EPA will allow the use of proprietary models in meeting the requirements for the GS regulation, as long as GS well operators using a proprietary model clearly disclose, to the Director's satisfaction, the code assumptions, relevant equations, and scientific basis. EPA adds that its Confidential Business Information requirements at 40 CFR 144.5 will apply to the use of proprietary models.

Commenter Name: Christine Reimer Letter ID: 0142 Commenter Organization: National Ground Water Association Comment ID: 22580

Comment: Preamble Questions: In some cases, owners or operators may choose to use proprietary models (i.e., not available for free to the general public). EPA says it is aware that the use of proprietary codes may prevent full evaluationof model results (e.g., NRC, 2007). Several popular codes in the petroleumreservoir engineering discipline are proprietary and owners or operators of particular sites may prefer to use these codes as they have previous experience with them, and they have been used in peer-reviewed studies to model CO2 sequestration. When using a proprietary model, owners or operators should clearly disclose the code assumptions, relevant equations, and scientific basis. EPA seeks comment on allowing the use of proprietary models for GS sites. EPA

Notice 68.

NGWA Response: Yes, use of commercial proprietary codes should be authorized. Proprietary doesn't mean secret. A proprietary code largely vetted by the industry can be the best application in many circumstances. To promote peer review and benchmarking, the assumptions and theories for all numerical models should be publicly available and the solution of any analytic equations used in the predictive process should be fully elaborated.

Response: As described above, EPA agrees that available proprietary models may meet the complex needs for calculating the AoRs of GS sites, and shares their concern about the need to evaluate the inputs and assumptions used. EPA will allow the use of proprietary models in meeting the requirements for the GS regulation, as long as GS well operators using a proprietary model clearly disclose, to the Director's satisfaction, the code assumptions, relevant equations, and scientific basis. EPA adds that its Confidential Business Information requirements at 40 CFR 144.5 will apply to the use of proprietary models.

Commenter Name: Brianne Metzger Letter ID: 0151 Commenter Organization: Spectra Energy Corp Comment ID: 21818

Comment: A. EPA Should Allow The Use Of Proprietary Models For Modeling CO2 Movement

andReservoir Pressure.

EPA correctly acknowledges that some companies use proprietary models for their current GS operations, and has requested comment on allowing the use of such models for GS sites. Spectra strongly agrees with the continued use of proprietary models. While Spectra would be willing to provide information pertaining to the underlying assumptions and scientific basis, subject to protection as confidential business information ("CBI"), we would object to any effort by the Agency to compel further disclosure regarding such models. Although we recognize that the Agency is required by law to take certain steps to protect CBI, we are mindful that such protections are not always fail-safe

and inadvertent disclosures of CBI are not uncommon. Such disclosures in the case of the critical infrastructure we operate or may operate in the future could be extremely detrimental and costly.

Response: EPA agrees that some of the available proprietary models may meet the needs for calculating the AoRs of GS sites. EPA will allow their use in meeting the requirements for the GS regulation, but clarifies that GS well operators using proprietary models are required to disclose, to the Director's satisfaction, the code assumptions, relevant equations, and scientific basis. EPA acknowledges that several proprietary models have been used by petroleum-reservoir engineering professionals as well as in peer-reviewed studies to model CO2 sequestration. EPA adds that its Confidential Business Information requirements at 40 CFR 144.5 will apply to the use of proprietary models. Information including model assumptions and equations are used by the Director to inform his/her decision to issue the permit and ensure that the requirements are met and the GS well will not endanger USDWs. EPA adds that its Confidential Business Information requirements at 40 CFR 144.5 will apply to the use of proprietary models.

Commenter Name: James Dooley Letter ID: 0156 Commenter Organization: Joint Global Change Research Institute, Pacific Northwest National Laboratory Comment ID:

22617

Comment: Page 43507. The USEPA specifically asks for comments on the appropriateness of allowing proprietary models to be used in support of a Class VI permit. There is nothing wrong with using proprietary models. The test as to whether it is appropriate to use proprietary models (or "open community" models) should be whether these models are seen by the USEPA and the technical community as providing robust, accurate, and useful results. It is much more important to understand a model’s track record in this regard than to ask for documentation of "code assumptions, relevant equations, and scientific basis." Given the inherent complexity of these models, asking for "code assumptions, relevant equations, and scientific basis" could result in the submittal of an extremely long technical document that is so dense it will not be read or the submittal of a very superficial treatment of the model. The USEPA should -- without delay -- begin deliberations on methodologies that could be used to transparently establish the robustness of these models and their results/outputs. This could be done - for example - through formal model intercomparisons using a set of test cases and repeating this process every couple of years. It will be far more useful to invest the time, thinking and if need be resources now to help establish which models are useful and for what applications than to request that each Class VI permit application include a detailed 100-1000 page description ofthe model used and how key geomechanical/geophysical processes were parameterized. USEPA is strongly encouraged to change the focus here from a process oriented assessment of how these models work to a more outcome oriented measure of the perceived usefulness and robustness of these models by the technical community and other stakeholders (e.g., Wall Street) as useful tools

for GS.

Response: EPA agrees that some of the available proprietary models may meet the needs for calculating the AoRs of GS sites. EPA will allow their use in meeting the requirements for the GS regulation, but clarifies that GS well operators using proprietary models are required to disclose, to the Director's satisfaction, the code assumptions, relevant equations, and scientific basis. EPA acknowledges that several proprietary models have been used by petroleum-reservoir engineering professionals as well as in peer-reviewed studies to model CO2 sequestration. EPA adds that its Confidential Business Information requirements at 40 CFR 144.5 will apply to the use of proprietary

models.

EPA does not plan to initiate a formal review of models or modeling methodologies, as the commenter suggests. Instead, EPA believes that it is appropriate to allow operators the flexibility to select modeling techniques that are most appropriate to site conditions and available types and amounts of data. The owner or operator must demonstrate, in the proposed AoR and corrective action plan required at §146.84(b), to the satisfaction of the Director, that the modeled AoR will be based on detailed geologic data collected on the site. EPA anticipates that any model that does this in a satisfactory manner will be approved by the Director. EPA acknowledges that modeling technology is expected to continuously improve, and encourages and expects owners or operators to use the best available multiphase computational models to determine the AoR. Reliance on improved models will likely increase the accuracy and quality of the AoR characterization, resulting in better protection of USDWs from endangerment.

Commenter Name: James Childress Letter ID: 0158 Commenter Organization: Gasification Technologies Council (GTC) Comment ID: 23778

Comment: EPA seeks comment on allowing the use of proprietary models for GS sites. EPA

Notice 68.

Proprietary models should be acceptable provided that supporting data for

validation are submitted.

Response: EPA agrees with commenters that available proprietary models may meet the complex needs for calculating the AoRs of GS sites, and shares their concern about the need to evaluate the inputs and assumptions used. EPA will allow the use of proprietary models in meeting the requirements for the GS regulation, as long as GS well operators using a proprietary model clearly disclose, to the Director's satisfaction, the code assumptions, relevant equations, and scientific basis. EPA adds that its Confidential Business Information requirements at 40 CFR 144.5 will apply to the use of proprietary models.

Commenter Name: Theresa Pugh Letter ID: 0169 Commenter Organization: American Public Power Association Comment ID: 23401

Comment: Use of proprietary models: EPA asked about AoR and proprietary models. APPA is not expert on models but has some general discomfort with relying solely onproprietary models owned/operated by a third party-particularly when there are only approximately five companies in the United States that have such sophisticated models for AoR modeling. Proprietary models are de rigueur in the oil and gas extractive industry. We would not seek to change that for such a critical industry to our economy and to our own natural resource needs. However, it would not lead to an easy future for power plant owner/operators to not know how site selection and AoR decisions are made because the owner/operator of the AoR work would use confidential the proprietary models from even the power plant owner/operator. It would be rare to have such a significant portion of the operational costs where the power plant’s management could not review the model or run a cross check proprietary models to affirm site selection or to do double checks after operations had begun. This is a tricky question for APPA. The AoR decisions will be fundamental to the entire geologic sequestration decision tree. Yet, if proprietary models are used, the power plant management will have little say over the geosequestration operations. Additionally, relying upon proprietary models for such a significant portion of the geologic sequestration decision making will be anti-competitive. It is not easy for power plants owner/operators to easily know what the costs of an operation will be for the consumers if they are relying upon proprietary AoR models at the beginning of the geologic sequestration process and relying upon these same models during the 40-50 year life of the plant. APPA would prefer that the use of a replicatable model is used. This may need considerable work by the U. S. EPA to ensure that the proprietary nature of these seismic modeling products and services are not exposed in a way that harms the oil field services industry. Perhaps the EPA can

review what confidential business information methods are undertaken in the Food and Drug Administration or Homeland Security Administration as those agencies review very confidential drug testing or security data which much be

confidential but still usable and able to be reviewed.

APPA respects that the true value in the oil and gas extractive industry is inthe quality of its seismic readings technology and models that make it the preeminent in the world. No one at APPA wants to tamper with that. We wonder if some sort of proprietary method can be arranged for the AoR models to be run off of proprietary models where the model can at least be reviewed or replicated for quality purposes by the state director and the power plant owner/operator. Without this ability to have a handle on operational costs and decisions made by the contractors to the power sector, many public power communities would be reticent to commit to a technology where the proprietary model sets in motion most major decisions without a way to review them or make mid-course

corrections.

Response: EPA agrees that available proprietary models may meet the complex needs for calculating the AoRs of GS sites, and shares their concern about the need to evaluate the inputs and assumptions used. EPA notes that several proprietary models are currently, successfully used by petroleum-reservoir engineering professionals as well as in peer-reviewed studies to model CO2 sequestration. EPA adds that its Confidential Business Information requirements at 40 CFR 144.5 will apply to the use of proprietary models.

EPA clarifies that owners or operators have flexibility to select the most appropriate models for the conditions at the GS site and based on the types and amount of data available given the wide rangeof site-specific conditions present at GS sites.

To ensure that all predictive models used for AoR calculations are meeting the Agency's expectations, 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.

Commenter Name: Kyle Isakower Letter ID: 0170 Commenter Organization: American Petroleum Institute Comment ID: 24224

Comment: Rule Provisions: 146.84 EPA Preamble Question: 12. In some cases, owners or operators may choose to use proprietary models (i.e., not available for free to the general public). EPA says it is aware that the use of proprietary codes may prevent full evaluationof model results (e.g., NRC, 2007). Several popular codes in the petroleumreservoir engineering discipline are proprietary and owners or operators of particular sites may prefer to use these codes as they have previous experience with them, and they have been used in peer-reviewed studies to model CO2 sequestration. When using a proprietary model, owners or operators should clearly disclose the code assumptions, relevant equations, and scientific basis. EPA seeks comment on allowing the use of proprietary models for GS sites. EPA

Notice 43507.

API Response: Use of proprietary models should be allowed. EPA’s Confidential Business Information requirements should apply to any proprietary model used.

Response: EPA agrees that some of the available proprietary models may meet the needs for calculating the AoRs of GS sites. EPA will allow their use in meeting the requirements for the GS regulation, but clarifies that GS well operators using proprietary models are required to disclose, to the Director's satisfaction, the code assumptions, relevant equations, and scientific basis. EPA acknowledges that several proprietary models have been used by petroleum-reservoir engineering professionals as well as in peer-reviewed studies to model CO2 sequestration. EPA adds that its Confidential Business Information requirements at 40 CFR 144.5 will apply to the use of proprietary

models.

Commenter Name: James Rower Letter ID: 0173 Commenter Organization: Utility Solid Waste Activities Group (USWAG) Comment ID: 23485 Other EPA Comment Codes and Descriptions: 3320 2.2.1.2 Comments opposed to requiring computational models to delineate the AoR

Comment: 8. Modeling

As most models now are proprietary, USWAG supports the use of proprietary models for use with CO2 GS sites. As EPA recognizes, many popular proprietary codes in the petroleum-reservoir engineering discipline have been used in peer-reviewed studies to model CO2 sequestration. 73 Fed. Reg. at 43507. These and other proprietary models should be available for use in modeling for Class VI CO2 GS wells, provided that they are based on accepted science and have been validated, and as long as the Owners or Operators using proprietary models disclose, as necessary, the code assumptions, relevant equations, and scientific basis ofeach model. USWAG believes that the use of computational fluid flow models for delineating the AoR of GS sites is acceptable but should not be required. Id.

Response: EPA agrees that some of the available proprietary models may meet the needs for calculating the AoRs of GS sites and will allow their use for GS projects. EPA acknowledges that several proprietary models have been used by petroleum-reservoir engineering professionals as well as in peer-reviewed studies to model CO2 sequestration. EPA plans to allow their use in meeting the requirements for the GS regulation, but clarifies that GS well operators using proprietary models are required to disclose, to the Director's satisfaction, the code assumptions, relevant equations, and scientific basis. EPA adds that its Confidential Business Information requirements at 40 CFR 144.5 will apply to the use of proprietary models.

EPA clarifies that the final rule will require the use of computational models. EPA believes that the unique aspects of GS merit the use of sophisticated computational modeling for delineation of the AoR, based on site-specific features and geology, including the presence of faults, fractures, and artificial penetrations. EPA believes that computational modeling of the AoR prior to injection will provide the best obtainable estimates of the extent of the CO2 plume over several years of active injection.

Commenter Name: Thomas Curtis Letter ID: 0181 Commenter Organization: American Water Works Association (AWWA) Comment ID: 23690 Other EPA Comment Codes and Descriptions: 3300 2.2.1 Delineating the AoR/Modeling CO2

movement
Comment: Category: Modeling

EPA Request for Comment: EPA proposes that the owners or operators of GS wells be required to delineate the AoR for CO2 GS sites using computational fluid flow models designed for the specific site conditions and injection regime. EPA seeks comment on the use of modeling for AoR delineation. EPA Notice 43506.

When using a proprietary model, owners or operators should clearly disclose the code assumptions, relevant equations, and scientific basis. EPA seeks comment on allowing the use of proprietary models for GS sites. EPA Notice 43507.

AWWA Response: The proposed rule depends heavily on computer modeling to track the carbon dioxide plume and demonstrate that it is contained within the confining zone. As stated by EPA, some of these models are proprietary and the rule is unclear how or if confirmation of the model results will be provided. Additionally, each of the individual proprietary models can show a different answer to the problem. Owner/operators need to ensure that their basis for the model is static, and that the basis does not change once more details are known about the movement of the plume. For example, the operation of the geologic sequestration system should be adjusted based on modeling results, and the model shouldn't be revised because the plume is moving in a direction not originally predicted.

AWWA recommends that EPA standardize on one specific model that is transparent and available for outside stakeholders to review, including the public. The other option is for EPA to develop a standard model that would be used for allgeologic sequestration projects. If EPA were to develop a standard model, a pilot program should be part of the model development so that the modeling results could be validated with real-life monitoring data. In either case, clearly stating the model assumptions made during model set-up is critical, and these assumptions must be made available to stakeholders when they are reviewing

the model results.

Response: The final rule does not require use of a standardized model. As described above, EPA believes that operators should have the flexibility to select models with which they are familiar and that are most appropriate to the site conditions and available data types and amounts. EPA also recognizes that a standardized model for AoR delineations could be effective as long as the model accounts for the expected variations in site conditions, and adds that a state or regional UIC Director could select one standard model if it took site-specific variations into account.

EPA does not envision that members of the public will evaluate the AoR delineation models themselves. The models and their inputs will, by necessity, entail an extensive amount of technical information that may not be easily understood by the public. EPA believes that it is the Director's responsibility, as a steward of public health and the environment, to review models, model inputs, and results and to determine whether the model is appropriate for predicting the AoR, and to distribute information that may be easily understood by the public (e.g., in the form of a fact sheet). EPA adds that its Confidential Business Information requirements at 40 CFR 144.5 will apply to the use of proprietary models.

Commenter Name: Bradley J. Field Letter ID: 0186 Commenter Organization: New York State Dept. of Environmental Conservation

Div. of Mineral Resources Comment ID:

25182

Comment: K. EPA seeks comment on allowing the use of proprietary models for GS sites.

NYSDEC-DMN Response: NYSDEC-DMN believes proprietary models should be allowed provided the Director has discretion to evaluate the accuracy of the modeling methodology. It should be noted that confidentiality of proprietary models will be subject to various jurisdictions and statutory limitations.

Response: EPA agrees that some of the available proprietary models may meet the needs for calculating the AoRs of GS sites. EPA will allow their use in meeting the requirements for the GS regulation, but clarifies that GS well operators using proprietary models are required to disclose, to the Director's satisfaction, the code assumptions, relevant equations, and scientific basis. Information including model assumptions and equations are used by the Director to inform his/her decision to issue the permit and ensure that the requirements are met and the GS well will not endanger USDWs. EPA adds that its Confidential Business Information requirements at 40 CFR 144.5 will apply to the use of proprietary models.

Commenter Name: Robert F. Van Voorhees Letter ID: 0190 Commenter Organization: Carbon Sequestration Council Comment ID: 24516

Comment: Rule Provisions or Federal Register Cite: 146.84 EPA Preamble Question: 12. In some cases, owners or operators may choose to use proprietary models (i.e., not available for free to the general public). EPA says it is aware that the use of proprietary codes may prevent full evaluationof model results (e.g., NRC, 2007). Several popular codes in the petroleumreservoir engineering discipline are proprietary and owners or operators of particular sites may prefer to use these codes as they have previous experience with them, and they have been used in peer-reviewed studies to model CO2 sequestration. When using a proprietary model, owners or operators should clearly disclose the code assumptions, relevant equations, and scientific basis. EPA seeks comment on allowing the use of proprietary models for GS sites. EPA

Notice 43507.

CSC Response: Use of proprietary models should be allowed. EPA’s Confidential Business Information requirements should apply to any proprietary model used.

Response: EPA agrees that some of the available proprietary models may meet the needs for calculating the AoRs of GS sites. EPA will allow their use in meeting the requirements for the GS regulation, but clarifies that GS well operators using proprietary models are required to disclose, to the Director's satisfaction, the code assumptions, relevant equations, and scientific basis. EPA acknowledges that several proprietary models have been used by petroleum-reservoir engineering professionals as well as in peer-reviewed studies to model CO2 sequestration. EPA adds that its Confidential Business Information requirements at 40 CFR 144.5 will apply to the use of proprietary models. Information including model assumptions and equations are used by the Director to inform his/her decision to issue the permit and ensure that the requirements are met and the GS well will not endanger USDWs. EPA adds that its Confidential Business Information requirements at 40 CFR 144.5 will apply to the use of proprietary models.

Commenter Name: Paul Pike Letter ID: 0198 Commenter Organization: Ameren Corporation Comment ID: 23946

Comment: MODELING

Ameren believes that any model used in evaluating Class VI CO2 GS project is acceptable provided that it is based on accepted science and has been validated, and as long as we if are using a proprietary model disclose, as necessary, the code assumptions, relevant equations, and scientific basis of the model.

Response: EPA agrees with commenters that available proprietary models may meet the complex needs for calculating the AoRs of GS sites, and shares their concern about the need to evaluate the inputs and assumptions used. EPA will allow the use of proprietary models in meeting the requirements for the GS regulation, as long as GS well operators using a proprietary model clearly disclose, to the Director's satisfaction, the code assumptions, relevant equations, and scientific basis. EPA adds that its Confidential Business Information requirements at 40 CFR 144.5 will apply to the use of proprietary models.

In response to comments suggesting that history matching or validation of these models is needed, EPA believes this is true for any model. EPA notes that the GS rule requires at §146.84(e) that the AoR be reevaluated to verify the CO2 plume is moving as predicted and to allow for necessaryrevisions to the AoR and corrective action, testing and monitoring, injection well plugging, postinjection site care and site closure, and emergency and remedial response plans. EPA clarifies, however, that the Agency will not perform independent validation of individual modeling products.

The Agency plans, every six years, to collect and review data on GS projects to determine whetherthe appropriate amount and types of information and appropriate documentation are being collected, and to determine if modifications to the requirements are appropriate or necessary.

Commenter Name: Craig R. Walters Letter ID: 0200 Commenter Organization: Anadarko Petroleum Corporation Comment ID: 24579

Comment: Rule Provisions: 146.84 EPA Rule Issue: 12. In some cases, owners or operators may choose to use proprietary models (i.e., not available for free to the general public). EPA says it is aware that the use of proprietary codes may prevent full evaluationof model results (e.g., NRC, 2007). Several popular codes in the petroleumreservoir engineering discipline are proprietary and owners or operators of particular sites may prefer to use these codes as they have previous experience with them, and they have been used in peerreviewed studies to model CO2 sequestration. When using a proprietary model, owners or operators should clearly disclose the code assumptions, relevant equations, and scientific basis. EPA seeks comment on allowing the use of proprietary models for GS sites. EPA

Notice 43507.

Anadarko Petroleum Corporation (APC) Response: It is critical to allow proprietary models to be used. EPA’s Confidential Business Information requirements should apply to any proprietary model used. APC recommends EPA allow the use of proprietary models and clearly state that CBI requirements will apply.

While there has been concern raised on the current model’s ability to predict fluid flow in saline reservoirs, the development of technologies in this area will only progress when there is an economic driver that proprietary models will provide. In addition, being able to see the assumptions and equations of the model will provide the regulating authority the ability to assess the models accuracy. The currently proposed regulations also contain requirements to revisit these models when the actual site data no longer supports the models conclusions, or at a minimum of every 10 years, which APC believes is sufficient to ensure the viability of the models and data generated from their use.

Response: EPA agrees that some of the available proprietary models may meet the needs for calculating the AoRs of GS sites. EPA will allow their use in meeting the requirements for the GS regulation, but clarifies that GS well operators using proprietary models are required to disclose, to the Director's satisfaction, the code assumptions, relevant equations, and scientific basis. EPA acknowledges that several proprietary models have been used by petroleum-reservoir engineering professionals as well as in peer-reviewed studies to model CO2 sequestration. EPA adds that its Confidential Business Information requirements at 40 CFR 144.5 will apply to the use of proprietary models. Information including model assumptions and equations are used by the Director to inform his/her decision to issue the permit and ensure that the requirements are met and the GS well will not endanger USDWs. EPA adds that its Confidential Business Information requirements at 40 CFR 144.5 will apply to the use of proprietary models.

EPA clarifies that the GS rule requires that the AoR be reevaluated (§146.84(e)) to verify that the CO2 plume is moving as predicted and to allow for necessary revisions to the AoR and corrective action plan. This process will also serve to validate the modeling approach, as the commentersuggests.

Regarding the commenter’s concern about current modeling ability to predict fluid flow in saline reservoirs, EPA adds that throughout development of the proposed GS regulation, EPA conducted anumber of technical workshops inviting expert advice regarding modeling, and evaluated peerreviewed journal articles and performed critical reviews pertaining to computational modeling of CO2 injection. Information collected from these efforts assured the Agency that available complex computational models can effectively simulate CO2 transport, fate and changes in formation pressure in three dimensions as a function of time. However, EPA agrees with the commenter that modeling technology will evolve and improve over the coming years. The Agency 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.

Commenter Name: Chris M. Hobson Letter ID: 0201 Commenter Organization: Southern Company Comment ID: 22167

Comment: Modeling- Southern Company supports EPA's suggestion to allow for use of proprietary models with CO2 GS sites, provided that the permit applicant discloses the code assumptions, relevant equations, and scientific basis of the model. Id. at 43507. Based on the valuable experience Southern Company has

Response: EPA agrees with commenters that available proprietary models may meet the complex needs for calculating the AoRs of GS sites, and shares their concern about the need to evaluate the inputs and assumptions used. EPA will allow the use of proprietary models in meeting the requirements for the GS regulation, as long as GS well operators using a proprietary model clearly disclose, to the Director's satisfaction, the code assumptions, relevant equations, and scientific basis. EPA adds that its Confidential Business Information requirements at 40 CFR 144.5 will apply to the use of proprietary models.

Commenter Name: John Corra Letter ID: 0205 Commenter Organization: Wyoming Department of Environmental Quality (DEQ) Comment ID:

22202

Comment: 6. Various issues where we agree with US EPA that the Director should have the discretion to determine, or require:

c. Allowing for the use of proprietary models.

Response: EPA agrees that some of the available proprietary models may meet the needs for calculating the AoRs of GS sites. EPA will allow their use in meeting the requirements for the GS regulation, but clarifies that GS well operators using proprietary models are required to disclose, to the Director's satisfaction, the code assumptions, relevant equations, and scientific basis. EPA acknowledges that several proprietary models have been used by petroleum-reservoir engineering professionals as well as in peer-reviewed studies to model CO2 sequestration. Information including model assumptions and equations are used by the Director to inform his/her decision to issue the permit and ensure that the requirements are met and the GS well will not endanger USDWs. EPA adds that its Confidential Business Information requirements at 40 CFR 144.5 will apply to the use of proprietary models.Commenter Name: Christopher Murray Letter ID: 0207 Commenter Organization: Pacific Northwest National Laboratory Comment ID: 22447 Other EPA Comment Codes and Descriptions: 3330 2.2.1.3 Applicability /adequacy of computational models (seeking comment)

Comment: VALIDATION OF MULTIPHASE COMPUTATIONAL MODELS

PROPOSED REGULATION

p. 43507, c. 1 Models used for GS sites should be based on accepted science and should be validated. In some cases, owners or operators may choose to use proprietary models (i.e., not available for free to the general public). EPA is aware that the use of proprietary codes may prevent full evaluation of model results (e.g ., NRC, 2007). Several popular codes in the petroleum-reservoir engineering discipline are proprietary and owners or operators of particular sites may prefer to use these codes as they have previous experience with them, and they have been used in peer-reviewed studies to model CO2 sequestration. When using a proprietary model, owners or operators should clearly disclose the code assumptions, relevant equations, and scientific basis.

DISCUSSION

We agree that computational models used for GS sites should be based on accepted science and should be validated. However, the proposed rule does not define

validation. We believe that these models must be validated in terms of their appropriateness for simulating the complexities of CO2 sequestration under the conditions present at the specific site being evaluated. The fact that a codehas been validated and previously used to model CO2 sequestration (even if peerreviewed) does not ensure that it is appropriate for use at all sites and under all conditions. For example, it is possible that, for a specific site, certain physical and/or geochemical processes must be considered that are not available in a given computational code. Whereas that code may have reasonably and successfully modeled CO2 sequestration at a dissimilar site, it may not be appropriate for the site being considered.

It may be appropriate for EPA to establish a suite of test problems that span the breadth of GS reservoir types (i.e., deep saline formations, depleted oil and gas reservoirs, faulted or fractured reservoirs, unmineable coal seams, basalts, salt domes, reactive carbonates, and shales), injection surface climatic extremes, injectate composition, single versus multiple wells, conditions (i.e., pressure reduction wells, and horizontal versus vertical injection wells), and physical/ geochemical processes deemed important in modeling CO2 sequestration (i.e. ., changes of state and chemical reactions). We suggest that this suite of problems be defined by experts in the field of CO2 sequestration modeling and code development, and that a variety of computational codes used in modeling GS sites be benchmarked using this suite. A subset of the suite of problems may be sufficient to validate a code for use at a particular site, however this subset must be rigorously defined (by EPA or the State, if it has established primacy for UIC regulation) based on the conditions specific to the site in question to ensure that the model being validated is appropriate for use at the site. Efforts are already underway to evaluate and comparecomputational codes being used to model GS sites. For example, several code intercomparison studies have been conducted to evaluate the capabilities and accuracy of numerical simulators for geological storage of green house gases (Pruess et al., 2004 and Law et al., 2003). In addition, the Inter-Partnership Simulation and Risk Working Group within the DOE Regional Partnerships is embarking on an effort to compare overall modeling methodologies on a jointly accessible data set. This will be more inclusive than a code intercomparison effort as the methodologies and conceptual models used may vary widely.

Model results that should be used to determine if a code is valid for solving a specified problem include plume area and maximum plume radius (as defined by 95% of the CO2 mass) at particular time planes, injected mass over the time period of simulation, pressure distribution, and CO2 phase). Based on the code benchmarks and expert knowledge, a tolerance must be defined that determines what constitutes acceptable results. This suite of test problems could be modified or augmented as the state-of -the-science progresses in modeling, ensuring that any computational code being used at a particular site is current with regard to accepted scientific principles and rigor.

In addition to validating particular computational codes using a set of standard benchmarks, the implementation of the conceptual model should also be validated by comparing model results to observed data, and by using model calibration and history matching to improve the model results. EPA understands the importance of history-matching of model simulations with monitoring as stated on p. 43507, c.

1.

PNNL RECOMMENDATION

EPA should establish a suite of test problems with specified parameters that could be used by the applicant to demonstrate the suitability of the computational code to be used for analysis of the proposed site. As computational approaches and methods improve, this suite of problems should be modified and/or updated to incorporate the state-of -the-knowledge in GS modeling.

We agree that proprietary models can be used, provided they can demonstrate they produce results within the defined acceptable tolerance, in addition to disclosing the code assumptions, relevant equations, and scientific basis. These same requirements must, of course, be met by all computational codes being used

at GS sites.

REFERENCES:

Law, D.H.-S., L.G.H. vander Meer andW.D. Gunter, 2003: Comparison of numerical simulators for greenhouse gas storage in coal beds, Part II: Flue gas injection. Proceedings of the 6th International Conference on Greenhouse Gas Control Technologies (GHGT-6), J. Gale and Y. Kaya (eds.), 1-4 October 2002, Kyoto, Japan, Pergamon, v.I, 563-568. Geologischen Gesellschaft,149,3,449-464.

Pruess K, J Garcia, TKovscek, C Oldenburg, J Rutqvist, C Steefel, and TXu. 2002.Intercomparison of Numerical Simulation Codes for Geologic Disposal of CO2. LBNL-51813, Lawrence Berkeley National Laboratory, Berkeley, California.

Response: EPA clarifies that an EPA-prepared technical background document, "Computational Modeling of Underground Injection of Carbon Dioxide for Determination of Area-of-Review and Potential Risk to Underground Sources of Drinking Water" (cited as USEPA, 2008d) was provided in the regulatory docket for the proposed GS rule. This document discusses, for example, uncertainty analysis in detail. This document was provided as a background to clarify what information EPA analyzed in order to draft the modeling requirements at §146.84(c)(1), as well as what actions EPA expects owners or operators and Directors to take in this area. For example, the document states: "The requirement for an a-priori AoR delineation based on modeling predictions stresses the need for uncertainty and sensitivity analyses for the initial prediction. Sensitivity analysis is recommended as the principal evaluation tool for characterizing the most and least important sources of uncertainty

in environmental models."

EPA agrees that in some cases, results from test-cases may be appropriate. In the technical background document (USEPA, 2008d), EPA provided several questions that should be raised during evaluation of models. One of these questions was "If using an independently developed or unverified code, are results from test-problems and comparisons to widely used codes presented?" Another was "Was relevant site characterization data gathered at a sufficiently high spatial resolution to inform model development? Was this data used in the model in a way that considers uncertainty?"

Regarding the suggestion that EPA establish a suite of test problems to demonstrate the suitability of the computational code, EPA notes that the Agency will not perform independent "tests" or validation of individual modeling products. EPA believes that operators should have the flexibility to select models with which they are familiar and that are most appropriate to site conditions and available data types and amounts.

EPA based this background document in part on guidance drafted by the National Research Council and on EPA's Council on Regulatory Environmental Modeling (CREM) document. EPA refers interested commenters to the document "Guidance on the Development, Evaluation and Application of Environmental Models," (74 FR 14551, March 31, 2009).

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.

Commenter Name: Richard Guinn Letter ID: 0210 Commenter Organization: Eastman Chemical Company Comment ID: 22728

Comment: EPA seeks comment on allowing the use of proprietary models for GS sites. EPA

Notice 68.

Proprietary models should be acceptable provided that supporting data for

validation are submitted.Response: EPA agrees with commenters that available proprietary models may meet the complex needs for calculating the AoRs of GS sites, and shares their concern about the need to evaluate the inputs and assumptions used. EPA will allow the use of proprietary models in meeting the requirements for the GS regulation, as long as GS well operators using a proprietary model clearly disclose, to the Director's satisfaction, the code assumptions, relevant equations, and scientific basis. EPA adds that its Confidential Business Information requirements at 40 CFR 144.5 will apply to the use of proprietary models.

In response to comments suggesting that history matching or validation of these models is needed, EPA believes this is true for any model. EPA notes that the GS rule requires at §146.84(e) that the AoR be reevaluated to verify the CO2 plume is moving as predicted and to allow for necessaryrevisions to the AoR and corrective action, testing and monitoring, injection well plugging, postinjection site care and site closure, and emergency and remedial response plans. EPA clarifies, however, that the Agency will not perform independent validation of individual modeling products.

The Agency 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.

Commenter Name: Edward Steadman Letter ID: 0220 Commenter Organization: The Energy and Environmental Research Center at the University of North Dakota Comment ID:

21613

Comment: Page 43507. Regarding the use of proprietary models: The use of proprietary models absolutely should be allowable. In many cases, such software packages are the only reliable models that can be applied with any real confidence in their results. That being said, the use of such models should not be required because, in some cases, especially those where adequate data exist, nonproprietary models can serve the purpose in a more cost-effective manner.

Response: EPA agrees with commenters that available proprietary models may meet the complex needs for calculating the AoRs of GS sites. EPA will allow, but not require, the use of proprietary models in meeting the requirements for the GS regulation, as long as GS well operators using a proprietary model clearly disclose, to the Director's satisfaction, the code assumptions, relevant equations, and scientific basis. EPA adds that its Confidential Business Information requirements at 40 CFR 144.5 will apply to the use of proprietary models.

Commenter Name: M. Granger Morgan Letter ID: 0233 Commenter Organization: Carnegie Mellon University on behalf of the CCS Reg Project Comment ID:

21916

Comment: 24. Use of proprietary models: Use of proprietary models has the potential to exaggerate information asymmetry among project operators, regulators and the public. If the project operator uses proprietary software for modeling, then they should be required to provide all key modeling assumptions, run sensitivity analyses on important inputs, or provide additional model runs of the data in a publicly available model acceptable to EPA.

Response: EPA shares the commenter’s concern about the need to evaluate the inputs and assumptions used. EPA will allow the use of proprietary models in meeting the requirements for theGS regulation, as long as GS well operators using a proprietary model clearly disclose, to the Director's satisfaction, the code assumptions, relevant equations, and scientific basis. EPA also agrees that sensitivity analyses should be presented by the owner or operator and evaluated by theDirector. If during the permit review, the Director determines that modeling results are too wideranging, further information will be required of the owner or operator. EPA adds that its Confidential Business Information requirements at 40 CFR 144.5 will apply to the use of proprietary models.

The Agency 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.

Commenter Name: Mark Bohrer Letter ID: 0241 Commenter Organization: North Dakota Industrial Commission Comment ID: 23232

Comment: 12 In some cases, owners or operators may choose to use proprietary models (i.e., not available for free to the general public). EPA says it is aware that the use of proprietary codes may prevent full evaluation of model results (e.g., NRC, 2007). Several popular codes in the petroleum-reservoir engineering discipline are proprietary and owners or operators of particular sites may prefer to use these codes as they have previous experience with them, and they have been used in peer-reviewed studies to model CO2 sequestration. When using a proprietary model, owners or operators should clearly disclose the code assumptions, relevant equations, and scientific basis. EPA seeks comment on allowing the use of proprietary models for GS sites. EPA Notice 43507.

The use of proprietary models is widely used and accepted in oil and gas reservoir simulation. These models are a logical fit to simulate carbon dioxide sequestration projects. These models are verified using a history-match. The regulatory agency responsible for monitoring carbon dioxide sequestration does not need access to the code in order to conduct or evaluate a history-match. A regulatory agency could conduct reservoir modeling using its own modeling software to compare. Elimination of these widely used and understood reservoir models would be unwise. The assumptions and equations used in the modeling along with a valid history match will provide the regulating authority the ability to assess the model’s accuracy.

