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.
Schlumberger Carbon Services Comments on “Requirements for Class VI Injection 

Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule” Contact: 

Andrew Duguid, Ph.D., P.E. aduguid@slb.com 

1

Underground Injection Control (UIC) Program: Federal Requirements for Class VI 

Injection Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule 

Comments from Schlumberger Carbon Services

Schlumberger is the world’s leading supplier of oilfield technology, integrated project 

management and information solutions that optimize reservoir performance. Founded in 

1926, the company employs more than 80,000 people of over 140 nationalities working 

in approximately 80 countries. Since the early 1990’s, Schlumberger has been involved in 

CO2 injection projects, providing services for subsurface characterization and 

monitoring, while also investing in specific research and development. Leveraging on its 

internal know how, Schlumberger has created in 2005 the Schlumberger Carbon Services 

(SCS) activity, which currently focuses on aligning the group strategy and resources with 

the current and future CO2 sequestration business environment, while managing the 

development of comprehensive technologies and project management services. 

Schlumberger Carbon Services have both experienced geo-technical personnel capable of 

evaluating all aspects of geologic storage as well as the technology needed to evaluate, 

design, construct and monitor storage sites 

Schlumberger feels that the proposed rule for geologic sequestration of carbon dioxide is 

a very good start and relatively few changes are needed to create a final rule under which 

geologic CO2 sequestration can become a commercial industry and an effective piece in 

the solution to climate change. 

Below we provide comments on the rule language (both general and detailed line-byline), the areas specifically identified for comment in the preamble, and on other aspects 

of the preamble. 

Comments on areas within the body of the proposed rule 

1. Schlumberger asks that the EPA expand the applicability of Class VI wells to 

cover wells injecting CO2 that is dissolved in water or brine. The current draft 

language for Section 146.81(b) states: 

This subpart applies to wells used to inject carbon dioxide specifically for 

the purpose of geologic sequestration, i.e., the long-term containment of a 

gaseous, liquid or supercritical carbon dioxide stream in subsurface 

geologic formations. 

We suggest that the EPA replace the current language with the following 

language: 

This subpart applies to wells used to inject carbon dioxide specifically for 

the purpose of geologic sequestration, i.e., the long-term containment of a 
Schlumberger Carbon Services Comments on “Requirements for Class VI Injection 

Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule” Contact: 

Andrew Duguid, Ph.D., P.E. aduguid@slb.com 

2

gaseous, liquid or supercritical carbon dioxide stream or carbon dioxide 

dissolved in water or brine into subsurface geologic formations. 

While we recognize today the injection of dissolved CO2 raises economic 

challenges we feel that there may be cases where the injection of dissolved CO2 

will make sense both in terms of economics and in terms of leakage risk. Unlike 

separate phase CO2, CO2 dissolved in water is not less dense than the formation 

fluid and will not be subject to buoyancy driven leakage. 

2. Schlumberger feels that the general prohibition on CO2 injection above the 

lowermost USDW should removed from the regulations. We feel that as long as 

the injection will not endanger USDWs the elevation with respect to the 

lowermost USDW is not important. However, if CO2 injection is allowed above 

the lowermost USDW we feel that the EPA must specify that there needs to be a 

confining unit both above and below the injection zone that is free of pathways 

that may allow for leakage of fluids out of the injection zone. The inclusion of a 

lower confining unit will be important because CO2-saturated brine or water is 

more dense than the native formation fluid and will sink. 

3. Schlumberger does not support the default post injection site care period of 50 

years. We feel that because the characterization and operation of the site will be 

based on the specific attributes of the site that the length of post injection site care 

should also be site specific information. In particular the criteria for ending the 

PISC period should be based on site performance and risk. We support the idea 

that the director approves final site closure. We suggest the following language 

for Section 146.93(b)(1): 

 

(1) The owner or operator shall continue to conduct monitoring as 

specified in the Director-approved post-injection site care and site closure 

plan, pursuant to the performance based criteria described in 146.93(b)(3). 

We suggest the following language for section 146.93(b)(2) 

(2) If the owner or operator can demonstrate to the satisfaction of the 

Director that the geologic sequestration project no longer poses an 

endangerment to USDWs, the Director may approve an amendment to the 

post-injection site care and site closure plan to reduce the frequency of 

monitoring or may authorize site closure. 

And we suggest the following language for section 146.93(b)(3) 

(3) Prior to authorization for site closure, the owner or operator must 

demonstrate to the Director, based on monitoring and other site-specific 

data that no additional monitoring is needed to assure that the geologic 

sequestration project does not pose an endangerment to USDWs, 

considering the following:. 
Schlumberger Carbon Services Comments on “Requirements for Class VI Injection 

Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule” Contact: 

Andrew Duguid, Ph.D., P.E. aduguid@slb.com 

3

(i) the estimated magnitude and extent of the AOR based on 

measurements and modeling; 

(ii) that CO2 movement and pressure changes match model predictions, 

(iii) the estimated location of the detectable CO2 plume based on 

measurement and modeling (measuring magnitude of saturation within the 

plume or mapping the edge of it); 

(iv) that there is no evidence of significant leakage of either CO2 or 

formation fluids that endanger USDWs; 

(v) that the CO2 plume and displaced formation fluid are not expected to 

migrate in the future in a manner that encounters a potential leakage 

pathway; and, 

(vi) that wells at the site are not leaking and have maintained integrity. 

4. Schlumberger supports the concept of testing and monitoring to track the CO2 

plume and the associated pressure front. We feel that without this monitoring the 

validation and updating of the models used to predict the size and shape of the 

AOR cannot be properly conducted and that the use of models to predict the size 

and shape of the AOR will be ineffective. However we feel that the language in 

section 146.90(g) is too restrictive. The current language states: 

(g) Testing and monitoring to track the extent of the carbon dioxide plume 

and the position of the pressure front by either monitoring for pressure 

changes in the first formation overlying the confining zone or using 

indirect, geophysical techniques (e.g., seismic, electrical, gravity, or 

electromagnetic surveys and/or down-hole carbon dioxide detection tools);

 

We feel that the restrictions placed in this language could adversely impact the 

efficiency of monitoring and modeling depending on site conditions. 

Schlumberger proposes the following alternate language: 

(g) Testing and monitoring to track the extent of the carbon dioxide plume 

and the position of the pressure front by either monitoring for pressure 

changes, using geophysical techniques (e.g., seismic, electrical, gravity, or 

electromagnetic surveys and/or down-hole carbon dioxide detection tools), 

other techniques that are approved by the director or a combination of 

techniques if multiple techniques are deemed necessary by the director;

Comments on areas within the preamble of the rule 

1. Schlumberger supports the idea that horizontal wells may be used for injection for 

geologic carbon sequestration. Horizontal CO2 injection wells have been 

successfully and safely used for CO2 injection at the Weyburn project in 

Saskatchewan, Canada. We feel that there will be sites with conditions that will 

make the use of horizontal wells necessary. 
Schlumberger Carbon Services Comments on “Requirements for Class VI Injection 

Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule” Contact: 

Andrew Duguid, Ph.D., P.E. aduguid@slb.com 

4

2. Now that the EPA has introduced the topics of the Comprehensive Environmental 

Response, Compensation, and Liability Act (CERCLA) and the Resource 

Conservation and Recovery Act (RCRA) we urge the EPA to clarify the roles of 

both with respect to CO2 injection under the UIC program. 

Schlumberger supports the EPA in defining the injected CO2 stream to exclude 

hazardous wastes. We feel that this definition implies that CO2 itself is not a 

hazardous waste under RCRA and that the injected CO2 stream can only be 

considered a hazardous waste if it is mixed with another hazardous waste. 

Schlumberger feels that supercritical and gaseous CO2 do not fit the definition of 

solid waste under RCRA which is limited to “solid, liquid, semisolid, and 

contained gaseous materials” and are therefore not regulated under RCRA. We 

encourage the EPA to explore this possibility and if in agreement, to adopt and 

espouse this position in the preamble for the final rule. We further feel that EPA 

should specify that uncontainerized supercritical CO2, like that at injected for CCS,

is not solid waste and therefore not subject to RCRA waste determination 

requirements. 

The preamble of the draft points out that under federally permitted release 

provision of CERCLA releases in compliance with a UIC permit are exempt from 

liability under CERCLA. Schlumberger fails to see how the any releases under 

the proposed rule that involves both characterization of the injection stream and 

characterization of the subsurface can fall outside the federally permitted release 

provision. We urge the EPA to better clarify any cases where injection of CO2 in 

accordance with a UIC permit is not released from liability under the federally 

permitted release provision of CERCLA. We cannot envision a permit being 

issued for an injection that could cause an unintended release, especially, in light 

of the information that is required in the permit application on the composition of 

the injection stream and on the chemical makeup of the subsurface. 

3. In the preamble of the draft U-tube technology is specifically called out as a 

technology available for high pressure fluid sampling. Schlumberger wants point 

out to the EPA there are other techniques for high pressure fluid sampling the use 

of wireline conveyed sample bottles. We want to ensure that no one particular 

technology is adopted or required for high pressure sampling. The selection of a 

single sampling technique (although not in the rule language) could cause the best 

available technology to be overlooked now or in the future. We propose that EPA 

either delete the reference to the U-tube samples of clarify that it is not the only 

solution available for taking high pressure samples 

4. Schlumberger appreciates that the EPA crated the Vulnerability Evaluation 

Framework (VEF) and we fully support the use of a logical set of steps to address 

the vulnerabilities or risks associated with geologic carbon sequestration. 

However, we are concerned that the VEF is not the only method that may be 
Schlumberger Carbon Services Comments on “Requirements for Class VI Injection 

Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule” Contact: 

Andrew Duguid, Ph.D., P.E. aduguid@slb.com 

5

successful for site evaluation and would like EPA to clarify that the VEF is one 

but not the only approach. 

 

Again we thank the US EPA for this chance to provide comment on the proposed rule. 

Any questions regarding these comments can be directed to: 

Andrew Duguid, Ph.D., PE 

Senior Wellbore Integrity Engineer 

Schlumberger Carbon Services 

4449 Easton Way, 2nd Floor 

Columbus, OH 43219 

 

Phone: (412) 427-7169 

aduguid@slb.com 
Schlumberger Carbon Services Comments on “Requirements for Class VI Injection 

Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule” Contact: 

Andrew Duguid, Ph.D., P.E. aduguid@slb.com 

6

Detailed Line-by-Line Comments 

Proposed Rule Schlumberger 

Suggested Revision 

Schlumberger 

Rationale 

§144.1 Purpose and scope 

of part 144. 

- - 

(f)(1)(viii) Subpart H of this 

part sets forth requirements for 

owners or operators of Class 

VI injection wells. 

- - 

(g) Scope of the permit or rule 

requirement. The UIC Permit 

Program regulates 

underground injections by six 

classes of wells (see definition 

of ‘‘well injection,’’ §144.3). 

The six classes of wells are 

set forth in §144.6. All owners 

or operators of these injection 

wells must be authorized 

either by permit or rule by the 

Director. 

- - 

§144.6 Classification of 

wells. 

- - 

(e) Class V. Injection wells not 

included in Class I, II, III, IV, or 

VI. Specific types of Class V 

injection wells are described in 

§144.81. 

- - 

(f) Class VI. Wells used for 

geologic sequestration of 

carbon dioxide beneath the 

lowermost formation 

containing a USDW. 

(f) Class VI. Wells used for 

geologic sequestration of 

carbon dioxide. 

We feel that sequestration can 

be conducted safely above 

USDWs as evidenced by the 

class 2 EOR experience. 

Also, the restriction to below 

the lowest USDW rules out 

many potential CCS sites. 

Subpart B —General 

Program Requirements 

- - 

§144.15 Prohibition of nonexperimental Class V wells 

for geologic sequestration. 

- - 

The construction, operation or 

maintenance of any nonexperimental Class V geologic 

sequestration well is 

prohibited. 

- We agree, there should be 

only one class of geologic 

sequestration well but CO2 

class V wells should be 

grandfathered. 

5. Adding Section 144.18 to 

read as follows. 

- - 

§144.18 Requirements for - - 
Schlumberger Carbon Services Comments on “Requirements for Class VI Injection 

Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule” Contact: 

Andrew Duguid, Ph.D., P.E. aduguid@slb.com 

7

Proposed Rule Schlumberger 

Suggested Revision 

Schlumberger 

Rationale 

Class VI wells. 

Owners or operators of Class 

VI wells must obtain a permit. 

Class VI wells are not 

authorized by rule to inject. 

- - 

Subpart D—Authorization by 

Permit 

- - 

§144.36 Duration of permits. - - 

(a) Permits for Class I and V 

wells shall be effective for a 

fixed term not to exceed 10 

years. UIC Permits for Class 

II, III and VI wells shall be 

issued for a period up to the 

operating life of the facility. 

- - 

7. Section 144.39 is amended 

by revising the second 

sentence in paragraph (a) 

introductory text and by 

revising the second sentence 

in paragraph (a)(3) 

introductory text to read as 

follows: 

- - 

§144.39 Modification or 

revocation and reissuance 

of permits. 

- - 

(a) For Class I hazardous 

waste injection wells, Class II, 

Class III or Class VI wells the 

following may be causes for 

revocation and reissuance as 

well as modification; and for all 

other wells the following may 

be cause for revocation or 

reissuance as well as 

modification when the 

permittee requests or agrees. 

- - 

(3) Permits other than for 

Class I hazardous waste 

injection wells, Class II, Class 

III or Class VI wells may be 

modified during their terms for 

this cause only as follows: 

- - 

Subpart E—Permit 

Conditions 

- - 

Section 144.51 is amended by 

revising the first sentence in 

paragraph (q)(1) and the first 

sentence in paragraph (q)(2) 

- - 
Schlumberger Carbon Services Comments on “Requirements for Class VI Injection 

Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule” Contact: 

Andrew Duguid, Ph.D., P.E. aduguid@slb.com 

8

Proposed Rule Schlumberger 

Suggested Revision 

Schlumberger 

Rationale 

to read as: 

§144.51 Conditions 

applicable to all permits. 

- - 

- - 

(q) (1) The owner or operator 

of a Class I, II, III or VI well 

permitted under this part shall 

establish mechanical integrity 

prior to commencing injection 

or on a schedule determined 

by the Director. Thereafter the 

owner or operator of Class I, 

II, and III wells must maintain 

mechanical integrity as 

defined in §146.8 and the 

owner or operator of Class VI 

wells must maintain 

mechanical integrity as 

defined in §146.89 of this 

chapter. 

- - 

(2) When the Director 

determines that a Class I, II, III 

or VI well lacks mechanical 

integrity pursuant to §146.8 or 

§146.89 for Class VI of this 

chapter, he/she shall give 

written notice of his/her 

determination to the owner or 

operator. 

- - 

9. Section 144.52 is amended 

by revising paragraph (a)(8) to 

read as follows: 

- - 

§144.52 Establishing permit 

conditions. 

- - 

(a)(8) Mechanical integrity. A 

permit for any Class I, II, III or 

VI well or injection project 

which lacks mechanical 

integrity shall include, and for 

any Class V well may include, 

a condition prohibiting injection 

operations until the permittee 

shows to the satisfaction of the 

Director under §146.08 

or§146.89 for Class VI that the 

well has mechanical integrity. 

- - 

10. Section 144.55 is 

amended by revising the first 

- - 
Schlumberger Carbon Services Comments on “Requirements for Class VI Injection 

Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule” Contact: 

Andrew Duguid, Ph.D., P.E. aduguid@slb.com 

9

Proposed Rule Schlumberger 

Suggested Revision 

Schlumberger 

Rationale 

sentence in paragraph (a) to 

read as follows: 

§144.55 Corrective Action. - - 

(a) Coverage. Applicants for 

Class I, II, (other than 

existing), III or VI injection well 

permits shall identify the 

location of all known wells 

within the injection well's area 

of review which penetrate the 

injection zone, or in the case 

of Class II wells operating over 

the fracture pressure of the 

injection formation, all known 

wells within the area of review 

penetrating formations 

affected by the increase in 

pressure. Applicants for Class 

VI shall perform corrective 

action as specified in §146.84. 

- - 

Subpart G—Requirements 

for Owners and Operators of 

Class V Injection Wells 

- - 

11. Section 144.80 is 

amended by revising the first 

sentence in paragraph (e) and 

by adding paragraph (f) to 

read as follows: 

- - 

§144.80 What is a Class V 

injection well? 

- - 

(e) Class V. Injection wells not 

included in Class I, II, III, IV or 

VI. 

- - 

(f) Class VI. Wells used for 

geologic sequestration of 

carbon dioxide. 

- - 

PART 146—UNDERGROUND 

INJECTION CONTROL 

PROGRAM: CRITERIA AND 

STANDARDS 

- - 

§146.5 Classification of 

injection wells. 

- - 

(e) Class V. Injection wells not 

included in Class I, II, III, IV or 

VI. 

- - 
Schlumberger Carbon Services Comments on “Requirements for Class VI Injection 

Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule” Contact: 

Andrew Duguid, Ph.D., P.E. aduguid@slb.com 

10

Proposed Rule Schlumberger 

Suggested Revision 

Schlumberger 

Rationale 

(f) Class VI. Wells used for 

geologic sequestration of 

carbon dioxide beneath the 

lowermost formation 

containing an underground 

source of drinking water 

(USDW). 

(f) Class VI. Wells used for 

geologic sequestration of 

carbon dioxide. 

We feel that sequestration can 

be conducted safely above 

USDWs as evidenced by the 

class 2 EOR experience. 

Also, the restriction to below 

the lowest USDW rules out 

many potential CCS sites. 

Subpart H—Criteria and 

Standards Applicable to 

Class VI Wells 

- - 

§146.81 Applicability. - - 

(a) This subpart establishes 

criteria and standards for 

underground injection control 

programs to regulate Class VI 

carbon dioxide geologic 

sequestration injection wells. 

- - 

(b) This subpart applies to 

wells used to inject carbon 

dioxide specifically for the 

purpose of geologic 

sequestration, i.e., the longterm containment of a 

gaseous, liquid or supercritical 

carbon dioxide stream in 

subsurface geologic 

formations. 

- - 

(c) This subpart applies to 

owners and operators of 

permit or rule-authorized Class 

I industrial, Class II, or Class V 

experimental carbon dioxide 

injection projects who seek to 

apply for a Class VI geologic 

sequestration permit for their 

well or wells. If the Director 

determines that USDWs will 

not be endangered, such wells 

are exempt, at the Director’s 

discretion, from the casing and 

cementing requirements at 

§§146.86(b) and 146.87(a)(1) 

through (3). 

(c) This subpart applies to 

owners and operators of 

permit or rule-authorized Class 

I industrial, Class II, or Class V 

experimental carbon dioxide 

injection projects who seek to 

apply for a Class VI geologic 

sequestration permit for their 

well or wells. If the Director 

determines that USDWs will 

not be endangered, such wells 

are exempt, at the Director’s 

discretion, from the casing and 

cementing requirements at 

§§146.86(b) and 146.87(a)(1) 

through (3) if the wells were 

constructed prior to January 1, 

2010. 

We feel that there needs to be 

a cutoff date for the 

grandfathering of wells so 

eventually all Class 6 wells are 

constructed to the same 

standard 
Schlumberger Carbon Services Comments on “Requirements for Class VI Injection 

Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule” Contact: 

Andrew Duguid, Ph.D., P.E. aduguid@slb.com 

11

Proposed Rule Schlumberger 

Suggested Revision 

Schlumberger 

Rationale 

(d) Definitions. The following 

definitions apply to this 

subpart. To the extent that 

these definitions conflict with 

those in §146.3 these 

definitions govern: 

- - 

Area of review means the 

region surrounding the 

geologic sequestration project 

that may be impacted by the 

injection activity. The area of 

review is based on 

computational modeling that 

accounts for the physical and 

chemical properties of all 

phases of the injected carbon 

dioxide stream. 

- - 

Carbon dioxide plume means 

the underground extent, in 

three dimensions, of an 

injected carbon dioxide 

stream. 

- - 

Carbon dioxide stream means 

carbon dioxide that has been 

captured from an emission 

source (e.g., a power plant), 

plus incidental associated 

substances derived from the 

source materials and the 

capture process, and any 

substances added to the 

stream to enable or improve 

the injection process. This 

subpart does not apply to any 

carbon dioxide stream that 

meets the definition of a 

hazardous waste under 40 

CFR part 261. 

Carbon dioxide stream carbon 

dioxide that has been captured 

from an industrial process that 

is injected in any physical 

state or dissolved in water or 

brine. It includes incidental 

associated substances derived 

from the source materials and 

the capture process, and any 

substances added to the 

stream to enable or improve 

the injection process. This 

subpart does not apply to any 

carbon dioxide stream that 

meets the definition of a 

hazardous waste under 40 

CFR part 261. 

We want to ensure that 

dissolved CO2 is specifically 

allowed as it may allow a 

solution to the upward 

buoyancy drive associated 

with separate phase CO2. 

Confining zone means a 

geologic formation, group of 

formations, or part of a 

formation stratigraphically 

overlying the injection zone 

that acts as a barrier to fluid 

movement. 

- - 
Schlumberger Carbon Services Comments on “Requirements for Class VI Injection 

Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule” Contact: 

Andrew Duguid, Ph.D., P.E. aduguid@slb.com 

12

Proposed Rule Schlumberger 

Suggested Revision 

Schlumberger 

Rationale 

Corrective action means the 

use of Director approved 

methods to assure that wells 

within the area of review do 

not serve as conduits for the 

movement of fluids into 

underground sources of 

drinking water (USDW). 

- - 

Geologic sequestration means 

the long-term containment of a 

gaseous, liquid or supercritical 

carbon dioxide stream in 

subsurface geologic 

formations. This term does not 

apply to its capture or 

transport. 

Geologic sequestration means 

the long-term containment of a 

carbon dioxide stream in 

subsurface geologic 

formations. This term does not 

apply to its capture or 

transport. 

CO2 stream was already 

defined and should e used 

here. 

Geologic sequestration project 

means an injection well or 

wells used to emplace a 

carbon dioxide stream 

beneath the lowermost 

formation containing a USDW. 

It includes the subsurface 

three-dimensional extent of 

the carbon dioxide plume, 

associated pressure front, and 

displaced brine, as well as the 

surface area above that 

delineated region. 

Geologic sequestration project 

means an injection well or 

wells used to emplace a 

carbon dioxide stream into an 

injection zone. It includes the 

subsurface three-dimensional 

extent of the carbon dioxide 

plume, associated pressure 

front, and displaced brine, as 

well as the surface area above 

that delineated region. 

- 

Injection zone means a 

geologic formation, group of 

formations, or part of a 

formation that is of sufficient 

areal extent, thickness, 

porosity, and permeability to 

receive carbon dioxide through 

a well or wells associated with 

a geologic sequestration 

project. 

Injection zone means a 

geologic formation, group of 

formations, or part of a 

formation that is of sufficient 

areal extent, thickness, 

porosity, and permeability to 

receive carbon dioxide through 

a well or wells associated with 

a geologic sequestration 

project. 

- 

Post-injection site care means 

appropriate monitoring and 

other actions (including 

corrective action) needed 

following cessation of injection 

to assure that USDWs are not 

endangered as required under 

§146.93. 

- - 
Schlumberger Carbon Services Comments on “Requirements for Class VI Injection 

Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule” Contact: 

Andrew Duguid, Ph.D., P.E. aduguid@slb.com 

13

Proposed Rule Schlumberger 

Suggested Revision 

Schlumberger 

Rationale 

Pressure front means the zone 

of elevated pressure that is 

created by the injection of 

carbon dioxide into the 

subsurface. For the purposes 

of this subpart, the pressure 

front of a carbon dioxide 

plume refers to a zone where 

there is a pressure differential 

sufficient to cause the 

movement of injected fluids or 

formation fluids into a USDW. 

Pressure front means the zone 

of elevated pressure that is 

created by the injection of the 

carbon dioxide stream into the 

subsurface, where there is a 

pressure differential sufficient 

to cause movement of the 

carbon dioxide stream or 

formation fluids into a USDW. 

- 

Site closure the point/time, as 

determined by the Director 

following the requirements 

under §146.93, at which the 

owner or operator of a GS site 

is released from post-injection 

site care responsibilities. 

Site closure means the 

point/time, as determined by 

the Director following the 

requirements under §146.93, 

at which the owner or operator 

of a GS project is released 

from post-injection site care 

responsibilities. 

Suggest using “GS project” to 

be consistent with other 

definitions 

Transmissive fault or fracture 

means a fault or fracture that 

has sufficient permeability and 

vertical extent to allow fluids to 

move between formations. 

Transmissive fault or fracture 

means a fault or fracture that 

has sufficient permeability and 

vertical extent to allow fluids to 

move beyond the confining 

zone. 

The term between formations 

is insufficient as it could also 

include multiple zones within a 

injection zone or between two 

zones above the confining 

unit. 

§146.82 Required Class VI 

permit information. 

- - 

This section sets forth the 

information which the owner or 

operator must submit to the 

Director in order to be 

permitted as a Class VI well. 

