John

Heinicke/Omaha/URSCor

p

06/06/200701:12 PM

To mashburn.jeff@epamail.epa.gov,

Joane.Lineburg@state.sd.us, Tim.Pavek@ellsworth.af.mil,

Jim.Gravette@langley.af.mil, Cindy.Hood@brooks.af.mil,

Joy.Lozano.ctr@brooks.af.mil, sembera_mark@bah.eom

ee Denny Jorgenson/Omaha/URSCorp@URSCORP,

afeee.iee.documents@brooks.af.mil

bee Terry Saldivar/Omaha/URSCorp

Subject EAFB - Transmittal ofSigned ESD for OUs 1,2,3,4,5,6,7,8,

11, and 12

NOTICE OF TRANSMITI'AL

Explanation Of Significant Differences To The Records Of Decision For Operable Units 1, 2,

3,4,5,6,7,8,11, and 12 (CDRL AOOID)

Ellsworth AFB, South Dakota

ACC Environmental Restoration Program 4-Base PBC

Contract FA8903-04-D-8679 Delivery Order 0053

This email is notification that we are transmiting the signed ESD to the distribution list below. You

should receive this transmittal tomorrow by Fed Ex. We are also transmitting the orignal signed signature

pages to Tim Pavek.

URS Group, Inc.

John J. Heinicke, P.E.

12120 Shamrock Plaza, Suite 300

Omaha, Nebraska 68154

402.952.2543

Distribution:

Cindy Hood, AFCEE (211)

Jim Gravette, Ace (liD)

Tim Pavek, EAFB (1/1)

Jeff Mashburn, EPA Region 8 (1/1)

Joane Lineburg, SDDENR (Ill)

Oil) denotes one CD copy and one hard copy

This transmittal is related to the following contract milestones:

LF-02, LF-03, LF-05, LF-06, RW-07, SS-n, and LF-21 Milestone 4.01.03

OT-20 Milestone 2.02.04

John J. Heinicke, P.E.

12120 Shamrock Plaza, Suite 300

Omaha, Nebraska 68154

402.952.2543

This e-mail and any attachments are confidential. If you receive this message in error or are not the intended recipient, you

should not retain, distribute, disclose or use any of this information and you should destroy the e-mail and any attachments or

copies.

4465 00001
EXPLANATION OF SIGNIFICANT DIFFERENCES

TO THE RECORDS OF DECISION FOR

OPERABLE UNITS 1,2,3,4,5,6,7,8,11, AND 12

For Remedial Action at:

Ellsworth Air Force Base, South Dakota

Prepared by:

United States Air Force

Ellsworth Air Force Base, South Dakota

May 1,2007

Terry Anderson

Director, Federal Facilities Program

Office of Ecosystems Protection and Remediation

U.S. Environmental Protection Agency Region VIII

Steven M. Pirner

Secretary, South Dakota Department of

Environment and Natural Resources

Date

Date

Date

4465 00002
EXPLANATION OF SIGNIFICANT DIFFERENCES

TO THE RECORDS OF DECISION FOR

OPERABLE UNITS 1,2,3,4,5,6,7,8,11, AND 12

For Remedial Action at:

Ellsworth Air Force Base, South Dakota

Prepared by:

United States Air Force

Ellsworth Air Force Base, South Dakota

May 1,2007

Timothy A. Byers, Colonel

U.S. Air Force

Director of Installations

Steven M. Pirner

Secretary, South Dakota Department of

Environment and Natural Resources

Date

Date

4465 00003
EXPLANATION OF SIGNIFICANT DIFFERENCES

TO THE RECORDS OF DECISION FOR

OPERABLE UNITS 1,2,3,4,5,6,7,8,11, AND 12

For Remedial Action at

Ellsworth Air Force Base, South Dakota

Prepared by:

United States Air Force

Ellsworth Air Force Base, South Dakota

May 1, 2007

Timothy A. Byers, Colonel

U.S. Air Force

Director of Installations

Terry Anderson

Director, Federal Facilities Program

Office of Ecosystems Protection and Remediation

U,S. Environme I Protection Agency Region VIII

Steven . Pirner

Secretary, South Dakota Department of

Environment and Natural Resources

Date

Date

4465 00004
Explanation of Significant Differences 

OU-11 Basewide Ground Water 

Ellsworth AFB, South Dakota 

Q:\1616\9962\Ellsworth\ESD Final\OU-11 ESD Final 050107.doc Page i 

May 1, 2007

TABLE OF CONTENTS 

Section Page

1.0 INTRODUCTION................................................................................................................................... 1

1.1 Statement of Purpose ............................................................................................................... 1

1.2 Site Locations ........................................................................................................................... 2

1.3 Lead and Support Agencies ..................................................................................................... 2

1.4 Statutory Citation for An Explanation of Significant Difference ................................................. 2

1.5 Date of Record of Decision....................................................................................................... 2

1.6 Administrative Record............................................................................................................... 3

2.0 SITE HISTORY AND SELECTED REMEDY......................................................................................... 4

2.1 Operable Unit 11....................................................................................................................... 4

2.1.1 OU-11 Site History and Contamination ..................................................................... 4

2.1.2 OU-11 Selected Remedy .......................................................................................... 6

2.2 Operable Unit 1......................................................................................................................... 7

2.2.1 OU-1 Site History and Contamination ....................................................................... 7

2.2.2 OU-1 Selected Remedy ............................................................................................ 8

2.3 Operable Unit 2......................................................................................................................... 8

2.3.1 OU-2 Site History and Contamination ....................................................................... 8

2.3.2 OU-2 Selected Remedy ............................................................................................ 9

2.4 Operable Unit 3......................................................................................................................... 9

2.4.1 OU-3 Site History and Contamination ....................................................................... 9

2.4.2 OU-3 Selected Remedy ........................................................................................... 10

2.5 Operable Unit 4........................................................................................................................ 10

2.5.1 OU-4 Site History and Contamination ...................................................................... 10

2.5.2 OU-4 Selected Remedy ........................................................................................... 11

2.6 Operable Unit 5........................................................................................................................ 11

2.6.1 OU-5 Site History and Contamination ...................................................................... 11

2.6.2 OU-5 Selected Remedy ........................................................................................... 12

2.7 Operable Unit 6........................................................................................................................ 12

2.7.1 OU-6 Site History and Contamination ...................................................................... 12

2.7.2 OU-6 Selected Remedy ........................................................................................... 12

2.8 Operable Unit 7........................................................................................................................ 13

2.8.1 OU-7 Site History and Contamination ...................................................................... 13

2.8.2 OU-7 Selected Remedy ........................................................................................... 13

2.9 Operable Unit 8........................................................................................................................ 13

2.9.1 OU-8 Site History and Contamination ...................................................................... 13

2.9.2 OU-8 Selected Remedy ........................................................................................... 14

2.10 Operable Unit 12...................................................................................................................... 14

2.10.1 OU-12 Site History and Contamination .................................................................... 14

2.10.2 OU-12 Selected Remedy ......................................................................................... 15

3.0 BASIS FOR SIGNIFICANT DIFFERENCE........................................................................................... 16

3.1 Transfer of Ground Water to OU-11 ........................................................................................ 16

3.2 Additional Treatment Technologies ......................................................................................... 16

4465 00005
Explanation of Significant Differences 

OU-11 Basewide Ground Water 

Ellsworth AFB, South Dakota 

Q:\1616\9962\Ellsworth\ESD Final\OU-11 ESD Final 050107.doc Page ii 

May 1, 2007

4.0 DESCRIPTION OF SIGNIFICANT DIFFERENCES ............................................................................. 20

4.1 Transfer of Ground Water to OU-11 ........................................................................................ 20

4.2 Additional Technolgies for Ground Water Remedial Action..................................................... 20

4.3 Expected Outcomes ................................................................................................................ 21

5.0 SUPPORT AGENCY COMMENTS ON ESD........................................................................................ 23

6.0 STATUTORY DETERMINATIONS....................................................................................................... 24

7.0 PUBLIC PARTICIPATION COMPLIANCE ........................................................................................... 25

8.0 REFERENCES..................................................................................................................................... 26

9.0 ACRONYMS AND ABBREVIATIONS .................................................................................................. 28

LIST OF FIGURES 

Figure 1 Ellsworth Air Force Base Location Map 

Figure 2 Operable Units Location Map 

Figure 3 Chlorinated VOC Plumes at OU-11 Area 1 

Figure 4 Chlorinated VOC Plumes at OU-11 Areas 2 

Figure 5 Chlorinated VOC Plumes at OU-1, OU-2, OU-4, and OU-12 

Figure 6 Chlorinated VOC Plumes at OU-7 

LIST OF ATTACHMENTS 

Attachment A Memorandum for Record (USAF 2005) 

4465 00006
Explanation of Significant Differences 

OU-11 Basewide Ground Water 

Ellsworth AFB, South Dakota 

Q:\1616\9962\Ellsworth\ESD Final\OU-11 ESD Final 050107.doc Page 1 

May 1, 2007

1.0 INTRODUCTION 

1.1 STATEMENT OF PURPOSE 

This Explanation of Significant Differences (ESD) addresses ground water at Ellsworth Air Force 

Base (AFB), as follows: 

• The ground water media for all operable units (OUs) are officially transferred to OU-11 

Basewide Ground Water. 

• Biodechlorination is added as a ground water treatment technology and soil vapor 

extraction (SVE) is added as a treatment technology at the Pride Hangar hotspot. 