Response: EPA agrees with commenters that available proprietary models may meet the complex needs for calculating the AoRs of GS sites, and shares their concern about the need to evaluate the inputs and assumptions used. EPA will allow the use of proprietary models in meeting the requirements for the GS regulation, as long as GS well operators using a proprietary model clearly disclose, to the Director's satisfaction, the code assumptions, relevant equations, and scientific basis. EPA adds that its Confidential Business Information requirements at 40 CFR 144.5 will apply to the use of proprietary models.

EPA acknowledges that several proprietary models are currently, successfully used by petroleumreservoir engineering professionals as well as in peer-reviewed studies to model CO2 sequestration.

Commenter Name: Kristin Henry Letter ID: 0242 Commenter Organization: Sierra Environmental Law Program, Sierra Club Comment ID: 23336Other EPA Comment Codes and Descriptions: 5540 2.10.2 Need for additional public participation requirements/ use of new information technology (seeking comment)

Comment: 2. The proposed rule allows an applicant to use proprietary modeling software to submit predictions of plume behavior and movement, storage capacity, and injection rates. Use of proprietary software would hinder public participation because the public could not test applicant’s modeling predictions. To ensure transparency in the application process, publicly available modeling programs must be required.

Response: EPA expects that permitting authorities would make some information about the model available to the public, such as information about the model used and the parameters modeled. However, EPA does not expect that members of the public would evaluate the AoR delineation models themselves. The models and their inputs will, by necessity, entail an extensive amount of technical information that may not be easily understood by the public. EPA believes that it is the Director's responsibility, as a steward of public health and the environment, to review models, model inputs, and results and to determine whether the model is appropriate for predicting the AoR, and to distribute information that may be easily understood by the public (e.g., in the form of a fact sheet).

In response to comments about the need for additional public participation and the use of new information technology, EPA shares the commenter’s concern about the need to evaluate the inputs and assumptions used, but disagrees that the use of proprietary models should be disallowed. EPA intends to allow the use of proprietary models in meeting the requirements for the GS regulation, as long as GS well operators using a proprietary model clearly disclose, to the Director's satisfaction, the code assumptions, relevant equations, and scientific basis.

EPA believes that operators should have the flexibility to select models with which they are familiar and that are most appropriate to the site conditions and available data types and amounts. EPA also recognizes that a standardized model for AoR delineations could be effective as long as the model accounts for the expected variations in site conditions, and adds that a state or regional UIC Director could select one standard model if it took site-specific variations into account. EPA has evaluated technical documents regarding several computational models that may be used for GS sites. Based on this review (as documented in the preamble to the proposed GS regulation and the background document "Computational Modeling of Underground Injection of Carbon Dioxide for Determination of Area-of-Review and Potential Risk to Underground Sources of Drinking Water"), EPA believes that several models meet the minimum requirements for models in the GS regulation. EPA adds that its Confidential Business Information requirements at 40 CFR 144.5 will apply to the use of proprietary models.

Commenter Name: Walter L. Baker Letter ID: 0253 Commenter Organization: Utah Division of Water Quality Comment ID: 22348

Comment: PROPRIETARY MODELING

We do not support the use of proprietary models for modeling CCGS projects. There should be complete transparency in all aspects of CCGS allowing for peer review of the models and assumptions associated with them. This process would be hindered by the use of proprietary models. Furthermore, there are numerous powerful modeling codes available in the public domain that have already been used in predicting fluid movement and geochemical reaction for CCGS.Response: EPA disagrees that the use of proprietary models should be disallowed. EPA acknowledges the commenter’s concerns about the need to evaluate the inputs and assumptions used in these models, and EPA intends to allow the use of proprietary models in meeting the requirements for the GS regulation. EPA clarifies, however, that GS well operators using proprietary models are required to disclose, to the Director's satisfaction, the code assumptions, relevant equations, and scientific basis. Information including model assumptions and equations are used by the Director to inform his/her decision to issue the permit and ensure that the requirements are met and the GS well will not endanger USDWs. EPA adds that its Confidential Business Information requirements (144.5) will apply to the use of proprietary models.

EPA clarifies, however, that GS well operators using proprietary models are required to disclose, to the Director's satisfaction, the code assumptions, relevant equations, and scientific basis. Information including model assumptions and equations are used by the Director to inform his/her decision to issue the permit and ensure that the requirements are met and the GS well will not endanger USDWs.

Letter ID: 0263 Commenter Organization: Interstate Oil & Gas Compact Commission Comment ID: 22798

Comment: III A. 2 Proposed Area ofReview and Corrective Action Requirements

M. EPA seeks comment on allowing the use of proprietary models for GS sites.

IOGCC Response: Proprietary models should be allowed provided the Director has discretion to evaluate the accuracy of the modeling methodology. It should be noted that confidentiality of proprietary models will be subject to statutory limitation in various jurisdictions.

Response: EPA will allow the use of proprietary models in meeting the requirements for the GS regulation, but clarifies that GS well operators using proprietary models are required to disclose, to the Director's satisfaction, the code assumptions, relevant equations, and scientific basis.

EPA adds that its Confidential Business Information requirements at 40 CFR 144.5 will apply to the use of proprietary models. Information including model assumptions and equations are used by the Director to inform his/her decision to issue the permit and ensure that the requirements are met and the GS well will not endanger USDWs.

The Agency 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.

Commenter Name: Mark Singer Letter ID: 0504 Commenter Organization: Green America Project, LLC Comment ID: 21247

Comment: There's a lot of discussion about modeling as a key to how they're going to analyze whether this is sufficient, and trying to predict injectate behavior based on modeling, getting data and then analyzing and trying to adapt.

The proposal does not sufficiently address transparency. Importantly, as thisdata comes in it should be made available to the public so that scientific and technical experts can analyze that.

Response: In response to the comment that the proposal does not sufficiently address transparency, GS well operators are required to disclose, to the Director's satisfaction, the code assumptions, relevant equations, and scientific basis. EPA adds that its Confidential Business Information requirements at 40 CFR 144.5 will apply to the use of proprietary models. Information including model assumptions and equations are used by the Director to inform his/her decision to issue the permit and ensure that the requirements are met and the GS well will not endanger USDWs.

Commenter Name: Becky English Letter ID: 0524 Commenter Organization: Sierra Club Comment ID: 21483

Comment: Secondly I wanted to point out that permit applications should not be able, applicants rather, should not be able to use proprietary software if they are not willing to disclose their modeling data. And their operating assumptions and explain their research methods more fully for a transparent, for transparency with the public; people such as myself and Sierra Club. We need complete transparency in order to give adequate public input. That is just obvious.

Response: EPA disagrees that the use of proprietary models should be disallowed. EPA will allow the use of proprietary models in meeting the requirements for the GS regulation, but clarifies that GS well operators using proprietary models are required to disclose, to the Director's satisfaction, the code assumptions, relevant equations, and scientific basis.

In response to the comment that the proposal does not sufficiently address transparency, EPA clarifies that GS well operators are required to disclose, to the Director's satisfaction, the code assumptions, relevant equations, and scientific basis. EPA adds that its Confidential Business Information requirements at 40 CFR 144.5 will apply to the use of proprietary models. Information including model assumptions and equations are used by the Director to inform his/her decision to issue the permit and ensure that the requirements are met and the GS well will not endanger USDWs.

EPA acknowledges commenters' concerns about the need to evaluate the inputs and assumptions used in these models, and will allow the use of proprietary models in meeting the requirements for the GS regulation. EPA clarifies, however, that GS well operators using proprietary models are required to disclose, to the Director's satisfaction, the code assumptions, relevant equations, and scientific basis. Information including model assumptions and equations are used by the Director to inform his/her decision to issue the permit and ensure that the requirements are met and the GS well will not endanger USDWs. EPA adds that its Confidential Business Information requirements at 40 CFR 144.5 will apply to the use of proprietary models.

To ensure that all predictive models used for AoR calculations are meeting the Agency's expectations, 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.

Commenter Name: Kevin Frederick Letter ID: 0525 Commenter Organization: Wyoming Department of Environmental Quality Comment ID: 21400

Comment: Discretion to allow the use of proprietary models. Wyoming, in particular, hasoptions available for applying for confidential treatment of proprietary models

and we believe that should be allowed at the discretion of the director as well.

Response: EPA agrees that some of the available proprietary models may meet the needs for calculating the AoRs of GS sites. EPA will allow their use in meeting the requirements for the GS regulation, but clarifies that GS well operators using proprietary models are required to disclose, to the Director's satisfaction, the code assumptions, relevant equations, and scientific basis. EPA acknowledges that several proprietary models have been used by petroleum-reservoir engineering professionals as well as in peer-reviewed studies to model CO2 sequestration. EPA adds that its Confidential Business Information requirements at 40 CFR 144.5 will apply to the use of proprietary models. Information including model assumptions and equations are used by the Director to inform his/her decision to issue the permit and ensure that the requirements are met and the GS well will not endanger USDWs.

Comment Code: 3400 2.2.2 Corrective Action



### Individual Comments

Commenter Name: Leslie Savage Letter ID: 0122 Commenter Organization: Railroad Commission of Texas (RRC) Comment ID: 24773 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language; 3700 2.2.5 Comments on the requirement for an AoR and corrective action plan

Comment: (II)(iii) How monitoring and operational data (e.g., injection rate and pressure) will be used to inform an area of review reevaluation; and

(iv) How corrective action will be conducted to meet the requirements of paragraph (d) of this section, including what corrective action will be performed prior to injection and what, if any, portions of the area of review will have corrective action addressed on a phased basis and how the phasing will be determined; how corrective action will be adjusted if there are changes in the area of review; and how THE site WILL BE accessed will be guaranteed for

future corrective action.

{Word Choice. Secure rather than guarantee. }

Response: The purpose of the corrective action requirement at §146.84(d) is to ensure that all wells in the AoR that have the potential to cause the movement of CO2 or other fluids into or between USDWs receive appropriate corrective action. In general, to meet this requirement, the owner or operator will mostly likely need to obtain the right of access to wells that may require corrective action, and demonstrate they have done this in their proposed AoR and corrective action plan. For this reason, the owner or operator must describe in the AoR and corrective action plan how site access will be guaranteed for future corrective action, as specified in §146.84(b)(2)(iv). The final rule retains the requirement as proposed.

Commenter Name: Leslie Savage Letter ID: 0122 Commenter Organization: Railroad Commission of Texas (RRC) Comment ID: 24777 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rulelanguage

Comment: (3) Determine which abandoned wells in the AOR have been plugged in a manner that prevents the movement of CO2 or FORMATION associated fluids that may endanger USDWs.

Response: EPA clarifies that the term "associated fluids" as proposed in §146.84(c)(3) refers to formation fluids, other injectates, etc. that may be present in the subsurface and affect movement of the CO2 plume and/or pressure front. EPA believes this terminology would incorporate any fluids in the subsurface that could potentially move through artificial penetrations and affect USDWs. EPA has revised the language at §146.84(c)(3) to read, "... carbon dioxide or other fluids that may endanger USDWs..."

Commenter Name: Christine Reimer Letter ID: 0142 Commenter Organization: National Ground Water Association Comment ID: 22551 Other EPA Comment Codes and Descriptions: 3300 2.2.1 Delineating the AoR/Modeling CO2

movement
Comment: Area of Review and Corrective Action

In the context of carbon storage, NGWA thinks it is important to distinguish between the CO2 plume footprint and the zone of elevated pressure. The rationale is given in the next section, but the following conditions should be met:

- No fixed radius can be used, a zone of endangering influence (ZEI) must be determined through modeling (but cannot be smaller than 1⁄4 mile in its smallest horizontal dimension) - In the volume generated by the CO2 plume footprint (plus appropriate buffer) (this volume is defined as the "primary AOR"): all penetrations between the base of the injection formation and the base of the USDW should be reviewed and any necessary corrective action should be taken before start of project.

- In the elevated pressure area but outside of the CO2 plume footprint (defined as the "secondary AOR"), all current penetrations through the primary seal and the injection formation should be reviewed. However the applicant should be allowed to perform corrective action in a pseudo-concentric phased manner ahead of and according to the development of the pressure plume.

- Secondary AOR/zone of elevated pressure cannot be computed independently of other injection projects in the vicinity. The impact of other sequestration projects must be included in determining injection rate / period of injection.

- Primary and secondary AOR must be periodically reviewed to ensure that modeling predictions are met. If they are not, the primary and secondary AOR should be revisited. The operator should keep track of any new penetration in the primary AOR volume and secondary AOR (for example, for oil and gas industry).

"Primary AOR" - Why "Volume of Review"

Because CO2 is strongly buoyant, it is not sufficient only to investigatepenetrations in the injection formation and primary seal. The whole volume potentially contacted by the CO2 plume should be reviewed. The review and corrective actions should be performed before the start of injection because there is no stopping the CO2 migration once started. The greatest degree of effort should be on the deeper wells in the injection zone and primary containment then on the secondary containment and seal (if any) and then on shallower wells but as many as possible of the shallower wells should be compiled too.

Delayed Corrective Action for "Secondary AOR"

A simple time-dependent secondary AOR that expands as the volume of injection increases and the CO2 migrates is not acceptable. The secondary AOR should be agreed upon and reviewed before injection starts but corrective action can be somewhat delayed. The secondary AOR consists of only the injection formation and seal as used in the current rules because only brine/formation water leakage is an issue in the elevated pressure area. The likely presence of a large elevated pressure area does not make realistic imposing corrective action on all wells before the start of a project. There is no need to provide corrective action to wells before the pressure significantly rises. If another problem (e.g., CO2 leakage) occurs earlier at another location and injection stops, pressure will not keep rising and will drop. In addition, delaying corrective action will allow taking advantage of technical improvements that will undoubtedly occur in

the next decades.

Response: EPA agrees that the AoR for a GS project should incorporate both the CO2 plume and the pressure front, and clarifies that the requirements for AoR delineation in the final rule incorporate both the CO2 plume and associated pressure front. This area would be modeled based on anticipated CO2 volumes to be injected and other site-specific information that would impact pressure changes in the subsurface. EPA agrees that both of these should be taken into account in determining corrective action needs and developing a testing and monitoring plan, and that the requirement to delineate the AoR at §146.84(c) addresses the potential risks raised by the commenters. EPA believes that the final GS requirements for delineating the AoR provide sufficient protection to USDWs, without introducing an overly complex regulatory process.

EPA acknowledges the commenter’s support of phased corrective action and 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.

Commenter Name: Kyle Isakower Letter ID: 0170 Commenter Organization: American Petroleum Institute Comment ID: 24163 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Rule Provision: 146.84(c)(3)

API Comments: (3) Determine which abandoned wells IDENTIFIED IN 146.84 (C) (2)in the area of review have been plugged (as required by §146.92) in a manner that prevents the movement of carbon dioxide or associated FORMATION fluids that may endanger USDWs.

Rationale: Remove as redundant.

Response: EPA clarifies that the term "associated fluids" as proposed in §146.84(c)(3) refers to formation fluids, other injectates, etc. that may be present in the subsurface and affect movement of the CO2 plume and/or pressure front. EPA believes this terminology would incorporate any fluids in the subsurface that could potentially move through artificial penetrations and affect USDWs. EPA has revised the language at §146.84(c)(3) to read, "... carbon dioxide or other fluids that may endanger USDWs..." EPA disagrees that deleting the term area of review is necessary and has retained the term in the final rule language.

Commenter Name: Kyle Isakower Letter ID: 0170 Commenter Organization: American Petroleum Institute Comment ID: 24165 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Rule Provision: 146.84(e)

API Comments: (e) If monitoring data indicate an endangerment to USDWs, the owner or operator must notify the Director and cease operations as required by §

146.94.

Rationale: This is not needed since §146.94 already specifies the notification and cessation of injection. API suggests the removal of this language as unnecessarily duplicative.

Response: Based on consideration of all public comments and other information, EPA deleted this provision from §146.84. The final rule now contains a provision in §146.91(c) that requires the owner or operator to report within 24 hours any evidence that the carbon dioxide stream or associated pressure front may cause an endangerment to a USDW. EPA believes this change consolidates reporting requirements in one place and provides additional clarity.

Commenter Name: James Rower Letter ID: 0173 Commenter Organization: Utility Solid Waste Activities Group (USWAG) Comment ID: 23489

Comment: On a related topic, USWAG would like to ensure that the obligation of Class VI Owners or Operators to plug or repair a pre-existing well within the AoR will not be viewed as excusing prior well owners or operators from fulfilling their own pre-existing legal obligations under applicable federal or state law to have properly closed the well in the first instance. Well plugging and repair obligations imposed on Class VI Owners or Operators should not supersede any pre-existing legal obligations that have yet to be fulfilled by previous owners or operators. To prevent this from occurring, the Final Rule should make clear that, in those circumstances where pre-existing wells in an AoR have not been properly closed and are now subject to well plugging and repair under a Class VI UIC permit, EPA and/or the applicable state regulatory agency should first look to see whether the responsible party for such closure is still available toproperly close the well as legally required before imposing such obligations on the Owner or Operator of the Class VI UIC permit.

Response: EPA clarifies that the purpose of the requirement to perform corrective action at §146.84(d) is to ensure that all wells in the AoR that have the potential to cause movement of CO2 or other fluids into or between USDWs receive appropriate corrective action. All needed corrective action must be performed by the GS well owner or operator as described in the approved AoR and corrective action plan, regardless of ownership of the wells in the AoR. Failure to do so would either preclude authorization to inject or, in the case of phased corrective action, be considered a violation of the permit and subject to applicable civil, criminal, or administrative penalties. EPA clarifies that UIC program authority is limited to the proper operation and plugging of injection wells, and that it does not have authority to require plugging of other types of wells.

Commenter Name: Frederick R. Eames Letter ID: 0178 Commenter Organization: CCS Alliance Comment ID: 23857

Comment: EPA should address gaining access to third party wells that may require corrective action. Most states require corrective action to be performed prior to injection and the "right of access" is taken into consideration during the adequacy determination of the corrective action plan. Some states, such as Texas, require corrective action prior to injection unless the owner/operator, after best efforts, is unable to get permission to access the property of a third party.[FN50] SDWA does not provide EPA the authority to require third parties to provide access to an owner/operator for the purposes of conducting corrective action. EPA should clarify how owner/operators and states will be expected to implement corrective action.

[FN 50] 30 TEX. ADMIN Code $ 305.151 (2008)

Prior to denying a permit application, the regulations should provide the owner or operator the opportunity to demonstrate that a project can maintain its safety and security, despite an uncorrected well. Otherwise, a potential GS site could go unutilized, even if the uncorrected well creates no actual risk of harm to USDWs. Moreover, well remediation should be applicable only to those wells that are likely to be impacted (meaning exposed to corrosive fluid and/or pressure above likely capillary entry pressure) early to mid phases of operation (e.g., one to 20 years).

Response: The purpose of the corrective action requirement at §146.84(d) is to ensure that all wells in the AoR that have the potential to cause the movement of CO2 or other fluids into or between USDWs receive appropriate corrective action. In general, to meet this requirement, the owner or operator most likely will need to obtain the right of access to wells that may require corrective action, and demonstrate they have done this in their proposed AoR and corrective action plan. In the AoR and corrective action plan, the owner or operator must describe how site access will be guaranteed for future corrective action, as specified in §146.84(b)(2)(iv). EPA adds that, in some circumstances, monitoring in the injection zone may be an appropriate corrective action technique. These types of determinations would need to be made by the Director on a site-specific basis.

Commenter Name: Daniel Plath Letter ID: 0188Commenter Organization: NiSource, Inc. Comment ID: 25229 Other EPA Comment Codes and Descriptions: 1610 1.3.1 Risks to USDWs; 3800 2.3 Proposed Injection Well Construction Requirements (40 CFR 146.86); 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 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.

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 pre-operational 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 long-standing 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.

Commenter Name: Daniel Plath Letter ID: 0188 Commenter Organization: NiSource, Inc. Comment ID: 25233 Other EPA Comment Codes and Descriptions: 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 ofpipe in the well while Section 146.84 would ensure that abandoned wells are properly plugged.

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

Commenter Name: Robert F. Van Voorhees Letter ID: 0190 Commenter Organization: Carbon Sequestration Council Comment ID: 24403 Other EPA Comment Codes and Descriptions: 1220 1.1.1.1 Terminology and definitions

Comment: Rule Provision: 146.81(d) [Definition - Corrective action]

Proposed CCS Group Recommendations: Support the proposed language.

Basis for CCS Group Comments: Agree with EPA’s rationale.

Response: EPA acknowledges the commenter’s support; the final GS rule retains the definition.

Commenter Name: Robert F. Van Voorhees Letter ID: 0190 Commenter Organization: Carbon Sequestration Council Comment ID: 24428 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Rule Provision: 146.84(b)(2)(iv)

Proposed CCS Group Recommendations: iv (II) How corrective action will be conducted to meet the requirements of paragraph (d) of this section, including what corrective action will be performed prior to injection and what, if any, portions of the area of review will have corrective action addressed on a phased basis and how the phasing will be determined; how corrective action will be adjusted if there are changes in the area of review; and how site access will be guaranteed ARRANGED for future corrective action.

Basis for CCS Group Comments: Future access cannot be guaranteed for an area in advance that may not even be within the boundaries of the AOR/ project.

Response: EPA is retaining this requirement as proposed. The purpose of the corrective action requirement at §146.84(d) is to ensure that all wells in the AoR that have the potential to cause the movement of CO2 or other fluids into or between USDWs receive appropriate corrective action. Ingeneral, to meet this requirement, the owner or operator will most likely need to obtain the right of access to wells that may require corrective action, and demonstrate they have done this in their proposed AoR and corrective action plan. In the AoR and corrective action plan, the owner or operator must describe how site access will be guaranteed for future corrective action as specified in §146.84(b)(2)(iv).

Commenter Name: Robert F. Van Voorhees Letter ID: 0190 Commenter Organization: Carbon Sequestration Council Comment ID: 24433 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Rule Provision: 146.84(c)(3)

Proposed CCS Group Recommendations: (3) Determine which abandoned wells IDENTIFIED PURSUANT TO 146.84 (C) (2) in the area of review have been plugged (as required by §146.92) in a manner that prevents the movement of

carbon dioxide or associated FORMATION fluids that may endanger USDWs.

Basis for CCS Group Comments: Remove "in the area of review" as redundant.

Response: EPA clarifies that the term "associated fluids," as proposed in §146.84(c)(3), refers to formation fluids, other injectates, etc., that may be present in the subsurface and affect movement of the CO2 plume and/or pressure front. EPA believes this terminology would incorporate any fluids in the subsurface that could potentially move through artificial penetrations and affect USDWs. EPA has revised the language at §146.84(c)(3) to read, "... carbon dioxide or other fluids that may endanger USDWs..." EPA disagrees that deleting the term area of review is necessary and has retained the term in the final rule language.

Commenter Name: Robert F. Van Voorhees Letter ID: 0190 Commenter Organization: Carbon Sequestration Council Comment ID: 24435 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Rule Provision: 146.84(e)

Proposed CCS Group Recommendations: (e) If monitoring data indicate an endangerment to USDWs, the owner or operator must notify the Director and cease operations as required by § 146.94.

Basis for CCS Group Comments: This is not needed since §146.94 already specifies the notification and cessation of injection. We suggest deletion of this language as unnecessarily duplicative.

Response: Based on consideration of all public comments and other information, EPA deleted this provision from §146.84. The final rule now contains a provision in §146.91(c) that requires the owner or operator to report within 24 hours any evidence that the carbon dioxide stream or associated pressure front may cause an endangerment to a USDW. EPA believes this change consolidates reporting requirements in one place and provides additional clarity.

Commenter Name: Paul Pike Letter ID: 0198Commenter Organization: Ameren Corporation Comment ID: 23948 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: We believe that use of the phrase "corrective action" to describe well plugging and repair risks confusion with the concept of corrective action under either RCRA or CERCLA. This potential confusion can lead to unwarranted negative associations with the phrase "corrective action," and we would suggest abandoning this phrase and instead use a phrase such as "well plugging and repair." We would then also support a phased approach to well plugging and repair ("corrective action") for CO2 GS wells as contemplated in the Proposal and it should be available to all Owners or Operators of CO2 GS wells rather than be available only at the discretion of the Director. 73 Fed. Reg. at

43507-08.

Response: EPA notes that the term "corrective action" at §146.84(d) has been used to describe the process of addressing improperly plugged wells in the AoR of injection wells since the inception of the UIC Program, e.g., at §146.7 and §146.64. While EPA is aware that the term has a different meaning under RCRA and CERCLA, this has not caused confusion in the past. The alternative term, "well plugging," suggested by the commenter is reserved for injection well plugging as indicated at §146.92.

Commenter Name: Craig R. Walters Letter ID: 0200 Commenter Organization: Anadarko Petroleum Corporation Comment ID: 24657 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language; 3700 2.2.5 Comments on the requirement for an AoR and corrective action plan

Comment: Rule Provision: 146.84(b)(2)(iv)

Anadarko Petroleum Corporation (APC) Comments: (iv II) How corrective action will be conducted to meet the requirements of paragraph (d) of this section, including what corrective action will be performed prior to injection and what, if any, portions of the area of review will have corrective action addressed on a phased basis and how the phasing will be determined; how corrective action will be adjusted if there are changes in the area of review; and how site access will be guaranteed ARRANGED for future corrective action.

Rationale: Future access cannot be guaranteed for an area in advance that may not even be within the boundaries of the AOR/ project.

Response: The purpose of the corrective action requirement at §146.84(d) is to ensure that all wells in the AoR that have the potential to cause the movement of CO2 or other fluids into or between USDWs receive appropriate corrective action. In general, to meet this requirement, the owner or operator will most likely need to obtain the right of access to wells that may require corrective action, and demonstrate they have done this in their proposed AoR and corrective action plan. The final rule retains the requirement as proposed.

Commenter Name: Craig R. Walters Letter ID: 0200 Commenter Organization: Anadarko Petroleum Corporation Comment ID: 24661 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rulelanguage

Comment: Rule Provision: 146.84(c)(3)

Anadarko Petroleum Corporation (APC) Comments: (3) Determine which abandoned wells IDENTIFIED IN 146.84 (C) (2) in the area of review have been plugged (as required by §146.92) in a manner that prevents the movement of carbon

dioxide or associated FORMATION fluids that may endanger USDWs.

Rationale: Remove as redundant.

Response: EPA clarifies that the term "associated fluids" as proposed in §146.84(c)(3) refers to formation fluids, other injectates, etc. that may be present in the subsurface and affect movement of the CO2 plume and/or pressure front. EPA believes this terminology would incorporate any fluids in the subsurface that could potentially move through artificial penetrations and affect USDWs. EPA has revised the language at §146.84(c)(3) to read, "... carbon dioxide or other fluids that may endanger USDWs..." EPA disagrees that deleting the term area of review is necessary and has retained the term in the final rule language.

Commenter Name: Craig R. Walters Letter ID: 0200 Commenter Organization: Anadarko Petroleum Corporation Comment ID: 24663 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Rule Provision: 146.84(e)

Anadarko Petroleum Corporation (APC) Comments: (e) If monitoring data indicate an endangerment to USDWs, the owner or operator must notify the Director and cease operations as required by § 146.94.

Rationale: This is not needed if §146.94 already specifies the notification and cessation of injection. APC suggests the removal of this language as unnecessarily duplicative.

Response: Based on consideration of all public comments and other information, EPA deleted this provision from §146.84. The final rule now contains a provision in §146.91(c) that requires the owner or operator to report within 24 hours any evidence that the carbon dioxide stream or associated pressure front may cause an endangerment to a USDW. EPA believes this change consolidates reporting requirements in one place and provides additional clarity.

Commenter Name: John King Letter ID: 0211 Commenter Organization: Shell Exploration and Production Company (SEPCo) Comment ID:

22768 Other EPA Comment Codes and Descriptions: 3530 2.2.3.1 AoR reevaluation frequency (seeking comment)

Comment: 2.Corrective Action

Corrective action is a familiar UIC program requirement. Given the potential scale of GS operations, EPA has proposed requirements for a corrective action plan contemplating periodic reassessment of the AOR and a phased implementationof corrective action. In general, this approach is prudent and practical, providing what will ultimately be a rigorous approach to corrective action while reducing regulatory burdens by permitting a phased implementation of corrective action requirements. However, SEPCo does not believe that a minimum frequency for reevaluation of the AOR should be required.

Recommendation:

The need for reevaluation of the AOR should be required -- if at all -- when there is site specific evidence that there is actually a need to reevaluate the AOR. Where monitoring results remain consistent with modeling results, a requirement to reevaluate the AOR should not be required.

Response: EPA believes that periodic AoR reevaluation at a set frequency is necessary to ensure protection of USDWs from endangerment and address the uncertainties inherent in predictive modeling. Periodic AoR reevaluations at §146.84(e) ensure that a deliberate effort is made to verify, based on monitoring and operational data, that the CO2 plume is moving within the subsurface as predicted. EPA believes that less frequent reevaluations or planning reevaluations only when a need is demonstrated may not be sufficient to appropriately model plume and pressure front movement, establish conditions for corrective action, and ensure protection of USDWs from endangerment. EPA agrees that site-specific factors should be considered in the reevaluation schedule, and notes that the AoR and corrective action plan must specify the site-specific monitoring and operational conditions that warrant reevaluation, as specified in §146.84(b)(2)(ii).

EPA clarifies that if site monitoring data agrees with the existing AoR delineation, a model recalibration may not be necessary, and the AoR reevaluation may consist of a demonstration that the current AoR delineation is adequate based on site monitoring data.

Commenter Name: Andrew Duguid Letter ID: 0226 Commenter Organization: Schlumberger Carbon Services Comment ID: 24021 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language; 3530 2.2.3.1 AoR reevaluation frequency (seeking comment)

Comment: Proposed Rule: (b) The owner or operator of a Class VI well must prepare, maintain, and comply with a plan to delineate the area of review for a proposed geologic sequestration project, periodically reevaluate the delineation, and perform corrective action that meets the requirements of this section and is acceptable to the Director. As a part of the permit application for approval by the Director, the owner or operator must submit an area of review and corrective action plan that includes the following information:

Schlumberger Suggested Revision: (b) The owner or operator of a Class VI well must prepare, maintain, and comply with a plan to delineate the area of review for a proposed geologic sequestration project, reevaluate the delineation, and perform corrective action that meets the requirements of this section in a manner and at a frequency acceptable to the Director. As a part of the permit application, the owner or operator must submit an area of review and corrective action plan that includes the following information:

Schlumberger Rationale: -Response: EPA disagrees with the proposed changes and retains the provisions as proposed. For additional information on EPA's approach to AoR and corrective action, please see the final rule and preamble.

Commenter Name: Andrew Duguid Letter ID: 0226 Commenter Organization: Schlumberger Carbon Services Comment ID: 24023 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Proposed Rule: (iv) How corrective action will be conducted to meet the requirements of paragraph (d) of this section, including what corrective action will be performed prior to injection and what, if any, portions of the area of review will have corrective action addressed on a phased basis and how the phasing will be determined; how corrective action will be adjusted if there are changes in the area of review; and how site access will be guaranteed for future

corrective action.

Schlumberger Suggested Revision: (iv) How corrective action will be conducted to meet the requirements of paragraph (d) of this section, including what corrective action will be performed prior to injection and what, if any, portions of the area of review will have corrective action addressed on a phased basis and how the phasing will be determined; how corrective action will be adjusted if there are changes in the area of review; and how site access will be arranged for future corrective action.

Schlumberger Rationale: Future access cannot be fully guaranteed for an area in advance that may not even be within the boundaries of the initial AOR/ project.

Response: EPA is retaining this requirement as proposed. The purpose of the corrective action requirement at §146.84(d) is to ensure that all wells in the AoR that have the potential to cause the movement of CO2 or other fluids into or between USDWs receive appropriate corrective action. In general, to meet this requirement, the owner or operator will most likely need to obtain the right of access to wells that may require corrective action, and demonstrate they have done this in their proposed AoR and corrective action plan. In the AoR and corrective action plan, the owner or operator must describe how site access will be guaranteed for future corrective action. §146.84(b)(2)(iv).

Commenter Name: Andrew Duguid Letter ID: 0226 Commenter Organization: Schlumberger Carbon Services Comment ID: 24027 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language; 5100 2.8.1 Injection well plugging activities (seeking comment) (40 CFR 146.92)

Comment: Proposed Rule: (3) Determine which abandoned wells in the area of review have been plugged (as required by §146.92) in a manner that prevents the movement of carbon dioxide or associated fluids that may endanger USDWs.

Schlumberger Suggested Revision: (3) Determine which abandoned wells identified in 146.84 (c) (2) have been plugged (as required by §146.92) in a manner that prevents the movement of carbon dioxide or formation fluids that may endangerUSDWs.

Schlumberger Rationale: -

Response: EPA acknowledges the comment. Based on its evaluation of all public comments and input on the proposed rule and NODA and Request for Comment, EPA has made many revisions to the GS Rule. See the final rule and preamble for further discussion on EPA's final approach.

Commenter Name: Andrew Duguid Letter ID: 0226 Commenter Organization: Schlumberger Carbon Services Comment ID: 24028 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Proposed Rule: (d) Owners or operators of Class VI wells must perform corrective

action on all wells in the area of review that are determined to need corrective action using methods necessary to prevent the movement of fluid into or between USDWs including use of corrosion resistant materials, where appropriate.

Schlumberger Suggested Revision: Owners or operators of Class VI wells must perform corrective action using corrosion resistant materials, when appropriate, on all wells identified in 146.84(c)(2) that are determined to need corrective

action".

Schlumberger Rationale: -

Response: EPA revised the text at §146.84(d) to require the use of materials that are "compatible with the carbon dioxide stream" Instead of corrosion resistant materials. EPA believes this language change addresses commenters' concerns and is also consistent with other language regarding materials requirements in the GS rule. EPA did not make the other suggested changes. See the final rule and preamble for further discussion on EPA's final approach.

Commenter Name: Michel Paque Letter ID: 0259 Commenter Organization: Ground Water Protection Council Comment ID: 24858 Other EPA Comment Codes and Descriptions: 1220 1.1.1.1 Terminology and definitions

Comment: EPA Proposal: Corrective action means the use of Director approved methods to

assure that wells within the area of review do not serve as conduits for the movement of fluids into underground sources of drinking water (USDW).

GWPC Recommendations: Support the proposed EPA language.

Rationale: Agree with EPA’s rationale.

Response: EPA acknowledges the commenter’s support; the final GS rule retains the definition.

Commenter Name: Michel Paque Letter ID: 0259 Commenter Organization: Ground Water Protection Council Comment ID: 24884 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: EPA Proposal: (iv) How corrective action will be conducted to meet therequirements of paragraph (d) of this section, including what corrective action will be performed prior to injection and what, if any, portions of the area of review will have corrective action addressed on a phased basis and how the phasing will be determined; how corrective action will be adjusted if there are changes in the area of review; and how site access will be guaranteed for future

corrective action.

GWPC Recommendations: (iv) How corrective action will be conducted to meet the requirements of paragraph (d) of this section, including what corrective action will be performed prior to injection and what, if any, portions of the area of review will have corrective action addressed on a phased basis and how the phasing will be determined; how corrective action will be adjusted if there are changes in the area of review; and how site access will be assured for future

corrective action.

Rationale: Replace "guaranteed" with "assured" Future access cannot be absolutely guaranteed for an area in advance that may not even be within the boundaries of the AOR/ project. However, assurance of access is a standard that is less onerous than guaranteed, it is firmer than another standard such as "arranged"

Response: EPA is retaining this requirement as proposed. The purpose of the corrective action requirement at §146.84(d) is to ensure that all wells in the AoR that have the potential to cause the movement of CO2 or other fluids into or between USDWs receive appropriate corrective action. In general, to meet this requirement, the owner or operator will most likely need to obtain the right of access to wells that may require corrective action, and demonstrate they have done this in their proposed AoR and corrective action plan. In the AoR and corrective action plan, the owner or operator must describe how site access will be guaranteed for future corrective action, as specified in §146.84(b)(2)(iv).

