Section J Attachment 6B_Schilling S1 DD.pdf

FINAL

DECISION DOCUMENT

FORMER SCHILLING ATLAS F MISSILE SITE S-1

BENNINGTON, KANSAS

FUDS PROJECT NO. B07KS025902

Prepared by

U.S. Army Corps of Engineers Kansas City District 601 East 12th Street

Kansas City, Missouri 64106

February 2017

Encl 1

Decision Document Former Schilling Atlas F Missile Site S-1 Bennington, Kansas

TABLE OF CONTENTS

LIST OF FIGURES ............................................................................................................ ii LIST OF ACRONYMS AND ABBREVIATIONS .......................................................... iii

1.0 DECLARATION

1.1 Site Name and Location

1.2 Statement of Basis and Purpose

1.3 Assessment of the Site

1.4 Description of the Selected Remedy

1.5 Statutory Determinations

1.6 Data Certification Checklist

1.7 Approval

2.0 DECISION SUMMARY

2.1 Site Name, Location, and Brief Description

2.2 Site History and Investigations

2.2.1 Site History

2.2.2 Previous Investigations and Response Actions

2.2.3 Response Action (2010)

2.3 Community Participation

2.4 Site Characteristics

2.4.1 Site Geology

2.4.2 Site Hydrogeology

2.4.3 Nature and Extent of Contamination - Soil

2.4.4 Nature and Extent of Contamination - Groundwater

2.4.5 Conceptual Site Model

2.5 Current and Future Land and Groundwater Use

2.5.1 Current and Future Missile Base Property Use

2.5.2 Current and Future Surrounding Land Use

2.5.3 Current and Future Groundwater Use

2.6 Summary of Site Risks

2.6.1 Human Health Risk

2.6.2 Ecological Risk

2.7 Remedial Action Objectives

2.8 Description of Remedial Alternatives

2.8.1 Alternative 1: No Further Action

2.8.2 Alternative 2: Long Term Monitoring with Alternate Water Supply

2.8.3 Alternative 3: Monitored Natural Attenuation (MNA) with Alternate Water

Supply

2.8.4 Alternative 4: In-Situ Treatment with MNA and Alternate Water Supply . 17

2.9 Summary of Comparative Analysis of Alternatives

2.9.1 Overall Protection of Human Health

2.9.2 Compliance with Applicable or Relevant and Appropriate Requirements .. 19

2.9.3 Long-term Effectiveness

2.9.4 Reduction of Toxicity, Mobility, or Volume

2.9.5 Short-term Effectiveness

2.9.6 Implementability

2.9.7 Cost 20

2.9.8 State Acceptance

2.9.9 Community Acceptance

2.10 Selected Final Remedy

2.10.1 Summary of Rationale for Selected Remedy

2.10.2 Description of Selected Remedy

2.11 Statutory Determination

2.11.1 Protection of Human Health and the Environment

2.11.2 Compliance with ARARs

2.11.3 Cost Effectiveness

2.11.4 Permanent Solution and Alternate Technology

2.11.5 Preference for Treatment as a Principal Element

2.11.6 Five-year Reviews

2.11.7 Significant Changes

3.0 RESPONSIVENESS SUMMARY

3.1 Summary of Comments and Responses

4.0 REFERENCES

LIST OF FIGURES

Figure 1 Regional Location Map Figure 2 Aerial Overview Figure 3 Former Site Layout Figure 4 Groundwater TCE/CIS-1,2-DCE Results Figure 5 Site Conceptual Exposure Model

LIST OF ACRONYMS AND ABBREVIATIONS

AFB – Air Force Base ARAR – Applicable or Relevant and Appropriate Requirement BLRA – Baseline Risk Assessment bgs – below ground surface CENWK – Corps of Engineers, Northwest Division, Kansas City District CERCLA – Comprehensive Environmental Response, Compensation and Liability Act cis-1,2-DCE – cis-1,2-dichloroethene COC – contaminant of concern DD – Decision Document DERP – Defense Environmental Restoration Program DoD – Department of Defense DO – dissolved oxygen EAB – enhanced anaerobic bioremediation EPA – U.S. Environmental Protection Agency FS – Feasibility Study FUDS – Formerly-Used Defense Sites ft – feet GRA – General Response Action GPM – gallon per minute HEW – Health, Education, and Welfare HI – Hazard Index HRC – Hydrogen Release Compound HVAC – Heating, Ventilation, and Air Conditioning ISCO – In-situ chemical oxidation KDHE – Kansas Department of Health and Environment LOB – Launch Operations Building LTM – Long-term Monitoring MCL – Maximum Contaminant Level MNA – Monitored Natural Attenuation NCP – National Oil and Hazardous Substances Pollution Contingency Plan NOFA – No Further Action NWK – Northwestern Division Kansas City O&M – operation and maintenance OCRWD2 - Ottawa County Rural Water District #2 RAO – Remedial Action Objective RfD – Reference Dose RG – remediation goal RI – Remedial Investigation RP – Rocket Propellant SAFB - Schilling Air Force Base SARA – Superfund Amendments and Reauthorization Act SI – Site Inspection SMS - Strategic Missile Squadron TCE – trichloroethene µg/L – microgram per liter USACE – U.S. Army Corps of Engineers UST – underground storage tank VOC – volatile organic compound

Bennington, Kansas

1.0 DECLARATION

1.1 Site Name and Location

FORMER SCHLLING ATLAS F MISSILE SITE S-1

BENNINGTON, OTTAWA COUNTY, KANSAS

FUDS PROJECT NUMBER – B07KS025902

1.2 Statement of Basis and Purpose

This Decision Document (DD) presents the selected remedy for the Former Schilling Atlas F Missile Site S-1 (S-1 Site) in Bennington, Kansas. The selected remedy was chosen in accordance with the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA), as amended by the Superfund Amendments and Reauthorization Act (SARA) and to the extent practicable, the National Oil and Hazardous Substances Pollution Contingency Plan (NCP). This decision document is based on the Administrative Record for this site. The Kansas Department of Health and Environment (KDHE) concurs with the selected remedy.