The ground water transfer to OU-11 involves the following OUs at Ellsworth AFB: 

• OU-1 (Fire Protection Training Area) 

• OU-2 (Landfill Nos. 1 and 6) 

• OU-3 (Landfill No. 2) 

• OU-4 (Landfill No. 3) 

• OU-5 (Landfill No. 4) 

• OU-6 (Landfill No. 5) 

• OU-7 (Weapons Storage Area) 

• OU-8 (Explosives Ordnance Disposal Area) 

• OU-12 (Hardfill No. 1) 

A Memorandum for Record, signed by the Remedial Project Managers for the U.S. Air Force 

(USAF), the U.S. Environmental Protection Agency (USEPA), and the South Dakota 

Department of Environment and Natural Resources (SDDENR), has already recognized that all 

contaminated ground water both on Base and off Base will be addressed as part of OU-11 

Basewide Ground Water (USAF 2005). This Memorandum for Record is attached and 

incorporated into this ESD. Based on previous Record of Decision (ROD) deferrals, OU-11 

Basewide Ground Water already includes contaminated ground water at OUs 9 and 10, except 

for ground water that is contaminated solely with petroleum hydrocarbons. Sites that are solely 

contaminated by petroleum-related constituents are being addressed under the State of South 

Dakota’s petroleum release program, pursuant to the Federal Facilities Agreement (FFA) 

(USEPA 1992). 

This ESD will allow the USAF to implement additional treatment technologies that are not 

included in the selected remedies for ground water at Ellsworth AFB. The additional treatment 

technologies are intended to reduce the overall timeframe required to manage the chlorinated 

volatile organic compound (VOC) ground water plumes and to reduce the toxicity and volume of 

the chlorinated VOCs. All components of the selected remedies for ground water, as specified 

by the RODs for OUs 1, 2, 3, 4, 5, 6, 7, 8, 11, and 12, will remain unchanged and in effect. 

4465 00007
Explanation of Significant Differences 

OU-11 Basewide Ground Water 

Ellsworth AFB, South Dakota 

Q:\1616\9962\Ellsworth\ESD Final\OU-11 ESD Final 050107.doc Page 2 

May 1, 2007

1.2 SITE LOCATIONS 

Ellsworth AFB is a USAF Air Combat Command installation located 12 miles east of Rapid City, 

South Dakota and adjacent to the City of Box Elder (see Figure 1). The Base is situated on 

approximately 4,858 acres in Meade and Pennington Counties, and includes runways, airfield 

operations, industrial areas, housing, and recreational facilities. Open land, containing 

individual residences, lies to the north, south, and west of Ellsworth AFB, while residential and 

commercial areas lie to the east. 

The locations of the chlorinated VOC plumes in ground water at OU-1, OU-2, OU-4, OU-7, 

OU-11, and OU-12 are shown on Figure 2. In addition, the locations of OU-3, OU-5, OU-6, and 

OU-8 are shown on Figure 2. Site descriptions are provided in Section 2 of this ESD. 

1.3 LEAD AND SUPPORT AGENCIES 

The USAF is the lead agency. The USEPA Region 8 and the SDDENR are the support 

agencies. 

1.4 STATUTORY CITATION FOR AN EXPLANATION OF SIGNIFICANT 

DIFFERENCE 

Section 117(c) of the Comprehensive Environmental Response, Compensation, and Liability Act 

(CERCLA), 42 United States Code (USC) §9617(c), and the National Contingency Plan (NCP) 

at Title 40 Code of Federal Regulations (40 CFR) §300.435(c)(2)(i), require that an ESD be 

prepared when differences in the remedial action significantly change but do not fundamentally 

alter the remedy selected in the ROD with respect to scope, performance, or cost. 

1.5 DATE OF RECORD OF DECISION 

The signature dates for each of the RODs affected by this ESD are listed below: 

• The ROD for OU-11 was issued in April 1997 (USAF 1997). The OU-11 ROD was 

signed by the USAF on April 23, 1997; by the USEPA on April 28, 1997; and by the 

SDDENR on April 29, 1997. At the time the OU-11 ROD was prepared and signed, 

ground water media from OU-9 and OU-10 had been deferred to OU-11 by their 

respective RODs (USAF 1996h and USAF 1996i). 

• The ROD for OU-1 was issued in April 1996 (USAF 1996a). The OU-1 ROD was signed 

by the USAF on May 15, 1996; by the USEPA on May 10, 1996; and by the SDDENR on 

May 9, 1996. 

• The ROD for OU-2 was issued in April 1996 (USAF 1996b). The OU-2 ROD was signed 

by the USAF on May 15, 1996; by the USEPA on May 10, 1996; and by the SDDENR on 

May 9, 1996. 

4465 00008
Explanation of Significant Differences 

OU-11 Basewide Ground Water 

Ellsworth AFB, South Dakota 

Q:\1616\9962\Ellsworth\ESD Final\OU-11 ESD Final 050107.doc Page 3 

May 1, 2007

• The ROD for OU-3 was issued in June 1996 (USAF 1996c). The OU-3 ROD was signed 

by the USAF on June 19, 1996; by the USEPA on June 7, 1996; and by the SDDENR on 

June 7, 1996. 

• The ROD for OU-4 was issued in April 1996 (USAF 1996d). The OU-4 ROD was signed 

by the USAF on May 15, 1996; by the USEPA on May 10, 1996; and by the SDDENR on 

May 9, 1996. 

• The ROD for OU-5 was issued in June 1996 (USAF 1996e). The OU-5 ROD was signed 

by the USAF on June 19, 1996; by the USEPA on June 7, 1996; and by the SDDENR on 

June 7, 1996. 

• The ROD for OU-6 was issued in September 1995 (USAF 1995). The OU-6 ROD was 

signed by the USAF on October 10, 1995; by the USEPA on October 18, 1995; and by 

the SDDENR on October 25, 1995. 

• The ROD for OU-7 was issued in June 1996 (USAF 1996f). The OU-7 ROD was signed 

by the USAF on June 19, 1996; by the USEPA on June 7, 1996; and by the SDDENR on 

June 7, 1996. 

• The ROD for OU-8 was issued in June 1996 (USAF 1996g). The OU-8 ROD was signed 

by the USAF on June 19, 1996; by the USEPA on June 7, 1996; and by the SDDENR on 

June 7, 1996. 

• The ROD for OU-12 was issued in April 1996 (USAF 1996j). The OU-1 ROD was 

signed by the USAF on May 15, 1996; by the USEPA on May 10, 1996; and by the 

SDDENR on May 9, 1996. 

1.6 ADMINISTRATIVE RECORD 

This ESD is supported by and, when issued, will become part of the Administrative Record file 

for the Base, in accordance with the NCP at 40 CFR §300.825(a)(2). 

The Administrative Record is available for review at: 

Ellsworth AFB Environmental Restoration Program 

28th Civil Engineer Squadron Office 

2103 Scott Drive, Building 8203 

Ellsworth AFB, South Dakota 57706 

Key documents and reports are also available for review at: 

Rapid City Library 

610 Quincy Street 

Rapid City, South Dakota 57701-3630 

4465 00009
Explanation of Significant Differences 

OU-11 Basewide Ground Water 

Ellsworth AFB, South Dakota 

Q:\1616\9962\Ellsworth\ESD Final\OU-11 ESD Final 050107.doc Page 4 

May 1, 2007

2.0 SITE HISTORY AND SELECTED REMEDY 

The USAF initiated environmental investigations at Ellsworth AFB in 1985. On August 30, 1990 

(55 FR 35509), Ellsworth AFB was listed on the USEPA’s National Priority List. An FFA was 

signed in January 1992 and went into effect on April 1, 1992 (USEPA 1992). Parties to the FFA 

include the USAF, USEPA Region 8, and the State of South Dakota. A total of 12 operable 

units were identified at Ellsworth AFB. 

This ESD officially transfers all ground water media to OU-11, and is focused on remediation of 

ground water containing chlorinated VOCs at Ellsworth AFB. Trichloroethene (TCE) and cis1,2-dichloroethene (cis-1,2-DCE) are the most frequently reported chlorinated VOCs in ground 

water at Ellsworth AFB. In the past, TCE was used as a cleaning solvent, and cis-1,2-DCE is a 

degradation product produced by the degradation of TCE. Other, less frequently detected 

chlorinated VOCs, including tetrachloroethene (PCE) and vinyl chloride (VC), have been 

detected in some ground water samples at the Base. 

The following discussions present the site history and contamination, as well as the selected 

remedies, for the various operable units at Ellsworth AFB that are addressed by this ESD. 

2.1 OPERABLE UNIT 11 

2.1.1 OU-11 Site History and Contamination 

OU-11 originally provided for a study of the overall Base ground water quality and 

characteristics. Investigations and remedial action decisions for ground water contamination at 

several sites not specifically included in other operable units were included in OU-11. During 

the course of the OU-11 investigation, two areas known as Area 1 and Area 2 were identified. 

These two areas are discussed individually below. 

OU-11 Area 1. OU-11 Area 1 is known as the South Docks area, and includes the ground 

water contamination (except for the petroleum-related contamination) that was deferred from 

OU-9 and OU-10 (see Figure 3). The South Docks area is located in the central part of the 

Base along the northeast side of the flightline. Land use above the area of ground water 

contamination at OU-11 Area 1 is aircraft taxiway and aircraft operations and maintenance. 