Commenter Name: Michel Paque Letter ID: 0259 Commenter Organization: Ground Water Protection Council Comment ID: 24887 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: EPA Proposal: (2) Using methods approved by the Director, identify all penetrations, including active and abandoned wells and underground mines, in the area of review that may penetrate the confining zone. Provide a description of each well’s type, construction, date drilled, location, depth, record of plugging and/or completion, and any additional information the Director may require; and

GWPC Recommendations: (2) Using methods approved by the Director, identify all known artificial penetrations into the confining zone, including active and abandoned wells and underground mines, in the area of review that may penetrate the confining zone. Provide a description of each well’s type, construction, date drilled, location, depth, record of plugging and/or completion, and any additional information the Director may require; and

Rationale: Insert "known artificial penetrations into the confining zone"EPA Proposal: (3) Determine which abandoned wells in the area of review have been plugged (as required by § 146.92) in a manner that prevents the movement of carbon dioxide or associated fluids that may endanger USDWs

GWPC Recommendations: (3) Determine which abandoned wells identified in 146.84 (c) (2) have been plugged (as required by §146.92) in a manner that prevents the movement of carbon dioxide or displaced formation fluids that may endanger

USDWs.

Rationale: Add identified in 146.84 (c) (2)

Remove "area of review" as redundant.

Suggest change "associated fluids" to "displaced formation fluids." Associated fluids is not defined so if EPA means displaced formation fluids the regulation should just use this term. Otherwise, you need to define associated fluids.

Response: EPA is retaining the requirement in 146.84(c)(2) as proposed. EPA agrees with commenters that, for most GS sites, relying on database and other public records searches (i.e., of "known" artificial penetrations) will be sufficient to meet the requirements at §146.84(c)(2). However, the Agency recognizes that there may be situations where additional surveys or research to locate wells may be appropriate. For example, there may be cases where the Director may determine that ground or airborne surveys for wells are appropriate, e.g., if there is reason to believe, based on knowledge of the site or of available data, that the incompleteness of information on known wells could compromise USDW protection from endangerment. In order to preserve the Director's discretion to require an operator to supplement a records search, EPA did not make the suggested change.

EPA clarifies that the term "associated fluids" as proposed in §146.84(c)(3) refers to formation fluids, other injectates, etc that may be present in the subsurface and affect movement of the CO2 plume and/or pressure front. EPA believes this terminology would incorporate any fluids in the subsurface that could potentially move through artificial penetrations and affect USDWs. EPA has revised the language at §146.84(c)(3) to read, "... carbon dioxide or other fluids that may endanger

USDWs..."

Commenter Name: Michel Paque Letter ID: 0259 Commenter Organization: Ground Water Protection Council Comment ID: 24889 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: EPA Proposal: (e) If monitoring data indicate an endangerment to USDWs, the owner or operator must notify the Director and cease operations as required by §

146.94.

GWPC Recommendations: Delete

Rationale: Why is this needed if 146.94 already specifies the notification and cessation of injection?Response: Based on consideration of all public comments and other information, EPA deleted this provision from §146.84. The final rule now contains a provision in §146.91(c) that requires the owner or operator to report within 24 hours any evidence that the carbon dioxide stream or associated pressure front may cause an endangerment to a USDW. EPA believes this change consolidates reporting requirements in one place and provides additional clarity.

Comment Code: 3420 2.2.2.1 Scope of the inventory process (e.g., reliance on publicly available information, depth of wells)



### Individual Comments

Commenter Name: Leslie Savage Letter ID: 0122 Commenter Organization: Railroad Commission of Texas (RRC) Comment ID: 24776 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: (2) Using methods approved by the Director, identify all KNOWN ARTIFICIAL penetrations THROUGH THE CONFINING ZONE, including active and abandoned wells and underground mines, in the area of review that may penetrate the confining

zone . Provide a description of each well's type, construction, date drilled, location, depth, record of plugging and/or completion, and any additional information the Director may require; and

Response: EPA is retaining this requirement as proposed. EPA agrees with commenters that, for most GS sites, relying on database and other public records searches (i.e., of "known" artificial penetrations) will be sufficient to meet the requirements at §146.84(c)(2). However, the Agency recognizes that there may be situations where additional surveys or research to locate wells may be appropriate. For example, there may be cases where the Director may determine that ground or airborne surveys for wells are appropriate, e.g., if there is reason to believe, based on knowledge of the site or of available data, that the incompleteness of information on known wells could compromise USDW protection from endangerment. In order to preserve the Director's discretion to require an operator to supplement a records search, EPA did not make the suggested change.

Commenter Name: James Dooley Letter ID: 0156 Commenter Organization: Joint Global Change Research Institute, Pacific Northwest National Laboratory Comment ID:

22636 Other EPA Comment Codes and Descriptions: 4710 2.7.1 Proposed submissions required for permit applications (seeking comment)

Comment: All Wells and "All Known Wells" are not the Same Page 43507 and 43517. The proposed Class VI rule needs to be much more precise in its use of language in a couple of key areas. The rule requires an applicant for a Class VI permit to "identify all artificial penetrations." What exactly does this mean? Is it all known artificial penetrations (the rule speaks to the operator "review(ing) available information")? What is the test for what is a known well or available information (does it require detailed field surveys or does one only need to do a quick search of a database of wells drilled in the area)? If on the other hand it means literally all human penetrations, then one must ask if this is technologically possible (e.g., are there technologies which would allow for theidentification of a small diameter non-steel walled well that has no visible surface features)? Is there a danger in asking for something that can not actually be delivered? One can guess what was likely meant by "identify all artificial penetrations" in terms of drafting this rule but it is not at all clear how this would be opperationalized at actual prospective GS sites.

More importantly on Page 43535 under "144.55 Corrective Action", the rule says that owners/operators need to identify the location of "all known wells" which seems to be a lesser standard. In the actual text of the rule (page 43526), the applicant is told "Only information of public record is required to be included on this map." Given how many times the rule and its preamble talk about old wells being a potential conduit for CO2 release from the storage formation, this seems like an overly lax threshold. It would seem appropriate to require the applicant survey the actual site itself for artificial penetrations that might not be in the public record (the survey could include a number of different methods / tools). Further on in this section, the applicant is asked to submit a "tabulation of all wells within the area of review which penetrate the injection or confining zones." Again, "all wells" and "all known wells" and how much work does one need to do to determine if they have tried to find "all the wells" must be better articulated in the final rule. This same kind of language shows up on page 43537 within the discussion of the Area of Review and

Corrective Action.

Lastly, given the large amounts of money involved in a commercial CO2 storage project, I would think that the electric production, oil and gas, or other large industrial company contemplating a large CCS-enabled facility would want (or be required) to go beyond simply collecting existing data as a way of decreasing risk and uncertainty. In this context, the proposed "requirement" for going beyond existing data could be imposed by entities other than state or federal environmental regulators and could be imposed by shareholders, a public utility commission, or a firm’s own board of directors. In terms of abandoned wells, it seems likely that commercial firms would see it to be in their own best interest to do some kind of physical search / assessment of whether there are any known or unknown wells within the area of review given the relatively minor cost associated with something like an aerial magnetic survey versus the costs associated with loss of CO2 and any fines, the cost associated with any required post-leakage activities, or simply the cost of litigation and or loss of good will associated with such sloppy management of a critical, capital intensive pollution abatement facility.

Response: EPA believes that, for the most part, data base and other public records searches will be sufficient to identify artificial penetrations in the AoR. This inventory and review process is similar to what is required of Class I and Class II injection well operators, that that the AoR and corrective action process for these well types has been successful.

EPA is developing guidance on AoR and corrective action for GS sites. 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 agrees with commenters that, for most GS sites, relying on database and other public records searches (i.e., of "known" artificial penetrations) will be sufficient to meet the requirements at §146.84(c)(2). However, the Agency recognizes that there may be situations where additional surveys or research to locate wells may be appropriate. For example, there may be cases where the Director may determine that ground or airborne surveys for wells are appropriate, e.g., if there is reason to believe, based on knowledge of the site or of available data, that the incompleteness of information on known wells could compromise USDW protection from endangerment. In order to preserve the Director's discretion to require an operator to supplement a records search, EPA did not make the suggested change. EPA encourages owners or operators to expand their searches, as the commenter suggests. EPA adds that all corrective action must be performed pursuant to the approved AoR and corrective action plan, which affords the Director the discretion to require any additional information needed (including information that is not publically available) to ensure that all necessary corrective action is performed.

Commenter Name: Kyle Isakower Letter ID: 0170 Commenter Organization: American Petroleum Institute Comment ID: 24162 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Rule Provision: 146.84(c)(2)

API Comments: (2) Using methods approved by the Director, Identify all KNOWN ARTIFICIAL penetrations INTO THE CONFINING ZONE AVAILABLE IN THE PUBLIC RECORD, including active and abandoned wells and underground mines, in the area of review that may penetrate REACH the confining zone. Provide a description of each well‘s type, construction, date drilled, location, depth, record of plugging and/or completion, and any additional information the Director may require; and

Rationale: Changed for consistency with earlier language.

Response: EPA is retaining this requirement as proposed. EPA agrees with commenters that, for most GS sites, relying on database and other public records searches (i.e., of "known" artificial penetrations) will be sufficient to meet the requirements at §146.84(c)(2). However, the Agency recognizes that there may be situations where additional surveys or research to locate wells may be appropriate. For example, there may be cases where the Director may determine that ground or airborne surveys for wells are appropriate, e.g., if there is reason to believe, based on knowledge of the site or of available data, that the incompleteness of information on known wells could compromise USDW protection from endangerment. In order to preserve the Director's discretion to require an operator to supplement a records search, EPA did not make the suggested change.

EPA clarifies that any well that penetrates the confining zone, even if it does not extend all the way through the confining formation, is to be included in the tabulation. 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.Commenter Name: James Taft Letter ID: 0172 Commenter Organization: Association of State Drinking Water Administrators (ASDWA) Comment ID:

23453

Comment: Drill Holes and Abandoned Wells:

EPA should consider options to ensure that mineral exploration drill holes and abandoned wells are accounted for on the AOR maps. States have serious concerns about the ability to account for all of these potential holes and open shear zones or faults that may allow migration from the injection zone to the fresh water aquifers, as well as leakage out of the geo- sequestration site and back into the atmosphere. The AOR should also be periodically reevaluated,

Response: EPA agrees with the commenter that many factors about a GS site—including mineral exploration drilling, abandoned wells, and open shear zones or faults—can affect containment. EPA believes that the requirement that the AoR and corrective action plan at §146.84(b) be based on detailed geologic data collected at the site (including the types of information cited by the commenter) will ensure that all potential risks are considered in GS permitting decisions.

EPA adds that the Director has the discretion to require the owner or operator to supplement a data records search, including requiring ground or airborne surveys for wells if there is reason to believe, based on knowledge of the site or of available databases, that the incompleteness of available information could compromise USDW protection. EPA adds that all corrective action must be performed pursuant to the approved AoR and corrective action plan, which affords the Director the discretion to require any additional information needed to ensure that all necessary corrective action is performed.

Commenter Name: Thomas Curtis Letter ID: 0181 Commenter Organization: American Water Works Association (AWWA) Comment ID: 24375 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Part 146.84(d) AWWA recommends revising this part to read:

Owners or operators of Class VI wells must perform corrective action on all wells and other artificial penetrations in the area of review that are determined to need corrective action using methods necessary to prevent the movement of fluid into or between USDWs and between the injection zones(s) and USDWs, including use of corrosion resistant materials, where appropriate.

Response: EPA revised the text at §146.84(d) to require the use of materials that are "compatible with the carbon dioxide stream." EPA believes this language change addresses commenters' concerns and is also consistent with other language regarding materials requirements in the GS rule. EPA believes that meeting the requirement for preventing "movement of fluid into or between USDWs" will prevent movement between the injection zone and USDWs; therefore, it did not make the suggested change.

Commenter Name: Robert F. Van Voorhees Letter ID: 0190 Commenter Organization: Carbon Sequestration Council Comment ID: 24432 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rulelanguage

Comment: Rule Provision: 146.84(c)(2)

Proposed CCS Group Recommendations: (2) Using methods approved by the Director, Identify all KNOWN ARTIFICIAL penetrations INTO THE CONFINING ZONE AVAILABLE IN THE PUBLIC RECORD, including active and abandoned wells and underground mines, in the area of review that may penetrate REACH the confining zone. Provide a description of each well’s type, construction, date drilled, location, depth, record of plugging and/or completion, and any additional information the Director may require; and

Basis for CCS Group Comments: Changed for consistency with earlier language.

Response: EPA is retaining the requirement as proposed. EPA agrees with commenters that, for most GS sites, relying on database and other public records searches (i.e., of "known" artificial penetrations) will be sufficient to meet the requirements at §146.84(c)(2). However, the Agency recognizes that there may be situations where additional surveys or research to locate wells may be appropriate. For example, there may be cases where the Director may determine that ground or airborne surveys for wells are appropriate, e.g., if there is reason to believe, based on knowledge of the site or of available data, that the incompleteness of information on known wells could compromise USDW protection. In order to preserve the Director's discretion to require an operator to supplement a records search, EPA did not make the suggested change.

EPA adds that all corrective action must be performed pursuant to the approved AoR and corrective action plan, which affords the Director the discretion to require any additional information needed (including information that is not publically available) to ensure that all necessary corrective action is performed.

Commenter Name: Craig R. Walters Letter ID: 0200 Commenter Organization: Anadarko Petroleum Corporation Comment ID: 24660 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Rule Provision: 146.84(c)(2)

Anadarko Petroleum Corporation (APC) Comments: (2) Using methods approved by the Director, identify all KNOWN ARTIFICIAL penetrations INTO THE CONFINING ZONE, including active and abandoned wells and underground mines, in the area of review that may penetrate the confining zone. Provide a description of each well’s type, construction, date drilled, location, depth, record of plugging and/or completion, and any additional information the Director may require; and

Rationale: Changed for consistency with earlier language.

Response: EPA is retaining the requirement as proposed. EPA agrees with commenters that, for most GS sites, relying on database and other public records searches (i.e., of "known" artificial penetrations) will be sufficient to meet the requirements at §146.84(c)(2). However, the Agency recognizes that there may be situations where additional surveys or research to locate wells may be appropriate. For example, there may be cases where the Director may determine that ground or airborne surveys for wells are appropriate, e.g., if there is reason to believe, based on knowledge ofthe site or of available data, that the incompleteness of information on known wells could compromise USDW protection from endangerment. In order to preserve the Director's discretion to require an operator to supplement a records search, EPA did not make the suggested change. EPA adds that all corrective action must be performed pursuant to the approved AoR and corrective action plan, which affords the Director the discretion to require any additional information needed (including information that is not publically available) to ensure that all necessary corrective action is performed.

Commenter Name: Kristin Henry Letter ID: 0242 Commenter Organization: Sierra Environmental Law Program, Sierra Club Comment ID: 23330

Comment: IX. Additional Well Identification Methods that do not rely on the Public Record Should be Required in Certain Provisions

The proposed rule at CFR§146.82(b) requires a map to be submitted with the permit that shows wells within the area of review, but only information of public record is required to be included on this map. CFR§146.82(e) also requires a tabulation of all wells within the area of review which penetrate the injection or confining zone(s), which includes information on the well’s type, construction, date drilled, location, depth, record of plugging and/or completion and any additional information that the Director may require.

Relying on information of public record in (b) is sufficient, but additional diligence is needed when it comes to wells that penetrate the injection or confining zone in (e). Information of public record is often incomplete and/or inaccurate. There are numerous orphaned or abandoned wells that are not listed on the public record that could affect the integrity of the confining zone. While it is possible to intercept some of these problems during operation, there are methods available today to identify wells not listed on the public record [FN40], which could identify potentially problematic wells in advance. Such a requirement should be included in the rule, and be made more general than

"tabulation" to allow the Director discretion for other data formats as needed:

[FN40: NETL , for example, has developed an electromagnetic system that can be used for aerial or ground-based identification of wells (casings).]

Response: EPA acknowledges that public records may not contain data on every artificial penetration in the AoR (or all of the data on each well that is required for the tabulation), particularly in areas with many older wells. However, EPA notes that the inventory and review process for GS wells required at §146.84(c)(2) is similar to what is required of Class I and Class II injection well operators, and that the AoR and corrective action process for these well types has been successful for

many years.

In response to comments suggesting that areas with extensive oil and gas exploration may be the most likely to have older, undocumented wells, EPA notes that states with long histories of hydrocarbon production tend to have invested the most resources into their well databases and, as a result, have detailed information about location and construction of wells within hydrocarbon fields. In addition, older wells, while likely to have the least sophisticated construction, also tend to be relatively shallow and would therefore be less likely to penetrate the confining zone.EPA adds that the Director has the discretion to require the owner or operator to supplement a data records search, including requiring ground or airborne surveys for wells, if there is reason to believe, based on knowledge of the site or of available data bases, that the incompleteness of available information could compromise USDW protection. EPA adds that all corrective action must be performed pursuant to the approved AoR and corrective action plan, which affords the Director the discretion to require any additional information needed (including information that is not publically available) to ensure that all necessary corrective action is performed.

Commenter Name: Kristin Henry Letter ID: 0242 Commenter Organization: Sierra Environmental Law Program, Sierra Club Comment ID: 23331 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: [In the paragraph below the text in all CAPS denotes added text.] §146.82(e): "A tabulation COMPILATION of all wells within the area of review which penetrate the injection or confining zone(s). TO SUPPLEMENT AND/OR VERIFY INFORMATION OF PUBLIC RECORD, OPERATORS SHALL USE REASONABLE METHODS

TO IDENTIFY

THE PRESENCE WELLS WITHIN THE AREA OF REVIEW THAT PENETRATE THE

INJECTION OR CONFINING ZONE(S). Such data must include a description [...]"

Response: EPA is retaining the requirement, which is now found in §146.82(a)(4), as proposed. EPA notes that the Director has the discretion in §146.84(c)(2) to require the owner or operator to supplement a data records search—including the use of ground, airborne, or geophysical (e.g., magnetic) surveys—if there is reason to believe that the incompleteness of available information could compromise USDW protection from endangerment. EPA adds that all corrective action must be performed pursuant to the approved AoR and corrective action plan, which affords the Director the discretion to require any additional information needed (including information that is not publically available) to ensure that all necessary corrective action is performed. 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.

Commenter Name: Kristin Henry Letter ID: 0242 Commenter Organization: Sierra Environmental Law Program, Sierra Club Comment ID: 23332

Comment: Additionally, to delineate the Area of Review, CFR§146.84(c)(2) requires operators to "...identify all penetrations, including active and abandoned wells and underground mines, in the area of review that may penetrate the confining zone". Again, the public record may not be sufficient to provide accurate information in all cases. Problematic wells may not be limited to the confining zone, as would be the case if confinement were to be breached, or if pressure effects caused by the injection caused fluid movement outside the defined confining zone. We recommend the following modification:Response: The requirements at §146.84(c)(2) are designed to afford owners or operators flexibility to identify and use appropriate resources to identify artificial penetrations in the AoR. EPA notes that the Director has the discretion to require the owner or operator to supplement a data records search—including the use of ground, airborne, or geophysical (e.g., magnetic) surveys—if there is reason to believe that the incompleteness of available information could compromise USDW protection from endangerment. Regarding the concern about identifying wells other than those that penetrate the confining zone, EPA adds that the Director the discretion to require any additional information needed to ensure that all necessary corrective action is performed, including information on wells that are above the confining zone, if site-specific information indicates such a need to ensure USDW protection.

Commenter Name: Kristin Henry Letter ID: 0242 Commenter Organization: Sierra Environmental Law Program, Sierra Club Comment ID: 23333 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: [In the paragraph below the text in all CAPS denotes added text.] "Using methods approved by the Director, identify all penetrations, including active and abandoned wells and underground mines, in the area of review that may penetrate the confining zone OR OTHERWISE ACT AS CONDUITS FOR FLUID MOVEMENT

INSIDE OR OUTSIDE THE CONFINING ZONE".

Response: For the reasons described in the response above, EPA is retaining the requirement as proposed.

Commenter Name: Kurt Waltzer Letter ID: 0250 Commenter Organization: Clean Air Task Force Comment ID: 22302

Comment: Additional well identification methods that do not rely on the public record should be required in certain provisions

§146.82(b) requires a map to be submitted with the permit that shows wells within the area of review - only information of public record is required to be included on this map. §146.82(e) requires a tabulation of all wells within the area of review which penetrate the injection or confining zone(s), including information on the well’s type, construction, date drilled, location, depth, record of plugging and/or completion and any additional information that the Director may require.

While we are comfortable with relying on information of public record in subsection (b), we believe that additional diligence is needed when it comes to wells that penetrate the injection or confining zone in subsection (e). Information of public record is often incomplete and/or inaccurate. There are numerous orphaned or abandoned wells that are not listed on the public record that could potentially affect the integrity of the confining zone. While generally it is possible to intercept these problems during operations, there are methods available today to identify wells not listed on the public record [FN22], which in many cases could identify potentially problematic wells in advance. A requirement to supplement public record information with fieldmeasurements should be included in the rule, and described with a term that is broader than "tabulation" in order to allow the Director to require other data

formats as needed:

[FN22: NETL , for example, has developed an electromagnetic system that can be used for areal or ground-based identification of wells (casings).]

Response: EPA acknowledges that public records may not contain data on every artificial penetration in the AoR (or all of the data on each well that is required for the tabulation), particularly in areas with many older wells. However, EPA notes that the inventory and review process for GS wells required at §146.84(c)(2) is similar to what is required of Class I and Class II injection well operators, that the AoR and corrective action process for these well types has been successful for

many years.

EPA adds that the Director has the discretion to require the owner or operator to supplement a data records search, including requiring ground or airborne surveys for wells, if there is reason to believe, based on knowledge of the site or of available data bases, that the incompleteness of available information could compromise USDW protection from endangerment. EPA adds that all corrective action must be performed pursuant to the approved AoR and corrective action plan, which affords the Director the discretion to require any additional information needed (including information that is not publically available) to ensure that all necessary corrective action is performed.

Commenter Name: Kurt Waltzer Letter ID: 0250 Commenter Organization: Clean Air Task Force Comment ID: 25256 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: [In the paragraph below the text in all CAPS denotes added text. See also EPA-HQ-OW-0390-0250.pdf to see the original formatting.]

§146.82(e): "A tabulation COMPILATION of all wells within the area of review which penetrate the injection or confining zone(s). TO SUPPLEMENT AND/OR VERIFY INFORMATION OF PUBLIC RECORD, OPERATORS SHALL USE REASONABLE METHODS

TO IDENTIFY

THE PRESENCE WELLS WITHIN THE AREA OF REVIEW THAT PENETRATE THE

INJECTION OR CONFINING ZONE(S). Such data must include a description [...]"

[FN22: NETL , for example, has developed an electromagnetic system that can be used for areal or ground-based identification of wells (casings).]

Additionally, we believe that problematic wells may not be limited to the confining zone, as would be the case if confinement were to be breached, or if pressure effects caused by the injection caused fluid movement outside the defined confining zone. We recommend the following modification in §146.84(c) (2):[In the paragraph below the text in all CAPS denotes added text. See also EPA-HQ-OW-0390-0250.pdf to see the original formatting.]

"Using methods approved by the Director, identify all penetrations, including active and abandoned wells and underground mines, in the area of review that may penetrate the confining zone OR OTHERWISE ACT AS CONDUITS FOR FLUID MOVEMENT

INSIDE OR OUTSIDE THE CONFINING ZONE".

Response: EPA is retaining the requirement at §146.82(b), which is now found in §146.82(a)(4), as proposed. EPA adds that all corrective action must be performed pursuant to the approved AoR and corrective action plan, which affords the Director the discretion to require any additional information needed (including information that is not publically available) to ensure that all necessary corrective action is performed. EPA notes that the Director has the discretion at §146.84(c)(2) to require the owner or operator to supplement a data records search—including the use of ground, airborne, or geophysical (e.g., magnetic) surveys—if there is reason to believe that the incompleteness of available information could compromise USDW protection from endangerment. For these reasons, EPA is retaining the requirement at §146.84(c)(2) as proposed.

Regarding the concern about identifying wells other than those that penetrate the confining zone, EPA adds that the Director the discretion to require any additional information needed to ensure that all necessary corrective action is performed, including information on wells that are above the confining zone, if site-specific information indicates such a need to ensure USDW protection.

Commenter Name: John McManus Letter ID: 0294 Commenter Organization: American Electric Power Comment ID: 25314 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: 6. Area of review and corrective action requirements

In proposed §144.55(a) the rule would require Class I, II (other than existing), III or VI permit applicants to identify the location "of all known wells within the injection well’s area of review which penetrate the injection zone" or, in the case of Class II wells operating over the fracture pressure of the injection formation, "all known wells within the area of review penetrating formations affected by the increase in pressure."

Since injection in deep saline formations will result in an area of elevated pressure (above the original reservoir pressure) that will be larger than the CO2 plume and could conceivably affect overlying or underlying formations, we have agreed that the requirement for Class II wells operating above the fracture pressure should also apply to Class VI wells. This would help prevent the unwanted migration of reservoir fluids from the injection zone as a result of the pressure increase. We therefore recommend that §144.55(a) be revised to read as follows, with revisions shown in blue:

"(a) Coverage. Applicants for Class I, II, (other than existing), or III, injection well permits shall identify the location of all known wells within the injection well's area of review which penetrate the injection zone. In the caseof Class II wells that operate over the fracture pressure of the injection formation, applicants shall also identify the location of all known wells within the area of review penetrating formations affected by the increase in pressure. For such wells which are improperly sealed, completed, or abandoned, the applicant shall also submit a plan consisting of such steps or modifications as are necessary to prevent movement of fluid into underground sources of drinking water (‘‘corrective action’’). Where the plan is adequate, the Director shall incorporate it into the permit as a condition. Where the Director’s review of an application indicates that the permittee’s plan is inadequate (based on the factors in §146.07), the Director shall require the applicant to revise the plan, prescribe a plan for corrective action as a condition of the permit under paragraph (b) of this section, or deny the application. The Director may disregard the provisions of §146.06 (Area of Review) and §146.07 (Corrective Action) when reviewing an application to permit an existing Class II well. Applicants for permits for Class VI wells [or for wells in other classes that are used for geologic sequestration and do not meet the criteria for §144.6(b) (4)][FN3] shall identify the location of all known wells within the area of review penetrating the injection zone and all known wells within the area of review which penetrate formations affected by the pressure front and shall perform corrective action as specified in §146.84."

3/ The undersigned, except NRDC which does not support the Group’s proposed bright line definition and language for §144.6(b)(4) (see MSG letter of Dec. 23, 2008), believe that this clause in brackets should be included.

Response: The final rule leaves §144.55 unchanged from the existing UIC requirements; i.e., Class VI wells are not addressed in this provision. Based on its evaluation of all public comments and input on the proposed rule and NODA and Request for Comment, EPA has made many revisions to the GS Rule. See the final rule and preamble for further discussion on EPA's final approach.

Comment Code: 3440 2.2.2.2 Evaluation of wells in the AoR (e.g., types of data to be reviewed)



### Individual Comments

Commenter Name: Christine Reimer Letter ID: 0142 Commenter Organization: National Ground Water Association Comment ID: 22587 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Proposed Rule: 144.55(a)

Proposed Revision: (a) Coverage. Applicants for Class I, II, (other than existing), III or VI injection well permits shall identify the location of all known wells within the injection well's area of review which penetrate the injection zone, or in the case of Class II wells operating over the fracture pressure of the injection formation, all known wells within the area of review penetrating formations affected by the increase in pressure. Applicants for Class VI shall perform mapping with sufficient resolution as to make acomprehensive effort to identify wells that are not in the public record using aerial photography, aerial survey, or other methods acceptable to the director corrective action as specified in §146.84 if needed

Rationale: Concern about the use of the term known wells. Public records search may not be adequate for older oil and gas wells, for example. Some language should be added so that A more proactive approach is used, e.g. physically walk site or do aerial review.

Response: The final rule leaves §144.55 unchanged from the existing UIC requirements; i.e., Class VI wells are not addressed in this provision. Based on its evaluation of all public comments and input on the proposed rule and NODA and Request for Comment, EPA has made many revisions to the GS Rule. See the final rule and preamble for further discussion on EPA's final approach.

Commenter Name: Christine Reimer Letter ID: 0142 Commenter Organization: National Ground Water Association Comment ID: 22596 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Proposed Rule: 146.84(c)(2)

Proposed revision: (2) Using methods approved by the Director, identify all penetrations, including active and abandoned wells and underground mines, in the area whose total depth is greater than the depth to the bottom of the lowermost USDW, including those penetrating the confining zone. Provide a description of each well’s type, construction, date drilled, location, depth, record of plugging and/or completion, and any additional information the Director may require; and

Rationale: This makes this consistent with NGWA's proposed section 146(a)(8)

Response: EPA clarifies that any well that penetrates the confining zone, even if it does not extend all the way through the confining formation, is to be included in the tabulation. EPA is issuing guidance on. 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, how to identify all wells that require corrective action, 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.

The final rule retains the language in §146.84(c)(2) as proposed. EPA clarifies that the mapping and cross sections required to be submitted under §146.82(a)(3) will define the limits of the confining zone, which would be accounted for in the AoR delineation and corrective action evaluation required at §146.84(c). EPA adds that owners or operators must also, under §146.82(a)(2), submit a map of the AoR that shows all injection wells, producing wells, abandoned wells, plugged wells or dry holes, deep stratigraphic boreholes, State or EPA approved subsurface cleanup sites, surface bodies of water, springs, mines (surface and subsurface), quarries, water wells and other pertinent surface features including structures intended for human occupancy and roads. EPA believes that these requirements address the commenter's concerns.

Commenter Name: Brianne Metzger Letter ID: 0151Commenter Organization: Spectra Energy Corp Comment ID: 21826

Comment: EPA has proposed requiring the applicant submit "the status of corrective action on wells in the area of review." 40 C.F.R. § 146.82(q). We believe it is unnecessary to require the inclusion of all wells within the AoR regardless of whether or not they penetrate the injection zone. There could be many

shallow wells within the AoR located hundreds or thousands of feet above the CO2 injection. Therefore, EPA should limit this requirement to the injection zone, injection pool, and only those wells that either intersect or penetrate the proposed reservoir, the cap rock, and possibly the porous strata directly above the injection zone, or wells that penetrate or are in close proximity to a gas storage reservoir.

The Agency has stated that only information of public record pertaining to all types of wells (injection, producing, abandoned) be included on the AoR. Data availability and use raises a question regarding the possible existence of other data which might be private, proprietary and/or not publicly available. Such non-publicly available data may or may not be relevant to the application process. However, EPA should clarify to what extent an applicant would be expected by EPA to develop or use information that is not contained in the public record.

Response: EPA clarifies that, under 146.84(c)(2), operators are required to identify all penetrations in the AoR that penetrate the confining zone, but that corrective action is needed only for those wells that are determined to need corrective action in order to prevent movement of fluid into or between USDWs. The well inventory/identification process is more inclusive than the corrective action process to allow the Director to ensure that all wells in the AoR are identified and those that need

corrective action receive it.

Commenter Name: James Childress Letter ID: 0158 Commenter Organization: Gasification Technologies Council (GTC) Comment ID: 23772 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: §146.84 Area of review and corrective action. (c) (2) "Using methods approved by the Director, identify all penetrations, including active and abandoned wells and underground mines, in the area of review that may penetrate the confining zone. Provide a description of each well's type, construction, date drilled, location, depth, record of plugging and/or completion, and any additional information the Director may require; and ..."

We recommend striking out "approved" and replacing with "prescribed". We recommend deleting the second sentence and replacing with "Where such information is available or can be obtained, provide a description of each well's type, construction, date drilled, location depth record of plugging and/or completion and any additional information prescribed by the director and ..." Acceptable methods for identifying deep wells into confining zones within the AoR should be prescribed by the EPA as part of the regulation. Accurate information is difficult to obtain for older wells within the AoR. Examples of other information that could be required by the Director should be clearly

stated.Response: EPA is retaining the language in §146.84(c)(2) as proposed. Based on its evaluation of all public comments and input on the proposed rule and NODA and Request for Comment, EPA has made many other revisions to the GS Rule. See the final rule and preamble for further discussion on EPA's final approach.

EPA acknowledges that public records may not contain data on every artificial penetration in the AoR (or all of the data on each well that is required for the tabulation), particularly in areas with many older wells. However, the Agency recognizes that there may be situations where additional surveys or research to locate information on wells may be appropriate. For example, there may be cases where the Director may determine that ground or airborne surveys for wells are appropriate, e.g., if there is reason to believe that the incompleteness of information on known wells could compromise USDW protection from endangerment. In order to preserve the Director's discretion to require an operator to supplement a records search, EPA did not make the suggested change. EPA adds that all corrective action must be performed pursuant to the approved AoR and corrective action plan, which affords the Director the discretion to require any additional information needed (including information that may not be publically available) to ensure that all necessary corrective action is performed. 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

Commenter Name: Andrew Duguid Letter ID: 0226 Commenter Organization: Schlumberger Carbon Services Comment ID: 24026

Comment: Proposed Rule: (2) Using methods approved by the Director, identify all penetrations, including active and abandoned wells and underground mines, in the area of review that may penetrate the confining zone. Provide a description of each well’s type, construction, date drilled, location, depth, record of plugging and/or completion, and any additional information the Director may require; and

Schlumberger Suggested Revision: -

Schlumberger Rationale: We feel that there needs to be some effort to identify unknown wells using aerial surveys or other methods. We support this language as long as it is interpreted to mean more than just a record search in areas that that have been explored or produced oil and gas or have had other deep wells.

Response: For most GS sites, relying on database and other public records searches (i.e., of "known" artificial penetrations) will be sufficient to meet the requirements at §146.84(c)(2). However, the Agency recognizes that there may be situations where additional surveys or research to locate wells may be appropriate. For example, the Director may determine that ground or airborne surveys for wells are appropriate, e.g., if there is reason to believe that the incompleteness of information on known wells could compromise USDW protection from endangerment. EPA adds that under §146.84(c)(2), the Director has the discretion to require the owner or operator to conduct additional searches. EPA adds that all corrective action must be performed pursuant to the approved AoR and corrective action plan, which affords the Director the discretion to require any additional information needed to ensure that all necessary corrective action is performed. EPA is issuingguidance on how to identify all wells that require corrective action; the guidance also describes the data that EPA recommends 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.

Commenter Name: Mark E. Fesmire Letter ID: 0237 Commenter Organization: New Mexico Oil Conservation Division (NMOCD) Comment ID: 23211

Comment: A. Section 144.55 "Corrective Action" - The question arises whether the analysis of the wells in the area of review should include those wells that not only penetrate the injection zone, but also those that penetrate the confining zone

also.

Response: The final rule leaves §144.55 unchanged from the existing UIC requirements; i.e., Class VI wells are not addressed in this provision. Based on its evaluation of all public comments and input on the proposed rule and NODA and Request for Comment, EPA has made many revisions to the GS Rule. See the final rule and preamble for further discussion on EPA's final approach.

Commenter Name: Kurt Waltzer Letter ID: 0250 Commenter Organization: Clean Air Task Force Comment ID: 22295 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: In proposed §144.55(a) the rule would require Class I, II (other than existing), III or VI permit applicants to identify the location "of all known wells within the injection well’s area of review which penetrate the injection zone" or, in the case of Class II wells operating over the fracture pressure of the injection formation, "all known wells within the area of review penetrating formations affected by the increase in pressure".

Since injection in deep saline formations will result in an area of elevated pressure (above the original reservoir pressure) that will be larger than the CO2 plume and could affect overlying or underlying formations, we believe that the latter requirement for Class II wells operating above the fracture pressure should also apply to Class VI wells. This would help prevent the unwanted migration of reservoir fluids from outside the injection zone through existing wells in the confining zone, as a result of the pressure increase. We therefore suggest that §144.55(a) be revised to read as follows:

[In the paragraph below the text in all CAPS denotes added text. See also EPA-HQ-OW-0390-0250.pdf to see the original formatting.]

