This comment letter response contains two parts:

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

Notes about the response letters:

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

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

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

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

• Each response letter includes: comment text; an EPA

‐ assigned comment code; and an

individual response. These are described and explained below.

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

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

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

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

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

appropriately addressed.

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

Comment ID. Additionally, one or more Comment Codes (i.e., unique topic area ID) was assigned to each discrete point raised by a commenter. This information was added to

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

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

construction requirements).

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

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

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

commenter was given a unique response.

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

Each letter response is a compilation of each comment and its individual response, compiled in the order of the original comment letter. As a result of this process, there is

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

and attention to each comment letter that was submitted.

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

Responses on each topic area are compiled and are also available in the rulemaking docket.Federal Requirements Under the Underg round Injection Control Program for Carbon Dioxide Geologic Sequestration Wells Docket No. EPA-HQ-OW-2008-0390

73 Fed. Reg. 43492 (July 25, 2008)

Comments of the Electric Power Research Institute

The Electric Power Research Institute (EPR I) is pleased to have the opportunity to provide comments on the Environmental Prot ection Agency’s proposed rule for the geologic storage (GS) of carbon dioxide (CO 2 ) under the Underground Injection Control (UIC) Program, issued on July 25, 2008 (Docket ID No. EPA-HQ-OW-2008-0390), 73 Fed. Reg. 43492.

EPRI conducts research on key issues facing th e electric power industr y on behalf of its members, energy stakeholders, and society. EPRI was established as an independent, nonprofit center for public inte rest energy and environmen tal research. Our members represent over 90% of th e electricity generated in the United States.

EPRI supports the development of a clear (unambiguous), reasonable, and flexible framework that enables wide depl oyment of geologic storage of CO 2 in a safe, environmentally protective, and cost-effective manner.

We focus our comments largely on the t echnical aspects of the proposed rule.

General comment

EPRI COMMENT#1: The proposed rule allows the EPA Director to make discretionary decisions regarding numerous program el ements including, but not limited to, characterization, monitoring, testing, and site cl osure. EPRI urges EPA to provide clarity in the final rule regarding the technical or ad ministrative criteria that trigger the need for discretionary decision making.

Specific comments

Specific EPRI comments on the EPA preamble a nd draft rule follow. EPA draft rules, interpretations or requests for comments ar e shown in bold print and are identified by page number where they appear in the Federal Register / Vol. 73, No. 144 / Friday, July 25, 2008 / Proposed Rules. EPRI comments immediately follow the EPA citation.

Preamble, page 43505: “The confining system should be of sufficient regional

thickness and lateral extent to contain the entire CO 2 plume and associated pressure front under the confining system follo wing the plume’s maximum lateral expansion.”

12/17/08EPRI COMMENT #2: The criteria for defi ning 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 b ackground will EPA use to define the location of the pressure front? Will the lateral extent of the CO 2 plume be defined by the leading edge of the dissolved plume or free-phase porti on of the plume? Given the difficulties in defining and measuring the lead ing edge of the plume and pr essure front, EPRI believes

that the technical focus shoul d be on demonstrating caprock containment, rather than tracking fronts.

Preamble, page 43505, §146.82(g), and § 146.90(d): “Today’s proposal would require owners or operators to submit geoche mical data on a) the injection zone, b) the confining zones, c) containment zone s above the confining zones in which any potentially migrating CO 2 could be trapped, d) all USDWs, and e) any other geologic zone or formation that is import ant to the proposed monitoring program.”

EPRI COMMENT #3A: EPA does not provide th e technical justification for collecting geochemical data from all zones, geologic formations and USDWs. We believe the

collection of data should be limited to zones needed to demonstrate system performance defined by the minimum siting criteria specified in §146.83(a)(1) and (a)(2). EPRI believes that system performance with the end goal of protecting USDW can be achieved by collecting geochemical data from a maximum of four zones for the reasons provided below:

1) Injection zone – during site characterization, chec k for conditions that could lead

to CO 2 -induced rock dissolution, potentially resulting in formation and injection well collapse (well integrity);

2) Primary confining zone – during site characterization, check for conditions that could lead to caprock dissolution and degr adation, potentially resulting in loss of

CO 2 containment with subsequent CO 2 movement through the primary barrier (caprock integrity);

3) Monitoring zone – a zone proposed by the applicant and approved by the EPA where performance monitoring is requir ed to take place in accordance with §146.90(d). The monitoring zone would lie between the primary confining zone and the USDW. It would be the only zone sampled on a routine schedule during

CO 2 injection operations and closur e to detect the leakage of CO 2 through the primary confining zone (performance monitoring) as noted ; and

4) USDW zone – during site characterization, collect optional samples at or near the closest USDW boundary to the injection zone to establish baseline water quality.

EPRI COMMENT #3B: Before promulgating th e rule, a comprehensive study of deep well fluid sampling techniques needs to be perf ormed to ensure that the techniques cited by EPA consistently produce samples that are re presentative of deep reservoir conditions. Otherwise, interpretation of geochemical data derived from methods producing

EPRI UIC comments Page 2 of 10 12/17/08inconsistent or non-representative sample da ta could result in e rroneous conclusions, including unnecessary or ina ppropriate corrective action. Co llecting representative deep well samples from confining zones is esp ecially challenging (see EPRI comment #14).

Preamble, page 43505-43506 and §146.83(b): “Tod ay’s proposal would provide the Director the discretion to require the owner or operator to identify and characterize additional confining and containment zo nes above the primary (i.e., lowermost) confining zone that could further impede vertical fluid movement and allow for pressure dissipation ... EPA specifically seek s comment on the merits of identifying

these additional zones.”

EPRI COMMENT #4A: From a technical pers pective, the key criterion for requiring

additional characterization should be that the applicant cannot de monstrate compliance with the minimum criteria for siting a GS project specified in §146.83(a)(1) and (a)(2) -- specifically if the applicant must rely on [a] multiple injection zones to receive the anticipated total volume ( §146.83(a)(1)) without fracturing th e formation or displacing fluids or [b] multiple confining units to impede vertical movement (§146.83(a)(2)). Section §146.83(b) requires characterization of additional zones that will impede fluid

movement, which seems redundant to §146.83 (a)(2). EPA should remove Section §146.83(b) and characterization of additional zo nes should be limited to those needed by the applicant to demonstrate capacity and containment (i.e., §146.83(a)(1) and (a)(2)).

EPRI COMMENT #4B: The minimum siting cr iterion specified in §146.83(a)(2) that states the confining zone must be “free of transmissive faults or fractur es” is too vague and open to interpretation by permit writers, potentially leading to inconsistent application throughout the United States. Fau lts and fractures are ubiquitous and quite common in deep sedimentary basins where the natural accumulation of thick sediments causes differential compaction and settling, resulting in fracturing and faulting.

However, some faults and fractures are sealed or have very low tr ansmissivity, allowing them to be present in the caprock without je opardizing containment. Therefore, if taken literally, the language in the proposed rule could limit permitt ing to those sites that are totally “free” of faults and fractures, potenti ally eliminating numerous sedimentary basins

with excellent CO 2 storage potential. EPRI recommends that the EPA remove the language “free of transmissive faults or fr actures” from this section of the rule and, instead, base its decision on a site-by-site demonstration of capacity and containment using data and model results provided by the applicant.

EPRI COMMENT #4C: Section §146.83(b) of th e rule states that the Director may require an applicant to characterize additional zones that will impede vertical fluid

movement that are “free of faults and fract ures.” Because fractur e-free confining units are rare and many confining units that contain fractures can provide effective confinement (see EPRI Comment #4B), and because §146.83(a)(2) provides for additional characterization of multiple confini ng zones if needed, EPRI recommends that

this section be eliminated.

EPRI UIC comments Page 3 of 10 12/17/08EPRI COMMENT #4D: If EPA retains the langu age in the rule requiring that confining

zones be free of transmissive faults and fractures, EPRI wa nts to point out that reliable techniques for characterizing deep faults/ fractures are rudimentary. Drilling through the fault or fracture plane and hydr aulically testing it to determin e its local transmissivity is

the most direct and reliable characteriz ation method. EPRI is concerned about any requirement to characterize the hydraulic pr operties of faults cutting across confining zones because this can only be achieved by drilling through and hydraulically testing the fault, creating potential fast-flow pathways in the caprock, potentially jeopardizing

containment.

Preamble, page 43507: “Today’s proposal does not prescribe the specific cements to be used to plug abandoned wells ...”

Also, preamble, page 43510: “EPA seek s comment regarding requirements for degradation-resistant well construction mate rials, such as acid-resistant cements and corrosion resistant casing.”