1.3 Assessment of the Site

The response action selected in this DD is necessary to protect the public health, welfare, and the environment from actual or threatened releases of hazardous substances into the environment.

1.4 Description of the Selected Remedy

The selected alternative for the S-1 Site is “Long-term Monitoring (LTM) with Alternate Water Supply.”

Major components of the selected remedy include the following:

• LTM of the current low-level groundwater contaminant of concern (COC) plume

• A permanent alternate water supply for current on-site residents

• Provision for a wellhead treatment system on the Ottawa County Rural Water

District #2 (OCRWD2) groundwater supply wells in the event of COC concentrations above the U.S. Environmental Protection Agency (EPA) Maximum Contaminant Levels (MCL).

1.5 Statutory Determinations

The selected remedy meets the requirements for remedial actions set forth in CERCLA Section 121, 42 United States Code (USC) Section 9621, because it meets the following requirements: 1) it is protective of human health and the environment; 2) it meets a level or standard of control of the hazardous substances, pollutants or contaminants, which at least attains the legally applicable or relevant and appropriate requirements under Federal and State laws; 3) it is cost-effective; and, 4) it utilizes permanent solutions and technologies to the maximum extent practicable.

CERCLA §121(c) requires a review of remedial actions that result in any hazardous substances, pollutants, or contaminants remaining at a site no less than every five years

Bennington, Kansas after the initiation of such remedial action. The purpose of these reviews is to ensure that human health and the environment continue to be adequately protected by the remedial action being conducted. As long as groundwater contaminants remain that precludes unrestricted use, the requirement for Five-Year Reviews will remain.

1.6 Data Certification Checklist

The following information is included in Section 2, Decision Summary:

• COCs and their respective concentrations

• Human health risks

• Source materials (if any) constituting principal threats and how they will be addressed

• Anticipated future land uses and future beneficial uses of groundwater, assessed in the baseline risk assessment

• Estimated capital cost, total present worth; and the number of years over which the remedy cost estimates are projected

• Key factors that led to remedy selection

1.7 Approval

The Northwestern Division Kansas City (NWK) U.S. Army Corps of Engineers (USACE) District Commander denotes acceptance of the proposed remedy in this DD as the final response action for the S-1 Site by signing the authorizing signature page at the end of this section.

DECISION DOCUMENT

FORMER SCHILLING ATLAS F MISSILE SITE S-1

BENNINGTON, KANSAS

APPROVAL

This Decision Document presents the selected remedy at the Former Schilling Atlas F Missile Site S-1 (S-1 Site) in Bennington, Kansas. The U.S. Army Corps of Engineers is the lead agency under the Defense Environmental Restoration Program (DERP) at the S- 1 Formerly-Used Defense Site and has developed this Decision Document consistent with CERCLA, as amended, and the National Oil and Hazardous Substances Pollution Contingency Plan (NCP). This Decision Document will be incorporated into the larger Administrative Record for the S-1 Site, which is available for public view at the Minneapolis Public Library, 519 Delia Avenue, Minneapolis, Kansas 67467. This document presents a selected remedy with a total present estimated worth of $987,500.

This Decision Document is hereby approved by the undersigned, pursuant to Memorandum DAIM-ZA, dated September 9, 2003, Subject: Policies for Staffing and Approving Decision Documents, and to Engineer Regulation 200-3-1, Formerly Used Defense Sites (FUDS) Program Policy.

APPROVED:

James J. Hearn, SES Date Director, Regional Business Northwestern Division

G0RBMJJH

Typewritten Text 4/20/2017

Bennington, Kansas

2.0 DECISION SUMMARY

This section provides an overview of the site characteristics, alternatives evaluated, and an analysis of those alternatives. It also identifies the selected remedy and explains how the remedy fulfills statutory and regulatory requirements.

2.1 Site Name, Location, and Brief Description

Site Name: Former Schilling Atlas F Missile Site S-1

Location: Bennington, Kansas

FUDS Project Number: B07KS025902

Lead Agency: U.S. Army Corps of Engineers, Kansas City District

State Support Agency: Kansas Department of Health and Environment

Federal Support Agency: U.S. Environmental Protection Agency, Region 7

Site Type: Former U.S. Department of Defense Atlas F Missile Base with Contaminated Groundwater

Site Description: The former Schilling Atlas F Missile Site S-1 is one of 12

Atlas “F” missile sites assigned to the former Schilling Air Force Base (SAFB) in Salina, Kansas. The S-1 Site is located in Ottawa County, Kansas, approximately five miles north-northeast of Bennington, Kansas (see Figure 1). The S-1 Site consists of approximately 18.4 acres in a rectangular area, and originally included a buffer area of an additional 250 acres (see Figure 2). The S-1 Site is under private ownership and the current owner lives on the property.

