Explanation of Significant ere nee for Operable Unit 1 · 2019-06-07 · 75CEG/ CEVR 7274 Wardleigh...

Hill Air Force Base, Utah

Final

Explanation of Significant Diff ere nee for Operable Unit 1 July 2006

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*1055938*

rmclinto

1055938

EXPLANATION OF SIGNIFICANT DIFFERENCE

FOR

OPERABLE UNIT 1

HILL AIR FORCE BASE, UTAH

July 2006

PREPARED BY:

Environmental Restoration Branch 75th Civil Engineer Group Hill Air Force Base, UT

EXPLANATION OF SIGNIFICANT DIFFERENCE OU 1 HILL AFB, UTAH

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OU 1 ESD Final 060712.doc

Explanation of Significant Difference Operable Unit 1 (OU 1)

Hill Air Force Base, Utah I. INTRODUCTION This Explanation of Significant Difference (ESD) relates to remedial actions selected by the United States Air Force (USAF) for implementation at Operable Unit 1 (OU 1) at Hill Air Force Base (AFB), Utah in a Record of Decision (ROD) issued in September 1998. Operable Unit 1 is comprised of five Installation Restoration Program (IRP) sites (LF001, LF003, FT009, FT081, and WP080). The selected remedial actions at OU 1 for the source area include the dewatering of the Source Area with extraction trenches, light non-aqueous phase liquid (LNAPL) recovery from the extraction trenches, groundwater treatment at the OU 2 Air Stripper Treatment Plant (ASTP) or Hill AFB Industrial Wastewater Treatment Plant (IWTP), and repair as well as operation and maintenance (O&M) of the landfill caps and passive gas vent system. For the non-source area at OU 1 selected remedial actions include upgrading the spring collection system and treatment of the collected surface water, excavating arsenic-contaminated spring sediments, and monitored natural attenuation. Several remedial actions, including Pond 10 modifications, environmental monitoring, and institutional and engineering controls, were selected for both source and non-source areas at OU 1. An ESD is required to address differences in the groundwater treatment remedial action for OU 1. In July 1987, the U.S. Environmental Protection Agency (EPA) placed Hill AFB on the National Priorities List (NPL) under Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA). In April 1991, Hill AFB entered a Federal Facility Agreement (FFA) with the Utah Department of Environmental Quality (UDEQ) and the EPA Region VIII to establish a procedural framework and schedule for implementing the appropriate response actions in accordance with existing regulations. Under the FFA and Executive Order 12580, Hill AFB is the lead agency for all CERCLA actions and UDEQ and the EPA are support agencies. Generally speaking, Hill AFB needs concurrence from both the EPA and UDEQ for significant decisions involving cleanup strategy, goals and methods. This ESD is issued in accordance with Section 117(c) of the CERCLA 42 U.S.C. § 9617(c), and Section 300.435(c)(2)(i) of the National Oil and Hazardous Substances Pollution Contingency Plan (NCP), which requires the USAF to issue such a document where a remedial action will differ in any significant, but not fundamental, respect from that selected by the USAF and described in the ROD. It has been prepared to provide the public with an explanation of the nature of the modification to the selected remedy set forth in the ROD and to summarize the information that supports this modification. The ESD will become part of the Administrative Record file (NCP 300.825(a)(2)) in the information repository (40 CFR 300.435(c)(2)(i)(A)) for Hill AFB which is located and available for public review at:

75CEG/ CEVR 7274 Wardleigh RD Hill AFB UT 84056-5137


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The Administrative Record is also available for public review at:

Weber State University - Ogden Campus Stewart Library 3850 University Circle Ogden, UT 84408 (801) 626-6403

Weber State University - Davis Campus Stewart Library 2750 University Park Blvd Layton, UT 84041-9099

The USAF concludes that the remedy selected in the ROD, as modified by this ESD, will meet the objectives and performance standards of the ROD.

II. SUMMARY OF THE SITE HISTORY, SITE CONDITIONS, AND SELECTED REMEDY

Operable Unit 1 is located on the eastern boundary of Hill AFB overlooking the Weber River Valley and primarily consists of groundwater contaminated with volatile organic compounds (VOCs) and includes the presence in the source area of light, non-aqueous phase liquid (LNAPL). The principal contaminant of concern at the site is cis-1,2-dichloroethene (DCE or cis-1,2-DCE). The shallow groundwater DCE plume extends off the Base to the north into South Weber City. The OU 1 site has been divided into ten source areas and two non-source areas. The source areas include the original disposal sites of contamination and are considered the source for migrating dissolved-phase contamination. The non-source areas include the contaminated water both on and off Base. The remedies selected for OU 1 are outlined in the ROD (HAFB EMR, 1998) as source area remedies, non-source area remedies, and remedies for both source and non-source areas are as follows: Source Area Remedies:

• dewatering of the source area with extraction trenches, • light non-aqueous phase liquid recovery from the extraction trenches, • groundwater treatment at the OU 2 Air Stripper Treatment Plant (ASTP) or Hill AFB

Industrial Wastewater Treatment Plant (IWTP), and • repair as well as operation and maintenance (O&M) of the landfill caps and passive gas

vent system.