The application for a permit for 

construction and operation of 

a Class VI well must include 

the following: 

- - 

(a) Information required in 40 

CFR 144.31 (e)(1) through (6); 

- - 
Schlumberger Carbon Services Comments on “Requirements for Class VI Injection 

Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule” Contact: 

Andrew Duguid, Ph.D., P.E. aduguid@slb.com 

14

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(b) A map showing the 

injection well(s) for which a 

permit is sought and the 

applicable area of review. 

Within the area of review, the 

map must show the number, 

or name and location of all 

injection wells, producing 

wells, abandoned wells, 

plugged wells or dry holes, 

deep stratigraphic boreholes, 

State or EPA approved 

subsurface cleanup sites, 

surface bodies of water, 

springs, mines (surface and 

subsurface), quarries, water 

wells and other pertinent 

surface features including 

structures intended for human 

occupancy and roads. The 

map should also show faults, if 

known or suspected. Only 

information of public record is 

required to be included on this 

map; 

(b) A map or electronic file 

(e.g. GIS file) showing the 

injection well(s) for which a 

permit is sought and the 

applicable area of review. 

Within the area of review, the 

map must show the number, 

or name and location of all 

injection wells, producing 

wells, abandoned wells, 

plugged wells or dry holes, 

deep stratigraphic boreholes, 

State or EPA approved 

subsurface cleanup sites, 

surface bodies of water, 

springs, mines (surface and 

subsurface), quarries, water 

wells and other pertinent 

surface features including 

structures intended for human 

occupancy and roads. The 

map should also show faults, if 

known or suspected with 

surface expressions. Only 

information of public record is 

required to be included on this 

map; 

This may mean more 

clarification. It seems strange 

to have deep faults on a 

surface map. Is the map to be 

of the surface or of the 

confining unit? Also, any map 

will be very busy so it may be 

useful to be able to submit an 

electronic file like a GIS file. 

(c) The area of review based 

on modeling, using data 

obtained during logging and 

testing of the well and the 

formation as required by 

paragraphs (l), (r), and (s) of 

this section; 

- We support this but it may 

need to be better clarified that 

the well must e drilled prior to 

the permit application 

(d) Information on the geologic 

structure and hydrogeologic 

properties of the proposed 

storage site and overlying 

formations, including: 

- - 

(1) Maps and cross sections of 

the area of review; 

- - 

(2) Location, orientation, and 

properties of known or 

suspected faults and fractures 

that may transect the confining 

zone(s) in the area of review 

and a determination that they 

would not interfere with 

containment; 

- - 
Schlumberger Carbon Services Comments on “Requirements for Class VI Injection 

Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule” Contact: 

Andrew Duguid, Ph.D., P.E. aduguid@slb.com 

15

Proposed Rule Schlumberger 

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(3) Information on seismic 

history including the presence 

and depth of seismic sources 

and a determination that the 

seismicity would not interfere 

with containment; 

(3) Information on seismic 

history of the area including 

the presence and depth of 

seismic sources and a 

determination that the 

seismicity would not interfere 

with containment; 

It seems like this requirement 

is at a larger scale than the 

AOR (maybe a regional scale) 

than the other requirements. 

This should be specified. 

(4) Data on the depth, areal 

extent, thickness, mineralogy, 

porosity, permeability and 

capillary pressure of the 

injection and confining 

zone(s); including 

geology/facies changes based 

on field data which may 

include geologic cores, 

outcrop data, seismic surveys, 

well logs, and names and 

lithologic descriptions; 

(4) Data on the depth, areal 

extent, thickness, mineralogy, 

porosity, permeability and 

capillary entry pressure of the 

injection and confining 

zone(s); including 

geology/facies changes based 

on field data which may 

include geologic cores, 

outcrop data, seismic surveys, 

well logs, and names and 

lithologic descriptions; 

Should this include capillary 

pressure or capillary entry 

pressure? 

(5) Geomechanical information 

on fractures, stress, ductility, 

rock strength, and in situ fluid 

pressures within the confining 

zone; and 

- - 

(6) Geologic and topographic 

maps and cross sections 

illustrating regional geology, 

hydrogeology, and the 

geologic structure of the local 

area. 

- - 

(e) A tabulation of all wells 

within the area of review which 

penetrate the injection or 

confining zone(s). Such data 

must include a description of 

each well's type, construction, 

date drilled, location, depth, 

record of plugging and/or 

completion, and any additional 

information the Director may 

require; 

- How will this be handled if all 

of this data is not available for 

each well? 

(f) Maps and stratigraphic 

cross sections indicating the 

general vertical and lateral 

limits of all USDWs, water 

wells and springs within the 

area of review, their positions 

relative to the injection zone(s) 

and the direction of water 

movement, where known; 

In - 
Schlumberger Carbon Services Comments on “Requirements for Class VI Injection 

Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule” Contact: 

Andrew Duguid, Ph.D., P.E. aduguid@slb.com 

16

Proposed Rule Schlumberger 

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(g) Baseline geochemical data 

on subsurface formations, 

including all USDWs in the 

area of review; 

(g) Baseline geochemical data 

on subsurface formations, 

including all USDWs and 

geochemically monitored in 

the area of review; 

All formations that are or may 

need to be geochemically 

monitored should be included 

(h) Proposed operating data: - - 

(1) Average and maximum 

daily rate and volume of the 

carbon dioxide stream; 

- - 

(2) Average and maximum 

injection pressure; 

- - 

(3) The source of the carbon 

dioxide stream; and 

- - 

(4) An analysis of the chemical 

and physical characteristics of 

the carbon dioxide stream; 

- - 

(i) The compatibility of the 

carbon dioxide stream with 

fluids in the injection zone and 

minerals in both the injection 

and the confining zone(s), 

based on the results of the 

formation testing program, and 

with the materials used to 

construct the well; 

- - 

(j) Proposed formation testing 

program to obtain an analysis 

of the chemical and physical 

characteristics of the injection 

zone and confining zone; 

- - 

(k) Proposed stimulation 

program and a determination 

that stimulation will not 

interfere with containment; 

- - 

(l) The results of the formation 

testing program as required in 

paragraph (j) of this section; 

- - 

(m) Proposed procedure to 

outline steps necessary to 

conduct injection operation; 

- - 

(n) Schematic or other 

appropriate drawings of the 

surface and subsurface 

- - 
Schlumberger Carbon Services Comments on “Requirements for Class VI Injection 

Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule” Contact: 

Andrew Duguid, Ph.D., P.E. aduguid@slb.com 

17

Proposed Rule Schlumberger 

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construction details of the well; 

(o) Injection well construction 

procedures that meet the 

requirements of §146.86; 

- - 

(p) Proposed area of review 

and corrective action plan that 

meets the requirements under 

§146.84; 

- - 

(q) The status of corrective 

action on wells in the area of 

review; 

- - 

(r) All available logging and 

testing program data on the 

well required by §146.87; 

- - 

(s) A demonstration of 

mechanical integrity pursuant 

to §146.89; 

- - 

(t) A demonstration, 

satisfactory to the Director, 

that the applicant has met the 

financial responsibility 

requirements under §146.85; 

- - 

(u) Proposed testing and 

monitoring plan required by 

§146.90; 

- - 

(v) Proposed injection well 

plugging plan required by 

§146.92(b); 

- - 

(w) Proposed post-injection 

site care and site closure plan 

required by §146.93(a); 

- - 

(x) Proposed emergency and 

remedial response plan 

required by §146.94; and 

- - 

(y) Any other information 

requested by the Director. 

- - 
Schlumberger Carbon Services Comments on “Requirements for Class VI Injection 

Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule” Contact: 

Andrew Duguid, Ph.D., P.E. aduguid@slb.com 

18

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§146.83 Minimum criteria for 

siting. 

- - 

(a) Owners or operators of 

Class VI wells must 

demonstrate to the satisfaction 

of the Director that the wells 

will be sited in areas with a 

suitable geologic system. The 

geologic system must be 

comprised of: 

- - 

(1) An injection zone of 

sufficient areal extent, 

thickness, porosity, and 

permeability to receive the 

total anticipated volume of the 

carbon dioxide stream; 

- - 

(2) A confining zone(s) that is 

free of transmissive faults or 

fractures and of sufficient areal 

extent and integrity to contain 

the injected carbon dioxide 

stream and displaced 

formation fluids and allow 

injection at proposed 

maximum pressures and 

volumes without initiating or 

propagating fractures in the 

confining zone(s); and 

- We support this language as it 

is written. 

(b) At the Director’s discretion, 

owners or operators of Class 

VI wells must identify and 

characterize additional zones 

that will impede vertical fluid 

movement, are free of faults 

and fractures that may 

interfere with containment, 

allow for pressure dissipation, 

and provide additional 

opportunities for monitoring, 

mitigation and remediation. 

(b) Owners or operators of 

Class VI wells must identify 

and characterize some 

additional zones, if they exist, 

that will impede vertical fluid 

movement, allow for pressure 

dissipation, and provide 

additional opportunities for 

monitoring, mitigation and 

remediation. Vertical faults 

and fractures that transect 

these zones must be 

identified. 

We believe that a site with a 

single confining can provide 

storage integrity, however, we 

feel that if there are additional 

confining layers at the site 

they should be characterized 

to get a better estimate of 

leakage risk to USDWs and 

possibly identify additional 

monitoring zones. 

§146.84 Area of review and 

corrective action. 

- - 

(a) The area of review is the 

region surrounding the 

geologic sequestration project 

that may be impacted by the 

injection activity. The area of 

review is based on 

(a) The area of review is 

based on computational 

modeling that accounts for 

physical and the chemical 

properties of all phases of the 

injected carbon dioxide 

- 
Schlumberger Carbon Services Comments on “Requirements for Class VI Injection 

Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule” Contact: 

Andrew Duguid, Ph.D., P.E. aduguid@slb.com 

19

Proposed Rule Schlumberger 

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computational modeling that 

accounts for the physical and 

chemical properties of all 

phases of the injected carbon 

dioxide stream. 

stream, the associated 

pressure front, and displaced 

brine. 

(b) The owner or operator of a 

Class VI well must prepare, 

maintain, and comply with a 

plan to delineate the area of 

review for a proposed geologic 

sequestration project, 

periodically reevaluate the 

delineation, and perform 

corrective action that meets 

the requirements of this 

section and is acceptable to 

the Director. As a part of the 

permit application for approval 

by the Director, the owner or 

operator must submit an area 

of review and corrective action 

plan that includes the following 

information: 

(b) The owner or operator of a 

Class VI well must prepare, 

maintain, and comply with a 

plan to delineate the area of 

review for a proposed geologic 

sequestration project, 

reevaluate the delineation, and 

perform corrective action that 

meets the requirements of this 

section in a manner and at a 

frequency acceptable to the 

Director. As a part of the 

permit application, the owner 

or operator must submit an 

area of review and corrective 

action plan that includes the 

following information: 

(1) The method for delineating 

the area of review that meets 

the requirements of paragraph 

- - 

(c) of this section, including 

the model to be used, 

assumptions that will be made, 

and the site characterization 

data on which the model will 

be based; 

- - 

(2) A description of: - - 

(i) The minimum fixed 

frequency, not to exceed 10 

years, the owner or operator 

proposes to reevaluate the 

area of review; 

Revision: (i) The owner or 

operator will reevaluate the 

AOR after two years, 5 years 

and then no less frequently 

than every 5 years for period 

of injection. This schedule 

may be relaxed at the 

discretion of the director in the 

post injection period if 

appropriate data exist to 

support the change. 

We feel that a frequency of 

every 10 years is too long to 

identify early discrepancies 

between the site performance 

and the site model. Seeing 

early difference will allow for 

earlier model updating and 

provide additional reduction in 

leakage risk and a better 

understanding of the site. 
Schlumberger Carbon Services Comments on “Requirements for Class VI Injection 

Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule” Contact: 

Andrew Duguid, Ph.D., P.E. aduguid@slb.com 

20

Proposed Rule Schlumberger 

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(ii) The monitoring and 

operational conditions that 

would warrant a reevaluation 

of the area of review prior to 

the next scheduled 

reevaluation as determined by 

the minimum fixed frequency 

established in paragraph 

(b)(2)(i) of this section. 

- - 

(iii) How monitoring and 

operational data (e.g., injection 

rate and pressure) will be used 

to inform an area of review 

reevaluation; and 

- - 

(iv) How corrective action will 

be conducted to meet the 

requirements of paragraph (d) 

of this section, including what 

corrective action will be 

performed prior to injection 

and what, if any, portions of 

the area of review will have 

corrective action addressed on 

a phased basis and how the 

phasing will be determined; 

how corrective action will be 

adjusted if there are changes 

in the area of review; and how 

site access will be guaranteed 

for future corrective action. 

(iv) How corrective action will 

be conducted to meet the 

requirements of paragraph (d) 

of this section, including what 

corrective action will be 

performed prior to injection 

and what, if any, portions of 

the area of review will have 

corrective action addressed on 

a phased basis and how the 

phasing will be determined; 

how corrective action will be 

adjusted if there are changes 

in the area of review; and how 

site access will be arranged 

for future corrective action. 

Future access cannot be fully 

guaranteed for an area in 

advance that may not even be 

within the boundaries of the 

initial AOR/ project. 

(c) Owners or operators of 

Class VI wells must perform 

the following actions to 

delineate the area of review, 

identify all wells that require 

corrective action, and perform 

corrective action on those 

wells: 

- - 

(1) Predict, using 

computational modeling, the 

projected lateral and vertical 

migration of the carbon dioxide 

plume and formation fluids in 

the subsurface from the 

commencement of injection 

activities until the plume 

movement ceases, pressure 

differentials sufficient to cause 

the movement of injected 

fluids or formation fluids into a 

USDW are no longer present, 

- We support this as written 
Schlumberger Carbon Services Comments on “Requirements for Class VI Injection 

Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule” Contact: 

Andrew Duguid, Ph.D., P.E. aduguid@slb.com 

21

Proposed Rule Schlumberger 

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or after a fixed time period as 

determined by the Director. 

The model must: 

(i) Be based on detailed 

geologic data collected to 

characterize the injection 

zone, confining zone and any 

additional zones; and 

anticipated operating data, 

including injection pressures, 

rates and total volumes over 

the proposed life of the 

geological sequestration 

project; 

(i) Be based on detailed 

geologic data collected to 

characterize the injection 

zone, confining zone(s), 

monitoring zones and any 

additional zones; and 

anticipated operating data, 

including injection pressures, 

rates and total volumes over 

the proposed life of the 

geological sequestration 

project; 

We feel that if there are 

secondary confining units that 

they should be included in the 

site model along with any 

transmissive zones between 

the primary and secondary 

confining units. 

(ii) Take into account any 

geologic heterogeneities, data 

quality, and their possible 

impact on model predictions; 

and 

- - 

(iii) Consider potential 

migration through faults, 

fractures, and artificial 

penetrations. 

- - 

(2) Using methods approved 

by the Director, identify all 

penetrations, including active 

and abandoned wells and 

underground mines, in the 

area of review that may 

penetrate the confining zone. 

Provide a description of each 

well’s type, construction, date 

drilled, location, depth, record 

of plugging and/or completion, 

and any additional information 

the Director may require; and 

- We feel that there needs to be 

some effort to identify 

unknown wells using aerial 

surveys or other methods. We 

support this language as long 

as it is interpreted to mean 

more than just a record search 

in areas that that have been 

explored or produced oil and 

gas or have had other deep 

wells. 
Schlumberger Carbon Services Comments on “Requirements for Class VI Injection 

Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule” Contact: 

Andrew Duguid, Ph.D., P.E. aduguid@slb.com 

22

Proposed Rule Schlumberger 

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(3) Determine which 

abandoned wells in the area of 

review have been plugged (as 

required by §146.92) in a 

manner that prevents the 

movement of carbon dioxide 

or associated fluids that may 

endanger USDWs. 

(3) Determine which 

abandoned wells identified in 

146.84 (c) (2) have been 

plugged (as required by 

§146.92) in a manner that 

prevents the movement of 

carbon dioxide or formation 

fluids that may endanger 

USDWs. 

- 

(d) Owners or operators of 

Class VI wells must perform 

corrective action on all wells in 

the area of review that are 

determined to need corrective 

action using methods 

necessary to prevent the 

movement of fluid into or 

between USDWs including 

use of corrosion resistant 

materials, where appropriate. 

Owners or operators of Class 

VI wells must perform 

corrective action using 

corrosion resistant materials, 

when appropriate, on all wells 

identified in 146.84(c)(2) that 

are determined to need 

corrective action”. 

- 

(e) If monitoring data indicate 

an endangerment to USDWs, 

the owner or operator must 

notify the Director and cease 

operations as required by 

§146.94. 

- - 

(f) At the minimum fixed 

frequency, not to exceed 10 

years, as specified in the area 

of review and corrective action 

plan, or when monitoring and 

operational conditions warrant, 

owners or operators must: 

(f) At the same frequency as 

the reevaluation of the AOR as 

specified in 146.84(c ) (2) (i), 

or when monitoring and 

operational conditions warrant, 

owners or operators must: 

- 

(1) Reevaluate the area of 

review in the same manner 

specified in paragraph (c)(1) of 

this section; 

- - 

(2) Identify all wells in the 

reevaluated area of review 

that require corrective action in 

the same manner specified in 

- - 
Schlumberger Carbon Services Comments on “Requirements for Class VI Injection 

Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule” Contact: 

Andrew Duguid, Ph.D., P.E. aduguid@slb.com 

23

Proposed Rule Schlumberger 

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Rationale 

paragraph (c)(2) of this 

section; 

(3) Perform corrective action 

on wells requiring corrective 

action in the reevaluated area 

of review in the same manner 

specified in paragraph (c)(3) of 

this section; and 

- - 

(4) Submit an amended area 

of review and corrective action 

plan or demonstrate to the 

Director through monitoring 

data and modeling results that 

no amendment to the area of 

review and corrective action 

plan is needed. 

(4) Submit an amended area 

of review and corrective action 

plan or demonstrate to the 

Director through monitoring 

data and modeling results that 

no change to the area of 

review and corrective action 

plan is needed. 

- 

(g) The emergency and 

remedial response plan (as 

required by §146.94) and a 

demonstration of financial 

responsibility (as described by 

§146.85) must account for the 

entire area of review, 

regardless of whether or not 

corrective action in the area of 

review is phased. 

- - 

§146.85 Financial 

responsibility. 

- - 

(a) The owner or operator 

must demonstrate and 

maintain financial 

responsibility and resources 

for corrective action (that 

meets the requirements of 

§146.84), injection well 

plugging (that meets the 

requirements of §146.92), 

post-injection site care and 

site closure (that meets the 

requirements of §146.93), and 

emergency and remedial 

response (that meets the 

requirements of §146.94) in a 

manner prescribed by the 

Director until: 

- - 
Schlumberger Carbon Services Comments on “Requirements for Class VI Injection 

Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule” Contact: 

Andrew Duguid, Ph.D., P.E. aduguid@slb.com 

24

Proposed Rule Schlumberger 

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Rationale 

(1) The Director receives and 

approves the completed postinjection site care and site 

closure plan; and 

- - 

(2) The Director determines 

that the site has reached the 

end of the post injection site 

care period. 

- - 

(b) The owner or operator 

must provide to the Director, at 

a frequency determined by the 

Director, written updates of 

adjustments to the cost 

estimate to account for any 

amendments to the area of 

review and corrective action 

plan (§146.84), the injection 

well plugging plan (§146.92), 

and the post-injection site care 

and site closure plan 

(§146.93). 

 (b) The owner or operator 

must provide to the Director, at 

the same frequency as the 

AOR reevaluation, written 

updates of adjustments to the 

cost estimate to account for 

any amendments to the area 

of review and corrective action 

plan (§146.84), the injection 

well plugging plan (§146.92), 

and the post-injection site care 

and site closure plan 

(§146.93). 

We feel that potential changes 

in the size of the AOR require 

that all site plans be 

reevaluated at the same 

frequency as the AOR. 

(c) The owner or operator 

must notify the Director of 

adverse financial conditions 

such as bankruptcy, that may 

affect the ability to carry out 

injection well plugging and 

post-injection site care and 

site closure. 

- - 

(d) The operator must provide 

an adjustment of the cost 

estimate to the Director if the 

Director has reason to believe 

that the original demonstration 

is no longer adequate to cover 

the cost of injection well 

plugging (as required by 

§146.92) and post-injection 

site care and site closure (as 

required by §146.93). 

- - 

§146.86 Injection well 

construction requirements. 

- - 

(a) General. The owner or 

operator must ensure that all 

Class VI wells are constructed 

and completed to: 

- - 
Schlumberger Carbon Services Comments on “Requirements for Class VI Injection 

Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule” Contact: 

Andrew Duguid, Ph.D., P.E. aduguid@slb.com 

25

Proposed Rule Schlumberger 

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(1) Prevent the movement of 

fluids into or between USDWs 

or into any unauthorized 

zones; 

(1) Prevent the movement of 

fluids into or between USDWs 

or into any unauthorized zones 

that causes endangerment; 

- 

(2) Permit the use of 

appropriate testing devices 

and workover tools; and 

- - 

(3) Permit continuous 

monitoring of the annulus 

space between the injection 

tubing and long string casing. 

- - 

(b) Casing and Cementing of 

Class VI Wells. 

- - 

(1) Casing and cement or 

other materials used in the 

construction of each Class VI 

well must have sufficient 

structural strength and be 

designed for the life of the 

geologic sequestration project. 

All well materials must be 

compatible with fluids with 

which the materials may be 

expected to come into contact 

and meet or exceed standards 

developed for such materials 

by the American Petroleum 

Institute, ASTM International, 

or comparable standards 

acceptable to the Director. The 

casing and cementing 

program must be designed to 

prevent the movement of fluids 

into or between USDWs. In 

order to allow the Director to 

determine and specify casing 

and cementing requirements, 

the owner or operator must 

provide the following 

information: 

- We support this language as 

written. 

(i) Depth to the injection zone; - - 

(ii) Injection pressure, external 

pressure, internal pressure 

and axial loading; 

(ii) Injection pressure, external 

pressure, internal pressure 

and axial loading; 

What is meant by external and 

internal pressure? 

(iii) Hole size; 

(iv) Size and grade of all 

casing strings (wall thickness, 

external diameter, nominal 

weight, length, joint 

specification and construction 

material); 

- - 
Schlumberger Carbon Services Comments on “Requirements for Class VI Injection 

Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule” Contact: 

Andrew Duguid, Ph.D., P.E. aduguid@slb.com 

26

Proposed Rule Schlumberger 

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(v) Corrosiveness of the 

carbon dioxide stream, and 

formation fluids; 

- - 

(vi) Down-hole temperatures; (vi) Down-hole temperatures 

and pressures; 

- 

(vii) Lithology of injection and 

confining zones; 

- - 

(viii) Type or grade of cement; 

and 

(viii) Type or grade of cement; 

and additives 

- 

(ix) Quantity, chemical 

composition, and temperature 

of the carbon dioxide stream. 

- - 

(2) Surface casing must 

extend through the base of the 

lowermost USDW and be 

cemented to the surface. 

(2) Surface casing must 

extend through the base of the 

lowermost USDW above the 

injection zone and be 

cemented to the surface. 

In some parts of the US the 

USDW is very deep and this 

standard may preclude 

geologic sequestration in 

these areas. 

(3) At least one long string 

casing, using a sufficient 

number of centralizers, must 

extend to the injection zone 

and must be cemented by 

circulating cement to the 

surface in one or more stages. 

- We support this language 

work by Carey et al and crow 

et al shows that CO2 can 

move above the top of the 

CO2 reservoir, so cementing 

to surface will provide the best 

chance to have maximum 

zonal isolation 

(4) Circulation of cement may 

be accomplished by staging. 

The Director may approve an 

alternative method of 

cementing in cases where the 

cement cannot be recirculated 

to the surface, provided the 

owner or operator can 

demonstrate by using logs that 

the cement does not allow 

fluid movement behind the 

well bore. 

- - 

(5) Cement and cement 

additives must be compatible 

with the carbon dioxide stream 

and formation fluids and of 

sufficient quality and quantity 

to maintain integrity over the 

design life the geologic 

sequestration project. The 

integrity and location of the 

cement shall be verified using 

technology capable of 

evaluating cement quality 

radially and identifying the 

location of channels to ensure 

that USDWs are not 

(5) Cement and cement 

additives must be suitable for 

use with the carbon dioxide 

stream and formation fluids 

and of sufficient quality and 

quantity to maintain integrity 

over the project life. The 

integrity and location of the 

cement shall be verified using 

technology capable of 

evaluating cement quality 

radially and identifying the 

location of channels to ensure 

that USDWs are not 

endangered. 

Well cements need to site and 

condition specific. There may 

be instances or places in the 

well that will require special 

cements. It is also that the 

cement in the well last as long 

as the project and post 

injection period. 
Schlumberger Carbon Services Comments on “Requirements for Class VI Injection 

Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule” Contact: 

Andrew Duguid, Ph.D., P.E. aduguid@slb.com 

27

Proposed Rule Schlumberger 

Suggested Revision 

Schlumberger 

Rationale 

endangered. 