Major buildings in this area, from northwest to southeast, include the Pride Hangar and hangars 

in Rows 50, 40, 30, and 20. Historically, the hangars have been used for docking and 

maintenance of aircraft. Hangars in the South Docks are now used for storage and 

maintenance of various support equipment and for periodic parking of aircraft. Potential 

contaminant sources include industrial waste lines, equipment wash racks, and historical 

chemical handling and disposal practices. There are no specific incidents of hazardous 

materials spills that have been documented. 

Depths to ground water at OU-11 Area 1 range from about 5 feet to 25 feet below grade. 

Ground water flow trends from northwest to southeast, and ground water discharges to the main 

Base drainage system at the South Docks Main seep area. The shallower depths to ground 

4465 00010
Explanation of Significant Differences 

OU-11 Basewide Ground Water 

Ellsworth AFB, South Dakota 

Q:\1616\9962\Ellsworth\ESD Final\OU-11 ESD Final 050107.doc Page 5 

May 1, 2007

water are in the downgradient seep area. Two separate chlorinated VOC ground water plumes 

have been identified in OU-11 Area 1: the “Pride Hangar Plume” and the “South Docks Main 

Plume”. 

The Pride Hangar Plume is approximately 1,400 feet long and is contained entirely within the 

Base. The highest concentration of TCE in ground water at Ellsworth AFB was detected at a 

former waste solvent tank site located outside of the northwest corner of the Pride Hangar. This 

underground storage tank was removed in 1992, and TCE was reported at 0.09 milligrams per 

kilogram in a soil sample collected from the floor of the excavation (approximately 10-foot 

depth). During the OU-11 RI, monitoring well MW941102 was installed approximately 40 feet 

south of the former waste solvent tank excavation, and TCE in ground water from the monitoring 

well was reported at 680 micrograms per liter (μg/L). Additional direct push ground water 

sampling in 2002 beneath the former tank found TCE concentrations as high as 30,000 μg/L. 

Ground water sampling in May 2006 found TCE as high as 4,100 μg/L and cis-1,2-DCE as high 

as 12,000 μg/L in this hotspot area (Earth Tech 2006c). Another monitoring well (MW941103), 

located about 500 feet downgradient of the hotspot had a detected TCE concentration of 

7,000 μg/L during the RI. The TCE concentration at MW941103 has declined to 520 μg/L in 

October 2006. The reduction in TCE concentrations in the hotspot area and throughout the 

Pride Hangar Plume is the result of remedial system operation and a source action that included 

biodechlorination and soil vapor extraction (SVE). The locations of remedial action systems in 

the Pride Hangar Plume are shown on Figure 3. 

The South Docks Main Plume is located immediately downgradient of the Pride Hangar Plume 

and is approximately 3,500 feet long. This plume, which runs along Hangar Rows 50 

through 20, generally has TCE concentrations less than 100 μg/L; however, there is a small 

hotspot near the downgradient end of the plume where TCE was detected as high as 140 μg/L 

in 2006. An extraction system is operated at 30 Row and at the end of the plume, just 

upgradient of the South Docks Main seep. The locations of the extraction systems at the South 

Docks Main Plume are shown on Figure 3. Current sampling results indicate that contaminant 

concentrations in the South Docks Main seep are below their respective federal maximum 

contaminant levels (MCLs) (URS 2007a). The South Docks Main Plume is contained entirely 

within the Base. 

The South Flight Line Drain Lift Station was installed in 2005 where a clay drain pipe discharged 

to the surface above a small pond. The drain line was traced several hundred feet to the west 

where it ended in the approximate location of a former 1950's fuel tank. The purpose of the 

drain line is not known. Groundwater is assumed to infiltrate along the length of the drain line. 

The effluent from this drain line has averaged 8.5 μg/L of TCE over the past 12 months and is 

being pumped to the FRA PH1 treatment facility for treatment. Treatment of this water started 

in February 2006. The source of the TCE has not been determined. The location of the drain 

line is shown on Figure 3. 

There is a chlorinated VOC plume between the Pride Hangar Plume and the BG05 Plume, 

which has been named the Twining/Risner Plume (see Figure 3). This plume was recently 

identified during a data gaps investigation in 2006 and it has not been fully delineated at the 

time of this ESD. Further investigation of this area will be done to delineate the extent of the 

Twining/Risner Plume. No remediation systems are currently installed or operating in the 

Twining/Risner Plume. 

4465 00011
Explanation of Significant Differences 

OU-11 Basewide Ground Water 

Ellsworth AFB, South Dakota 

Q:\1616\9962\Ellsworth\ESD Final\OU-11 ESD Final 050107.doc Page 6 

May 1, 2007

OU-11 Area 2. OU-11 Area 2 is the BG04 and the BG05 Study Areas located in the eastcentral to northeast portion of the Base (see Figure 4). Land use above the BG04 Plume 

includes Base housing, administration, open space, and industrial. Land use above the BG05 

Plume includes Base housing, administration, recreation, and industrial. The BG04 Plume is 

approximately 1.5 miles long and the BG05 Plume is approximately 1.25 miles long. In the past, 

these two plumes combined into a single plume that extended approximately 4.5 miles to the 

east of the Base boundary. This off-Base plume was delineated in 1997 and 1998 and is 

currently being monitored for natural attenuation in accordance with the OU-11 ROD. Ellsworth 

AFB has provided an alternate water supply to off-Base residents whose property has been 

affected by this contamination, which is also in accordance with the OU-11 ROD. Currently, 

three extraction systems operate in OU-11 Area 2: the BG04 West system, the BG04 Base 

boundary system, and the BG05 Base boundary system. Currently, the BG04 West system has 

been turned off for a treatability study in that area. The locations of these extraction systems is 

shown on Figure 4. TCE concentrations within a portion of the off-Base plume are below MCLs 

due to operation of the extraction systems at the Base boundary locations and natural 

attenuation. 

A data gaps investigation was completed in 2006 to better delineate the BG04 and BG05 

plumes and to find the contaminant sources. The BG04 and BG05 plumes contain TCE with 

concentrations up to 400 μg/L (screening level data from direct push sampling in 2006) in 

upgradient source areas. Other chlorinated VOCs that have been detected above MCLs in at 

least one of these plumes include PCE, cis-1,2-DCE, and VC. Based on the results of data 

gaps investigation, it appears that the primary TCE source is located in the vicinity of a former 

Liquid Oxygen (LOX) facility at Building 7235. TCE was likely used in the past to clean piping 

and equipment at the former LOX facility. 

Other sources of chlorinated VOCs exist in the BG04/BG05 Study Area, but they appear to be 

less substantial and the history of specific chemical usage is not known. Two separate plumes 

have been identified. There is a relatively small plume, about 600 feet long, at the Small Arms 

Range with a maximum detected TCE concentration of 445 μg/L (screening level data from 

direct push sampling in 2006). There is another small, isolated plume located in the housing 

area just north of Spearfish Avenue with a detected TCE concentration of 53 μg/L (screening 

level data from direct push sampling in 2006). These two plumes do not have remediation 

systems. 

2.1.2 OU-11 Selected Remedy 

The selected remedy for OU-11 is described in the OU-11 ROD (USAF 1997). The remedial 

action objectives for OU-11, per the OU-11 ROD, are: 

• Prevent future human exposures to on-Base ground water with contaminants exceeding 

State of South Dakota Ground-Water Quality Standards and Federal MCLs. 

• Prevent additional ground water containing contaminants above State of South Dakota 

Ground-Water Quality Standards and Federal MCLs from moving off-Base. 

• Prevent human exposure to off-Base ground water with contaminants exceeding State of 

South Dakota Ground-Water Quality Standards and Federal MCLs. 

4465 00012
Explanation of Significant Differences 

OU-11 Basewide Ground Water 

Ellsworth AFB, South Dakota 

Q:\1616\9962\Ellsworth\ESD Final\OU-11 ESD Final 050107.doc Page 7 

May 1, 2007

The selected remedy for OU-11 Area 1 is ground water extraction and treatment with 

containment, and includes the following major components: 

• Ground water removal and treatment in the South Docks Study Area. 

• On-Base containment of ground water containing contaminants at concentrations above 

Federal MCLs and State of South Dakota Ground-Water Quality Standards. 

• Institutional controls and long-term monitoring. 

The selected remedy for OU-11 Area 2 is ground water containment/extraction and treatment, 

and includes the following major components: 

• Ground water removal and treatment along the northeast Base boundary and at areas of 

high contaminant concentrations on Base. 

• Natural attenuation of low contaminant concentration areas, primarily off Base. 

• Alternative water supply to residents affected by contamination coming from the Base. 

• Additional investigation to determine the eastern extent of off-Base ground water 

contamination. 

• Institutional controls and long-term monitoring. 

The treatment components that have been installed at OU-11 Areas 1 and 2 are shown on 

Figures 3 and 4. 

2.2 OPERABLE UNIT 1 

2.2.1 OU-1 Site History and Contamination 

OU-1 is the Base’s former fire protection training area. The Base fire department burned fuels, 

oils, and solvents at this location from 1942 to 1990. Land use at OU-1 is industrial. Two 

separate ground water contaminant plumes have been identified at OU-1 as the “OU-1 Main 

Plume” and the “OU-1 East Plume” (see Figure 5). 