EPRI COMMENT #5: We question the adequ acy of the evidence employed to justify requiring the use of corrosion resistant cem ents in all cases. The laboratory study performed by Duguid, et al. (2004) cited by EPA exposed portland cement samples to acidified waters in an aggr essive flow configuration unc haracteristic of a borehole environment. In contrast, the field study by Crow, et al. (2008) performed on a 30 year old production well is characteri stic of a borehole environmen t. Side-wall cores of the casing, acoustic bond logs and we ll integrity tests did not show signs of casing corrosion, leakage or cement-bond degradation. While si de-wall cores of the cement indicated that

CO 2 -induced cement alteration had occurred, th e hydraulic integrity of the cement seal was still highly effective. EPA states th at the cement alteration found in the study

demonstrates that CO 2 migrated up the borehole. We que stion this conclusion and believe the study is not conclusive on this point. Gi ven that the study was performed on a natural

CO 2 reservoir, free and dissolved CO 2 are expected to be present throughout the stratigraphic column from the top of the reservoir through the c onfining unit to the

surface. Therefore, an alternativ e hypothesis is that the native CO 2 present in the confining unit or caprock adjacent to the cement seal caused the observed alteration. Evidence that the cement underwent greater a lteration at the cement-formation interface adjacent to the caprock compared to the cemen t-casing interface located further from the caprock helps support this hypothesis. Most impo rtantly, the seal maintained its integrity, exhibiting very low cement matrix, and low interface permeabilities, as determined by laboratory and vertical interf erence tests in the field, resp ectively. However, should the EPA eventually adopt a requirement for corrosi on-resistant materials, we believe EPA is taking the correct approach by not prescribing the type of corrosion-resistant cements and casing to be used in well completions a nd abandonments; a numb er of materials are available and selection of a given materi al may be driven by site-specific well

characteristics.

EPRI UIC comments Page 4 of 10 12/17/08Duguid, A., M. Radonjic, R. Bruant, T. Mandecki, G. Scherer, and M. Celia. 2004. The Effect of CO2 Sequestration on Oil Well Ce ments. Presented at the Greenhouse Gas Technologies Conference (GHGT–7), September 5–9, 2004. Vancouver, Canada.

Crow, W., D.B. Williams., B. Carey, M. Celia , and S. Gasda. 2008. CO2 Capture Project Field Study of A Wellbore from a Natura l CO2 Reservoir. Presented at the 7 th Annual Conference on Carbon Capture and Se questration, May 5–8, 2008. Pittsburgh, Pennsylvania.

Preamble, page 43507: “EPA seeks comment on the applicability of computational

fluid flow models for delinea ting the AoR of GS sites.”

Also preamble, page 43507 “EPA seeks comm ent on requiring the reevaluation of the site AoR on a periodic basis, und er what conditions the AoR should be reevaluated, and the appropriateness of a 10 year minimum fixed frequency for

AoR reevaluation.”

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 appropria te and provides a flexible, phased approach to assessing the number of abandoned wells requiring mitigation.

The proposed rule uses an arbitrary 10-year minimum fixe d frequency for AoR reevaluation and does not present the techni cal 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 includi ng the observed speed of the plume and its anticipated arrival time at th e edge of the computed AoR. Or, if plume speed cannot be observed directly (e.g., no CO 2 is observed in wells completed in the monitoring zone) nor indirectly (e.g., using remote monitoring techniques like seismic), then the model predictions for CO 2 plume speed and arrival at the AoR boundary should be used to set the reevaluation frequency.

Preamble, page 43508: “Today’s proposal woul d give the Director the discretion to allow owners or operators to perform correct ive 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 CO 2 and cost-effective management of the storage operation. Therefore, it will encourage GS project development.

Preamble, page 43509: “EPA seeks comment on the proposed GS well requirements for depth of surface casing, the cementing of long-string casing, and construction with a packer set opposite a cemented interval.”

EPRI UIC comments Page 5 of 10 12/17/08EPRI COMMENT #8: Cementing the entire length of the long-string casing is not standard practice in the oil and natural gas industry and not adequately justified by EPA in the preamble to the rule. Compared to CO 2 , natural gas is highly flammable and, in the absence of pressure gradients, much more buoyant because of its lower density and higher mobility in the formation. In contrast, during CO 2 injection, where pressure gradients are large and buoyancy effects are co mparatively small, models show that CO 2 dries out the formation around the well (P ruess and Spycher, 2006), significantly lowering the risk of cement corrosion. Th erefore, cementing standards adopted for natural gas wells designed to be protective of USDWs should be more than adequate for ensuring safe and permanent sequestration of the injected CO 2 . Wellbore conditioning prior to cementing and a well designed and executed cementing operation have greater impact on the cement integrity than the overall length of the cement seal. EPRI encourages the EPA to develop and adopt less stringent cementing requirements for the long-string casing, consistent with natural gas wells currently in use. (See for example, Chapter 4 Development, Regulation, and Conservation of Oil and Gas Resources, Article 3 Requirements, Section 1722.4 Cementing Casing, in the State of California, California Code of Regulations , Title 14: Natural Resources; Division 2: Department of Conservation, Publication No. PRC04).

Pruess, K. and N. Spycher, 2006. ECO2N - A New TOUGH2 Fluid Property Module for

Studies of CO 2 Storage in Saline Aquifers, Proceedings: TOUGH Symposium 2006, Lawrence Berkeley National Laboratory, Berkeley, California, May 15–17, 2006.

Preamble, page 43509: “EPA seeks comment on the merits of horizontal well drilling techniques for GS wells and the applicability of well construction requirements discussed in this proposal.”

EPRI COMMENT #9: We agree with the EPA arguments for this technology and,

therefore, believe the merits of horizontal injection wells ar e correctly stated. In addition, the rule provides flexibility and will encour age GS project developm ent, especially in lower permeability formations n eeding additional injectivity.

Preamble, page 43511: “In case of well fa ilure, a down-hole shut-off device would isolate the injectate below USDWs, rather than just below the surface. EPA seeks comment on the merits of requiring do wn-hole shut-off valves in GS wells.”

EPRI COMMENT #10: Since a downhole shut-off valve would just prevent CO 2 from flowing from the injection zone up the production tubing to the atmosphere if the wellhead were damaged, it doesn’t serve a f unction in protecting USDWs. Further, because, recorded cases of catastrophic wellhead failure are rare, and the valve would not protect CO 2 from backflowing to the surface should the packer also fail, EPRI does not believe that a down-hole shut-off valve provides more safety than an easier-to-maintain

near-surface shut-off valve. In addition, a downhole valve will inte rfere with logging operations, mechanical integrity testing, vi deo inspection logs, etc. Downhole tools

EPRI UIC comments Page 6 of 10 12/17/08typically associated with thes e activities are deployed by wi reline inside the production tubing, requiring that the opera tor needlessly kill the well, and remove the tubing and valve to gain access to the section of well below the valve position.

Preamble, page 43512: “In summary, EPA is soliciting comment on whether CO 2 injection should be allowed into an in jection zone above the lowermost USDW, when the Director determines that geologi c conditions (e.g., thousands of feet of intervening formations between the injection zone and the overlying and/or underlying USDWs) exist that will prevent fluid movement into adjacent USDWs. EPA is also requesting comments on whether aquifer exemptions should be allowed for the purpose of Class VI injection, and under what conditions should such aquifer exemptions be approved. Fina lly, EPA seeks comment on whether the Agency should set a minimum in jection depth requirement for CO 2 GS, rather than require that such injection take place below the lowermost USDW.”

EPRI COMMENT #11: EPRI believes that a propos ed GS site should be considered to be protective of USDWs as long as the applicant demonstrates to the EPA that it meets the minimum siting criteria specified in §146.83(a)(1), (a)(2) (also see EPRI Comment #4). Whether or not the injection zone lies above or below the lower most USDW, or below a given depth, is not important as long as the minimum criteria are met.

Preamble, page 43513: “EPA seeks co mment on the use of tracers in CO 2 GS operations, and any potential impact of tr acers on human health or ecosystems as they relate to USDWs.”

EPRI COMMENT #12: Too little is known about how tracers (especia lly PFT's) partition

between the CO 2 , water and oil phase and how they adsorb onto organic or mineral surfaces at reservoir conditions (high temperatur es and pressure) to conclude that they act

as conservative tracers. Any tracer added to the CO 2 that is soluble in water will lose mass to the water phase and will not act as a conservative tracer for the CO 2 phase. EPA should not require the use of tracers unless and until more is known about their fate and

transport.

Preamble, page 43514 & 43515: “Under today’s proposal, owners or operators would be required to track th e subsurface extent of the CO 2 plume and pressure front using pressure gauges in the first fo rmation overlying the confining zone or using indirect geophysical techniques (e.g., seismic, electrical, gravity, or electromagnetic surveys) or other down-hole CO 2 detection tools, monitor for geochemical changes in subsurface format ions, and if directed, monitor at the surface. Today’s proposal would also require owners or operators to monitor ground water quality and geochemical ch anges above the confining system.”