2.2 Site History and Investigations

2.2.1 Site History

Construction started on the 12 Schilling Atlas F Missile complexes in 1959. Operation of the Schilling S-1 Missile complex was the responsibility of the 550th Strategic Missile Squadron (SMS), which was assigned to the 310th Bombardment Wing at SAFB in April 1961.

The 550th SMS was declared “Operationally Ready” in October of 1962, and was the nation’s first squadron to have hardened underground silo complexes equipped with intercontinental ballistic missiles with a range of 6,400 to 9,000 nautical miles.

The missile fuel, Rocket Propellant-1 (RP-1) (kerosene), was permanently stored in the missile. When first delivered to a launch site, the missile was fueled by a tanker truck or from the RP-1 catchment tank that was located near the surface (see Figure 3). A cooling tower located northeast of the silo supplied chilled water to the diesel-electric generators located within the silo. On November 19, 1964, the Department of Defense (DoD) announced that Atlas F Missile sites would be deactivated. The deactivation plan involved four phases:

• Removal/transportation/storage of missiles

• Preservation of sites/complexes

• Screening and re-utilization

• Disposition of real property and installed equipment

Real property reported to be included in the U.S. General Services Administration disposal included:

• Quonset hut with lighting

• Heating and fuel tanks

• Outer boundary fences

• Chain link fences, posts, and gates

• Street lights and poles

• All site designation signs

Schilling Atlas F Missile Site S-1 was determined to be excess on 25 June 1965.

Between 1966 and 1994, the property was conveyed through various entities. On September 16, 1994, the property was conveyed to the current owner. Currently, the wells are inactive, with one well being obstructed at a relatively shallow depth and the other well obstructed deeper, but still above the water table. Trichloroethene (TCE) contamination, identified at other Atlas Missile sites, has also been identified at Site S-1.

Bennington, Kansas

2.2.2 Previous Investigations and Response Actions

Environmental investigation and remediation activities at the S-1 Site were initiated by USACE in 1988 and have continued to the present. These investigations and remedial activities are listed below:

• Final Engineering Report (1998)

• Preliminary Assessment (2005)

• Preliminary Assessment (2009)

• Response Action (2010)

• Site Inspection (SI) (2011)

• Remedial Investigation (RI) (2013)

• Feasibility Study (FS) (2015)

• Proposed Plan (2016)

The only COCs present at the S-1 Site are TCE and cis-1,2-dichloroethene (cis-1,2-DCE) in the groundwater. The source of groundwater contamination is associated with historical use of the property, specifically the sump and the former sand filter. TCE concentrations exceeding the remediation goal (RG) of 5 micrograms per liter (µg/L), are limited to the missile base property in monitoring wells MW-06 and MW-02. The current TCE plume is shown on Figure 4. TCE was not detected in soil above action-levels.

TCE is the only contaminant posing an unacceptable risk. A degradation product of TCE, cis-1,2-DCE was detected well below its MCL of 70 µg/L.

OCRWD2 performed a wellfield assessment in 2010 in the 40-acre section surrounding the missile base property. The assessment indicated that conditions were favorable for the development of an expansion wellfield in the area of the S-1 Site. In 2013, four Rural Water District Supply Wells were installed by OCRWD2, after reviewing USACE data, and concluding that TCE contamination will not have a significant effect on their wellfield. The rural water supply wells are shown on Figure 4.

2.2.3 Response Action (2010)

In 2010, bottled water was provided to the current on-site resident when the owner’s drinking water well exceeded the MCL for TCE.

2.3 Community Participation

The Proposed Plan for Site wide Groundwater was made available to the public on April 11, 2016, in the Administrative Record. A copy of the Administrative Record, which contains the Proposed Plan and its supporting documentation (RI Reports, FS Report and other related reports), is available at the following location:

Minneapolis Public Library 519 Delia Avenue Minneapolis, Kansas 67467

The notice of availability of the Proposed Plan and date of the public meeting were published on April 7, 2016, in the Minneapolis Messenger. The public comment period was held from April 11, 2016, to May 13, 2016. A public meeting was held on May 11, 2016, at the Minneapolis Public Library. The public was encouraged to participate in the decision-making process by providing comments on the Proposed Plan and attending the public meeting. No comments were received from the public during the public comment period or the public meeting.

2.4 Site Characteristics

2.4.1 Site Geology

Soils in the vicinity of the S-1 Site are dominated by three mapped soil units. These include the Edalgo-Hedville complex, the Wells loam, and the Geary silt loam. The evaluation of soil in the vicinity of the S-1 Site is complicated by the following two issues. First, it can be difficult to distinguish between soil and bedrock within the Dakota Formation outcrop area. This is because of the continental nature of the Dakota deposits and a lack of cementation in much of this section, resulting in bedrock that behaves much like a soil (from an engineering perspective). Second, a considerable portion of the S-1 Site was excavated to a depth of approximately 50 feet (ft) to enable construction of underground facilities for the Atlas Missile site. Within this area, it is expected that the backfill consists of excavated material that was then replaced as engineered fill and bears little resemblance to pre-construction conditions (USACE, 2012).

