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.
Serving Wyoming Since 1933

WYOMING STATE GEOLOGICAL SURVEY

P.O. BOX 1347 · LARAMIE, WYOMING 82073-1347

307/766-2286 · FAX 307/766-2605

E-MAIL: wsgs-info@uwyo.edu ·WEB: www.wsgs.uwyo.edu

STATE GEOLOGIST – Ronald C. Surdam

GEOLOGICAL SURVEY BOARD

Ex Officio

Governor Dave Freudenthal

William A. Gern Don J. Likwartz 

Ronald C. Surdam

Appointed

R. Terry Leigh Christopher E. Mullen

John P. Simons John E. Trummel

Wallace L. Ulrich

Date: November 19, 2008

RE: Docket ID NO. EPA-HQ-OW-2008-0390

From: Ronald Surdam, Director/State Geologist, Wyoming State Geological 

Survey, rsurdam@uwyo.edu, 307-766-2286 ext. 223

With regard to the recently proposed “Geological Aspects of the Proposed 

Environmental Protection Agency’s Federal Requirements under the Underground 

Injection Control (UIC) Program for Carbon Dioxide (CO2) Geological 

Sequestration (GS) Wells”, the Wyoming State Geological Survey has the 

following comments.

The requirements of injecting CO2 only below the lowermost Underground 

Source of Drinking Water (USDW) aquifer will make it impossible to inject CO2 

into deep saline aquifers in Rock Mountain Laramide Basins (RMLB). The 

problem is when the deep geological sequestration CO2 targets in RMLB (i.e., deep 

saline aquifers) occur near the surface, they contain USDW. For example, at a 

depth of 10,000 to 15,000 feet, a stratigraphic unit such as, but not limited to the 

Madison Limestone, typically has salinity > 10,000 ppm. However, this same unit 

at 0-3,000 feet depth typically has salinity < 500 ppm. Near the surface, the 

aquifer is recharged with copious quantities of fresh meteoric water; but, because 

of geohydrologic characteristics common to Laramide Basins of Wyoming, the 

fresh water does not circulate into the deeper portions of the basin. Instead, it 

discharges in the form of springs or into streams/rivers near the margin of the basin 

typically along bounding faults or breached, anticlinal structures. As a 

consequence, due to a lack of mixing meteoric and connate fluids, the fluid in the 

same unit at a depth of 10,000 feet maintains salinities more near the original 

depositional environment (i.e., marine waters with salinities > 30,000 ppm). If the 

formation fluid was part of a continuous fluid-flow system, the whole rock/fluid 

system would have been flushed during the Pleistocene when recharge rates were 

much higher than today. Observations made in all of Wyoming’s Laramide Basins 

demonstrate that fluid-flow systems in the deep saline aquifers are 

compartmentalized resulting in an absence of shallow-formation water mixing with 

deep basin brines. 
Serving Wyoming Since 1933

The ramifications of declaring a stratigraphic unit in Rocky Mountain Basins 

a USDW aquifer because it supplies fresh water at shallow depth are immense. 

The stratigraphic section beneath units such as the Paleozoic Madison Limestone 

and the Tensleep Sandstone (or stratigraphic equivalent units) is relatively thin in 

Wyoming. If the intention is to use geological CO2 sequestration as an effective 

mitigation tool for global climate change, the stratigraphic section between the 

Tensleep/Madison does not have the storage volume required to accommodate the 

huge quantities of CO2 that will need to be geologically sequestered. 

The Wyoming State Geological Survey suggests that our Nation will be 

much better served if the proposed regulations for geological CO2 sequestration, 

with respect to injecting CO2 only below the lowest USDW aquifer, be modified as 

follows: “Geological CO2 sequestration will be allowed in deep saline aquifers in 

Rocky Mountain Laramide Basins unless it can be demonstrated that the injected 

CO2 will have a deleterious effect on USDW.”

If this change is not made, the geological sequestration of CO2 will be far 

more onerous than injecting H2S into the deep portion of RMLB. For economic 

and regulatory purposes, the regulations as proposed will make geological 

sequestration of CO2 impossible. To promulgate a geological CO2 sequestration 

regulation for RMLB out of the context of Rocky Mountain Laramide geology will 

make it extremely difficult to mitigate the effects of greenhouse emissions on 

climate change in the West. The Wyoming State Geological Survey requests that 

the United States Environmental Protection Agency act favorably on the changes 

herein described.
Letter ID: 0132 

Commenter: Ronald Surdam 

Organization: Wyoming State Geological Survey 

Letter ID: 0132 Comment ID: 21542 Letter Lines: 28 to 76 

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

USDW 

Comment: The requirements of injecting CO2 only below the lowermost Underground Source 