EPRI COMMENT #13: Refer to EPRI comment #2 for questions regarding how EPA

intends to define each front and the need to demonstrate containment instead. Also, EPRI

EPRI UIC comments Page 7 of 10 12/17/08comments #3B and #14 for representative geochemical sampling and sampling of lowyield formations, respectively.

EPRI is not aware of any remote field meas urements, including seismic techniques, that

can be used to determine th e position of the dissolved CO 2 front. Therefore, definition of

the CO 2 front should be limited to th e leading edge of the free-CO 2 plume if remote monitoring techniques are used. Remote mon itoring techniques may not work in all geologic settings. Very small pressure changes measured in the first formation overlying the confining zone may be masked by other pressure effects. For example, relatively large barometric pressure fluctuations tran slated down the well to the monitoring zone, changes in fluid pressure caused by n earby pumping wells, or limited transducer resolution, accuracy and electroni c noise may interfere with or distort the pressure signal, making it difficult to measure the pressure fr ont. Appropriateness of detection tools will

need to be evaluated on a site -by-site basis, and the proposed rule recognizes this need. However, EPRI believes the emphasis should be on demonstrating containment through

careful characterization of th e storage reservoir and caproc k, coupled with predictive CO 2 fate and transport models of reservoir and cap rock performance, rather than on plume and pressure front tracking, as the latter may not be practical or possible.

Preamble, page 43515: “Monitoring within the confining zone for pressure, pH, salinity, or the presence of dissolved minerals, heavy metals, or organic contaminants requires direct access to the subsurface via monitoring wells.”

EPRI COMMENT #14: See EPRI comment #3B. We believe that measuring pressure in a deep confining zone is possible, but collecting representative deep well samples from confining zones for geochemical characterizat ion may not be techni cally possible (with emphasis on representative ). This could lead to errone ous results and conclusions. EPA currently requires that all mon itoring wells be purged of “stagnant” groundwater in the well prior to sampling to produce a “fresh” sa mple from the adjacent formation that is representative of the formation fluid. Low-yi eld confining units are typically purged dry prior to sampling or pumped at a very slow rate to prevent the formation from being dewatered. In either case, this typically results in significant sample depressurization when sampling deep wells. Important geoche mical parameters incl uding pH, alkalinity, and dissolved metals (which are depende nt on groundwater pH) will change when depressurization occurs, produc ing erroneous analytical re sults. The u-tube sample method described by Friefeld et al (2005) cannot be used to overcome this limitation for low-yield confining zones.

Freifeld B.M., R.C. Trautz, Y.K. Kharaka, T.J. Phelps, L.R. Myer, S.D. Hovorka, D.J. Collins (2005) The U-tube: a novel system fo r acquiring borehole fluid samples from a deep geologic CO 2 sequestration experiment. Journa l of Geophysical Research, 110,

B10203, doi:10.1029/2005JB003735.

EPRI UIC comments Page 8 of 10 12/17/08Preamble, page 43517: “EPA seeks comment on the merits of requiring plans for monitoring, AoR, and post-injection site ca re as part of a permit application.”

EPRI COMMENT #15: Submitting a monitoring and AoR plan with the application seems practical since these act ivities will occur in the reas onably near future after the permit is issued. However, requiring too much specificity in a post-injection site care plan as part of the permit application may cement in methods that will be obsolete by the time the GS project enters the post-inject ion phase, 20-50 years from the permit date. EPA could instead require that a preliminary post-injection site care plan be submitted at the time of application outlining the general approach and parameters needed to

demonstrate closure, and that a final detailed plan be pr epared for approval a certain period of time prior to implementation of this phase.

Preamble, page 43518: “Today’s proposal would require owners or operators to submit a well plugging plan at the same time the permit application is submitted and to have this plan approved by the Director.”

EPRI COMMENT #16: Again, well plugging and abandonment are activities that take place far in the future, perhaps several decades off. Therefore, submitting this plan at the time of permit application could render it obs olete when implementation is needed. EPA could instead require a preliminary plan outlin ing the general approach at the time of application and require that a final detailed plugging and abandonment plan be submitted for approval a certain period of time prior to implementation of this activity, allowing for the incorporation and use of new/better technologies.

Preamble, page 43519-43520: “EPA requests comment on the proposed use of a tentative 50-year fixed timeframe that could be modified at the Di rector’s discretion based on monitoring and modeling data.”

EPRI COMMENT #17: EPA’s 50-year fixed timeframe described in the preamble appears to be based on profe ssional judgment interpreting a limited number of citations and/or modeling scenarios. We question the need for defining a fixed timeframe of any length because it runs counter to the EPA’s implied intent to close sites based on the owner/operator’s ability to meet specific pe rformance criteria defined in §146.93(b). (See

EPRI comment #2, #13, and #18 re garding these criteria (i .e., front tracking and stability)).

Preamble, page 43520: “Once the owners or operators provide documentation that demonstrates that the models predicting CO 2 movement are consistent with monitoring results and that there are no lo nger risks of endangerment to USDWs, they could request that the Director authoriz e site closure. EPA is also proposing to allow the Director to shorten or length en the 50-year time frame based on performance of the site... EPA wishes to emphasize that site closure cannot occur

EPRI UIC comments Page 9 of 10 12/17/08until monitoring and modeling data establis h to the Director’s satisfaction that potential risks of endangerment to USDWs have ceased.”

EPRI COMMENT #18: EPA’s requirement for demonstrating plume stability for site closure is based on the ability to both observe and successfully model the speed and stability of the advancing CO 2 front, a very discrete boundary that is difficult to define, model accurately when complex reservoir he terogeneity and fast flow pathways are present, and measure in the field on a la rge scale. (See also EPRI’s comment #2 on defining the front). If remote methods like su rface seismic, cross-well seismic or gravity

are not successful in tr acking front position, and CO 2 is never directly detected in sentinel

observations wells, then m odel validation based on CO 2 front position may be questioned. In such a case, if the model predicts the continued advance of the CO 2 front

while the observed data do not, the EPA Director may not be satisfied with the absence of a potential risk of endangerment to USDWs and may unnecessarily delay site closure for

decades. EPRI recommends that the final ru le contain alternative provisions for site

closure if model validation is unsuccessful.

EPRI UIC comments Page 10 of 10 12/17/08Letter ID: 0168

Commenter: Michael J. Miller Organization: Electric Power Research Institute (EPRI)

Letter ID: 0168 Comment ID: 22491 Letter Lines: 42 to 46

Comment Code: 1260 1.1.1.5 More certainty/stringency is needed

Comment: EPRI COMMENT#1: The proposed rule allows the EPA Director to make discretionary decisions regarding numerous program el ements including, but not limited to, characterization, monitoring, testing, and site closure. EPRI urges EPA to provide clarity in the final rule rega rding the technical or administrative criteria that trigger the need for discretionary decision making.

Individual Response: EPA is developing guidances for Stat es that describe the process of applying for and receiving primary enforcement au thority (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 re quirements. The guidance

will describe areas of Directorial discretion and considerations for how that discretion would be exercised. This guidance will be available on EPA’s website at http://water.epa.gov/type/groundwat er/uic/wells_se questration.cfm.

The Agency believes that the Class VI requirement s balance site-specific flexibility with USDW protection. Rather than setting performance or technology-based st andards for GS projects, EPA is adopting a flexible approach, where operators of GS projects would develop and implement site-specific plans for delineating the AoR, tes ting and monitoring the s ite, performing corrective action, and post-injection site car e. EPA believes that the plans— which would be reviewed and approved by the Director and pe riodically updated throughout the life of the project—promote an ongoing dialogue between the operator and the Dire ctor that will encourage use of the most appropriate technologies for a particular project.

Letter ID: 0168 Comment ID: 22492 Letter Lines: 56 to 70

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

Comment Code: 4650 2.6.5 CO2 plume and pressure fr ont tracking (seeking comment)

Comment: Preamble, page 43505: "The confining syst em 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 lateral expansion."

EPRI COMMENT #2: The criteria for defini ng the leading edge of the plume and associated pressure front are not specif ied in the rule, nor is the basis for determining if these criteria are met -- physical measurement or numerical

1computation. 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? Give n the difficulties in defining and measuring the leading edge of the plume and pressure front, EP RI believes that

the technical focus should be on demonstra ting caprock containment, rather than tracking fronts.

Individual 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 fr ont (defined at §146.81) is the zone of elevated pressure that is created by the injection of CO2 in to the subsurface. The pressure front of a CO2 plume refers to a zone where there is a pressure differential suffici ent to cause the movement of injected fluids or

formation fluids into a USDW. Th e pressure front includes all ar eas 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 defi nes the edge of the pressure front is dependent on properties of the injection and confini ng zones, including permeability, porosity, and compressibility, the distance between the in jection zone and the lowermost USDW, and operational conditions including injection pressure and rate. For these reasons, the definition of the pressure front is site- and pr oject-specific, and a single pressu re value can not be provided for all sites. EPA is developing guidance on AoR and co rrective 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 guida nce 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/groundwat er/uic/wells_se questration.cfm.

