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.Comments on EPA Prop osed Class VI Rule

Docket ID No. EPA-HQ-OW-2008-0390 Larry R Myer lrmyer@lbl.gov Lawrence Berkeley National Laboratory Berkeley CA 94720

Phone 510-486-6456

The proposed Class VI rule addresses all of th e important issues which must be addressed in order to protect USDWs wh en geologic sequestration of CO 2 is undertaken. Actions required by the rule are generally conserva tive, which is good, but, in three areas, discussed below, requirements are ove rly, and unnecessarily, conservative.

A 50 year site care period is unnecessary and certainly impractical, and should be removed from the rule. It is unlikely that any owner/operator would, or could, provide assurance of its ability to take re sponsibility for the fate of the CO 2 for 50 years. The risks associated with storage decrease rapidly afte r injection stops because of stabilization of the plume and dissipation of pressure, so the co ncept of linking post-injection site care to plume stabilization and pressure decrease is a good one. However, there is not sufficient knowledge at this time to quantify the require d time. It is known that the time required for trapping processes, such as residual gas trapping, to immobilize the plume varies, so a single number for the site care period is not appropriate in any even t. Given the current state of knowledge the rule should only stat e that the operator should demonstrate at closure that the plume has sufficiently stabil ized and pressure decreased so as to not adversely impact the USDW.

The requirement that injection pressure shoul d not exceed 90 percent of fracture pressure is also unnecessarily conservative and restrictive because it precludes use of hydrofracturing as a reservoir s timulation technique. It is impor tant that the seal not be fractured, but purposeful fracturi ng of the injection interval wi ll likely be advantageous in many instances, just as it is in hydroc arbon production. Carefully engineered hydrofracturing operations carried out in co njunction with a monitoring program, should

be allowed.

Setting the interval for cementing of the casing as the entire casing lengthl seems arbitrary and unjustified. A conservative ceme nting program is justified. It is unclear, however, why 4000 ft of cement is sufficient for a 4000 ft deep well and insufficient for a 10,000 ft deep well. For very deep wells the co sts and difficulties in cementing the entire casing length go up dramatically. The risks of loosing the whole well also increase significantly with the increased difficulty of the operation. Of highest priority is a high quality cement bond through the formation(s) fo rming the primary seal of the storage reservoir. Beyond that, cementing should not be required beyond that which is practical in a single stage cementing program.Letter ID: 0149 Commenter: Larry Myer Organization: Lawrence Berkeley National Labo ratory (Berkeley Lab) U.S. Department of Energy (DOE)

Letter ID: 0149 Comment ID: 21796 Letter Lines: 24 to 28

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

Comment: The proposed Class VI rule addresses all of the important issues which must be addressed in order to protect USDWs wh en geologic sequestration of CO2 is undertaken. Actions required by the rule are generally conser vative, which is good, but, in three areas, discussed be low, requirements are overly, and unnecessarily, conservative.

Individual Response: EPA acknowledges the comment. The re quirements for GS projects are tailored to address the unique issues associated with GS, including large injection volumes, the relative buoyancy of CO2, its corro sivity in the presence of water, the potential presence of impurities in captured CO2, and its mobility within subsurface geologic formations.

Please see the remainder of EPA's responses to th is comment for further details. For additional information on EPA's final regulatory approach, pl ease see the final rule and preamble as well as the rulemaking docket.

Letter ID: 0149 Comment ID: 21797 Letter Lines: 30 to 43

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

Comment: A 50 year site care period is unnecessary and certainly impractical, and should

be removed from the rule. It is unlik ely that any owner/operator would, or could, provide assurance of its ability to take responsibility for the fate of the CO2 for 50 years. The risks associated with storage decrease rapidly after injection stops because of stabilizat ion of the plume and dissipation of pressure, so the concept of linking post-injection site care to plume stabilization and pressure decrease is a good one. However, there is not sufficient knowledge at this time to qu antify the required time. It is known that the time required for trapping processe s, such as residual gas trapping, to immobilize the plume varies, so a single number for the site care period is not appropriate in any event. Given the curre nt state of knowledge the rule should only state that the operator should demons trate at closure that the plume has sufficiently stabilized and pressure decrea sed so as to not adversely impact the

USDW.

Individual Response: EPA disagrees that a post-injection si te care timeframe of 50 years is excessive or unnecessary in most cases. EPA proposed a default post-injection site care

1timeframe of 50 years based on a review of research studies, industry reports, and existing environmental programs. This analysis was in cluded in an EPA-prepared background document

that is available in the federal docket, titled Computational Modeling of Underground Injection

of Carbon Dioxide for Determination of Area- of-Review and Potential Risk to Underground Sources of Drinking Water. EPA assessed variou s default timeframes based on additional review of research studies and evaluation of public comments. While numerous commenters suggested that EPA shorten the monitoring timeframe, none of the commenters provided sufficient data or

other evidence to warrant a ch ange in the proposed timeframe. While the 10- or 30-year timeframe suggested by some of these commenters may be within the timeframe suggested in some studies, EPA believes that the potential risks of endangering USDWs will likely not decline within these timeframes and available data, including data submitted by commenters, do not support a different default timeframe.