of 

Drinking Water (USDW) aquifer will make it impossible to inject CO2 into deep 

saline aquifers in Rock Mountain Laramide Basins (RMLB). The problem is when 

the deep geological sequestration CO2 targets in RMLB (i.e., deep saline 

aquifers) occur near the surface, they contain USDW. For example, at a depth of 

10,000 to 15,000 feet, a stratigraphic unit such as, but not limited to the 

Madison Limestone, typically has salinity > 10,000 ppm. However, this same unit 

at 0-3,000 feet depth typically has salinity < 500 ppm. Near the surface, the 

aquifer is recharged with copious quantities of fresh meteoric water; but, 

because of geohydrologic characteristics common to Laramide Basins of Wyoming, 

the fresh water does not circulate into the deeper portions of the basin. 

Instead, it discharges in the form of springs or into streams/rivers near the 

margin of the basin typically along bounding faults or breached, anticlinal 

structures. As a consequence, due to a lack of mixing meteoric and connate 

fluids, the fluid in the same unit at a depth of 10,000 feet maintains 

salinities more near the original depositional environment (i.e., marine waters 

with salinities > 30,000 ppm). If the formation fluid was part of a continuous 

fluid-flow system, the whole rock/fluid system would have been flushed during 

the Pleistocene when recharge rates were much higher than today. Observations 

made in all of Wyoming’s Laramide Basins demonstrate that fluid-flow systems in 

the deep saline aquifers are compartmentalized resulting in an absence of 

shallow-formation water mixing with deep basin brines. 

The ramifications of declaring a stratigraphic unit in Rocky Mountain Basins a 

USDW aquifer because it supplies fresh water at shallow depth are immense. The 

stratigraphic section beneath units such as the Paleozoic Madison Limestone and 

the Tensleep Sandstone (or stratigraphic equivalent units) is relatively thin in 

Wyoming. If the intention is to use geological CO2 sequestration as an 

effective mitigation tool for global climate change, the stratigraphic section 

between the Tensleep/Madison does not have the storage volume required to 

accommodate the huge quantities of CO2 that will need to be geologically 

sequestered. 

The Wyoming State Geological Survey suggests that our Nation will be much better 

served if the proposed regulations for geological CO2 sequestration, with 

1
2

respect to injecting CO2 only below the lowest USDW aquifer, be modified as 

follows: “Geological CO2 sequestration will be allowed in deep saline aquifers 

in Rocky Mountain Laramide Basins unless it can be demonstrated that the 

injected CO2 will have a deleterious effect on USDW.” 

If this change is not made, the geological sequestration of CO2 will be far more 

onerous than injecting H2S into the deep portion of RMLB. For economic and 

regulatory purposes, the regulations as proposed will make geological 

sequestration of CO2 impossible. To promulgate a geological CO2 sequestration 

regulation for RMLB out of the context of Rocky Mountain Laramide geology will 

make it extremely difficult to mitigate the effects of greenhouse emissions on 

climate change in the West. The Wyoming State Geological Survey requests that 

the United States Environmental Protection Agency act favorably on the changes 

herein described. 

Individual Response: EPA acknowledges that there are limited circumstances where injection 

above the lowermost USDW can be performed 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 owners or operators can seek a waiver of the Class VI injection 

depth requirements for injection into non-USDW formations above and/or between USDWs. It 

establishes: 1) requirements specifying information that owners or operators must submit, and 

Directors must consider, in consultation with PWSS Directors; 2) procedures for public notice of 

a waiver application and for Director-Regional Administrator communication; 3) the waiver 

issuance process; and, 4) additional requirements that apply to owners or operators of Class VI 

wells granted a waiver of the injection depth requirements to ensure 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 owners or operators who undertake CO2 injection for GS. The 

Agency believes this approach: 1) responds to concerns about local and regional geologic storage 

capacity limitations imposed by the proposed injection depth requirements; 2) allows for a more 

site-specific assessment of injection depth for GS projects; 3) accommodates injection into 

different formation types; 4) allows 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 aquifer exemptions for GS. Finally, 

EPA’s approach to addressing injection depth variability through a waiver process responds to 

concerns about future drinking water resource availability and the need to ensure that high 

quality water remains available in sufficient quantities to supply drinking water needs. For 

additional information on the waiver approach, please see the final rule and preamble, as well as 

EPA's responses to comments on the Notice of Data Availability and Request for Comment.