EPA is also developing guidance on testing and monitoring to assi st 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 techno logies and recommended approaches for implementing a testing a nd monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs, injecti on 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/groundwat er/uic/wells_sequestration.cfm. In addition, in January 2009, DOE published a best practices manual entitled "Monitoring, Verificat ion, 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.

2Letter ID: 0168 Comment ID: 22493 Letter Lines: 72 to 114

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

Comment Code: 4660 2.6.6 Geochemical monitoring

Comment: Preamble, page 43505, §146.82(g), and § 146.90(d): "Today’s proposal would require owners or operators to submit geoc hemical data on a) the injection zone, b) the confining zones, c) containment z ones above the confining zones in which any potentially migrating CO2 could be tr apped, d) all USDWs, and e) any other geologic zone or formation that is im portant to the proposed monitoring program."

EPRI COMMENT #3A: EPA does not provide the technical justification for collecting geochemical data from all zone s, geologic formations and USDWs. We

believe the collection of data should be limited to zones needed to demonstrate system performance defined by the mini mum siting criteria specified in §146.83(a)(1) and (a)(2). EPRI believes that system performance with the end goal of protecting USDW can be achieved by collecting geochemical data from a

maximum of four zones for th e reasons provided below:

1) Injection zone -- during site charac terization, check for conditions that

could lead to CO2-induced rock dissol ution, potentially resulting in formation and injection well collapse (well integrity);

2) Primary confining zone -- during site characterization, ch eck for conditions that could lead to caprock dissolution a nd degradation, potentially resulting in loss of CO2 containment with subsequent CO2 movement through the primary barrier (caprock integrity);

3) Monitoring zone -- a z one proposed by the applican t and approved by the EPA where performance monitoring is required to take place in accordance with §146.90(d). The monitoring zone would lie betw een the primary confining zone and the USDW. It would be the only zone sa mpled on a routine schedule during CO2 injection operations and closure to detect the l eakage of CO2 through the primary confining zone (performance monitoring) as noted ; and

4) USDW zone -- during site characteri zation, collect optional samples at or near the closest USDW boundary to the inje ction zone to establish baseline water quality.

EPRI COMMENT #3B: Before promulgating th e rule, a comprehensive study of deep well fluid sampling techniques needs to be performed to ensure that the techniques cited by EPA consistently produ ce samples that are representative of deep reservoir conditions. Otherwise, interpretation of geochemical data derived from methods producing incons istent or non-representati ve sample data could result in erroneous conclusions, incl uding unnecessary or inappropriate

3corrective action. Collecting representative deep well samples from confining zones is especially challengi ng (see EPRI comment #14).

Individual Response: The GS regulation, at §146.82(a)(6), re quires the owner or operator to submit baseline geochemical data on subsurface geologic formations. EPA is not specifying for

which formations this information should be su bmitted to allow flexibility, but examples may include the following formations: a) the injection zone, b) the confining zones, c) containment zones above the confining zones in which any pot entially migrating CO2 could be trapped, d) all USDWs, and e) any other geologic zone or formation that is important to the proposed monitoring program. The Director has the authority to request a dditional geochemical data as

well.

EPA believes that the necessary sampling techni ques are available, and is developing guidance on site characterization for GS proj ects to assist owners or oper ators and Directors in evaluating permit requirements and applications under §146. 82. The guidance provides recommendations regarding characterizing the regi onal geology and hydrogeology of a proposed GS site as well as performing the necessary geochemical, geomechani cal, and geophysical analyses of the injection and confining zone. The guidance can be found on EPA’s website at http://water.epa.gov/type/groundwat er/uic/wells_se questration.cfm.

On the topic of sampling, EPA recognizes that the collection of repr esentative ground water samples from depth poses challenges and that speci al methods, such as U-tubes, will be needed to preserve the integrity of such samples. EP A is developing guidance on testing and monitoring to assist owners or operators and Directors in evaluating requiremen ts under §146.90, including proposed monitoring plans. The guidance descri bes available technol ogies and recommended approaches for implementing a testing a nd monitoring plan, including pre-operational geophysical logging and testing of injection wells, MITs, injecti on 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/groundwat er/uic/wells_se questration.cfm.

Regarding the comment about the technical justif ications and difficulty of sampling within the confining zone, EPA clarifies th at §146.90(d) requires owners and operators to monitor ground water quality and geochemical changes above the confining zone(s), rath er than within the confining zone.

Letter ID: 0168 Comment ID: 22494 Letter Lines: 116 to 134

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

Comment: Preamble, page 43505-43506 and §146.83(b): "Toda y’s proposal would provide the Director the discretion to require the owner or operator to identify and characterize additional confining and cont ainment zones above the primary (i.e.,

4lowermost) confining zone that could furt her impede vertical fluid movement and allow for pressure dissipation ... EPA specifically seeks comment on the merits of identifying these additional zones."

EPRI COMMENT #4A: From a technical perspe ctive, the key criterion for requiring

additional characterization should be th at the applicant ca nnot demonstrate compliance with the minimum criteria fo r siting a GS project specified in §146.83(a)(1) and (a)(2) -- specifically if the applicant must rely on [a] multiple injection zones to receive th e anticipated total volume (§146.83(a)(1)) without fracturing the formation or displa cing fluids or [b] multiple confining units to impede vertical movement (§146.83(a)(2)). Section §146.83(b) requires

characterization of additional zones that will impede fluid movement, which seems redundant to §146.83 (a)(2). EPA should remove Section §146.83(b) and

characterization of additional zones shoul d be limited to those needed by the applicant to demonstrate capacity and containment (i.e., §146 .83(a)(1) and (a) (2)).

Individual Response: EPA retains the requirement to iden tify additional containment/confining zones, if required by the Di rector, as proposed (§146.83(b)). EPA acknowledges that such additional zones may not be needed in all circumst ances, and clarifies that this requirement is at the Director's discretion, based on his or her understanding of a part icular site. EPA believes that, in some situations, the presence of additional confining and containment zones above the primary (i.e., lowermost) confining zone can improve USDW protecti on. These layers could further impede vertical fluid movement and al low for pressure dissipation, and also provide additional sites for monitoring, mitigation, and re mediation. The Agency's decision is supported by commenters representing states, water associati ons, and an electric utility who assert that these requirements promote a flexible, risk-base d, site-specific approach to characterizing and permitting a site for GS projects, and are intende d to improve understanding of the project as a whole and promote better modeling of the site.

Letter ID: 0168 Comment ID: 22495 Letter Lines: 136 to 151

Comment Code: 3110 2.1.1 Proposed siting requirements (i.e., injection/confining zones, trapping mechanism)

Comment: EPRI COMMENT #4B: The minimum siting crit erion specified in §146.83(a)(2) that states the confining zone mu st be "free of transmissive faults or fractures" is too vague and open to interpretation by permit writers, potentially leading to inconsistent application throughout the Un ited States. Faults and fractures are ubiquitous and quite common in deep se dimentary basins where the natural

accumulation of thick sediments causes differential compaction and settling, resulting in fracturing and faulting. Howe ver, some faults and fractures are sealed or have very low transmissivit y, allowing them to be present in the caprock without jeopardizing containment. Therefore, if taken literally, the language in the proposed rule could limit permitting to those sites that are totally "free" of faults and fractures , potentially eliminating numerous

5sedimentary basins with excellent CO2 stor age potential. EPRI recommends that the EPA remove the language "free of transm issive faults or fr actures" from this section of the rule and, instead, ba se its decision on a site-by-site demonstration of capacity and containment using data and model results provided by the applicant.

Individual Response: EPA disagrees that the language is va gue. The Agency believes that the requirement at §146.83(a)(2) that the confining zone be free of transmissive faults or fractures is appropriate for Class VI wells a nd is necessary to ensure contai nment of the injectate and that requiring the confining zone to be free of transmissive faults maximizes protection of USDWs from endangerment. Class I hazardous waste injec tion well operators must also meet a similar requirement that the site is free of transmissive faults or fracture s; they have successfully made such demonstrations in the past. EPA is deve loping guidance on site characterization for GS projects to assist owners or operators and Directors in ev aluating permit requirements and applications under §146.82. The gui dance provides recommendati ons regarding characterizing the regional geology and hydrogeology of a propos ed GS site as well as performing the necessary geochemical, geomechanical, and geophysic al analyses of the injection and confining zone. The guidance can be found on EPA’s website at http://water.epa.gov/type/groundwater /uic/wells_sequestration.cfm.