The OU-1 Main Plume is the primary area of contamination at the former fire training area, and 

has mixed fuel and solvent-related contaminants. At monitoring well MW930101, located near 

the upgradient edge of the Main Plume, TCE and cis-1,2-DCE were detected at 84 μg/L and 

990 μg/L (respectively) in 1993. Concentrations at this well have decreased to 14J μg/L of TCE 

and 320 μg/L of cis-1,2-DCE in 2006. At monitoring well MW930110, located near the 

downgradient edge of the Main Plume, cis-1,2-DCE has been detected since analysis for that 

compound began in 1998. Detected concentrations of cis-1,2-DCE have generally increased 

from 13 μg/L in 1998 to 150 μg/L in 2006. TCE was initially detected at this well in 2001 and, 

in 2006, TCE was detected at 6.3 μg/L (URS 2007a). Direct push investigations in this 

downgradient area of the Main Plume were completed in 2005 to delineate the southeasterly 

extent of the Main Plume and found the plume is contained within the Base (Earth Tech 2005 

and Earth Tech 2006). A ground water and SVE system are currently operated at the OU-1 

Main Plume. The locations of the extraction system components at the OU-1 Main Plume are 

shown on Figure 5. 

4465 00013
Explanation of Significant Differences 

OU-11 Basewide Ground Water 

Ellsworth AFB, South Dakota 

Q:\1616\9962\Ellsworth\ESD Final\OU-11 ESD Final 050107.doc Page 8 

May 1, 2007

The OU-1 East Plume is a small TCE plume located entirely within the Base. The maximum 

detected TCE concentration at monitoring well MW930107, located within the East Plume, was 

60 μg/L in 1993. TCE concentrations have generally decreased with time and, in 2006, the 

detected TCE concentration at this well was 9.9 μg/L (URS 2007a). Concentrations of cis1,2-DCE at this well have been mostly below the laboratory reporting limit. The OU-1 East 

Plume is monitored but does not have a remediation system. 

2.2.2 OU-1 Selected Remedy 

A ROD for an interim remedial action (IRA) for OU-1 was signed on May 16, 1995. The final 

selected remedy for OU-1 is described in the OU-1 ROD (USAF 1996a). The remedial action 

objectives for OU-1, per the OU-1 ROD, are: 

• Achieve the ground water clean-up goals set forth in Table 2-1 (refer to OU-1 ROD, 

Table 2-1, for tabulated goals). 

• Achieve the soil clean-up goals set forth in Table 2-2 (refer to OU-1 ROD, Table 2-2, for 

tabulated goals). 

The selected remedy for OU-1 is source area soil and ground water treatment, and includes the 

following major components: 

• Continued operation of the interim remedial action (IRA) which consisted of 

contaminated ground water removal, soil vapor extraction (SVE), and treatment. 

• Installation of additional SVE wells within the historical burn-pit area to be added to the 

existing IRA SVE system. 

• Removal of contaminated ground water using additional ground water wells and 

collection trenches to be added to the IRA ground water recovery system. 

• Treatment of ground water at the existing IRA treatment plant. 

• Institutional controls for the area. 

• Long-term monitoring. 

• Long-term operation and maintenance of equipment. 

The treatment components that have been installed at OU-1, which include SVE and ground 

water extraction and treatment systems, are shown on Figure 5. 

2.3 OPERABLE UNIT 2 

2.3.1 OU-2 Site History and Contamination 

OU-2 consists of two landfills, Landfill Nos. 1 and 6, located in the southwest portion of 

Ellsworth AFB. A TCE plume was identified at Landfill No. 1 during the RI in 1993 (see 

Figure 5). This TCE plume migrated off Base approximately 800 feet to the southeast. Land 

use above this plume is industrial on Base and agricultural off Base. 

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TCE concentrations measured on the downgradient edge of the landfill at the Base boundary 

(MW930205) were 8 μg/L in September 1993 and reached a high of 27 μg/L in July 2002. A 

leaking water line along the north side of the landfill, which is now repaired, may have artificially 

raised ground water levels and increased the amount of TCE migration in ground water. 

Investigations completed in 2005 found TCE at 679 μg/L in a temporary monitoring well installed 

within Landfill No. 1 (Earth Tech 2005 and Earth Tech 2006a). The temporary well was 

replaced with permanent monitoring well MW060201 in 2006, and TCE was detected in this well 

at 80 μg/L and cis-1,2-DCE was detected at 21 μg/L (URS 2007a). The OU-2 Plume is now 

entirely within the Base due to operation of an extraction system at the Base boundary. The 

location of the OU-2 extraction system is shown on Figure 5. 

2.3.2 OU-2 Selected Remedy 

The selected remedy for OU-2 is described in the OU-2 ROD (USAF 1996b). The remedial 

action objectives for OU-2, per the OU-2 ROD, are: 

• Provide protection against direct contact with contents of the landfills. 

• Provide protection against ingestion of contaminated ground water at concentrations 

exceeding regulatory or risk-based goals. 

• Minimize the potential for transport of contaminants in the soils and ground water 

beyond the boundaries of the landfills. 

The selected remedy for OU-2 Landfill No. 1 is an earth cover and institutional controls, and 

includes the following major components: 

• Construction an earth cover, capable of sustaining perennial vegetation, over areas of 

the landfill that are not adequately covered. Filling in low areas and grading the entire 

landfill area to provide for positive drainage off the site. 

• Institutional controls for the landfill area. 

• Long-term ground water monitoring. 

• Long-term maintenance of soil cover. 

• Realignment and lining of the storm water channel. 

Earthwork associated with the selected remedy was completed in 1997. Since that time, 

migration of a chlorinated VOC plume required the installation of a ground water extraction 

system at the Base boundary. This system pumps water to the Building 6908 treatment facility. 

The extraction system location is shown on Figure 5. 

2.4 OPERABLE UNIT 3 

2.4.1 OU-3 Site History and Contamination 

OU-3 is the Landfill No. 2 area, located in the northeast portion of Ellsworth AFB. The landfill 

site covers approximately 1 acre, with four identified trenches to the north and two formerly 

disturbed soil areas in the southeast and southwest corners. The landfill operated for 

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approximately 1 year, from 1964 to 1965. Combustible refuse including shop waste was burned 

at the site, and the trenches were used for disposal of metal and industrial and household 

refuse. Vinyl chloride was detected in ground water above its MCL of 2 μg/L at two monitoring 

wells during the RI in 1993. Land use at OU-3 is open space. 

2.4.2 OU-3 Selected Remedy 

The selected remedy for OU-3 is described in the OU-3 ROD (USAF 1996c). The remedial 

action objectives for OU-3, per the OU-3 ROD, are: 

• Prevent ingestion and dermal contact with landfill contents. 

• Reduce mobility of potential contaminants in the landfill. 

• Control surface water runoff and erosion of the landfill cover. 

The selected remedy for OU-3 is a vegetated soil cover, and includes the following major 

components: 

• Placing a soil cover capable of sustaining perennial vegetation over the landfill area. 

• A pre-design study to examine the need for landfill gas control measures. 

• Institutional controls for the landfill area. 

• Long-term ground water monitoring and long-term maintenance of soil cover. 

Earthwork and monitoring well installation associated with the selected remedy was completed 

in 1996. Long-term monitoring and maintenance started in 1997 and continues to the present 

time. 

2.5 OPERABLE UNIT 4 

2.5.1 OU-4 Site History and Contamination 

OU-4 is a landfill (Landfill No. 3) with a chlorinated VOC plume that has migrated beyond the 

landfill boundary (see Figure 5). The landfill portion of OU-4 is situated on about 40 acres in the 

southwest part of the Base. The landfill was operated from 1965 through 1975 as a trench fill 

and is currently inactive. The landfill received general refuse, liquid shop wastes, paint, 

industrial sewer sludge and oil, and soils containing the herbicide Pramitol and sodium 

chromate coolant. Two contaminant plumes, the “OU-4 Southwest Plume” and the “OU-4 South 

Plume”, have been identified downgradient of the landfill. Land use above the OU-4 plumes is 

industrial on Base and agricultural off Base. 

The OU-4 Southwest Plume, a mixed fuel and solvent plume, resulted from former activities in 

the southwest corner of Landfill No. 3 that included operation of a gravel-filled waste oil pit in the 

mid-1970s and use of the area to stage asphalt and drums containing waste oil and fuel. An 

extraction system was formerly operated in this area and the contaminant levels are currently 

below their federal MCLs. This former plume area is currently being monitored. 

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The OU-4 South Plume is a TCE plume that begins near the southeast portion of Landfill No. 3 

and has migrated south and southeast. The source area appears to cover a relatively small 

area in the southeast corner of the Landfill No. 3. TCE concentrations as high as 12,000 μg/L 

(in MW030401) were detected at the South Plume source area in 2003. TCE concentrations in 

the source area have been reduced because of oil and lactate injections; however, TCE 

concentrations as high as 2,000 μg/L remain just 100 feet in the downgradient direction (Earth 

Tech 2006b). The South Plume is currently about 1 mile long and has migrated approximately 

1,000 feet beyond the Base boundary. The highest detected concentration of TCE in the offBase portion of the plume was 5.9 μg/L in 2006 (URS 2007a). Extraction systems are operated 

near the OU-4 South Plume source and at the Base boundary. The locations of the extraction 

systems at OU-4 are shown on Figure 5. 

2.5.2 OU-4 Selected Remedy 

A ROD for interim remedial action (IRA) for OU-4 was signed on May 16, 1995. The final 

selected remedy for OU-4 is described in the OU-4 ROD (USAF 1996d). The remedial action 

objective for OU-4 ground water, per the OU-4 ROD, is to: 

• Prevent inhalation, dermal contact, and ingestion of ground water containing 

contaminants at concentrations exceeding remediation goals. Remediation goals are 

defined in the OU-4 ROD as MCLs or risk-based State Ground Water Quality Standards. 