The Dakota Formation dominates the bedrock geology in the vicinity of the S-1 Site and outcrops throughout the immediate area. Because the Dakota Formation is composed of continental sediments, there is little lateral continuity of individual lithologic units in general, although there is less variability than usual in the area of the site. The primary variation in geology at the site is a general thickening of the fine-grained deposits found at the surface from south to north. Both the coarse-grained and fine-grained deposits contain zones with weak and strongly cemented sediments. The primary cement is iron oxide. The uppermost unit consisted of approximately 5 to 20 feet of interbedded clay, silt, and mudstone. Sandstone of the Dakota Formation was the dominant lithologic unit encountered in the site borings. In those borings that were advanced to the underlying shale, the sandstone varied in thickness from approximately 87 to 117 feet. The sandstone was generally fine-grained and poorly cemented, although there are zones where the sandstone is well cemented with iron oxide. Underlying the Dakota Formation was a grey to black shale, probably representing the Kiowa Formation.

2.4.2 Site Hydrogeology

The Dakota Aquifer is the water-bearing bedrock unit at the S-1 Site. The Dakota overlies the Kiowa Shale, which acts as an aquitard. Clay, silt, siltstone, and mudstone overlie the Dakota Aquifer. Groundwater flows generally from east to west across the Site, with a gradient of approximately 0.002 ft/ft. Based on water-level data taken at MW-10S and MW-10D during the Remedial Investigation (RI), there appears to be no significant vertical flow gradient within the aquifer, although this may change now that the OCRWD2 wellfield is operating. No hydraulic testing was conducted in the field as

Bennington, Kansas part of this RI effort. OCRWD2 has performed hydraulic testing of the Dakota Aquifer and results of this testing indicated specific capacities of the four wells between 13 and 50+ gallons per minute per foot of drawdown. The groundwater consultant for the OCRWD2 has stated that this section of Dakota Aquifer is as good as he has seen, both from the production and water-quality standpoint. The OCRWD2 has indicated that their test-wells can be monitored for water quality in the future.

2.4.3 Nature and Extent of Contamination - Soil

Soil samples were collected during four separate field efforts (1989, 2005, 2011, and 2013), and in each case the TCE and cis-1,2-DCE analytical results were either below detection limits or below both EPA risk-based screening levels and KDHE Tier 2 RSK’s for residential soil and soil-to-groundwater values. It should be noted that the soil analytical procedure utilized for the Site Inspection and RI efforts was chosen for its ability to detect VOCs at very low concentrations.

2.4.4 Nature and Extent of Contamination - Groundwater

The most prevalent COC in groundwater is TCE. The other COC defined in the Feasibility Study (FS) was cis-1,2-DCE. The extent of TCE and cis-1,2-DCE impacts have been delineated both on- and off-site, and in the vertical dimension as well. Figure 4 illustrates the extent of the TCE plume during the February 2013 sampling event, and data from the event indicates that all TCE detections above the MCL occur onsite, centered on the missile silo. A larger plume that is below the TCE MCL extends offsite, slightly to the south, and approximately 900 ft to the west. The relatively low TCE and cis-1,2-DCE concentrations suggest that the source of the contamination was quite small to begin with or is nearly fully depleted.

The shape of the plume conforms, for the most part, with the generally westward flowing groundwater. The only exception to this pattern is the slight bulge to the south of MW-01 resulting from concentrations detected in MW-09. Well MW-01, in addition to supplying the water needs of the onsite residents, is also used to irrigate a vegetable garden just to the east of it, and has been pumped hard in times of drought. Although the effect that pumping MW-01 has had on the area of the plume below the MCL is unknown, the area of the plume greater than the MCL has been reasonably delineated.

Quarterly sampling of MW-01 has been conducted since April 2009, and TCE results have ranged between 1.7 µg/L and 5.7 µg/L. The highest results correlate with seasonal irrigation periods when the well is heavily pumped. The onsite residents have been supplied with bottled water for drinking and cooking purposes following the detection of TCE above its MCL in August 2010 and July/August 2012.

2.4.5 Conceptual Site Model

A conceptual site model (Figure 5) was developed for the S-1 Site. It was used to evaluate the potential pathways that might result in human exposure to contaminants. It also depicts the contaminant sources, pathways, exposure routes, and possible current and future receptors.

2.5 Current and Future Land and Groundwater Use

2.5.1 Current and Future Missile Base Property Use

The S-1 Site property is currently used as a primary residence by the landowner. The landowner resides in a manufactured home situated on a concrete pad to the west of the missile silo. Underground structures associated with the former missile base are used as a storage facility by the current owner. The owner plans to remain on the property for the foreseeable future.

2.5.2 Current and Future Surrounding Land Use

The area in the immediate vicinity of the S-1 Site is sparsely populated, with the nearest resident a half mile to the northwest, with most people living on farms and small ranches.

The land surrounding the S-1 Site property is anticipated to remain agricultural for the foreseeable future.

2.5.3 Current and Future Groundwater Use

Prior to 2010, groundwater at the S-1 Site was used for drinking water by the current resident. Bottled drinking water was provided in 2010, however, the current resident still uses groundwater for showering and lawn and garden use.

OCRWD2 installed four water-supply wells within the quarter section surrounding the S-1 Site. These supply wells produce water from the deep portion of the Dakota Aquifer.

OCRWD2 located these supply wells in the same aquifer impacted by TCE contamination. Two of the supply wells are located hydraulically downgradient of the site (to the west) and have the potential to be impacted by the TCE groundwater plume.

