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.Document ID: EPA

- HQ

- OW

- 2008

- 0390

- 119

Last Name: McCormic

First Name: Rob

Title:

Organization: Dallas County Park Cities Municipal Utility District

City:

State:

Zip Code:

Phone Number:

Fax Number:

Country Code:

Email Address:

Current Category Code: 252

Comment: Concerning the proposed rule allowing Geological Sequestration of Carbon Dioxide, what

safeguards are there against accidently activating or reactivating seismic (earthquake) faults at or near a

proposed sequestration s ite, particularly with injecting "supercritical" liquid CO2?Letter ID: 0119

Commenter: Rob McCormic

Organization: Dallas County Park Ci ties Municipal Utility District

Letter ID: 0119 Comment ID: 22069 Letter Lines: 15 to 18

Comment Code: 1620 1.3.2 Induced seismicity

Comment: Concerning the proposed rule allo wing Geological Sequestration of

Carbon Dioxide, what safeguards are ther e against accidently activating or

reactivating seismic (earthqua ke) faults at or near a proposed sequestration

site, particularly with injec ting "supercritical " liquid CO2?

Individual Response: EPA acknowledges that induced seismi city is a risk that may be

associated with GS but maintains that the risk is low (IPCC, 2005). The GS rule contains several

requirements to address seismic risk. First, as part of the site char acterization process under

§146.82, owners or operators must submit information about the seismic history of and seismic

sources near a proposed GS s ite; data on known or suspecte d faults in the AoR; and

geomechanical information on fractures, stress, ductility, rock strengt h, and in situ fluid

pressures within the confining zone as specified in §146.82(a)(3). This information is evaluated

by the Director, who determines the suitability of a potential project site for GS. Any sites with

the potential for reopening or reac tivation of faults or unaccepta ble seismic risk that could

otherwise interfere with contai nment will not be permitted as GS sites. During injection, the

pressure in the injection zone must not exceed 90 percent of the fracture pressure of the injection

zone as specified in §146.88(a); this requirement is intended to prevent the opening of fractures

or faults through over-pressuriza tion of the injection zone.

To support consistent interpretation and applic ation of the safeguards related to induced

seismicity in the GS rule, EPA is developing guid ance on site characterizati on for GS projects to

assist owners or operators and Directors in evaluating permit requirements and applications

under §146.82. The guidance provides recommendati ons to owners or operators regarding

information to support characterizing the re gional geology and hydroge ology of a proposed GS

site as well as how to perform the necessa ry geochemical, geomechanical, and geophysical

analyses of the injection and confining zone. EP A expects that this guidance will assist permit

writers and UIC Directors in making an objectiv e decision about requirin g additional confining

layers. The guidance can be found on EPA’s website at

http://water.epa.gov/type/groundwater /uic/wells_sequestration.cfm.

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