The selected remedy for OU-4 ground water, pump and treat, includes the following major 

components: 

• Continued operation of the interim remedial action (IRA) which consists of removal and 

treatment of contaminated ground water. 

• Installation of recovery trenches and/or additional extraction wells to be added to the 

existing IRA ground water recovery system. 

• Treatment of removed ground water at the treatment plant built for the IRA. 

• Discharge of treated ground water to the surface water drainage, to the Base 

wastewater treatment plant, or by underground injection. 

The ground water treatment components that have been installed at OU-4 are shown on 

Figure 5. 

2.6 OPERABLE UNIT 5 

2.6.1 OU-5 Site History and Contamination 

OU-5 is the Landfill No. 4 area, located near the northern perimeter of Ellsworth AFB. The 

landfill site covers approximately 10 acres. The landfill operated from the 1940s to 1986, 

primarily for disposal of construction debris and hardfill materials. General refuse was also 

disposed of at Landfill No. 4. Land use at OU-5 is open space. 

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2.6.2 OU-5 Selected Remedy 

The selected remedy for OU-5 is described in the OU-5 ROD (USAF 1996e). The remedial 

action objectives for OU-5, per the OU-5 ROD, are: 

• Provide protection against direct contact or ingestion of the landfill contents. 

• Minimize infiltration through the landfill. 

• Control surface water runoff and erosion of the landfill cover. 

The selected remedy for OU-5 is covering, and includes the following major components: 

• Placing a soil cover capable of sustaining perennial vegetation over the landfill area. 

• Institutional controls for the landfill area. 

• Long-term ground water monitoring and long-term maintenance of the soil cover. 

Earthwork to install the soil cover was completed in 1996. Long-term monitoring and 

maintenance started in 1997 and continues to the present time. In 2001 and again in 2002, 

repairs were made to steep slopes along the northern flank of the landfill where landslide 

conditions existed. The repairs included the installation of underdrains to lower ground water 

levels in the area and reduce the movement of landfill contents and soil cover materials. 

Current inspections show these repairs have been effective. 

2.7 OPERABLE UNIT 6 

2.7.1 OU-6 Site History and Contamination 

OU-6 is the Landfill No. 5 area, located in the southeastern portion of Ellsworth AFB. The 

landfill site covers approximately 7 acres. The landfill operated from 1960 to 1980, primarily for 

disposal of construction debris and hardfill materials. Disposal of household waste, shop waste, 

and wastewater treatment plant sludge may have taken place; however, no direct physical 

evidence of household or hazardous/industrial waste disposal was found at OU-6 during the 

1993 RI. Land use at OU-6 is industrial. 

2.7.2 OU-6 Selected Remedy 

The selected remedy for OU-6 is described in the OU-6 ROD (USAF 1995). The remedial 

action objectives for OU-6, per the OU-6 ROD, are: 

• Prevent dermal contact and ingestion of surface soils within OU-6. 

• Reduce the mobility of potential contaminants in the landfill. 

• Prevent the ingestion of sediments within OU-6. 

The selected remedy for OU-6 is capping, and includes the following major components: 

• Placing a soil cover capable of sustaining perennial vegetation over the landfill area. 

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• Modification of the storm water discharge point and drainage. 

• Institutional controls for the landfill area. 

• Long-term ground water, surface water, and sediment monitoring. 

• Long-term maintenance of the soil cover. 

Earthwork to install the soil cover was completed in 1995. Long-term monitoring and 

maintenance started in 1996 and continues to the present time. 

2.8 OPERABLE UNIT 7 

2.8.1 OU-7 Site History and Contamination 

OU-7 is located in the northwest corner of Ellsworth AFB. A records search documented TCE 

use and disposal in small quantities at the site. Ground water monitoring results since 1997 

have shown a TCE plume at the northeast corner of the site (see Figure 6). This plume is being 

monitored, and monitoring results indicate the ground water plume is slowly shrinking. In 2006, 

the highest detected TCE concentration was 23 μg/L (URS 2007a). The OU-7 Plume is 

currently about 1,000 feet long and is contained entirely within the Base. Land use above the 

OU-7 Plume is industrial and open space. 

2.8.2 OU-7 Selected Remedy 

The selected remedy for OU-7 is described in the OU-7 ROD (USAF 1996f). The remedial 

action objective for OU-7 ground water, per the OU-7 ROD, is to: 

• Prevent inhalation, dermal contact, and ingestion of ground water containing 

contaminants at concentrations exceeding remediation goals. Remediation goals are 

defined in the OU-7 ROD as MCLs. 

The selected remedy for OU-7 ground water, institutional controls with additional monitoring, 

includes the following major components: 

• Institutional controls for ground water use. 

• Implementing a long-term ground water monitoring and maintenance program. 

The OU-7 Plume is currently being monitored, and no remediation systems have been 

implemented at this plume. 

2.9 OPERABLE UNIT 8 

2.9.1 OU-8 Site History and Contamination 

OU-8 is located in the northern portion of Ellsworth AFB and covers an area of approximately 12 

acres. The site was used in the 1950s and 1960s for EOD operations. Two distinct areas, the 

EOD Area and the Debris Burial Area, have been identified. The EOD Area includes a Pramitol 

spill, burn pit, burn furnace, and detonation site. The Debris Burial Area is the disposal site for 

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debris generated by detonation of explosives at the EOD Area. Land use at OU-8 is open 

space. 

2.9.2 OU-8 Selected Remedy 

The selected remedy for OU-8 is described in the OU-8 ROD (USAF 1996g). The remedial 

action objectives for OU-8, per the OU-8 ROD, were separated for the EOD Area and Debris 

Disposal Area, as follows: 

• EOD Area: 

– Prevent contaminated surface soil from migrating off site. 

– Provide protection against direct contact or ingestion of surface soils containing 

contaminants. 

• Debris Disposal Area: 

– Contain buried and exposed debris and prevent contaminated surface soil from 

migrating off site. 

– Provide protection against direct contact or ingestion of soils containing 

contaminants. 

The selected remedy for both the EOD Area and Debris Disposal Area within OU-8 is a 

vegetated soil cover with institutional controls, and includes the following major components: 

• Constructing an earth cover over a portion of the EOD Area and the entire Debris 

Disposal Area. 

• Institutional controls for the EOD Area and the Debris Disposal Area. 

• Long-term sediment sampling at the EOD Area. 

• Long-term maintenance of the earth covers at the EOD Area and the Debris Disposal 

Area. 

Earthwork to install the soil covers was completed in 1996. 720 cubic yards of contaminated 

soil was removed and one new monitoring wells was also installed in 1996. Long-term 

monitoring and maintenance began in 1997 and continues to the present time. 

2.10 OPERABLE UNIT 12 

2.10.1 OU-12 Site History and Contamination 

OU-12 is a hardfill site that was active from the late 1950s to the late 1970s. The site reportedly 

received construction debris, and three separate hardfill areas were identified. Final covers 

were installed over each of the hardfill areas in 1996. Land use above the OU-12 Plume is 

aircraft operations and maintenance. 

Ground water monitoring results since 1997 have been nondetect in downgradient wells; 

however, ground water monitoring in the OU-12 upgradient monitoring well (MW931201) has 

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found TCE concentrations ranging from 7 μg/L in 1993 to 13 μg/L in 2006 (URS 2007b). Direct 

push ground water samples collected in this area in 2005 (Earth Tech 2006a) and 2006 (URS 

2007b) indicate that the TCE plume at OU-12 is approximately 600 feet long and is contained 

entirely within the Base. The delineated OU-12 Plume is shown on Figure 5. 

2.10.2 OU-12 Selected Remedy 

The selected remedy for OU-12 is described in the OU-12 ROD (USAF 1996j). The remedial 

action objectives for OU-12, per the OU-12 ROD, only addressed the hardfills. At that time, the 

risk assessment did not identify ground water as a pathway of concern. Ground water 

monitoring is currently on going at the OU-12 Plume. 

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3.0 BASIS FOR SIGNIFICANT DIFFERENCE 

3.1 TRANSFER OF GROUND WATER TO OU-11 

This ESD officially transfers the ground water components of the individual RODs for OUs 1, 2, 

3, 4, 5, 6, 7, 8, and 12 to OU-11. The selected remedies for soil at these OUs have already 

been completed, so only the ground water remedies are ongoing. Ground water remedies for 

OU-9 and OU-10 have previously been deferred to OU-11. Consolidating all selected ground 

water remedies and monitoring into OU-11 is being done to simplify management and reporting 

for the remaining ground water remedial actions. 

3.2 ADDITIONAL TREATMENT TECHNOLOGIES 

Chlorinated VOCs are one of the major ground water contaminants at Ellsworth AFB, and TCE 

is the most frequently reported compound in ground water. The current site remedies for 

ground water at OU-11 Area 1, OU-11 Area 2, OU-1, OU-2, and OU-4 use ground water 

extraction and treatment (including vacuum dewatering and dual phase extraction) for 

containment of the contaminated ground water and removal of contaminants. These remedial 

systems have been in place and operating for up to ten years. The ground water extraction and 

treatment remedy has limited capability to reduce TCE mass, so operation of these extraction 

systems may extend indefinitely into the future to maintain protectiveness. 

