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 the Proposed Rule

Federal Requirements under the Underground Injection Control Program for Carbon

Dioxide Geologic Sequestration Wells, 40 CFR Parts 144 and 146, Environmental

Protection Agency (Docke t ID No. EPA–HQ–OW–2008–0390)

This proposed rule was published in the Federal Register , Vol. 73, No. 144, pp. 43492-43541.

These comments were prepared by Edward Mehnert, Illinois State Geological Survey,

Champaign, IL. Contact info: mehnert@isgs.illinois.edu or 217/244-2765.

Technical Comments

p. 43497, IIC: USEPA needs to develop an effective way to handle cross-state boundary issues.

Cross-state boundary issues could be a problem when dealing with pressure front s in a setting

like the Mt. Simon Sandstone, which is present beneath several Midw estern states. In addition,

many stationary CO 2 sources are located along state boundari es (i.e., power plants along major

rivers).

p.43506, IIIA2 Proposed Area of Review: Does the area of review need to be one contiguous

area? For a deep saline aquifer with no structural trap, it may be beneficial to have two separate

areas of review—one for the CO 2 plume and another for the pressu re front at a distant USDW

boundary. In this setting, the pr essure front may move brine upg radient into a portion of the

aquifer that contains fresher water (<10,000 mg/L TDS). The distance between the injection

well and the “freshwater” section of th e aquifer may be more than 100 miles.

p.43506, IIIA2 Proposed Area of Review: I agree that models offer the best approach to predict

the potential effect of CO 2 injection into an aquifer. What happens when multiple injection wells

are operated in the same aquifer su ch that well interferen ce is an issue? How do you manage this

situation if different models are utilized? As an alternative to many stand-alone models, can a

regional model with common boundary and initial conditions be developed and then a local

model with detailed site data would be adde d to this regional model? The Twin Cities

Metropolitian Groundwater Flow model

( http://www.pca.state.mn.us/wat er/groundwater/metromodel.html ) is an example of this concept.

p.43514, IIIA6 Monitoring Requirements: The comple te list of monitori ng procedures may not

be necessary in all settings, such as deep saline aquifers (>5,000 ft below ground surface). I

hope that these rules will remain fl exible such that they can bene fit from the research currently

being conducted by the USDOE-fu nded partnerships. Their Phas e III efforts should provide

valuable information on the feasibility and value of various monitoring methods.Letter ID: 0221

Commenter: Edward Mehnert

Organization: Illinois Stat e Geological Survey

Letter ID: 0221 Comment ID: 21636 Letter Lines: 28 to 33

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

ownership

Comment: Technical Comments p. 43497, IIC: USEPA need s to develop an effective way to

handle cross-state boundary issues. Cross- state boundary issues could be a

problem when dealing with pressure fr onts in a setting like the Mt. Simon

Sandstone, which is present beneath seve ral Midwestern states. In addition,

many stationary CO2 sources are loca ted along state boundaries (i.e., power

plants along major rivers).

Individual Response: EPA acknowledges that CO2 plumes may cross state or ev en international

boundaries and encourages cooperation and coor dination among permitting authorities. The final

Class VI GS rule, at §146.82(a)(2), requires the ow ner or operator to identi fy all State, Tribal,

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

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

and ensure that they are involve d in any necessary processes; th is new requirement was added to

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

anticipates that State-State/State-Tribal communication on GS permitting will facilitate

information sharing and encourag e safe, protective projects.

Letter ID: 0221 Comment ID: 21637 Letter Lines: 35 to 41

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

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

CFR 146.90)

Comment: p.43506, IIIA2 Proposed Area of Review: Does th e area of review need to be one

contiguous area? For a deep saline aquifer with no stru ctural trap, it may be

beneficial to have two separate areas of review--one for the CO2 plume and

another for the pressure front at a dist ant USDW boundary. In this setting, the

pressure front may move brine upgradien t into a portion of the aquifer that

contains fresher water (

well and the "freshwater" section of the aquifer may be more than 100 miles.