Letter ID: 0168 Comment ID: 22496 Letter Lines: 153 to 159

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

Comment: EPRI COMMENT #4C: Section §146.83(b) of the rule states that the Director may require an applicant to characterize additional zones that will impede vertical

fluid movement that are "free of faults and fractures." Because fracture-free confining units are rare and many confin ing units that contain fractures can provide effective confinement (see EPRI Comment #4B), and because §146.83(a)(2) provides for additional characterization of multiple confining zones if needed,

EPRI recommends that this section be eliminated.

Individual Response: The Agency believes that the re quirement at §146.83(a)(2) that the confining zone(s) be free of transmissive faults or fractures is appropriate for Class VI wells and is necessary to ensure containment of the inject ate and that requiring the confining zone to be

free of transmissive faults maximizes protection of USDWs from endangerment.

EPA retains the requirement to identify additi onal containment/confining zones, if required by the Director, as proposed (§146.83(b)). EPA acknowle dges that such additional zones may not be needed in all circumstances, and clarifies that this requirement is at the Director's discretion, based on his or her understanding of a particular site. EPA believes that, in some situations, the presence of additional confining and containm ent zones above the primary (i.e., lowermost) confining zone can improve USDW protection. These layers could further impede vertical fluid movement and allow for pressure dissipation, an d also provide additional sites for monitoring,

6mitigation, and remediation.

Letter ID: 0168 Comment ID: 22497 Letter Lines: 161 to 170

Comment Code: 3110 2.1.1 Proposed siting requirements (i.e., injection/confining zones, trapping mechanism)

Comment: EPRI COMMENT #4D: If EPA retains the la nguage in the rule requiring that confining zones be free of transmissive faults and fractures, EPRI wants to point out that reliable tec hniques for characterizing deep faults/fractures are rudimentary. Drilling through the fault or fracture plane and hydraulically testing it to determine its local transmissi vity is the most direct and reliable

characterization method. EPRI is concerned about any requirement to characterize the hydraulic properties of fa ults cutting across confin ing zones because this can only be achieved by drilling through a nd hydraulically testing the fault, creating potential fast-flow pathways in the caprock, potentially jeopardizing

containment.

Individual Response: While core samples obtained through drilling and hydraulic testing are direct methods to obtain such information, geophysical techniques such as seismic or electromagnetic surveys can also be used in ma ny geologic settings to demonstrate the absence of or identify and characterize the presence of faults or fractures. At sites where deep faults (even with little or no surface expression) are present, processing and interpreting data from multiple geophysical sensing methods has been shown to dete ct faults better than analysis of data from individual methods (Goussev et al, 2004). Drilling through faults or fractures with appropriate well design, materials, and operati on, would not result in an increas e in their permeability or a decrease in CO2 containment properties of the re lated CO2 storage reservoir. In some cases, the use of complementary drilling and geophysical methods might provide the most dependable characterization of potential transmissive faults and fractures. EPA adds th at the Director must evaluate all geologic data on the site to ensure protection of USDWs from endangerment before approving a site for a GS project.

Letter ID: 0168 Comment ID: 22498 Letter Lines: 172 to 216

Comment Code: 3862 2.3.3.1 Use of corrosion-resistant construction materials (seeking comment)

Comment Code: 3864 2.3.3.2 Use of corrosion-resistant cements (seeking comment)

Comment Code: 5100 2.8.1 Injection well plugging activ ities (seeking comment) (40 CFR 146.92)

Comment: Preamble, page 43507: "Today’s proposal doe s not prescribe the specific cements to be used to plug abandoned wells..."

Also, preamble, page 43510: "EPA seek s comment regarding requirements for

7degradation-resistant well construction materials, such as acid-resistant cements and corrosion resistant casing."

EPRI COMMENT #5: We question the adequacy of the evidence em ployed to justify requiring the use of corrosion resistant cements in all cases. The laboratory study performed by Duguid, et al. (2004) cited by EPA exposed portland cement samples to acidified waters in an aggre ssive flow configurat ion uncharacteristic of a borehole environment. In contrast, the field study by Crow, et al. (2008) performed on a 30 year old production we ll is characteristic of a borehole

environment. Side-wall cores of th e casing, acoustic bond logs and well integrity tests did not show signs of casing corrosion, leakage or cement-bond degradation. While side-wa ll cores of the cement indicated that CO2-induced cement alteration had occurred, the hydrauli c integrity of the cement seal was still highly effective. EP A states that the cement alteration found in the study demonstrates that CO2 migrated up the bor ehole. We question this conclusion and believe the study is not conclusive on this point. Given that the study was performed on a natural CO2 reservoir, free and dissolved CO2 are expected to be present throughout the stratigraphic column from the top of the reservoir through the confining unit to the surface. Therefore, an alternative hypothesis is that the native CO2 present in the c onfining unit or caprock adjacent to the

cement seal caused the observed alterati on. Evidence that the cement underwent greater alteration at the cement-forma tion interface adjacent to the caprock compared to the cement-casi ng interface located further from the caprock helps support this hypothesis. Most importantly, the seal maintained its integrity, exhibiting very low cement matrix, a nd low interface permeabilities, as determined by laboratory and vertical interference tests in the field, respectively. However, should the EPA eventually adopt a requirement for corrosion-resistant materials, we believe EPA is taking the correct approach by not prescribing the type of corrosion-resistant cements and casing to be used in well completions and abandonments; a numbe r of materials are available and selection of a given material may be driven by site-specific well

characteristics.

Duguid, A., M. Radonjic, R. Bruant, T. Mandecki, G. Scherer, and M. Celia. 2004. The Effect of CO2 Sequestra tion on Oil Well Cements. Presented at the Greenhouse Gas Technologies Conference (GHGT-7), September 5-9, 2004. Vancouver, Canada.

Crow, W., D.B. Williams., B. Carey, M. Celia, and S. Gasda. 2008. CO2 Capture Project Field Study of A Wellbore from a Na tural CO2 Reservoir. Presented at the 7th Annual Conference on Carbon Captur e and Sequestration, May 5-8, 2008. Pittsburgh, Pennsylvania.

Individual Response: EPA considered both field and lab st udies in developing the requirements for Class VI well construction. The Duguid stud y referenced by the commenter examined a CO2-saturated brine flux condition that may be fo und in some injection environments such as a saline aquifer. The Crow study mentioned was a we ll that produced gaseous CO2 from a natural

8CO2 deposit. In the studies examined, cement alteration and corrosion was found to occur at differing rates. Factors such as contact with brine, temperature, CO2 flux, and time between cement curing and CO2 exposure may all be rele vant. See the discussion of Class VI well construction requirements in the preamble to th e final GS rule for additional information.

EPA clarifies that corrosion-resist ant cement is not specifically re quired in a Class VI injection well. Rather, as stated in §146.86(b)(1), casings and cement used must have sufficient strength and be designed for the life of the sequestration project. Further, materi als must meet standards listed in the rule and be compatible with fluids with which the materials may be expected to come into contact. Therefore, some well materials may need to be acid-resistant and some may not if they do not come in contact with the CO2 stream or other corrosiv e fluids and if approved by the Director.

EPA clarifies that the GS rule does not prescr ibe the specific cements to be used to plug abandoned wells in the AoR because industry sta ndards, such as those developed by API or ASTM International, reflect the current state of the science and the expert ise of industrial users on CO2-compatible materials, as specified in §146.92(b). Providing flexibility to choose materials for plugging, provided they are compatible with the inject ed fluid, is consistent with requirements for other injection well classes an d will allow operators to utilize improved well technologies as they become ava ilable in the future without a need to amend the regulation.

EPA plans to, every six years, co llect and review project data on early GS projects and continue to monitor field and laboratory research to de termine whether the appr opriate amount and types of information and appropriate documentation are being collected, a nd to determine if modifications to the requirements are appropriate or necessary.

Letter ID: 0168 Comment ID: 22499 Letter Lines: 218 to 219 ; 226 to 228

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

Comment: Preamble, page 43507: "EPA seeks comment on the applicability of computational

fluid flow models for delineat ing 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 revi ew (AoR) is appropriate and provides a flexible, phased approach to assessing the number of abandoned wells requiring mitigation.

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

9Letter ID: 0168 Comment ID: 22500 Letter Lines: 221 to 224 ; 230 to 239

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

Comment: Also preamble, page 43507 "EPA seeks co mment 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 tec hnical criteria EPA used in determining this frequency. EPRI believes that it would be more logical to base the frequency of AoR reevaluation on perfor mance measures including the observed speed of the plume and its anticipated arri val time at the edge of the computed AoR. Or, if plume speed cannot be observed directly (e.g., no CO 2 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 shoul d be used to set the reevaluation frequency.