Non-Source Area Remedies: • upgrading the spring collection system and treatment of the collected surface water at the

OU 2 ASTP, a new remote treatment plant, or the IWTP • excavating arsenic-contaminated spring sediments and disposing in a permitted facility,

and • monitored natural attenuation.

Remedies for both Source and Non-Source Areas: • modifications to allow dewatering of Pond 10 after rainfall events, • Waste Oil/Phenol Pit containment,


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• installation of an upgradient soil/bentonite cut-off wall, • environmental monitoring, • institutional and engineering controls, such as water right and well drilling restrictions and

fencing with warning signs to restrict access to exposure areas. • operations, maintenance, and replacement of remedial components, and • designation of a Corrective Action Management Unit (CAMU) to facilitate remedial

actions.

III. DESCRIPTION OF AND BASIS FOR THE DIFFERENCES Groundwater Treatment Groundwater at OU 1 is extracted using five extraction trenches and three spring collection systems. Originally, extracted groundwater was sent to the Hill AFB IWTP for pre-treatment and was then sent on to a Publicly-Owned Treatment Works (POTW) for final treatment. An August 2000 change in the Central Weber Sewer Improvement District (CWSID) permit limit for VOCs, allows for a concentration of 2,130 μg/L total VOCs in effluent discharged to the CWSID. As a result of the change in the permit limit, studies were conducted in 2003 (URS, 2003) and 2004 (URS, 2004) and discussions were held with CWSID representatives to determine the feasibility of sending OU 1 groundwater directly to CWSID for treatment. Due to favorable results of the studies and the discussions with CWSID, modifications to the OU 1 effluent piping network were made during 2004 to allow the discharge of OU 1 groundwater to CWSID. Permission was obtained from CWSID and the groundwater effluent from OU 1 was re-routed on February 28, 2005 from the Hill AFB IWTP to CWSID. An increased sampling program was implemented for the first six months of the OU 1 effluent transition from the Hill AFB IWTP to CWSID. Figure 1 shows the OU 1 groundwater effluent concentrations of total VOCs for the first six months (March-August 2005) of OU 1 effluent discharge to CWSID. As is evident from Figure 1, the concentration has been below the total VOC permit limit. These effluent concentrations for the first 6 months of discharge to CWSID are similar to the concentrations measured for OU 1 effluent since system start-up in 2001 (URS, 2004) The fact that extracted groundwater at OU 1 is no longer being pre-treated at the Hill AFB IWTP or OU 2 ASTP constitutes a significant, but not fundamental, difference to the selected remedy outlined in the ROD. A significant change to a remedy is one that incrementally changes a component of a remedy (such as cost) but does not fundamentally alter the remedy (such as a change in the selected extraction trench remedy). This new procedure still provides safe and effective groundwater treatment with no additional environmental risk. The OU 1 groundwater effluent concentrations will be maintained by the O&M contractor in accordance with contract requirements. In compliance with the terms of the discharge permit with CWSID, the compliance point is sampled quarterly in conjunction with the base wide compliance program (HAFB EMR, 2005). If necessary, the effluent can be re-routed to the Hill AFB IWTP. By rerouting the effluent from the Hill AFB IWTP to the CWSID, unit treatment costs have decreased by approximately 99%. Depending on the flow from the groundwater treatment system, the projected annual cost savings are from $300,000 to $800,000.


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0

500

1000

1500

2000

2500

Feb-05 Mar-05 Apr-05 May-05 Jun-05 Jul-05 Aug-05

Date

Tot

al V

OC

Con

cent

ratio

n in

ug/

L

Total VOC Permit Limit 2,130 ug/L

Figure 1 – OU 1 Groundwater Effluent Total VOCs Concentration Over Time.

IV. PUBLIC PARTICIPATION This ESD was discussed during the January 26, 2006 RAB meeting. Discussion and questions included public notification procedures for ESDs and total VOC concentrations discharged to and measured at the CWSID treatment plant. The RAB provided approval for both the process Hill AFB is using to prepare this ESD and for the technical differences documented in this ESD. The RAB will be notified of the submission of the finalized ESD at the first quarterly RAB meeting after the ESD is signed. Hill AFB will publish a notice of availability and a brief description of the ESD in the local newspaper, Ogden Standard Examiner, the week following that RAB meeting. This ESD and the information upon which it is based will be included in the Administrative Record for this Site. The Administrative Record also includes the ROD and all documents that formed the basis for USAF’s selection and EPA and UDEQ’s concurrence of the remedial action for the Site. These components meet the public participation requirement set out in Section 300.435(c)(2)(i) of the NCP.


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V. REFRENCES (HAFB EMR, 1998) Record of Decision - Operable Unit 1 (IRP Sites LF01, WP02, LF03, FT09, FT81, and WP80). Hill AFB EMR. September 1998. (HAFB EMR, 2005) Long-Term Groundwater Monitoring Project, Final Calendar Year 2005 Basewide Monitoring and Maintenance Work Plan. Prepared by CH2MHill. August 2005. (URS, 2003) Memorandum from URS to Hill AFB EMR. Optimization of OU 1 and OU 2 Effluent to CWSID. URS. October 2003. (URS, 2004) Memorandum from URS to Hill AFB EMR. OU 1 and OU 2 Effluent Treatment Configurations and Potential Impacts to CWSID Permit. URS. December 2004.