"Coverage. Applicants for Class I, II, (other than existing), or III, or VI injection well permits shall identify the location of all known wells within the injection well's area of review which penetrate the injection zone. In the case of Class II wells operating over the fracture pressure of the injection formation, applicants shall identify the location of all known wells within thearea of review penetrating formations affected by the increase in pressure. Applicants for Class VI SHALL IDENTIFY THE LOCATION OF ALL KNOWN WELLS

WITHIN

THE AREA OF REVIEW PENETRATING THE INJECTION ZONE AND ALL KNOWN WELLS

WHICH

PENETRATE FORMATIONS AFFECTED BY THE INCREASE IN PRESSURE AND shall perform corrective action as specified in Sec. 146.84."

Response: The final rule leaves §144.55 unchanged; i.e., Class VI wells are not addressed in this provision. Based on its evaluation of all public comments and input on the proposed rule and NODA and Request for Comment, EPA has made many revisions to the GS Rule. See the final rule and preamble for further discussion on EPA's final approach.

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



### Individual Comments

Commenter Name: Homer Spencer Letter ID: 0120 Commenter Organization: Canitron Systems Inc. Comment ID: 22071 Other EPA Comment Codes and Descriptions: 1310 1.1.2.4 Comments on other "out of scope" issues, e.g., pore space ownership; 1350 1.1.3.3 Comments on the need for GS technology

Comment: For the past four years, our company has been field testing our proprietary systems and methods for utilizing a low melting point fusible metal alloy to mold in situ plugs in wells to repair gas leakage problems. Our focus has been on repair of vent gas flows that occur because of channels that exist within the cement surrounding production casing in wells. Our field tests have been carried out with permission of the Alberta Energy Resources Control Board ("ERCB") and under their scrutiny. We presently have a proposal under consideration by the ERCB and the Canadian Association of Petroleum Producers (CAPP) to add our methods to the approved well abandonment protocols presently

under review in Alberta.

We believe our methods are directly applicable to the problem of long term leakage of sequestered GHG from wells that penetrate a reservoir used for the sequestration. Obviously, it makes neither economic nor environmental sense to capture, concentrate, compress, deliver, and inject CO2 into depleted reservoirs or saltwater formations if there is not a reliable sealing method used on existing wells in that reservoir to prevent the CO2 leaking back into the atmosphere. We believe that our plugging methods can assure long term success in preventing this leakage.

We use an alloy of bismuth and tin for our sealing medium. This alloy is nontoxic and will not corrode or cause corrosion in the relevant well environment from either chemical or galvanic processes. We believe we can seal a well against gas flow even if the well casing has been entirely corroded away. The important properties of the alloy that cause it to be effective are:1) it expands about 1% by volume when solidifying from the liquid phase; 2) it is impermeable to gas flow; 3) it seals effectively in dirty oily casing; 4) it has a high specific gravity to facilitate displacement of other fluids present during the deployment process; and 5) it has a very low viscosity and surface tension such that it will enter small fissures, and absorb into and wet permeable rocks such as sandstone.

Only small amounts of the alloy are required to form a seal with the differential pressure strength required to seal GHG sequestration wells. We set the plugs using an electric heater deployed on a wire line. The procedure is both fast and inexpensive. We have data to back the above contentions, including corrosion tests carried out in a CO2/saltwater environment with a pH of 3 that indicate plug life in steel casing in excess of 10,000 years.

Response: EPA thanks the commenters for the information on available well materials. EPA believes that the regulation affords owners or operators flexibility to use various materials and techniques to perform corrective action, provided they meet with the Director's approval.

Commenter Name: Leslie Savage Letter ID: 0122 Commenter Organization: Railroad Commission of Texas (RRC) Comment ID: 24778 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: (d) Owners or operators of Class VI wells must perform corrective action USING CORROSION RESISTANT MATERIAL, WHEN APPROPRIATE, on all wells IDENTIFIED IN §146.84(C)(2) in the AOR that are determined to need corrective action using methods necessary to prevent the movement of fluid into or between USDWs including use of corrosion resistant materials, where appropriate.

Response: EPA revised the text at §146.84(d) to require the use of materials that are "compatible with the carbon dioxide stream." EPA believes this language change addresses commenters' concerns and is also consistent with other language regarding materials requirements in the GS rule.

Commenter Name: Bonnie Lovelace Letter ID: 0152 Commenter Organization: Montana Department of Environmental Quality (MDEQ) Comment ID:

22114

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.

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.

Commenter Name: Kyle Isakower Letter ID: 0170Commenter Organization: American Petroleum Institute Comment ID: 24164 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Rule Provision: 146.84(d)

API Comments: (d) Owners or operators of Class VI wells must perform corrective

action USING MATERIALS SUITABLE FOR USE WITH THE CARBON DIOXIDE STREAM

AND FORMATION FLUIDS, on all wells in the area of review IDENTIFIED IN 146.84(C) (2) that are determined to need corrective action". using methods necessary to prevent the movement of fluid into or between USDWs including use of corrosion resistant materials, where appropriate.

Rationale: Experience with CO2 based EOR strongly supports the use of many conventional materials that might not meet the technical definition of

"corrosion resistant".

Response: EPA revised the text at §146.84(d) to require the use of materials that are "compatible with the carbon dioxide stream." EPA believes this language change addresses commenters' concerns and is also consistent with other language regarding materials requirements in the GS rule.

Commenter Name: Robert J. Finley Letter ID: 0180 Commenter Organization: Illinois State Geological Survey Comment ID: 23626 Other EPA Comment Codes and Descriptions: 3200 2.2 Proposed Area of Review and Corrective Action Requirements (40 CFR 146.84)

Comment: 146.84

(c)

Who determines what corrective action is required in the area of review? If a Class II well has been plugged in conformance with Class II requirements is that presumed to be adequate? Different state agencies (in a primacy state) may be responsible for Class II and Class VI wells, potentially complicating oversight

of corrective action.

Response: The GS regulation does not specify the corrective action methods to be used on wells within the AoR to meet the requirements of §146.84(d) and instead allows flexibility to ensure that all corrective action is appropriate to the well, the CO2 injection, and other site-specific conditions. All corrective action must be appropriate to the GS site to ensure that the well does not allow CO2 or other fluids to move into or endanger USDWs and must be approved by the Director. EPA recognizes that wells plugged in accordance with Class II requirements may also be appropriately plugged for a CO2 GS project. EPA adds that all corrective action must be performed pursuant to the approved AoR and corrective action plan, which affords the Director the discretion to require any additional information needed to ensure that all necessary corrective action is performed.

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.

Commenter Name: Robert F. Van Voorhees Letter ID: 0190 Commenter Organization: Carbon Sequestration Council Comment ID: 24434 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Rule Provision: 146.84(d)

Proposed CCS Group Recommendations: Owners or operators of Class VI wells must perform corrective action USING MATERIALS SUITABLE FOR USE WITH THE CARBON DIOXIDE STREAM AND FORMATION FLUIDS, on all wells in the area of review IDENTIFIED IN 146.84(C)(2) that are determined to need corrective action". using methods necessary to prevent the movement of fluid into or between USDWs including use of corrosion resistant materials, where appropriate.

Basis for CCS Group Comments: Experience with CO2 based EOR strongly supports the use of many conventional materials that might not meet the technical

definition of "corrosion resistant".

Response: EPA revised the text at §146.84(d) to require the use of materials that are "compatible with the carbon dioxide stream." EPA believes this language change addresses commenters' concerns and is also consistent with other language regarding materials requirements in the GS rule.

Commenter Name: Craig R. Walters Letter ID: 0200 Commenter Organization: Anadarko Petroleum Corporation Comment ID: 24662 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Rule Provision: 146.84(d)

Anadarko Petroleum Corporation (APC) Comments: (d) Owners or operators of Class VI wells must perform corrective action USING MATERIALS SUITABLE FOR USE WITH THE CARBON DIOXIDE STREAM AND FORMATION FLUIDS, on all wells in the area of

review IDENTIFIED IN 146.84(C)(2) that are determined to need corrective action". using methods necessary to prevent the movement of fluid into or between USDWs including use of corrosion resistant materials, where appropriate.

Rationale: Experience with CO2 based EOR strongly supports the use of many conventional materials that might not meet the technical definition of

"corrosion resistant".

Response: EPA revised the text at §146.84(d) to require the use of materials that are "compatible with the carbon dioxide stream." EPA believes this language change addresses commenters' concerns and is also consistent with other language regarding materials requirements in the GS rule.

Commenter Name: Michel Paque Letter ID: 0259Commenter Organization: Ground Water Protection Council Comment ID: 24888 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Rule Provision: 146.84(d)

EPA Proposal: (d) Owners or operators of Class VI wells must perform corrective

action on all wells in the area of review that are determined to need corrective action using methods necessary to prevent the movement of fluid into or between USDWs including use of corrosion resistant materials, where appropriate.

GWPC Recommendations: (d) Owners or operators of Class VI wells must perform corrective action using materials suitable for use with carbon dioxide streams, on all wells identified in 146.84(c)(2) that are determined to need corrective

action".

Rationale: Re-write as follows "Owners or operators of Class VI wells must perform corrective action using corrosion resistant materials, when appropriate, on all wells identified in 146.84(c)(2) that are determined to need corrective

action".

Response: EPA revised the text at §146.84(d) to require the use of materials that are "compatible with the carbon dioxide stream." EPA believes this language change addresses commenters' concerns and is also consistent with other language regarding materials requirements in the GS rule.

Comment Code: 3500 2.2.3 Area of Review Reevaluation (seeking comment)



### Individual Comments

Commenter Name: Paul Pike Letter ID: 0111 Commenter Organization: Ameren Corporation on behalf of USWAG Comment ID: 22405 Other EPA Comment Codes and Descriptions: 1250 1.1.1.4 Flexibility is needed (performancebased standards); 5000 2.8 Proposed Well Plugging and Post-Injection Site Care Requirements

Comment: 6. Because of the widely varied characteristics and limitations of different carbon dioxide sequestration projects, it is essential to incorporate performance-based standards into the Final Rule, leading to a site-specific approach to requirements for Area of Review reevaluation and post-injection site care and closure periods.

Response: The post-injection site care requirements in the final GS rule, as specified in §146.93(b), incorporate a combination of a fixed timeframe and a performance standard approach. 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 thepermitting 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 adjustthe 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 is developing guidance to assist owners or operators in evaluating well plugging, post-injection site care, and site closure requirements of §146.92 and §146.93. Additionally, the guidance will assist Directors in evaluating proposed well plugging plans and post-injection site care and site closure plans under §146.92 and §146.93. The guidance describes recommended approaches for how an owner or operator could plug injection and monitoring wells; perform post-injection monitoring; demonstrate the appropriateness of an alternative post-injection site care time frame; demonstrate non endangerment; and perform site closure activities. The guidance will be available on EPA's web site, at http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

In response to comments about AoR evaluation, EPA disagrees that the GS regulation should includeperformance-based standards for AoR calculation. However, EPA believes that consideration of sitespecific conditions is appropriate for the AoR calculation and reevaluation process. EPA believes that the flexibility incorporated into the AoR and corrective action plans and the provision for AoR reevaluation as required at §146.84(e) provide for an ongoing review of the site and a dialogue between the Director and the owner or operator to ensure that the most appropriate modeling and corrective action technologies are used to protect USDWs from endangerment.

Commenter Name: Leslie Savage Letter ID: 0122 Commenter Organization: Railroad Commission of Texas (RRC) Comment ID: 24779 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: (f) At the minimum fixed frequency, not to exceed 10 years, as AS specified in the AOR and corrective action plan, or when monitoring and operational conditions warrant, the owner or operator must:

Response: EPA believes that periodic AoR reevaluation at a set frequency is necessary to ensure protection of USDWs from endangerment and address the uncertainties inherent in predictive modeling. Periodic AoR reevaluations at §146.84(e) ensure that a deliberate effort is made to verify, based on monitoring and operational data, that the CO2 plume is moving within the subsurface as predicted. EPA believes that less frequent reevaluations may not be sufficient to appropriately model plume and pressure front movement, establish conditions for corrective action, and ensure protection of USDWs from endangerment.

EPA clarifies that if site monitoring data agrees with the existing AoR delineation, a model recalibration may not be necessary, and the AoR reevaluation may consist of a demonstration that the current AoR delineation is adequate based on site monitoring data.

Based on the comments received (including those by water associations, an energy company, associations, industries, states, and environmental groups), EPA has changed the minimum frequency for the AoR reevaluation from 10 years to at least every 5 years. 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.Commenter Name: Leslie Savage Letter ID: 0122 Commenter Organization: Railroad Commission of Texas (RRC) Comment ID: 24780 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: (4) Submit an amended AOR and corrective action plan or demonstrate to the Director through monitoring data and modeling results that no CHANGE amendment to the AOR and corrective action plan is needed.

{Appropriate frequency of determining AoR might not be "fixed." Owner or operator might need to reevaluate AoR frequently at first, particularly with deep brine formations about which there is little history, and then at expanding intervals as more information is known.}

Response: EPA agrees that site-specific factors should be considered in the reevaluation schedule, and notes that the AoR and corrective action plan must specify the site-specific monitoring and operational conditions that warrant reevaluation, as specified in §146.84(b)(2)(ii). 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. However, EPA believes that setting a minimum reevaluation frequency is appropriate. In the final rule, 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.

Commenter Name: Theresa Pugh Letter ID: 0169 Commenter Organization: American Public Power Association Comment ID: 23399

Comment: Area of Review: APPA has nominal background in Area of Review, but we do believe that AoR sites require periodic review. Given the fact that carbon sequestration technology is still developing, and the widely varied characteristics and limitations of different CO2 GS projects, it is essential to incorporate performance-based standards into the Final Rule, with site-tailored approaches to requirements for Area of Review ("AoR") reevaluation and post-injection site care and closure periods. APPA believes that the AoR should be periodically reviewed at least every five years for the first 10 years. At the conclusion of the tenth year APPA believes that a less stringent periodic review should be allowed by the director if he so chooses. However, APPA believes that the

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 theinherent uncertainties in modeling CO2 movement, the emerging nature of GS technology, riskbased targeting of monitoring activities, and the unique nature of CO2 GS. EPA disagrees that a longer reevaluation frequency in the later years of the project is appropriate, however. EPA believes that the same justifications for reevaluations will continue to apply. EPA adds that if site monitoring data agrees with the existing AoR delineation, the AoR reevaluation may consist of a demonstrationthat the current AoR delineation is adequate based on site monitoring data.

Commenter Name: Kyle Isakower Letter ID: 0170 Commenter Organization: American Petroleum Institute Comment ID: 24160 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language; 3700 2.2.5 Comments on the requirement for an AoR and corrective action plan

Comment: Rule Provision: 146.84(b)(2)

API Comments: (2) A description of: (i) The minimum fixed frequency, not to exceed 10 years, the owner or operator proposes to reevaluate the area of review; (ii) The monitoring and operational conditions that would warrant a reevaluation of the area of review prior to the next scheduled reevaluation as determined by the minimum fixed frequency established in paragraph (b)(2)(i) of

this section. (iii) (I) How monitoring and operational data (e.g., injection rate and pressure) will be used to inform an area of review reevaluation; and

No rationale provided

Rule Provision: 146.84(b)(2)

API Comments: (iv II) How corrective action will be conducted to meet the requirements of paragraph (d) of this section, including what corrective action will be performed prior to injection and what, if any, portions of the area of review will have corrective action addressed on a phased basis and how the phasing will be determined; how corrective action will be adjusted if there are changes in the area of review; and how site access will be guaranteed

ARRANGED for future corrective action.

Rationale: Future access cannot be guaranteed for an area in advance that may not even be within the boundaries of the AOR/ project.

Response: EPA disagrees with the suggested changes. Regarding reevaluation of the AoR, EPA believes that periodic AoR reevaluation at a set frequency of at least every five years is necessary to ensure protection of USDWs from endangerment and address the uncertainties inherent in predictive modeling. Periodic AoR reevaluations at §146.84(e) ensure that a deliberate effort is made to verify, based on monitoring and operational data, that the CO2 plume is moving within the subsurface as predicted. EPA believes that less frequent reevaluations may not be sufficient to appropriately model plume and pressure front movement, establish conditions for corrective action, and ensure protection of USDWs from endangerment.

EPA clarifies that if site monitoring data agrees with the existing AoR delineation, a model recalibration may not be necessary, and the AoR reevaluation may consist of a demonstration that the current AoR delineation is adequate based on site monitoring data.

To the comment on site access, EPA clarifies that the purpose of the corrective action requirement at §146.84(d) is to ensure that all wells in the AoR that have the potential to cause the movement of CO2 or other fluids into or between USDWs receive appropriate corrective action. In general, tomeet this requirement, the owner or operator will most likely need to obtain the right of access to wells that may require corrective action, and demonstrate they have done this in their proposed AoR and corrective action plan. The final rule retains the requirement as proposed.

Commenter Name: James Taft Letter ID: 0172 Commenter Organization: Association of State Drinking Water Administrators (ASDWA) Comment ID:

23454

Comment: into the atmosphere. The AOR should also be periodically reevaluated, particularly as improved predictive models and new data become available.

Response: EPA agrees with the commenter that periodic AoR reevaluations are appropriate. This final rule retains this provision.

Commenter Name: Quinlan J. Shea Letter ID: 0177 Commenter Organization: Edison Electric Institute Comment ID: 23588

Comment: As with a phased approach to corrective action, a phased approach to evaluation and reevaluation of the AOR may prove more practical for operators while affording the necessary protection for USDW. As noted above, some projects may implicate relatively constrained areas in terms of the size of the receiving formation, allowing operators to conduct a broader investigation at the outset more efficiently; for larger projects, it may make sense to consider allowing a phased plan for AOR evaluation and reevaluation that would provide for a certain amount of investigation at the outset with more detailed evaluations to follow over the life of a project.

Response: EPA agrees that site-specific factors should be considered in the reevaluation schedule, and notes that the AoR and corrective action plan must specify the site-specific monitoring and operational conditions that warrant reevaluation, as specified in §146.84(b)(2)(ii). 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. However, EPA believes that setting a minimum reevaluation frequency is appropriate. In the final rule, 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.

Commenter Name: Robert F. Van Voorhees Letter ID: 0190 Commenter Organization: Carbon Sequestration Council Comment ID: 24426 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language; 3700 2.2.5 Comments on the requirement for an AoR and corrective action plan

Comment: Rule Provision: 146.84(b)(2)(i) & (ii)

Proposed CCS Group Recommendations: (i) The minimum fixed frequency, not to exceed 10 years, the owner or operator proposes to reevaluate the area of review; (ii) The monitoring and operational conditions that would warrant areevaluation of the area of review prior to the next scheduled reevaluation as determined by the minimum fixed frequency established in paragraph (b)(2)(i) of

this section.

Basis for CCS Group Comments: These provisions in (i) and (ii) are rendered unnecessary by the revisions to section 146.84(b).

Response: EPA believes that periodic AoR reevaluation at a set frequency of at least every five years is necessary to ensure protection of USDWs from endangerment and address the uncertainties inherent in predictive modeling. Periodic AoR reevaluations at §146.84(e) ensure that a deliberate effort is made to verify, based on monitoring and operational data, that the CO2 plume is moving within the subsurface as predicted. EPA believes that less frequent reevaluations may not be sufficient to appropriately model plume and pressure front movement, establish conditions for corrective action, and ensure protection of USDWs from endangerment.

EPA clarifies that if site monitoring data agrees with the existing AoR delineation, a model recalibration may not be necessary, and the AoR reevaluation may consist of a demonstration that the current AoR delineation is adequate based on site monitoring data.

Commenter Name: Robert F. Van Voorhees Letter ID: 0190 Commenter Organization: Carbon Sequestration Council Comment ID: 24427 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language; 3700 2.2.5 Comments on the requirement for an AoR and corrective action plan

Comment: Rule Provision: 146.84(b)(2)(iii)

Proposed CCS Group Recommendations: iii (I) How monitoring and operational data (e.g., injection rate and pressure) will be used to inform an area of review reevaluation; and

Basis for CCS Group Comments: Agree with EPA’s rationale.

Response: EPA acknowledges the comment and the final rule retains this provision.

Commenter Name: Robert F. Van Voorhees Letter ID: 0190 Commenter Organization: Carbon Sequestration Council Comment ID: 24436 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Rule Provision: 146.84(f)

Proposed CCS Group Recommendations: (f) At the minimum fixed frequency, not to exceed 10 years, as specified in the approved area of review and corrective action plan, or When monitoring and operational conditions warrant, owners or

operators must:

Basis for CCS Group Comments: Rather than a fixed time period, we recommend following a performance based approach that would be based on significant changes in injection parameters or anomalous monitoring results.Response: EPA agrees that site-specific factors should be considered in the reevaluation schedule, and notes that the AoR and corrective action plan must specify the site-specific monitoring and operational conditions that warrant reevaluation, as specified in §146.84(b)(2)(ii). 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. However, EPA believes that setting a minimum reevaluation frequency is appropriate. In the final rule, the Agency changed the minimum frequency for the AoR reevaluation at §146.84(e) from ten years to at least every five 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.

Commenter Name: Craig R. Walters Letter ID: 0200 Commenter Organization: Anadarko Petroleum Corporation Comment ID: 24656 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language; 3700 2.2.5 Comments on the requirement for an AoR and corrective action plan

Comment: Rule Provision: 146.84(b)(2)

Anadarko Petroleum Corporation (APC) Comments: (i) The minimum fixed frequency, not to exceed 10 years, the owner or operator proposes to reevaluate the area of review;

(ii) The monitoring and operational conditions that would warrant a reevaluation of the area of review prior to the next scheduled reevaluation as determined by the minimum fixed frequency established in paragraph (b)(2)(i) of this

section.

(iii) (i) How monitoring and operational data (e.g., injection rate and pressure) will be used to inform an area of review reevaluation; and

No rationale provided

Response: EPA believes that periodic AoR reevaluation at a set frequency of at least every five years is necessary to ensure protection of USDWs from endangerment and address the uncertainties inherent in predictive modeling. Periodic AoR reevaluations at §146.84(e) ensure that a deliberate effort is made to verify, based on monitoring and operational data, that the CO2 plume is moving within the subsurface as predicted. EPA believes that less frequent reevaluations may not be sufficient to appropriately model plume and pressure front movement, establish conditions for corrective action, and ensure protection of USDWs from endangerment.

EPA clarifies that if site monitoring data agrees with the existing AoR delineation, a model recalibration may not be necessary, and the AoR reevaluation may consist of a demonstration that the current AoR delineation is adequate based on site monitoring data.

Commenter Name: Paul L. Carpinone Letter ID: 0212 Commenter Organization: Tampa Electric Company Comment ID: 22906 Other EPA Comment Codes and Descriptions: 1250 1.1.1.4 Flexibility is needed (performancebased standards); 5200 2.8.2 Post injection site care (seeking comment) (40 CFR 146.93)Comment: - Because carbon sequestration technology is still developing and the characteristics and limitations of CO2 GS projects will vary greatly from one site to another it is essential to incorporate performance-based standards into the Final Rule, leading to a site-tailored approach to requirements for Area of Review ("AoR") reevaluation and post-injection site care and closure periods.

Response: The PISC requirements in the final GS rule, as specified in §146.93(b), incorporate a combination of a fixed timeframe and a performance standard approach. EPA believes that a default PISC timeframe of 50 years, with Director's discretion to shorten or lengthen this timeframe, combined with a site-specific Director’s discretion to create an alternative PISC time frame, ensures that USDWs are protected. 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 non-endangerment of USDWs pursuant to requirements at §146.93(c). EPA expects that the Director will consider the types of information the commenter describes in determining whether the plume and pressure front no longer pose a risk of endangerment to USDWs and post-injection site care monitoring may be discontinued. 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 disagrees that the GS regulation should include performance-based standards for AoR calculation. However, EPA believes that consideration of site-specific conditions is appropriate for the AoR calculation and reevaluation process. EPA believes that the flexibility incorporated into the AoR and corrective action plans and the provision for AoR reevaluation as required at §146.84(e) provide for an ongoing review of the site and a dialogue between the Director and the owner or operator to ensure that the most appropriate modeling and corrective action technologies are used to protect USDWs from endangerment. However, EPA believes that setting a minimum reevaluation frequency is appropriate. In the final rule, 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.

Commenter Name: Diane VanDe Hei Letter ID: 0213 Commenter Organization: Association of Metropolitan Water Agencies (AMWA) Comment ID:

22927 Other EPA Comment Codes and Descriptions: 5560 2.10.3 Enhancing the public participation process (seeking comment)

Comment: In addition, AMWA recommends that local drinking water utilities be included in the AoR review process, as drinking water or potential drinking water sources may become threatened due to a change in plume direction or behavior. Public involvement also needs to be a mandatory part of the AoR reevaluation process.Response: EPA agrees that coordination between GS project owners or operators, program Directors, drinking water utilities that may be affected by GS activities, and the public is important. EPA encourages GS project operators and permitting authorities to use the Internet and other available tools to explain potential GS projects, describe the technology, and post information on the latest developments, including schedules for hearings, briefings, and other opportunities for involvement. EPA has added a requirement at §124.10(c)(1)(xi) that state and local oil and gas regulatory agencies and state agencies regulating mineral exploration and recovery, the PWSS program director, and all agencies that oversee injection wells in the state must be notified as part of the public notice process for a Class VI permit.

EPA encourages permitting authorities to notify and involve as many stakeholders as possible including drinking water organizations and local water utilities. §124.10(c)(1)(x)(A) requires notification "to any unit of local government having jurisdiction over the area where the facility is proposed to be located; and (B) to each State agency having any authority under State law with respect to the construction or operation of such facility."

EPA anticipates that drinking water associations and local water utilities will express interest in and be notified of draft permits and public hearings as required under §124.10(c)(1)(ix) and 40 CFR Part 25.5 (where EPA is providing public information) which requires the permitting authority to notify all interested parties.

EPA notes that public notice is required if the Director determines that a major permit modification is necessary as a result of an AoR reevaluation or other indication that the plume is moving in a manner other than predicted. See §144.39(a)(5).

Commenter Name: Diane VanDe Hei Letter ID: 0213 Commenter Organization: Association of Metropolitan Water Agencies (AMWA) Comment ID:

22944 Other EPA Comment Codes and Descriptions: 5560 2.10.3 Enhancing the public participation process (seeking comment)

Comment: plume direction or behavior. Public involvement also needs to be a mandatory part of the AoR reevaluation process.

Response: EPA notes that, public notice is required if the Director determines that a major permit modification is necessary as a result of an AoR reevaluation. See §144.39(a)(5).

Commenter Name: Olon Plunk Letter ID: 0217 Commenter Organization: Xcel Energy, Inc. Comment ID: 21560

Comment: corrective action in a timely manner. Finally, the rule should explicitly allow for future expansion of the AoR if necessary, provided the objective to protect

USDWs continues to be met.

Response: EPA acknowledges that the AoR for a GS project may change over time, and for this reason, the rule requires owner or operator to periodically review the AoR. EPA believes that periodic reevaluation of the AoR as required at §146.84(e) is appropriate to address the unique conditions posed by GS, including the anticipated injection volumes and associated size of CO2 plumes, as well as to address potential uncertainty in AoR modeling.EPA clarifies that the purpose of the requirement to perform an initial AoR delineation at §46.84(c)(1) is to predict as closely as possible, the ultimate extent of the CO2 plume and pressure front. The reevaluation should be considered adjustments to address changes that could not have been anticipated before injection commences.

Commenter Name: M. Granger Morgan Letter ID: 0233 Commenter Organization: Carnegie Mellon University on behalf of the CCS Reg Project Comment ID:

21908 Other EPA Comment Codes and Descriptions: 3630 2.2.4.1 Comments in favor of allowing phased corrective action

Comment: Specific comments on the proposed rule

17. Iterative Area of Review: We support the proposal to reevaluate iteratively the area of review over the project life cycle and to allow phased corrective action (sec. 146.84).

Response: EPA acknowledges the commenter’s support of AoR reevaluations and phased corrective action. EPA believes that the AoR reevaluation process at §146.84(e) provides additional opportunities to verify that the models have accurately predicted movement of the CO2 plume and to make any needed adjustments to corrective action or monitoring at the site, and has retained this approach in the final rule.

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.

Commenter Name: Kurt Waltzer Letter ID: 0250 Commenter Organization: Clean Air Task Force Comment ID: 25257 Other EPA Comment Codes and Descriptions: 4610 2.6.1 Testing and monitoring plan requirement (seeking comment)

Comment: Perhaps inadvertently, the proposed rule does not explicitly require updating of several of the required plans. In most but not all cases, there is a rather ambiguous requirement to "maintain" a given plan. Explicit requirements to make updates as warranted appear to be missing from provisions relating to:

• the testing and monitoring plan required by §146.90 (the ambiguous word "maintain" is used and there appears to be no requirement that estimated plugging costs be kept current);

Response: The final rule includes provisions that owners or operators 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, as specified in §146.84(c), §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. These reviews must be performed within one year of an AoR reevaluation, following any significant changes to the facility (e.g., the addition of monitoring or injection wells), or when required by the Director.Commenter Name: Michel Paque Letter ID: 0259 Commenter Organization: Ground Water Protection Council Comment ID: 24838 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language; 5700 2.12 Comments on the proposed duration of Class VI permits (seeking comment)

Comment: Rule Provision: 144.36

EPA Proposal: 6. Section 144.36 is amended by revising the first two sentences in paragraph (a) to read as follows:

§ 144.36 Duration of permits.

(a) Permits for Class I and V wells shall be effective for a fixed term not to exceed 10 years. UIC Permits for Class II, III and VI wells shall be issued for a period up to the operating life of the facility. * * *

* * * * *

GWPC Recommendations: Support the proposed language.

Rationale: The proposed provision is considered acceptable as long as the iterative reevaluation process established for AoRs also applies to other aspects of the project including modeling, characterization, operational decisions, monitoring, financial assurance, etc. It is recognized that Directors may also depend on 144.39 regarding modification and revocation of Class VI permits.

Response: EPA acknowledges the commenter’s support and notes that the final rule retains this requirement. The final rule maintains the lifetime permit provision and clarifies that the permit extends through the post-injection site care period (144.36(a)). It also adds a requirement that the Director review each Class VI permit at least once every 5 years to determine whether it should be modified, revoked and reissued, terminated or a minor modification made as provided in §§144.39, 144.40, or 144.41. The Director’s review will be informed by the owners’ or operators’ iterative reevaluation of the 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 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. EPA believes that the iterative process of developing and executing the various plans required of GS well operators in thefinal rule (e.g., for AoR and corrective action, testing and monitoring, injection well plugging, postinjection 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.

EPA emphasizes that the final rule requires owners or operators to revise their cost estimates for financial assurance within 60 days of amendments to the AoR and corrective action plan, the injection well plugging plan, the post-injection site care and site closure plan, or the emergency and remedial response plan (40 CFR 146.85(c)(2).EPA emphasizes that, 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 permit modifications would 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 pursuant to requirements under 40 CFR Part 124.

Commenter Name: Michel Paque Letter ID: 0259 Commenter Organization: Ground Water Protection Council Comment ID: 24883 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language; 3700 2.2.5 Comments on the requirement for an AoR and corrective action plan

Comment: Rule Provision: 146.84(b)(2)

EPA Proposal: (2) A description of:

(i) The minimum fixed frequency, not to exceed 10 years, the owner or operator proposes to reevaluate the area of review;

(ii) The monitoring and operational conditions that would warrant a reevaluation of the area of review prior to the next scheduled reevaluation as determined by the minimum fixed frequency established in paragraph (b)(2)(i) of this section.

(iii) How monitoring and operational data (e.g., injection rate and pressure) will be used to inform an area of review reevaluation; and

GWPC Recommendations: Delete (i) and (ii)

Rationale: Suggest deletion of (i) as this is handled by "manner and at a frequency acceptable to the Director in (b)

Suggest deletion of (ii) for same reason as comment on (i)

Response: EPA believes that periodic AoR reevaluation at a set frequency of at least every 5 years is necessary to ensure protection of USDWs from endangerment and address the uncertainties inherent in predictive modeling. Periodic AoR reevaluations at §146.84(e) ensure that a deliberate effort is made to verify, based on monitoring and operational data, that the CO2 plume is moving within the subsurface as predicted. EPA believes that less frequent reevaluations may not be sufficient to appropriately model plume and pressure front movement, establish conditions for corrective action, and ensure protection of USDWs from endangerment.

EPA clarifies that if site monitoring data agrees with the existing AoR delineation, a model recalibration may not be necessary, and the AoR reevaluation may consist of a demonstration that the current AoR delineation is adequate based on site monitoring data.

Commenter Name: John McManus Letter ID: 0294Commenter Organization: American Electric Power Comment ID: 25317 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language; 4700 2.7 Proposed Recordkeeping and Reporting Requirements (40 CFR 146.91)

Comment: In addition, we recommend the following new §146.95:

"146.95 Plan Maintenance and Update

"(a) Owners or operators must submit an annual statement, signed by an appropriate company official, confirming that the company has:

"(i) reviewed the monitoring and operational data that are relevant to a decision on whether to reevaluate the area of review and the monitoring and operational data that are relevant to a decision on whether to update a plan identified in §146.82(p) or (u) through (x) or the quality assurance plan for all testing and monitoring requirements; and

"(ii) determined whether any updates were warranted by material change in the monitoring and operational data or in the evaluation of the monitoring and operational data by the owner or operator.

"(b) Owners or operators must submit either the updated plan or a summary of the modifications for each plan for which an update was determined to be warranted pursuant to subsection (a) of this section. The Director may require submission of copies of any updated plans and/or additional information regarding whether or not updates of any particular plans are warranted.

"(c) The Director may require the revision of any required plan whenever the Director determines that such a revision is necessary to comply with the requirements of this subchapter."

Response: EPA agrees with the commenter that review of the GS project plans is appropriate. The final rule includes provisions that owners or operators 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 (these provisions are added at §146.84(c), §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. These reviews must be performed within one year of an AoR reevaluation, following any significant changes to the facility (e.g., the addition of monitoring or injection wells), or when required by the Director.

Comment Code: 3530 2.2.3.1 AoR reevaluation frequency (seeking comment)



### Individual Comments

Commenter Name: Karl R. Moor Letter ID: 0109 Commenter Organization: Southern Company, on behalf of Edison Electric Institute (EEI) Comment ID:

22006

Comment: For example, the Agency has proposed a 10-year default period for operators toreevaluate periodically the proper scope of the Area of Review. If such a review were required when triggered by appropriate circumstances, the Area of Review would be reviewed only when necessary, but as often as necessary. In this way, allowing site- specific performance characteristics to guide regulatory requirements means that those projects that pose the greater risk for potential harm to sources of drinking water reevaluate their Areas of Review as often as needed, and those projects that do not pose such risks are not burdened by unnecessary reevaluations. At a minimum, a default period for reevaluations of the proper scope of the Area of Review should be determined by site-specific characteristics at the time of permitting.

Response: EPA agrees that site-specific factors should be considered in the reevaluation schedule, and notes that the AoR and corrective action plan must specify the site-specific monitoring and operational conditions that warrant reevaluation, as specified in §146.84(b)(2)(ii). 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.

However, EPA believes that setting a minimum reevaluation frequency is appropriate. In the final rule, 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.

Commenter Name: Leslie Savage Letter ID: 0122 Commenter Organization: Railroad Commission of Texas (RRC) Comment ID: 24748 Other EPA Comment Codes and Descriptions: 1250 1.1.1.4 Flexibility is needed (performancebased standards)

Comment: 5. EPA should provide more flexibiilty in operation. For example, allow an EOR operator to demonstrate that CO2 is sequestered, and instead of a 10-year default period for reevaluation of the area of review, allow the timing for suchreevaluation to be determined based on site-specific characteristics and sitespecific monitoring of the CO2 plume and pressure front.

Response: EPA disagrees that the GS regulation should include performance-based standards for AoR calculation. However, EPA believes that consideration of site-specific conditions is appropriate for the AoR calculation and reevaluation process. EPA believes that the flexibility incorporated into the AoR and corrective action plans and the provision for AoR reevaluation as required at §146.84(e) provide for an ongoing review of the site and a dialogue between the Director and the owner or operator to ensure that the most appropriate modeling and corrective action technologies are used to protect USDWs from endangerment.