(c) Tubing and packer. - - 

(1) All owner and operators of 

Class VI wells must inject 

fluids through tubing with a 

packer set at a depth opposite 

a cemented interval at the 

location approved by the 

Director. 

- - 

(2) In order for the Director to 

determine and specify 

requirements for tubing and 

packer, the owner or operator 

must submit the following 

information: 

- - 

(i) Depth of setting; - - 

(ii) Characteristics of the 

carbon dioxide stream 

(chemical content, 

corrosiveness, temperature, 

and density); 

- - 

(iii) Injection pressure; - - 

(iv) Annular pressure; - - 

(v) Injection rate (intermittent 

or continuous) and volume of 

the carbon dioxide stream; 

- - 

(vi) Size of casing; and - - 

(vii) Tubing tensile, burst, and 

collapse strengths. 

- - 

§146.87 Logging, sampling, 

and testing prior to injection 

well operation. 

- - 
Schlumberger Carbon Services Comments on “Requirements for Class VI Injection 

Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule” Contact: 

Andrew Duguid, Ph.D., P.E. aduguid@slb.com 

28

Proposed Rule Schlumberger 

Suggested Revision 

Schlumberger 

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(a) During the drilling and 

construction of a Class VI 

injection well, the owner or 

operator must run appropriate 

logs, surveys and tests to 

determine or verify the depth, 

thickness, porosity, 

permeability, and lithology of, 

and the salinity of any 

formation fluids in, all relevant 

geologic formations to assure 

conformance with the injection 

well construction requirements 

under §146.86, and to 

establish accurate baseline 

data against which future 

measurements may be 

compared. The owner or 

operator must submit to the 

Director a descriptive report 

prepared by a knowledgeable 

log analyst that includes an 

interpretation of the results of 

such logs and tests. At a 

minimum, such logs and tests 

must include: 

(a) During the drilling and 

construction of a Class VI 

injection well, the owner or 

operator must run appropriate 

logs, surveys and tests to 

determine or verify the depth, 

thickness, porosity, 

permeability, and lithology of, 

and the salinity of any 

formation fluids in, all relevant 

geologic formations to assure 

conformance with the injection 

well construction requirements 

under §146.86, and to 

establish accurate baseline 

data against which future 

measurements may be 

compared. The owner or 

operator must submit to the 

Director a descriptive report 

prepared by a knowledgeable 

log analyst that includes an 

interpretation of the results of 

such logs and tests. The 

Director may require such logs 

and tests as may be needed 

after taking into account the 

availability of similar data in 

the area of the drilling site to 

ensure that the data is 

equivalent to the data as 

would be collected based on 

such logs and tests as:: 

In well defined areas, these 

evaluations are frequently 

unnecessary. The director 

should have discretion to 

select the appropriate 

requirements necessary to 

ensure that sufficient baseline 

data and information are 

available. For example, in an 

area where a number of wells 

are being drilled, the logging 

of surface hole yields little 

useful additional information. 

(1) Deviation checks during 

drilling on all holes constructed 

by drilling a pilot hole which 

are enlarged by reaming or 

another method. Such checks 

must be at sufficiently frequent 

intervals to determine the 

location of the borehole and to 

assure that vertical avenues 

for fluid movement in the form 

of diverging holes are not 

created during drilling; and 

- - 

(2) Before and upon 

installation of the surface 

casing: 

- - 

(i) Resistivity, spontaneous 

potential, and caliper logs 

before the casing is installed; 

and 

- - 
Schlumberger Carbon Services Comments on “Requirements for Class VI Injection 

Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule” Contact: 

Andrew Duguid, Ph.D., P.E. aduguid@slb.com 

29

Proposed Rule Schlumberger 

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(ii) A cement bond and 

variable density log, and a 

temperature log after the 

casing is set and cemented. 

- - 

(3) Before and upon 

installation of the long string 

casing: 

- - 

(i) Resistivity, spontaneous 

potential, porosity, caliper, 

gamma ray, fracture finder 

logs, and any other logs the 

Director requires for the given 

geology before the casing is 

installed; and 

- - 

(ii) A cement bond and 

variable density log, and a 

temperature log after the 

casing is set and cemented. 

(ii) Cement evaluation logs 

after the casing is set and 

cemented to evaluate cement 

quality radially with sufficient 

resolution to identify channels 

or changes to the cement 

quality. 

Radial is key to finding 

pathways but the resolution 

must be sufficient to see the 

pathways. See the pathway 

identified in Crow et al 

(4) A series of tests designed 

to demonstrate the internal 

and external mechanical 

integrity of injection wells, 

which may include: 

(4) Test(s) designed to 

demonstrate the internal and 

external mechanical integrity 

of injection wells, which may 

include: 

- 

(i) A pressure test with liquid 

or gas; 

- - 

(ii) A tracer survey such as 

oxygen-activation logging; 

(ii) Diagnostic tools such as 

oxygen-activation logging; 

Technical correction 

(iii) A temperature or noise log; - - 

(iv) A casing inspection log, if 

required by the Director; and 

- - 

(5) Any alternative methods 

that provide equivalent or 

better information and that are 

required of and/or approved of 

by the Director. 

- We interpret that (5) applies to 

146.87(a) 

(b) The owner or operator 

must take and submit to the 

Director whole cores or 

sidewall cores of the injection 

zone and confining system 

and formation fluid samples 

from the injection zone(s). The 

Director may accept cores 

from nearby wells if the owner 

or operator can demonstrate 

that core retrieval is not 

possible and that such cores 

are representative of 

(b) The owner or operator 

must submit to the Director a 

report describing whole cores 

or sidewall cores 

representative of the injection 

zone and confining system 

and formation fluid samples 

from the injection zone(s). The 

Director may accept data from 

cores and fluid samples from 

nearby wells if the owner or 

operator can demonstrate that 

such data are representative 

The information required 

should be sufficient to properly 

describe the injection and 

confining zones. 
Schlumberger Carbon Services Comments on “Requirements for Class VI Injection 

Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule” Contact: 

Andrew Duguid, Ph.D., P.E. aduguid@slb.com 

30

Proposed Rule Schlumberger 

Suggested Revision 

Schlumberger 

Rationale 

conditions at the well. The 

Director may require the 

owner or operator to core 

other formations in the 

borehole. 

of conditions at the well. 

(c) The owner or operator 

must record the fluid 

temperature, pH, conductivity, 

reservoir pressure and the 

static fluid level of the injection 

zone(s). 

(c) Prior to injection well 

operation, the owner or 

operator must record the 

formation temperature, 

formation fluid pH and 

conductivity, and reservoir 

pressure of the injection 

zone(s). 

- 

(d) At a minimum, the owner 

or operator must determine or 

calculate the following 

information concerning the 

injection and confining 

zone(s): 

- - 

(1) Fracture pressure; - - 

(2) Other physical and 

chemical characteristics of the 

injection and confining zones; 

and 

- - 

(3) Physical and chemical 

characteristics of the formation 

fluids in the injection zone. 

- - 

(e) Upon completion, but prior 

to operation, the owner or 

operator must conduct the 

following tests to verify 

hydrogeologic characteristics 

of the injection zone: 

(d) At any time prior to 

injection well operation, the 

owner or operator must 

determine fracture pressures 

of the injection and confining 

zones and conduct tests to 

verify hydrogeologic and 

geomechanical characteristics 

of the injection zone, e.g.: 

- 

(1) A pump test; or - - 

(2) Injectivity tests. - - 
Schlumberger Carbon Services Comments on “Requirements for Class VI Injection 

Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule” Contact: 

Andrew Duguid, Ph.D., P.E. aduguid@slb.com 

31

Proposed Rule Schlumberger 

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(f) The owner or operator must 

provide the Director with the 

opportunity to witness all 

logging and testing by this 

subpart. The owner or 

operator must submit a 

schedule of such activities to 

the Director 30 days prior to 

conducting the first test and 

submit any changes to the 

schedule 30 days prior to the 

next scheduled test. 

(f) The owner or operator must 

provide the Director with the 

opportunity to witness all 

logging and testing by this 

subpart. The owner or 

operator must submit a 

schedule of such activities to 

the Director upon spudding the 

well and submit any changes 

to the schedule 48 hours prior 

to the scheduled test. 

The changes reflect the 

realities of flexible rig 

schedules and consistency 

with Class II practices. 

§146.88 Injection well 

operating requirements. 

- - 

(a) Except during stimulation, 

the owner or operator must 

ensure that injection pressure 

does not exceed 90 percent of 

the fracture pressure of the 

injection zone so as to assure 

that the injection does not 

initiate new fractures or 

propagate existing fractures in 

the injection zone. In no case 

may injection pressure initiate 

fractures in the confining 

zone(s) or cause the 

movement of injection or 

formation fluids that 

endangers a USDW. 

(a) Except during stimulation, 

the owner or operator must 

ensure that injection pressure 

does not exceed 90 percent of 

the hydraulic fracture pressure 

of the confining zone so as to 

assure that the injection does 

not initiate new fractures or 

propagate existing fractures in 

the confining zone. In no case 

may injection pressure initiate 

fractures in the confining 

zone(s) or cause the 

movement of injection or 

formation fluids that 

endangers a USDW. 

Maintaining the integrity of the 

confining zone is the critical 

parameter. 

(b) Injection between the 

outermost casing protecting 

USDWs and the well bore is 

prohibited. 

(b) Injection of the CO2 stream 

between the outermost casing 

protecting USDWs and the 

well bore is prohibited. 

- 

(c) The owner or operator 

must fill the annulus between 

the tubing and the long string 

casing with a non-corrosive 

fluid approved by the Director. 

The owner or operator must 

maintain on the annulus a 

pressure that exceeds the 

operating injection pressure, 

unless the Director determines 

that such requirement might 

harm the integrity of the well. 

(c) The owner or operator 

must fill the annulus between 

the tubing and the long string 

casing with a non-corrosive 

fluid approved by the Director. 

Industry experience with the 

Class II UIC program does not 

support this requirement. 
Schlumberger Carbon Services Comments on “Requirements for Class VI Injection 

Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule” Contact: 

Andrew Duguid, Ph.D., P.E. aduguid@slb.com 

32

Proposed Rule Schlumberger 

Suggested Revision 

Schlumberger 

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(d) Other than during periods 

of well workover 

(maintenance) approved by 

the Director in which the 

sealed tubing-casing annulus 

is of necessity disassembled 

for maintenance or corrective 

procedures, the owner or 

operator must maintain 

mechanical integrity of the 

injection well at all times. 

- - 

(e) The owner or operator 

must install and use 

continuous recording devices 

to monitor: the injection 

pressure; the rate, volume, 

and temperature of the carbon 

dioxide stream; and the 

pressure on the annulus 

between the tubing and the 

long string casing and annulus 

fluid volume; and must install 

and use alarms and automatic 

down-hole shut-off systems, 

designed to alert the operator 

and shut-in the well when 

operating parameters such as 

annulus pressure, injection 

rate or other parameters 

approved by the Director 

diverge beyond permitted 

ranges and/or gradients 

specified in the permit; 

- - 

(f) If a down-hole automatic 

shutdown is triggered or a loss 

of mechanical integrity is 

discovered, the owner or 

operator must immediately 

investigate and identify as 

expeditiously as possible the 

cause of the shutoff. If, upon 

such investigation, the well 

appears to be lacking 

mechanical integrity, or if 

monitoring required under 

paragraph (e) of this section 

otherwise indicates that the 

well may be lacking 

mechanical integrity, the 

owner or operator must: 

- - 
Schlumberger Carbon Services Comments on “Requirements for Class VI Injection 

Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule” Contact: 

Andrew Duguid, Ph.D., P.E. aduguid@slb.com 

33

Proposed Rule Schlumberger 

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(1) Immediately cease 

injection; 

- - 

(2) Take all steps reasonably 

necessary to determine 

whether there may have been 

a release of the injected 

carbon dioxide stream into any 

unauthorized zone; 

- - 

(3) Notify the Director within 

24 hours 

(3) Notify the Director within 

24 hours of discovery; 

- 

(4) Restore and demonstrate 

mechanical integrity to the 

satisfaction of the Director 

prior to resuming injection; and 

- - 

(5) Notify the Director when 

injection can be expected to 

resume. 

- - 

§146.89 Mechanical 

integrity. 

- - 

(a) A Class VI well has 

mechanical integrity if: 

- - 

(1) There is no significant leak 

in the casing, tubing or packer; 

and 

- - 

(2) There is no significant fluid 

movement into a USDW 

through channels adjacent to 

the injection well bore. 

- - 

(b) To evaluate the absence of 

significant leaks under 

paragraph (a)(1) of this 

section, owners or operators 

must, following an initial 

annulus pressure test, 

continuously monitor injection 

pressure, rate, injected 

volumes, and pressure on the 

annulus between tubing and 

long stem casing and annulus 

fluid volume as specified in 

§146.88 (e); 

- - 

(c) At least once per year, the 

owner or operator must use 

one of the following methods 

to determine the absence of 

significant fluid movement 

under paragraph (a)(2) of this 

section: 

- - 
Schlumberger Carbon Services Comments on “Requirements for Class VI Injection 

Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule” Contact: 

Andrew Duguid, Ph.D., P.E. aduguid@slb.com 

34

Proposed Rule Schlumberger 

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Schlumberger 

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(1) A tracer survey such as 

oxygen-activation logging; 

- - 

(2) A temperature or noise log; 

or 

- - 

(3) A casing inspection log, if 

required by the Director. 

- - 

(d) The Director may require 

any other test to evaluate 

mechanical integrity under 

paragraph (a)(1) or (a)(2) of 

this section. Also, the Director 

may allow the use of a test to 

demonstrate mechanical 

integrity other than those listed 

above with the written 

approval of the Administrator. 

To obtain approval, the 

Director must submit a written 

request to the Administrator, 

which must set forth the 

proposed test and all technical 

data supporting its use. The 

Administrator must approve 

the request if it will reliably 

demonstrate the mechanical 

integrity of wells for which its 

use is proposed. Any alternate 

method approved by the 

Administrator will be published 

in the Federal Register and 

may be used in all States in 

accordance with applicable 

State law unless its use is 

restricted at the time of 

approval by the Administrator. 

- - 

(e) In conducting and 

evaluating the tests 

enumerated in this section or 

others to be allowed by the 

Director, the owner or operator 

and the Director must apply 

methods and standards 

generally accepted in the 

industry. When the owner or 

operator reports the results of 

mechanical integrity tests to 

the Director, he/she shall 

include a description of the 

test(s) and the method(s) 

used. In making his/her 

- - 
Schlumberger Carbon Services Comments on “Requirements for Class VI Injection 

Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule” Contact: 

Andrew Duguid, Ph.D., P.E. aduguid@slb.com 

35

Proposed Rule Schlumberger 

Suggested Revision 

Schlumberger 

Rationale 

evaluation, the Director must 

review monitoring and other 

test data submitted since the 

previous evaluation. 

(f) The Director may require 

additional or alternative tests if 

the results presented by the 

owner or operator under 

paragraph (d) of this section 

are not satisfactory to the 

Director to demonstrate that 

there is no significant leak in 

the casing, tubing or packer or 

significant movement of fluid 

into or between USDWs 

resulting from the injection 

activity as stated in 

paragraphs (a)(1) and (2) of 

this section. 

- - 

§146.90 Testing and 

monitoring requirements. 

- - 

The owner or operator of a 

Class VI well must prepare, 

maintain, and comply with a 

testing and monitoring plan to 

verify that the geologic 

sequestration project is 

operating as permitted and is 

not endangering USDWs. The 

testing and monitoring plan 

must be submitted with the 

permit application, for Director 

approval, and must include a 

description of how the owner 

or operator will meet the 

requirements of this section. 

Testing and monitoring 

associated with geologic 

sequestration projects must, at 

a minimum, include: 

- - 
Schlumberger Carbon Services Comments on “Requirements for Class VI Injection 

Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule” Contact: 

Andrew Duguid, Ph.D., P.E. aduguid@slb.com 

36

Proposed Rule Schlumberger 

Suggested Revision 

Schlumberger 

Rationale 

(a) Analysis of the carbon 

dioxide stream with sufficient 

frequency to yield data 

representative of its chemical 

and physical characteristics; 

- - 

(b) Installation and use, except 

during well workovers as 

defined in §146.86(d), of 

continuous recording devices 

to monitor injection pressure, 

rate and volume; the pressure 

on the annulus between the 

tubing and the long string 

casing; and the annulus fluid 

volume; 

- 146.86(d) does not exist; 

perhaps 146.88(d) is what was 

intended. 

(c) Corrosion monitoring of the 

well materials for loss of mass, 

thickness, cracking, pitting and 

other signs of corrosion must 

be performed on a quarterly 

basis to ensure that the well 

components meet the 

minimum standards for 

material strength and 

performance set forth in 

§146.86(b) by: 

(c) Corrosion monitoring of the 

well materials for loss of mass, 

thickness, cracking, pitting and 

other signs of corrosion must 

be performed quarterly and 

may be modified to be less 

frequent as approved by the 

Director based on construction 

materials, operating 

conditions, and monitoring 

history to ensure that the well 

components meet the 

minimum standards for 

material strength and 

performance set forth in 

§146.86(b) by: 

Allows application of 

performance based approach. 

(1) Placing coupons of the well 

construction materials in 

contact with the carbon 

dioxide stream; or 

(1) Analyzing coupons of the 

well construction materials 

placed in contact with the 

carbon dioxide stream; or 

- 

(2) Routing the carbon dioxide 

stream through a loop 

constructed with the material 

used in the well; or 

(2) Routing the carbon dioxide 

stream through a loop 

constructed with the material 

used in the well and inspecting 

the materials in the loop; or 

- 

(3) Using an alternative 

method approved by the 

Director; 

(3) Using an alternative 

method, materials, or time 

period approved by the 

Director; 

- 

(d) Periodic monitoring of the 

ground water quality and 

geochemical changes above 

the confining zone(s) that may 

be a result of carbon dioxide 

(d) Periodic monitoring of the 

ground water quality for 

geochemical changes above 

the confining zone(s) that may 

be a result of carbon dioxide 

- 
Schlumberger Carbon Services Comments on “Requirements for Class VI Injection 

Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule” Contact: 

Andrew Duguid, Ph.D., P.E. aduguid@slb.com 

37

Proposed Rule Schlumberger 

Suggested Revision 

Schlumberger 

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movement through the 

confining zone or additional 

identified zones: 

movement through the 

confining zone or additional 

identified zones: 

(1) The location and number of 

monitoring wells must be 

based on specific information 

about the geologic 

sequestration project, 

including injection rate and 

volume, geology, the presence 

of artificial penetrations and 

other factors; 

(1) The location and number of 

monitoring wells must be 

based on specific information 

about the geologic 

sequestration project, 

including injection rate and 

volume, geology, the presence 

of artificial penetrations and 

other relevant factors as 

warranted by a riskassessment; 

The monitoring should be 

designed to reduce risk 

(2) The monitoring frequency 

and spatial distribution of 

monitoring wells must be 

based on baseline 

geochemical data that has 

been collected under 

§146.82(a)(6) and any 

modeling results in the area of 

review evaluation required by 

§146.84(b); 

(2) The monitoring frequency 

and spatial distribution of 

monitoring wells must be 

based on geological and 

geophysical data that has 

been collected under 

§146.82(d) and any modeling 

results in the area of review 

evaluation required by 

§146.84(b); 

Geochemical data does not 

seem have a high degree of 

relevance in selecting 

monitoring well sites. 

(e) A demonstration of 

external mechanical integrity 

pursuant to §146.89(c) at least 

once per year throughout the 

duration of the geologic 

sequestration project; 

(e) A demonstration of 

external mechanical integrity 

pursuant to §146.89(c) at least 

once per year throughout the 

life of the well; 

- 

(f) A pressure fall-off test at 

least once every five years 

unless more frequent testing is 

required by the Director based 

on site specific information; 

(f) A pressure fall-off test or 

other equivalent test that 

identifies reservoir conditions 

with respect to flow dynamics 

at least once every five years 

unless more frequent testing is 

required by the Director based 

on site specific information; 

Allows more flexibility while 

still providing the needed 

information 

(g) Testing and monitoring to 

track the extent of the carbon 

dioxide plume and the position 

of the pressure front by either 

monitoring for pressure 

changes in the first formation 

overlying the confining zone or 

using indirect, geophysical 

techniques (e.g., seismic, 

(g) Testing and monitoring to 

track the extent of the carbon 

dioxide plume and the position 

of the pressure front. 

Monitoring outside of the 

injection zone provides little 

information of value for 

tracking and monitoring the 

injected plume. Examples of 

how to test and monitor could 

be included in the Preamble. 
Schlumberger Carbon Services Comments on “Requirements for Class VI Injection 

Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule” Contact: 

Andrew Duguid, Ph.D., P.E. aduguid@slb.com 

38

Proposed Rule Schlumberger 

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Schlumberger 

Rationale 

electrical, gravity, or 

electromagnetic surveys 

and/or down-hole carbon 

dioxide detection tools); 

(h) At the Director’s discretion, 

surface air monitoring and/or 

soil gas monitoring to detect 

movement of carbon dioxide 

that could endanger a USDW. 

(h) At the Director’s discretion 

based on site-specific 

conditions and risk-based 

factors, surface air monitoring 

and/or soil gas monitoring to 

detect movement of carbon 

dioxide that could endanger a 

USDW. 

In most situations soil and air 

monitoring does not provide 

an effective method of 

protecting USDWs. 

(1) The testing and monitoring 

plan must be based on 

potential vulnerabilities within 

the area of review; 

(1) The testing and monitoring 

plan must be based on sitespecific geologic factors, 

modeling, and riskassessment within the area of 

review; 

- 

(2) The monitoring frequency 

and spatial distribution of 

surface air monitoring and/or 

soil gas monitoring must 

reflect baseline data and the 

monitoring plan must include 

how the proposed monitoring 

will yield useful information on 

the area of review delineation 

and/or compliance with 

standards under 40 CFR 

144.12; 

- - 

(i) Any additional monitoring, 

as required by the Director, 

necessary to support, 

upgrade, and improve 

computational modeling of the 

area of review evaluation 

required under §146.84(b) and 

to determine compliance with 

standards under 40 CFR 

144.12; and 

- - 

(j) A quality assurance and 

surveillance plan for all testing 

and monitoring requirements. 

- - 

§146.91 Reporting 

requirements. 

- - 
Schlumberger Carbon Services Comments on “Requirements for Class VI Injection 

Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule” Contact: 

Andrew Duguid, Ph.D., P.E. aduguid@slb.com 

39

Proposed Rule Schlumberger 

Suggested Revision 

Schlumberger 

Rationale 

The owner or operator must, 

at a minimum, provide the 

following reports to the 

Director, for each permitted 

Class VI well: 

- - 

(a) Semi-annual reports 

containing: 

- - 

(1) Any changes to the 

physical, chemical and other 

relevant characteristics of the 

carbon dioxide stream from 

the proposed operating data; 

(1) Any significant changes to 

the physical, chemical and 

other relevant characteristics 

of the carbon dioxide stream 

from the proposed operating 

data; 

Minor changes could just be 

due to uncertainty in 

measurements or models 

(2) Monthly average, 

maximum and minimum 

values for injection pressure, 

flow rate and volume, and 

annular pressure; 

- - 

(3) A description of any event 

that exceeds operating 

parameters for annulus 

pressure or injection pressure 

as specified in the permit; 

- - 

(4) A description of any event 

which triggers a shutdown 

device required pursuant to 

§146.88(e) and the response 

taken; 

- - 

(5) The monthly volume of the 

carbon dioxide stream injected 

over the reporting period and 

project cumulatively; 

- - 

(6) Monthly annulus fluid 

volume added; and 

- - 

(7) The results of monitoring 

prescribed under §146.90. 

- - 

(b) Report, within 30 days the 

results of: 

- - 

(1) Periodic tests of 

mechanical integrity; 

- - 

(2) Any other test of the 

injection well conducted by the 

permittee if required by the 

Director; and 

- - 

(3) Any well workover. - - 
Schlumberger Carbon Services Comments on “Requirements for Class VI Injection 

Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule” Contact: 

Andrew Duguid, Ph.D., P.E. aduguid@slb.com 

40

Proposed Rule Schlumberger 

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Schlumberger 

Rationale 

(c) Owners or operators must 

submit reports in an electronic 

format acceptable to the 

Director. At the discretion of 

the Director, other formats 

may be accepted. 

- - 

§146.92 Injection well 

plugging. 

- - 

(a) Prior to the well plugging, 

the owner or operator must 

flush each Class VI injection 

well with a buffer fluid, 

determine bottomhole 

reservoir pressure, and 

perform a final mechanical 

integrity test. 

(a) Prior to the well plugging, 

the owner or operator must 

flush each Class VI injection 

well with a buffer fluid, 

determine bottomhole 

reservoir pressure, and 

perform a final external 

mechanical integrity test. 