Two additional supply wells are located hydraulically up-gradient of the Site (to the east) and USACE considers it extremely unlikely that these wells will be impacted by the TCE groundwater plume. OCRWD2 typically operates two wells at a time, one upgradient and one downgradient from the Site. The groundwater extracted by the two operating supply wells is combined before entering the OCRWD2 distribution system. The closest water supply well is located approximately 750 ft from the western S-1 Site boundary.

The location of the OCRWD2 supply wells are shown on Figure 4.

2.6 Summary of Site Risks

2.6.1 Human Health Risk

The BLRA human health evaluation was completed to characterize the potential carcinogenic risk and non-carcinogenic health hazard to human receptors exposed to site-related contaminants (TCE and cis-1,2-DCE) under current and hypothetical future land use conditions if no remedial action is performed. Contaminant concentrations in environmental media under the future exposure scenario were assumed to remain the same as those concentrations measured under current conditions.

The only chemicals requiring quantitative evaluation of potential cancer risks were TCE, and cis-1,2-DCE. Using the maximum concentrations of these chemicals detected in groundwater at the S-1 Site, the RI Report presented an excess cancer risk relating to household use (including drinking, inhalation, and dermal exposures for adult-child exposures) of 2.3 in 100,000 (2.3E-05), which is within the CERCLA cancer risk range of 1 in 10,000 to 1 in 1,000,000 (1.0E-04 to 1.0E-06). Nearly all of this risk was related to oral exposures to TCE, in part because the cancer risk calculations included the assumption that TCE may cause cancer via a mutagenic mode of action, resulting in greater cancer risks for infants, children, and sub-adults.

These chemicals were also evaluated for non-cancer toxicity related to household uses of groundwater. For the non-cancer hazard index (HI), child risks are greater because of their greater body water exposure relative to their body size, than adults or a prorated adult-child exposure scenario.

For the same two chemicals (TCE and cis-1,2-DCE), and again using maximum detections in groundwater at the S-1 Site, a cumulative non-cancer hazard index of 2.5 was calculated, which is above the CERCLA threshold of 1, and thereby warrants

Bennington, Kansas consideration for remediation. The majority of the non-cancer toxicity was also related to oral exposures (of a child) to TCE with a hazard quotient of 2.0.

For perspective, it is noted that the maximum concentration of TCE in groundwater from the S-1 Site, used in both the cancer and non-cancer risk calculations, was 16 µg/L, which is also above the MCL of 5 µg/L for public water supplies. TCE is one of two COCs identified for the S-1 Site, the second being cis-1,2-DCE.

2.6.2 Ecological Risk

A brief Screening Level Ecological Risk Assessment was prepared as part of the SI (USACE, 2012). This assessment examined all data collected previously for the S-1 Site and compared available soil, surface water, and sediment data with relevant ecological screening level benchmarks (e.g., ecological soil screening levels). The results of this assessment indicated that none of the chemicals detected in soil, surface water and sediment, that were directly related to former site activities posed a risk to ecological receptors inhabiting the S-1 Site. Based on these results, no further evaluation of the ecological risk is warranted.

2.7 Remedial Action Objectives

The Remedial Action Objectives (RAO) for the S-1 Site focus on groundwater to mitigate future potential exposure risks to residents. RAOs established for the site are:

• Prevent exposure to contamination presenting a cancer risk above the CERCLA risk range of 1 in 10,000 to 1 in 1,000,000 (1.0E-04 to 1.0E-06) or an HI above 1 from potable use of groundwater containing COCs above the Preliminary Remedial Goals.

The RAOs and cleanup levels are based on Applicable or Relevant and Appropriate Requirements (ARAR). The ARARs for the S-1 Site are listed below and discussed in more detail in the Feasibility Study:

• Federal ARARs

- Safe Drinking Water Act – National Drinking Water Regulations and

Implementation (40 CFR 141 Subpart G)

Final Cleanup Levels for the COCs at the S-1 Site are the MCLs, as presented below.

Contaminant of Concern Maximum Contaminant Level trichloroethene (TCE) 5 µg/L cis-1,2-dichloroethene (cis-1,2-DCE) 70 µg/L

The Remedial Design/Remedial Action Work Plan will be used to implement the DD. It will define a monitoring program that will be used to make reliable determinations as to whether the final cleanup levels have been achieved.

Bennington, Kansas

2.8 Description of Remedial Alternatives

The remedial alternatives considered for the S-1 Site are presented in this section based on the results of the FS (USACE, 2015). The four remedial alternatives are as follows:

2.8.1 Alternative 1: No Further Action

The “No Further Action” alternative is required to be considered in the CERCLA process. No remedial activities are included in this alternative, and the alternative is used to establish a baseline for comparison with the other remedial alternatives. Under this alternative, no actions or controls would be taken at the S-1 Site to reduce contaminant concentrations and prevent exposure to groundwater contamination.

2.8.2 Alternative 2: Long Term Monitoring with Alternate Water Supply LTM with an alternate water supply would ensure contamination is detected before it reaches receptor sites and would comply with ARARs. Monitoring has already been implemented. At the S-1 Site, dispersion and dilution are the primary natural attenuation mechanisms at work, and they are very gradual. It is estimated that the groundwater will reach the RAOs in approximately 20 years. Five-year reviews of the remedial action will be conducted as part of this alternative to evaluate the effectiveness and protectiveness of the remedy.

