3033 Campus Drive North, Suite 290, Minneapolis, Minnesota 55441

September 3, 2003

Mr. Mark Mailander

Area Engineer, Black Hills Area Office

U.S. Army Corps of Engineers

631 Saint Anne Street, Suite 101

Rapid City, South Dakota 57701-4667

Subject: Contract DACW45-94-D-0001, DO-54, WAD 1

Pride Hangar Source Remediation Recommendation

Serial Letter 1-54-RA-301

FXBM 20037001

Dear Mr. Mailander:

BACKGROUND Telephone

Earth Tech, Inc. (Earth Tech), has monitored an area of high trichloroethylene (TCE) 763.551. 1001

contamination near the norl;hwest comer of the Pride Hangar. We presented a discussion of

remedial options for this area in Serial Letter 1-48-RA-362, dated February 13, 2003. These Facsimile

recommendations were discussed by the RPM group at the February and April 2003 RPM

meetings. It was agreed that we needed to consider how these recommendations could be 763.551.2499

implemented within the framework of the CERCLA process. Robert Todd evaluated this

question and prepared a memo that was distributed in serial letter 1-48-RA-411, dated

July 21, 2003. He concluded that the remedial option could be handled as a significant

change, requiring an Explanation of Significant Difference (ESD), but not requiring a

ROD amendment. In subsequent weekly teleconferences, the RPM group agreed with that

conclusion. It was also agreed that Earth Tech should issue a letter documenting the

proposed remedial option and justifying the use of Hydrogen Release Compound (HRC).

This letter is intended to fulfill that requirement.

This letter incorporates the evaluation and recommendations contained in the February 2003

letter; the regulatory discussion prepared by Robert Todd; and contains additional

information supporting the use of HRC. By addressing this "hot spot" area as recommended

herein, the required operational period of the remediation system located down gradient may

be shortened.

PRIDE HANGAR LIMITED DIRECT PUSH SOIL INVESTIGATION

Limited soil and ground water monitoring was conducted in May 2002 at the northwest

corner of the Pride Hangar to determine the extent of a potential source area identified during

previous direct push monitoring. The previous direct push work found TCE concentrations in

ground water samples of up to 30,000 ug/l. The May 2002 investigation consisted of the

advancement of nine direct push soil borings to further define the apparent source area. The

direct push soil borings were advanced to the water table. One ground water sample and up

to two soil samples were collected from each soil boring. The monitoring results showed that

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Mr. Mark Mailander

U.S. Army Corps of Engineers

September 3, 2003

Page 2

the main source of the TCE contamination appears to be localized near the northwest corner

of the Pride Hangar. There also appears to be an smaller source up-gradient. The results of

the supplemental investigation are presented on Figure 1 and in Table 1 of the July 15, 2002,

LTM report (Serial Letter 1-43-RA-383).

EXISTING TREATMENT SYSTEM

The existing Pride Hangar total fluids extraction system consists of eight well points located

southeast of the Pride Hangar and a vacuum pump located in a below-grade equipment vault

immediately adjacent to the site. The system was designed to address a source area of

chlorinated volatile organic compounds (VOCs) near the Pride Hangar. Total fluids

(soil vapor and ground water) are removed from the subsurface by applying a high vacuum to

the well points. Total fluids flow through underground vacuum conveyance piping to the

equipment vault. Vapor and liquid are separated in the vault. Soil vapor is discharged to the

atmosphere through a vent stack. Ground water is pumped to the FRA Pump House No. 1

Treatment Facility. Two of the well points in this system have been taken offline as the

plume in the vicinity of the points has been remediated.

The existing treatment system adequately addresses/prevents the down gradient migration of

the Pride Hangar TCE plume but does not rapidly address the contaminant hot spot located

northwest of the Pride Hangar. Addressing the localized hot spot at the northwest corner of

the Pride Hangar should significantly decrease the time required by the total fluids extraction

system to clean up the TCE plume in this area.

SOURCE TREATMENT OPTIONS

Several remedial alternatives have been evaluated to determine the most practical and

effective method to treat the apparent source area that is located near the northwest corner of

the Pride Hangar. The main difficulty is the location on the operational side of the building,

which limits structures that can be placed in this area. Also, the size of the Pride Hangar and

the numerous underground utilities make an extension of the existing remediation system or

the installation of a new remediation system very difficult. For these reasons, we have

focused on remediation options that minimize utility and facility construction in this

congested area. The remediation strategies presented below address residual soil

contamination and ground water contamination.