VI. AGENCY COMMENTS Utah Department of Environmental Quality Comments, submitted by Mohammad Slam on March 14, 2006:

Comment: Please include the cost savings realized through the ESD for OU1.

Response: Changes were made in the ESD to reflect the cost savings for the Groundwater Treatment Remedy.

United States Environmental Protection Agency comments, submitted by Charles Sands on March 13, 2006:

Comment: The Introduction section generally includes identification of the lead and support Agencies. Neither the role of USEPA or the State of Utah Department of Environmental Quality appears to be acknowledged. Although I am not familiar with Air Force’s perception of their role in Federal Facility cleanups with other state and federal entities, I would urge recognition of the roles as defined in the Federal Facilities Agreement, particularly if the AF agrees these documents are still in effect.

Response: Discussion of the FFA, lead, and support agencies added to Section I. Comment: Section IV, Public Participation – Suggest the final document include whether/when public notice in newspaper was published and results of Restoration Advisory Board Meeting/comments. Not clear if public comments were solicited or received. Were there TAG comments?

Response: This final ESD includes the date of public notice in the local newspaper as well as mention of discussion contents at the RAB meetings. RAB members provided comments on the ESD process and explanation of this specific ESD at the 27 October 2005 meeting. No other public comments were solicited as Section 300.435(c)(2)(i) of the NCP does not require public comment and ESD guidance (Chapter 7 of A Guide to


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Preparing Superfund Proposed Plans, Records of Decision, and other Remedy Decision Documents, p. 7-5) states that “A formal public comment period is not required when issuing an ESD.” There are no TAG comments.

Comment: Section IV, Public Participation – Suggest inclusion of NCP reference, Section 300.435 (c)(2 )(i), related to Public Participation Compliance.

Response: Reference included in Section I of the draft. Added to Section IV of the final. Comment: Section VI Agency Comments – this section is blank. Did EPA Region 8 or UDEQ have any comments for either ESD?

Response: The draft was prepared for agency comment. Those comments and Hill AFB response are included in this final.

Comment: Section VII, Statutory Determination Requirements – Suggest reference CERCLA Section 121 met.

Response: Reference added to Section VII of the final . Comment: Signature delegation - Did the Region and State of Utah delegated the signature/concurrence to the project level? Usually this is a Branch Chief or Division Director function.

Response: Appropriate signatories for the EPA and UDEQ were confirmed and the appropriate signatures are now included (EPA = Max H. Dodson, Assistant Regional Administrator and UDEQ = Dianne R. Nielson, Executive Director)

Comment: Section III, last paragraph – “Figure 1 shows GW effluent concentrations for the first 6 months…”. Most of the data if for the first 4 months – are you satisfied that this is sufficient data to account for seasonal/historic variations. If you can make a statement about historic GW effluent concentrations into the AFB IWTP which supports this decision, add that information.

Response: Yes, we are satisfied that samples collected during these six months are representative of effluent leaving OU 1. Historically, there has been limited variability in the effluent concentrations from OU 1 and the results from the first 6 months are within the expected range. During the first six months of the transition an increased sampling regime was implemented to verify compliance. Text has been added to reference documentation of similarity to historical concentrations.

Comment: Section III, last paragraph – “GW effluent concentrations will be monitored in the future and if necessary…”. Can you add more specifics such as the frequency, and when/where this was agreed upon (e.g. RAB meeting, Monitoring document, etc).

,,

EXPLANATION OF SIGNIFICANT DIFFERENCE OU I HILL AFB, UTAH

PAGEB

Response: Text modified to reflect ongoing responsibility of the O&M contractor to monitor and maintain effluent concentrations as well as the quarterly compliance point sampling per the permit with CWSID.

VII. STATUTORY DETERMINATIONS

The Applicable or Relevant and Appropriate Requirements (ARARs) addressed by the ROD for OU 1 are not modified by this ESD. Considering the clarifications regarding the selected remedies presented in this ESD, the USAF, EPA, and UDEQ all concur that the source area and non-source area remedies, including remedies common to both source and non-source areas, at OU I remain protective of human health and the environment, comply with federal and state requirements that were identified in the ROD as ARARs, and are cost-effective. There are no changes to the anticipated remediation time frame as a result of the Air Force's adoption of these differences from the ROD. The remedy satisfies CERCLA Section 121.

Signatures

SCOTT D. CHAMBERS Colonel, USAF Commander 75th Air Base Wing (AFMC) Hill Air Force Base Utah

~~ Director Federal Facilities Program EPA Region VIII

2f>'~t9l Date

Date

~ Executive Director Utah Department of Environmental Quality

OU I ESD Final 060712.doc

Explanation of Significant ere nee for Operable Unit 1 · 2019-06-07 · 75CEG/ CEVR 7274 Wardleigh...

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