Many of the components that 

would be tested by an internal 

MIT are removed or tested 

during the plugging process. 

(b) Well Plugging Plan. The 

owner or operator of a Class 

VI well must prepare, 

maintain, and comply with a 

plan that is acceptable to the 

Director. The requirement to 

maintain and implement an 

approved plan is directly 

enforceable regardless of 

whether the requirement is a 

condition of the permit. The 

well plugging plan must be 

submitted as part of the permit 

application and must include 

the following information: 

- - 

(1) Appropriate test or 

measure to determine 

bottomhole reservoir pressure; 

- - 

(2) Appropriate testing 

methods to ensure mechanical 

integrity as specified in 

§146.89; 

(2) Appropriate testing 

methods to ensure final 

external mechanical integrity 

as specified in §146.89(c); 

Many of the components that 

would be tested by an internal 

MIT are removed or tested 

during the plugging process. 

(3) The type and number of 

plugs to be used; 

- - 

(4) The placement of each 

plug including the elevation of 

the top and bottom of each 

plug; 

- - 

(5) The type and grade and 

quantity of material to be used 

in plugging. The material must 

be compatible with the carbon 

dioxide stream; and 

(5) The type and grade and 

quantity of material to be used 

in plugging. The material must 

be suitable for use with the 

carbon dioxide stream; and 

- 

(6) The method of placement - - 
Schlumberger Carbon Services Comments on “Requirements for Class VI Injection 

Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule” Contact: 

Andrew Duguid, Ph.D., P.E. aduguid@slb.com 

41

Proposed Rule Schlumberger 

Suggested Revision 

Schlumberger 

Rationale 

of the plugs. 

(c) Notice of intent to plug. The 

owner or operator must notify 

the Director at least 60 days 

before plugging of a well. At 

this time, if any changes have 

been made to the original well 

plugging plan, the owner or 

operator must also provide the 

revised well plugging plan. At 

the discretion of the Director, a 

shorter notice period may be 

allowed. 

- - 

(d) Plugging report. Within 60 

days after plugging or at the 

time of the next semi-annual 

report (whichever occurs 

earlier) the owner or operator 

must submit a plugging report 

to the Director. If the semiannual report is due less than 

15 days after completion of 

plugging, then the report must 

be submitted within 60 days 

after plugging. The report must 

be certified as accurate by the 

owner or operator and by the 

person who performed the 

plugging operation (if other 

than the owner or operator.) 

(d) Plugging report. Within 60 

days after plugging the owner 

or operator must submit a 

plugging report to the Director. 

The report must be certified as 

accurate by the owner or 

operator and by the person 

who performed the plugging 

operation (if other than the 

owner or operator.) 

Simplification 

§146.93 Post-injection site 

care and site closure. 

- - 

(a) The owner or operator of a 

Class VI well must prepare, 

maintain, and comply with a 

plan for post-injection site care 

and site closure that meets the 

requirements of paragraph 

(a)(2) of this section and is 

acceptable to the Director. 

- - 

(1) The owner or operator 

must submit the post-injection 

site care and site closure plan 

as a part of the permit 

application to be approved by 

the Director. 

- - 

(2) The post-injection site care 

and site closure plan must 

include the following 

- - 
Schlumberger Carbon Services Comments on “Requirements for Class VI Injection 

Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule” Contact: 

Andrew Duguid, Ph.D., P.E. aduguid@slb.com 

42

Proposed Rule Schlumberger 

Suggested Revision 

Schlumberger 

Rationale 

information: 

(i) The pressure differential 

between pre-injection and 

predicted post-injection 

pressures in the injection 

zone; 

- - 

(ii) The predicted position of 

the carbon dioxide plume and 

associated pressure front at 

site closure as demonstrated 

in the area of review 

evaluation required under 

§146.84(b); 

- - 

(iii) A description of postinjection monitoring location, 

methods, and proposed 

frequency; and 

- - 

(iv) A proposed schedule for 

submitting post-injection site 

care monitoring results to the 

Director. 

- - 

(3) Upon cessation of 

injection, owners or operators 

of Class VI wells must either 

submit an amended postinjection site care and site 

closure plan or demonstrate to 

the Director through 

monitoring data and modeling 

results that no amendment to 

the plan is needed. 

- - 

(4) The owner or operator may 

modify and resubmit the postinjection site care and site 

closure plan for the Director’s 

approval within 30 days of 

such change. 

- - 

(b) The owner or operator 

shall monitor the site following 

the cessation of injection to 

show the position of the 

carbon dioxide plume and 

pressure front and 

demonstrate that USDWs are 

not being endangered. 

- - 
Schlumberger Carbon Services Comments on “Requirements for Class VI Injection 

Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule” Contact: 

Andrew Duguid, Ph.D., P.E. aduguid@slb.com 

43

Proposed Rule Schlumberger 

Suggested Revision 

Schlumberger 

Rationale 

(1) The owner or operator 

shall continue to conduct 

monitoring as specified in the 

Director-approved postinjection site care and site 

closure plan for at least 50 

years following the cessation 

of injection. At the Director’s 

discretion, the monitoring will 

continue until the geologic 

sequestration project no 

longer poses an 

endangerment to USDWs. 

(1) The owner or operator 

shall continue to conduct 

monitoring as specified in the 

Director-approved postinjection site care and site 

closure plan, pursuant to the 

performance based criteria 

described in 146.93(3). 

The 50 year default period is 

not based on any scientific or 

technical information and 

could be considered arbitrary 

and capricious. 

(2) If the owner or operator 

can demonstrate to the 

satisfaction of the Director 

before 50 years, based on 

monitoring and other sitespecific data, that the geologic 

sequestration project no 

longer poses an 

endangerment to USDWs, the 

Director may approve an 

amendment to the postinjection site care and site 

closure plan to reduce the 

frequency of monitoring or 

may authorize site closure 

before the end of the 50-year 

period. 

(2) If the owner or operator 

can demonstrate to the 

satisfaction of the Director that 

the geologic sequestration 

project no longer poses an 

endangerment to USDWs, the 

Director may approve an 

amendment to the postinjection site care and site 

closure plan to reduce the 

frequency of monitoring or 

may authorize site closure. 

- 

(3) Prior to authorization for 

site closure, the owner or 

operator must submit to the 

Director a demonstration, 

based on monitoring and other 

site-specific data, that the 

carbon dioxide plume and 

pressure front have stabilized 

and that no additional 

monitoring is needed to assure 

that the geologic sequestration 

project does not pose an 

endangerment to USDWs. 

(3) Prior to authorization for 

site closure, the owner or 

operator must demonstrate to 

the Director, based on 

monitoring and other sitespecific data that no additional 

monitoring is needed to assure 

that the geologic sequestration 

project does not pose an 

endangerment to USDWs, 

considering the following:. 

(i) the estimated magnitude 

and extent of the AOR based 

on measurements and 

modeling; 

(ii) that CO2 movement and 

pressure changes match 

model predictions, 

(iii) the estimated location of 

the detectable CO2 plume 

based on measurement and 

modeling (measuring 

magnitude of saturation within 

Establishes the performance 

based criteria for selecting the 

monitoring period. 
Schlumberger Carbon Services Comments on “Requirements for Class VI Injection 

Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule” Contact: 

Andrew Duguid, Ph.D., P.E. aduguid@slb.com 

44

Proposed Rule Schlumberger 

Suggested Revision 

Schlumberger 

Rationale 

the plume or mapping the 

edge of it); 

(iv) that there is no evidence of 

significant leakage of either 

CO2 or formation fluids that 

endanger USDWs; 

(v) that the CO2 plume and 

displaced formation fluid are 

not expected to migrate in the 

future in a manner that 

encounters a potential leakage 

pathway; and, 

(vi) that wells at the site are 

not leaking and have 

maintained integrity. 

(4) If such a demonstration 

cannot be made (i.e., if the 

carbon dioxide plume and 

pressure front have not 

stabilized) after the 50 year 

period, the owner or operator 

must submit to the Director a 

plan to continue post-injection 

site care. 

Delete No longer necessary 

(c) Notice of intent for site 

closure. The owner or operator 

must notify the Director at 

least 120 days before site 

closure. At this time, if any 

changes have been made to 

the original post-injection site 

care and site closure plan, the 

owner or operator must also 

provide the revised plan. At 

the discretion of the Director, a 

shorter notice period may be 

allowed. 

- - 

(d) After the Director has 

authorized site closure, the 

owner or operator must plug 

all monitoring wells in a 

manner which will not allow 

movement of injection or 

- - 
Schlumberger Carbon Services Comments on “Requirements for Class VI Injection 

Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule” Contact: 

Andrew Duguid, Ph.D., P.E. aduguid@slb.com 

45

Proposed Rule Schlumberger 

Suggested Revision 

Schlumberger 

Rationale 

formation fluids that 

endangers a USDW. 

(e) Once the Director has 

authorized site closure, the 

owner or operator must submit 

a site closure report within 90 

days that must thereafter be 

retained at a location 

designated by the Director. 

The report must include: 

(e) Once the Director has 

authorized site closure, the 

owner or operator must submit 

a site closure report within 90 

days after completion of all 

closure operations. The report 

must include: 

What is the retention period? 

Many other programs have a 

three year limit for retention of 

records. EPA is the steward 

of information at this point of 

the project, not the owner or 

operator. 

(1) Documentation of 

appropriate injection and 

monitoring well plugging as 

specified in §146.92 and 

paragraph (c) of this section. 

The owner or operator must 

provide a copy of a survey plat 

which has been submitted to 

the local zoning authority 

designated by the Director. 

The plat must indicate the 

location of the injection well 

relative to permanently 

surveyed benchmarks. The 

owner or operator must also 

submit a copy of the plat to the 

Regional Administrator of the 

appropriate EPA Regional 

Office; 

(1) Documentation of 

appropriate injection and 

monitoring well plugging as 

specified in §146.92 and 

paragraph (c) of this section. 

The owner or operator must 

provide a copy of a survey plat 

which has been submitted to 

the local zoning authority 

designated by the Director. 

The plat must indicate the 

location of the injection well(s) 

relative to permanently 

surveyed benchmarks. The 

owner or operator must also 

submit a copy of the plat to the 

Regional Administrator of the 

appropriate EPA Regional 

Office; 

- 

(2) Documentation of 

appropriate notification and 

information to such State, local 

and tribal authorities as have 

authority over drilling activities 

to enable such State and local 

authorities to impose 

appropriate conditions on 

subsequent drilling activities 

that may penetrate the 

injection and confining 

zone(s); and 

- - 

(3) Records reflecting the 

nature, composition and 

volume of the carbon dioxide 

stream. 

- - 
Schlumberger Carbon Services Comments on “Requirements for Class VI Injection 

Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule” Contact: 

Andrew Duguid, Ph.D., P.E. aduguid@slb.com 

46

Proposed Rule Schlumberger 

Suggested Revision 

Schlumberger 

Rationale 

(f) Each owner or operator of a 

Class VI injection well must 

record a notation on the deed 

to the facility property or any 

other document that is 

normally examined during title 

search that will in perpetuity 

provide any potential 

purchaser of the property the 

following information: 

- - 

(1) The fact that land has been 

used to sequester carbon 

dioxide; 

- - 

(2) The name of the State 

agency, local authority, and/or 

tribe with which the survey plat 

was filed, as well as the 

address of the Regional 

Environmental Protection 

Agency Office to which it was 

submitted; and 

- - 

(3) The volume of fluid 

injected, the injection zone or 

zones into which it was 

injected, and the period over 

which injection occurred. 

- - 

(g) The owner or operator 

must retain for three years 

following site closure, records 

collected during the postinjection site care period. The 

owner or operator must deliver 

the records to the Director at 

the conclusion of the retention 

period, and the records must 

thereafter be retained at a 

location designated by the 

Director for that purpose. 

- - 

§146.94 Emergency and 

remedial response. 

- - 

(a) As part of the permit 

application, the owner or 

operator must provide the 

Director with an emergency 

and remedial response plan 

that describes actions to be 

taken to address movement of 

the injection or formation fluids 

that may cause an 

endangerment to a USDW 

- - 
Schlumberger Carbon Services Comments on “Requirements for Class VI Injection 

Wells for the Geologic Sequestration of Carbon Dioxide - Proposed Rule” Contact: 

Andrew Duguid, Ph.D., P.E. aduguid@slb.com 

47

Proposed Rule Schlumberger 

Suggested Revision 

Schlumberger 

Rationale 

during construction, operation, 

closure and post-closure 

periods. 

(b) If the owner or operator 

obtains evidence that the 

injected carbon dioxide stream 

and associated pressure front 

may cause an endangerment 

to a USDW, the owner or 

operator must: 

(b) If the owner or operator 

obtains evidence that the 

injected carbon dioxide stream 

or associated pressure front 

endangers a USDW, the 

owner or operator must: 

- 

(1) Immediately cease 

injection; 

(2) Take all steps reasonably 

necessary to identify and 

characterize any release; 

(2) Take all steps reasonably 

necessary to identify and 

characterize the 

endangerment posed; 

- 

(3) Notify the Director within 

24 hours; and 

(3) Notify the Director within 

24 hours of becoming aware 

of the endangerment; and 

- 

(4) Implement the emergency 

and remedial response plan 

approved by the Director. 

- - 

(c) The Director may allow the 

operator to resume injection 

prior to remediation if the 

owner or operator 

demonstrates that the injection 

operation will not endanger 

USDWs. 

- - 

(d) The owner or operator 

must notify the Director and 

obtain his approval prior to 

conducting any well workover. 

(d) The owner or operator 

must notify the Director prior to 

conducting any well workover 

in response to any case of 

endangerment. 

In critical situations, time spent 

obtaining approval could 

adversely affect the ability to 

conduct operations or 

increase the level of 

endangerment. 
Letter ID: 0226 

Commenter: Andrew Duguid 

Organization: Schlumberger Carbon Services 

Letter ID: 0226 Comment ID: 23995 Letter Lines: 37 to 40 

Comment Code: 1420 1.2.1.1 Support the GS rulemaking 

Comment: Schlumberger feels that the proposed rule for geologic sequestration of carbon 

dioxide is a very good start and relatively few changes are needed to create a 

final rule under which geologic CO2 sequestration can become a commercial 

industry and an effective piece in the solution to climate change. 

Individual Response: EPA believes that the creation of a new injection well class (VI) under the 

existing UIC Program is necessary to enable the use of GS as a climate change mitigation 

technology in a manner that protects USDWs from endangerment. EPA agrees that the UIC 

Program, under the authority of the SDWA, provides a strong framework for regulating injection 

of CO2 for GS and adds that the GS regulation tailors the UIC requirements to address the 

unique issues associated with large-scale 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. 

Letter ID: 0226 Comment ID: 23996 Letter Lines: 48 to 70 

Comment Code: 1220 1.1.1.1 Terminology and definitions 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment: 1. Schlumberger asks that the EPA expand the applicability of Class VI wells to 

cover wells injecting CO2 that is dissolved in water or brine. The current 

draft language for Section 146.81(b) states: 

This subpart applies to wells used to inject carbon dioxide specifically 

for the purpose of geologic sequestration, i.e., the long-term 

containment of a gaseous, liquid or supercritical carbon dioxide stream 

in subsurface geologic formations. 

We suggest that the EPA replace the current language with the following 

language: 

This subpart applies to wells used to inject carbon dioxide specifically 

for the purpose of geologic sequestration, i.e., the long-term 

containment of a gaseous, liquid or supercritical carbon dioxide stream 

or carbon dioxide dissolved in water or brine into subsurface geologic 

formations. 

1
While we recognize today the injection of dissolved CO2 raises economic 

challenges we feel that there may be cases where the injection of dissolved CO2 

will make sense both in terms of economics and in terms of leakage risk. 

Unlike separate phase CO2, CO2 dissolved in water is not less dense than the 

formation fluid and will not be subject to buoyancy driven leakage. 

Individual Response: EPA disagrees with the suggested change. §146.81(b) reads as follows: 

“This subpart applies to any wells used to inject carbon dioxide specifically for the purpose of 

geologic sequestration, i.e., the long-term containment of a gaseous, liquid, or supercritical 

carbon dioxide stream in subsurface geologic formations.” Nothing in the rule precludes the 

injection of dissolved CO2, as long as the CO2 does not meet the definition of a hazardous waste 

under 40 CFR part 261. 

Based on its evaluation of all public comments and input on the proposed rule and the NODA 

and Request for Comment, EPA has made many revisions to the Class VI GS rule. Please see the 

final rule and preamble for additional information. 

Letter ID: 0226 Comment ID: 23997 Letter Lines: 72 to 80 

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

USDW 

Comment: 2. Schlumberger feels that the general prohibition on CO2 injection above the 

lowermost USDW should removed from the regulations. We feel that as long as the 

injection will not endanger USDWs the elevation with respect to the lowermost 

USDW is not important. However, if CO2 injection is allowed above the lowermost 

USDW we feel that the EPA must specify that there needs to be a confining unit 

both above and below the injection zone that is free of pathways that may allow 

for leakage of fluids out of the injection zone. The inclusion of a lower 

confining unit will be important because CO2-saturated brine or water is more 

dense than the native formation fluid and will sink. 

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 agrees that proper siting, monitoring, and containment capacity are critical elements of 

Class VI injection for GS. However, the Agency also believes that injection into non-USDW 

2
formations above and between USDWs presents unique challenges related to movement of CO2 

in the subsurface, which requires a unique approach to ensure that USDWs are protected. 

Therefore, the Agency believes that additional requirements are appropriate and necessary for 

wells that would inject into non-USDWs above and between USDWs. 

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. 

Letter ID: 0226 Comment ID: 23998 Letter Lines: 82 to 120 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

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

Comment Code: 5300 2.8.3 Site closure activities (40 CFR 146.93) 

Comment: 3. Schlumberger does not support the default post injection site care period of 

50 years. We feel that because the characterization and operation of the site 

will be based on the specific attributes of the site that the length of post 

injection site care should also be site specific information. In particular the 

criteria for ending the PISC period should be based on site performance and 

risk. We support the idea that the director approves final site closure. We 

suggest the following language for Section 146.93(b)(1): 

(1) The owner or operator shall continue to conduct monitoring as 

specified in the Director-approved post-injection site care and site 

closure plan, pursuant to the performance based criteria described in 

146.93(b)(3). 

We suggest the following language for section 146.93(b)(2) 

(2) If the owner or operator can demonstrate to the satisfaction of the 

Director that the geologic sequestration project no longer poses an 

endangerment to USDWs, the Director may approve an amendment to the 

post- injection site care and site closure plan to reduce the 

frequency of monitoring or may authorize site closure. 

And we suggest the following language for section 146.93(b)(3) 

(3) Prior to authorization for site closure, the owner or operator must 

demonstrate to the Director, based on monitoring and other sitespecific data that no additional monitoring is needed to assure that 

the geologic sequestration project does not pose an endangerment to 

USDWs, considering the following:. 

(i) the estimated magnitude and extent of the AOR based on measurements 

and modeling; (ii) that CO2 movement and pressure changes match model 

3
predictions, (iii) the estimated location of the detectable CO2 plume 

based on measurement and modeling (measuring magnitude of saturation 

within the plume or mapping the edge of it); (iv) that there is no 

evidence of significant leakage of either CO2 or formation fluids that 

endanger USDWs; (v) that the CO2 plume and displaced formation fluid are 

not expected to migrate in the future in a manner that encounters a 

potential leakage pathway; and, (vi) that wells at the site are not 

leaking and have maintained integrity. 

Individual Response: The PISC requirements in the final GS rule, as specified in §146.93(b), 

incorporate a combination of a fixed timeframe and a performance standard approach. EPA 

believes that a default PISC timeframe of 50 years, with Director's discretion to shorten or 

lengthen this timeframe, combined with a site-specific Director’s discretion to create an 

alternative PISC time frame, ensures that USDWs are protected. The GS rule offers owners or 

operators flexibility regarding the duration of the PISC timeframe by: (1) allowing the Director 

discretion to shorten or lengthen the PISC timeframe during the PISC period based on sitespecific data, pursuant to requirements at §146.93(b); or (2) affording 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 nonendangerment of USDWs pursuant to requirements at §146.93(c). 

EPA expects that the Director would consider the types of information the commenter describes 

in determining whether the plume and pressure front no longer pose a risk of endangerment to 

USDWs and post-injection site care monitoring may be discontinued. 

EPA believes that a default post-injection site care 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 accommodate site-specific circumstances and various 

geologic conditions, and addresses commenters’ concerns, while ensuring USDW protection. 

Both approaches will utilize site-specific data, and be based on pressure monitoring and USDW 

impacts. 

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 proposed well plugging plans and post-injection site 

care and site closure plans under §146.92 and §146.93. The guidance describes recommended 

approaches for how an owner or operator could plug injection and monitoring wells; perform 

post-injection monitoring; demonstrate the appropriateness of an alternative post-injection site 

care time frame; demonstrate non endangerment; and perform site closure activities. The 

guidance will be available at http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm. 

Letter ID: 0226 Comment ID: 23999 Letter Lines: 122 to 146 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

4
Comment Code: 4650 2.6.5 CO2 plume and pressure front tracking (seeking comment) 

Comment: 4. Schlumberger supports the concept of testing and monitoring to track the CO2 

plume and the associated pressure front. We feel that without this monitoring 

the validation and updating of the models used to predict the size and shape of 

the AOR cannot be properly conducted and that the use of models to predict the 

size and shape of the AOR will be ineffective. However we feel that the 

language in section 146.90(g) is too restrictive. The current language states: 

(g) Testing and monitoring to track the extent of the carbon dioxide 

plume and the position of the pressure front by either monitoring for 

pressure changes in the first formation overlying the confining zone or 

using indirect, geophysical techniques (e.g., seismic, electrical, 

gravity, or electromagnetic surveys and/or down-hole carbon dioxide 

detection tools); 

We feel that the restrictions placed in this language could adversely impact the 

efficiency of monitoring and modeling depending on site conditions. 

Schlumberger proposes the following alternate language: 

(g) Testing and monitoring to track the extent of the carbon dioxide 

plume and the position of the pressure front by either monitoring for 

pressure changes, using geophysical techniques (e.g., seismic, 

electrical, gravity, or electromagnetic surveys and/or down-hole carbon 

dioxide detection tools), other techniques that are approved by the 

director or a combination of techniques if multiple techniques are 

deemed necessary by the director; 

Individual Response: EPA has revised this requirement in the final rule. The final GS 

regulation, at §146.90(g)(1), requires all GS project owners or operators to monitor directly for 

pressure changes in the injection zone. EPA believes that pressure monitoring in the injection 

zone is necessary to track the development and movement of the pressure front and CO2 plume. 

In addition, §146.90(g)(2) requires owners or operators to track the position of the CO2 plume 

using indirect methods (e.g., seismic, electrical, gravity, or electromagnetic surveys and/or 

down-hole CO2 detection tools), unless the Director determines based on site-specific geology, 

that such methods are not appropriate. EPA is affording Director's discretion regarding the use of 

geophysical techniques at some sites because the Agency recognizes that geophysical methods 

are not appropriate in all geologic settings. EPA clarifies that this determination will be made by 

the Director based on the site-specific geologic information submitted by the owner or operator 

with their permit application. 

EPA believes that this approach provides flexibility to develop a site-specific monitoring plan, 

ensures that direct monitoring is available to track the movement of the CO2 and validate 

models, and recognizes that indirect techniques are not appropriate in all situations. The owner or 

operator's approved testing and monitoring plan will include the site-specific details, 

technologies, testing and monitoring frequencies, and other pertinent information. 

5
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 recommended approaches for implementing a 

testing and monitoring plan, including pre-operational geophysical logging and testing of 

injection wells, MITs, injection 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/groundwater/uic/wells_sequestration.cfm. 

Letter ID: 0226 Comment ID: 24000 Letter Lines: 150 to 155 

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

Comment: 1. Schlumberger supports the idea that horizontal wells may be used for 

injection for geologic carbon sequestration. Horizontal CO2 injection 

wells have been successfully and safely used for CO2 injection at the 

Weyburn project in Saskatchewan, Canada. We feel that there will be 

sites with conditions that will make the use of horizontal wells 

necessary. 

Individual Response: In this final rule, EPA allows the use of horizontal wells at GS projects. In 

the proposed rule, EPA sought comment on the appropriateness of horizontal drilling techniques 

for Class VI wells, and commenters representing energy companies, electric utilities, the oil and 

gas industry, CCS associations, states, and the public, unanimously supported the concept and 

provided many reasons why horizontal 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 ensure the protection of USDWs from endangerment. 

Letter ID: 0226 Comment ID: 24001 Letter Lines: 157 to 160 

Comment Code: 1630 1.3.3 RCRA/hazardous waste issues (seeking comment) 

Comment Code: 1640 1.3.4 CERCLA issues (seeking comment) 

Comment: 2. Now that the EPA has introduced the topics of the Comprehensive 

Environmental Response, Compensation, and Liability Act (CERCLA) and the 

Resource Conservation and Recovery Act (RCRA) we urge the EPA to clarify 

the roles of both with respect to CO2 injection under the UIC program. 