GROUND WATER CONTAMINATION

Earth Tech recommends the application of Hydrogen Release Compound (HRC) to remediate

the area of elevated TCE in ground water. This is feasible because the source area is limited

in size, and there is ground water flow that will deliver the HRC to the down gradient portion

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Mr. Mark Mailander

U.S. Army Corps of Engineers

September 3, 2003

Page 3

of the plume as it is being funneled to the Pride Hangar ground water extraction system.

Geology in this area is fairly uniform so the HRC can be injected through the entire thickness

of the aquifer. This is an innovative technique that has been used effectively elsewhere and

allows us to avoid the problems associated with utility and facility construction in this

congested area.

Injection of HRC in this area would also treat water TCE-impacted water flowing from the

smaller up-gradient source area.

This technique has been used previously at Ellsworth AFB to remediation dichloroethane

(DCA) contamination located southeast of the Munitions Storage Area. The site is

designated as Site 88413 and is being remediated under the Ellsworth AFB Compliance

Program. The monitoring of that remediation is still in progress, but results to date show that

the technique is effective. DCA concentration is being monitored in two monitor wells. In

one well (MW968413-03), the DCA concentration has been reduced from 240ppb to <1 ppb.

In the second well (MW028413-01), the DCA concentration has been reduced from 40ppb to

27 ppb.

Based on these results, we expect HRC to be effective in treating the TCE contamination in

the ground water near the Pride Hangar. A potential drawback of the technique is that, given

the high contaminant concentration, more than one HRC application may be required. Also,

in rare occasions ground water chemistry limits the effectiveness of HRC, but that concern

can be addressed prior to implementing the injection of HRC as the remedy. Water chemistry

information will be collected to determine the amount of HRC that would be required to

remediate the area of high TCE concentration, then design the HRC injection program based

on the water chemistry data.

We believe that this technique can be implemented within the CERCLA framework as a

significant change that would require an Explanation of Significant Difference (ESD), but

would not require a Record of Decision (ROD) amendment. This subject was reviewed in

serial letter 1-48-RA-411, dated July 21, which contained the memo prepared by Robert

Todd. That letter and memo are included as an attachment to this letter.

SOIL CONTAMINATION

Previous monitoring indicates there is some residual contamination in the vadose zone and

capillary fringe in the "hot spot" area. The impacted area is currently covered with paving,

which prevents water from infiltrating through the vadose zone and carrying contaminants

down to the ground water. However, as long as the TCE remains in the vadose zone, it is a

potential source of ground water contamination and although there is generally no infiltration

in this area additional contaminant mass can be added to the ground water during periods

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Mr. Mark Mailander

U.S. Army Corps of Engineers

September 3, 2003

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when the water table is elevated. Therefore, we recommend that this contamination be

remediated along with the ground water in the area of elevated TCE concentration. Soil

vapor extraction (SVE) would be the most effective remedial technology. A temporary SVE

system for this area would consist of two SVE wells, installed in the delineated source area,

and a small SVE blower. The wells would be connected via above ground piping to the SVE

blower and the off gas would be discharged to the atmosphere. The SVE system would be

run for a maximum one operational season running from May to October. We believe the

SVE system could be placed at the northwest corner of the Pride Hangar with minimal

disruption to operational activities in this area.

We will be prepared to discuss these recommendations with the RPM group during the

September 8 RPM meeting.

Thank you.

Very truly yours,

Earth Tech, Inc.

Project Manager

File: 53039/01.2020

cc: Dell Petersen Len Havel

Jim Haggins Jeff Mashburn

Bob Todd Joane Lineburg

Dwight Pochant Greg Brooks

Mark Mercier Joe Odegaard

L:\WORK\TERC\53039_48\WPLDO-48SERIAL LETTERS\48RA362.DOC

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July 21, 2003

Area Engineer, Black Hills Area Office

U.S. Army Corps of Engineers

631 Saint Anne Street, Suite 101

Rapid City, South Dakota 57701-4667

Subject: Contract DACW 45-94-D-0001, DO-48

Pride Hangar Hotspot Remediation

Ellsworth AFB, South Dakota

Serial Letter 1-48-RA-411

Dear Mr. Mailander:

Earth Tech submitted a letter (1-48-RA-362, dated February 13, 2003)recommending options for

treatment of the ground water hot spot near the Pride Hangar. This issue has been discussed at

RPM meetings and weekly teleconferences. Subsequently, Bob Todd has researched the

regulatory aspects of the recommendations, and his memo is attached to this letter.