Individual Response: EPA disagrees that the requirement at §146.84(e) for a periodic AoR

reevaluation is arbitrar y. EPA proposed the ten-year frequenc y based on input from stakeholders and experts at the technical workshops on "Geo logical Considerations and AoR Studies" and "Modeling and Reservoir Simulation for Geologic Carbon Storage." EPA also requested comment on the ten-year frequency. In the pr eamble to the proposed rule, EPA identified benefits to periodically r eevaluating 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 t hose areas subject to the greatest potential risk.

Based on the comments received (including those by water associati ons, an energy company, associations, industries, states, and envir onmental groups), EPA has changed the minimum frequency for the AoR reevaluation from 10 years to at least every 5 year s. EPA believes that this revised frequency addresse s commenters' concerns about th e inherent uncertainties in modeling CO2 movement, the emerging nature of GS technology, risk-b ased 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 a nd address the uncertainties i nherent in predictive modeling. Periodic AoR reevaluations at §146.84( e) ensure that a deliberate effo rt 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, estab lish conditions for corre ctive 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

10process of developing and executing the variou s plans required of GS well operators (e.g., for AoR and corrective action, testi ng and monitoring, injection we ll plugging, post-injection site care, and emergency and remedial response) inst ead of period permit renewals (e.g., of 10 years for Class I wells). EPA believes the iterative pr ocess and subsequent reevaluations of the AoR and corrective action, testing and monitoring, an d 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 aspect s 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.

Letter ID: 0168 Comment ID: 22501 Letter Lines: 241 to 247

Comment Code: 3630 2.2.4.1 Comments in favor of allowing phased corrective action

Comment: Preamble, page 43508: "Today’s proposal w ould give the Direct or the discretion to allow owners or operators to perf orm corrective action on an iterative, phased basis over the operationa l life of a GS project."

EPRI COMMENT #7: A phased approach for corrective action simultaneously ensures permanence of the stored CO2 and cost-e ffective management of the storage operation. Therefore, it will encour age GS project development.

Individual Response: EPA acknowledges the commenter’s s upport 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, avoi ding delays in project start-up, allowing for use of future, improved corrective act ion techniques and addressing unanticipated changes in the movement of the CO2 plume or pressure front . EPA believes that the phased corrective action approach is appropriate for GS projects, and retained it at §146.84(b)(2)(iv) in the final GS regulation.

Letter ID: 0168 Comment ID: 22502 Letter Lines: 249 to 275

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

Comment: Preamble, page 43509: "EPA seeks comment on the proposed GS well requirements for depth of surface casing, the cemen ting of long-string casing, and construction with a packer set opposite a cemented interval."

EPRI COMMENT #8: Cementing the entire le ngth of the long-st ring casing is not standard practice in the oil and natu ral gas industry and not adequately justified by EPA in the preamble to the ru le. Compared to CO2, natural gas is highly flammable and, in the absence of pr essure gradients, much more buoyant because of its lower density and higher mobility in the formation. In contrast, during CO2 injection, where pressure gr adients are large and buoyancy effects

11are comparatively small, models show th at CO2 dries out the formation around the well (Pruess and Spycher, 2006), signifi cantly lowering the risk of cement corrosion. Therefore, cementing standards adopted for natural gas wells designed to be protective of USDWs should be more than adequate for ensuring safe and permanent sequestration of the inject ed CO2. Wellbore conditioning prior to cementing and a well designed and execute d cementing operati on have greater impact on the cement integrity than the ove rall length of the cement seal. EPRI encourages the EPA to develop and adoptless stringent cementing requirements for the long-string casing, consistent with natural gas wells cu rrently in use. (See for example, Chapter 4 Development, Regulation, and Conservation of Oil and Gas Resources, Article 3 Requirements, Section 1722.4 Cementing Casing, in the State of California, California Code of Regulations, Title 14: Natural Resources; Division 2: Depa rtment of Conservation, Publication No. PRC04).

Pruess, K. and N. Spycher, 2006. ECO2N - A New TOUGH2 Fluid Property Module for Studies of CO2 Storage in Saline Aqui fers, Proceedings: TOUGH Symposium 2006, Lawrence Berkeley National Laboratory, Berkeley, California, May 15-17, 2006.

Individual Response: EPA disagrees that the construction requirements for Class VI wells at §146.86 are not justifiable. The Class VI well requir ements address the uni que nature of CO2 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), and were informed by numerous stakeholder workshops, EPA and DOE research, and oil and gas industry studies on we ll construction. EPA a dds that commenters representing states, a water a ssociation, and industry supported th is provision, saying that the requirement provides, at a reas onable cost, corrosion protect ion of the casing; prevents undesirable migration of fluids behind the casi ng; provides support to th e casing; and provides multiple barriers against endangerment of USDWs. EPA adds that cementing of deep wells has been performed successfully in the past, for example, by owners or operators of Class I hazardous and Class I municipal wast e disposal wells. Some of these wells, which must meet the same cementing requirements for long-string casing as Class VI wells, are up to 12,000 feet deep (EPA, 2001).

EPA recognizes that the GS rule includes require ments (e.g., cementing the entire length of the long-string casing) that ar e not standard practice in the oil and natural gas industry, but believes that there are significant opera tional differences between ER a nd GS. For example, the volume of CO2 anticipated to be injected in Class VI wells is significantly greater than for Class II wells. Reservoir pressure conditions wi ll be different, with Class VI injection operations involving large volumes of CO2 and likely having higher pressures within th eir storage formations than Class II ER projects. In addition, CO2 in the presence of water may be corrosive to well materials. For these reasons, EPA believes that GS is sufficiently different from Class II ER operations to warrant the tail ored construction requirements for Class VI wells at §146.86.

Letter ID: 0168 Comment ID: 22503 Letter Lines: 277 to 285

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

12Comment: Preamble, page 43509: "EPA seeks commen t on the merits of horizontal well drilling techniques for GS wells and th e applicability of well construction requirements discussed in this proposal."

EPRI COMMENT #9: We agree with the EP A arguments for this technology and, therefore, believe the merits of horiz ontal injection wells are correctly stated. In addition, the rule provides fl exibility and will enco urage GS project development, especially in lower perm eability formations needing additional injectivity.

Individual Response: In the final rule, EPA allows the use of horizontal wells at GS projects. In the proposed rule, EPA sought comment on the appr opriateness of horizonta l drilling techniques for Class VI wells, and commenters representing energy companies, el ectric utilities, the oil and gas industry, CCS associations, states, and the public, unanimously suppo rted the concept and provided many reasons why horizonta l wells could be beneficial at GS sites. Based on an evaluation of these comments and additional research by EPA, the Agency has concluded that horizontal wells that are properly constructed, logged, and tested for mechanical integrity (i.e., to meet the requirements of the GS rule) can ensu re the protection of USDW s from endangerment.

Letter ID: 0168 Comment ID: 22504 Letter Lines: 287 to 302

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

Comment: Preamble, page 43511: "In case of well failure, a down-hole shut-off device would isolate the injectate below USDWs, ra ther than just below the surface. EPA seeks comment on the merits of requiring dow n-hole shut-off valves in GS wells."

EPRI COMMENT #10: Since a downhole shut-off valve would just prevent CO2 from flowing from the injection zone up the pr oduction tubing to the atmosphere if the wellhead were damaged, it doesn’t se rve a function in pr otecting USDWs. Further, because, recorded cases of ca tastrophic wellhead fail ure are rare, and the valve would not protect CO2 from backflowing to the surface should the packer also fail, EPRI does not believe that a down-hole shut -off valve provides more safety than an easier-to-maintain near-surface shut-off valve. In addition,

a downhole valve will interfere with l ogging operations, mechanical integrity testing, video inspection logs, etc. Downhole tools typically associated with these activities are deployed by wire line inside the production tubing, requiring that the operator needlessly kill the well, and remove the tubing and valve to gain access to the section of well below the valve position.

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

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

13discretion to mandate automatic down-hole shut -off devices in onshore situations that may warrant their use. However, the Agency believ es that offshore Class VI wells present unique construction and operational conditi ons, including isolation from shorelines and the need to construct wells through the water column and the subsurface, which may delay response time in

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

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

EPA believes that requiring auto matic surface shut-off devices instead of down-hole devices for onshore wells provides more flexibility to ow ners or operators when performing required mechanical integrity tests. A dditionally, this requirement a ddresses concerns about risks associated with routine well workovers that may be complicated by the presence of down-hole devices while still maintaining USDW protection.

Letter ID: 0168 Comment ID: 22505 Letter Lines: 304 to 320

Comment Code: 4324 2.4.4.1.2 Comments opposed to requiring injection below the lowermost

USDW

Comment: Preamble, page 43512: "In summary, EPA is soliciting comment on whether CO2 injection should be allowed into an injection zone above the lowermost USDW, when the Director determines that geol ogic conditions (e.g., thousands of feet of intervening formations between the in jection zone and th e overlying and/or underlying USDWs) exist that will prevent fluid movement into adjacent USDWs. EPA is also requesting comments on whethe r aquifer exemptions should be allowed for the purpose of Class VI injection, and under what conditions should such aquifer exemptions be approved. Finally, EP A seeks comment on whether the Agency should set a minimum injection depth require ment for CO2 GS, rather than require that such injection take place below the lowermost USDW."