However, EPA believes that setting a minimum reevaluation frequency is appropriate. In the final rule, 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.Commenter Name: Leslie Savage Letter ID: 0122 Commenter Organization: Railroad Commission of Texas (RRC) Comment ID: 24772 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language; 3700 2.2.5 Comments on the requirement for an AoR and corrective action plan

Comment: (2) A description of: (i) The minimum fixed frequency, not to exceed 10 years, the owner or operator proposes to reevaluate the area of review; (ii) The monitoring and operational conditions that would warrant a reevaluation of the area of review prior to the next scheduled reevaluation as determined by the minimum fixed frequency established in paragraph (b)(2)(i) of this section.

{Suggest that there be no minimum fixed frequency for reevaluation of the AoR, but that such review be based on site-specific circumstances. }

Response: EPA believes that periodic AoR reevaluation at a set frequency of at least every 5 years is necessary to ensure protection of USDWs from endangerment and address the uncertainties inherent in predictive modeling. Periodic AoR reevaluations at §146.84(e) ensure that a deliberate effort is made to verify, based on monitoring and operational data, that the CO2 plume is moving within the subsurface as predicted. EPA believes that less frequent reevaluations may not be sufficient to appropriately model plume and pressure front movement, establish conditions for corrective action, and ensure protection of USDWs from endangerment.

EPA clarifies that if site monitoring data agrees with the existing AoR delineation, a model recalibration may not be necessary, and the AoR reevaluation may consist of a demonstration that the current AoR delineation is adequate based on site monitoring data.

Commenter Name: Dawn A. Thorne Letter ID:

0134 Commenter Organization: University of Utah Energy and Geoscience Institute on behalf of the Southwest Regional Partnership Comment

ID: 21655 Other EPA Comment Codes and Descriptions: 3560 2.2.3.2 Conditions that merit reevaluation of the AoR (seeking comment)

Comment: - Section 146.84(b)(2)(i) "A description of The minimum fixed frequency, not to exceed 10 years, the owner or operator proposes to reevaluate the area of review; "

Section 146.84(b)(2)(ii) "The monitoring and operational conditions that would warrant a reevaluation of the area of review prior to the next scheduled reevaluation as determined by the minimum fixed frequency established in paragraph (b)(2)(i) of this section "

Response/Discussion: The SWP recommends adopting a risk/performance-based approach to AoR re¬evaluation. Since each site is unique, it may be best for the operator to work directly with the EPA Director to establish an evaluation schedule that would occur as often as needed, but not more than needed. The SWP agrees that re-evaluations should be based on updating, revising, and calibrating computational models with site-specific data.

Response: EPA agrees that site-specific factors should be considered in the reevaluation schedule, and notes that the AoR and corrective action plan must specify the site-specific monitoring andoperational conditions that warrant reevaluation, as specified in §146.84(b)(2)(ii). 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.

However, EPA believes that periodic AoR reevaluation at a set frequency is necessary to ensure protection of USDWs from endangerment and address the uncertainties inherent in predictive modeling. Periodic AoR reevaluations at §146.84(e) ensure that a deliberate effort is made to verify, based on monitoring and operational data, that the CO2 plume is moving within the subsurface as predicted. EPA believes that less frequent reevaluations may not be sufficient to appropriately model plume and pressure front movement, establish conditions for corrective action, and ensure protection of USDWs from endangerment.

EPA clarifies that if site monitoring data agrees with the existing AoR delineation, a model recalibration may not be necessary, and the AoR reevaluation may consist of a demonstration that the current AoR delineation is adequate based on site monitoring data.

Commenter Name: Dwight Lockwood, PE, QEP Letter ID: 0141 Commenter Organization: Global Energy, Inc. Comment ID: 23108

Comment: It seems that the geology and capacity of the horizon can dictate the frequency but perhaps five years will prove reasonable in many cases.

Response: EPA agrees that site-specific factors should be considered in the reevaluation schedule, and notes that the AoR and corrective action plan must specify the site-specific monitoring and operational conditions that warrant reevaluation, as specified in §146.84(b)(2)(ii). 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. However, EPA believes that setting a minimum reevaluation frequency is appropriate. In the final rule, the Agency changed the minimum frequency for the AoR reevaluation at §146.84(e) from 10 years to 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.

Commenter Name: Christine Reimer Letter ID: 0142 Commenter Organization: National Ground Water Association Comment ID: 22571 Other EPA Comment Codes and Descriptions: 4650 2.6.5 CO2 plume and pressure front tracking (seeking comment)

Comment: MMV should be conducted hand-in-hand with modeling over the entire period that MMV is occurring, with each new round of measurements being incorporated into a new iteration of the appropriate site models. An iterative measurement-modeling approach will allow for the best understanding of the shape and size of the AoR. It will also help identify areas of uncertainty in the model that may be reduced with changes in the MMV plan. Changes identified in the size of the AoR and for risk of leakage will help ensure that MMV is carried out at the right frequency and in the right locations. The timing of the MMV operations should be flexibleand adjustable based on the performance of the site and the site models. It is likely that the site data from early in the operation will probably be more valuable than data from later in the operation for assessing the performance of the site and identifying and reducing uncertainties. MMV operations that are not continuous should be conducted more frequently at the start of the operational phase and then be allowed to become less frequent if the site is performing safely and in concert with the model predictions. The initial, more frequent monitoring should be specified in the permit as an experimental phase of the injection project. The continuation of injection should be contingent upon successful containment of the injected CO2 during the experimental phase.

Response: 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. Monitoring associated with injection wells and the movement of the CO2 plume is necessary to verify that the injectate is confined in the target formations and does not endanger USDWs.

EPA agrees that monitoring data should be used to review model assumptions, verify computational model projections, and, when necessary, provide input for model refinements. As data are collected at an injection site, model parameters can be adjusted to match observations (i.e., for model calibration), which in turn improves the predictive capability of the model. As a GS project proceeds, both monitoring and modeling will evolve, with monitoring results supporting effective AoR reevaluations and leading to improved model predictions.

As described above, EPA does not agree that each GS site should have to be permitted as a Class V experimental technology well before being authorized to operate as a full-scale Class VI well. EPA does not consider it appropriate to permit CO2 injection wells that are testing the injectivity or appropriateness of an individual formation (e.g., as a prelude to a commercial-scale operation) as Class V experimental technology wells. Such wells should be permitted as Class VI wells.

EPA clarifies that some monitoring frequencies are specified in §146.90; others will be established in the monitoring and testing plan submitted with the permit application under §146.90. The Director may require changes in the frequencies when the plan is updated, as is required at least every 5 years (or when there are changes to the facility or at the request of the Director).

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. The guidance can be found on EPA’s website at http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Christine Reimer Letter ID: 0142 Commenter Organization: National Ground Water Association Comment ID: 22582

Comment: Preamble Questions: EPA seeks comment on requiring the reevaluation of the site AoR on a periodic basis, under what conditions the AoR should be reevaluated, and the appropriateness of a 10-year minimum fixed frequency for AoR

reevaluation. EPA Notice 72.NGWA Response: Yes, reevaluation is needed and at a higher frequency than 10 years, particularly at the beginning.

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 theinherent uncertainties in modeling CO2 movement, the emerging nature of GS technology, riskbased 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.

Commenter Name: Christine Reimer Letter ID: 0142 Commenter Organization: National Ground Water Association Comment ID: 22583 Other EPA Comment Codes and Descriptions: 3630 2.2.4.1 Comments in favor of allowing phased corrective action

Comment: Preamble Questions: EPA proposes to allow a phased approach to corrective action but says this may not be appropriate in all situations; therefore EPA is proposing that the Director have the discretion to decide to allow this approach, based on the understanding of relevant geologic and site conditions. EPA invites public comment on the merits and frequency of reevaluation of the AoR as well as the phased corrective action approach for GS wells. EPA Notice

74.

NGWA Response: Yes, phased corrective action is a good idea. It will allow targeting of those wells most in need of corrective action and optimize financial resources as the pressure/CO2 plume may deviate from the initial AoR. That's why it is important to review AoR more often than 10 years.

Response: EPA acknowledges the commenter’s support of phased corrective action and 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.

Also, as described above, EPA changed the minimum frequency for the AoR reevaluation at §146.84(e) from 10 years to 5 years in the final GS rule.

Commenter Name: Christine Reimer Letter ID: 0142 Commenter Organization: National Ground Water Association Comment ID: 22593 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Proposed Rule: 146.84(b)(2)(i)Proposed revision: (i) The owner or operator will reevaluate the AOR after two yearsof operational testing (prior to issuance of the operating permit), and after 5 years and then no less frequently than every 5 years for the life of the project;

Rationale: NGWA believes that a frequency of every 10 years is too long to identify early discrepancies between the site performance and the site model. Seeing early difference will allow for earlier model updating and provide additional reduction in leakage risk.

Response: As described above, EPA agrees that reevaluations of the AoR every ten years may not be sufficient to ensure protection of USDWs from endangerment, and has 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.

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.

Commenter Name: Christine Reimer Letter ID: 0142 Commenter Organization: National Ground Water Association Comment ID: 22597 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Proposed Rule: 146.84(f)

Proposed revision: (f) At the minimum fixed frequency, not to exceed two years if under operational testing (prior to issuance of the operating permit), or 5 years (if operating permit has been issued), as specified in the area of review and corrective action plan or when monitoring and operational conditions

warrant, owners or operators must:

Rationale: This makes this consistent with NGWA's proposed revision to Section 146.84(b)(2)(i)

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 theinherent uncertainties in modeling CO2 movement, the emerging nature of GS technology, riskbased 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.

Commenter Name: Richard Driggans Letter ID: 0145 Commenter Organization: Tennessee Valley Authority Comment ID: 23152Comment: 3. Area of Review (AoR) - The proposed rule requested comment on requiring reevaluation of the site AoR on a periodic basis and the appropriateness of a 10year minimum fixed frequency for AoR re-evaluation. TVA supports a reevaluation frequency not to exceed 10 years. Periodic AoR re-evaluation will be needed given the enormous volumes of CO2 that would be injected, the potentially high mobility of CO2 in the subsurface, the lengthy timeframes likely for CO2 GS operations, and the uncertainty of the original model-predicted AoR limits,especially where multiple injections might occur below the same aquifer (noncontiguous but merging CO2 pressure fronts).

In practice, much of what is required in an AoR evaluation (e.g., well field monitoring, computational fluid dynamics model calibration/verification, and updated prediction of future limits of the CO2 plume) will be performed on an on-going basis to support well-field operation and monitoring. If after 10years, updated modeling shows no significant change in AoR limits, the AoR reevaluation should merely require presenting the latest modeling results and possibly confirming that no new penetrations have been identified and therefore no new corrective actions are necessary.

Response: EPA believes 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 theinherent uncertainties in modeling CO2 movement, the emerging nature of GS technology, riskbased 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.

EPA adds that if site monitoring data agrees with the existing AoR delineation, a model recalibration may not be necessary, and the AoR reevaluation may consist of a demonstration that the current AoR delineation is adequate based on site monitoring data.

Commenter Name: Brianne Metzger Letter ID: 0151 Commenter Organization: Spectra Energy Corp Comment ID: 21820

Comment: We also support the Agency’s position that any reevaluation of the AoR occur at a minimum fixed frequency, not to exceed 10 years. As well, we agree with providing the Director discretion to require more frequent reevaluation, as appropriate, if the monitoring or modeling suggests that the CO2 plume is not behaving as originally predicted and could result in endangerment to underground sources of drinking water (USDWs). Based on our experience with AGR, we believe that a frequency of between 3-5 years may be more reasonable and appropriate and would support such a determination; but in any event, we agree that such reevaluation should not exceed 10 years.

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 ten years to at least every five 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.

Commenter Name: Bonnie Lovelace Letter ID: 0152 Commenter Organization: Montana Department of Environmental Quality (MDEQ) Comment ID:

22112

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 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

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.

Commenter Name: Steven Pirner Letter ID: 0153 Commenter Organization: South Dakota Department of Environment and

Natural Resources Comment ID:

22145

Comment: 146.84 Area of review and corrective action - (b) (2) (i) the need to reevaluate the area of review a maximum of every 10 years - great clause, we have potential for problems in our Class II program where operators could potentially over inject, especially if the life of permit expires

Response: EPA acknowledges the commenters’ support for reevaluation of the AoR. Based on evaluation of the public comments on this topic, EPA has 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 response to the comment that operators could potentially over-inject, EPA clarifies that the purpose of the requirement to perform an initial AoR delineation at §46.84(c)(1) is to predict, as closely as possible, the ultimate extent of the CO2 plume and pressure front. The reevaluation should be considered as adjustments to address changes that could not have been anticipated before injection commences.Commenter Name: James Childress Letter ID: 0158 Commenter Organization: Gasification Technologies Council (GTC) Comment ID: 23780

Comment: EPA seeks comment on requiring the reevaluation of the site AoR on a periodic basis, under what conditions the AoR should be reevaluated, and the appropriateness of a 10-year minimum fixed frequency for AoR reevaluation. EPA

Notice 72.

10 years is a reasonable period of time to reevaluate the site AoR during injection.

Response: Based on evaluation of the public comments on this topic, EPA has changed the minimum frequency for the AoR reevaluation at §146.84(e) from 10 years to at least every 5 years. EPA believes that this revised frequency addresses concerns raised by commenters representing water associations, an energy company, associations, industries, states, and environmental groups 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.

The 5-year reevaluation frequency, particularly during early stages of GS deployment, will also support EPA's adaptive approach to the GS rulemaking. EPA is using an adaptive approach to regulating GS. The Agency 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.

Commenter Name: Michael J. Miller Letter ID: 0168 Commenter Organization: Electric Power Research Institute (EPRI) Comment ID: 22500

Comment: Also preamble, page 43507 "EPA seeks comment on requiring the reevaluation of the site AoR on a periodic basis, under what conditions the AoR should be reevaluated, and the appropriateness of a 10 year minimum fixed frequency for

AoR reevaluation."

The proposed rule uses an arbitrary 10-year minimum fixed frequency for AoR reevaluation and does not present the technical criteria EPA used in determining this frequency. EPRI believes that it would be more logical to base the frequency of AoR reevaluation on performance measures including the observed speed of the plume and its anticipated arrival time at the edge of the computed AoR. Or, if plume speed cannot be observed directly (e.g., no CO2 is observed in wells completed in the monitoring zone) nor indirectly (e.g., using remote monitoring techniques like seismic), then the model predictions for CO2 plume speed and arrival at the AoR boundary should be used to set the reevaluation frequency.

Response: EPA disagrees that the requirement at §146.84(e) for a periodic AoR reevaluation is arbitrary. EPA proposed the ten-year frequency based on input from stakeholders and experts at the technical workshops on "Geological Considerations and AoR Studies" and "Modeling and Reservoir Simulation for Geologic Carbon Storage." EPA also requested comment on the ten-year frequency. In the preamble to the proposed rule, EPA identified benefits to periodically reevaluating the AoR, including allowing refinement to the AoR delineation based on real-world conditions and monitoring results, increasing confidence in the modeled predictions, and targeting monitoring in those areassubject to the greatest potential risk.

Based on the comments received (including those by water associations, an energy company, associations, industries, states, and environmental groups), EPA has changed the minimum frequency for the AoR reevaluation from 10 years to at least every 5 years. 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.

EPA believes that periodic AoR reevaluation at a set frequency is necessary to ensure protection of USDWs from endangerment and address the uncertainties inherent in predictive modeling. Periodic AoR reevaluations at §146.84(e) ensure that a deliberate effort is made to verify, based on monitoring and operational data, that the CO2 plume is moving within the subsurface as predicted. EPA believes that less frequent reevaluations may not be sufficient to appropriately model plume and pressure front movement, establish conditions for corrective action, and ensure protection of USDWs from endangerment.

EPA adds that the GS rule at §146.84(e) requires the AoR reevaluation, along with the iterative process of developing and executing the various plans required of GS well operators (e.g., for AoR and corrective action, testing and monitoring, injection well plugging, post-injection site care, and emergency and remedial response) instead of period permit renewals (e.g., of 10 years for Class I wells). EPA believes the iterative process and subsequent reevaluations of the AoR and corrective action, testing and monitoring, and emergency and remedial response plans are preferable to a periodic permit reapplication and review of the entire permit because they focus time and resources to the most critical aspects of the permit. Additionally, AoRs reevaluated after at least every 5 years of injection will provide data on GS projects to inform EPA's adaptive rulemaking approach.

Commenter Name: Kyle Isakower Letter ID: 0170 Commenter Organization: American Petroleum Institute Comment ID: 24166 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Rule Provision: 146.84(f)

API Comments: (f) At the minimum fixed frequency, not to exceed 10 years, as specified in the approved area of review and corrective action plan, or W hen monitoring and operational conditions warrant, owners or operators must:

Rationale: Rather than a fixed time period, API recommends following a performance based approach that would be based on significant changes in injection parameters or anomalous monitoring results.

Response: EPA believes that periodic AoR reevaluation at a set frequency is necessary to ensure protection of USDWs from endangerment and address the uncertainties inherent in predictive modeling. Periodic AoR reevaluations at §146.84(e) ensure that a deliberate effort is made to verify, based on monitoring and operational data, that the CO2 plume is moving within the subsurface as predicted. EPA believes that less frequent reevaluations may not be sufficient to appropriately model plume and pressure front movement, establish conditions for corrective action, and ensure protection of USDWs from endangerment.EPA clarifies that if site monitoring data agrees with the existing AoR delineation, a model recalibration may not be necessary, and the AoR reevaluation may consist of a demonstration that the current AoR delineation is adequate based on site monitoring data.

Based on the comments received (including those by water associations, an energy company, associations, industries, states, and environmental groups), EPA has changed the minimum frequency for the AoR reevaluation from ten years to at least every five years. 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.

Commenter Name: Kyle Isakower Letter ID: 0170 Commenter Organization: American Petroleum Institute Comment ID: 24226

Comment: Rule Provisions: 146.84 EPA Preamble Question: 14. EPA seeks comment on requiring the reevaluation of the site AoR on a periodic basis, under what conditions the AoR should be reevaluated, and the appropriateness of a 10- year minimum fixed frequency for

AoR reevaluation. EPA Notice 43507.

API Response: Rather than a fixed time period, API recommends following a performance based approach that would be based on significant changes in injection parameters or anomalous monitoring results.

Response: EPA believes that periodic AoR reevaluation at a set frequency is necessary to ensure protection of USDWs from endangerment and address the uncertainties inherent in predictive modeling. Periodic AoR reevaluations at §146.84(e) ensure that a deliberate effort is made to verify, based on monitoring and operational data, that the CO2 plume is moving within the subsurface as predicted. EPA believes that less frequent reevaluations may not be sufficient to appropriately model plume and pressure front movement, establish conditions for corrective action, and ensure protection of USDWs from endangerment.

EPA clarifies that if site monitoring data agrees with the existing AoR delineation, a model recalibration may not be necessary, and the AoR reevaluation may consist of a demonstration that the current AoR delineation is adequate based on site monitoring data.

Commenter Name: James Rower Letter ID: 0173 Commenter Organization: Utility Solid Waste Activities Group (USWAG) Comment ID: 23486

Comment: 9. Area of Review and Corrective Action

USWAG appreciates the importance and complexity of proper AoR evaluation. See id. The Proposal would require Owners or Operators to invest a significant

amount of time and resources in the initial delineation of the AoR. Provided that the Program's requirements are satisfied in the initial determination of the AoR, USWAG believes that a requirement for AoR reevaluations every ten years or at any other fixed period is unnecessary; this will result in the arbitrary imposition of costs that may be wholly unwarranted. A more appropriate approach would be performance-based, with reevaluation required upon occurrence of some triggering event. One example of a triggering event could be a significantdeviation from previously modeled scenarios, provided that the level of deviation that would require reevaluation is clearly defined by the regulating agency. As with many other decisions related to implementation of the Class VI CO2 GS program, determinations such as these are best made on a local level by regulators having the most familiarity with the characteristics and constraints of a given geologic setting for a CO2 GS project.

Response: EPA disagrees that the requirement at §146.84(e) for a periodic AoR reevaluation is arbitrary. EPA proposed the ten-year frequency based on input from stakeholders and experts at the technical workshops on "Geological Considerations and AoR Studies" and "Modeling and Reservoir Simulation for Geologic Carbon Storage." EPA also requested comment on the ten-year frequency. In the preamble to the proposed rule, EPA identified benefits to periodically reevaluating the AoR, including allowing refinement to the AoR delineation based on real-world conditions and monitoring results, increasing confidence in the modeled predictions, and targeting monitoring in those areas subject to the greatest potential risk.

Based on the comments received (including those by water associations, an energy company, associations, industries, states, and environmental groups), EPA has changed the minimum frequency for the AoR reevaluation from 10 years to at least every 5 years. 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.

EPA adds that the GS rule at §146.84(e) requires the AoR reevaluation, along with the iterative process of developing and executing the various plans required of GS well operators (e.g., for AoR and corrective action, testing and monitoring, injection well plugging, post-injection site care, and emergency and remedial response) instead of period permit renewals (e.g., of 10 years for Class I wells). EPA believes the iterative process and subsequent reevaluations of the AoR and corrective action, testing and monitoring, and emergency and remedial response plans are preferable to a periodic permit reapplication and review of the entire permit because they focus time and resources to the most critical aspects of the permit. Additionally, AoRs reevaluated after at least every 5 years of injection will provide data on GS projects to inform EPA's adaptive rulemaking approach.

Commenter Name: Pamela Faggert Letter ID: 0175 Commenter Organization: Dominion Comment ID: 23523

Comment: 3. Area of Review

Unlike existing UIC classes of wells, the Area of Review (AoR), the area within which all pre-existing wells must be identified and studied to determine whetherthey have been properly completed or plugged, will be determined on a sitespecific basis using computational fluid flow models. Whereas Dominion supports the site-specific determination for AoR, we urge EPA to eliminate the arbitrary 10-year maximum between periodic reevaluation of the AoR. Tying reevaluation to the triggering of appropriate circumstances will provide equivalent protection of USDW while also ensuring that those projects posing greater relative risks receive greater scrutiny through more stringent reevaluation requirements while those projects posing fewer relative risks are relieved of costly regulatory

burdens.The Agency should avoid requiring an arbitrary 10 year maximum between periodic reevaluations of the AoR and instead should rely on site specific circumstances to determine periodic review schedules.

Response: EPA disagrees that the requirement at §146.84(e) for a periodic AoR reevaluation is arbitrary. EPA proposed the ten-year frequency based on input from stakeholders and experts at the technical workshops on "Geological Considerations and AoR Studies" and "Modeling and Reservoir Simulation for Geologic Carbon Storage." EPA also requested comment on the ten-year frequency. In the preamble to the proposed rule, EPA identified benefits to periodically reevaluating the AoR, including allowing refinement to the AoR delineation based on real-world conditions and monitoring results, increasing confidence in the modeled predictions, and targeting monitoring in those areas subject to the greatest potential risk.

Based on the comments received (including those by water associations, an energy company, associations, industries, states, and environmental groups), EPA has changed the minimum frequency for the AoR reevaluation from 10 years to at least every 5 years. 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.

EPA adds that the GS rule at §146.84(e) requires the AoR reevaluation, along with the iterative process of developing and executing the various plans required of GS well operators (e.g., for AoR and corrective action, testing and monitoring, injection well plugging, post-injection site care, and emergency and remedial response) instead of period permit renewals (e.g., of 10 years for Class I wells). EPA believes the iterative process and subsequent reevaluations of the AoR and corrective action, testing and monitoring, and emergency and remedial response plans are preferable to a periodic permit reapplication and review of the entire permit because they focus time and resources to the most critical aspects of the permit. Additionally, AoRs reevaluated after at least every 5 years of injection will provide data on GS projects to inform EPA's adaptive rulemaking approach.

Commenter Name: Quinlan J. Shea Letter ID: 0177 Commenter Organization: Edison Electric Institute Comment ID: 23552

Comment: EEI is concerned that a broad, unconstrained requirement for periodic reevaluation of the area of review (AOR) that would apply in the same manner to all potential project sites is unwarranted as a matter of presumption. The schedule for AOR review should be a matter addressed through permitting and a plan for development and operation.

Response: EPA is retaining the approach of setting a minimum fixed frequency for reevaluating the AoR but has, based on commenters' input, changed the frequency from 10 years to at least every 5 years, as specified in §146.84(e). EPA agrees with commenters that site-specific information is an important factor in determining an appropriate AoR reevaluation frequency, and adds that the owner or operator's AoR and corrective action plan must describe the minimum fixed frequency for reevaluating the AoR and the site-specific conditions on which this frequency is based.

Commenter Name: Quinlan J. Shea Letter ID: 0177 Commenter Organization: Edison Electric Institute Comment ID: 23586

Comment: C. Periodic Reevaluation of AOR and Corrective Action RequirementsThe second general area of concern addressed in these comments relates to EPA‘s proposed provisions concerning the AOR for CO2 storage projects. In a departure from AOR procedures currently in place under the UIC program, the proposed regulations would require operators to reevaluate the proper scope of the AORperiodically at a minimum fixed frequency to be set by the program directorcurrently proposed as no less than once every 10 years, with discretion to require more frequent reevaluation. The apparent assumption underlying this proposed requirement is that the location of injected CO2, and thus the location and extent of potential impact, could change--or perhaps more importantly, could change from what is expected at the outset of a project--over time.

As EEI commented in our May 15, 2008, pre-rulemaking comments, a broad, unconstrained requirement for periodic reevaluation of the AOR that would apply in the same manner to all potential project sites is unwarranted as a matter of presumption. Although the proposed rules provide for some discretion in terms of the review period, they nonetheless would require periodic reevaluation for every project at least once every 10 years. Several factors argue against such an approach:

- Consideration of specific circumstances should be required: While EEI is not necessarily opposed to an appropriately drafted provision requiring periodic reevaluation of the AOR under certain circumstances, any requirement for such review should not be a universally applicable requirement potentially applied devoid of any context. Rather, AOR reevaluation provisions should be triggered by reasonable parameters, taking into consideration site-specific issues, as discussed in the general principles set forth above. AOR issues are inherently site-specific; different projects--and even different geographical regions ofthe country--likely warrant different approaches. A default no-less-than-onceevery-10-years provision does not allow for adequate consideration of specific circumstances. Tying reevaluation to the triggering of appropriate circumstances will provide equivalent protection for USDW while also ensuring that those projects posing greater relative risks receive greater scrutiny through more stringent reevaluation requirements and those projects posing fewer relative risks are relieved of unnecessary regulatory burdens. At a minimum, any default period for reevaluation should be determined based on site-specific characteristics at the time of project permitting.

- Unknown trade-offs militate against a universal requirement: It is impossible to know what the relevant trade-offs are as to the initial AOR versus potential later assessments of the AOR. For example, in certain instances it is foreseeable that a project owner may seek a relatively more constrained AOR for an initial portion of the project life, and propose periodic AOR reevaluations as a function of project experience. In other instances, a broader initial AOR may be appropriate, with a correspondingly reduced need for periodic reevaluations. Further, operators will generally model the entire life of the project and will likely include additional acreage in the AOR in any event.

Response: EPA is retaining the approach of setting a minimum fixed frequency for reevaluating the AoR but has, based on commenters' input, changed the frequency from 10 years to at least every 5years, as specified in §146.84(e).

EPA agrees that site-specific factors, including monitoring and operational data, should be considered in the reevaluation schedule, and notes that the AoR and corrective action plan must specify the site-specific monitoring and operational conditions that warrant reevaluation, as specified in §146.84(b)(2)(ii). 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 at least every 5 year reevaluation schedule is not sufficiently protective of USDWs.

Commenter Name: Frederick R. Eames Letter ID: 0178 Commenter Organization: CCS Alliance Comment ID: 23855

Comment: EPA also proposes requiring the reevaluation of the site AoR on a periodic basis, suggesting a 10-year minimum fixed frequency for AoR reevaluation. The CCS Alliance agrees that a 10-year minimum is reasonable for reevaluating the AoR delineation, given that long-term CO2 storage may produce an AoR differing from other types of UIC injection plumes and should therefore be reevaluated to assure project safety and stability.

Response: Based on evaluation of the public comments on this topic, EPA has changed the minimum frequency for the AoR reevaluation at §146.84(e) from 10 years to at least every 5 years. EPA believes that this revised frequency addresses concerns raised by commenters representing water associations, an energy company, associations, industries, states, and environmental groups 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.

The 5-year reevaluation frequency, particularly during early stages of GS deployment, will also support EPA's adaptive approach to the GS rulemaking. EPA is using an adaptive approach to regulating GS. The Agency 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.

Commenter Name: Thomas Curtis Letter ID: 0181 Commenter Organization: American Water Works Association (AWWA) Comment ID: 23653

Comment: In its comments, AWWA makes several recommendations for the following specific items to be included in the final regulation:

- Reevaluation of the area of review annually for the first ten years, and then every five years for the remaining life of the project;

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 shehas reason to believe, based on site-specific information, that a five-year reevaluation schedule is not sufficiently protective of USDWs.

Commenter Name: Thomas Curtis Letter ID: 0181 Commenter Organization: American Water Works Association (AWWA) Comment ID: 23691

Comment: Category: Area of Review (AoR)

EPA Request for Comment: EPA seeks comment on requiring the reevaluation of the site AoR on a periodic basis, under what conditions the AoR should be reevaluated, and the appropriateness of a 10-year minimum fixed frequency for

AoR reevaluation. EPA Notice 43507.

EPA proposes to allow a phased approach to corrective action but says this may not be appropriate in all situations; therefore EPA is proposing that the Director have the discretion to decide to allow this approach, based on the understanding of relevant geologic and site conditions. EPA invites public comment on the merits and frequency of reevaluation of the AoR as well as the phased corrective action approach for GS wells. EPA Notice 43508.

AWWA Response: AWWA recommends that the area of review be reevaluated more frequently than suggested by EPA in the proposed regulation. AWWA recommends that the AoR be reevaluated annually for the first ten years of the project, and then every five years for the remaining operating period of the project. However, criteria should be established to trigger a shorter review period (based on a risk management approach) any time during the five-year time periods. For example, reevaluation of the AoR could be triggered by a shift in plume direction or sudden change in plume size or pressure. The local drinking water utilities, commissions, and planning boards need to be included in the AoR review process in the event that one of their drinking water sources becomes threatened due to a change in plume direction or behavior. Public involvement also needs to be a mandatory part of the AoR reevaluation process

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.

Commenter Name: Thomas Curtis Letter ID: 0181 Commenter Organization: American Water Works Association (AWWA) Comment ID: 23733 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Part 146.84(d) Based upon our comments in the previous section of this document,AWWA recommends revising this part to read:

At the minimum fixed frequency, not to exceed one (1) year for the first ten (10) years of the operation of the carbon sequestration project and not to exceed five (5) years after the first ten year time period, as specified in the approved area of review and corrective action plan, or when monitoring and operational conditions warrant, owners or operators must:

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.

Commenter Name: Bradley J. Field Letter ID: 0186 Commenter Organization: New York State Dept. of Environmental Conservation

Div. of Mineral Resources Comment ID:

25184 Other EPA Comment Codes and Descriptions: 3560 2.2.3.2 Conditions that merit reevaluation of the AoR (seeking comment)

Comment: M. EPA seeks comment on requiring the reevaluation of the site AoR on a periodic basis, under what conditions the AoR should be reevaluated, and the appropriateness of a 10 year minimum fixed frequency for AoR reevaluation.

NYSDEC-DMN Response: AoR reevaluation frequency could be based on the amount of CO2 injected relative to the total proposed injection volume of CO2. For example, reevaluation of AoR could be required for every 20% injected but in no event less than every five years or at any other time at the discretion of the Director. Such a frequency would allow an operator to gather sufficient operating history and monitoring data for subsequent reevaluation.

Response: EPA disagrees with the commenter's suggestion to tie the AoR reevaluation frequency to the volume or percentage of CO2 injected. EPA believes that it is important to set an AoR reevaluation frequency (i.e., at least every five years) to ensure that the project is reviewed and any necessary updates to the project plans or the permit are made on a regular schedule, regardless of the pace at which the injection is completed.

EPA believes that the commenter's proposed approach has the potential to lead to AoR reevaluation schedules that are not sufficiently frequent to ensure protection of USDWs from endangerment, if for some reason the variables (rate or volume) are such that reevaluation based on percentages are not triggered within 5 years. In addition, EPA believes this approach may complicate the administrative process of determining and tracking the reevaluation schedule.

For this reason, EPA has, at §146.84(e), adopted the 5 year interval (an adjustment from the ten year interval in the proposed rule) recommended by many commenters. EPA adds that the Director hasdiscretion to require reevaluation more frequently, such as when monitoring data differ significantly from modeled predictions, or when there are appreciable operational changes (e.g., injection rates).

Commenter Name: Robert F. Van Voorhees Letter ID: 0190 Commenter Organization: Carbon Sequestration Council Comment ID: 24336

Comment: 3. AOR Reevaluation

The proposed rule requires periodic reevaluation of the AOR determination on a frequency of at least once every ten years. We recommend an alternative approach.

Reevaluation of the AOR is a significant exercise that ought to be triggered only when information suggests that there is actually a need for reevaluation. At the same time, it is important to recognize that injection well operations provide an ongoing stream of information - injection pressure information in particular - that might suggest the need for reevaluation of the AOR. Consequently, it does not make sense to require reevaluation of the AOR on any fixed schedule; instead, it makes sense to consider the need to reevaluate the AOR on a regular basis, and to reevaluate the AOR if - but only if - there is evidence of a need to do so (i.e., if information becomes available that is materially inconsistent with assumptions underlying an existing AOR determination).

The proposed rule would already require a semi-annual report of injection operations. 73 Fed. Reg. at 43540. We recommend that these periodic reports be annual, consistent with Class II requirements, and that these reports include an assessment of the need for reevaluation of the AOR. Specifically, we support the

Ground Water Protection Council’s CO2 Committee recommendation 7.6 that

operators:

Report annually, or at a frequency acceptable to the Director, the characteristics and cumulative volumes (annual and total) of injected fluids, injection pressures, injection rates, annular pressures for each injection well, the results of any mechanical integrity tests conducted during this time period, available site integrity monitoring results, the extent of the injected CO2 and the pressure front based on current

data.

Update site operations as appropriate and site modeling results annually, or at a frequency acceptable to the Director, to reflect current data. Compare the updated results to the previous results. Identify and explain to the Director any discrepancies between the updated results and the previous results.

This approach will provide a reasonably frequent consideration of the need for reevaluation of the AOR, ensuring that the AOR is reevaluated promptly when necessary but that there is no need to reevaluate the AOR when monitoring results remain consistent with modeling results such that a requirement to reevaluate the AOR would be unnecessary.Response: EPA agrees that site-specific factors, including monitoring and operating data, should be considered in the reevaluation schedule, and notes that the AoR and corrective action plan must specify the site-specific monitoring and operational conditions that warrant reevaluation, as specified in §146.84(b)(2)(ii). 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. However, EPA believes that setting a minimum reevaluation frequency is appropriate. In the final rule, the Agency changed the minimum frequency for the AoR reevaluation at §146.84(e) from ten years to at least every five years in the final GS rule. EPA believes that this revised frequency addresses commenters' concerns about theinherent uncertainties in modeling CO2 movement, the emerging nature of GS technology, riskbased 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.

Commenter Name: Robert F. Van Voorhees Letter ID: 0190 Commenter Organization: Carbon Sequestration Council Comment ID: 24518

Comment: Rule Provisions or Federal Register Cite: 146.84 EPA Preamble Question: 14. EPA seeks comment on requiring the reevaluation of the site AoR on a periodic basis, under what conditions the AoR should be reevaluated, and the appropriateness of a 10-year minimum fixed frequency for

AoR reevaluation. EPA Notice 43507.

CSC Response: Rather than a fixed time period, CSC recommends following a performance based approach that would require reevaluation of the AOR as, but only as, it is necessary, as determined by consideration of whether there are significant unexpected changes in injection parameters or monitoring results.