We will be available to discuss these reconlmendations at future weekly teleconferences or at

the next RPM meeting.

Very truly yours,

Earth Tech, Inc.

Keith J. Anderson, P.E.

Project Manager

Attachment

cc: Dell Petersen Len Havel

Jim Haggins Mark Mercier

Dwight Pochant Bob Todd

Jeff Mashburn Joe Odegaard

Joane Lineburg

file: 53039/01.3010

L:\WORK\TERCL53039_48\WPkDO-48 SERIAL LETTERS_48RA411 .DOC

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TECHNICAL MEMO

TO: Keith Anderson-Earth Tech

FROM: Bob Todd-RDTA

DATE: 7/17/2003

SUBJECT: EAFB OU-11 Post ROD Remedy Change

OU-11 Description

OU-11 is one of twelve operable units identified at EAFB. This OU is described as

Basewide Ground Water, EIIsworth Air Force Base. OU-11 provided for a study of the

overall Base ground-water quality and characteristics. Investigations and remedial

action decisions for ground water contamination at numerous sites on the Base, not

specifically covered.in another OU, were included in this OU to provide overall Base

coverage of the ground water conditions. The OU investigations and remedial action

recommendations were divided into two areas; Area 1 is the South Docks Study Area

and Area 2 is the BG-04/BG-05 Study Area and OU-08 ground water.

Area 1 includes the South Docks and areas of ground water contamination in OU-9 and

OU-10 that were deferred to OU-11. Ground water contamination in OU-10 is the result

of releases of petroleum hydrocarbon products. Therefore, the remedial actions are

being addressed through the State of South Dakota Petroleum Release Program. The

ground water contamination in Area 1 is confined to areas within the Base boundaries.

Recent monitoring and investigations in the area near the Pride Hangar have reported

ground water concentration of TCE at 30,000 ug/L.

COC's in Area 1 ground water include VOC's, SVOC's, and TPH. TCE is the most

frequently reported VOC. In addition ground water samples have been reported to

contain total-l, 2-dichloroethene, chloroform, pentachlorophenol, chrysene and TPH.

Area 2 is in the vicinity of monitor wells BG-04 and BG-05. The ground water

contamination in these areas has been found to move off-Base at the eastern Base

boundary. It was determined that OU-08 ground water did not require remedial action;

however, compliance monitoring is being conducted as part of the OU-11 remedy.

COC's in Area 2 ground water include TCE, DCE, BTEX, PCE and TPH. Off-Base

ground water plume contamination is primarily TCE and its degradation products.

Selected Remedy

Evaluation of remedial alternatives for OU-11 during the development of the Feasibility

Study, Proposed Plan and ROD in part utilized the Presumptive Remedy Strategy.

Specifically the Response Strategy and Ex-Situ Treatment Technologies for

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OU-11 Post ROD Remedy Addition Page 1

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Contaminated Ground Water at CERCLA Sites (OSWER Directive 9283.1-12) was

applied to the site condition during the remedy evaluation.

Area 1

The selected remedy for 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 Maximum Contaminant Levels (MCLs) and State of South Dakota

Ground Water Quality Standards.

[] Institutional controls and long-term monitoring.

Area 2

The selected remedy for Area 2 is ground water containment/extraction and treatment

and includes the following major components:

13 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.

Pride Hanqar Issue

Ongoing monitoring of ground water in the area of the Pride Hangar has provided

information indicating a possible "hot spot" or source area for elevated TCE

contamination in this area. Earth Tech has completed a number of limited soil and

ground water sampling events near the northwest corner of the Pride Hangar to

determine the extent of a potential source area identified during previous direct push

investigations. These investigations have reported TCE concentration in ground water

samples of up to 30, 000 ug/L.

The existing Pride Hangar total fluids extraction system consists of eight well points

located southeast of the Pride Hangar and a vacuum pump located in a below-grade

equipment vault immediately adjacent to the site. The system was designed to address

a source area of chlorinated volatile organic compounds (VOCs) near the Pride Hangar.

Total fluids (soil vapor and ground water) are removed from the subsurface by applying

a high vacuum to the well points. Total fluids flow through underground vacuum

conveyance piping to the equipment vault. Vapor and liquid are separated in the vault.

Soil vapor is discharged to the atmosphere through a vent stack. Ground water is

pumped to the FRA Pump House No. 1 Treatment Facility.