Alternative 2 would provide a permanent alternate water supply not impacted by site-related COCs above MCLs. Bottled water is currently being supplied to the on-site residence.

This alternative also includes an option for the installation and long-term operation of a wellhead treatment system for rural water supply wells located to the west of the S-1 Site.

However, this would only be implemented in the event that the rural water supply becomes impacted with COC concentrations exceeding the MCLs.

2.8.3 Alternative 3: Monitored Natural Attenuation (MNA) with Alternate Water Supply MNA with alternate water supply would also ensure contamination is detected before it reaches receptor sites. It would also comply with ARARs similar to LTM. It would measure and report any natural attenuation that is taking place in the groundwater. This would ensure a better understanding of contaminant fate and transport. MNA is also fairly low cost versus the more active alternative (Alternative 4). As stated for Alternative 2, dispersion and dilution are the primary natural attenuation mechanisms.

The timeframe for remediation is similar to that of Alternative 2. Five-year reviews of the remedial action will be conducted as part of this alternative to evaluate the effectiveness and protectiveness of the remedy.

Alternative 3 would provide a permanent alternate water supply not impacted by site-related COCs above MCLs. Bottled water is currently being supplied to the on-site residence.

Bennington, Kansas

This alternative also includes an option for the installation and long-term operation of a wellhead treatment system for rural water supply wells located to the west of the S-1 Site.

However, this would only be implemented in the event that the rural water becomes impacted with COC concentrations exceeding the MCLs.

2.8.4 Alternative 4: In-Situ Treatment with MNA and Alternate Water Supply In-situ treatment with MNA and alternate water supply would remove groundwater contamination through either enhanced anaerobic bioremediation (EAB) or in-situ chemical oxidation (ISCO) treatment. This would be followed by MNA to ensure remaining contamination is detected before it reaches receptors, which would comply with ARARs. This would be an active remedial alternative, which potentially reduces the remedial timeframe to between 5 (assuming 90% mass source removal) to 10 years (assuming 75% mass source removal), which is below the 20 years estimated for Alternatives 2 and 3. This assumes that the in-situ treatment medium can be properly distributed throughout the contaminated zone. The cost is higher than Alternatives 2 and 3 to implement in the first few years for the injections, but could potentially reduce the remedial timeframe and thus, the overall monitoring costs. Five-year reviews of the remedial action will be conducted as part of this alternative to evaluate the effectiveness and protectiveness of the remedy.

Alternative 4 would provide a permanent alternate water supply not impacted by site-related COCs above MCLs. Bottled water is currently being supplied to the on-Site residence.

This alternative also includes an option for the installation and long-term operation of a wellhead treatment system for rural water supply wells located to the west of the S-1 Site.

However, this would only be implemented in the event that the rural water supply becomes impacted with COC concentrations exceeding the MCLs.

2.9 Summary of Comparative Analysis of Alternatives

The EPA under the NCP has developed nine criteria that balance health, technical, and cost considerations to determine the most appropriate remedial alternative. These criteria are used in the decision-making process to select a remedial action that is protective of human health and the environment, attains ARARs, and is cost effective. The four remedial alternatives described in Section 2.8 have been evaluated and compared using the nine criteria set forth under the NCP. These nine criteria are summarized below:

1. Overall Protection of Human Health and the Environment – Overall protection of human health and the environment addresses whether or not a remedy provides adequate protection and describes how risks posed through each pathway are eliminated, reduced, or controlled through treatment, engineering controls, or institutional controls.

Bennington, Kansas

2. Compliance with ARARs – Compliance with ARARs addresses whether or not a remedy will meet all of the ARARs of other federal and state environmental statutes and requirements or provides grounds for invoking a waiver.

3. Long-term Effectiveness and Permanence – Long-term effectiveness and permanence refers to the ability of a remedy to maintain reliable protection of human health and the environment over time, once cleanup goals have been met.

4. Reduction of Toxicity, Mobility or Volume Through Treatment – Reduction of toxicity, mobility, or volume through treatment is the anticipated ability of the treatment to reduce the toxicity, mobility or volume of the waste and, if possible, to what extent.

5. Short-term Effectiveness – Short-term effectiveness addresses the period of time needed to achieve protection and any adverse impacts on human health and the environment that may be posed during the construction and implementation period until cleanup goals are achieved.

6. Implementability – Implementability is the technical and administrative feasibility of a remedy, including the availability of materials and services needed to implement a particular option.

7. Cost – Cost includes estimated capital, operation, maintenance costs, and net present worth costs.

8. State Acceptance – State acceptance is the evaluation of the technical and administrative issues and concerns the state may have regarding each of the alternatives.

9. Community Acceptance – Community acceptance is based on the evaluation of public comments received on the PP.

The first two criteria are considered Threshold Criteria and each alternative must meet these criteria to receive further consideration. The next five criteria represent the Primary Balancing Criteria on which the alternative analysis is based. The final two criteria are the Modifying Criteria and include State Acceptance and Community Acceptance, which were evaluated following the public comment period.

2.9.1 Overall Protection of Human Health

Alternatives 2, 3, and 4 are protective of human health and the environment. All three alternatives use monitoring as a way to measure the performance of the chosen alternative and to detect contamination before it reaches receptor sites. These alternatives also provide an alternative water supply to the on-site residence, which removes the direct exposure risk from ingestion or showering with contaminated groundwater.