Response: EPA agrees that site-specific factors should be considered in the reevaluation schedule, and notes that the AoR and corrective action plan must specify the site-specific monitoring and operational conditions that warrant reevaluation, as specified in §146.84(b)(2)(ii). 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. However, EPA believes that setting a minimum reevaluation frequency is appropriate. In the final rule, the Agency changed the minimum frequency for the AoR reevaluation at §146.84(e) from ten years to at least every five 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.

Commenter Name: Andy Horn Letter ID: 0196 Commenter Organization: Colorado Ground Water Association (CGWA) Comment ID: 23934

Comment: Issue 12. The timeframe of Area of Review Reevaluation should be revised to require more frequent reevaluation during the beginning of a projectimplementation and then less frequent reevaluation as the GS reservoir is shown to maintain integrity.

The AoR should schedule be reevaluated annually during the first five years, biannually during the five to 10-year period and then on a 5-year schedule afterwards until closure. Following closure, reevaluation should be performed on a 10-year frequency until the operator is released from liability.

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 five 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.

To the comment regarding post closure reevaluations, EPA presumes the commenter is referring to the post-injection site care period. (EPA clarifies that site closure occurs after a demonstration that the GS project no longer poses a risk to USDWs.)

Commenter Name: Paul Pike Letter ID: 0198 Commenter Organization: Ameren Corporation Comment ID: 23947

Comment: AREA OF REVIEW AND CORRECTIVE ACTION

Ameren will be required to invest a significant amount of time and resources in the initial delineation of the Area of Review ("AoR"), but we believe that requiring AoR reevaluations every ten years or at any other fixed period is unnecessary. A performance-based approach would be more appropriate, with reevaluation required upon occurrence of some triggering event; one example of a triggering event could be a significant deviation from previously modeled scenarios, provided that the level of deviation that would require reevaluation is agreed to be the permitee and the regulating agency in the permitting

process.

Response: EPA believes that periodic AoR reevaluation at a set frequency is necessary to ensure protection of USDWs from endangerment and address the uncertainties inherent in predictive modeling. Periodic AoR reevaluations at §146.84(e) ensure that a deliberate effort is made to verify, based on monitoring and operational data, that the CO2 plume is moving within the subsurface as predicted. EPA believes that less frequent reevaluations may not be sufficient to appropriately model plume and pressure front movement, establish conditions for corrective action, and ensure protection of USDWs from endangerment.

EPA clarifies that if site monitoring data agrees with the existing AoR delineation, a model recalibration may not be necessary, and the AoR reevaluation may consist of a demonstration that the current AoR delineation is adequate based on site monitoring data.Commenter Name: Craig R. Walters Letter ID: 0200 Commenter Organization: Anadarko Petroleum Corporation Comment ID: 24581

Comment: Rule Provisions: 146.84 EPA Rule Issue: 14. EPA seeks comment on requiring the reevaluation of the site AoR on a periodic basis, under what conditions the AoR should be reevaluated, and the appropriateness of a 10- year minimum fixed frequency for AoR

reevaluation. EPA Notice 43507.

Anadarko Petroleum Corporation (APC) Response: Ten years is acceptable as long as reevaluation at this frequency is coupled with the ongoing duty to monitor for changes that would trigger an earlier reevaluation of the AoR.

Response: Based on evaluation of the public comments on this topic, EPA has changed the minimum frequency for the AoR reevaluation at §146.84(e) from ten years to at least every five years. EPA believes that this revised frequency addresses concerns raised by commenters representing water associations, an energy company, associations, industries, states, and environmental groups 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.

The five-year reevaluation frequency, particularly during early stages of GS deployment, will also support EPA's adaptive approach to the GS rulemaking. EPA is using an adaptive approach to regulating GS. The Agency 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.

Commenter Name: Craig R. Walters Letter ID: 0200 Commenter Organization: Anadarko Petroleum Corporation Comment ID: 24664 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Rule Provision: 146.84(f)

Anadarko Petroleum Corporation (APC) Comments: (f) At the minimum fixed frequency, not to exceed 10 years, as specified in the APPROVED area of review and corrective action plan, or when monitoring and operational conditions

warrant, owners or operators must:

Rationale: Clarification.

Response: EPA did not make the suggested change, but agrees that AoR reevaluations must take place as specified in approved AoR and corrective action plan. EPA clarifies that owners or operators must develop, implement, and update a Director-approved AoR and corrective action plan as required under §146.84(b). EPA is developing guidance for owners or operators on how to prepare the required GS project plans. The guidance will be available on EPA's web site, at http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Thomas Curtis Letter ID: 0204Commenter Organization: American Water Works Association (AWWA) Comment ID: 22184

Comment: - Reevaluation of the Area of Review should occur annually for the first ten years, and then every five years for the remaining life of the project.

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.

Commenter Name: Diane VanDe Hei Letter ID: 0206 Commenter Organization: Association of Metropolitan Water Agencies (AMWA) Comment ID:

22211

Comment: geosequestration project. In addition, an annual reevaluation of the project’s area of review (AoR) should be conducted for at least the first 10 years of a geosequestration project and then every five years for the remaining operating period of the project. CCS is a developing technology and additional data and

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.

Commenter Name: Christopher Murray Letter ID: 0207 Commenter Organization: Pacific Northwest National Laboratory Comment ID: 22433

Comment: Area of Review Reevaluation. . .. . . . . . . . . . . . . . . . Page 6 Comparisons of monitoring data with model results should be made and reported annually, especially in the initial years of operation, to ensure that the site is behaving as expected or predicted.

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 CO2GS. 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.

Commenter Name: Christopher Murray Letter ID: 0207 Commenter Organization: Pacific Northwest National Laboratory Comment ID: 22444

Comment: AREA OF REVIEW REEVALUATION

PROPOSED REGULATION

p. 43507, c. 3 When monitoring data differ significantly from modeled redictions or when there are appreciable operational changes (e.g., rates) reevaluation may be mandated prior to the minimum fixed frequency. At no time would area of review reevaluations occur less frequently than every 10 years.

DISCUSSION

The conclusion reached by EPA that the AoR should be reevaluated over time based on comparisons of incoming monitoring and site characterization data with model predictions is very important. However, the definition of "significantly" needs to be clarified in the regulation, otherwise interpretation will be a constant point of confusion.

Based on PNNL's experience in modeling GS projects, comparison of monitoring data with model prediction, especially in the initial years of operation, would be extremely valuable in assessing our understanding of the reservoir behavior.

Models of CO2 injection into deep formations are sensitive to estimates of permeability in the formation. Permeability can vary over orders of magnitude in a formation, and this can have a large impact on estimates of pressure response, and hence the AoR. As the size of the injected CO2 plume grows with time, it will encounter areas of the formation that may have different permeability than was measured at the injection well, and the AoR may vary over time.

PNNL RECOMMENDATION

We recommend that comparisons of monitoring data with model results be made and reported annually, to ensure that the site is behaving as expected or predicted. If at any time the monitoring data or comparisons of observed and predicted pressure response suggest anomalous behavior, this could suggest a need for a reevaluation of the AoR (and AoM; see previous comments), at the discretion of the

Director.

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 addressescommenters' 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.

EPA also agrees with the commenter that inconsistencies between monitoring data and predictions about CO2 plume and pressure front movement would warrant a reevaluation of the AoR. For this reason, the AoR and corrective action plan must specify the site-specific monitoring and operational conditions that warrant reevaluation, as specified in §146.84(b)(2)(ii).

EPA is developing guidance on preparing and updating AoR and corrective action plans that will clarify the requirements for reevaluations. The guidance will be available on EPA's web site, at http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Michael Stroben Letter ID: 0209 Commenter Organization: Duke Energy Comment ID: 22684 Other EPA Comment Codes and Descriptions: 3300 2.2.1 Delineating the AoR/Modeling CO2

movement
Comment: REEVALUATION OF AREA OF REVIEW ("AoR")

Current UIC regulations require the owner/operator of a proposed injection site to determine the AoR based on the area necessary to include the calculated cone of pressure influence. The amount of CO2 that will be injected at a GS site over the life of a project will be tens if not hundreds of millions of tons. This quantity of CO2 along with uncertain dispersion characteristics makes it next to impossible to determine the correct AoR utilizing a fixed radius or simple

mathematical method.

Acceptable methods for determining the AoR should include but not be limited to multiphase fluid flow models. It is anticipated that modeling will improve over time as experience with CO2 sequestration increases. Demonstration projects should not be constrained by allowing only the use of current models. Any model based on accepted science that has been validated should be acceptable. Models should be calibrated using actual site data once it becomes available.

The AoR for a GS site for CO2 will be dynamic and in all probability irregular in shape. Based on the quantity of CO2 to be sequestered at a site, the AoR could be hundreds of square miles. A significant amount of time and money would be needed to complete an up-front evaluation of the life of a project AoR. A large portion of this effort could be wasted since the injection plumb may not travel as anticipated. As a result of this uncertainty, Duke Energy recommends a phased evaluation for the AoR. The AoR should be reviewed periodically (every ten years or as agreed upon by the Director). This would allow any necessary corrective actions to be focused where needed. This approach would allow projects to proceed more expeditiously, reduce start-up costs and because of the periodic review, provide greater protection to USDW.

Response: EPA clarifies that the AoR must be delineated as part of the permit application, asrequired at §§146.82(a)(2) and 146.82(c)(1). The Agency believes that AoR delineation using computational modeling that accounts for the multiphase flow of CO2 and native fluids (i.e., naturally occurring salty water), including density-driven flow (i.e., buoyancy), is necessary to ensure protection of USDWs from endangerment. The computational models used for this purpose are required to predict the fate of injected CO2 and changes in formation pressure. EPA believes that the requirements at 146.84(c)(1) to delineate the AoR using computational modeling are appropriate and encompass the significant processes that could affect the location of the CO2 plume and associated pressure front.

EPA agrees that modeling technology is likely to improve over time, and EPA believes that future AoR reevaluations, as required at 146.84(e), should incorporate the best modeling available. Periodic reevaluations also ensure that a deliberative effort is made to verify, based on monitoring and operational data, that the CO2 plume is moving within the subsurface as predicted. However, EPA clarifies that the AoR delineation process will not be phased. Owners or operators must delineate the entire AoR of the project prior to receiving an operating permit. This evaluation must include the entire region surrounding the geologic sequestration project where USDWs may be endangered by the injection activity.

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.

Commenter Name: Richard Guinn Letter ID: 0210 Commenter Organization: Eastman Chemical Company Comment ID: 22730

Comment: EPA seeks comment on requiring the reevaluation of the site AoR on a periodic basis, under what conditions the AoR should be reevaluated, and the appropriateness of a 10-year minimum fixed frequency for AoR reevaluation. EPA

Notice 72.

10 years is a reasonable period of time to reevaluate the site AoR during injection.

Response: Based on evaluation of the public comments on this topic, EPA has changed the minimum frequency for the AoR reevaluation at §146.84(e) from 10 years to at least every 5 years. EPA believes that this revised frequency addresses concerns raised by commenters representing water associations, an energy company, associations, industries, states, and environmental groups 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.

The 5-year reevaluation frequency, particularly during early stages of GS deployment, will also support EPA's adaptive approach to the GS rulemaking. EPA is using an adaptive approach to regulating GS. The Agency 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.

Commenter Name: John King Letter ID: 0211Commenter Organization: Shell Exploration and Production Company (SEPCo) Comment ID:

22768 Other EPA Comment Codes and Descriptions: 3400 2.2.2 Corrective Action

Comment: 2.Corrective Action

Corrective action is a familiar UIC program requirement. Given the potential scale of GS operations, EPA has proposed requirements for a corrective action plan contemplating periodic reassessment of the AOR and a phased implementation of corrective action. In general, this approach is prudent and practical, providing what will ultimately be a rigorous approach to corrective action while reducing regulatory burdens by permitting a phased implementation of corrective action requirements. However, SEPCo does not believe that a minimum frequency for reevaluation of the AOR should be required.

Recommendation:

The need for reevaluation of the AOR should be required -- if at all -- when there is site specific evidence that there is actually a need to reevaluate the AOR. Where monitoring results remain consistent with modeling results, a requirement to reevaluate the AOR should not be required.

Response: EPA believes that periodic AoR reevaluation at a set frequency is necessary to ensure protection of USDWs from endangerment and address the uncertainties inherent in predictive modeling. Periodic AoR reevaluations at §146.84(e) ensure that a deliberate effort is made to verify, based on monitoring and operational data, that the CO2 plume is moving within the subsurface as predicted. EPA believes that less frequent reevaluations or planning reevaluations only when a need is demonstrated may not be sufficient to appropriately model plume and pressure front movement, establish conditions for corrective action, and ensure protection of USDWs from endangerment. EPA agrees that site-specific factors should be considered in the reevaluation schedule, and notes that the AoR and corrective action plan must specify the site-specific monitoring and operational conditions that warrant reevaluation, as specified in §146.84(b)(2)(ii).

EPA clarifies that if site monitoring data agrees with the existing AoR delineation, a model recalibration may not be necessary, and the AoR reevaluation may consist of a demonstration that the current AoR delineation is adequate based on site monitoring data.

Commenter Name: Diane VanDe Hei Letter ID: 0213 Commenter Organization: Association of Metropolitan Water Agencies (AMWA) Comment ID:

22943 Other EPA Comment Codes and Descriptions: 3560 2.2.3.2 Conditions that merit reevaluation of the AoR (seeking comment)

Comment: - 73 FR 43507 -EPA seeks comment on requiring the reevaluation of the site AoR on a periodic basis, under what conditions the AoR should be reevaluated, and the appropriateness of a 10 year minimum fixed frequency for AoR reevaluation.

Response: As carbon sequestration is an emerging technology that has not yetbeen tested on a large scale in the U.S., AMWA believes at this time that a tenyear minimum frequency for AoR evaluation is not sufficient. AMWA recommends instead that the AoR be reevaluated annually for the first ten years of theproject and then every five years for the remaining operating period of the project.

AMWA also recommends that the final rule include criteria to trigger a shorter review period at earlier intervals should monitoring detect a sudden change in CO2 plume movement, size or pressure. In addition, AMWA recommends that local drinking water utilities be included in the AoR review process, as existing or potential drinking water sources could become threatened due to a change in plume direction or behavior. Public involvement also needs to be a mandatory

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.

EPA agrees that other aspects about a GS project may trigger the need for an AoR reevaluation, and adds that the AoR and corrective action plan must also specify the site-specific monitoring and operational conditions that warrant reevaluation, as specified in §146.84(b)(2)(ii). 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. 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.

Regarding the suggestion that local drinking water utilities be included in the AoR review process, EPA added text to §144.39(a)(5) that permit modifications would 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. EPA encourages permitting authorities to notify and involve as many stakeholders as possible about permit modifications, including drinking water organizations and local water utilities.

Commenter Name: Andrew Duguid Letter ID: 0226 Commenter Organization: Schlumberger Carbon Services Comment ID: 24021 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language; 3400 2.2.2 Corrective Action

Comment: Proposed Rule: (b) The owner or operator of a Class VI well must prepare, maintain, and comply with a plan to delineate the area of review for a proposed geologic sequestration project, periodically reevaluate the delineation, and perform corrective action that meets the requirements of this section and is acceptable to the Director. As a part of the permit application for approval by the Director, the owner or operator must submit an area of review and corrective action plan that includes the following information:

Schlumberger Suggested Revision: (b) The owner or operator of a Class VI wellmust prepare, maintain, and comply with a plan to delineate the area of review for a proposed geologic sequestration project, reevaluate the delineation, and perform corrective action that meets the requirements of this section in a manner and at a frequency acceptable to the Director. As a part of the permit application, the owner or operator must submit an area of review and corrective action plan that includes the following information:

Schlumberger Rationale: -

Response: EPA disagrees with the proposed changes and retains the provisions as proposed. For additional information on EPA's approach to AoR and corrective action, please see the final rule and preamble.

Commenter Name: Andrew Duguid Letter ID: 0226 Commenter Organization: Schlumberger Carbon Services Comment ID: 24022 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Proposed Rule: (i) The minimum fixed frequency, not to exceed 10 years, the owner or operator proposes to reevaluate the area of review;

Schlumberger Suggested Revision: Revision: (i) The owner or operator will reevaluate the AOR after two years, 5 years and then no less frequently than every 5 years for period of injection. This schedule may be relaxed at the discretion of the director in the post injection period if appropriate data exist to support the change.

Schlumberger Rationale: We feel that a frequency of every 10 years is too long to identify early discrepancies between the site performance and the site model. Seeing early difference will allow for earlier model updating and provide additional reduction in leakage risk and a better understanding of the site.

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.

Commenter Name: Andrew Duguid Letter ID: 0226 Commenter Organization: Schlumberger Carbon Services Comment ID: 24029 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Proposed Rule: (f) At the minimum fixed frequency, not to exceed 10 years, as specified in the area of review and corrective action plan, or when monitoringand operational conditions warrant, owners or operators must:

Schlumberger Suggested Revision: (f) At the same frequency as the reevaluation of the AOR as specified in 146.84(c ) (2) (i), or when monitoring and operational conditions warrant, owners or operators must:

Schlumberger Rationale: -

Response: EPA disagrees with the proposed changes and retains the provisions as proposed. EPA believes that the commenter’s suggested edit has substantively the same meaning as the proposed text. For additional information on EPA's approach to AoR and corrective action, please see the final rule and preamble.

Commenter Name: A. James Mayer Letter ID: 0230 Commenter Organization: A. J. Mayer International on behalf of the American Energy Security Initiative Comment ID:

21888

Comment: 5. EPA should provide more flexibility in operational requirements including allowing an EOR/EGR/ECBM operator to demonstrate that CO2 is sequestered rather than the prescriptive 10-year default period for reevaluation of the area of

review.

Response: EPA clarifies that the AoR reevaluation required at §146.84(e) is not intended to serve as a replacement for monitoring of the site or demonstrating containment. While the two are linked— monitoring and operational data will inform the AoR reevaluation and changes to the calculated AoR may necessitate changes to the testing and monitoring plan—EPA believes that periodic monitoring, including ground water sampling and plume and pressure front tracking, are necessary to ensure that CO2 is not endangering USDWs.

EPA is retaining the approach of setting a minimum fixed frequency for reevaluating the AoR but has, based on commenters' input, changed the frequency from 10 years to at least every 5 years, as specified in §146.84(e). EPA agrees with commenters that site-specific information is an important factor in determining an appropriate AoR reevaluation frequency, and adds that the owner or operator's AoR and corrective action plan must describe the minimum fixed frequency for reevaluating the AoR and the site-specific conditions on which this frequency is based.

Commenter Name: Steven B. Corneli Letter ID: 0234 Commenter Organization: NRG Energy, Inc. Comment ID: 23163

Comment: 2. AoR Reevaluation

The proposed rule requires a re-evaluation of the AoR determination on a frequency not to exceed once every ten years. NRG agrees with the Carbon Sequestration Council’s recommended alternative approach to re-evaluate the AoR only when site specific operation and monitoring data suggest that there is a

need for a new evaluation of the AoR. Periodic AoR re-evaluation will most likely be necessary given the enormous volumes of CO2 that would be injected into the subsurface, the lengthy timeframes likely for GS operations, and the potential uncertainty of the original model prediction. We believe that it is impractical and cost prohibitive to require re-evaluation of the AoR on a fixedschedule. Re-evaluation of the AoR should only be conducted when monitoring and testing data are determined to be inconsistent with the modeling results.

Response: EPA agrees that site-specific factors should be considered in the reevaluation schedule, and notes that the AoR and corrective action plan must specify the site-specific monitoring and operational conditions that warrant reevaluation, as specified in §146.84(b)(2)(ii). 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. However, EPA believes that setting a minimum reevaluation frequency is appropriate. In the final rule, 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.

EPA believes that periodic AoR reevaluation at a set frequency is necessary to ensure protection of USDWs from endangerment and address the uncertainties inherent in predictive modeling. Periodic AoR reevaluations at §146.84(e) ensure that a deliberate effort is made to verify, based on monitoring and operational data, that the CO2 plume is moving within the subsurface as predicted. EPA believes that less frequent reevaluations may not be sufficient to appropriately model plume and pressure front movement, establish conditions for corrective action, and ensure protection of USDWs from endangerment.

EPA clarifies that if site monitoring data agrees with the existing AoR delineation, a model recalibration may not be necessary, and the AoR reevaluation may consist of a demonstration that the current AoR delineation is adequate based on site monitoring data.

Commenter Name: Abbie Krebsbach Letter ID: 0235 Commenter Organization: Montana-Dakota Utilities Co. Comment ID: 23184

Comment: Periodic Reevaluation of Area of Review (AOR)

The proposed regulations would require operators to reevaluate the proper scope of the AOR periodically at a minimum fixed frequency to be set by the program director, currently proposed as no less than once every 10 years, with the discretion to require more frequent reevaluation. AOR reevaluation provisionsshould be triggered by reasonable parameters, taking into consideration sitespecific issues. AOR issues are inherently site-specific; different projects, and even different geographical regions of the country, likely warrant different approaches.

Montana-Dakota believes that tying reevaluation to the triggering of appropriate circumstances will provide equivalent protection for USDW while also ensuring that those projects posing greater relative risks receive greater scrutiny through more stringent reevaluation requirements, and those projects posing fewer relative risks are relieved of unnecessary regulatory burdens. At aminimum, any default period for reevaluation should be determined based on sitespecific characteristics at the time of project permitting.

Response: EPA agrees that site-specific information is an important factor in determining whenAoR reevaluations are appropriate, per §146.84(e), 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 also believes that periodic AoR reevaluation at a set frequency is necessary to ensure protection of USDWs from endangerment and address the uncertainties inherent in predictive modeling. Periodic AoR reevaluations at §146.84(e) ensure that a deliberate effort is made to verify, based on monitoring and operational data, that the CO2 plume is moving within the subsurface as predicted.

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.

Commenter Name: Mark Bohrer Letter ID: 0241 Commenter Organization: North Dakota Industrial Commission Comment ID: 23234

Comment: 14. EPA seeks comment on requiring the reevaluation of the site AoR on a periodic basis, under what conditions the AoR should be reevaluated, and the appropriateness of a 10-year minimum fixed frequency for AoR reevaluation. EPA

Notice 43507.

It is appropriate to reevaluate the AOR on a periodic basis. The conditions and frequency under which the AOR is reevaluated should be based upon monitoring.

Response: EPA agrees that site-specific factors, including monitoring data, should be considered inthe reevaluation schedule, and notes that the AoR and corrective action plan must specify the sitespecific monitoring and operational conditions that warrant reevaluation, as specified in §146.84(b)(2)(ii). 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. However, EPA believes that setting a minimum reevaluation frequency is appropriate. In the final rule, the Agency changed the minimum frequency for the AoR reevaluation at §146.84(e) from 10 years to 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.

Commenter Name: Kristin Henry Letter ID: 0242 Commenter Organization: Sierra Environmental Law Program, Sierra Club Comment ID: 23329 Other EPA Comment Codes and Descriptions: 4750 2.7.5 Comments on the merit of annual reports (seeking comment)

Comment: An update or redefinition of the AOR at a minimum fixed frequency of ten years is not sufficient. The operator should be required to submit an annual assessment under stating whether they deem a revision of the AOR necessary, explaining their reasoning based on site-specific operational and other data. The Director should examine and approve or reject this submission, requiring arevision of the AOR as needed. The same updating procedure should apply to all other plans: monitoring, closure, etc. We believe that this arrangement encourages honest and truthful reporting of data and site performance without placing excessive burdens on redefining the AOR if such revision is not needed. It also leaves a clear accountability trail for both operator and Director in case of disputes.

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.

EPA also agrees that periodic reviews of the other plans based on the AoR reevaluation is appropriate. The final GS rule includes provisions that owners or operators 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, as specified in §146.84(c), §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. These reviews must be performed within one year of an AoR reevaluation, following any significant changes to the facility (e.g., the addition of monitoring or injection wells), or when required by the Director.

EPA agrees that the AoR reevaluations offer a good opportunity to promote a dialogue between the owner or operator and the permitting authority. The final GS rule, at §§146.84(c), 146.90(j), and 146.94(d), 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. Owners or operators must review each plan and identify necessary amendments to the plan or demonstrate to the Director that no amendment is needed. These reviews must be performed within one year of an AoR reevaluation, following any significant changes to the facility (e.g., the addition of monitoring or injection wells), or when required by the Director. In no case can reviews occur less often than once every five years. For additional information, please see the final rule and the preamble for a discussion of EPA's final approach to recordkeeping and reporting.

Commenter Name: Kurt Waltzer Letter ID: 0250 Commenter Organization: Clean Air Task Force Comment ID: 22308

Comment: Even though proposed §146.84(f) requires "reevaluation" of the AOR at a "minimum" fixed frequency of ten years or "when operational and monitoring conditions warrant" (the "and" should be an "or"), §146.84 runs the risk that revisions will not be made on a timely basis. Default periods have a way of becoming the standard way of doing business. We recommend imposing a continual obligation on operators to assess whether the AOR should be revised, a requirement for an annual report stating whether circumstances during the preceding year warranted a revision, and a requirement that revisions be done when required by the Director as well as when the operator determines thatconditions warrant. To accomplish this, it will be useful to break down the concept of "reevaluation" into two ideas - "assessment" of the need to revise the AOR and the actual process of "revision." There are several portions of §146.84 that will need to be changed in order to incorporate these suggestions. We believe that these suggestions will incentivize honest and truthful reportingof data and site performance while avoiding the excessive burden of "reevaluating" or revising the Area of Review if such work is not needed. Moreover, a continuous obligation to assess whether revisions are needed, when coupled with the annual reporting requirement just suggested, will create a clear accountability trail for both operator and Director in case of disputes.

Response: EPA agrees with commenters that reevaluations of the AoR every ten years may not be sufficient, and has changed the minimum frequency for the AoR reevaluation from 10 years to at least every 5 years, as specified in §146.84(e). EPA believes that this revised frequency addresses commenters' concerns that more frequent reevaluations are necessary to address 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. To the comment that a "minimum frequency" tends to become a standard frequency, which may not be adequate for some sites, EPA clarifies that the Director has discretion to require more frequent AoR reevaluations based on site specific information to ensure that USDWs are protected from endangerment.

EPA recognizes that there are many unknowns about how GS projects will unfold including: the practicalities of permitting, operating, monitoring, and closing a GS project. To address this, the Agency is using an adaptive approach to regulating GS. The Agency 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 an annual reevaluation of the AoR is appropriate, because this timeframe would not, in many cases, allow for the generation and collection of sufficient data on which evaluate modeled predictions. However, EPA adds that the Director has discretion to require more frequent reevaluations based on site specific information such as when monitoring data differ significantly from modeled predictions, or when there are appreciable operational changes (e.g., injection rates).

EPA adds that the final GS rule includes provisions that owners or operators review and update the AoR and corrective action plan throughout the life of the project, as specified in §146.84(c). Owners or operators must review the plan and identify necessary amendments to the plan or demonstrate to the Director that no amendment is needed. The review must be performed within one year of an AoR reevaluation, following any significant changes to the facility (e.g., the addition of monitoring or injection wells), or when required by the Director. EPA believes that these new provisions could address the commenter’s suggestions.

Commenter Name: Walter L. Baker Letter ID: 0253 Commenter Organization: Utah Division of Water Quality Comment ID: 22349

Comment: RE-EVALUATION OF THE AREA OF REVIEW

Given that there is not extensive experience in tracking the movement of large volumes of injected CO2 and associated formation fluids, we support EPA's intent to require periodic re-evaluation of the Area of Review. We feel strongly thatmonitoring results should inform the Director in determining an appropriate frequency for re-evaluation and that this should be an iterative process resulting in the continuing refinement of the site-specific predictive model.

Response: EPA agrees with commenters that reevaluations of the AoR every ten years may not be sufficient, and has changed the minimum frequency for the AoR reevaluation from 10 years to 5 years, as specified in §146.84(e). EPA believes that this revised frequency addresses commenters' concerns that more frequent reevaluations are necessary to address 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.

EPA agrees that site-specific information, including monitoring data, is an important factor in determining when AoR reevaluations are appropriate, and adds that the final rule also requires owners or operators to identify in the AoR and corrective action plan site-specific triggers for reevaluation before five years. EPA anticipates that anomalous monitoring data would be one such trigger.

EPA recognizes that there are many unknowns about how GS projects will unfold including: the practicalities of permitting, operating, monitoring, and closing a GS project. To address this, the Agency is using an adaptive approach to regulating GS. The Agency 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.

Commenter Name: Michel Paque Letter ID: 0259 Commenter Organization: Ground Water Protection Council Comment ID: 24890 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: EPA Proposal: (f) At the minimum fixed frequency, not to exceed 10 years, as specified in the area of review and corrective action plan, or when monitoring and operational conditions warrant, owners or operators must:

(1) Reevaluate the area of review in the same manner specified in paragraph (c) (1) of this section;

(2) Identify all wells in the reevaluated area of review that require corrective action in the same manner specified in paragraph (c)(2) of this section;

GWPC Recommendations: (f) As specified in the approved area of review and corrective action plan, or when monitoring and operational conditions warrant,

owners or operators must

(1) Reevaluate the area of review in the same manner specified in paragraph (c) (1) of this section;

(2) Identify all wells in the reevaluated area of review that require corrective action in the same manner specified in paragraph (c)(2) of this section;

Rationale: Delete "At the minimum fixed frequency, not to exceed 10 years".Insert "approved" before "area of review" in (f).

Response: EPA disagrees with the suggested edit, and believes that periodic AoR reevaluation at a set frequency is necessary to ensure protection of USDWs from endangerment and address the uncertainties inherent in predictive modeling. Periodic AoR reevaluations at §146.84(e) ensure that a deliberate effort is made to verify, based on monitoring and operational data, that the CO2 plume is moving within the subsurface as predicted. EPA believes that less frequent reevaluations may not be sufficient to appropriately model plume and pressure front movement, establish conditions for corrective action, and ensure protection of USDWs from endangerment.

EPA clarifies that if site monitoring data agrees with the existing AoR delineation, a model recalibration may not be necessary, and the AoR reevaluation may consist of a demonstration that the current AoR delineation is adequate based on site monitoring data.

Letter ID: 0263 Commenter Organization: Interstate Oil & Gas Compact Commission Comment ID: 22800

Comment: III A. 2 Proposed Area ofReview and Corrective Action Requirements

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

IOGCC Response: Note: This comment is based on the traditional AoR requirement. Most states do an annual project review with the operator not only to evaluate the project's performance but to determine if additional measures are needed. Setting a frequency should be performance based and should be left to the Director's discretion, but in no event less than every two years. Only if thereview determines that remodeling, further study or additional downhole monitoring is necessary, should such work be done. Additionally, such additional work should be done as needed, not at a set time interval.

Response: EPA believes that periodic AoR reevaluation at a set frequency of at least every 5 years is necessary to ensure protection of USDWs from endangerment and address the uncertainties inherent in predictive modeling. Periodic AoR reevaluations at §146.84(e) ensure that a deliberate effort is made to verify, based on monitoring and operational data, that the CO2 plume is moving within the subsurface as predicted. EPA believes that less frequent reevaluations may not be sufficient to appropriately model plume and pressure front movement, establish conditions for corrective action, and ensure protection of USDWs from endangerment.

EPA adds that the AoR and corrective action plan must specify the site-specific monitoring and operational conditions that warrant reevaluation, as specified in §146.84(b)(2)(ii). 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.

Commenter Name: Steven Chester Letter ID: 0264 Commenter Organization: Michigan Department of Environmental Quality Comment ID:(MDEQ) 22835

Comment: EPA (III. A. 2.) proposes periodic re-evaluation of the Area of Review (AoR), with a 10year minimum fixed frequency.

- Staff believes that the frequency of re-evaluation should be based on the results of the initial modeling and subsequent monitoring and that a fixed 10-year minimum should not be mandated.

Response: EPA believes that periodic AoR reevaluation at a set frequency of at least every five years is necessary to ensure protection of USDWs from endangerment and address the uncertainties inherent in predictive modeling. Periodic AoR reevaluations at §146.84(e) ensure that a deliberate effort is made to verify, based on monitoring and operational data, that the CO2 plume is moving within the subsurface as predicted. EPA believes that less frequent reevaluations may not be sufficient to appropriately model plume and pressure front movement, establish conditions for corrective action, and ensure protection of USDWs from endangerment.

EPA clarifies that if site monitoring data agrees with the existing AoR delineation, a model recalibration may not be necessary, and the AoR reevaluation may consist of a demonstration that the current AoR delineation is adequate based on site monitoring data.

Commenter Name: Michael Moore Letter ID: 0265 Commenter Organization: North American Carbon Capture & Storage Association (NACCSA) Comment ID:

22852

Comment: - Area of Review Reevaluation: NACCSA questions the inclusion of a requirement that the area of review by reevaluated at least every ten years.

Response: EPA believes that periodic AoR reevaluation at a set frequency of at least every 5 years is necessary to ensure protection of USDWs from endangerment and address the uncertainties inherent in predictive modeling. Periodic AoR reevaluations at §146.84(e) ensure that a deliberate effort is made to verify, based on monitoring and operational data, that the CO2 plume is moving within the subsurface as predicted. EPA believes that less frequent reevaluations may not be sufficient to appropriately model plume and pressure front movement, establish conditions for corrective action, and ensure protection of USDWs from endangerment.

Commenter Name: Michael Moore Letter ID: 0265 Commenter Organization: North American Carbon Capture & Storage Association (NACCSA) Comment ID:

22864

Comment: 3. Area of Review Reevaluation

EPA's proposal would require that the owner or operator periodically reevaluate the AoR during the injection operation. Reevaluations would occur at a minimum fixed frequency, not to exceed 10 years, as agreed upon by the Director. We question the need for this requirement to be mandatory in light of the rule's extensive monitoring requirements. In the event that on going monitoring indicated a problem, appropriate action could be taken at that time without separately requiring a complete AoR reevaluation according to a pre-defined schedule.

We recommend that EPA provide the AoR reevaluation is at the discretion of theAdministration if the Administration determines that site-specific data, reservoir characteristics and/or monitoring or modeling data dictate that such

a reevaluation would be warranted.

Response: As described above, EPA believes that periodic AoR reevaluation at a set frequency of at least every 5 years is necessary to ensure protection of USDWs from endangerment and address the uncertainties inherent in predictive modeling. Periodic AoR reevaluations at §146.84(e) ensure that a deliberate effort is made to verify, based on monitoring and operational data, that the CO2 plume is moving within the subsurface as predicted. EPA believes that less frequent reevaluations may not be sufficient to appropriately model plume and pressure front movement, establish conditions for corrective action, and ensure protection of USDWs from endangerment.

In response to the suggestion that site-specific factors should dictate the reevaluation schedule, EPA notes that the AoR and corrective action plan must specify the site-specific monitoring and operational conditions that warrant reevaluation, as specified in §146.84(b)(2)(ii). 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.

EPA clarifies that if site monitoring data agrees with the existing AoR delineation, a model recalibration may not be necessary, and the AoR reevaluation may consist of a demonstration that the current AoR delineation is adequate based on site monitoring data.

Commenter Name: John McManus Letter ID: 0294 Commenter Organization: American Electric Power Comment ID: 25316 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: 8. Reevaluation of the Area of Review and Revision and Maintenance of Plans

Although the proposed §146.84(f) would require "reevaluation" of the aor at a "minimum" fixed frequency of ten years or "when operational and monitoring conditions warrant," the specific language of §146.84 runs the risk that revisions will not be made on a timely basis. We recommend imposing a continual obligation on operators to assess whether the aor itself, the aor and corrective action plan and all other plans required by the regulations should be revised, requiring an annual certification stating that the owner or operator has reviewed the circumstances (including operating and monitoring data) during the preceding year to determine whether these circumstances warranted a revision of the aor and any plans, and requiring that revisions be done when required by the director as well as when the operator determines that conditions warrant. To accomplish this, it is useful to break down the concept of "reevaluation" into two ideas - "assessment" of the need to revise the aor and all plans and the actual process of "revision." we believe that these suggestions will result in increased accuracy and reliability in the site performance data while avoiding work that is not warranted by the site data and site performance. Moreover, a continuous obligation to assess whether revisions are needed, when coupled with an annual certification requirement (see proposed §146.91(d) below) will create a clear accountability trail for both operator and director in case of disputes. Given this annual certification process, we believe it is unnecessary to requirea reevaluation on a fixed basis every 10 years in every case.