EPRI COMMENT #11: EPRI believes that a pro posed GS site should be considered to be protective of USDWs as long as the appl icant demonstrates to the EPA that it meets the minimum siting criteria specified in §146.83(a)(1), (a)(2) (also see EPRI Comment #4). Whether or not the inj ection zone lies above or below the lower most USDW, or below a given depth, is not important as long as the minimum

criteria are met.

Individual Response: EPA acknowledges that there are lim ited circumstances where injection above the lowermost USDW can be performe d in a manner that protects USDWs from endangerment, as long as appropriate protections are in place. The final GS rule at §146.95 establishes a process by which owne rs or operators can seek a waiv er of the Class VI injection depth requirements for injecti on into non-USDW formations above and/or between USDWs. It establishes: 1) requirements spec ifying information that owners or operators must submit, and Directors must consider, in consultation with PW SS Directors; 2) procedures for public notice of a waiver application and for Director-Regiona l Administrator communicat ion; 3) the waiver

14issuance process; and, 4) additiona l requirements that apply to owne rs or operators of Class VI wells granted a waiver of the in jection depth requirements to en sure USDW protection above and below the injection zone.

EPA believes that these requirements will ensure USDW protection while providing flexibility to UIC program Directors and owne rs or operators who undertak e CO2 injection for GS. The Agency believes this approach: 1) responds to co ncerns about local and re gional geologic storage capacity limitations imposed by th e proposed injection depth require ments; 2) allows for a more site-specific assessment of injection depth for GS projects; 3) accommodates injection into different formation types; 4) a llows for injection of CO2 for GS into non-USDWs above and/or between USDWs when appropriate and where it can be demonstrated that USDWs will be protected; and 5) responds to concerns about the use of aqui fer exemptions for GS. Finally, EPA’s approach to addressing injection depth va riability through a waiver process responds to concerns about future drinking wa ter resource availability and the need to ensure that high quality water remains available in sufficient qua ntities to supply drinking water needs. For additional information on the waiver approach, pleas e see the final rule and preamble, as well as EPA's responses to comments on the Notice of Data Availability and Request for Comment.

Letter ID: 0168 Comment ID: 22506 Letter Lines: 322 to 332

Comment Code: 4490 2.4.5 Use of tracers and potential im pact on human health or ecosystems (seeking comment)

Comment: Preamble, page 43513: "EPA seeks comment on the use of tracers in CO2 GS operations, and any potential impact of tracer s on human health or ecosystems as they relate to USDWs."

EPRI COMMENT #12: Too little is known a bout how tracers (e specially PFT's) partition between the CO2, water and oil pha se and how they adsorb onto organic

or mineral surfaces at reservoir conditions (high temperatures and pressure) to conclude that they act as conservative tracers. Any tracer added to the CO2 that

is soluble in water will lose mass to the water phase and will not act as a conservative tracer for the CO2 phase. EP A should not require the use of tracers unless and until more is known about their fate and transport.

Individual Response: EPA agrees that the use of tracers shoul d not be required at all GS sites, but should be available as an option. For this reason, EPA does not require the use of tracers at all GS sites; however, the Director has discretion to require their us e if he/she determines that the use of tracers could improve monitoring of the site and enhance USDW protection from endangerment. The rule will also allow their use if proposed by the owner or operator and approved by the Director.

EPA continues to follow new and ongoing research on the safety and efficacy of tracers. For example, studies at the Frio Brine Pilot Experi ment site (Dayton, TX) used various types of tracers, including perfluorocar bon tracers (PFTs), sulfur hexa fluoride, and the noble gases krypton, neon, and xenon. These studies (e.g., Phel ps and Cole, 2008; Hovorka et al., 2004;

15McCallum et al., 2005) found that tracers can pr ovide useful CO2 monitoring information at injection wells at depth and at near-surface locations. At Frio, tr acers enabled quantification of CO2 plume behavior and provide d a technique for model validity testing (McCallum et al., 2005). EPA will continue to track research related to tracer use. The Agency plans to, every six years, collect and review data on GS projects to determine whether the appropriate amount and types of information and appropriate documenta tion are being collected, and to determine if modifications to the requirements are appropriate or necessary.

Letter ID: 0168 Comment ID: 22507 Letter Lines: 334 to 364

Comment Code: 4655 2.6.5.1 Plume tracking techniques/ geophysical methods (seeking comment)

Comment: Preamble, page 43514 & 43515: "Under today’ s proposal, owners or operators would be required to track the subsurface extent of the CO2 plume and pressure front using pressure gauges in the firs t formation overlying the confining zone or using indirect geophysical techniques (e.g., seismic, electrical, gravity, or electromagnetic surveys) or other down- hole CO2 detection tools, monitor for geochemical changes in subsurface formati ons, and if directed, monitor at the surface. Today’s proposal would also requi re owners or operators to monitor ground water quality and geochemical cha nges above the confining system."

EPRI COMMENT #13: Refer to EPRI comment #2 for questions regarding how EPA

intends to define each front and the need to demonstrate containment instead. Also, EPRI comments #3B and #14 for repr esentative geochemical sampling and sampling of low-yield formations, respectively.

EPRI is not aware of any remote fi eld measurements, including seismic techniques, that can be used to dete rmine the position of the dissolved CO2 front. Therefore, definition of the CO2 fr ont should be limited to the leading edge of the free-CO2 plume if remote m onitoring techniques are used. Remote monitoring techniques may not work in all geologic settings. Very small pressure changes measured in the first formation overlying the confining zone may be masked by other pressure effects. For ex ample, relatively large barometric pressure fluctuations translated down th e well to the monito ring zone, changes in fluid pressure caused by nearby pump ing wells, or limited transducer resolution, accuracy and el ectronic noise may interfer e with or distort the pressure signal, making it difficult to measure the pressure front. Appropriateness of detection tools will need to be evaluated on a site-by-site basis, and the proposed rule recognizes th is need. However, EPRI believes the emphasis should be on demonstrating contai nment through careful characterization of the storage reservoir and caprock, coupled with predictive CO2 fate and transport models of reservoir and caprock performance, rather than on plume and pressure front tracking, as the latter may not be practical or possible.

Individual Response: In response to comments regarding the pressure front at GS sites, EPA

16clarifies that the pressu re front (defined at §146.8 1) is the zone of elevated pressure that is created by the injection of CO2 in to the subsurface. The pressure front of a CO2 plume refers to a zone where there is a pressure differential suffici ent to cause the movement of injected fluids or

formation fluids into a USDW. Th e pressure front includes all ar eas 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 depende nt on properties of the injection and confining zones, including permeab ility, porosity, and compre ssibility, the distance between the injection zone a nd the lowermost USDW, and op erational conditions including injection pressure and rate. For these reasons, th e definition of the pressu re front is site- and project-specific, and a singl e pressure value can not be provided for all sites.

EPA has revised the final rule, at §146.90(g), to require owners or operators to perform monitoring to track the extent of the CO2 plume and pressure fr ont. The owner or operator must use direct methods to monitor for pressure chan ges in the injection zone. Indirect methods (e.g., seismic, electrical, gravity, or electromagnetic surveys and/or down-hol e CO2 detection tools) are required unless the Director de termines, based on site-specific geology that such methods are not appropriate.

EPA believes that pressure monitoring in th e injection zone is n ecessary to track the development and movement of the pressure front and CO2 plume. Monitoring can also identify needed remedial actions, provide inputs for AoR reevaluation m odeling, evaluate predictions of plume movement, and target additional geoche mical and surface monitoring needs. Knowledge of the location of the CO2 plume and the associated pressure front will assure the public that GS projects are proceeding according to plan, provide sufficient information to the owner or operator and Director, or allow for appr opriate actions to address any indication that USDWs may be endangered.

EPA is affording Director's disc retion regarding the use of geophys ical techniques at some sites because the Agency recognizes that geophysical methods are not appropriate in all geologic settings. For example, geophysical methods are diffi cult to execute in areas that are structurally and topographically complex or where lithologies have limited contrast in density, porosity, permeability, and other physical properties. EPA clarifies that this determination will be made by the Director based on the site-specific geologi c information submitted by the owner or operator with their permit application.

Letter ID: 0168 Comment ID: 22508 Letter Lines: 366 to 389

Comment Code: 4660 2.6.6 Geochemical monitoring

Comment: Preamble, page 43515: "Monitoring within th e confining zone for pressure, pH, salinity, or the presence of dissolved minerals, heavy metals, or organic contaminants requires direct access to the subsurface via monitoring wells."