Individual Response: EPA received many comments regarding the need for clarity with respect 

to RCRA regulations and statute to CO2 streams that are geologically sequestered under the final 

Class VI UIC well requirements. As a result, EPA has decided to initiate a separate proposed 

rulemaking specifically to examine the issue of RCRA applicability to CO2 streams being 

geologically sequestered, including the possible option of a conditional exemption from the 

6
RCRA requirements for CO2 GS in Class VI wells. EPA will consider these comments as part of 

its development of that proposal. The Agency will consider issues particular to RCRA in the 

context of that separate rulemaking, and recommends that the commenter read that proposed rule 

when it is published. The Agency notes that commenters who wish to submit comments on the 

RCRA proposal will need to do so during the comment period for that rule. Finally, EPA also 

notes that the final GS rule, which adds new regulations for Class VI wells under the Safe 

Drinking Water Act (SDWA), is not making any changes to the RCRA regulations. 

EPA clarifies that CO2 itself is not listed as a hazardous substance under CERCLA; however, the 

CO2 stream may contain a listed hazardous substance (such as mercury) or may mobilize 

substances in the subsurface that could react with ground water to produce listed hazardous 

substances (such as sulfuric acid). Whether such substances may result in CERCLA liability 

from a sequestration facility depends entirely on the composition of the specific CO2 stream and 

the environmental media in which it is stored (e.g., soil or ground water). CERCLA exempts 

from liability, under CERCLA section 107, 42 U.S.C. 9607, certain “federally permitted 

releases” (FPR) as defined in CERCLA, 42 U.S.C. 9601(10). Class VI permits will need to be 

carefully structured to ensure that they prevent potential releases from the well which are outside 

the scope of the Class VI permit. 

Letter ID: 0226 Comment ID: 24002 Letter Lines: 162 to 176 

Comment Code: 1630 1.3.3 RCRA/hazardous waste issues (seeking comment) 

Comment: Schlumberger supports the EPA in defining the injected CO2 stream to 

exclude hazardous wastes. We feel that this definition implies that CO2 

itself is not a hazardous waste under RCRA and that the injected CO2 

stream can only be considered a hazardous waste if it is mixed with 

another hazardous waste. 

Schlumberger feels that supercritical and gaseous CO2 do not fit the 

definition of solid waste under RCRA which is limited to "solid, liquid, 

semisolid, and contained gaseous materials" and are therefore not 

regulated under RCRA. We encourage the EPA to explore this possibility 

and if in agreement, to adopt and espouse this position in the preamble 

for the final rule. We further feel that EPA should specify that 

uncontainerized supercritical CO2, like that at injected for CCS, is not 

solid waste and therefore not subject to RCRA waste determination 

requirements. 

Individual Response: EPA received many comments regarding the applicability of the RCRA 

regulations and statute to CO2 streams that are geologically sequestered under the final Class VI 

UIC well requirements. As a result, EPA has decided to initiate a separate proposed rulemaking 

specifically to examine the issue of RCRA applicability to CO2 streams being geologically 

sequestered, including the possible option of a conditional exemption from the RCRA 

requirements for CO2 GS in Class VI wells. EPA will consider these comments as part of its 

development of that proposal. The Agency will consider issues particular to RCRA in the context 

7
of that separate rulemaking, and recommends that the commenter read that proposed rule when it 

is published. The Agency notes that commenters who wish to submit comments on the RCRA 

proposal will need to do so during the comment period for that rule. Finally, EPA also notes that 

the final GS rule, which adds new regulations for Class VI wells under the Safe Drinking Water 

Act (SDWA), is not making any changes to the RCRA regulations. 

Letter ID: 0226 Comment ID: 24003 Letter Lines: 178 to 190 

Comment Code: 1640 1.3.4 CERCLA issues (seeking comment) 

Comment: The preamble of the draft points out that under federally permitted 

release provision of CERCLA releases in compliance with a UIC permit are 

exempt from liability under CERCLA. Schlumberger fails to see how the 

any releases under the proposed rule that involves both characterization 

of the injection stream and characterization of the subsurface can fall 

outside the federally permitted release provision. We urge the EPA to 

better clarify any cases where injection of CO2 in accordance with a UIC 

permit is not released from liability under the federally permitted 

release provision of CERCLA. We cannot envision a permit being issued 

for an injection that could cause an unintended release, especially, in 

light of the information that is required in the permit application on 

the composition of the injection stream and on the chemical makeup of 

the subsurface. 

Individual Response: CERCLA exempts from liability, under CERCLA section 107, 42 U.S.C. 

9607, certain “federally permitted releases” (FPR) as defined in CERCLA, 42 U.S.C. 9601(10). 

Therefore, Class VI requirements and permits will need to be carefully structured to ensure that 

they do not “authorize” inappropriate releases, and would need to prevent potential releases from 

the well which are outside the scope of the Class VI permit. Furthermore, EPA is promulgating 

the GS rule under the authority of the SDWA. To the extent the commenter is seeking 

interpretations of CERCLA and its related provisions, such as the definition of a federally 

permitted release, such interpretations are beyond the scope of this rulemaking. 

Letter ID: 0226 Comment ID: 24004 Letter Lines: 192 to 202 

Comment Code: 4610 2.6.1 Testing and monitoring plan requirement (seeking comment) 

Comment: 3. In the preamble of the draft u-tube technology is specifically called 

out as a technology available for high pressure fluid sampling. 

Schlumberger wants point out to the epa there are other techniques for 

high pressure fluid sampling the use of wireline conveyed sample 

bottles. We want to ensure that no one particular technology is adopted 

or required for high pressure sampling. The selection of a single 

sampling technique (although not in the rule language) could cause the 

best available technology to be overlooked now or in the future. We 

8
propose that epa either delete the reference to the u-tube samples of 

clarify that it is not the only solution available for taking high 

pressure samples 

Individual Response: 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. However, EPA is not requiring the use of U-tubes for 

sampling under the final rule. 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 recommended approaches 

for implementing a testing and monitoring plan, including pre-operational geophysical logging 

and testing of injection wells, MITs, injection 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/groundwater/uic/wells_sequestration.cfm. 

Letter ID: 0226 Comment ID: 24005 Letter Lines: 204 to 209 

Comment Code: 1820 1.4.1.1 Vulnerability Evaluation Framework (VEF) 

Comment: 4. Schlumberger appreciates that the EPA crated the Vulnerability 

Evaluation Framework (VEF) and we fully support the use of a logical set 

of steps to address the vulnerabilities or risks associated with 

geologic carbon sequestration. However, we are concerned that the VEF 

is not the only method that may be successful for site evaluation and 

would like EPA to clarify that the VEF is one but not the only approach. 

Individual Response: The Agency clarifies that the VEF is intended to be a risk screening tool, 

but it is not a required component of the GS site selection process. The UIC Class VI well permit 

application requirements, including the minimum criteria for siting at §146.83, and the 

information requirements at §146.82 provide the basis for determining whether a proposed GS 

site is geologically appropriate and the proposed operations are technically viable, safe, and will 

not endanger USDWs. 

EPA believes that requiring appropriate site characterization by the owner or operator and 

providing an appropriate degree of flexibility to the Director to evaluate site-specific geologic 

data will afford the greatest protection of USDWs. The issuance of a UIC Class VI permit is 

determined based on evaluation of site-specific permit information pursuant to the requirements 

at §§146.82 and 146.83. The Director may consider some components of the VEF (e.g., 

information regarding wells, faults, and pressure changes) when assessing the appropriateness of 

a site for GS; however, the Director's permit approval determination is based on UIC Class VI 

requirements and not the VEF. 

9
Letter ID: 0226 Comment ID: 24006 Letter Lines: 230 to 240 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

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

USDW 

Comment: §144.6 Classification of wells. 

Proposed Rule:(f) Class VI. Wells used for geologic sequestration of carbon 

dioxide beneath the lowermost formation containing a USDW. 

Schlumberger Suggested Revision: (f) Class VI. Wells used for geologic 

sequestration of carbon dioxide. 

Schlumberger Rationale: We feel that sequestration can be conducted safely above 

USDWs as evidenced by the class 2 EOR experience. Also, the restriction to below 

the lowest USDW rules out many potential CCS sites. 

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 adds that it has revised the definition of a Class VI well to read as follows: “Wells that are 

not experimental in nature that are used for geologic sequestration of carbon dioxide beneath the 

lowermost formation containing a USDW; or, wells used for geologic sequestration of carbon 

dioxide that have been granted a waiver of the injection depth requirements pursuant to 

requirements at §146.95 of this chapter; or, wells used for geologic sequestration of carbon 

dioxide that have received an expansion to the areal extent of an existing Class II enhanced oil 

recovery or enhanced gas recovery aquifer exemption pursuant to §§146.4 of this chapter and 

144.7(d).” 

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. 

Letter ID: 0226 Comment ID: 24007 Letter Lines: 242 to 251 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

10
Comment Code: 2066 1.5.3.3 Grandfathering construction of Class V wells (seeking comment) 

Comment: §144.15 Prohibition of non-experimental Class V wells for geologic 

sequestration. 

Proposed Rule: The construction, operation or maintenance of any nonexperimental Class V geologic sequestration well is prohibited. 

Schlumberger Suggested Revision: - 

Schlumberger Rationale: We agree, there should be only one class of geologic 

sequestration well but CO2 class V wells should be grandfathered. 

Individual Response: EPA agrees that many Class V experimental technology wells are 

designed and constructed to withstand exposure to CO2. The final GS rule provides for the 

construction of these wells to be grandfathered per §146.81(c), provided the owner or operator 

can demonstrate to the Director that the wells were engineered and constructed to meet the 

requirements at §146.86(a) and ensure protection of USDWs, in lieu of requirements at 

§146.86(b) and §146.87(a). EPA clarifies that only the construction requirements are 

grandfathered and that all other Class VI requirements (reporting, monitoring, mechnical 

integrity testing, etc.) must be met following a determination under §146.81(c). 

Letter ID: 0226 Comment ID: 24008 Letter Lines: 253 to 264 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

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

USDW 

Comment: §146.5 Classification of injection wells. 

Proposed Rule:(f) Class VI. Wells used for geologic sequestration of carbon 

dioxide beneath the lowermost formation containing an underground source of 

drinking water (USDW). 

Schlumberger Suggested Revision: (f) Class VI. Wells used for geologic 

sequestration of carbon dioxide. 

Schlumberger Rationale: We feel that sequestration can be conducted safely above 

USDWs as evidenced by the class 2 EOR experience. Also, the restriction to below 

the lowest USDW rules out many potential CCS sites. 

Individual Response: Please see the response to the commenter’s suggested revision to 

§144.6(f). 

11
Letter ID: 0226 Comment ID: 24009 Letter Lines: 266 to 287 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment Code: 2060 1.5.3 Comments on grandfathering of existing wells (seeking comment) 

Comment Code: 3800 2.3 Proposed Injection Well Construction Requirements (40 CFR 

146.86) 

Comment: §146.81 Applicability. 

Proposed Rule: (c) This subpart applies to owners and operators of permit or 

rule-authorized Class I industrial, Class II, or Class V experimental carbon 

dioxide injection projects who seek to apply for a Class VI geologic 

sequestration permit for their well or wells. If the Director determines that 

USDWs will not be endangered, such wells are exempt, at the Director’s 

discretion, from the casing and cementing requirements at §§146.86(b) and 

146.87(a)(1) through (3). 

Schlumberger Suggested Revision: (c) This subpart applies to owners and 

operators of permit or rule-authorized Class I industrial, Class II, or Class V 

experimental carbon dioxide injection projects who seek to apply for a Class VI 

geologic sequestration permit for their well or wells. If the Director 

determines that USDWs will not be endangered, such wells are exempt, at the 

Director’s discretion, from the casing and cementing requirements at §§146.86(b) 

and 146.87(a)(1) through (3) if the wells were constructed prior to January 1, 

2010. 

Schlumberger Rationale: We feel that there needs to be a cutoff date for the 

grandfathering of wells so eventually all Class 6 wells are constructed to the 

same standard 

Individual Response: EPA agrees that many Class I, Class II, and Class V experimental 

technology wells are designed and constructed to withstand exposure to CO2. The final GS rule 

provides for the construction of these wells to be grandfathered per §146.81(c), provided the 

owner or operator can demonstrate to the Director that the wells were engineered and constructed 

to meet the requirements at §146.86(a) and ensure protection of USDWs, in lieu of requirements 

at §146.86(b) and §146.87(a). EPA clarifies that only the construction requirements are 

grandfathered and that all other Class VI requirements (reporting, monitoring, mechanical 

integrity testing, etc.) must be met following a determination under §146.81(c). 

EPA does not plan to institute a "cut-off date" for this requirement since conversion is a sitespecific decision. EPA believes that the requirement should be based on the specific aspects of 

the well's construction, not on the date on which it was constructed. 

Letter ID: 0226 Comment ID: 24010 Letter Lines: 289 to 306 

Comment Code: 1220 1.1.1.1 Terminology and definitions 

12
Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment: Proposed Rule: Carbon dioxide stream means carbon dioxide that has been captured 

from an emission source (e.g., a power plant), plus incidental associated 

substances derived from the source materials and the capture process, and any 

substances added to the stream to enable or improve the injection process. This 

subpart does not apply to any carbon dioxide stream that meets the definition of 

a hazardous waste under 40 CFR part 261. 

Schlumberger Suggested Revision:: Carbon dioxide stream carbon dioxide that has 

been captured from an industrial process that is injected in any physical state 

or dissolved in water or brine. It includes incidental associated substances 

derived from the source materials and the capture process, and any substances 

added to the stream to enable or improve the injection process. This subpart 

does not apply to any carbon dioxide stream that meets the definition of a 

hazardous waste under 40 CFR part 261. 

Schlumberger Rationale: We want to ensure that dissolved CO2 is specifically 

allowed as it may allow a solution to the upward buoyancy drive associated with 

separate phase CO2. 

Individual Response: EPA disagrees with the suggested edit. The final definition of carbon 

dioxide stream at §146.81(d) remains unchanged and reads as: “carbon dioxide that has been 

captured from an emission source (e.g., a power plant), plus incidental associated substances 

derived from the source materials and the capture process, and any substances added to the 

stream to enable or improve the injection process. This subpart does not apply to any carbon 

dioxide stream that meets the definition of a hazardous waste under 40 CFR part 261.” As 

described above, nothing in the rule precludes the injection of dissolved CO2, as long as the CO2 

does not meet the definition of a hazardous waste under 40 CFR part 261. 

Based on its evaluation of all public comments and input on the proposed rule and the NODA 

and Request for Comment EPA has made many revisions to the GS rule. Please see the final rule 

and preamble for additional information. 

Letter ID: 0226 Comment ID: 24011 Letter Lines: 308 to 316 

Comment Code: 1220 1.1.1.1 Terminology and definitions 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment: Proposed Rule:Geologic sequestration means the long-term containment of a 

gaseous, liquid or supercritical carbon dioxide stream in subsurface geologic 

formations. This term does not apply to its capture or transport. 

Schlumberger Suggested Revision: Geologic sequestration means the long-term 

containment of a carbon dioxide stream in subsurface geologic formations. This 

term does not apply to its capture or transport. 

13
Schlumberger Rationale: CO2 stream was already defined and should e used here. 

Individual Response: EPA disagrees with the suggested change. The final definition of geologic 

sequestration at §146.81(d) reads as follows: “[T]he long-term containment of a gaseous, liquid, 

or supercritical carbon dioxide stream in subsurface geologic formations. This term does not 

apply to carbon dioxide capture or transport.” 

Based on its evaluation of all public comments and input on the proposed rule and the NODA 

and Request for Comment, EPA has made many revisions to the Class VI GS rule. Please see the 

final rule and preamble for additional information. 

Letter ID: 0226 Comment ID: 24012 Letter Lines: 318 to 330 

Comment Code: 1220 1.1.1.1 Terminology and definitions 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment: Proposed Rule: Geologic sequestration project means an injection well or wells 

used to emplace a carbon dioxide stream beneath the lowermost formation 

containing a USDW. It includes the subsurface three-dimensional extent of the 

carbon dioxide plume, associated pressure front, and displaced brine, as well as 

the surface area above that delineated region. 

Schlumberger Suggested Revision: Geologic sequestration project means an 

injection well or wells used to emplace a carbon dioxide stream into an 

injection zone. It includes the subsurface three-dimensional extent of the 

carbon dioxide plume, associated pressure front, and displaced brine, as well as 

the surface area above that delineated region. 

Schlumberger Rationale: - 

Individual Response: The Agency has modified the definition of geologic sequestration project 

at §146.81(d) to read as follows: “Geologic sequestration project means an injection well or 

wells used to emplace a carbon dioxide stream beneath the lowermost formation containing a 

USDW; or, wells used for geologic sequestration of carbon dioxide that have been granted a 

waiver of the injection depth requirements pursuant to requirements at §146.95; or, wells used 

for geologic sequestration of carbon dioxide that have received an aquifer exemption expansion. 

It includes the subsurface three-dimensional extent of the carbon dioxide plume, associated 

pressure front, and displaced brine, as well as the surface area above that delineated region.” 

Based on its evaluation of all public comments and input on the proposed rule and the NODA 

and Request for Comment, EPA has made many revisions to the Class VI GS rule. Please see the 

final rule and preamble for additional information. 

14
Letter ID: 0226 Comment ID: 24013 Letter Lines: 332 to 342 

Comment Code: 1220 1.1.1.1 Terminology and definitions 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment: Proposed Rule: Injection zone means a geologic formation, group of formations, 

or part of a formation that is of sufficient areal extent, thickness, porosity, 

and permeability to receive carbon dioxide through a well or wells associated 

with a geologic sequestration project. 

Schlumberger Suggested Revision: Injection zone means a geologic formation, 

group of formations, or part of a formation that is of sufficient areal extent, 

thickness, porosity, and permeability to receive carbon dioxide through a well 

or wells associated with a geologic sequestration project. 

Schlumberger Rationale: - 

Individual Response: EPA disagrees with the suggested edit. The definition of injection zone at 

§146.81(d) remains unchanged and reads as follows: “[A] geologic formation, group of 

formations, or part of a formation that is of sufficient areal extent, thickness, porosity, and 

permeability to receive carbon dioxide through a well or wells associated with a geologic 

sequestration project.” 

Based on its evaluation of all public comments and input on the proposed rule and the NODA 

and Request for Comment, EPA has made many revisions to the Class VI GS rule. Please see the 

final rule and preamble for additional information. 

Letter ID: 0226 Comment ID: 24014 Letter Lines: 344 to 353 

Comment Code: 1220 1.1.1.1 Terminology and definitions 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment: Proposed Rule: Pressure front means the zone of elevated pressure that is 

created by the injection of carbon dioxide into the subsurface. For the purposes 

of this subpart, the pressure front of a carbon dioxide plume refers to a zone 

where there is a pressure differential sufficient to cause the movement of 

injected fluids or formation fluids into a USDW. 

Schlumberger Suggested Revision: Pressure front means the zone of elevated 

pressure that is created by the injection of the carbon dioxide stream into the 

subsurface, where there is a pressure differential sufficient to cause movement 

of the carbon dioxide stream or formation fluids into a USDW. 

Individual Response: EPA disagrees with the suggested edit. The final definition of pressure 

front at §146.81(d) is unchanged and reads as follows: “[T]he zone of elevated pressure that is 

created by the injection of carbon dioxide into the subsurface. For the purposes of this subpart, 

15
the pressure front of a carbon dioxide plume refers to a zone where there is a pressure differential 

sufficient to cause the movement of injected fluids or formation fluids into a USDW.” 

Based on its evaluation of all public comments and input on the proposed rule and the NODA 

and Request for Comment, EPA has made many revisions to the Class VI GS rule. Please see the 

final rule and preamble for additional information. 

Letter ID: 0226 Comment ID: 24015 Letter Lines: 357 to 367 

Comment Code: 1220 1.1.1.1 Terminology and definitions 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment: Proposed Rule: Site closure the point/time, as determined by the Director 

following the requirements under §146.93, at which the owner or operator of a GS 

site is released from post-injection site care responsibilities. 

Schlumberger Suggested Revision: Site closure means the point/time, as 

determined by the Director following the requirements under §146.93, at which 

the owner or operator of a GS project is released from post-injection site care 

responsibilities. 

Schlumberger Rationale: Suggest using "GS project" to be consistent with other 

definitions 

Individual Response: EPA disagrees with the suggested edit. The final definition of site closure 

at §146.81(d) is unchanged and reads as follows: “The point/time, as determined by the Director 

following the requirements under §146.93, at which the owner or operator of a GS site is 

released from post-injection site care responsibilities.” 

Based on its evaluation of all public comments and input on the proposed rule and the NODA 

and Request for Comment, EPA has made many revisions to the Class VI GS rule. Please see the 

final rule and preamble for additional information. 

Letter ID: 0226 Comment ID: 24016 Letter Lines: 369 to 379 

Comment Code: 1220 1.1.1.1 Terminology and definitions 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment: Proposed Rule: Transmissive fault or fracture means a fault or fracture that has 

sufficient permeability and vertical extent to allow fluids to move between 

formations. 

Schlumberger Suggested Revision: Transmissive fault or fracture means a fault or 

fracture that has sufficient permeability and vertical extent to allow fluids to 

move beyond the confining zone. 

16
Schlumberger Rationale: The term between formations is insufficient as it could 

also include multiple zones within a injection zone or between two zones above 

the confining unit. 

Individual Response: EPA disagrees with the suggested edit. The final definition of 

transmissive fault or fracture at §146.81(d) is unchanged and reads as follows: “[A] fault or 

fracture that has sufficient permeability and vertical extent to allow fluids to move between 

formations.” 

Based on its evaluation of all public comments and input on the proposed rule and the NODA 

and Request for Comment, EPA has made many revisions to the Class VI GS rule. Please see the 

final rule and preamble for additional information. 

Letter ID: 0226 Comment ID: 24017 Letter Lines: 381 to 473 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

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

Comment: §146.82 Required Class VI permit information. 

Proposed Rule: (b) A map showing the injection well(s) for which a permit is 

sought and the applicable area of review. Within the area of review, the map 

must show the number, or name and location of all injection wells, producing 

wells, abandoned wells, plugged wells or dry holes, deep stratigraphic 

boreholes, State or EPA approved subsurface cleanup sites, surface bodies of 

water, springs, mines (surface and subsurface), quarries, water wells and other 

pertinent surface features including structures intended for human occupancy and 

roads. The map should also show faults, if known or suspected. Only information 

of public record is required to be included on this map; 

Schlumberger Suggested Revision: (b) A map or electronic file (e.g. GIS file) 

showing the injection well(s) for which a permit is sought and the applicable 

area of review. Within the area of review, the map must show the number, or name 

and location of all injection wells, producing wells, abandoned wells, plugged 

wells or dry holes, deep stratigraphic boreholes, State or EPA approved 

subsurface cleanup sites, surface bodies of water, springs, mines (surface and 

subsurface), quarries, water wells and other pertinent surface features 

including structures intended for human occupancy and roads. The map should also 

show faults, if known or suspected with surface expressions. Only information of 

public record is required to be included on this map; 

Schlumberger Rationale: This may mean more clarification. It seems strange to 

have deep faults on a surface map. Is the map to be of the surface or of the 

confining unit? Also, any map will be very busy so it may be useful to be able 

to submit an electronic file like a GIS file. 

17
Proposed Rule: (c) The area of review based on modeling, using data obtained 

during logging and testing of the well and the formation as required by 

paragraphs (l), (r), and (s) of this section; 

Schlumberger Suggested Revision: - 

Schlumberger Rationale: We support this but it may need to be better clarified 

that the well must e drilled prior to the permit application 

Proposed Rule: (3) Information on seismic history including the presence and 

depth of seismic sources and a determination that the seismicity would not 

interfere with containment; 

Schlumberger Suggested Revision: (3) Information on seismic history of the area 

including the presence and depth of seismic sources and a determination that the 

seismicity would not interfere with containment; 

Schlumberger Rationale: It seems like this requirement is at a larger scale than 

the AOR (maybe a regional scale) than the other requirements. This should be 

specified. 

Proposed Rule: (4) Data on the depth, areal extent, thickness, mineralogy, 

porosity, permeability and capillary pressure of the injection and confining 

zone(s); including geology/facies changes based on field data which may include 

geologic cores, outcrop data, seismic surveys, well logs, and names and 

lithologic descriptions; 

Schlumberger Suggested Revision: (4) Data on the depth, areal extent, thickness, 

mineralogy, porosity, permeability and capillary entry pressure of the injection 

and confining zone(s); including geology/facies changes based on field data 

which may include geologic cores, outcrop data, seismic surveys, well logs, and 

names and lithologic descriptions; 

Schlumberger Rationale: Should this include capillary pressure or capillary 

entry pressure? 