Individual Response: EPA clarifies that the requirements for AoR delineation incorporate both

the CO2 plume and associated pressure front. EPA agrees that both of these should be taken into

account in determining corrective action needs and developing a te sting and monitoring plan, and

that the requirement to delineate the AoR at 146.84( c) addresses the poten tial risks raised by the

1commenters. EPA believes that the final GS requirements for delineating the AoR provide

sufficient protection to USDWs, without introdu cing an overly complex regulatory process.

Letter ID: 0221 Comment ID: 21638 Letter Lines: 43 to 52

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

Comment: p.43506, IIIA2 Proposed Area of Review: I ag ree that models offer the best

approach to predict the potential effect of CO2 injection into an aquifer. What

happens when multiple injection wells are op erated in the same aquifer such that

well interference is an issue? How do you manage this situation if different

models are utilized? As an alternativ e to many stand-alone models, can a

regional model with common boun dary and initial conditions be developed and then

a local model with detailed site data w ould be added to this regional model?

The Twin Cities Metropolitian Groundwater Flow model

(http://www.pca.state.mn.us/water/groundwater/metromodel.ht ml) is an example of

this concept.

Individual Response: EPA agrees that the impacts of multiple operators injecting into

hydraulically connected formations must be accounted for in the AoR modeling. EPA adds that

the owner or operator must demonstrate in the proposed AoR and corrective action plan to the

satisfaction of the Director that the modeled AoR will be based on detailed site-specific geologic

data collected during the site characterizati on process including consideration of existing

conditions (e.g., current injection activities). EP A anticipates that, where multiple operators are

involved, the Director would not approve modeli ng that does not account for changes that may

result from all injection operations in a fo rmation or a series of hydraulically connected

formations. EPA acknowledges the commenter's reference to the Twin Cities Metropolitan

Groundwater Flow model. The Agency anticipate s that many such examples will be developed

as GS projects are deployed and new modeling products are developed to address this new

application.

EPA is developing guidance on AoR and corrective act ion at GS Class VI s ites to assist owners

or operators and Directors in evaluating requi rements and proposed AoR and corrective action

plans under 146.84. The guidance describes EPA's reco mmended approaches for the data to be

considered in an initial AoR delineation, how to apply computat ional 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.

Letter ID: 0221 Comment ID: 21639 Letter Lines: 54 to 59

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

CFR 146.90)

2Comment: p.43514, IIIA6 Monitoring Requirements: Th e complete list of monitoring

procedures may not be necessary in all se ttings, such as deep saline aquifers

(>5,000 ft below ground surface). I hope that these rules will remain flexible

such that they can benefit from the re search currently bei ng conducted by the

USDOE-funded partnerships. Their Phase III efforts should provide valuable

information on the feasibility and va lue of various monitoring methods.

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

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

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

plans is to ensure that the monitoring performe d at a site is appropria te for site operational

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

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

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

project in consultation with the Director.

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

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

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

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

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

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

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

groundwater samples for chemical analysis. Many options currently exis t for complying with

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

injection zone.

EPA believes, however, that implementing a testing and monitoring plan that includes all of the

required elements under §146.90 is essential to ensuring USDW protection. Please see the

preamble to the final rule for a complete justif ication of the elements of a GS testing and

monitoring regime.

Flexibility is also provided re garding how to monitor for the sp ecific data required by the final

rule. The testing and monitoring plan is develope d by the owner or operato r in consultation with

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

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

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

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

available technologies and reco mmended approaches for implem enting a testing and monitoring

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

injection well testing during ope ration, groundwater quali ty monitoring, tracking the CO2 plume

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

Director for specific GS projects. The guidance can be found on EPA’s website at

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

EPA is using an adaptive approach to regulati ng GS. EPA will collect and review project data on

34 early GS projects to determine whether the appr opriate amount and type s of information and

appropriate documentation are required and being collected. The Agency will evaluate the

information and determine if modifications to the requirements are necessary.