EPA acknowledges that some studies indicate that trapping may begi n in less than 50 years, as the commenter notes; however, this trapping may also take up to hundreds or thousands of years to be complete (IPCC, 2005). If this trap ping is not complete, the potential for USDW endangerment still exists as CO2 may persist as a buoyant plume. EPA therefore believes that to ensure USDW protection from endangerment, a default timeframe for post-injection site care will be necessary in most cases. The default 50 year post-injection site care timeframe represents a reasonable and protective monitoring period ba sed on a review of research studies, industry reports, and existing environmental program s, and evaluation of public comments.

However, the GS rule offers owners or operators flexibility regarding th e duration of the PISC timeframe by: (1) allowing the Director discretio n to shorten or lengthen the PISC timeframe during the PISC period based on site-specific data , pursuant to requirements at §146.93(b); or (2) affording the Director discretion to allow a Cl ass VI well owner or operator to demonstrate, based on substantial data during the permitting pro cess, that an alternative PISC timeframe may be appropriate if it ensures non-endangermen t of USDWs pursuant 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.

EPA recognizes that there are chal lenges associated with assuring funding for activities that will occur far in the future. However, the Agency be lieves that in order to protect USDWs from endangerment under the SDWA, operators must demonstrate under §146.85 that financial resources are available to plug the injection well and provide post-injection site care at the point in time that the first CO2 is injected.

To the comment about the cost of post-injection site care, EPA does not ag ree that post-injection

2site care timeframes longer than 30 years will be prohibitively expensive. In fact, EPA believes that post-injection site care monitoring will re present a relatively minor component of total project cost, and will provide an essential level of protection from endangerment for USDWs. A

discussion of the costs attributed to monitori ng technologies (used durin g injection and the postinjection site care timeframes) is available in the Technology and Cost Document for the GS

rule, which is in the federal docket for this rule making. EPA believes that it is logical to make use of existing monitoring infrastructure at a GS site in order to ensure USDWs are not endangered.

Letter ID: 0149 Comment ID: 21798 Letter Lines: 45 to 51

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

Comment: The requirement that injection pressure should not exceed 90 percent of fracture pressure is also unnecessarily conservativ e and restrictive be cause it precludes use of hydrofracturing as a reservoir stimulation tec hnique. It is important

that the seal not be fr actured, but purposeful fract uring of the injection interval will likely be advantageous in many instances, just as it is in hydrocarbon production. Carefully engineered hydrofracturing ope rations carried out in conjunction with a monito ring program, should be allowed.

Individual Response: EPA clarifies that the in jection pressure limit at §146.88(a) applies only to the period of injection, not well stimulation. In addition, EP A recognizes that there may be well completions which require intermittent treatments that include stimulation to improve wellbore injectivity. Stimulati on of the injection zone during a well workover will be permissible, if approved by the Di rector (operators seeking to use stimulation must submit the proposed stimulation program as part of the permit application under §146.82(a)(9)). EPA has also added a requirement that owners or operators notify the Director in advance of any planned stimulation activities, as speci fied at §146.91(d). During injection, the injection pressure must not exceed 90 percent of the fracture pressure, as specified in §146.88(a). EPA clarifies that the injection pressure limit at §146.88(a) applies only to the period of injectio n, not well stimulation.

Letter ID: 0149 Comment ID: 21799 Letter Lines: 53 to 62

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

Comment: Setting the interval for cementing of th e casing as the entire casing lengthl seems arbitrary and unjustified. A conserva tive cementing program is justified. It is unclear, however, why 4000 ft of cement is sufficient for a 4000 ft deep well and insufficient for a 10,000 ft deep we ll. For very deep wells the costs and difficulties in cementing the entire casing length go up dramatically. The risks of loosing the whole well also increase significantly with the increased difficulty of the operation. Of highest priority is a high quality cement bond through the formation(s) forming the prim ary seal of the storage reservoir. Beyond that, cementing should not be require d beyond that which is practical in

34 a single stage cementing program.

Individual Response: EPA disagrees that the construction requirements for Class VI wells at §146.86 are arbitrary or unjustified. Th e final GS rule requires, at §146.86(b)(2), that the surface casing must extend through the base of the lo wermost USDW and be cemented to the surface, and that at least one long string casing must be cemented to the surface in one or more stages at §146.86(b)(3). It does not, however, specify how cementing must be accomplished, and it allows the owner or operator to propose alternate methods that provide a sufficient amount of cement to meet the standard that USDWs are protected from endangerment. EPA notes that there are many potential ways to meet the requirement , such as the use of staged cementing.

The Class VI well requirements address the unique nature of CO2 GS (i ncluding 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 mob ility within subsurface geologic formations). 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 Cl ass I municipal waste disposal wells. Some of

these wells, which must meet the same cemen ting requirements for long-string casing as Class VI wells, are up to 12,000 feet deep (EPA, 2001).

EPA recognizes concerns regardi ng construction of Class VI wells where the lowermost USDW is very deep. To further address comments on d eep injection wells, the final GS rule at §146.95 includes requirements for owners or operators that seek a waiver of the injection depth requirements. Owners or operators of wells opera ting under injection depth waivers must comply with additional construction require ments to ensure that wells used to inject above or between USDWs are protective. See the discussion of the wa iver approach in the preamble to the final GS

rule for additional information.