Implementation of a technology that can reduce the TCE mass will shorten the timeframe 

required to manage the chlorinated VOC ground water plumes at Ellsworth AFB. Since the 

OU-11 ROD was signed in 1997, considerable work has been done to advance the field of 

enhanced bioremediation for in-situ treatment of ground water containing chlorinated VOCs. 

This advancement of the enhanced bioremediation technology, along with related work being 

completed at Ellsworth AFB, led to the following recommendation in the Final Five Year Review 

for Ellsworth AFB (USAF 2005b): “[T]he first technology of choice for remediation of chlorinated 

solvent contamination in ground water is in-situ biodechlorination...Generally, in the Ellsworth 

AFB sites, in-situ biodechlorination is considered a potentially valuable supplement to the 

existing ground water pump and treat systems.” 

In-situ biodechlorination is proposed for ground water treatment, with the option for 

supplemental vapor extraction at the Pride Hangar hotspot. The primary purpose of adding 

these treatment technologies to the on-going extraction systems is to reduce the overall 

timeframe required to manage the chlorinated VOC ground water plumes by reducing the mass 

of chlorinated VOCs in ground water. In-situ biodechlorination is proposed by this ESD due to 

positive results of treatability studies at Ellsworth AFB and the success of this process at other 

remediation sites, including other Air Force installations. 

The in-situ biodechlorination process involves stimulation of naturally-occurring bacteria or 

introduced bacteria to convert or dechlorinate the chlorinated VOCs along the following 

degradation pathway: 

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PCE > TCE > cis-1,2-DCE > VC > ethene 

Biostimulation can be accomplished by injecting a biodegradable organic substrate into 

contaminated ground water. The injected organic substrate is initially fermented to produce 

hydrogen and low molecular weight fatty acids, which in turn provide carbon and energy for 

anaerobic biodegradation. Biodechlorination is a biological process whereby specific bacteria, 

under anaerobic conditions, use the chlorine as an electron acceptor to reduce the more 

oxygenated chlorinated ethenes along the degradation pathway shown above. To be 

successful, a microbial community capable of reducing the chlorinated VOCs all the way to 

ethene must be present or introduced. The bacteria species Dehalococcoides ethenogenes

(DHC), strains 195 and FL2, have been found to drive the process all the way to ethene at 

numerous other sites (Maymo-Gatell et al. 1997, Loffler et al. 2000, and Durant et al. 2004) and 

in bench scale tests performed on ground water and soil from Ellsworth AFB. 

Bioaugmentation (i.e., injection of DHC into contaminated ground water) has been 

demonstrated to be effective in treating ground water contaminated with dissolved chlorinated 

VOCs in field demonstrations at Dover Air Force Base, Dover, Delaware and at Kelly Air Force 

Base, San Antonio, Texas. At Kelly Air Force Base, no Dehalococcoides species were detected 

in field samples prior to their injection for bioaugmentation. Successful field demonstrations of 

bioaugmentation have been completed on concentrations of chlorinated VOCs that have ranged 

from 30 μg/L to dense non-aqueous-phase liquids. Geologic conditions where successful 

demonstrations have been completed range from fractured basalt to shallow silty gravel and 

sand (Durant et al. 2004). 

The biodechlorination process has been tested at several of the Ellsworth AFB chlorinated VOC 

ground water plumes as discussed below: 

• OU-4 Biodechlorination Treatability Study (Earth Tech 2006a). This treatability study at 

OU-4 involved work at four locations, referred to as Elements 1 through 4, within the 

OU-4 South Plume. Various electron donors at different concentrations and frequencies 

were injected into ground water through 1-inch diameter injection wells installed at each 

of the elements. The various electron donors included 50 percent emulsified food grade 

soy oil, 5 percent sodium lactate, 17 percent emulsified soy oil, and dilute sodium 

lactate. Several findings of this study are: 

– Addition of electron donor material was proven effective at reducing TCE 

concentrations. 

– Both emulsified oil and lactate were effective electron donor materials. However, low 

pH conditions that limit the biodechlorination process were observed at some 

locations, and sodium lactate has a very low pH. 

– At some locations with thin saturated zones and where relatively low quantities of 

electron donors were injected, TCE concentrations remained essentially unchanged. 

Increasing the injected quantity of electron donor coupled with reducing the injection 

spacing should improve distribution, which in turn should improve effectiveness of 

the biodechlorination process. 

• Pride Hangar Source Action (Earth Tech 2006b). In-situ biodechlorination was 

implemented at the Pride Hangar hotspot from January 2004 to November 2005, and 

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involved pressure injection of emulsified soy oil and multiple gravity injections of dilute 

sodium lactate. Several findings and conclusions of this work are: 

– Significant reductions of TCE concentrations were achieved. Monitoring suggests 

biodechlorination is responsible for these reductions, although some evidence 

suggests that some abiotic reactions with reduced compounds such as iron sulfate 

may contribute to the TCE reduction. 

– TCE was reduced all the way to ethene without the addition of DHC, and DHC have 

been detected in some ground water samples. It appears that bioaugmentation (i.e., 

addition of DHC to the treatment zones) may not be required at the Pride Hangar. 

– The naturally occurring high sulfate concentrations create a high demand for reduced 

carbon sources, which is in direct competition with the biodechlorination process. 

The dilute sodium lactate concentrations were not able to create a lasting reduced 

environment. 

– Gravity injection was not effective at three of the five injection wells. 

• In-situ Reductive Treatment (IRT) Treatability Study (URS, on-going). This treatability 

study includes both laboratory (bench scale) and field (pilot scale) testing of an 

emulsified oil mixture that contains a small percentage of sodium lactate and emulsifiers. 

The bench-scale test used ground water and soil from the BG04 site, and tested the 

emulsified oil mixture by itself, with vitamin B12 additive, and with addition of the KB1 

strain of DHC. The pilot-scale test involved injecting emulsified oil, mixed with water at 

various amounts from 1.5 percent oil to 10 percent oil, into permeable treatment walls 

that span the contaminant plumes at BG04, Pride Hangar, and OU-4. The findings of 

this work are: 

– In the laboratory, TCE was completely degraded to ethene using emulsified oil and 

the KB1 strain of DHC. Emulsified oil alone showed little TCE reduction, whereas 

emulsified oil with vitamin B12 showed some TCE reduction. 

– Pressure injection of an emulsified oil solution through closely spaced direct push 

points appears to adequately distribute the oil in ground water, based on reduced 

conditions measured at the line of injection points and downgradient of the line of 

injection. 

– The emulsified oil organic substrate has been in place for 5 months, and reducing 

conditions with complete sulfate reduction are observed at the Pride Hangar and 

OU-4 test sites, where the mix designs were 5 percent oil and 10 percent oil. Less 

reducing conditions are observed at the BG04 test site, where the mix design was 

only 1.5 percent oil. 

– TCE degradation all the way to ethene was observed 3 months after injection at the 

Pride Hangar test site. TCE degradation has not been observed in the first 5 months 

following injection at either the OU-4 test site or the BG04 test site. It appears that 

the OU-4 South Plume may need to be bioaugmented with DHC, whereas the BG04 

Plume needs a higher concentration of organic substrate and may also require 

bioaugmentation. 

General conclusions, based on the data from the biodechlorination work and tests at Ellsworth 

AFB, are summarized below: 

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• Biodechlorination can be an effective remedial technology to reduce TCE levels in 

ground water at Ellsworth AFB. 

• Various biostimulants have been effective to a degree, but emulsified soy oil blended 

with sodium lactate has been demonstrated in bench scale testing to completely reduce 

TCE to ethene with the addition of DHC. This same organic substrate has been shown 

in the field to be effective at the Pride Hangar, where there is evidence of DHC from the 

biodechlorination work done at the hotspot. 

• Biostimulation alone may not be sufficient to achieve complete reduction of TCE at 

Ellsworth AFB. In some areas, bioaugmentation (addition of DHC) may be necessary if 

performance monitoring indicates the process has stalled at cis-1,2-DCE or VC. 

As a supplement to the in-situ biodechlorination at the Pride Hangar hotspot, use of an existing 

SVE system is proposed if needed to prevent vapor migration from ground water through the 

soil and into the Pride Hangar building. This system consists of a series of several wells 

screened in the vadose zone and connected to a small blower that discharges directly to the 

atmosphere. The vapor extraction system was tested in 2004 and can readily be turned on to 

remove vapors in this area, as deemed necessary, following the proposed biodechlorination 

work. 

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4.0 DESCRIPTION OF SIGNIFICANT DIFFERENCES 

4.1 TRANSFER OF GROUND WATER TO OU-11 

This ESD officially transfers the ground water components of the individual RODs for OUs 1, 2, 

3, 4, 5, 6, 7, 8, and 12 to OU-11. Ellsworth AFB will continue to perform all remedial actions and 

monitoring required under CERCLA, the FFA, and the RODs established for each individual OU. 

4.2 ADDITIONAL TECHNOLGIES FOR GROUND WATER REMEDIAL ACTION 

This ESD provides for the application of biodechlorination technology to remediate ground water 

contaminated with chlorinated VOCs and the option to operate an existing SVE system at the 

Pride Hangar Hotspot. Several electron donor materials may be used to stimulate in-situ 

biodechlorination, including emulsified soy oil, sodium lactate, molasses, hydrogen, or other 

proprietary organic substrate materials. In addition to the biostimulant, a culture of DHC will be 

introduced into the subsurface where it is found, through monitoring, to be necessary for 

effective biodechlorination. 