An annual certification requirement can also be used to enhance the ability of both Director and operators to keep track of which plans require updating and whether or not plans that ought to be updated have in fact been revised. Such a shared understanding is essential if there is to be the "ongoing dialogue" between regulators and operators that EPA anticipates. We considered the inclusion of an annual report as described in the preamble at 73 Fed. Reg. 43518, but concluded that the benefits of that particular report would be outweighed by the burden. The annual certification we are recommending would be uch simpler. We recommend:

That §146.84(f) be revised to read as follows:

"(f) (1) Notwithstanding the requirement in paragraph (2)(i) of this subsection to perform a reevaluation of the area of review at the frequency set forth in the area of review and corrective action plan, the owner or operator must also conduct the following whenever warranted by material change in the monitoring and operational data or in the evaluation of the monitoring and operational data by the owner or operator:

"(i) reevaluate the area of review by performing all of the actions specified in paragraphs (c)(1) through (3) of this section to delineate the area of review and identify all wells that require corrective action;

"(ii) perform corrective action on wells requiring corrective action in the reevaluated area of review in the same manner specified in paragraph (d) of this section; and

"(iii) submit an amended area of review and corrective action plan or demonstrate to the Director through monitoring data and modeling results that no change to the area of review and corrective action plan is needed.

"(2) Except as provided in paragraph (3) of this subsection, the owner or operator shall also conduct a reevaluation by performing all of the actions specified in subparagraphs (1)(i) through (iii) of this subsection:

"(i) Within the time periods specified in the area of review and corrective action plan for conducting such a reevaluation of the area of review; or

"(ii) If an area of review evaluation or reevaluation has not been performed pursuant to §146.84(c) and (d) for the geologic sequestration project during the preceding ten (10) years, then within six months after the passage of that 10-year period.

"(3) The Director shall waive the requirement for a reevaluation pursuant to either §146.84(f)(2)(i) or (ii) if the owner or operator demonstrates to the Director through monitoring and operational data and modeling results, such as those reviewed annually pursuant to section 146.95, that such a reevaluation is not warranted by material change."Response: EPA disagrees with the proposed changes and believes that periodic AoR reevaluation at a set frequency of at least every 5 years is necessary to ensure protection of USDWs from endangerment and address the uncertainties inherent in predictive modeling. Periodic AoR reevaluations at §146.84(e) ensure that a deliberate effort is made to verify, based on monitoring and operational data, that the CO2 plume is moving within the subsurface as predicted. EPA believes that less frequent reevaluations may not be sufficient to appropriately model plume and pressure front movement, establish conditions for corrective action, and ensure protection of USDWs from endangerment.

EPA agrees that site-specific information will influence the need for AoR reevaluations, and clarifies that if site monitoring data agrees with the existing AoR delineation, a model recalibration may not be necessary, and the AoR reevaluation may consist of a demonstration that the current AoR delineation is adequate based on site monitoring data.

Commenter Name: Scott Anderson Letter ID: 0520 Commenter Organization: Environmental Defense Fund Comment ID: 21430 Other EPA Comment Codes and Descriptions: 3300 2.2.1 Delineating the AoR/Modeling CO2

movement
Comment: We think the AOR's area of reviews need to be calculated as intended and updated as necessary. We think ten year updates is far too infrequent and we think that there are some technical problems with the way the AOR is defined in the rule. We believe the EPA's intention is to use elevated pressure as the main guide to AOR delineation, but in our judgment the definition just does not say that.

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 theinherent uncertainties in modeling CO2 movement, the emerging nature of GS technology, riskbased targeting of monitoring activities, and the unique nature of CO2 GS.

EPA agrees that the AoR definition should account for the impact of the CO2 plume on USDWs. The Agency has carefully considered all comments on the AoR definition at 146.84(a) and modified it to read as follows: The region surrounding the geologic sequestration project where USDWs may be endangered by the injection activity. The area of review is delineated using computational modeling that accounts for the physical and chemical properties of all phases of the injected CO2 stream and is based on available site characterization, monitoring, and operational data.

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



### Individual Comments

Commenter Name: Dawn A. Thorne Letter ID:

0134Commenter Organization: University of Utah Energy and Geoscience Institute on behalf of the Southwest Regional Partnership Comment

ID: 21655 Other EPA Comment Codes and Descriptions: 3530 2.2.3.1 AoR reevaluation frequency (seeking comment)

Comment: - Section 146.84(b)(2)(i) "A description of The minimum fixed frequency, not to exceed 10 years, the owner or operator proposes to reevaluate the area of review; "

Section 146.84(b)(2)(ii) "The monitoring and operational conditions that would warrant a reevaluation of the area of review prior to the next scheduled reevaluation as determined by the minimum fixed frequency established in paragraph (b)(2)(i) of this section "

Response/Discussion: The SWP recommends adopting a risk/performance-based approach to AoR re¬evaluation. Since each site is unique, it may be best for the operator to work directly with the EPA Director to establish an evaluation schedule that would occur as often as needed, but not more than needed. The SWP agrees that re-evaluations should be based on updating, revising, and calibrating computational models with site-specific data.

Response: EPA agrees that site-specific factors should be considered in the reevaluation schedule, and notes that the AoR and corrective action plan must specify the site-specific monitoring and operational conditions that warrant reevaluation, as specified in §146.84(b)(2)(ii). 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.

However, EPA believes that periodic AoR reevaluation at a set frequency is necessary to ensure protection of USDWs from endangerment and address the uncertainties inherent in predictive modeling. Periodic AoR reevaluations at §146.84(e) ensure that a deliberate effort is made to verify, based on monitoring and operational data, that the CO2 plume is moving within the subsurface as predicted. EPA believes that less frequent reevaluations may not be sufficient to appropriately model plume and pressure front movement, establish conditions for corrective action, and ensure protection of USDWs from endangerment.

EPA clarifies that if site monitoring data agrees with the existing AoR delineation, a model recalibration may not be necessary, and the AoR reevaluation may consist of a demonstration that the current AoR delineation is adequate based on site monitoring data.

Commenter Name: Christine Reimer Letter ID: 0142 Commenter Organization: National Ground Water Association Comment ID: 22591 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language; 4710 2.7.1 Proposed submissions required for permit applications (seeking comment)

Comment: Proposed Rule: 146.82(c)

Revision or Comment: Proposed Revision: 2(c ) Re-evaluation of Area of Review. After completion of the operational testing period, the Area of Review shall be re-evaluated, using a calibrated, multi-phase fluid flow model. The data collection during operational testing must be adequate for calibration of the model. If a calibrated model cannot be prepared using data collected duringoperational testing, the owner or operator shall apply for a new period of operational testing of up to two years in order to collect the required data.

No rationale provided

Response: EPA agrees that AoR reevaluations should be based on the same type of modeling that is used to perform the initial delineation, but disagrees that the suggested change is necessary. EPA clarifies that all AoR modeling (including that which supports reevaluations) should be based on accepted, verified, and validated scientific methods. Under requirements at §146.84(b), the owner or operator must demonstrate in the proposed AoR and corrective action plan, to the satisfaction of the Director that the modeled AoR (and all updates) will be based on detailed geologic data collected on the site. EPA anticipates that any model that does this in a comprehensive and satisfactory manner would be approved by the Director.

Commenter Name: Christine Reimer Letter ID: 0142 Commenter Organization: National Ground Water Association Comment ID: 22594 Other EPA Comment Codes and Descriptions: 5600 2.11 Comments related to UIC Program primacy for Class VI wells

Comment: Proposed Rule: 146.84(c)

Comment: There should be somewhere in the rules a requirement that "mutual interference effects" should trigger reevaluation and re-delineation of the AORs of all projects that are interferring with each other. In essence, when a new project is submitted for permitting, there should be a system-wide, "regional" entity charged with ensuring that AORs for each project are appropriate, andperhaps that a "hybrid" or "combo AOR" be defined for the set of mutuallyinterferring projects.

No rationale provided

Response: EPA anticipates that the impacts of multiple operators injecting into hydraulically

connected formations will be accounted for in the initial AoR calculation. EPA adds that the owner or operator must demonstrate, in the proposed AoR and corrective action plan, to the satisfaction of the Director that the modeled AoR will be based on detailed geologic data collected on the site and includes consideration of existing conditions such as the presence of multiple operators. 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 GS project.

EPA understands that the CO2 plumes for large GS projects may cross State, Tribal, Territorial, EPA Regional, or national boundaries. The final 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, as specified in §146.82(b) and ensure that they are involved in any necessary processes (e.g., development of the emergency and remedial response plan, as specified in §146.94).The Agency encourages transparency in the permitting process and anticipates that State-State/StateTribal communication on GS permitting will facilitate information sharing and encourage safe, protective projects.Because some GS projects will require coordination across State, Tribal and Territorial jurisdictions, the Agency will work with the appropriate entities to facilitate communication among States, Tribes, and Territories interested in obtaining primacy during the implementation phase of the GS regulation. Such communication may involve other organizations such as the Sierra Club, NDWAC, associations, and other experts. However, the responsibility for addressing such subjects ultimately rests with the States, Tribes, and Territories with primacy. In addition, EPA is developing guidances for states that describe the process of applying for and receiving primary enforcement responsibility (primacy) for GS Class VI wells under Section 1422 of SDWA, as well as the technical and administrative issues on developing GS regulations that are the equivalent of minimum Federal criteria and requirements. The guidance will be available at http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Bonnie Lovelace Letter ID: 0152 Commenter Organization: Montana Department of Environmental Quality (MDEQ) Comment ID:

22113

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

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.

Commenter Name: Bradley J. Field Letter ID: 0186 Commenter Organization: New York State Dept. of Environmental Conservation

Div. of Mineral Resources Comment ID:

25184 Other EPA Comment Codes and Descriptions: 3530 2.2.3.1 AoR reevaluation frequency (seeking comment)

Comment: M. EPA seeks comment on requiring the reevaluation of the site AoR on a periodic basis, under what conditions the AoR should be reevaluated, and theappropriateness of a 10 year minimum fixed frequency for AoR reevaluation.

NYSDEC-DMN Response: AoR reevaluation frequency could be based on the amount of CO2 injected relative to the total proposed injection volume of CO2. For example, reevaluation of AoR could be required for every 20% injected but in no event less than every five years or at any other time at the discretion of the Director. Such a frequency would allow an operator to gather sufficient operating history and monitoring data for subsequent reevaluation.

Response: EPA disagrees with the commenter's suggestion to tie the AoR reevaluation frequency to the volume or percentage of CO2 injected. EPA believes that it is important to set an AoR reevaluation frequency (i.e., at least every five years) to ensure that the project is reviewed and any necessary updates to the project plans or the permit are made on a regular schedule, regardless of the pace at which the injection is completed.

EPA believes that the commenter's proposed approach has the potential to lead to AoR reevaluation schedules that are not sufficiently frequent to ensure protection of USDWs from endangerment, if for some reason the variables (rate or volume) are such that reevaluation based on percentages are not triggered within 5 years. In addition, EPA believes this approach may complicate the administrative process of determining and tracking the reevaluation schedule.

For this reason, EPA has, at §146.84(e), adopted the 5 year interval (an adjustment from the ten year interval in the proposed rule) recommended by many commenters. EPA adds that the Director has discretion to require reevaluation more frequently, such as when monitoring data differ significantly from modeled predictions, or when there are appreciable operational changes (e.g., injection rates).

Commenter Name: John King Letter ID: 0211 Commenter Organization: Shell Exploration and Production Company (SEPCo) Comment ID:

22748

Comment: - Area of Review Reevaluation:

- The need for reevaluation of the AOR should be required – if at all – when there is site-specific evidence that there is actually a need to reevaluate the AOR. Where monitoring results remain consistent with modeling results, a requirement to reevaluate the AOR should not be required.

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, including monitoring data, 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 how best to evaluate 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.Commenter Name: Diane VanDe Hei Letter ID: 0213 Commenter Organization: Association of Metropolitan Water Agencies (AMWA) Comment ID:

22943 Other EPA Comment Codes and Descriptions: 3530 2.2.3.1 AoR reevaluation frequency (seeking comment)

Comment: - 73 FR 43507 -EPA seeks comment on requiring the reevaluation of the site AoR on a periodic basis, under what conditions the AoR should be reevaluated, and the appropriateness of a 10 year minimum fixed frequency for AoR reevaluation.

Response: As carbon sequestration is an emerging technology that has not yetbeen tested on a large scale in the U.S., AMWA believes at this time that a tenyear minimum frequency for AoR evaluation is not sufficient. AMWA recommends instead that the AoR be reevaluated annually for the first ten years of the project and then every five years for the remaining operating period of the project.

AMWA also recommends that the final rule include criteria to trigger a shorter review period at earlier intervals should monitoring detect a sudden change in CO2 plume movement, size or pressure. In addition, AMWA recommends that local drinking water utilities be included in the AoR review process, as existing or potential drinking water sources could become threatened due to a change in plume direction or behavior. Public involvement also needs to be a mandatory

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.

EPA agrees that other aspects about a GS project may trigger the need for an AoR reevaluation, and adds that the AoR and corrective action plan must also specify the site-specific monitoring and operational conditions that warrant reevaluation, as specified in §146.84(b)(2)(ii). 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. 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.

Regarding the suggestion that local drinking water utilities be included in the AoR review process, EPA added text to §144.39(a)(5) that permit modifications would 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. EPA encourages permitting authorities to notify and involve as many stakeholders as possible about permit modifications, including drinking water organizations and local water utilities.Comment Code: 3630 2.2.4.1 Comments in favor of allowing phased corrective action



### Individual Comments

Commenter Name: Doug Louis Letter ID: 0121 Commenter Organization: Kansas Corporation Commission Comment ID: 22079

Comment: Phased corrective action for GS wells that lie in front of the path of a CO2 plume would allow companies to concentrate current capital expenditures on wells that represent the highest risk. Wells that might be affected in the distant future would be deemed a lower risk thus given a lower priority.

Response: EPA acknowledges the commenter’s support of phased corrective action and 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. EPA clarifies that wells that might not be affected for some time are not necessarily considered to pose a lower risk; rather they are considered to not pose a risk for the first several years of injection.

Commenter Name: Dawn A. Thorne Letter ID:

0134 Commenter Organization: University of Utah Energy and Geoscience Institute on behalf of the Southwest Regional Partnership Comment

ID: 21656

Comment: - Section 146.84(3)(d) "Owners or operators of Class VI wells must perform

corrective action on all wells in the area of review that are determined to need corrective action using methods necessary to prevent the movement of fluid into or between USDWs including use of corrosion resistant materials, where appropriate."

Response/Discussion: The SWP strongly supports a phased approach to corrective actions as indicated in the Federal Register, page 43508. This discussion includes the following benefits to phased corrective actions: "There are potential benefits to implementing phased corrective action. Phasing in the corrective action would benefit the owner or operator by spreading out the burden and costs of corrective action and not delaying initiation of the GS project while corrective action is performed at wells that may not be affected by the injection for several decades. Initial corrective action would focus on those penetrations that pose a potential endangerment to USDWs from injection of CO2 in the near term. Deferring corrective action on some of the wells at the outer reaches of the predicted plume can improve USDW protection by giving these

later corrective action efforts the benefit of newer corrective action techniques. Additionally, this approach can prevent the unnecessary burden of performing corrective action in areas far from the injection zone that may never be impacted This approach would still assure that all wells in the AoR that need corrective action eventually receive it, as is the case in current UIC requirements."Response: EPA acknowledges the commenter’s support of phased corrective action and 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.

Commenter Name: Christine Reimer Letter ID: 0142 Commenter Organization: National Ground Water Association Comment ID: 22583 Other EPA Comment Codes and Descriptions: 3530 2.2.3.1 AoR reevaluation frequency (seeking comment)

Comment: Preamble Questions: EPA proposes to allow a phased approach to corrective action but says this may not be appropriate in all situations; therefore EPA is proposing that the Director have the discretion to decide to allow this approach, based on the understanding of relevant geologic and site conditions. EPA invites public comment on the merits and frequency of reevaluation of the AoR as well as the phased corrective action approach for GS wells. EPA Notice

74.

NGWA Response: Yes, phased corrective action is a good idea. It will allow targeting of those wells most in need of corrective action and optimize financial resources as the pressure/CO2 plume may deviate from the initial AoR. That's why it is important to review AoR more often than 10 years.

Response: EPA acknowledges the commenter’s support of phased corrective action and 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.

Also, as described above, EPA changed the minimum frequency for the AoR reevaluation at §146.84(e) from 10 years to 5 years in the final GS rule.

Commenter Name: Brianne Metzger Letter ID: 0151 Commenter Organization: Spectra Energy Corp Comment ID: 21821

Comment: C. Phased Corrective Action Is An Appropriate Approach.

Spectra Energy agrees with the Agency’s idea of allowing for phased corrective action. We believe this is a reasonable approach, given the potential size of the CO2 plume for commercial-scale operations (50 square miles or larger). Requiring corrective action for the entire AoR prior to injection would likely result in substantial delays in permitting and project implementation. We agree that at a minimum, as part of the AoR process, all wells that penetrate the confining or injection zone must be identified. One question that warrants clarification by EPA, however, is the ability to gain access to third party wells that may over time require corrective action. Most states requirecorrective action to be performed prior to injection and the “right of access” is taken into consideration during the adequacy determination of the corrective action plan. Some states, such as Texas, require corrective action prior to injection unless the owner/operator, after best efforts, is unable to get permission to access the property of a third party. 30 TEX. ADMIN. CODE § 305.151 (2008). Since SDWA does not provide EPA the authority to require third parties to provide access to an owner/operator for the purposes of conducting corrective action, we believe it is important for the Agency in the Final GS Rule to discuss and clarify how owner/operators and states will be expected to implement corrective action based on an iterative approach.

Response: EPA acknowledges the commenter’s support of phased corrective action and 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.

EPA agrees that securing access to all wells that require corrective action is important. In general, to meet the corrective action requirement, the owner or operator will most likely need to obtain the right of access to wells that may require corrective action, and demonstrate they have done this in their proposed AoR and corrective action plan. In the AoR and corrective action plan, the owner or operator must describe how site access will be guaranteed for future corrective action, as specified in §146.84(b)(2)(iv). The final rule retains the requirement to guarantee site access as proposed.

Commenter Name: Michael J. Miller Letter ID: 0168 Commenter Organization: Electric Power Research Institute (EPRI) Comment ID: 22501

Comment: Preamble, page 43508: "Today’s proposal would give the Director the discretion to allow owners or operators to perform corrective action on an iterative, phased basis over the operational life of a GS project."

EPRI COMMENT #7: A phased approach for corrective action simultaneously ensures permanence of the stored CO2 and cost-effective management of the storage operation. Therefore, it will encourage GS project development.

Response: EPA acknowledges the commenter’s support of phased corrective action and 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.

Commenter Name: Kyle Isakower Letter ID: 0170 Commenter Organization: American Petroleum Institute Comment ID: 24227

Comment: Rule Provisions: 146.84(f) EPA Preamble Question: 15. EPA proposes to allow a phased approach to corrective action but says this may not be appropriate in all situations; therefore EPA is proposing that the Director have the discretion to decide to allow thisapproach, based on the understanding of relevant geologic and site conditions. EPA invites public comment on the merits and frequency of reevaluation of the AoR as well as the phased corrective action approach for GS wells. EPA Notice

43508.

API Response: API supports the EPA proposal. The phased approach allows the sound economic execution of the project over time without endangering USDWs. This approach prevents an operator from the unnecessary expense of remediating wells in an area that ultimately may not be affected by the storage project. Frequency of reevaluation should be based on site performance as noted in the prior comment.

Response: EPA acknowledges the commenter’s support of phased corrective action and 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.

Regarding the comment that AoR reevaluation frequency should be based on site performance, as described above, EPA believes that periodic AoR reevaluation at a set frequency of at least every five years is necessary to ensure protection of USDWs from endangerment and address the uncertainties inherent in predictive modeling. Periodic AoR reevaluations at §146.84(e) ensure that a deliberate effort is made to verify, based on monitoring and operational data, that the CO2 plume is moving within the subsurface as predicted.

Commenter Name: James Rower Letter ID: 0173 Commenter Organization: Utility Solid Waste Activities Group (USWAG) Comment ID: 23488

Comment: Most importantly, USWAG supports a phased approach to corrective action (well plugging and repair) for CO2 GS wells as contemplated in the Proposal. 73 Fed. Reg. at 43507-08. However, a phased approach to well plugging and repair for CO2 GS wells should be available to all Owners or Operators of CO2 GS wells rather than be available only at the discretion of the Director. Id. at 43508 (proposal "would give the Director the discretion to allow owners or operators to perform corrective action on an iterative, phased basis... "); see also id. at 43536-37 (including proposed § 146.84(b), which would require Owners or Operators of Class VI wells to, inter alia, "perform corrective action that meets the requirements of this section and is acceptable to the Director").

As EPA recognizes, the AoR for CO2 GS sites may be extensive; requiring well plugging and repair to be complete for all wells in a CO2 GS AoR prior to commencement of the injection project would be overly burdensome, unnecessary, and unrealistic. This is particularly true given that the AoR may be shown, through periodic AoR reevaluations, to have expanded or shifted, identifying new wells for plugging and repair. USWAG supports an approach that would require the Owner or Operator of a Class VI well to perform pre-injection well plugging and repair on only those wells within the portion of the AoR that would be intersected by the CO2 plume or pressure front during the initial years of injection. Well plugging and repair for the rest of the AoR should be allowed totake place as the injection project progresses, ensuring that, eventually, "all wells in the AoR that need corrective action [well plugging and repair] eventually receive it." 73 Fed. Reg. at 43508.

Response: EPA acknowledges the commenter’s support of phased corrective action and 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. EPA clarifies that, if monitoring or modeling data indicate a change in the AoR (i.e., an expansion or shift), the owner or operator would need to review and amend the AoR and corrective action plan and follow the amended plan.

EPA does not agree that a phased approach to corrective action should be available to all owners or operators because phased corrective may not be appropriate at all GS sites. EPA believes that, given the wide range of conditions at GS sites, the Director is in the best position to make decisions about the appropriateness of phased corrective action based on his or her knowledge of the local geologic and site conditions. EPA is developing guidances for states that help to describe the technical and administrative issues a state may need to consider when developing GS regulations that are the equivalent of minimum federal criteria and requirements; this guidance will provided recommended approaches for Directors to exercise discretion. The guidances will be available on EPA's web site, at http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Pamela Faggert Letter ID: 0175 Commenter Organization: Dominion Comment ID: 23524

Comment: Dominion supports the requirement to conduct corrective action within the AoR provided the Director can authorize phased corrective action when warranted based on site specific performance and conditions. As with other discretionary authority proposed, there should be requirements establishing bounds for exercising such discretion to avoid arbitrary application of such authority.

Directorial discretion should be subject to guidelines as to when phased corrective action should NOT be permitted.

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 has retained it at §146.84(b)(2)(iv) in the final GS regulation.

EPA does not agree that a phased approach to corrective action should be available to all owners or operators, because phased corrective may not be appropriate at all GS sites. EPA believes that, given the wide range of conditions at GS sites, the Director is in the best position to make decisions about the appropriateness of phased corrective action based on his or her knowledge of the local geologic and site conditions. EPA is developing guidances for states that help to describe the technical and administrative issues a state may need to consider when developing GS regulations that are the equivalent of minimum federal criteria and requirements; this guidance will provided recommendedapproaches for Directors to exercise discretion. The guidances will be available on EPA's web site, at http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Quinlan J. Shea Letter ID: 0177 Commenter Organization: Edison Electric Institute Comment ID: 23587

Comment: The proposed regulations also include a requirement to conduct corrective action within the AOR, but would give the UIC program director discretion to allow corrective action to be conducted in phases over the operational life of the project. A phased corrective action approach has merit, particularly where periodic reevaluations of the AOR are to be required. A phased approach will help ensure that all necessary corrective action is taken, but also that unnecessary corrective action is avoided. It may also serve to ease the initial financial burden on operators and provide increased certainty from an investment standpoint. However, the proposed rules leave the possibility of a phased approach to the program director‘s discretion and contain no guidelines for the exercise of such discretion. Any discretionary requirement should be tempered by suitable criteria for its exercise. Likewise, any financial assurance requirements related to corrective action that may be imposed should be tied to the corrective action approach that is to be taken in any given case. For example, where phased corrective action is permitted, corresponding provisions for phased financial assurance would provide a greater ability to price the activities at issue accurately. A more detailed discussion of financial

assurance issues is below.

Response: EPA agrees that phased corrective action should be allowed and has retained this provision in the final rule §146.84(b)(2)(iv). However, EPA disagrees that decisions of the Director regarding phased corrective action would be made arbitrarily. The GS rule provides for Director's discretion because EPA believes that, given the wide range of conditions at GS sites, the Director is in the best position to make decisions about the appropriateness of phased corrective action based on his or her knowledge of the local geologic and site conditions.

EPA does not agree that a phased approach to corrective action should be available to all owners or operators, because phased corrective may not be appropriate at all GS sites. EPA believes that, given the wide range of conditions at GS sites, the Director is in the best position to make decisions about the appropriateness of phased corrective action based on his or her knowledge of the local geologic and site conditions. EPA is developing guidances for states that help to describe the technical and administrative issues a state may need to consider when developing GS regulations that are the equivalent of minimum federal criteria and requirements; this guidance will provided recommended approaches for Directors to exercise discretion. The guidances will be available on EPA's web site, at http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Regarding financial responsibility for corrective action, EPA clarifies that the owner or operator must demonstrate and maintain financial responsibility for all needed corrective action, regardless of whether it is to be phased. EPA is developing guidance on financial responsibility that will discuss approaches to how to estimate appropriate costs for all required activities. For additional information on EPA's approach to financial responsibility for Class VI wells, please see the final rule and preamble.Commenter Name: Frederick R. Eames Letter ID: 0178 Commenter Organization: CCS Alliance Comment ID: 23856

Comment: 2. Phased Corrective Action

The CCS Alliance phased correction action and believes such an approach is reasonable, given the potential size of the CO2 plume for commercial-scale GS operations. Requiring up-front corrective action for the entire AoR prior to injection could result in substantial delays in permitting and project implementation. At a minimum, as part of the AoR process, wells that penetrate the confining or injection zone must be identified. Identifying problematic wells up-front may increase short-term costs, but should reduce risk and liability over the long-term.

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.

Commenter Name: Thomas Curtis Letter ID: 0181 Commenter Organization: American Water Works Association (AWWA) Comment ID: 23692

Comment: AWWA recommends that a phased corrective action plan be developed as a result of the AoR reevaluation. This would prevent owner/operators from performing unnecessary work in the event that the plume migrates in a different direction than originally predicted. However, AWWA recommends that the required corrective actions be completed at least two years before the plume is expected to reach the specific location. Corrective actions should include reentering and replugging old or abandoned wells that have not been certified to be closed in accordance with the sequestration requirements. Also, in the case where old wells were plugged with cement that is not compatible with carbon dioxide, these wells should be re-entered and replugged. Finally, old wells for which no records exist should be re-entered and replugged to ensure that a pathway for carbon dioxide to escape is not provided.

One issue that EPA needs to consider in the final regulation is the potential cost differential for either performing all of the necessary corrective actions immediately or by phasing them in over time. If the corrective actions are phased in, EPA needs to require that the owner/operator provide financial assurance that the corrective action measures will still be performed even if the company goes out of business and the carbon dioxide plume continues to migrate.

Response: 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. EPA believes 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 agrees with the commenter that phased corrective action must account for any changes in the AoR, as demonstrated through a reevaluation or other site-specific data. For this reason, the final rule includes provisions that owners or operators review and update the AoR and corrective action plan throughout the life of the project, as specified in §146.84(c). These reviews must be performed within one year of an AoR reevaluation, following any significant changes to the facility (e.g., the addition of monitoring or injection wells), or when required by the Director.

EPA also agrees that corrective action techniques must be appropriate for CO2 GS. All corrective action performed under §146.84(d) must be appropriate to the GS site and the injectate/formation fluid chemistry to ensure that the well does not allow CO2 or other fluids to move into or endanger

USDWs.

Regarding financial responsibility for corrective action, EPA clarifies that the owner or operator must demonstrate and maintain financial responsibility for all needed corrective action, regardless of whether it is to be phased. EPA is developing guidance on financial responsibility that will discuss approaches to how best to estimate appropriate costs for all required activities. The guidance will be available on EPA's web site, at http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Bradley J. Field Letter ID: 0186 Commenter Organization: New York State Dept. of Environmental Conservation

Div. of Mineral Resources Comment ID:

25185

Comment: N. EPA invites public comment on the merits and frequency of reevaluation of the AoR as well as the phased corrective action approach for GS wells.

NYSDEC-DMN Response: Same as the two comments above for frequency of AoR reevaluation. With respect to the proposed phased corrective action approach for wells, NYSDEC-DMN agrees with the stated approach for the reasons given provided a permit can be suspended or revoked for failure to perform the corrective actions in a timely manner. However, NYSDEC-DMN believes all wells potentially impacted within the first five years of operation should be addressed prior to first injection of CO2.

Response: EPA agrees that corrective action on wells should be completed several years in advance of the anticipated arrival of the CO2 plume or pressure front. However, EPA does not believe that it is appropriate to set a specific time for completing corrective action in the regulation due to uncertainty in delineating the CO2 plume movement during certain time frames. Instead, such decisions would be incorporated into the AoR and corrective action plan for each project, as specified in §146.84(b)(2)(iv), which would be developed by the owner or operator and approved by the Director based on the geology of the site and the wells in the AoR.

All needed corrective action (whether phased or not) must be performed by the owner or operator as described in the approved AoR and corrective action plan and on the approved schedule to ensure that deficient wells in the AoR are addressed in a timely manner; failure to do so will either preclude authorization to inject or, in the case of phased corrective action, be considered a violation of the permit and subject to applicable civil, criminal, or administrative penalties under SDWA §1423.

Commenter Name: Robert F. Van Voorhees Letter ID: 0190Commenter Organization: Carbon Sequestration Council Comment ID: 24335

Comment: 2. Corrective Action

Corrective action is a familiar UIC program requirement. Given the potential scale of GS operations, EPA has proposed requirements for a corrective action plan contemplating a phased implementation of corrective action. In general, this approach is prudent and practical, providing a rigorous approach to corrective action while reducing regulatory burdens by permitting a phased implementation of corrective action requirements.

Response: EPA acknowledges the commenter’s support of phased corrective action and 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.

Commenter Name: Robert F. Van Voorhees Letter ID: 0190 Commenter Organization: Carbon Sequestration Council Comment ID: 24519

Comment: Rule Provisions or Federal Register Cite: 146.84(f) EPA Preamble Question: 15. EPA proposes to allow a phased approach to corrective action but says this may not be appropriate in all situations; therefore EPA is proposing that the Director have the discretion to decide to allow this approach, based on the understanding of relevant geologic and site conditions. EPA invites public comment on the merits and frequency of reevaluation of the AoR as well as the phased corrective action approach for GS wells. EPA Notice

43508.

CSC Response: CSC supports the EPA proposal. The phased approach allows the sound economic execution of the project over time without endangering USDWs. This approach prevents an operator from the unnecessary expense of remediating wells in an area that ultimately may not be affected by the storage project. Frequency of reevaluation should be based on site performance as noted in the prior comment.

Response: EPA acknowledges the commenter’s support of phased corrective action and 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.

Regarding the comment that some wells identified in the original AoR ultimately may not be affected by the storage project, EPA clarifies that, if monitoring or modeling data indicate a change in the AoR, the owner or operator would need to review and amend the AoR and corrective action plan and follow the amended plan.

Regarding the comment that AoR reevaluation frequency should be based on site performance, as described above, EPA believes that periodic AoR reevaluation at a set frequency of at least everyfive years is necessary to ensure protection of USDWs from endangerment and address the uncertainties inherent in predictive modeling. Periodic AoR reevaluations at §146.84(e) ensure that a deliberate effort is made to verify, based on monitoring and operational data, that the CO2 plume is moving within the subsurface as predicted.

Commenter Name: Paul Pike Letter ID: 0198 Commenter Organization: Ameren Corporation Comment ID: 23949

Comment: A CO2 GS site may have an extensive AoR and requiring well plugging and repair to be complete for all wells in a CO2 GS AoR prior to commencement of the injection project would be unnecessary, and unrealistic. We instead support an approach that would require the Owner or Operator of a Class VI well to perform pre-injection well plugging and repair on only those wells within the portion of the AoR that would be intersected by the CO2 plume or pressure front during the initial years of injection. Well plugging and repair for the rest of the AoR should be allowed to take place as the injection project progresses, ensuring that, eventually, "all wells in the AoR that need corrective action [well plugging and repair] eventually receive it." 73 Fed. Reg. at 43508.

Response: EPA acknowledges the commenter’s support of phased corrective action and 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.

Commenter Name: Craig R. Walters Letter ID: 0200 Commenter Organization: Anadarko Petroleum Corporation Comment ID: 24582

Comment: Rule Provisions: 146.84(f) EPA Rule Issue: 15. EPA proposes to allow a phased approach to corrective action but says this may not be appropriate in all situations; therefore EPA is proposing that the Director have the discretion to decide to allow this approach, based on the understanding of relevant geologic and site conditions. EPA invites public comment on the merits and frequency of reevaluation of the AoR as well as the phased corrective action approach for GS wells. EPA Notice

43508.

Anadarko Petroleum Corporation (APC) Response: APC supports the EPA proposal. The phased approach allows the sound economic execution of the project over time without endangering USDWs. This approach prevents an operator from remediating wells in an area that ultimately may not be affected by the storage project.

Allowing a phased approach for corrective action is also imperative for economic success of many projects. The upfront capital cost for sequestration will be extensive, and requiring corrective action upfront may be economically unfeasible. For instance Anadarko has spent over $10 million addressing historic wells at one of our EOR operations; this site is significantly smaller than those that may be involved in large sequestration projects. Therefore, allowing corrective actions in a phased manner will provide the flexibility needed toaddress operational and economic issues. Beyond the potential for significant economic expenditure, the availability of work-over rigs may also provide a difficult time-delay for starting sequestration projects.

Frequency of reevaluation should be based on site performance as noted in the prior comment.

Response: EPA acknowledges the commenter’s support of phased corrective action and 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.

Regarding the comment that AoR reevaluation frequency should be based on site performance, as described above, EPA believes that periodic AoR reevaluation at a set frequency of at least every five years is necessary to ensure protection of USDWs from endangerment and address the uncertainties inherent in predictive modeling. Periodic AoR reevaluations at §146.84(e) ensure that a deliberate effort is made to verify, based on monitoring and operational data, that the CO2 plume is moving within the subsurface as predicted.

Commenter Name: John Corra Letter ID: 0205 Commenter Organization: Wyoming Department of Environmental Quality (DEQ) Comment ID:

22203

Comment: 6. Various issues where we agree with US EPA that the Director should have the discretion to determine, or require:

d. Allowing for a phased approach to corrective action.

Response: EPA agrees that there are potential benefits to phased corrective action, including distributing the burden and costs of corrective action over time and not delaying initiation of the GS project. 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. However, EPA recognizes that a phased approach to corrective action may not be appropriate in all situations, and that the Director is in the best position to make decisions about the appropriateness of phased corrective action based on his or her knowledge of the local geologic and site conditions. For this reason, the GS rule affords the Director discretion in determining whether phased corrective action is appropriate at a given GS site.