Proposed Rule: (e) A tabulation of all wells within the area of review which 

penetrate the injection or confining zone(s). Such data must include a 

description of each well's type, construction, date drilled, location, depth, 

record of plugging and/or completion, and any additional information the 

Director may require; 

Schlumberger Suggested Revision: - 

Schlumberger Rationale: How will this be handled if all of this data is not 

18
available for each well? 

Proposed Rule: (f) Maps and stratigraphic cross sections indicating the general 

vertical and lateral limits of all USDWs, water wells and springs within the 

area of review, their positions relative to the injection zone(s) and the 

direction of water movement, where known; 

Schlumberger Suggested Revision: In 

Schlumberger Rationale: - 

Proposed Rule: (g) Baseline geochemical data on subsurface formations, including 

all USDWs in the area of review; 

Schlumberger Suggested Revision: (g) Baseline geochemical data on subsurface 

formations, including all USDWs and geochemically monitored in the area of 

review; 

Schlumberger Rationale: All formations that are or may need to be geochemically 

monitored should be included 

Individual Response: EPA agrees that deep faults would not be expressed on a surface map, but 

information on such faults should be provided in cross sections, which are also required as part 

of the materials that support a permit application. 

EPA agrees that submittal of support information electronically is beneficial. The final GS rule 

requires owners or operators to submit permit applications, including supporting information, to 

EPA in an electronic format (§146.91(e)). 

Regarding seismic information, EPA acknowledges that, due to the nature of seismic events and 

records, available information would likely address an area that is larger than the delineated 

AoR. EPA clarifies that the intent of this requirements is to ensure that the Director has sufficient 

information on which to base a determination of the suitability of a potential project site for GS. 

EPA clarifies that information on capillary entry pressure must be submitted. EPA believes that 

capillary entry pressure measurements on core samples are necessary to quantify the amount of 

buoyant force the confining zone can maintain before failure (World Resources Institute, 2008). 

Regarding the requirement to submit tabulations of all wells within the AoR, EPA acknowledges 

that public records may not contain data on every artificial penetration in the AoR (or all of the 

data on each well that is required for the tabulation), particularly in areas with many older wells. 

However, EPA notes that the inventory and review process for GS wells required at 

§146.84(c)(2) is similar to what is required of Class I and Class II injection well operators, that 

the AoR and corrective action process for these well types has been successful for many years. 

EPA adds that the Director has the discretion to require the owner or operator to supplement a 

data records search, including requiring ground or airborne surveys for wells, if there is reason to 

19
believe, based on knowledge of the site or of available data bases, that the incompleteness of 

available information could compromise USDW protection from endangerment. 

Regarding baseline geochemical data, EPA is not specifying for which formations this 

information should be submitted 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 potentially 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 additional geochemical data as well. 

EPA agrees that not all of the information listed at §146.82 of the proposed regulation will be 

available at the time the owner or operator develops their initial permit application. In response 

to comments and based on an evaluation of the proposed requirements at §146.82, the Agency 

revised this subpart so that the final regulation specifies separate requirements for information to 

be submitted with the permit application and before well construction is approved (at §146.82(a)) 

and information to be submitted before operation of the well is authorized (at §146.82(c)). 

EPA is developing guidance on site characterization for GS projects to assist owners or operators 

and Directors in evaluating permit requirements and applications under §146.82. The guidance 

provides recommendations regarding characterizing the regional geology and hydrogeology of a 

proposed GS site as well as performing the necessary geochemical, geomechanical, and 

geophysical 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: 0226 Comment ID: 24018 Letter Lines: 475 to 485 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment Code: 3100 2.1 Proposed Geologic Siting Requirements (40 CFR 146.83) 

Comment: §146.83 Minimum criteria for siting. 

Proposed Rule: (2) A confining zone(s) that is free of transmissive faults or 

fractures and of sufficient areal extent and integrity to contain the injected 

carbon dioxide stream and displaced formation fluids and allow injection at 

proposed maximum pressures and volumes without initiating or propagating 

fractures in the confining zone(s); and 

Schlumberger Suggested Revision: - 

Schlumberger Rationale: We support this language as it is written. 

Individual Response: EPA acknowledges the comment and the final rule retains the text at 

§146.83 as proposed. 

20
Letter ID: 0226 Comment ID: 24019 Letter Lines: 487 to 503 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment Code: 3120 2.1.2 Need to identify additional confining and containment zones 

(seeking comment) 

Comment: Proposed Rule: (b) At the Director’s discretion, owners or operators of Class VI 

wells must identify and characterize additional zones that will impede vertical 

fluid movement, are free of faults and fractures that may interfere with 

containment, allow for pressure dissipation, and provide additional 

opportunities for monitoring, mitigation and remediation. 

Schlumberger Suggested Revision: (b) Owners or operators of Class VI wells must 

identify and characterize some additional zones, if they exist, that will impede 

vertical fluid movement, allow for pressure dissipation, and provide additional 

opportunities for monitoring, mitigation and remediation. Vertical faults and 

fractures that transect these zones must be identified. 

Schlumberger Rationale: We believe that a site with a single confining can 

provide storage integrity, however, we feel that if there are additional 

confining layers at the site they should be characterized to get a better 

estimate of leakage risk to USDWs and possibly identify additional monitoring 

zones. 

Individual Response: EPA retains the requirement to identify additional containment/confining 

zones, if required by the Director, as proposed (§146.83(b)). EPA acknowledges 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 containment 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, and also provide 

additional sites for monitoring, mitigation, and remediation. The Agency's decision is supported 

by commenters representing states, water associations, and an electric utility who assert that 

these requirements promote a flexible, risk-based, site-specific approach to characterizing and 

permitting a site for GS projects, and are intended to improve understanding of the project as a 

whole and promote better modeling of the site. 

Letter ID: 0226 Comment ID: 24020 Letter Lines: 505 to 517 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment Code: 3200 2.2 Proposed Area of Review and Corrective Action Requirements (40 

CFR 146.84) 

Comment: §146.84 Area of review and corrective action. 

Proposed Rule: (a) The area of review is the region surrounding the geologic 

21
sequestration project that may be impacted by the injection activity. The area 

of review is based on computational modeling that accounts for the physical and 

chemical properties of all phases of the injected carbon dioxide stream. 

Schlumberger Suggested Revision: (a) The area of review is based on 

computational modeling that accounts for physical and the chemical properties of 

all phases of the injected carbon dioxide stream, the associated pressure 

front, and displaced brine. 

Schlumberger Rationale: - 

Individual Response: Based on review of all public comments on the AoR definition at 

146.84(a), the Agency has modified it to read as follows: The region surrounding the geologic 

sequestration project where USDWs may be endangered by the injection activity. The area of 

review is delineated using computational modeling that accounts for the physical and chemical 

properties of all phases of the injected CO2 stream and is based on available site 

characterization, monitoring, and operational data. The definition in the proposed rule accounted 

for the varying physical and chemical properties of the CO2 including free-phase and waterdissolved CO2, as the commenter suggests. The definition in the final rule will continue to do so. 

EPA is developing guidance on AoR and corrective 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 guidance 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/groundwater/uic/wells_sequestration.cfm. 

Letter ID: 0226 Comment ID: 24021 Letter Lines: 518 to 534 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment Code: 3400 2.2.2 Corrective Action 

Comment Code: 3530 2.2.3.1 AoR reevaluation frequency (seeking comment) 

Comment: Proposed Rule: (b) The owner or operator of a Class VI well must prepare, 

maintain, and comply with a plan to delineate the area of review for a proposed 

geologic sequestration project, periodically reevaluate the delineation, and 

perform corrective action that meets the requirements of this section and is 

acceptable to the Director. As a part of the permit application for approval by 

the Director, the owner or operator must submit an area of review and corrective 

action plan that includes the following information: 

Schlumberger Suggested Revision: (b) The owner or operator of a Class VI well 

must prepare, maintain, and comply with a plan to delineate the area of review 

for a proposed geologic sequestration project, reevaluate the delineation, and 

22
perform corrective action that meets the requirements of this section in a 

manner and at a frequency acceptable to the Director. As a part of the permit 

application, the owner or operator must submit an area of review and corrective 

action plan that includes the following information: 

Schlumberger Rationale: - 

Individual Response: EPA disagrees with the proposed changes and retains the provisions as 

proposed. For additional information on EPA's approach to AoR and corrective action, please see 

the final rule and preamble. 

Letter ID: 0226 Comment ID: 24022 Letter Lines: 536 to 548 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment Code: 3530 2.2.3.1 AoR reevaluation frequency (seeking comment) 

Comment: Proposed Rule: (i) The minimum fixed frequency, not to exceed 10 years, the 

owner or operator proposes to reevaluate the area of review; 

Schlumberger Suggested Revision: Revision: (i) The owner or operator will 

reevaluate the AOR after two years, 5 years and then no less frequently than 

every 5 years for period of injection. This schedule may be relaxed at the 

discretion of the director in the post injection period if appropriate data 

exist to support the change. 

Schlumberger Rationale: We feel that a frequency of every 10 years is too long 

to identify early discrepancies between the site performance and the site model. 

Seeing early difference will allow for earlier model updating and provide 

additional reduction in leakage risk and a better understanding of the site. 

Individual Response: EPA agrees with commenters that reevaluations of the AoR every ten 

years may not be sufficient to appropriately model plume and pressure front movement, establish 

conditions for corrective action, and ensure protection of USDWs from endangerment. For these 

reasons, the Agency changed the minimum frequency for the AoR reevaluation at §146.84(e) 

from 10 years to at least every 5 years in the final GS rule. EPA believes that this revised 

frequency addresses commenters' concerns about the inherent uncertainties in modeling CO2 

movement, the emerging nature of GS technology, risk-based targeting of monitoring activities, 

and the unique nature of CO2 GS. In addition, the Director has discretion to require more 

frequent AoR reevaluation if he or she has reason to believe, based on site-specific information, 

that a five-year reevaluation schedule is not sufficiently protective of USDWs. 

Letter ID: 0226 Comment ID: 24023 Letter Lines: 550 to 567 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment Code: 3400 2.2.2 Corrective Action 

23
Comment: Proposed Rule: (iv) How corrective action will be conducted to meet the 

requirements of paragraph (d) of this section, including what corrective action 

will be performed prior to injection and what, if any, portions of the area of 

review will have corrective action addressed on a phased basis and how the 

phasing will be determined; how corrective action will be adjusted if there are 

changes in the area of review; and how site access will be guaranteed for future 

corrective action. 

Schlumberger Suggested Revision: (iv) How corrective action will be conducted to 

meet the requirements of paragraph (d) of this section, including what 

corrective action will be performed prior to injection and what, if any, 

portions of the area of review will have corrective action addressed on a phased 

basis and how the phasing will be determined; how corrective action will be 

adjusted if there are changes in the area of review; and how site access will be 

arranged for future corrective action. 

Schlumberger Rationale: Future access cannot be fully guaranteed for an area in 

advance that may not even be within the boundaries of the initial AOR/ project. 

Individual Response: EPA is retaining this requirement as proposed. The purpose of the 

corrective action requirement at §146.84(d) is to ensure that all wells in the AoR that have the 

potential to cause the movement of CO2 or other fluids into or between USDWs receive 

appropriate corrective action. In general, to meet this requirement, the owner or operator will 

most likely need to obtain the right of access to wells that may require corrective action, and 

demonstrate they have done this in their proposed AoR and corrective action plan. In the AoR 

and corrective action plan, the owner or operator must describe how site access will be 

guaranteed for future corrective action. §146.84(b)(2)(iv). 

Letter ID: 0226 Comment ID: 24024 Letter Lines: 569 to 577 

Comment Code: 3310 2.2.1.1 Comments in favor of requiring computational models to 

delineate the AoR (seeking comment) 

Comment: Proposed Rule: (1) Predict, using computational modeling, the projected lateral 

and vertical migration of the carbon dioxide plume and formation fluids in the 

subsurface from the commencement of injection activities until the plume 

movement ceases, pressure differentials sufficient to cause the movement of 

injected fluids or formation fluids into a USDW are no longer present, 

Schlumberger Suggested Revision: - 

Schlumberger Rationale: We support this as written 

Individual Response: EPA acknowledges the commenter’s support; the final GS rule retains the 

provision with minor modifications to require the use of existing data in predicting the AoR. 

24
Letter ID: 0226 Comment ID: 24025 Letter Lines: 579 to 592 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

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

trapping mechanism) 

Comment: Proposed Rule: (i) Be based on detailed geologic data collected to characterize 

the injection zone, confining zone and any additional zones; and anticipated 

operating data, including injection pressures, rates and total volumes over the 

proposed life of the geological sequestration project; 

Schlumberger Suggested Revision: (i) Be based on detailed geologic data 

collected to characterize the injection zone, confining zone(s), monitoring 

zones and any additional zones; and anticipated operating data, including 

injection pressures, rates and total volumes over the proposed life of the 

geological sequestration project; 

Schlumberger Rationale: We feel that if there are secondary confining units that 

they should be included in the site model along with any transmissive zones 

between the primary and secondary confining units. 

Individual Response: EPA agrees that all geologic data about the site, including confining 

zone(s) and transmissive zones, should be addressed in the model but disagrees that the 

suggested revision is necessary. EPA clarifies that the AoR delineation model must be based on 

detailed geologic data collected to characterize the injection zone, confining zone and any 

additional zones (§146.84(c)(1)(i)). 

Letter ID: 0226 Comment ID: 24026 Letter Lines: 594 to 606 

Comment Code: 3440 2.2.2.2 Evaluation of wells in the AoR (e.g., types of data to be 

reviewed) 

Comment: Proposed Rule: (2) Using methods approved by the Director, identify all 

penetrations, including active and abandoned wells and underground mines, in the 

area of review that may penetrate the confining zone. Provide a description of 

each well’s type, construction, date drilled, location, depth, record of 

plugging and/or completion, and any additional information the Director may 

require; and 

Schlumberger Suggested Revision: - 

Schlumberger Rationale: We feel that there needs to be some effort to identify 

unknown wells using aerial surveys or other methods. We support this language as 

long as it is interpreted to mean more than just a record search in areas that 

that have been explored or produced oil and gas or have had other deep wells. 

25
Individual Response: For most GS sites, relying on database and other public records searches 

(i.e., of "known" artificial penetrations) will be sufficient to meet the requirements at 

§146.84(c)(2). However, the Agency recognizes that there may be situations where additional 

surveys or research to locate wells may be appropriate. For example, the Director may determine 

that ground or airborne surveys for wells are appropriate, e.g., if there is reason to believe that 

the incompleteness of information on known wells could compromise USDW protection from 

endangerment. EPA adds that under §146.84(c)(2), the Director has the discretion to require the 

owner or operator to conduct additional searches. EPA adds that all corrective action must be 

performed pursuant to the approved AoR and corrective action plan, which affords the Director 

the discretion to require any additional information needed to ensure that all necessary corrective 

action is performed. EPA is issuing guidance on how to identify all wells that require corrective 

action; the guidance also describes the data that EPA recommends 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/groundwater/uic/wells_sequestration.cfm. 

Letter ID: 0226 Comment ID: 24027 Letter Lines: 608 to 617 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment Code: 3400 2.2.2 Corrective Action 

Comment Code: 5100 2.8.1 Injection well plugging activities (seeking comment) (40 CFR 

146.92) 

Comment: Proposed Rule: (3) Determine which abandoned wells in the area of review have 

been plugged (as required by §146.92) in a manner that prevents the movement of 

carbon dioxide or associated fluids that may endanger USDWs. 

Schlumberger Suggested Revision: (3) Determine which abandoned wells identified 

in 146.84 (c) (2) have been plugged (as required by §146.92) in a manner that 

prevents the movement of carbon dioxide or formation fluids that may endanger 

USDWs. 

Schlumberger Rationale: - 

Individual Response: EPA acknowledges the comment. Based on its evaluation of all public 

comments and input on the proposed rule and NODA and Request for Comment, EPA has made 

many revisions to the GS Rule. See the final rule and preamble for further discussion on EPA's 

final approach. 

Letter ID: 0226 Comment ID: 24028 Letter Lines: 619 to 629 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment Code: 3400 2.2.2 Corrective Action 

26
Comment: Proposed Rule: (d) Owners or operators of Class VI wells must perform corrective 

action on all wells in the area of review that are determined to need corrective 

action using methods necessary to prevent the movement of fluid into or between 

USDWs including use of corrosion resistant materials, where appropriate. 

Schlumberger Suggested Revision: Owners or operators of Class VI wells must 

perform corrective action using corrosion resistant materials, when appropriate, 

on all wells identified in 146.84(c)(2) that are determined to need corrective 

action". 

Schlumberger Rationale: - 

Individual Response: EPA revised the text at §146.84(d) to require the use of materials that are 

"compatible with the carbon dioxide stream" Instead of corrosion resistant materials. EPA 

believes this language change addresses commenters' concerns and is also consistent with other 

language regarding materials requirements in the GS rule. EPA did not make the other suggested 

changes. See the final rule and preamble for further discussion on EPA's final approach. 

Letter ID: 0226 Comment ID: 24029 Letter Lines: 631 to 639 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment Code: 3530 2.2.3.1 AoR reevaluation frequency (seeking comment) 

Comment: Proposed Rule: (f) At the minimum fixed frequency, not to exceed 10 years, as 

specified in the area of review and corrective action plan, or when monitoring 

and operational conditions warrant, owners or operators must: 

Schlumberger Suggested Revision: (f) At the same frequency as the reevaluation 

of the AOR as specified in 146.84(c ) (2) (i), or when monitoring and 

operational conditions warrant, owners or operators must: 

Schlumberger Rationale: - 

Individual Response: EPA disagrees with the proposed changes and retains the provisions as 

proposed. EPA believes that the commenter’s suggested edit has substantively the same meaning 

as the proposed text. For additional information on EPA's approach to AoR and corrective 

action, please see the final rule and preamble. 

Letter ID: 0226 Comment ID: 24030 Letter Lines: 641 to 650 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment Code: 3700 2.2.5 Comments on the requirement for an AoR and corrective action 

plan 

27
Comment: Proposed Rule: (4) Submit an amended area of review and corrective action plan 

or demonstrate to the Director through monitoring data and modeling results that 

no amendment to the area of review and corrective action plan is needed. 

Schlumberger Suggested Revision: (4) Submit an amended area of review and 

corrective action plan or demonstrate to the Director through monitoring data 

and modeling results that no change to the area of review and corrective action 

plan is needed. 

Schlumberger Rationale: - 

Individual Response: EPA disagrees with the suggested change and believes the proposed text 

is clear as written. For additional information on EPA's approach to AoR and corrective action, 

please see the final rule and preamble. 

Letter ID: 0226 Comment ID: 24031 Letter Lines: 652 to 667 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment Code: 5400 2.9 Proposed Financial Responsibility and Long-Term Care 

Requirements 

Comment: §146.85 Financial responsibility. 

Proposed Rule: (b) The owner or operator must provide to the Director, at a 

frequency determined by the Director, written updates of adjustments to the cost 

estimate to account for any amendments to the area of review and corrective 

action plan (§146.84), the injection well plugging plan (§146.92), and the postinjection site care and site closure plan (§146.93). 

Schlumberger Suggested Revision: (b) The owner or operator must provide to the 

Director, at the same frequency as the AOR reevaluation, written updates of 

adjustments to the cost estimate to account for any amendments to the area of 

review and corrective action plan (§146.84), the injection well plugging plan 

(§146.92), and the post-injection site care and site closure plan (§146.93). 

Schlumberger Rationale: We feel that potential changes in the size of the AOR 

require that all site plans be reevaluated at the same frequency as the AOR. 

Individual Response: EPA agrees that it is important to periodically update cost estimates that 

support financial responsibility determinations. The final GS rule, at §146.85(c), requires the 

owner or operator to provide annual updates to the cost estimate to account for any amendments 

to the AoR and corrective action plan, the injection well plugging plan, the PISC and site closure 

plan, and the emergency and remedial response plan. Owners or operators must also adjust the 

estimates for inflation annually under §146.85(c)(2). EPA adds that the Director can also require 

the owner or operator to provide an adjustment of the cost estimate if the Director determines 

28
that the original demonstration is no longer adequate, as specified at §146.85(e). See the final 

rule and preamble for further discussion of EPA's final approach to financial responsibility. 

Letter ID: 0226 Comment ID: 24032 Letter Lines: 669 to 677 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment Code: 3800 2.3 Proposed Injection Well Construction Requirements (40 CFR 

146.86) 

Comment: §146.86 Injection well construction requirements. 

Proposed Rule: (1) Prevent the movement of fluids into or between USDWs or into 

any unauthorized zones; 

Schlumberger Suggested Revision:(1) Prevent the movement of fluids into or 

between USDWs or into any unauthorized zones that causes endangerment; 

Schlumberger Rationale: - 

Individual Response: EPA disagrees with the suggested edit. EPA believes that protection of 

USDWs from endangerment and prevention of fluid movement between formations is 

paramount, and believes that the language as proposed meets the standards in SDWA §1421. 

Appropriately designed and constructed wells are necessary to prevent endangerment to USDWs 

and maintain integrity of the well throughout the lifetime of a GS project. This is the foundation 

of the requirements for construction and pre-operational testing of Class VI wells at §§146.86 

and 146.87. 

Letter ID: 0226 Comment ID: 24033 Letter Lines: 679 to 692 

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

Comment: Proposed Rule: (1) Casing and cement or other materials used in the construction 

of each Class VI well must have sufficient structural strength and be designed 

for the life of the geologic sequestration project. All well materials must be 

compatible with fluids with which the materials may be expected to come into 

contact and meet or exceed standards developed for such materials by the 

American Petroleum Institute, ASTM International, or comparable standards 

acceptable to the Director. The casing and cementing program must be designed to 

prevent the movement of fluids into or between USDWs. In order to allow the 

Director to determine and specify casing and cementing requirements, the owner 

or operator must provide the following information: 

Schlumberger Suggested Revision: - 

Schlumberger Rationale: We support this language as written. 

29
Individual Response: EPA agrees that cement that is compatible with the CO2 and formation 

fluids will enhance Class VI well integrity and has retained this provision in the final rule. EPA 

also agrees that developing technology in the field of acid-resistant cement will provide the 

industry with future benefits. In the interest of USDW protection, the Agency requires that the 

materials used in Class VI wells must be compatible with fluids with which they may come in 

contact, as required in §146.86(b)(1). 

Letter ID: 0226 Comment ID: 24034 Letter Lines: 694 to 700 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment Code: 3820 2.3.1 Well construction procedures 

Comment: Proposed Rule: (ii) Injection pressure, external pressure, internal pressure and 

axial loading; 

Schlumberger Suggested Revision: (ii) Injection pressure, external pressure, 

internal pressure and axial loading; 

Schlumberger Rationale: What is meant by external and internal pressure? 

Individual Response: The internal and external pressure mentioned in §146.86(b)(1)(ii) refers to 

pressure on the well casing. Internal pressures could be caused by cement or annular fluids; 

external pressures could be caused by cementing against the borehole or pressure head from 

formations. See the discussion of Class VI well construction requirements in the preamble to the 

final GS rule for additional information. Additionally, EPA is developing guidance on the 

construction of Class VI wells. This guidance will be available on EPA’s website at 

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

Letter ID: 0226 Comment ID: 24035 Letter Lines: 702 to 706 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment Code: 3800 2.3 Proposed Injection Well Construction Requirements (40 CFR 

146.86) 

Comment: Proposed Rule: (vi) Down-hole temperatures; 

Schlumberger Suggested Revision: (vi) Down-hole temperatures and pressures; 

Schlumberger Rationale: - 

Individual Response: EPA believes the requirement at 146.86(b)(1)(ii), which requires 

consideration of Injection pressure, external pressure, internal pressure, and axial loading 

addresses this concern, and therefore the proposed change is unnecessary. 

30
Letter ID: 0226 Comment ID: 24036 Letter Lines: 714 to 721 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment Code: 3822 2.3.1.1 Depth of surface casing (seeking comment) 

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

Comment: Proposed Rule: (2) Surface casing must extend through the base of the lowermost 

USDW and be cemented to the surface. 

Schlumberger Suggested Revision: (2) Surface casing must extend through the base 

of the lowermost USDW above the injection zone and be cemented to the surface. 

Schlumberger Rationale: In some parts of the US the USDW is very deep and this 

standard may preclude geologic sequestration in these areas. 

Individual Response: EPA disagrees with the suggested edit or that the surface casing 

requirements in the GS rule preclude injection below deep USDWs. The final GS rule at 

§146.86(b)(2) requires that surface casing extend through the base of the lowermost USDW and 

be cemented to the surface through the use of a single or multiple strings of casing and cement. It 

does not, however, specify how cementing must be accomplished, and gives flexibility to the 

owner or operator to propose alternate methods- to 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. 

EPA recognizes concerns regarding construction of Class VI wells where the lowermost USDW 

is very deep. To further address comments on deep 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 operating under injection depth waivers must comply 

with additional construction requirements to ensure that wells used to inject above or between 

USDWs are protective. See the discussion of the waiver approach in the preamble to the final GS 

rule for additional information. 