Alternative 1, No Further Action (NOFA), is not protective of human health and the

Bennington, Kansas environment as no action is performed with this alternative. It, therefore, does not meet the Threshold Criteria.

2.9.2 Compliance with Applicable or Relevant and Appropriate

Requirements Alternatives 2, 3, and 4 would comply with ARARs. Alternative 1, NOFA, would not comply with ARARs and thus does not meet the Threshold Criteria. Therefore, NOFA is not evaluated further for Primary Balancing and Modifying Criteria.

2.9.3 Long-term Effectiveness

Alternatives 2 and 3 will have long-term effectiveness in preventing exposure to receptor sites by monitoring the groundwater for contaminants and supplying the impacted on-site residence with an alternate water supply. Alternative 3 would be better in assessing remedy effectiveness than Alternative 2. The additional MNA data, analysis, and reporting required in Alternative 3 would provide a better understanding of the fate and transport of contaminants at the S-1 Site.

In-situ treatments are more suitable for sites with a homogenous, permeable aquifer. The contaminated groundwater at the S-1 Site exists in a fairly homogenous course-grained aquifer. Therefore, Alternative 4 would likely be effective in reducing contaminant concentrations in the aquifer. The substrate for an EAB injection could effectively last up to one year before a reinjection of substrate would be needed. For ISCO, there are chemical oxidation products that could last up to six months before a reinjection is needed. In-situ treatment would be more aggressive, and would reduce the levels of contamination faster than the other alternatives. However, COC concentrations are relatively low and in-situ treatment has the potential to produce treatment residuals that could degrade the overall aquifer quality. Since the aquifer is a source of potable water, the creation of treatment residuals would have to be closely monitored to ensure that nearby potable water wells are not adversely impacted. In-situ treatment of contaminated groundwater could potentially reduce the remedial timeframe over Alternatives 2 and 3.

2.9.4 Reduction of Toxicity, Mobility, or Volume

Alternatives 2 and 3 do not provide active treatment. However, Alternative 3 would determine whether conditions are favorable for natural attenuation processes to reduce, the toxicity, mobility, and volume of contamination in groundwater. These processes could potentially reduce chlorinated solvents to harmless levels or to nonhazardous constituents. Also, the concentration of contaminants would decrease over time due to physical non-destructive means such as dispersion and dilution of contamination in the aquifer.

Alternative 4 is the only remedial alternative that provides active treatment in attempting to reduce the mass, toxicity, mobility, or volume of contamination. These treatments depend on the ability to deliver an injectant, be it an EAB substrate or a chemical oxidant into the aquifer. Once in the aquifer, the substrate from an EAB injection could effectively last up to one year before a reinjection would be needed. For ISCO, there are chemical oxidation products that could last up to six months before a reinjection is

Bennington, Kansas needed. In-situ treatment would be more aggressive, and they would remove more contamination faster than the other alternatives. However, this depends on an injection strategy that could distribute the injected substrate or chemical oxidant in such a way to ensure that the reactant byproducts did not significantly impact the nearby potable water wells. In-situ treatment of contaminated groundwater would also reduce the remedial timeframe over Alternatives 2 and 3.

2.9.5 Short-term Effectiveness

Alternatives 2, 3, and 4 would be effective in protecting the community, worker health, and environment during implementation. These alternatives are immediately effective due to the connection of the on-site residence to an alternate water supply system. The plume is not projected to impact the nearby adjacent rural water wells.

2.9.6 Implementability

Monitoring wells are already in place, however additional wells may be required during remedial design in order to complete the monitoring network. Thus, Alternatives 2 and 3 can easily be implemented. Alternative 4 could be implemented by installing injection wells or utilizing temporary injection wells. However, a strategy would be needed to address the production of treatment residuals to ensure that the aquifer was not significantly degraded.

A rural water service main is located at the northern end of the S-1 Site entry road. One option for providing an alternate water supply under Alternatives 2, 3, and 4 would require extending a service lateral to the on-site residence. Installing a replacement potable water well as an alternate water supply option under Alternatives 2, 3, and 4 would require locating the replacement well on-site and there is potential for the replacement well to impact the configuration of the COC plume. Under Alternative 4, the replacement well could also be impacted by the injected substrate of an EAB injection or the chemical oxidant associated with ISCO.

2.9.7 Cost

The lowest to highest costing alternatives are in this order: Alternative 1, Alternative 2, Alternative 3, and Alternative 4. Additional cost details can be found in the 2015 FS. It should be noted that the FS outlined estimated costs for installation and long-term operation of well-head treatment for the rural water supply wells. Given the low plume concentrations and the distance between the plume and rural water supply wells it is unlikely these wells will become contaminated above MCLs, thus this estimated cost was removed from the overall cost. The estimated costs and the present value cost for each alternative are summarized as follows:

Costs for Remedial Alternatives

Alternative Estimated Cost Present Value Cost

Alternative 1-NOFA $0 $0 Alternative 2 -LTM with Alternate

Water Supply1 $1,132,700 $987,500

Alternative 3-MNA with Alternate Water Supply1 $1,466,100 $1,274,400

Alternative 4 – In-situ Treatment with MNA and Alternate Water Supply1 $1,887,1002 to $2,049,3003 $1,838,9002 to $1,964,7003

Notes:

1Alternate Water Supply costs represent connecting the current land owner to rural water. The cost for connecting to rural water is slightly higher than the cost for installing an alternate water supply well, and therefore, represents a worst case cost scenario.