Commenter Name: Olon Plunk Letter ID: 0217 Commenter Organization: Xcel Energy, Inc. Comment ID: 21559

Comment: deliberate and proactive preventive measures. In addition, Xcel Energy advocates a phased approach to well plugging and repair, allowing expansion of the scope of wells within the AoR over time on an iterative basis as dictated by actual project progress and/or new information. As noted in the proposed rule, the AoR can also include pre-existing wells owned by other owners or operators. Geologic storage project owners and operators should not be held responsible to close, repair, or replace these pre-existing wells or take other corrective action where the pre-existing well owner or responsible party has an existingobligation to do so under the law. Current or past owners or operators of preexisting wells should not be rewarded for ignoring their responsibilities under the law, and should be penalized for failure to implement already required corrective action in a timely manner. Finally, the rule should explicitly allow

Response: EPA clarifies that the purpose of the requirement to perform corrective action at §146.84(d) is to ensure that all wells in the AoR that have the potential to cause movement of CO2 or other fluids into or between USDWs receive appropriate corrective action. All needed corrective action must be performed by the owner or operator as described in the approved AoR and corrective action plan, regardless of ownership. Failure to do so would either preclude authorization to inject or, in the case of phased corrective action, be considered a violation of the permit and subject to applicable civil, criminal, or administrative penalties.

EPA clarifies that, if monitoring or modeling data indicate a change in the AoR, the owner or operator would need to review and amend the AoR and corrective action plan and follow the amended plan.

Commenter Name: Tiffany Rau Letter ID: 0224 Commenter Organization: Hydrogen Energy International Comment ID: 21677

Comment: necessary. HEI agrees with the proposal to allow a phased approach to conduct corrective action in an Area of Review that has pre-existing well penetrations.

Response: EPA acknowledges the commenter’s support of phased corrective action and 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.

Commenter Name: Brian Williams Letter ID: 0225 Commenter Organization: BP Alternative Energy North America, Inc. (BP) Comment ID: 21722

Comment: necessary. BP agrees with the proposal to allow a phased approach to conduct corrective action in an Area of Review that has pre-existing well penetrations.

Response: EPA acknowledges the commenter’s support of phased corrective action and 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.

Commenter Name: M. Granger Morgan Letter ID: 0233 Commenter Organization: Carnegie Mellon University on behalf of the CCS Reg Project Comment ID:

21908 Other EPA Comment Codes and Descriptions: 3500 2.2.3 Area of Review Reevaluation (seeking comment)

Comment: Specific comments on the proposed rule17. Iterative Area of Review: We support the proposal to reevaluate iteratively the area of review over the project life cycle and to allow phased corrective action (sec. 146.84).

Response: EPA acknowledges the commenter’s support of AoR reevaluations and phased corrective action. EPA believes that the AoR reevaluation process at §146.84(e) provides additional opportunities to verify that the models have accurately predicted movement of the CO2 plume and to make any needed adjustments to corrective action or monitoring at the site, and has retained this approach in the final rule.

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.

Commenter Name: Steven B. Corneli Letter ID: 0234 Commenter Organization: NRG Energy, Inc. Comment ID: 23164

Comment: 3. Corrective Action

EPA proposes to allow a phased approach to corrective action for GS wells. NRG agrees that this approach is prudent and practical given the enormous volumes of CO2 that would be injected for a geologic sequestration project. Implementation of a phased corrective action to address risk associated with artificial penetrations such as plugged well borings would reduce project costs and also reduce the regulatory burdens of the permitting process.

Response: EPA acknowledges the commenter’s support of phased corrective action and 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.

Commenter Name: Abbie Krebsbach Letter ID: 0235 Commenter Organization: Montana-Dakota Utilities Co. Comment ID: 23185

Comment: A phased corrective action approach as proposed in the rule has merit particularly where periodic reevaluations of the AOR are to be required. A phased approach will help ensure that all necessary corrective action is taken, but also that unnecessary corrective action is avoided.

Response: EPA acknowledges the commenter’s support of phased corrective action and 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.Regarding the comment that some wells may not need corrective action, EPA clarifies that, if monitoring or modeling data indicate a change in the AoR, the owner or operator would need to review and amend the AoR and corrective action plan and follow the amended plan. EPA clarifies that all wells in the AoR of a GS project that need corrective action must receive it at some point.

Commenter Name: Mark Bohrer Letter ID: 0241 Commenter Organization: North Dakota Industrial Commission Comment ID: 23235

Comment: 15. EPA proposes to allow a phased approach to corrective action but says this may not be appropriate in all situations; therefore EPA is proposing that the Director have the discretion to decide to allow this approach, based on the understanding of relevant geologic and site conditions. EPA invites public comment on the merits and frequency of reevaluation of the AoR as well as the phased corrective action approach for GS wells. EPA Notice 43508.

A phased approach is appropriate. Corrective action for some aspects of the project may not be necessary at the outset and a phased approach would allow an operator to optimize capital expenditures to make a project more feasible. Wholesale corrective action at the outset of a project may ultimately result in corrective action in areas unaffected by the project. In addition, the procurement of rigs and other equipment and the time necessary to conduct corrective actions in areas that might not be affected for a significant period of time could unnecessarily delay a sequestration project.

Response: EPA acknowledges the commenter’s support of phased corrective action and 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. EPA clarifies that all wells in the AoR of a GS project that need corrective action must receive it at some point.

Regarding the comment that some wells identified in the original AoR ultimately may not be affected by the storage project, EPA clarifies that, if monitoring or modeling data indicate a change in the AoR, the owner or operator would need to review and amend the AoR and corrective action plan and follow the amended plan.

Commenter Name: Walter L. Baker Letter ID: 0253 Commenter Organization: Utah Division of Water Quality Comment ID: 22350

Comment: ALLOWING FOR DIRECTOR DISCRETION IN PHASED APPROACH TO

CORRECTIVE ACTION

We support EPA's intention to allow Director's discretion in allowing a phased approach to corrective action for wells that penetrate the injection zone withinthe Area of Review. As stated above, this allows for a risk-based, sitespecific approach in setting permit requirements for the protection of USDWs and other natural resources thereby increasing the number of sites that could potentially be used for CCGS.Response: EPA acknowledges the commenter’s support of phased corrective action and 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.

EPA recognizes that a phased approach to corrective action may not be appropriate in all situations, and that the Director is in the best position to make decisions about the appropriateness of phased corrective action based on his or her knowledge of the local geologic and site conditions. For this reason, the GS rule affords the Director discretion in determining whether phased corrective action is appropriate at a given GS site.

Commenter Name: Kevin Frederick Letter ID: 0525 Commenter Organization: Wyoming Department of Environmental Quality Comment ID: 21401

Comment: And finally discretion to allow for a phased approach to corrective action.

Response: EPA agrees that there are potential benefits to phased corrective action, including distributing the burden and costs of corrective action over time and not delaying initiation of the GS project. 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. However, EPA recognizes that a phased approach to corrective action may not be appropriate in all situations, and that the Director is in the best position to make decisions about the appropriateness of phased corrective action based on his or her knowledge of the local geologic and site conditions. For this reason, the GS rule affords the Director discretion in determining whether phased corrective action is appropriate at a given GS site.

Commenter Name: Doug Louis Letter ID: 0530 Commenter Organization: Kansas Corporation Commission Comment ID: 21342

Comment: Phased corrective action for GS wells that lie in front of the path of a CO2 plume would allow companies to concentrate current capital expenditures on wells that represent the highest risk. Wells that might be affected in the distant future would be deemed a lower risk, thus given a lower priority.

Response: EPA acknowledges the commenter’s support of phased corrective action and 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. EPA clarifies that wells that might not be affected for some time are not necessarily considered to pose a lower risk; rather they are considered to not pose a risk for the first several years of injection.

Comment Code: 3660 2.2.4.2 Comments opposed to allowing phased corrective action



### Individual CommentsCommenter Name: John Hanger Letter ID: 0130 Commenter Organization: Pennsylvania Dept. of Env. Protection Comment ID: 21506

Comment: -The rule proposes phased corrective action (plugging of existing penetrations) after injection begins, but the corrective action is to occur in advance of the CO2 plume. The rule should require all corrective action to occur before injection begins, or, if phased corrective action is to be approved, then the operator must post a 100 percent performance bond with the permitting agency before the permit is issued. The performance bond is to be in the amount necessary for the permitting agency to immediately complete the corrective action should the owner/operator fail to do so in a timely manner.

Response: EPA disagrees that phased corrective action is inappropriate for GS projects, and retains this provision in the final GS regulation. EPA acknowledges the concern regarding the uncertainty in AoR modeling, and notes that addressing this is the intent of the AoR reevaluation process. EPA adds that the final rule includes a requirement that the AoR be reevaluated every 5 years or when monitoring or operational conditions warrant a reevaluation as identified at §146.84(b)(2)(ii).

Allowing phased corrective action is at the discretion of the Director. Any state, in developing a primacy package that is concerned that phased corrective action cannot be safely implemented based on the geologic or other conditions can prohibit Director's discretion to allow phased corrective

action.

EPA clarifies that owners or operators must also demonstrate and maintain financial responsibility for all corrective action, as specified in §146.85, whether it is performed prior to injection or phased.

Commenter Name: Steven Chester Letter ID: 0264 Commenter Organization: Michigan Department of Environmental Quality (MDEQ) Comment ID:

22836

Comment: EPA (I II . A. 2.) proposes phased corrective action for wells in the AoR.

- Staff believes phased corrective action should not be allowed, since there is much uncertainty in the modeled results--specifically in the timesat which the plume will reach various wells--due to typically sparse or nonexistent geologic data in the AoR.

Response: EPA disagrees that phased corrective action is inappropriate for GS projects, and retains this provision in the final GS regulation. EPA acknowledges the concern regarding the uncertainty in AoR modeling, and notes that addressing this is the intent of the AoR reevaluation process. EPA adds that the final rule includes a requirement that the AoR be reevaluated every five years or when monitoring or operational conditions warrant a reevaluation as identified at §146.84(b)(2)(ii).

Allowing phased corrective action is at the discretion of the Director. Any state, in developing a primacy package that is concerned that phased corrective action cannot be safely implemented based on the geologic or other conditions, can prohibit Director's discretion to allow phased corrective

action.

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

### Individual Comments

Commenter Name: Leslie Savage Letter ID: 0122 Commenter Organization: Railroad Commission of Texas (RRC) Comment ID: 24771 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: (b) The owner or operator of a Class VI well must prepare, maintain, and comply with a plan to delineate the AOR for a proposed geologic sequestration project, periodically reevaluate the delineation, and perform corrective action that meets the requirements of this section AT A FREQUENCY AND IN A MANNER THAT

and is acceptable to the Director. As a part of the permit application for approval by the Director , the owner or operator must submit an area of review and corrective action plan that includes the following information:

Response: EPA disagrees with the suggested change, and is retaining the approach of setting a minimum fixed frequency for reevaluating the AoR but has, based on commenters' input, changed the frequency from 10 years to at least every 5 years, as specified in §146.84(e). EPA agrees with commenters that site-specific information is an important factor in determining an appropriate AoR reevaluation frequency, and adds that the owner or operator's AoR and corrective action plan must describe the minimum fixed frequency for reevaluating the AoR and the site-specific conditions on which this frequency is based. EPA adds that the Director will evaluate the proposed plan in connection with a review of a vast amount of geologic and proposed operating data in determining whether to approve the plan. EPA is developing guidance on recommended approaches for preparing all of the required GS project plans, which will address considerations for determining an appropriate AoR reevaluation schedule. The guidance will be available on EPA's web site, at http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Leslie Savage Letter ID: 0122 Commenter Organization: Railroad Commission of Texas (RRC) Comment ID: 24772 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language; 3530 2.2.3.1 AoR reevaluation frequency (seeking comment)

Comment: (2) A description of: (i) The minimum fixed frequency, not to exceed 10 years, the owner or operator proposes to reevaluate the area of review; (ii) The monitoring and operational conditions that would warrant a reevaluation of the area of review prior to the next scheduled reevaluation as determined by the minimum fixed frequency established in paragraph (b)(2)(i) of this section.

{Suggest that there be no minimum fixed frequency for reevaluation of the AoR, but that such review be based on site-specific circumstances. }

Response: EPA believes that periodic AoR reevaluation at a set frequency of at least every 5 years is necessary to ensure protection of USDWs from endangerment and address the uncertainties inherent in predictive modeling. Periodic AoR reevaluations at §146.84(e) ensure that a deliberate effort is made to verify, based on monitoring and operational data, that the CO2 plume is moving within the subsurface as predicted. EPA believes that less frequent reevaluations may not be sufficient to appropriately model plume and pressure front movement, establish conditions for corrective action, and ensure protection of USDWs from endangerment.EPA clarifies that if site monitoring data agrees with the existing AoR delineation, a model recalibration may not be necessary, and the AoR reevaluation may consist of a demonstration that the current AoR delineation is adequate based on site monitoring data.

Commenter Name: Leslie Savage Letter ID: 0122 Commenter Organization: Railroad Commission of Texas (RRC) Comment ID: 24773 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language; 3400 2.2.2 Corrective Action

Comment: (II)(iii) How monitoring and operational data (e.g., injection rate and pressure) will be used to inform an area of review reevaluation; and

(iv) How corrective action will be conducted to meet the requirements of paragraph (d) of this section, including what corrective action will be performed prior to injection and what, if any, portions of the area of review will have corrective action addressed on a phased basis and how the phasing will be determined; how corrective action will be adjusted if there are changes in the area of review; and how THE site WILL BE accessed will be guaranteed for

future corrective action.

{Word Choice. Secure rather than guarantee. }

Response: The purpose of the corrective action requirement at §146.84(d) is to ensure that all wells in the AoR that have the potential to cause the movement of CO2 or other fluids into or between USDWs receive appropriate corrective action. In general, to meet this requirement, the owner or operator will mostly likely need to obtain the right of access to wells that may require corrective action, and demonstrate they have done this in their proposed AoR and corrective action plan. For this reason, the owner or operator must describe in the AoR and corrective action plan how site access will be guaranteed for future corrective action, as specified in §146.84(b)(2)(iv). The final rule retains the requirement as proposed.

Commenter Name: Bonnie Lovelace Letter ID: 0152 Commenter Organization: Montana Department of Environmental Quality (MDEQ) Comment ID:

22118 Other EPA Comment Codes and Descriptions: 4610 2.6.1 Testing and monitoring plan requirement (seeking comment); 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.

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 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.

Commenter Name: Michael Mudd Letter ID: 0167 Commenter Organization: FutureGen Alliance (FGIA) Comment ID: 22473 Other EPA Comment Codes and Descriptions: 4610 2.6.1 Testing and monitoring plan requirement (seeking comment)

Comment: A-7 Record Keeping and Reporting Requirements III-A-7 We support the requirement for 1) a monitoring and testing plan 2) an AoR and Correction Action Plan and 3) a Post-Injection Site Care and Site Closure plan.

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 guidance for owners or operators describing recommended approaches to prepare the project plans. The guidance will be available on EPA's web site, at http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

EPA agrees that developing, implementing, and periodically reviewing the required GS project plans is an important part of assuring that a GS project is operating properly and is crucial for the early detection of potential endangerment to USDWs. 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 also agrees that the site-specific plans required for GS projectswill maximize protection of USDWs from endangerment.

Commenter Name: Kyle Isakower Letter ID: 0170 Commenter Organization: American Petroleum Institute Comment ID: 24159 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Rule Provision: 146.84(b)

API Comments: (b) The owner or operator of a Class VI well must prepare, maintain, and comply with a plan to delineate the area of review for a proposed geologic sequestration project, periodically reevaluate the delineation, and perform corrective action that meets the requirements of this section and is IN A MANNER AND AT A FREQUENCY acceptable to the Director. As a part of the permit application, for approval by the Director the owner or operator must submit an area of review and corrective action plan that includes the following

information:

Rationale: Clarification.

Response: EPA disagrees with the suggested change, and is retaining the approach of setting a minimum fixed frequency for reevaluating the AoR but has, based on commenters' input, changed the frequency from ten years to at least every five years, as specified in §146.84(e). EPA agrees with commenters that site-specific information is an important factor in determining an appropriate AoR reevaluation frequency, and adds that the owner or operator's AoR and corrective action plan must describe the minimum fixed frequency for reevaluating the AoR and the site-specific conditions on which this frequency is based. EPA adds that the Director will evaluate the proposed plan in connection with a review of a vast amount of geologic and proposed operating data in determining whether to approve the plan. EPA is developing guidance describing recommended approaches to preparing all of the required GS project plans, which will address considerations for determining an appropriate AoR reevaluation schedule. The guidance will be available on EPA's web site at http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Kyle Isakower Letter ID: 0170 Commenter Organization: American Petroleum Institute Comment ID: 24160 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language; 3500 2.2.3 Area of Review Reevaluation (seeking comment)

Comment: Rule Provision: 146.84(b)(2)

API Comments: (2) A description of: (i) The minimum fixed frequency, not to exceed 10 years, the owner or operator proposes to reevaluate the area of review; (ii) The monitoring and operational conditions that would warrant a reevaluation of the area of review prior to the next scheduled reevaluation as determined by the minimum fixed frequency established in paragraph (b)(2)(i) of

this section. (iii) (I) How monitoring and operational data (e.g., injection rate and pressure) will be used to inform an area of review reevaluation; andNo rationale provided

Rule Provision: 146.84(b)(2)

API Comments: (iv II) How corrective action will be conducted to meet the requirements of paragraph (d) of this section, including what corrective action will be performed prior to injection and what, if any, portions of the area of review will have corrective action addressed on a phased basis and how the phasing will be determined; how corrective action will be adjusted if there are changes in the area of review; and how site access will be guaranteed

ARRANGED for future corrective action.

Rationale: Future access cannot be guaranteed for an area in advance that may not even be within the boundaries of the AOR/ project.

Response: EPA disagrees with the suggested changes. Regarding reevaluation of the AoR, EPA believes that periodic AoR reevaluation at a set frequency of at least every five years is necessary to ensure protection of USDWs from endangerment and address the uncertainties inherent in predictive modeling. Periodic AoR reevaluations at §146.84(e) ensure that a deliberate effort is made to verify, based on monitoring and operational data, that the CO2 plume is moving within the subsurface as predicted. EPA believes that less frequent reevaluations may not be sufficient to appropriately model plume and pressure front movement, establish conditions for corrective action, and ensure protection of USDWs from endangerment.

EPA clarifies that if site monitoring data agrees with the existing AoR delineation, a model recalibration may not be necessary, and the AoR reevaluation may consist of a demonstration that the current AoR delineation is adequate based on site monitoring data.

To the comment on site access, EPA clarifies that the purpose of the corrective action requirement at §146.84(d) is to ensure that all wells in the AoR that have the potential to cause the movement of CO2 or other fluids into or between USDWs receive appropriate corrective action. In general, to meet this requirement, the owner or operator will most likely need to obtain the right of access to wells that may require corrective action, and demonstrate they have done this in their proposed AoR and corrective action plan. The final rule retains the requirement as proposed.

Commenter Name: Kyle Isakower Letter ID: 0170 Commenter Organization: American Petroleum Institute Comment ID: 24167 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Rule Provision: 146.84(f)(4)

API Comments: (4) Submit an amended area of review and corrective action plan or demonstrate to the Director through monitoring data and modeling results that no

amendment CHANGE to the area of review and corrective action plan is needed.

Rationale: Clarification

Response: EPA disagrees with the suggested changes and believes the proposed text is clear as written. For additional information on EPA's approach to AoR and corrective action, please see thefinal rule and preamble.

Commenter Name: Robert F. Van Voorhees Letter ID: 0190 Commenter Organization: Carbon Sequestration Council Comment ID: 24425 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Rule Provision: 146.84(b)

Proposed CCS Group Recommendations: (b) The owner or operator of a Class VI well must prepare, maintain, and comply with a plan to delineate the area of review for a proposed geologic sequestration project, periodically reevaluate the delineation, and perform corrective action that meets the requirements of this

section and is IN A MANNER AND AT A FREQUENCY acceptable to the Director. As a part of the permit application, for approval by the Director the owner or operator must submit an area of review and corrective action plan that includes the following information:

Basis for CCS Group Comments: Clarification.

Response: EPA disagrees with the suggested change, and is retaining the approach of setting a minimum fixed frequency for reevaluating the AoR but has, based on commenters' input, changed the frequency from ten years to at least every five years, as specified in §146.84(e). EPA agrees with commenters that site-specific information is an important factor in determining an appropriate AoR reevaluation frequency, and adds that the owner or operator's AoR and corrective action plan must describe the minimum fixed frequency for reevaluating the AoR and the site-specific conditions on which this frequency is based. EPA adds that the Director will evaluate the proposed plan in connection with a review of a vast amount of geologic and proposed operating data in determining whether to approve the plan. EPA is developing guidance describing recommended approaches to preparing all of the required GS project plans, which will address considerations for determining an appropriate AoR reevaluation schedule. The guidance will be available on EPA's web site, at http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Robert F. Van Voorhees Letter ID: 0190 Commenter Organization: Carbon Sequestration Council Comment ID: 24426 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language; 3500 2.2.3 Area of Review Reevaluation (seeking comment)

Comment: Rule Provision: 146.84(b)(2)(i) & (ii)

Proposed CCS Group Recommendations: (i) The minimum fixed frequency, not to exceed 10 years, the owner or operator proposes to reevaluate the area of review; (ii) The monitoring and operational conditions that would warrant a reevaluation of the area of review prior to the next scheduled reevaluation as determined by the minimum fixed frequency established in paragraph (b)(2)(i) of

this section.

Basis for CCS Group Comments: These provisions in (i) and (ii) are rendered unnecessary by the revisions to section 146.84(b).Response: EPA believes that periodic AoR reevaluation at a set frequency of at least every five years is necessary to ensure protection of USDWs from endangerment and address the uncertainties inherent in predictive modeling. Periodic AoR reevaluations at §146.84(e) ensure that a deliberate effort is made to verify, based on monitoring and operational data, that the CO2 plume is moving within the subsurface as predicted. EPA believes that less frequent reevaluations may not be sufficient to appropriately model plume and pressure front movement, establish conditions for corrective action, and ensure protection of USDWs from endangerment.

EPA clarifies that if site monitoring data agrees with the existing AoR delineation, a model recalibration may not be necessary, and the AoR reevaluation may consist of a demonstration that the current AoR delineation is adequate based on site monitoring data.

Commenter Name: Robert F. Van Voorhees Letter ID: 0190 Commenter Organization: Carbon Sequestration Council Comment ID: 24427 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language; 3500 2.2.3 Area of Review Reevaluation (seeking comment)

Comment: Rule Provision: 146.84(b)(2)(iii)

Proposed CCS Group Recommendations: iii (I) How monitoring and operational data (e.g., injection rate and pressure) will be used to inform an area of review reevaluation; and

Basis for CCS Group Comments: Agree with EPA’s rationale.

Response: EPA acknowledges the comment and the final rule retains this provision.

Commenter Name: Robert F. Van Voorhees Letter ID: 0190 Commenter Organization: Carbon Sequestration Council Comment ID: 24437 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Rule Provision: 146.84(f)(4)

Proposed CCS Group Recommendations: (4) Submit an amended area of review and corrective action plan or demonstrate to the Director through monitoring data and modeling results that no amendment CHANGE to the area of review and corrective action plan is needed.

Basis for CCS Group Comments: Clarification

Response: EPA disagrees with the suggested change and believes the proposed text is clear as written. For additional information on EPA's approach to AoR and corrective action, please see the final rule and preamble.

Commenter Name: Craig R. Walters Letter ID: 0200 Commenter Organization: Anadarko Petroleum Corporation Comment ID: 24655 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Rule Provision: 146.84(b)Anadarko Petroleum Corporation (APC) Comments: (b) The owner or operator of a Class VI well must prepare, maintain, and comply with a plan to delineate the area of review for a proposed geologic sequestration project, periodically reevaluate the delineation, and perform corrective action that meets the requirements of this section and is IN A MANNER AND AT A FREQUENCY acceptable to the Director. As a part of the permit application, for approval by the Director the owner or operator must submit an area of review and corrective action plan that includes the following information:

Rationale: Clarification.

Response: EPA disagrees with the suggested changes and believes the proposed text is clear as written. EPA believes that review and approval of the AoR and corrective action plan, including the reevaluation frequency of at least every five years, by the Director (and in the context of all information submitted by the owner or operator with the permit application) is important to ensuring USDW protection.

Commenter Name: Craig R. Walters Letter ID: 0200 Commenter Organization: Anadarko Petroleum Corporation Comment ID: 24656 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language; 3500 2.2.3 Area of Review Reevaluation (seeking comment)

Comment: Rule Provision: 146.84(b)(2)

Anadarko Petroleum Corporation (APC) Comments: (i) The minimum fixed frequency, not to exceed 10 years, the owner or operator proposes to reevaluate the area of review;

(ii) The monitoring and operational conditions that would warrant a reevaluation of the area of review prior to the next scheduled reevaluation as determined by the minimum fixed frequency established in paragraph (b)(2)(i) of this

section.

(iii) (i) How monitoring and operational data (e.g., injection rate and pressure) will be used to inform an area of review reevaluation; and

No rationale provided

Response: EPA believes that periodic AoR reevaluation at a set frequency of at least every five years is necessary to ensure protection of USDWs from endangerment and address the uncertainties inherent in predictive modeling. Periodic AoR reevaluations at §146.84(e) ensure that a deliberate effort is made to verify, based on monitoring and operational data, that the CO2 plume is moving within the subsurface as predicted. EPA believes that less frequent reevaluations may not be sufficient to appropriately model plume and pressure front movement, establish conditions for corrective action, and ensure protection of USDWs from endangerment.

EPA clarifies that if site monitoring data agrees with the existing AoR delineation, a model recalibration may not be necessary, and the AoR reevaluation may consist of a demonstration that the current AoR delineation is adequate based on site monitoring data.Commenter Name: Craig R. Walters Letter ID: 0200 Commenter Organization: Anadarko Petroleum Corporation Comment ID: 24657 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language; 3400 2.2.2 Corrective Action

Comment: Rule Provision: 146.84(b)(2)(iv)

Anadarko Petroleum Corporation (APC) Comments: (iv II) How corrective action will be conducted to meet the requirements of paragraph (d) of this section, including what corrective action will be performed prior to injection and what, if any, portions of the area of review will have corrective action addressed on a phased basis and how the phasing will be determined; how corrective action will be adjusted if there are changes in the area of review; and how site access will be guaranteed ARRANGED for future corrective action.

Rationale: Future access cannot be guaranteed for an area in advance that may not even be within the boundaries of the AOR/ project.

Response: The purpose of the corrective action requirement at §146.84(d) is to ensure that all wells in the AoR that have the potential to cause the movement of CO2 or other fluids into or between USDWs receive appropriate corrective action. In general, to meet this requirement, the owner or operator will most likely need to obtain the right of access to wells that may require corrective action, and demonstrate they have done this in their proposed AoR and corrective action plan. The final rule retains the requirement as proposed.

Commenter Name: Craig R. Walters Letter ID: 0200 Commenter Organization: Anadarko Petroleum Corporation Comment ID: 24665 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Rule Provision: 146.84(f)(4)

Anadarko Petroleum Corporation (APC) Comments: (4) Submit an amended area of review and corrective action plan or demonstrate to the Director through monitoring data and modeling results that no amendment CHANGE to the area of review and corrective action plan is needed.

Rationale: Clarification.

Response: EPA disagrees with the suggested change and believes the proposed text is clear as written. For additional information on EPA's approach to AoR and corrective action, please see the final rule and preamble.

Commenter Name: Andrew Duguid Letter ID: 0226 Commenter Organization: Schlumberger Carbon Services Comment ID: 24030 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: Proposed Rule: (4) Submit an amended area of review and corrective action plan or demonstrate to the Director through monitoring data and modeling results thatno amendment to the area of review and corrective action plan is needed.

Schlumberger Suggested Revision: (4) Submit an amended area of review and corrective action plan or demonstrate to the Director through monitoring data and modeling results that no change to the area of review and corrective action plan is needed.

Schlumberger Rationale: -

Response: EPA disagrees with the suggested change and believes the proposed text is clear as written. For additional information on EPA's approach to AoR and corrective action, please see the final rule and preamble.

Commenter Name: Kurt Waltzer Letter ID: 0250 Commenter Organization: Clean Air Task Force Comment ID: 22309 Other EPA Comment Codes and Descriptions: 4750 2.7.5 Comments on the merit of annual reports (seeking comment)

Comment: The rule should require updating when warranted of all of the proposed "plans" and should require an annual report that summarizes whether not updates have been warranted, and whether or not updates have been undertaken

We applaud EPA for proposing to require the creation, use, and updating of various "plans" during the operating life of a facility. By creating such an iterative process, and basing it on monitoring and other operational data that become available through time, EPA can assure that facilities are managed in a way that adapts to changing circumstances. This approach also has the potential to enable what the Preamble calls an "ongoing dialogue" between operators and regulators, especially if the rule is enhanced by the annual reporting requirement suggested below for inclusion in §146.91.

Perhaps inadvertently, the proposed rule does not explicitly require updating of several of the required plans. In most but not all cases, there is a rather ambiguous requirement to "maintain" a given plan. Explicit requirements to make updates as warranted appear to be missing from provisions relating to:

Response: EPA acknowledges the commenters' support of the AoR and corrective action plan, and retains the requirement in the final regulation §146.84(b). EPA believes that the iterative process by which monitoring and operational data are used to validate the original AoR calculation, along with the combined knowledge and ongoing dialogue between the owner or operator and the Director on the local geologic conditions will be critical in developing and implementing plans that protect USDWs from endangerment.

EPA adds that the final rule includes provisions that owners or operators 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, as specified in §146.84(c), §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. These reviews must be performed within one year of an AoR reevaluation, following any significant changes to the facility (e.g., the addition of monitoring or injection wells), or when required by the Director.EPA clarifies that the final rule does not require an annual report.

Commenter Name: Michel Paque Letter ID: 0259 Commenter Organization: Ground Water Protection Council Comment ID: 24882 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: EPA Proposal: (b) The owner or operator of a Class VI well must prepare, maintain, and comply with a plan to delineate the area of review for a proposed geologic sequestration project, periodically reevaluate the delineation, and perform corrective action that meets the requirements of this section and is acceptable to the Director. As a part of the permit application for approval by the Director, the owner or operator must submit an area of review and corrective action plan that includes the following information:

(1) The method for delineating the area of review that meets the requirements of paragraph (c) of this section, including the model to be used, assumptions that will be made, and the site characterization data on which the model will be based;

GWPC Recommendations: (b) The owner or operator of a Class VI well must prepare, maintain, and comply with a plan to delineate the area of review for a proposed geologic sequestration project, reevaluate the delineation, and perform corrective action that meets the requirements of this section in a manner and at a frequency acceptable to the Director. As a part of the permit application, the owner or operator must submit an area of review and corrective action plan that includes the following information:

Rationale: Suggest deletion of "periodically." See Workgroup recommendation 7.6

from

Recommendations for the Regulatory Management of Geologic Sequestration of CO2 Under the UIC Program

Replace with "in a manner and at a frequency"

Delete "for approval by the Director,". Director’s approval is implicit in a permit application.

Response: EPA disagrees with the suggested change, and is retaining the approach of setting a minimum fixed frequency for reevaluating the AoR but has, based on commenters' input, changed the frequency from 10 years to at least every 5 years, as specified in §146.84(e). EPA agrees with commenters that site-specific information is an important factor in determining an appropriate AoR reevaluation frequency, and adds that the owner or operator's AoR and corrective action plan must describe the minimum fixed frequency for reevaluating the AoR and the site-specific conditions on which this frequency is based. EPA adds that the Director will evaluate the proposed plan in connection with a review of a vast amount of geologic and proposed operating data in determining whether to approve the plan. EPA is developing guidance describing approaches to preparing all of the required GS project plans, which will address considerations for determining an appropriate AoRreevaluation schedule. The guidance will be available on EPA's web site, at http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm.

Commenter Name: Michel Paque Letter ID: 0259 Commenter Organization: Ground Water Protection Council Comment ID: 24883 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language; 3500 2.2.3 Area of Review Reevaluation (seeking comment)

Comment: Rule Provision: 146.84(b)(2)

EPA Proposal: (2) A description of:

(i) The minimum fixed frequency, not to exceed 10 years, the owner or operator proposes to reevaluate the area of review;

(ii) The monitoring and operational conditions that would warrant a reevaluation of the area of review prior to the next scheduled reevaluation as determined by the minimum fixed frequency established in paragraph (b)(2)(i) of this section.

(iii) How monitoring and operational data (e.g., injection rate and pressure) will be used to inform an area of review reevaluation; and

GWPC Recommendations: Delete (i) and (ii)

Rationale: Suggest deletion of (i) as this is handled by "manner and at a frequency acceptable to the Director in (b)

Suggest deletion of (ii) for same reason as comment on (i)

Response: EPA believes that periodic AoR reevaluation at a set frequency of at least every 5 years is necessary to ensure protection of USDWs from endangerment and address the uncertainties inherent in predictive modeling. Periodic AoR reevaluations at §146.84(e) ensure that a deliberate effort is made to verify, based on monitoring and operational data, that the CO2 plume is moving within the subsurface as predicted. EPA believes that less frequent reevaluations may not be sufficient to appropriately model plume and pressure front movement, establish conditions for corrective action, and ensure protection of USDWs from endangerment.

EPA clarifies that if site monitoring data agrees with the existing AoR delineation, a model recalibration may not be necessary, and the AoR reevaluation may consist of a demonstration that the current AoR delineation is adequate based on site monitoring data.

Commenter Name: Michel Paque Letter ID: 0259 Commenter Organization: Ground Water Protection Council Comment ID: 24891 Other EPA Comment Codes and Descriptions: 1240 1.1.1.3 Suggested changes/edits to rule language

Comment: EPA Proposal:(3) Perform corrective action on wells requiring corrective action in the reevaluated area of review in the same manner specified in paragraph (c) (3) of this section; and(4) Submit an amended area of review and corrective action plan or demonstrate to the Director through monitoring data and modeling results that no amendment to the area of review and corrective action plan is needed.

GWPC Recommendations: (3) Perform corrective action on wells requiring corrective action in the reevaluated area of review in the same manner specified in paragraph (c)(3) of this section; and

(4) Submit an amended area of review and corrective action plan or demonstrate to the Director through monitoring data and modeling results that no change to the area of review and corrective action plan is needed.

Rationale: Suggest "change" instead of "amendment" in (4) because the term amendment is typically construed to mean an official permit modification

process.

Response: EPA disagrees with the suggested change regarding the term “amendment.” EPA believes that, in some cases an amendment to the AoR and corrective action plan may warrant a permit modification. EPA added text to §144.39(a)(5) that permit modifications, requiring public notice and comment, are 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. EPA made this change because the Agency recognizes that the AoR reevaluation process and any subsequent modifications to the plans may generate significant levels of public

interest.

EPA clarifies that if site monitoring data agrees with the existing AoR delineation, a model recalibration may not be necessary, and the AoR reevaluation may consist of a demonstration that the current AoR delineation is adequate based on site monitoring data.

Commenter Name: George Peridas Letter ID: 0534 Commenter Organization: Natural Resources Defense Council (NRDC) Comment ID: 21462 Other EPA Comment Codes and Descriptions: 4600 2.6 Proposed Plume and Pressure Front Monitoring Requirements (40 CFR 146.90)

Comment: The requirements for extensive monitoring is another example. This architectural design nature of having to continue to update the proposed plans, operational parameters, closure plans, etcetera as modeling data comes in and that is monitoring comes in. I think it is a very sound one which should be maintained

Response: EPA acknowledges the commenter's support of the AoR and corrective action plan, and retains the requirement in the final regulation §146.84(b). EPA believes that the iterative process by which monitoring and operational data are used to validate the original AoR calculation, along with the combined knowledge and ongoing dialogue between the owner or operator and the Director on the local geologic conditions will be critical in developing and implementing plans that protect USDWs from endangerment.

EPA agrees that monitoring data should be used to review model assumptions, verify computational model projections, and, when necessary, provide input for model refinements. As data are collected at an injection site, model parameters can be adjusted to match observations (i.e., for model calibration or), which in turn improves the predictive capability of the model. As a GS projectproceeds, both monitoring and modeling will evolve, with monitoring results supporting effective AoR reevaluations and leading to improved model predictions.

EPA believes that developing and following testing and monitoring plans is an important part of assuring that a GS project is operating properly and is crucial for the early detection of potential endangerment to USDWs. EPA also believes that periodic updates to the plan 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.