The biostimulant and DHC will be injected into the saturated zone through direct push points, 

temporary injection wells, or existing wells. The biostimulant and DHC will be injected as a 

permeable barrier, positioned perpendicular to ground water flow, which will allow contaminated 

ground water to flow through the in-situ treatment zone under its natural gradient. The 

biostimulant and DHC may also be injected in a grid pattern where higher TCE source 

concentrations have been found, such as the Pride Hangar hotspot. This ESD will allow for 

implementation of in-situ biodechlorination technology in the following chlorinated VOC plumes: 

OU-1 Main Plume, OU-2 Plume, OU-4 South Plume, OU-11 Area 1 Pride Hangar Plume, OU-11 

Area 1 South Docks Main Plume, OU-11 Area 2 BG04 Plume, and OU-11 Area 2 BG05 Plume. 

This ESD will also provide the USAF the option to implement in-situ biodechlorination 

technology in the following chlorinated VOC plumes: OU-1 East Plume, OU-7 Plume, OU-11 

Area 1 South Flightline Drain Trench, OU-11 Area 1 Twining/Risner Plume, OU-11 Area 2 Small 

Arms Range Plume, OU-11 Area 2 Spearfish Avenue Plume, and OU-12 Plume. If new 

contaminant plumes are discovered in the future, the biodechlorination technology may be used; 

however, discovery of a new plume will require further assessment to select an appropriate 

remedy. 

Implementation of the biodechlorination technology will require meeting the substantive portions 

of the Federal Underground Injection Control Rule The proposed injections are planned to 

occur over the next 2 years (2007 and 2008 construction seasons), with follow-up injections in 

2009 and 2010. The performance of the remedy will be monitored within each plume that is 

being treated to track contaminant conditions and other important indicators of the 

biodechlorination process. Performance monitoring will be designed to ensure the remedy is 

working properly and to optimize the subsurface conditions needed for the biodechlorination 

process to be successful. The specific location of each in-situ reductive treatment barrier and 

grid injection zone, as well as a detailed performance monitoring program, will be developed 

4465 00026
Explanation of Significant Differences 

OU-11 Basewide Ground Water 

Ellsworth AFB, South Dakota 

and described in a Remedial Action Work Plan, which will be submitted to both the USEPA and 

SDDENR for approval. 

This ESD also provides for the application of SVE at the Pride Hangar hotspot, if it is needed to 

prevent vapor migration from the ground water through the soil and into the Pride Hangar 

building. The SVE system is already installed at the hotspot area and has been previously 

tested, so starting up this system will not require significant effort. 

Both the biodechlorination and SVE technologies will be implemented as supplements to the 

final remedies that are already in place at Ellsworth AFB. These final remedies, which are 

currently mandated by the RODs for each operable unit, will remain in effect during 

implementation of the additional treatment technologies proposed in this ESD. At this time, 

there are no proposed modifications to the established remediation goals for ground water on 

the Base, which are currently federal MCLs and State of South Dakota Ground Water 

Standards. Pending actual performance of the remedy, the USAF may decide to propose 

alternate cleanup levels for on-Base groundwater that are protective of human health and the 

environment. This would require a ROD Amendment. 

4.3 EXPECTED OUTCOMES 

Application of the biodechlorination and SVE technologies is expected to significantly reduce the 

timeframe to turn off the currently operating extraction systems, from an estimate of over 30 

years to less than 5 years. It is estimated that the operating extraction wells will be shut off as 

soon as 2010, and this action would require a ROD Amendment. The estimated costs for the 

current extraction system operation versus the estimated costs to implement the proposed insitu biodechlorination are compared below. The costs have been estimated as total costs over 

a 30 year time frame, and they include capital cost, O&M costs, and monitoring costs. 

Estimated 30 Year Cost for Current Remedy

Capital Cost O&M Cost LTM Cost Total

OU-1 Extraction System $0 $2,860,000 $180,000 $3,040,000

OU-2 Extraction System 0 500,000 30,000 530,000

OU-4 Extraction System 0 3,450,000 360,000 3,810,000

OU-7 Monitoring 0 0 150,000 150,000

OU-11 Extraction Systems 0 9,870,000 380,000 10,250,000

OU-12 Monitoring 0 0 180,000 180,000

Total for All Extraction Systems and Monitoring $0 $16,680,000 $1,280,000 $17,960,000

Estimated 30 Year Cost for Proposed Biodechlorination

Capital Cost O&M Cost LTM Cost Total

OU-1 Main Plume $170,000 $0 $140,000 $310,000

OU-2 Plume 60,000 0 50,000 110,000

OU-4 South Plume 1,010,000 0 310,000 1,320,000

OU-11 Area 1 Pride Hangar Plume 1,130,000 0 80,000 1,210,000

OU-11 Area 1 South Docks Main Plume 900,000 0 70,000 970,000

OU-11 Area 2 BG04 Plume 2,030,000 0 120,000 2,150,000

OU-11 Area 2 BG05 Plume 450,000 0 60,000 510,000

Total for All Extraction Systems and Monitoring $5,750,000 $0 $830,000 $6,580,000

Site Name

Site/Plume Name

Q:\1616\9962\Ellsworth\ESD Final\OU-11 ESD Final 050107.doc Page 21 4465 00027 May 1, 2007
Explanation of Significant Differences 

OU-11 Basewide Ground Water 

Ellsworth AFB, South Dakota 

The cost reduction for implementing the proposed biodechlorination is estimated to be 

approximately $11,400,000 (approximately a 63 percent reduction), based on the 30-year 

operating timeframe. The cost reduction is likely to be even higher, since operation of the 

extraction systems would be required until the chlorinated plumes naturally dissipate to 

protective levels, which is likely more than 30 years. This cost reduction results primarily from 

the elimination of costs associated with O&M of the active extraction systems. 

The estimated cost to implement the optional biodechlorination and SVE is shown below. The 

total estimated cost for the optional treatment is $770,000. If this optional treatment is 

completed, the cost reduction of all treatment versus current extraction systems would be 

$10,600,000 (approximately a 59 percent reduction). 

Site/Plume Name Estimated Cost to Implement Optional Biodechlorination and SVE

OU-1 East Plume Assume 200 foot long in-situ biodechlorination zone $80,000

OU-7 Plume Assume 100 foot long in-situ biodechlorination zone 40,000

OU-11 Area 1 Pride Hangar Hotspot Assume operation of existing SVE for 12 months 10,000

OU-11 Area 1 Twining/Risner Plume Assume 1,000 foot long in-situ biodechlorination zone 400,000

OU-11 Area 2 Small Arms Range Plume Assume 400 foot long in-situ biodechlorination zone 160,000

OU-11 Area 2 Spearfish Avenue Plume Assume 200 foot long in-situ biodechlorination zone 80,000

Total for All Optional Treatment $770,000

Q:\1616\9962\Ellsworth\ESD Final\OU-11 ESD Final 050107.doc Page 22 4465 00028 May 1, 2007
Explanation of Significant Differences 

OU-11 Basewide Ground Water 

Ellsworth AFB, South Dakota 

Q:\1616\9962\Ellsworth\ESD Final\OU-11 ESD Final 050107.doc Page 23 

May 1, 2007

5.0 SUPPORT AGENCY COMMENTS ON ESD 

The USAF consulted with USEPA Region 8 and the SDDENR during the preparation of this 

ESD. This ESD was drafted with their cooperation and support. All regulatory agency 

comments have been addressed and incorporated into this document. The USEPA Region 8 

and SDDENR concur with this ESD. 

4465 00029
Explanation of Significant Differences 

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Ellsworth AFB, South Dakota 

Q:\1616\9962\Ellsworth\ESD Final\OU-11 ESD Final 050107.doc Page 24 

May 1, 2007

6.0 STATUTORY DETERMINATIONS 

This ESD officially transfers all ground water into OU-11 and allows the USAF to implement 

additional treatment technologies that are not included in the selected ground water remedies 

for OU-1, OU-2, OU-3, OU-4, OU-5, OU-6, OU-7, OU-8, OU-11, and OU-12. It is consistent 

with CERCLA §121 (42 USC §9621) and the NCP (40 CFR §300). The proposed remedy 

additions are protective of human health and the environment; comply with Federal and State 

Applicable or Relevant and Appropriate Requirements identified in the Records of Decision, and 

are cost-effective. The remedial action objectives and clean-up standards are not being 

changed. The proposed remedy additions utilize permanent solutions and alternative treatment 

technologies to the maximum extent practicable to achieve the statutory preference for 

permanent reduction in contaminant toxicity, mobility, or volume. They will produce a more 

rapid and cost-effective cleanup of the chlorinated VOCs in ground water at Ellsworth AFB. 

4465 00030
Explanation of Significant Differences 

OU-11 Basewide Ground Water 

Ellsworth AFB, South Dakota 

Q:\1616\9962\Ellsworth\ESD Final\OU-11 ESD Final 050107.doc Page 25 

May 1, 2007

7.0 PUBLIC PARTICIPATION COMPLIANCE 

When this ESD is finalized, a Notice of Availability and a brief description of the ESD will be 

published in the Rapid City Journal and the Black Hills Bandit, as required by the NCP at 

40 CFR §300.435(c). Additionally, this ESD will be made available to the public and become 

part of the Administrative Record. 