EPRI COMMENT #14: See EPRI comment #3B. We believe that measuring pressure in a deep confining zone is possible, but colle cting representative deep well samples from confining zones for geochemical ch aracterization may not be technically

17possible (with emphasis on representative) . This could lead to erroneous results and conclusions. EPA currently re quires that all monitoring wells be purged of "stagnant" groundw ater in the well prior to sampling to produce a "fresh" sample from the adjacent formation that is representative of the formation fluid. Low-yield confining units are typically purged dry prior to sampling or pumped at a very slow rate to prevent the formation from being dewatered. In either case, this typically results in significant sample depressurization when sampling deep wells . Important geochemical parameters including pH, alkalinity, and dissolved metals (which are dependent on groundwater pH) will change when depressurization occurs, producing erroneous analytical results. The u-tube sample me thod described by Friefeld et al (2005)

cannot be used to overcome this limita tion for low-yield confining zones.

Freifeld B.M., R.C. Trautz, Y.K. Kharaka, T.J. Phelps, L.R. Myer, S.D. Hovorka, D.J. Collins (2005) The U-tube: a novel system for acquiring borehole fluid samples from a deep geologic CO2 sequestration experiment. Journal of Geophysical Research, 110, B10203, doi:10.1029/2005JB003735.

Individual Response: As described above, EPA recognizes that the collection of representative ground water samples from depth poses challenges and that special methods, such as U-tubes, will be needed to preserve the integrity of such samples. 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.

Letter ID: 0168 Comment ID: 22509 Letter Lines: 391 to 416

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

Comment: Preamble, page 43517: "EPA seeks comment on the merits of requiring plans for monitoring, AoR, and post-inj ection site care as part of a permit application."

EPRI COMMENT #15: Submitting a monitoring and AoR plan with the application seems practical since these activities will occur in the reasonably near future after the permit is issued. However, requi ring too much specificity in a postinjection site care plan as part of the permit application may cement in methods that will be obsolete by the time the GS project enters th e post-injection phase, 20-50 years from the permit date . EPA could instead require that a preliminary post-injection site care plan be submitted at the time of application outlining the general approach and parameters needed to demonstrate closure, and that a final detailed plan be prepared for approval a certain period of time prior to implementation of this phase.

Preamble, page 43518: "Today’s proposal w ould require owners or operators to submit a well plugging plan at the same time the permit application is submitted and to have this plan ap proved by the Director."

18EPRI COMMENT #16: Again, well plugging and abandonment are activities that take place far in the future, perhaps severa l decades off. Therefore, submitting this plan at the time of permit applic ation could render it obsolete when implementation is needed. EPA could in stead require a preliminary plan outlining the general approach at the tim e of application and require that a final detailed plugging and abandonment plan be submitted for approval a certain period of time prior to implementati on of this activity, allowing for the incorporation and use of new/better technologies.

Individual Response: EPA believes that incorporating the plans into the permit rather than establishing specific requirements for correctiv e action, monitoring, inje ction well plugging, and post-injection site care in the regulation provide th e appropriate flexibility to address the variety of site-specific conditions that ma y be encountered at GS sites.

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

EPA recognizes that the injection well plugging and post-in jection site care and site closure plans may need to be modified when injection ceases, as well as prior to site closure, which is why §146.92(c) and §146.93(a) require review of these plans to ascertain whether the plan needs to be modified. EPA notes that §144.39 and §144.41 c ontain requirements regarding permit modifications that may be triggered as a result of these plan modifications.

Please see the final rule and the discussion of the Class VI proj ect plans in the preamble for

additional information.

Letter ID: 0168 Comment ID: 22510 Letter Lines: 418 to 428

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

Comment: Preamble, page 43519-43520: "EPA requests comment on the proposed use of a tentative 50-year fixed timeframe that c ould be modified at the Director’s

discretion based on monitori ng and modeling data."

EPRI COMMENT #17: EPA’s 50-year fixed ti meframe described in the preamble

19appears to be based on prof essional judgment interpreti ng a limited number of citations and/or modeling scenarios. We question the need for defining a fixed timeframe of any length because it runs c ounter to the EPA’s implied intent to close sites based on the owner/operator’s ability to meet specific performance criteria defined in §146.93(b). (See EP RI comment #2, #13, a nd #18 regarding these criteria (i.e., front tracking and stability)).

Individual Response: EPA disagrees with this comment. In determining the post-injection site care-timeframe for the proposed regulation, EP A reviewed industry reports, existing environmental programs, and initial GS research studies. EPA provided a synthesis of pertinent results from GS modeling studies in the preambl e to the proposed regula tion. Further explanation of this analysis was included in an EPA-prep ared background document that is available in the federal docket, titled "Computa tional Modeling of Underground In jection of Carbon Dioxide for

Determination of Area-of-Review and Potentia l Risk to Underground Sources of Drinking Water." Based on review of these studies, m odeling results indicate that the CO2 plume stabilization may occur on the timeframe of 10- 100 years after the cessa tion of injection. EPA believes that a 50-year default post-injection si te care timeframe is a reasonable midpoint for most GS projects and available data, includi ng data submitted by commenters, do not support a different default timeframe, and has reta ined this in the final regulation.

EPA agrees that some owners or op erators will be able to demonstrate, in less than 50 years, that the pressure front and plume no longer pose a risk of endangerment to USDWs. However, based on studies, EPA believes that the 50 year default time frame is wa rranted in most cases based on

additional review of research studies and reports and eval uation of public comments. EPA believes that the best way to address all possi bilities, while ensuring USDW protection from endangerment, is to set a 50 year default post-inj ection site care timefram e, with flexibility to: (1) allow 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) afford 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-e ndangerment of USDWs pursuan t to requirements at §146.93(c).

EPA believes that a default post-injection site car e timeframe of 50 years, with flexibility to adjust the timeframe for a limited number of GS projects during the permitting process where

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

Letter ID: 0168 Comment ID: 22511 Letter Lines: 430 to 452

Comment Code: 5260 2.8.2.3 Adjusting the post-injecti on timeframe (seeking comment)

Comment Code: 5280 2.8.2.4 USDW non-endangerment demonstrations

20Comment: Preamble, page 43520: "Once the owners or operators provide documentation that demonstrates that the models predicti ng CO2 movement are consistent with monitoring results and that there are no l onger risks of endangerment to USDWs, they could request that th e Director authorize site closure. EPA is also proposing to allow the Director to shorte n or lengthen the 50-year time frame based on performance of the site... EPA wish es to emphasize that site closure cannot occur until monitoring and modeling data establish to the Director’s satisfaction that potential risks of en dangerment to USDWs have ceased."

EPRI COMMENT #18: EPA’s requirement for de monstrating plume stability for site closure is based on the ability to both observe and successfully model the speed and stability of the advanc ing CO2 front, a very disc rete boundary that is difficult to define, model accurately when complex reservoir heterogeneity and fast flow pathways are present, and meas ure in the field on a large scale. (See also EPRI’s comment #2 on defining the fr ont). If remote methods like surface seismic, cross-well seismic or gravity are not successful in tracking front position, and CO2 is never directly detect ed in sentinel observations wells,

then model validation based on CO2 front position may be questioned. In such a case, if the model predicts the continued advance of the CO2 front while the observed data do not, the EPA Director may not be satisfied with the absence of a potential risk of endangerment to US DWs and may unnecessarily delay site

closure for decades. EPRI recommends that the final rule contain alternative provisions for site closure if m odel validation is unsuccessful.

Individual Response: EPA acknowledges that many site-sp ecific factors will influence the determination of when the CO2 plume and pressu re front no longer pose a risk of endangerment

to USDWs. It is for this reason that EPA believe s that individual UIC Dir ectors, in consultation with operators, will be in the best position to determine whether additional post-injection site care is needed. EPA expects this decision to be made based on relevant site data and in consultation with all potentia lly impacted parties.

EPA also agrees that a complete cessation of pl ume movement may not occur at some sites for long time periods due to density differences, natu ral formation flow gradients and diffusion. EPA clarifies that a complete cessati on of plume movement is not requi red, only a demonstration that the plume and pressure front no longer pos e a risk of endangerment to USDWs.

EPA is developing guidance to assist owners or operators in evaluating well plugging, postinjection site care, and site closure requirements of §146.92 and §146.93. Additionally, the guidance will assist Directors in evaluating propo sed well plugging plans a nd post-injection site care and site closure plans under §146.92 a nd §146.93. The guidance describes recommended approaches for how an owner or operator coul d plug injection and m onitoring wells; perform post-injection monitoring; dem onstrate non endangerment; and perf orm site closure activities. The guidance will be available at http://water.epa.gov/type/groundwat er/uic/wells_se questration.cfm.

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