Letter ID: 0226 Comment ID: 24037 Letter Lines: 723 to 731 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

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

Comment: Proposed Rule: (3) At least one long string casing, using a sufficient number of 

centralizers, must extend to the injection zone and must be cemented by 

circulating cement to the surface in one or more stages. 

Schlumberger Suggested Revision: - 

Schlumberger Rationale: We support this language work by Carey et al and crow et 

al shows that CO2 can move above the top of the CO2 reservoir, so cementing to 

31
surface will provide the best chance to have maximum zonal isolation 

Individual Response: EPA agrees that the requirement for long-string casing of Class VI wells 

at §146.86(b) will offer the best protection against fluid movement behind the casing, between 

formations, and above the injection zone and will ensure competency of Class VI wells and 

protect USDWs from endangerment. The buoyant nature of CO2 dictates deep well construction 

procedures that address movement of fluid behind the casing and provide necessary barriers to 

CO2 leakage outside of the injection zone. In developing the construction requirements for Class 

VI wells, EPA reviewed the work cited by Carey et al. (2007) and Crow et al. (2008). EPA 

agrees that they offer important justification for the establishment of tailored requirements. 

Letter ID: 0226 Comment ID: 24038 Letter Lines: 733 to 750 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

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

Comment: Proposed Rule: (5) Cement and cement additives must be compatible with the 

carbon dioxide stream and formation fluids and of sufficient quality and 

quantity to maintain integrity over the design life the geologic sequestration 

project. The integrity and location of the cement shall be verified using 

technology capable of evaluating cement quality radially and identifying the 

location of channels to ensure that USDWs are not 

Schlumberger Suggested Revision: (5) Cement and cement additives must be 

suitable for use with the carbon dioxide stream and formation fluids and of 

sufficient quality and quantity to maintain integrity over the project life. The 

integrity and location of the cement shall be verified using technology capable 

of evaluating cement quality radially and identifying the location of channels 

to ensure that USDWs are not endangered. 

Schlumberger Rationale: Well cements need to site and condition specific. There 

may be instances or places in the well that will require special cements. It is 

also that the cement in the well last as long as the project and post injection 

period. 

Individual Response: EPA recognizes that each GS project will be unique and, for this reason, 

the rule provides flexibility regarding the selection and use of cements for Class VI wells that are 

appropriate to the site-specific conditions of the project. With the permit application, the owner 

or operator must submit well construction procedures, as specified at §146.82 (a)(12), that 

demonstrate that the well as constructed will prevent unacceptable fluid movement; allow the use 

of appropriate testing devices and workover tools; and allow continuous monitoring of the 

annulus space between the injection tubing and long-string casing, as specified at §146.86(a). 

The Director will evaluate the procedures in the context of geological and proposed operating 

data about the site. EPA adds that the rule does not specify cements to be used; rather, it provides 

owners or operators with the flexibility to choose, as long as the cements are compatible with the 

CO2 stream and formation fluids and of sufficient quality and quantity to maintain integrity over 

32
the design life of the GS project, as specified at §146.86(b)(5). 

See the discussion of Class VI well construction requirements in the preamble to the final GS 

rule for additional information. Additionally, EPA is developing guidance on the construction of 

Class VI wells. This guidance will be available on EPA’s website at 

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

Letter ID: 0226 Comment ID: 24039 Letter Lines: 752 to 784 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment Code: 3866 2.3.3.3 Logging and testing requirements (40 CFR 146.87) 

Comment: §146.87 Logging, sampling, and testing prior to injection well operation. 

Proposed Rule: (a) During the drilling and construction of a Class VI injection 

well, the owner or operator must run appropriate logs, surveys and tests to 

determine or verify the depth, thickness, porosity, permeability, and lithology 

of, and the salinity of any formation fluids in, all relevant geologic 

formations to assure conformance with the injection well construction 

requirements under §146.86, and to establish accurate baseline data against 

which future measurements may be compared. The owner or operator must submit to 

the Director a descriptive report prepared by a knowledgeable log analyst that 

includes an interpretation of the results of such logs and tests. At a minimum, 

such logs and tests must include: 

Schlumberger Suggested Revision: (a) During the drilling and construction of a 

Class VI injection well, the owner or operator must run appropriate logs, 

surveys and tests to determine or verify the depth, thickness, porosity, 

permeability, and lithology of, and the salinity of any formation fluids in, all 

relevant geologic formations to assure conformance with the injection well 

construction requirements under §146.86, and to establish accurate baseline data 

against which future measurements may be compared. The owner or operator must 

submit to the Director a descriptive report prepared by a knowledgeable log 

analyst that includes an interpretation of the results of such logs and tests. 

The Director may require such logs and tests as may be needed after taking into 

account the availability of similar data in the area of the drilling site to 

ensure that the data is equivalent to the data as would be collected based on 

such logs and tests as:: 

Schlumberger Rationale: In well defined areas, these evaluations are frequently 

unnecessary. The director should have discretion to select the appropriate 

requirements necessary to ensure that sufficient baseline data and information 

are available. For example, in an area where a number of wells are being 

drilled, the logging of surface hole yields little useful additional 

information. 

33
Individual Response: EPA disagrees that the requirements for logs, surveys, and tests are 

unnecessary. All logs, surveys, and tests listed at §146.87(a) are necessary to verify information 

about the injection and confining zones and ensure that the well is being drilled and cased as 

approved, and has mechanical integrity. This information is needed to demonstrate that the well 

can be operated and tested in a manner that protects USDWs from endangerment. While the tests 

do provide information on some of the same items, each test provides unique pieces of 

information that build on each other and allow for interpretations not possible with a single test. 

EPA notes that the Director has the discretion at §146.87(a)(5) to approve alternative methods 

that provide equivalent or better information. EPA believes that logs and tests must be performed 

on each well drilled regardless of existing information about the area to account for the 

complexity of CO2 injection well construction and the buoyancy of CO2. Existing lithologic and 

geologic information may lack the details needed for site-specific well design and the geology 

needed to support protection of USDWs from endangerment. 

Letter ID: 0226 Comment ID: 24040 Letter Lines: 786 to 794 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment Code: 3866 2.3.3.3 Logging and testing requirements (40 CFR 146.87) 

Comment: Proposed Rule: (ii) A cement bond and variable density log, and a temperature 

log after the casing is set and cemented. 

Schlumberger Suggested Revision: (ii) Cement evaluation logs after the casing is 

set and cemented to evaluate cement quality radially with sufficient resolution 

to identify channels or changes to the cement quality. 

Schlumberger Rationale: Radial is key to finding pathways but the resolution 

must be sufficient to see the pathways. See the pathway identified in Crow et al 

Individual Response: EPA agrees with the suggested change. In the final GS rule, 

§146.87(a)(2)(ii) reads as follows: "A cement bond and variable density log to evaluate cement 

quality radially, and a temperature log after the casing is set and cemented." 

Letter ID: 0226 Comment ID: 24041 Letter Lines: 796 to 803 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment Code: 3866 2.3.3.3 Logging and testing requirements (40 CFR 146.87) 

Comment: Proposed Rule: (4) A series of tests designed to demonstrate the internal and 

external mechanical integrity of injection wells, which may include: 

Schlumberger Suggested Revision: (4) Test(s) designed to demonstrate the 

internal and external mechanical integrity of injection wells, which may 

include: 

34
Schlumberger Rationale: - 

Individual Response: EPA disagrees that the suggested edit is necessary, and the final rule 

retains the text as proposed. 

Letter ID: 0226 Comment ID: 24042 Letter Lines: 805 to 810 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment Code: 3866 2.3.3.3 Logging and testing requirements (40 CFR 146.87) 

Comment: Proposed Rule: (ii) A tracer survey such as oxygen-activation logging; 

Schlumberger Suggested Revision: (ii) Diagnostic tools such as oxygenactivation logging; 

Schlumberger Rationale: Technical correction 

Individual Response: EPA disagrees that the allowing the use of unspecified "diagnostic tools" 

would provide the same amount of information as the requirement to perform a tracer survey. 

The track record for tracer surveys in evaluating mechanical integrity has been proven over time. 

The Agency clarifies that a tracer survey is one of the mechanical integrity tests that may be 

required by the Director or used by the owner or operator. 

Letter ID: 0226 Comment ID: 24043 Letter Lines: 812 to 817 

Comment Code: 3866 2.3.3.3 Logging and testing requirements (40 CFR 146.87) 

Comment: Proposed Rule: (5) Any alternative methods that provide equivalent or better 

information and that are required of and/or approved of by the Director. 

Schlumberger Suggested Revision: - 

Schlumberger Rationale: We interpret that (5) applies to 146.87(a) 

Individual Response: EPA clarifies that the Director has the discretion at §146.87(a)(5) to 

approve alternative logging, sampling, and testing methods that provide equivalent or better 

information than those specified in §146.87(a)(1-4). The Director may not allow MIT methods 

that have not been approved by EPA, pursuant to §146.89(e). 

Letter ID: 0226 Comment ID: 24044 Letter Lines: 819 to 835 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment Code: 3866 2.3.3.3 Logging and testing requirements (40 CFR 146.87) 

35
Comment: Proposed Rule: (b) The owner or operator must take and submit to the Director 

whole cores or sidewall cores of the injection zone and confining system and 

formation fluid samples from the injection zone(s). The Director may accept 

cores from nearby wells if the owner or operator can demonstrate that core 

retrieval is not possible and that such cores are representative of conditions 

at the well. The Director may require the owner or operator to core other 

formations in the borehole. 

Schlumberger Suggested Revision: (b) The owner or operator must submit to the 

Director a report describing whole cores or sidewall cores representative of the 

injection zone and confining system and formation fluid samples from the 

injection zone(s). The Director may accept data from cores and fluid samples 

from nearby wells if the owner or operator can demonstrate that such data are 

representative of conditions at the well. 

Schlumberger Rationale: The information required should be sufficient to 

properly describe the injection and confining zones. 

Individual Response: EPA clarifies that it is not the Agency's intent that physical cores be 

submitted to the Director. In the final GS rule, EPA has revised the first sentence of §146.87(b) 

to read as follows: "The owner or operator must take whole cores or sidewall cores of the 

injection zone and confining system and formation fluid samples from the injection zone(s), and 

must submit to the Director a detailed report prepared by a log analyst that includes: well log 

analyses (including well logs), core analyses, and formation fluid sample information...." 

EPA clarifies that §146.87(b) allows information on cores from nearby wells to be submitted 

only if the operator can demonstrate that core retrieval is not possible and that cores from nearby 

wells are representative of conditions at the Class VI well. If the Director approves the use of 

alternate cores and determines that additional logs, such as video logs, are necessary to evaluate 

the site, he/she has authority under §146.87(a)(5) to require additional information. 

Letter ID: 0226 Comment ID: 24045 Letter Lines: 837 to 845 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment Code: 3866 2.3.3.3 Logging and testing requirements (40 CFR 146.87) 

Comment: Proposed Rule: (c) The owner or operator must record the fluid temperature, pH, 

conductivity, reservoir pressure and the static fluid level of the injection 

zone(s). 

Schlumberger Suggested Revision: (c) Prior to injection well operation, the 

owner or operator must record the formation temperature, formation fluid pH and 

conductivity, and reservoir pressure of the injection zone(s). 

Schlumberger Rationale: - 

36
Individual Response: EPA clarifies that all logging, sampling and testing for characteristics of 

the injection zone required in §146.87 are, as defined in the title to that section, to be performed 

prior to injection well operation. EPA adds that §146.82(c)(7) requires that the Director evaluate 

the results of all logging and testing prior to authorizing injection. 

Letter ID: 0226 Comment ID: 24047 Letter Lines: 858 to 871 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment Code: 3866 2.3.3.3 Logging and testing requirements (40 CFR 146.87) 

Comment: Proposed Rule:(f) The owner or operator must provide the Director with the 

opportunity to witness all logging and testing by this subpart. The owner or 

operator must submit a schedule of such activities to the Director 30 days prior 

to conducting the first test and submit any changes to the schedule 30 days 

prior to the next scheduled test. 

Schlumberger Suggested Revision: (f) The owner or operator must provide the 

Director with the opportunity to witness all logging and testing by this 

subpart. The owner or operator must submit a schedule of such activities to the 

Director upon spudding the well and submit any changes to the schedule 48 hours 

prior to the scheduled test. 

Schlumberger Rationale: The changes reflect the realities of flexible rig 

schedules and consistency with Class II practices. 

Individual Response: EPA disagrees that the 30-day notification requirement is unreasonable. 

The 30-day notification mirrors the current requirement for logging and testing of new Class I 

wells, as described in §146.66. Acknowledging the developing nature of CO2 GS, EPA believes 

that involvement by the permitting authority in each project will provide much needed field data 

for assurance of USDW protection from endangerment and will help update and refine the 

permitting process. Adequate timing of notification will ensure the Director's ability to be 

involved. 

Letter ID: 0226 Comment ID: 24048 Letter Lines: 873 to 891 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment Code: 4110 2.4.1.1 Injection pressure limitations 

Comment: §146.88 Injection well operating requirements. 

Proposed Rule: (a) Except during stimulation, the owner or operator must ensure 

that injection pressure does not exceed 90 percent of the fracture pressure of 

the injection zone so as to assure that the injection does not initiate new 

fractures or propagate existing fractures in the injection zone. In no case may 

37
injection pressure initiate fractures in the confining zone(s) or cause the 

movement of injection or formation fluids that endangers a USDW. 

Schlumberger Suggested Revision: (a) Except during stimulation, the owner or 

operator must ensure that injection pressure does not exceed 90 percent of the 

hydraulic fracture pressure of the confining zone so as to assure that the 

injection does not initiate new fractures or propagate existing fractures in the 

confining zone. In no case may injection pressure initiate fractures in the 

confining zone(s) or cause the movement of injection or formation fluids that 

endangers a USDW. 

Schlumberger Rationale: Maintaining the integrity of the confining zone is the 

critical parameter. 

Individual Response: EPA agrees that maintaining the integrity of the confining zone is critical 

in order to protect USDWs from endangerment. However, EPA also believes that the injection 

pressure should not exceed 90 percent of the fracture pressure of the injection zone. The final 

rule retains this provision at §146.88(a). EPA believes that the 90 percent requirement, which 

was suggested by IOGCC and permit writers whom EPA consulted when writing the regulation, 

is a satisfactory margin of safety for well operation. 

Letter ID: 0226 Comment ID: 24049 Letter Lines: 847 to 856 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment Code: 3866 2.3.3.3 Logging and testing requirements (40 CFR 146.87) 

Comment: Proposed Rule: (e) Upon completion, but prior to operation, the owner or 

operator must conduct the following tests to verify hydrogeologic 

characteristics of the injection zone: 

Schlumberger Suggested Revision: (d) At any time prior to injection well 

operation, the owner or operator must determine fracture pressures of the 

injection and confining zones and conduct tests to verify hydrogeologic and 

geomechanical characteristics of the injection zone, e.g.: 

Schlumberger Rationale: - 

Individual Response: EPA disagrees that the suggested edit is necessary, and the final rule 

retains the text as proposed. 

Letter ID: 0226 Comment ID: 24050 Letter Lines: 893 to 899 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment Code: 4000 2.4 Proposed Injection Well Operating Requirements (40 CFR 146.88) 

38
Comment: Proposed Rule: (b) Injection between the outermost casing protecting USDWs and 

the well bore is prohibited. 

Schlumberger Suggested Revision: (b) Injection of the CO2 stream between the 

outermost casing protecting USDWs and the well bore is prohibited. 

Schlumberger Rationale: - 

Individual Response: EPA retains the provision as proposed, and clarifies that injection 

between the casing and the well bore is prohibited. This is consistent with requirements for other 

injection well classes in the UIC program. 

Letter ID: 0226 Comment ID: 24051 Letter Lines: 901 to 912 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment Code: 4000 2.4 Proposed Injection Well Operating Requirements (40 CFR 146.88) 

Comment: Proposed Rule: (c) The owner or operator must fill the annulus between the 

tubing and the long string casing with a non-corrosive fluid approved by the 

Director. The owner or operator must maintain on the annulus a pressure that 

exceeds the operating injection pressure, unless the Director determines that 

such requirement might harm the integrity of the well. 

Schlumberger Suggested Revision: (c) The owner or operator must fill the annulus 

between the tubing and the long string casing with a non-corrosive fluid 

approved by the Director. 

Schlumberger Rationale: Industry experience with the Class II UIC program does 

not support this requirement. 

Individual Response: EPA believes that maintaining an annulus pressure that is higher than the 

injection pressure, as required at §146.88(c), will ensure that if there are leaks in the tubing, the 

annulus fluid will move into the tubing, rather than the injectate moving out of the tubing and 

potentially along the outside of the well. EPA believes this requirement is appropriate and 

necessary for Class VI wells given the potential high volumes and supercritical nature of the 

CO2 injectate, potential geomechanical stresses in the wellbore, and the potential for movement 

of the CO2 in the event of a mechanical integrity loss. 

Letter ID: 0226 Comment ID: 24052 Letter Lines: 914 to 919 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment Code: 4000 2.4 Proposed Injection Well Operating Requirements (40 CFR 146.88) 

Comment: Proposed Rule: (3) Notify the Director within 24 hours 

39
Schlumberger Suggested Revision: (3) Notify the Director within 24 hours of 

discovery; 

Schlumberger Rationale: - 

Individual Response: The final rule text at §146.88(f) now reads, "If a shutdown (i.e., downhole or at the surface) is triggered or a loss of mechanical integrity is discovered." Therefore the 

notice required at §146.88(f)(3) must be provided within 24 hours of an automatic shut-off 

device being triggered or a loss of mechanical integrity being discovered. EPA believes this 

provision is necessary to ensure timely response to potential USDW endangerment. 

Letter ID: 0226 Comment ID: 24053 Letter Lines: 921 to 931 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

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

CFR 146.90) 

Comment: §146.90 Testing and monitoring requirements. 

Proposed Rule: (b) Installation and use, except during well workovers as defined 

in §146.86(d), of continuous recording devices to monitor injection pressure, 

rate and volume; the pressure on the annulus between the tubing and the long 

string casing; and the annulus fluid volume; 

Schlumberger Suggested Revision: - 

Schlumberger Rationale: 146.86(d) does not exist; perhaps 146.88(d) is what was 

intended. 

Individual Response: EPA acknowledges the comment; the final rule contains the suggested 

revision. 

Letter ID: 0226 Comment ID: 24054 Letter Lines: 933 to 945 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment Code: 4630 2.6.3 Corrosion monitoring 

Comment: Proposed Rule: (c) Corrosion monitoring of the well materials for loss of mass, 

thickness, cracking, pitting and other signs of corrosion must be performed on a 

quarterly basis to ensure that the well components meet the minimum standards 

for material strength and performance set forth in §146.86(b) by: 

Schlumberger Suggested Revision: (c) Corrosion monitoring of the well materials 

for loss of mass, thickness, cracking, pitting and other signs of corrosion must 

be performed quarterly and may be modified to be less frequent as approved by 

40
the Director based on construction materials, operating conditions, and 

monitoring history to ensure that the well components meet the minimum standards 

for material strength and performance set forth in §146.86(b) by: 

Schlumberger Rationale: Allows application of performance based approach. 

Individual Response: EPA believes that corrosion monitoring is appropriate given the 

potentially corrosive nature of the CO2 stream. CO2 in the presence of water becomes acidic, 

potentially accelerating corrosion of well materials. The CO2 stream for a GS project may also 

contain small volumes of impurities that could contribute to corrosion. For these reasons, the 

final rule requires quarterly corrosion monitoring at §146.90(c), as proposed. 

Letter ID: 0226 Comment ID: 24055 Letter Lines: 947 to 953 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment Code: 4630 2.6.3 Corrosion monitoring 

Comment: Proposed Rule: (1) Placing coupons of the well construction materials in contact 

with the carbon dioxide stream; or 

Schlumberger Suggested Revision: (1) Analyzing coupons of the well construction 

materials placed in contact with the carbon dioxide stream; or 

Schlumberger Rationale: - 

Individual Response: Based on its evaluation of all public comments and input on the proposed 

rule and NODA and Request for Comment EPA has made many revisions to the GS rule. See the 

final rule and preamble for further discussion on EPA's final approach. 

Letter ID: 0226 Comment ID: 24056 Letter Lines: 955 to 962 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment Code: 4630 2.6.3 Corrosion monitoring 

Comment: Proposed Rule: (2) Routing the carbon dioxide stream through a loop constructed 

with the material used in the well; or 

Schlumberger Suggested Revision: (2) Routing the carbon dioxide stream through a 

loop constructed with the material used in the well and inspecting the materials 

in the loop; or 

Schlumberger Rationale: - 

Individual Response: Based on its evaluation of all public comments and input on the proposed 

41
rule and NODA and Request for Comment EPA has made many revisions to the GS rule. See the 

final rule and preamble for further discussion on EPA's final approach. 

Letter ID: 0226 Comment ID: 24057 Letter Lines: 964 to 969 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment Code: 4630 2.6.3 Corrosion monitoring 

Comment: Proposed Rule: (3) Using an alternative method approved by the Director; 

Schlumberger Suggested Revision: (3) Using an alternative method, materials, or 

time period approved by the Director; 

Schlumberger Rationale: - 

Individual Response: Based on its evaluation of all public comments and input on the proposed 

rule and NODA and Request for Comment EPA has made many revisions to the GS rule. See the 

final rule and preamble for further discussion on EPA's final approach. 

Letter ID: 0226 Comment ID: 24058 Letter Lines: 971 to 980 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment Code: 4660 2.6.6 Geochemical monitoring 

Comment: Proposed Rule: (d) Periodic monitoring of the ground water quality and 

geochemical changes above the confining zone(s) that may be a result of carbon 

dioxide movement through the confining zone or additional identified zones: 

Schlumberger Suggested Revision: (d) Periodic monitoring of the ground water 

quality for geochemical changes above the confining zone(s) that may be a result 

of carbon dioxide movement through the confining zone or additional identified 

zones: 

Schlumberger Rationale: - 

Individual Response: EPA did not make the suggested change. Based on its evaluation of all 

public comments and input on the proposed rule and NODA and Request for Comment EPA has 

made many revisions to the GS rule. See the final rule and preamble for further discussion on 

EPA's final approach. 

Letter ID: 0226 Comment ID: 24059 Letter Lines: 982 to 992 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

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

42
Comment: Proposed Rule: (1) The location and number of monitoring wells must be based on 

specific information about the geologic sequestration project, including 

injection rate and volume, geology, the presence of artificial penetrations and 

other factors; 

Schlumberger Suggested Revision: (1) The location and number of monitoring wells 

must be based on specific information about the geologic sequestration project, 

including injection rate and volume, geology, the presence of artificial 

penetrations and other relevant factors as warranted by a risk-assessment; 

Schlumberger Rationale: The monitoring should be designed to reduce risk 

Individual Response: EPA agrees that monitoring plans and methods need to be site-specific 

and believes that the monitoring requirements for GS sites at §146.90 provide an appropriate 

level of flexibility in structuring a testing and monitoring plan that protects USDWs from 

endangerment. EPA retains the requirement regarding placement of monitoring wells, but adds 

that any additional relevant site-specific information must be considered in the development of 

the testing and monitoring plan to ensure USDW protection from endangerment. 

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 recommended approaches for implementing a 

testing and monitoring plan, including pre-operational geophysical logging and testing of 

injection wells, MITs, injection 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/groundwater/uic/wells_sequestration.cfm. 

Letter ID: 0226 Comment ID: 24060 Letter Lines: 994 to 1005 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment Code: 4660 2.6.6 Geochemical monitoring 

Comment: Proposed Rule: (2) The monitoring frequency and spatial distribution of 

monitoring wells must be based on baseline geochemical data that has been 

collected under §146.82(a) (6) and any modeling results in the area of review 

evaluation required by §146.84(b); 

Schlumberger Suggested Revision: (2) The monitoring frequency and spatial 

distribution of monitoring wells must be based on geological and geophysical 

data that has been collected under §146.82(d) and any modeling results in the 

area of review evaluation required by §146.84(b); 

Schlumberger Rationale:Geochemical data does not seem have a high degree of 

relevance in selecting monitoring well sites. 

43
Individual Response: EPA believes that baseline characterization of the site, including the 

geochemical data and initial modeling, will be highly valuable in selection of monitoring well 

locations and in refining plans for monitoring frequency. The GS rule stipulates that the 

monitoring frequency and spatial distribution of monitoring wells must be based on baseline 

geochemical data that were collected during the initial site characterization and the area of 

review evaluation at §146.90(d)(2). The details of the geochemical monitoring will be based on 

site-specific information and described in the Director-approved testing and monitoring plan. 