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OU-11 Post ROD Remedy Addition Page 2

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The existing treatment system adequately addresses/prevents the down-gradient

migration of the Pride Hangar TCE plume but does not rapidly address the contaminant

hot spot located northwest of the Pride Hangar.

The location of the Pride Hangar in the South Docks Area presents a number of physical

limitations to the installation of additional total fluids extraction wells. This is a very

congested area and there are considerable underground utilities in the area making

installation of piping and related equipment nearly impossible. Earth Tech has

recommended additional remedial action to remove this "Hot Spot" near the Pride

Hangar.

ProposedAdditional Remedial Action

Ground water

Earth Tech proposes to apply the Hydrogen Release Compound (HRC) technology to

address the area of elevated TCE in ground water. This remedy would be utilized as an

addition to the existing remedy and the overall OU-11 remedial action would remain

ground water extraction and treatment with containment.

Soil

Earth Tech proposes to apply soil vapor extraction to remove TCE in the vadose zone,

since elevated TCE concentrations in the area soil could act as a continuing source of

TCE in ground water. This action would require the installation of a temporary SVE

system consisting of two new SVE wells and a small SVE blower. This technology is the

same as currently being applied to the total fluids wells in the South Docks Area without

the addition of ground water extraction pumps. Extension of the existing system into the

area near the Pride Hangar has the same construction problems with existing utilities

and underground obstructions as does the installation of additional ground water

extractionwells.

ReclulatorvIssues

The remedial actions in place at OU-11 were developed under the CERCLA program

utilizing the FS and Proposed Plans. The selected remedy was documented in the OU11 ROD as outlined above. The conditions at the Pride Hangar were discovered postROD during investigations designed to identify potential sources of elevated TCE in the

South Docks Area. The identified conditions warrant additional remedial actions in this

area to assure that the site cleanup requirements are met.

Sections 117 (c) and (d) of CERCLA contain provisions for addressing and documenting

changes to an alternative that occur after a ROD has been signed. In addition the

National Oil and Hazardous Substances Pollution Contingency Plan (NCP) (55 FR 8666-

8865, March 8, 1990) includes requirements for post ROD public information and

comment in sections 300.435(c)(2) and 300.825(b) and (c).

The CERCLA program recognizes that post-ROD information could affect how the

selected remedy should be implemented. EPA has prepared guidance documents that

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OU-11 Post ROD Remedy Addition Page 3

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provide appropriate responses to these post-ROD situations. Two documents are

available that outline the steps necessary to ensure compliance with CERCLA.

[3 "Guide to Addressing Pre-ROD and Post-ROD Changes" -OSWER 9355.3-02FS4, April 1991.

13 "Interim Final Guidance on Preparing Superfund Decision Documents" -OSWER

Directive 9355.3-02.

These documents describe the steps necessary to institute a post-ROD addition/change

to a selected remedy. The lead Agency reviewing the proposed change must determine

if the extent or scope of the modification is: non-significant or minor; significant; or

fundamental. Non-significant changes include things like the final number of extraction

wells or the volume of soil to be treated. Significant changes include items such as

having to treat soils off-site in a Subtitle C facility rather than placing soil on-site in under

Subtitle D requirements. Fundamental changes entail a change in the overall remedy

such as using pump and treat rather than natural attenuation, or thermal nitrification

rather than soil washing.

The application of HRC and SVE at the Pride Hangar for "hot spot" remediation does not

eliminate the overall remedy selected for ground water at OU-11. The proposed

additional effort is a supplement to the selected final remedy. Under this approach the

change would be a significant change to the ROD.

CERCLA requires that an Explanation of Significant Differences (ESD) be prepared if a

significant change is made to a remedy Post-ROD. To be in compliance with CERCLA

in this situation the following must be included in the ESD:

[] The change must be documented.

[] Summarize the information that led to making the change

[] Affirm that the revised remedy complies with CERCLA section 121.

[] The public needs to be informed of change in the remedy

The "Guide to Addressing Pre-ROD and Post-ROD Changes" -OSWER 9355.3-

02FS-4, April 1991, indicates that during the period that the ESD is being prepared

pre-design, design, construction, and operation of the remedy may proceed. In

addition the following should be completed:

[] Consult with supporting agencies

[] Publish a notice of the proposed change in local newspapers (Fact Sheet

Format).

13 Place a copy of the ESD in the Administrative Record.

Mr.KeithAnderson 8/5/2003

OU-11PostRODRemedyAddition Page4

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