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: Con trac t DACW45-94-D-0001, DO-54, WAD 1 Pride Hangar Source Remediation Recommendation Serial Letter 1-54-RA-301 FXBM 20037001 D e ar M r . M ailand er: BAC K GR O UND Te l ephone 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 LIM I TED DIRECT PUSH SO I L I NVESTIGAT IO N Limit e d s oil an d groun d w at e r monito ring w a s c ondu c t ed in M ay 2 00 2 at the northwes t c o rn er of the Prid e Han gar to d e t ermin e the ex t e nt of a p ot e ntial s ource are a id e ntifi e d du rin g pre viou s d i rec t p u sh monitoring

. T he p re viou s di rec t p u sh w ork found TCE c onc e ntration s in ground w at e r s ampl es of up to 30,000 ug / l . The M ay 2 00 2 inv es tigati o n con s i s t e d of the advanc e m e nt of nin e di rec t p u sh s oil b oring s to furthe r defi n e the ap pare nt s ource ar e a . The d i rec t pu sh s oi l b oring s we r e a d van ce d to the w at er tab l e. O n e ground w at er s amp l e an d up t o two so il s a mp l es were c olle c t ed from e a ch so il b oring

. T he monito ring res ult s sh o we d th a t

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_ T E C H A Tyc o Infrastruc t ure Services Company 

# 4013 001Mr. Mark Mai lander U.S. Army Corps of Engineers September 3, 20 0 3 Page 2 the main source of the T CE 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 TRE A TMENT 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. A ddressing 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. A lso, 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 facili ty construction in this congested area. The remediation strategies presented below address residual soil contamination and ground water contamination. G R OUND WA T ER C O N T AMIN ATIO N
Earth T ech recommen ds th e ap plication o f H yd rogen R elea s e Compo un d (HR C ) to re m e d iate th e area of elevate d TCE in ground w ater
. T h i s i s f ea s i b le b ecau s e th e s ource area i s limite d in s i z e, an d th ere i s ground w ater fl o w th at w ill deliver th e HR C to th e do w n gra d ient p orti o n

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## 4013 002Mr. Mark Mailander U.S. Army C o rps o f Eng i neers September 3, 20 0 3 Page 3

o f the plume as i t i s be i ng funneled to the Pri de Hangar gro und water extracti o n system. Ge o l o gy i n th i s area i s fai rl y uniform s o the HRC can be i njected thro ugh the entire th i ckness o f the aquife r . T h i s i s an i nn o vative technique that has been used effectively elsewhere and al lo ws us to av oi d the pro b l ems ass o ciat ed w i th util i ty and fac ili ty c o nstructio n i n th i s c o ngested area. Injectio n o f HRC i n th i s area would als o treat water T CE- i mpacted water fl o wing fro m the smaller up-grad i ent s o urce area. T his techn i que has been used previ o us l y at Ellsw o rth AFB to remediati o n d i ch lo ro ethane (DCA) c o ntami natio n lo cated s o utheast o f the Munitio ns St o rage Area. The site is designated as Site 88413 and i s be i ng r emed i at ed under the El l sw o rth AFB C o mp li ance Pro gram. T he m o n i t o ring o f that remediatio n i s sti ll i n pro gress, but resu l ts to date sh o w that the technique is effecti v e. DCA concentrati o n is being mon i tored 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. S O I L 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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## 4013 003Mr. Mark Mailander U.S. Army Corps of Engineers September 3, 2003 Page 4 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 dis ru ption 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\ T ERC\53039_48\WPLDO-48SERIAL LETTERS\48RA362.DOC

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_ T E C H A tqco INTERNATIO NALLTD .C OMPANY 

## 4013 004July 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 D A C W 45- 9 4

- D-0001, D O -4 8 Pride Hangar Hotspo t R e m ediation Ell s worth A F B, South D akota 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 rec o nlmendations 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 SERI A L LETTERS_48R A 411 .DOC



## 4013 005TE CHNICAL 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 twel v e 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 i ncludes 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 repo r ted 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 o ff -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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## 4013 006Contaminated 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 se l ected remedy for Area 2 is ground w ater c o ntainment/ 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 On g oing mo n ito r ing o f g r ou n d wat e r in th e a r ea o f th e P r ide Han g a r h a s p r ovid e d in f or m atio n indicati n g a po ss ibl e " hot s pot " or s ou r c e a r ea f o r e l e vat ed T C E conta m inatio n in thi s a r ea. Earth T e ch ha s co m pl e t e d a nu m b e r of limit ed s oil a nd ground wat e r s ampli ng e v e n ts n ea r t h e northw es t corn e r o f th e Pri d e Han g a r to det e r m in e t h e e xt e nt o f a potential s ourc e a re a id e nti f i ed du r ing pr e viou s di r ect p u sh 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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## 4013 007

### 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 Pr i de 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 programutilizing 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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## 4013 008provide 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.

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