Letter ID: 0226 Comment ID: 24061 Letter Lines: 1007 to 1015 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment Code: 4546 2.5.2.2 MIT frequency (seeking comment) 

Comment: Proposed Rule: (e) A demonstration of external mechanical integrity pursuant to 

§146.89(c) at least once per year throughout the duration of the geologic 

sequestration project; 

Schlumberger Suggested Revision: (e) A demonstration of external mechanical 

integrity pursuant to §146.89(c) at least once per year throughout the life of 

the well; 

Schlumberger Rationale: - 

Individual Response: EPA is retaining the language as proposed. EPA clarifies that the 

monitoring and testing plan requirements in §146.90 cover the period prior to well plugging. 

External MITs are not required once a well is plugged, as this test would no longer be possible in 

a plugged well. If a well is plugged prior to site closure, no further MITs are required for that 

well. 

Letter ID: 0226 Comment ID: 24062 Letter Lines: 1017 to 1027 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment Code: 4640 2.6.4 Pressure fall-off testing (seeking comment) 

Comment: Proposed Rule: (f) A pressure fall-off test at least once every five years 

unless more frequent testing is required by the Director based on site specific 

information; 

Schlumberger Suggested Revision: (f) A pressure fall-off test or other 

equivalent test that identifies reservoir conditions with respect to flow 

dynamics at least once every five years unless more frequent testing is required 

by the Director based on site specific information; 

Schlumberger Rationale: Allows more flexibility while still providing the needed 

44
information 

Individual Response: EPA believes that pressure fall-off testing is necessary for GS wells. 

Pressure fall-off tests are designed to verify that modeled projections of reservoir pressure 

decline agree with measured pressure decline profiles. These tests can be useful in AoR 

calculations and reevaluations and may also indicate mischaracterization of site geology and the 

presence of leakage pathways. EPA therefore believes that pressure fall-off testing is conducted 

at least once every five years and the final GS regulation includes this requirement at §146.90(f). 

Pressure fall-off tests may be conducted in conjunction with other well performance tests (i.e., 

mechanical integrity testing) to ensure safe and effective operations. 

Letter ID: 0226 Comment ID: 24063 Letter Lines: 1029 to 1040 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

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

Comment: Proposed Rule: (g) Testing and monitoring to track the extent of the carbon 

dioxide plume and the position of the pressure front by either monitoring for 

pressure changes in the first formation overlying the confining zone or using 

indirect, geophysical techniques (e.g., seismic, electrical, gravity, or 

electromagnetic surveys and/or down-hole carbon dioxide detection tools); 

Schlumberger Suggested Revision: (g) Testing and monitoring to track the extent 

of the carbon dioxide plume and the position of the pressure front. 

Schlumberger Rationale:Monitoring outside of the injection zone provides little 

information of value for tracking and monitoring the injected plume. Examples of 

how to test and monitor could be included in the Preamble. 

Individual Response: As described above, EPA has revised this requirement in the final rule. 

The final GS regulation, at §146.90(g)(1), requires all GS project owners or operators to monitor 

directly for pressure changes in the injection zone. EPA believes that pressure monitoring in the 

injection zone is necessary to track the development and movement of the pressure front and 

CO2 plume. In addition, §146.90(g)(2) requires owners or operators to track the position of the 

CO2 plume using indirect methods (e.g., seismic, electrical, gravity, or electromagnetic surveys 

and/or down-hole CO2 detection tools), unless the Director determines based on site-specific 

geology, that such methods are not appropriate. 

Letter ID: 0226 Comment ID: 24064 Letter Lines: 1042 to 1051 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment Code: 4670 2.6.7 Surface air monitoring and/or soil gas monitoring (seeking 

comment) 

Comment: Proposed Rule: (h) At the Director’s discretion, surface air monitoring and/or 

45
soil gas monitoring to detect movement of carbon dioxide that could endanger a 

USDW. 

Schlumberger Suggested Revision: (h) At the Director’s discretion based on sitespecific conditions and risk- based factors, surface air monitoring and/or soil 

gas monitoring to detect movement of carbon dioxide that could endanger a USDW. 

Schlumberger Rationale: In most situations soil and air monitoring does not 

provide an effective method of protecting USDWs. 

Individual Response: EPA acknowledges that air and soil gas monitoring to ensure USDW 

protection is not necessary at all GS sites and agrees that the decision to use surface monitoring 

and the selection of monitoring methods for the purpose of USDW protection will be sitespecific. 

In the final rule, at §146.90(h), the decision to require such monitoring as an additional measure 

to ensure USDW protection rests with the Director as a means of identifying leaks that may pose 

a risk to USDWs and informing emergency notification of a Class VI owner or operator and UIC 

Director in the event of a USDW endangerment, pursuant to requirements at §146.91(c). 

The Agency believes that surface air and soil gas monitoring, when coupled with subsurface 

monitoring, may be appropriate at some GS projects to ensure USDW protection. EPA also 

acknowledges that surface air and soil gas measurements are subject to variability and may not 

be suitable in all settings as a method to ensure USDW protection. However, EPA does not 

believe that this should entirely preclude their use. The decision to use surface monitoring and 

the selection of monitoring methods will be site-specific (e.g., may be influenced by geology, 

injection depth, and operational conditions) and must be based on potential risks to USDWs 

within the AoR. 

Letter ID: 0226 Comment ID: 24065 Letter Lines: 1053 to 1060 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment Code: 4610 2.6.1 Testing and monitoring plan requirement (seeking comment) 

Comment: Proposed Rule: (1) The testing and monitoring plan must be based on potential 

vulnerabilities within the area of review; 

Schlumberger Suggested Revision: (1) The testing and monitoring plan must be 

based on site-specific geologic factors, modeling, and risk-assessment within 

the area of review; 

Schlumberger Rationale: - 

Individual Response: EPA anticipates that the testing and monitoring plan will address sitespecific geologic factors, modeling, and risk-assessment. EPA is developing guidance on how 

best to develop the various required project plans, including the testing and monitoring plan. The 

46
guidance can be found on EPA’s website at 

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

Based on its evaluation of all public comments and input on the proposed rule and NODA and 

Request for Comment EPA has made many revisions to the GS rule. See the final rule and 

preamble for further discussion on EPA's final approach. 

Letter ID: 0226 Comment ID: 24066 Letter Lines: 1062 to 1072 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

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

comment) 

Comment: §146.91 Reporting requirements. 

Proposed Rule: (1) Any changes to the physical, chemical and other relevant 

characteristics of the carbon dioxide stream from the proposed operating data; 

Schlumberger Suggested Revision: (1) Any significant changes to the physical, 

chemical and other relevant characteristics of the carbon dioxide stream from 

the proposed operating data; 

Schlumberger Rationale: Minor changes could just be due to uncertainty in 

measurements or models 

Individual Response: EPA retained this provision as proposed. The final rule at §146.91(a)(3) 

requires reporting of all exceedances of operating parameters. EPA disagrees with the suggestion 

to report only "significant" exceedances. Making a determination as to whether an exceedance is 

"significant" is not the purpose of the requirement. EPA believes that the ability of an operator to 

consistently meet operating requirements and avoid exceedances provides evidence of a wellmanaged GS project that is in compliance with the Class VI permit. If multiple exceedances 

occur, the Director should be aware of such occurrences and determine whether these indicate 

non-compliance at the site, and require the appropriate course of action (e.g., a well workover, 

modification of operating parameters, or imposition of a penalty). Please see the final rule and 

the discussion of testing and monitoring in the preamble for additional information. 

EPA clarifies that the rule, at §146.91(c), also requires operators to notify the Director, within 24 

hours, of any event that may cause endangerment to a USDW. If such events occur outside of 

business hours (e.g., over night), operators must report to the Director within 24 hours, and 

permitting agencies have staff and procedures to respond to these types of calls 24 hours a day, 7 

days a week. 

Letter ID: 0226 Comment ID: 24067 Letter Lines: 1074 to 1086 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

47
Comment Code: 5100 2.8.1 Injection well plugging activities (seeking comment) (40 CFR 

146.92) 

Comment: §146.92 Injection well plugging. 

Proposed Rule: (a) Prior to the well plugging, the owner or operator must flush 

each Class VI injection well with a buffer fluid, determine bottomhole reservoir 

pressure, and perform a final mechanical integrity test. 

Schlumberger Suggested Revision: (a) Prior to the well plugging, the owner or 

operator must flush each Class VI injection well with a buffer fluid, determine 

bottomhole reservoir pressure, and perform a final external mechanical integrity 

test. 

Schlumberger Rationale: Many of the components that would be tested by an 

internal MIT are removed or tested during the plugging process. 

Individual Response: EPA agrees that only an external MIT is required, and has modified the 

GS rule at §146.92(a) to require owners or operators to perform a final external mechanical 

integrity test prior to the well plugging. 

Letter ID: 0226 Comment ID: 24068 Letter Lines: 1088 to 1095 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment Code: 5100 2.8.1 Injection well plugging activities (seeking comment) (40 CFR 

146.92) 

Comment: Proposed Rule: (2) Appropriate testing methods to ensure mechanical integrity as 

specified in §146.89; 

Schlumberger Suggested Revision: (2) Appropriate testing methods to ensure final 

external mechanical integrity as specified in §146.89(c); 

Schlumberger Rationale: Many of the components that would be tested by an 

internal MIT are removed or tested during the plugging process. 

Individual Response: EPA agrees that only an external MIT is required, and has modified the 

GS rule at §146.92(a) to require owners or operators to perform a final external mechanical 

integrity test prior to the well plugging. 

Letter ID: 0226 Comment ID: 24069 Letter Lines: 1097 to 1104 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment Code: 5100 2.8.1 Injection well plugging activities (seeking comment) (40 CFR 

146.92) 

48
Comment: Proposed Rule: (5) The type and grade and quantity of material to be used in 

plugging. The material must be compatible with the carbon dioxide stream; and 

Schlumberger Suggested Revision: (5) The type and grade and quantity of material 

to be used in plugging. The material must be suitable for use with the carbon 

dioxide stream; and 

Schlumberger Rationale: - 

Individual Response: EPA believes, considering the potentially corrosive nature of CO2 when 

it is in contact with water, that the requirement that the material must be compatible with the 

CO2 stream is appropriate. The final rule retains this requirement. 

Letter ID: 0226 Comment ID: 24070 Letter Lines: 1106 to 1120 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment Code: 5100 2.8.1 Injection well plugging activities (seeking comment) (40 CFR 

146.92) 

Comment: Proposed Rule: (d) Plugging report. Within 60 days after plugging or at the time 

of the next semi-annual report (whichever occurs earlier) the owner or operator 

must submit a plugging report to the Director. If the semi-annual report is due 

less than 15 days after completion of plugging, then the report must be 

submitted within 60 days after plugging. The report must be certified as 

accurate by the owner or operator and by the person who performed the plugging 

operation (if other than the owner or operator.) 

Schlumberger Suggested Revision: (d) Plugging report. Within 60 days after 

plugging the owner or operator must submit a plugging report to the Director. 

The report must be certified as accurate by the owner or operator and by the 

person who performed the plugging operation (if other than the owner or 

operator.) 

Schlumberger Rationale: Simplification 

Individual Response: EPA has revised the text at §146.92(d) to reduce confusion. The final rule 

text reads, "Within 60 days after plugging the owner or operator must submit a plugging report to 

the Director." 

Letter ID: 0226 Comment ID: 24071 Letter Lines: 1122 to 1152 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

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

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

49
Comment: §146.93 Post-injection site care and site closure. 

Proposed Rule: (1) The owner or operator shall continue to conduct monitoring as 

specified in the Director-approved post-injection site care and site closure 

plan for at least 50 years following the cessation of injection. At the 

Director’s discretion, the monitoring will continue until the geologic 

sequestration project no longer poses an endangerment to USDWs. 

Schlumberger Suggested Revision: (1) The owner or operator shall continue to 

conduct monitoring as specified in the Director-approved post-injection site 

care and site closure plan, pursuant to the performance based criteria described 

in 146.93(3). 

Schlumberger Rationale: The 50 year default period is not based on any 

scientific or technical information and could be considered arbitrary and 

capricious. 

Proposed Rule: (2) If the owner or operator can demonstrate to the satisfaction 

of the Director before 50 years, based on monitoring and other site-specific 

data, that the geologic sequestration project no longer poses an endangerment to 

USDWs, the Director may approve an amendment to the post-injection site care and 

site closure plan to reduce the frequency of monitoring or may authorize site 

closure before the end of the 50-year period. 

Schlumberger Suggested Revision: (2) If the owner or operator can demonstrate to 

the satisfaction of the Director that the geologic sequestration project no 

longer poses an endangerment to USDWs, the Director may approve an amendment to 

the post- injection site care and site closure plan to reduce the frequency of 

monitoring or may authorize site closure. 

Schlumberger Rationale: - 

Individual Response: EPA disagrees that a post-injection site care timeframe of 50 years is 

excessive in most cases or is arbitrary and capricious. EPA proposed a default post-injection site 

care timeframe of 50 years based on a review of research studies, industry reports, and existing 

environmental programs. This analysis was included 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 various 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 change 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 

50
commenters, do not support a different default timeframe. However, EPA recognizes that 

alternative timeframes may be appropriate under limited, specific circumstances. 

For this reason, the GS rule offers owners or operators flexibility regarding the duration of the 

PISC timeframe by: (1) allowing the Director discretion to shorten or lengthen the PISC 

timeframe during the post-injection period based on site-specific data, pursuant to requirements 

at §146.93(b); or (2) affording the Director discretion to allow a Class VI well owner or operator 

to demonstrate, during the permitting process based on substantial data, that an alternative PISC 

timeframe may be appropriate if it ensures non-endangerment of USDWs pursuant to 

requirements at §146.93(c). 

EPA believes however, that to ensure USDW protection from endangerment, a default timeframe 

for post-injection site care will be necessary in all but a limited number of cases. This default 50 

year post-injection site care timeframe represents a reasonable and protective monitoring period 

based on a review of research studies, industry reports, and existing environmental programs, 

and evaluation of public comments. 

EPA believes that a default post-injection site care 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 accommodate site-specific circumstances and various 

geologic conditions, and addresses commenters’ concerns, while ensuring USDW protection. 

Both approaches will utilize site-specific data, and be based on pressure monitoring and USDW 

impacts. 

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 proposed well plugging plans and post-injection site 

care and site closure plans under §146.92 and §146.93. The guidance describes recommended 

approaches for how an owner or operator could plug injection and monitoring wells; perform 

post-injection monitoring; demonstrate the appropriateness of an alternative post-injection site 

care time frame; demonstrate non endangerment; and perform site closure activities. The 

guidance will be available at http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm. 

Letter ID: 0226 Comment ID: 24072 Letter Lines: 1154 to 1175 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment Code: 5300 2.8.3 Site closure activities (40 CFR 146.93) 

Comment: Proposed Rule: (3) Prior to authorization for site closure, the owner or 

operator must submit to the Director a demonstration, based on monitoring and 

other site-specific data, that the carbon dioxide plume and pressure front have 

stabilized and that no additional monitoring is needed to assure that the 

geologic sequestration project does not pose an endangerment to USDWs. 

51
Schlumberger Suggested Revision: (3) Prior to authorization for site closure, 

the owner or operator must demonstrate to the Director, based on monitoring and 

other site-specific data that no additional monitoring is needed to assure that 

the geologic sequestration project does not pose an endangerment to USDWs, 

considering the following:. (i) the estimated magnitude and extent of the AOR 

based on measurements and modeling; (ii) that CO2 movement and pressure changes 

match model predictions, (iii) the estimated location of the detectable CO2 

plume based on measurement and modeling (measuring magnitude of saturation 

within (iv) that there is no evidence of significant leakage of either CO2 or 

formation fluids that endanger USDWs; (v) that the CO2 plume and displaced 

formation fluid are not expected to migrate in the future in a manner that 

encounters a potential leakage pathway; and, (vi) that wells at the site are not 

leaking and have maintained integrity. 

Schlumberger Rationale: Establishes the performance based criteria for selecting 

the monitoring period. the plume or mapping the edge of it); 

Individual Response: The post-injection site care requirements in the final GS rule, §146.93(b), 

incorporate a combination of a fixed timeframe and a performance standard approach. 

Specifically , the GS rule offers owners or operators flexibility regarding the duration of the 

PISC timeframe by: (1) allowing the Director discretion to shorten or lengthen the PISC 

timeframe during the post-injection period based on site-specific data, pursuant to requirements 

at §146.93(b); or (2) affording the Director discretion to allow a Class VI well owner or operator 

to demonstrate, during the permitting process based on substantial data, that an alternative PISC 

timeframe may be appropriate if it ensures non-endangerment of USDWs pursuant to 

requirements at §146.93(c). 

EPA believes however, 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 based on a review of 

research studies, industry reports, and existing environmental programs, and evaluation of public 

comments. 

EPA believes that a default post-injection site care 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 accommodate site-specific circumstances and various 

geologic conditions, and addresses commenters’ concerns, while ensuring USDW protection. 

Both approaches will utilize site-specific data, and be based on pressure monitoring and USDW 

impacts. 

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 proposed well plugging plans and post-injection site 

care and site closure plans under 146.92 and 146.93. The guidance describes recommended 

approaches for how an owner or operator could plug injection and monitoring wells; demonstrate 

the appropriateness of an alternative post-injection site care time frame; perform post-injection 

52
monitoring; demonstrate non endangerment; and perform site closure activities. The guidance 

will be available at http://water.epa.gov/type/groundwater/uic/wells_sequestration.cfm. 

Letter ID: 0226 Comment ID: 24073 Letter Lines: 1186 to 1196 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment Code: 5300 2.8.3 Site closure activities (40 CFR 146.93) 

Comment: Proposed Rule: (e) Once the Director has authorized site closure, the owner or 

operator must submit a site closure report within 90 days that must thereafter 

be retained at a location designated by the Director. The report must include: 

Schlumberger Suggested Revision: (e) Once the Director has authorized site 

closure, the owner or operator must submit a site closure report within 90 days 

after completion of all closure operations. The report must include: 

Schlumberger Rationale: What is the retention period? Many other programs have a 

three year limit for retention of records. EPA is the steward of information at 

this point of the project, not the owner or operator. 

Individual Response: EPA disagrees that the owner or operator should not be responsible for 

record retention such as site closure reports. EPA believes that the requirements that the owner or 

operator retain for ten years following site closure, records collected during the post-injection 

site care period at §146.93(f) and §146.93(h) are appropriate for the post-injection and site 

closure period to ensure that data are available to support non-endangerment demonstrations and 

to address any concerns that may arise following site closure. This data will also support EPA's 

review of project data as part of the adaptive rulemaking approach. 

Letter ID: 0226 Comment ID: 24074 Letter Lines: 1198 to 1214 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment Code: 5300 2.8.3 Site closure activities (40 CFR 146.93) 

Comment: Proposed Rule: (1) Documentation of appropriate injection and monitoring well 

plugging as specified in §146.92 and paragraph (c) of this section. The owner or 

operator must provide a copy of a survey plat which has been submitted to the 

local zoning authority designated by the Director. The plat must indicate the 

location of the injection well relative to permanently surveyed benchmarks. The 

owner or operator must also submit a copy of the plat to the Regional 

Administrator of the appropriate EPA Regional Office; 

Schlumberger Suggested Revision: (1) Documentation of appropriate injection and 

monitoring well plugging as specified in §146.92 and paragraph (c) of this 

53
section. The owner or operator must provide a copy of a survey plat which has 

been submitted to the local zoning authority designated by the Director. The 

plat must indicate the location of the injection well(s) relative to permanently 

surveyed benchmarks. The owner or operator must also submit a copy of the plat 

to the Regional Administrator of the appropriate EPA Regional Office; 

Schlumberger Rationale: - 

Individual Response: The GS regulation at §146.93(g) requires the owner or operator to record 

a notation on the deed to the facility property or other similar document examined during a title 

search that the land has been used to sequester CO2 on the deed to the facility property at the 

time of site closure. 

Letter ID: 0226 Comment ID: 24075 Letter Lines: 1216 to 1252 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

Comment Code: 5800 2.13 Comments on emergency and remedial response (40 CFR 146.94) 

Comment: §146.94 Emergency and remedial response. 

Proposed Rule: (b) If the owner or operator obtains evidence that the injected 

carbon dioxide stream and associated pressure front may cause an endangerment to 

a USDW, the owner or operator must: 

Schlumberger Suggested Revision: (b) If the owner or operator obtains evidence 

that the injected carbon dioxide stream or associated pressure front endangers a 

USDW, the owner or operator must: 

Schlumberger Rationale: - 

Proposed Rule: (2) Take all steps reasonably necessary to identify and 

characterize any release; 

Schlumberger Suggested Revision: (2) Take all steps reasonably necessary to 

identify and characterize the endangerment posed; 

Schlumberger Rationale: - 

Proposed Rule: (3) Notify the Director within 24 hours; and 

Schlumberger Suggested Revision: (3) Notify the Director within 24 hours of 

becoming aware of the endangerment; and 

Schlumberger Rationale:- 

Proposed Rule: (d) The owner or operator must notify the Director and obtain his 

54
approval prior to conducting any well workover. 

Schlumberger Suggested Revision: (d) The owner or operator must notify the 

Director prior to conducting any well workover in response to any case of 

endangerment. 

Schlumberger Rationale:In critical situations, time spent obtaining approval 

could adversely affect the ability to conduct operations or increase the level 

of endangerment. 

Individual Response: After consideration of comments, EPA has finalized the rule language in 

§146.94(b) as proposed. In the introductory section of §146.94(b), EPA clarifies that the pressure 

front, as defined in §146.81, is a zone where the pressure differential is sufficient to cause the 

movement of injected fluids or formation fluids into a USDW. Therefore, displaced formation 

fluids are implicitly included in the requirements for §146.94. EPA also clarifies that owners or 

operators must take action when the CO2 stream or pressure front may cause endangerment. In 

order to prevent the endangerment of USDWs, as required under §1421 of the SDWA, EPA 

expects the owner or operator to act preemptively and not wait until endangerment has occurred. 

This language is consistent with existing UIC requirements for other well classes and EPA’s 

authority under the SDWA. 

EPA clarifies that the Agency expects that owners or operators should take care not to damage 

the well when ceasing injection under §146.94(b)(1). At §146.94(b)(2), EPA is maintaining the 

requirement to “characterize the release.” In order to prevent the endangerment of USDWs, as 

required under §1421 of the SDWA, EPA expects the owner or operator to act preemptively and 

not wait until endangerment has occurred. This language is consistent with existing UIC 

requirements for other well classes and EPA’s authority under the SDWA. 

Concerning commenters’ suggestions for §146.94(b)(3), EPA clarifies that the 24 hours begins 

when the owner or operator obtains evidence of possible endangerment. EPA believes the rule 

language is clear on this requirement. 

Since proposal, EPA has modified the final regulatory language at §146.94(d) to clarify what 

constitutes a workover to address a well failure (which invokes remedial actions) and what 

constitutes a maintenance-type workover. For maintenance-type workovers (i.e., those that are 

scheduled in advance), the owner or operator must notify and gain approval from the Director 

prior to beginning the workover. In the final GS regulation, EPA has moved this requirement to 

the reporting requirements at §146.91(d) to clarify its intent. 

Regarding concerns that notification could delay responses, EPA clarifies that the GS rule, at 

§146.94(b), describes procedures owners or operators must take in emergency situations. 

Specifically, upon determining that there is a problem with the well that may endanger a USDW, 

the owner or operator must first cease injection, then take all steps reasonably necessary to 

identify and characterize any release, notify the Director, and implement the approved 

emergency and remedial response plan, which may include a well workover. EPA believes that 

ceasing injection (which the owner or operator would do immediately and before notifying the 

55
Director) is the immediate action necessary to prevent or mitigate endangerment of USDWs, as 

required under the SDWA. 

Letter ID: 0226 Comment ID: 24970 Letter Lines: 1177 to 1184 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

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

Comment: Proposed Rule: (4) If such a demonstration cannot be made (i.e., if the carbon 

dioxide plume and pressure front have not stabilized) after the 50 year period, 

the owner or operator must submit to the Director a plan to continue postinjection site care. 

Schlumberger Suggested Revision: Delete 

Schlumberger Rationale: No longer necessary 

Individual Response: As described above, EPA believes that a default post-injection site care 

timeframe of 50 years, with allowance of Director's discretion to shorten or lengthen this 

timeframe or approve an alternative PISC timeframe, is appropriate to ensure that USDWs are 

protected, while accounting for the variety of site-specific circumstances that may come in to 

play at GS sites. EPA expects that the Director would consider the types of information the 

commenter describes in determining whether the plume and pressure front no longer pose a risk 

of endangerment to USDWs and post-injection site care monitoring may be discontinued. 

Letter ID: 0226 Comment ID: 24971 Letter Lines: 708 to 712 

Comment Code: 1240 1.1.1.3 Suggested changes/edits to rule language 

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

Comment: Proposed Rule: (viii) Type or grade of cement; and 

Schlumberger Suggested Revision: (viii) Type or grade of cement; and additives 

Schlumberger Rationale: - 

Individual Response: EPA agrees with the suggestion that §146.86(b)(1)(viii) be revised to also 

address cement additives. In the final GS rule, the subparagraph reads as follows: "Type or grade 

of cement and cement additives." 

56