4465 00031
Explanation of Significant Differences 

OU-11 Basewide Ground Water 

Ellsworth AFB, South Dakota 

Q:\1616\9962\Ellsworth\ESD Final\OU-11 ESD Final 050107.doc Page 26 

May 1, 2007

8.0 REFERENCES 

Durant, N., D. Major., E. Cox, and M. McMaster. 2004. Bioaugmentation to Enhance 

Anaerobic Bioremediation of Chlorinated Solvent in Groundwater: Six Case Studies. 

Principles and Practices of Enhanced Anaerobic Bioremdiation of Chlorinated Solvents 

(Final), Appendix E.13. Prepared for the Air Force Center for Environmental Excellence, 

the Naval Facilities Engineering Service Center, and the Environmental Security 

Technology Certification Program. August. 

Earth Tech. 2005. Technical Memorandum. April/May 2005 – Field Investigation at OU-1, 

OU-2, OU-3, OU-4, and Pride Hangar. July 18. 

Earth Tech. 2006a. Technical Memorandum. September/October 2005 – Field Investigation. 

February 20. 

Earth Tech. 2006b. Biodechlorination Final Report. Operational Unit 4 Treatability Study. 

Ellsworth Air Force Base, South Dakota. U.S. Air Force Air Combat Command. Prepared 

for U.S. Army Corps of Engineers, Omaha District. June. 

Earth Tech. 2006c. Memo. Final Treatment Report for Pride Hangar Source Action. June 23. 

Loffler, F., Q. Sun, J. Li, and J. Tiedje. 2000. 16S rRNA Gene-Based Detection of 

Tetrachloroethene-Dechlorinating Desulfuromonas and Dehalococcoides Species. Applied 

Environmental Microbiology. Vol. 66(4). P. 1369-1374. 

Maymo-Gatell, X., J.M. Gossett, and S.H. Zindler. 1997. Dehalococcus Ethenogenes Strain 

195: Ethene Production From Halogenated Aliphatics (abstract). In Situ and On-Site 

Bioremediation. Vol. 3. P. 23. Alleman, B.C. and A. Leeson (Eds.). Battelle Press, 

Columbus, OH. 

URS. 2007a. Final April 2006 Long-Term Monitoring Report. Ellsworth Air Force Base, South 

Dakota. ACC 4-Base PBC. Prepared for ACC, Ellsworth AFB, and AFCEE. January. 

URS. 2007b. Technical Memorandum. OU-12 Data Gaps Investigation. Prepared for ACC, 

Ellsworth AFB, and AFCEE. Preview Draft Version. January. 

USAF. 1995. Final Record of Decision for Remedial Action at Operable Unit 6, Ellsworth 

Air Force Base, South Dakota. September. 

USAF. 1996a. Final Record of Decision for Remedial Action at Operable Unit 1, Ellsworth 

Air Force Base, South Dakota. April. 

USAF. 1996b. Final Record of Decision for Remedial Action at Operable Unit 2, Ellsworth 

Air Force Base, South Dakota. April. 

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Ellsworth AFB, South Dakota 

Q:\1616\9962\Ellsworth\ESD Final\OU-11 ESD Final 050107.doc Page 27 

May 1, 2007

USAF. 1996c. Final Record of Decision for Remedial Action at Operable Unit 3, Ellsworth 

Air Force Base, South Dakota. June. 

USAF. 1996d. Final Record of Decision for Remedial Action at Operable Unit 4, Ellsworth 

Air Force Base, South Dakota. April. 

USAF. 1996e. Final Record of Decision for Remedial Action at Operable Unit 5, Ellsworth 

Air Force Base, South Dakota. June. 

USAF. 1996f. Final Record of Decision for Remedial Action at Operable Unit 7, Ellsworth 

Air Force Base, South Dakota. June. 

USAF. 1996g. Final Record of Decision for Remedial Action at Operable Unit 8, Ellsworth 

Air Force Base, South Dakota. June. 

USAF. 1996h. Final Record of Decision for Remedial Action at Operable Unit 9, Ellsworth 

Air Force Base, South Dakota. April. 

USAF. 1996i. Final Record of Decision for Remedial Action at Operable Unit 10, Ellsworth 

Air Force Base, South Dakota. April. 

USAF. 1996j. Final Record of Decision for Remedial Action at Operable Unit 12, Ellsworth 

Air Force Base, South Dakota. April. 

USAF. 1997. Final Record of Decision for Remedial Action at Operable Unit 11, Ellsworth 

Air Force Base, South Dakota. April. 

USAF. 2005a. Memorandum for Record. Notification of Transfer of Groundwater Portion of 

the RODs (Records of Decision) for Operable Units (OUs) 1, 2, 3, 4, 5, 6, 7, 8, and 12 to 

the ROD for OU-11 Base-wide Groundwater. July 7. 

USAF. 2005b. Final Five Year Review. Ellsworth Air Force Base, South Dakota. 

September 23. 

USEPA. 1992. Federal Facilities Agreement Under CERCLA Section 120. In the Matter of: 

The U.S. Department of the Air Force, Ellsworth Air Force Base, South Dakota. EPA ID 

No. SD2572924644. January. 

USEPA. 1999. A Guide to Preparing Superfund Proposed Plans, Records of Decision, and 

Other Remedy Selection Decision Documents, Office of Solid Waste and Emergency 

Response. EPA 540-R-98-031, OSWER 9200.1-23P, PB98-963241. July. 

4465 00033
Explanation of Significant Differences 

OU-11 Basewide Ground Water 

Ellsworth AFB, South Dakota 

Q:\1616\9962\Ellsworth\ESD Final\OU-11 ESD Final 050107.doc Page 28 

May 1, 2007

9.0 ACRONYMS AND ABBREVIATIONS 

AFB Air Force Base 

CERCLA Comprehensive Environmental Response, Compensation and Liability Act 

CFR Code of Federal Regulations 

cis-1,2-DCE cis-1,2-Dichloroethlene 

DHC Dehalococcoides 

ESD Explanation of Significant Differences 

FFA Federal Facilities Agreement 

IRA Interim Remedial Action 

LOX Liquid Oxygen 

μg/L Micrograms per Liter 

MCL Maximum Contaminant Level 

NCP National Contingency Plan 

OU Operable Unit 

PCE Tetrachloroethene 

ROD Record of Decision 

SDDENR South Dakota Department of Environment and Natural Resources 

SVE Soil Vapor Extraction 

TCE Trichloroethene 

USC United States Code 

USAF United States Air Force 

USEPA United States Environmental Protection Agency 

VC Vinyl Chloride 

VOCs Volatile Organic Compounds 

4465 00034
Explanation of Significant Differences 

OU-11 Basewide Ground Water 

Ellsworth AFB, South Dakota 

Q:\1616\9962\Ellsworth\ESD Final\OU-11 ESD Final 050107.doc May 1, 2007

FIGURES 

4465 00035
SOUTH DAKOTA

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DU-11, EXPLANATION OF SIGNIFICANT DIFFERENCES "

~'L.. ...l 4465 00036....J
4465 00037
4465 00038
4465 00039
4465 00040
4465 00041
Explanation of Significant Differences 

OU-11 Basewide Ground Water 

Ellsworth AFB, South Dakota 

Q:\1616\9962\Ellsworth\ESD Final\OU-11 ESD Final 050107.doc May 1, 2007

ATTACHMENT A 

Memorandum of Record (USAF 2005) 

4465 00042
DEPARTMENT OF THE AIR FORCE

HEADQUARTERS 28TH MISSION SUPPORT GROUP (ACC)

ELLSWORTH AIR FORCE BASE, SOUTH DAKOTA

7 July 2005

MEMORANDUM FOR RECORD

FROM: 28 CES/CEVR

SUBJECT: Notification ofTransfer ofthe Groundwater Portion ofthe RODs (Records of Decision for Operable Units

(OUs): 1,2,3,4,5,6, 7, 8, and 12 to the ROD for OU-II, Base-wide Groundwater

1. This memorandum is notification that Ellsworth Air Force Base is administratively transferring the groundwater

component ofthe individual RODs (Records ofDecision) for OUs (Operable Units) 1,2,3,4,5,6, 7, 8, and 12 to the

ROD for OU-II, the base-wide groundwater operable unit. The selected remedies for soil at these OUs have already

been completed, so only the groundwater remedies are ongoing. Groundwater remedies for OU-9 and OU-lO were

already deferred to OU-II.

2. Consolidating all selected groundwater remedies and monitoring into OU-II will greatly simplify management and

reporting for the remaining groundwater remedial actions. Ellsworth AFB will continue to perform all remedial actions

and monitoring required under CERCLA (Comprehensive Environmental Response Compensation and Liability Act),

the FFA (Federal Facility Agreement), and the ROD (Record ofDecision) established for each individual OU.

1st Ind, US EPA Region 8 (1effMashburn)

MEMORANDUM FOR SD DENR (JOANE LINEBURG)

Concurl1SiP': Ii IIF.

2d Ind, SD DENR (Joane Lineburg)

MEMORANDUMFOR28CE~CEVR(DELLPETERSE~

Concur!MbIi 01 la.

DELL

4JS~ S. PETERSEN, P.E., USAF RPM

Chief, Environmental Remediation Element

7 /;~/os= DATE

JEFF MASIIDunJ~, TIAFB p!'...{

US EPA REGION 8

DATE

JOANE

SDDENR

UNEBURG,

.

EAFBR1'~

afd: G:\CEVR Files\ZOOS-06-15 Transfer ofOUs Ltt-SDDENR & EPA.doc

qfo6aCPower Por}lmerica 4465 00043