2Cost represents an assumed mass removal of 90% for the in-situ treatment alternative and represents a shorter post-treatment monitoring period than the 75% mass removal option.

3Cost represents an assumed mass removal of 75% for the in-situ treatment alternative and represents a longer post-treatment monitoring period than the 90% mass removal option.

2.9.8 State Acceptance

The state (KDHE) expressed support for Alternative 2 as the selected remedy in a letter dated February 25, 2016.

2.9.9 Community Acceptance

No comments were received from the public during the Proposed Plan public comment period (April 11, 2016, to May 13, 2016) nor during the public meeting (May 11, 2016).

2.10 Selected Final Remedy

Alternative 2, LTM with Alternate Water Supply, is the selected remedy for the S-1 Site.

KDHE provided a letter dated February 25, 2016 that indicated concurrence with selection of Alternative 2 as the S-1 Site remedy.

2.10.1 Summary of Rationale for Selected Remedy

The preferred alternative satisfies the requirements of CERCLA: (1) protective of human health and the environment; (2) complies with the ARAR; (3) cost-effective; and (4) use permanent solutions and alternative treatment technologies and resource recovery technologies to the maximum extent practicable.

Alternative 2 was selected as it meets the Threshold Criteria and provides an appropriate balance among the Balancing and Modifying Criteria. Of the alternatives that met the Threshold Criteria, Alternative 2 was the most cost effective. Alterative 3 required the sampling of natural attenuation parameters. Current sampling has shown that little natural attenuation is occurring at this site other than the mechanisms of dilution and dispersion meaning these extra perimeters would add no significant benefit to the Site, while costing significantly more than alternative 2. Additionally, due to the relatively low TCE groundwater concentrations the implementation of Alternative 4 would be

Bennington, Kansas difficult and have limited effectiveness at this site. Therefore Alternative 2 is more implementable than Alternative 4.

2.10.2 Description of Selected Remedy

The selected remedy addresses groundwater contamination emanating from the S-1 Site through LTM. The program will likely evolve over time, but will be designed to meet the RAOs. The specific monitoring locations and monitoring program will be defined in the Remedial Design/Remedial Action Work Plan that implements this DD. A permanent alternate water supply, not impacted by site-related COCs above MCLs, will be provided to the on-site residence.

This alternative also includes the option for installation and long-term operation of a wellhead treatment system for rural water supply wells located to the west of the S-1 Site.

However, this would only be implemented in the event that the rural water supply becomes impacted with COC concentrations exceeding the MCLs.

Major components for the selected remedy include the following:

• Establish a LTM plan for monitoring, sampling, data analysis, and reporting of the groundwater contamination

• Provision for a permanent alternate water supply to current on-site residents

• Wellhead treatment system on the rural water supply wells in the event they become impacted by COCs above MCLs

2.11 Statutory Determination

The selected remedy meets the requirements for remedial actions set forth in CERCLA Section 121, 42 USC Section 9621, because: (1) it is protective of human health and the environment; (2) it meets a level or standard of control of the hazardous substances, pollutants or contaminants, which at least attains the legally applicable or relevant and appropriate requirements under federal and state laws; (3) it is cost-effective; and (4) it utilizes permanent solutions and technologies to the maximum extent practicable.

Because this remedy will result in hazardous substances, pollutants or contaminants remaining above levels that allow for unlimited use and unrestricted exposure, a policy five-year review will be conducted within five years after initiation of the remedial action to ensure the remedy is, or will be, protective of human health and the environment. As long as wastes remain that preclude unrestricted use, five-year reviews of the remedial action will be required.

2.11.1 Protection of Human Health and the Environment

The remedy will be protective of human health and environment by conducting LTM, which will continue until groundwater RGs are achieved. It will also provide, as a contingency, an alternate water supply to other area residences if their drinking water supplies become impacted by site-related COCs above the RGs, thus, mitigating their

Bennington, Kansas exposure risks to groundwater contamination. The implementation of LTM will identify contamination above the RGs and enable the identification of any drinking water wells with TCE above the RG.

2.11.2 Compliance with ARARs

The selected remedy will comply with ARARs. Final cleanup levels are presented in the following table:

Contaminant of Concern Final Cleanup

Level Basis for Final Cleanup Level trichloroethene (TCE) 5 µg/L Maximum Contaminant Level* cis-1,2-dichloroethene (cis-1,2-DCE) 70 µg/L Maximum Contaminant Level*

*40 CFR 141

2.11.3 Cost Effectiveness

The selected remedy is considered cost effective because it provides long-term effectiveness and permanence at a reasonable cost as compared to other alternatives.

2.11.4 Permanent Solution and Alternate Technology

The selected remedy provides a permanent solution for remediation using LTM and provided a permanent alternate water supply to the current on-site residence to minimize human exposure to contaminated groundwater.

2.11.5 Preference for Treatment as a Principal Element

The contaminant plume concentrations at the S-1 Site are relatively low, well-defined, and appear to be decreasing. The relatively low TCE concentrations at the S-1 Site limits the effectiveness of in-situ treatment technologies. Thus, the main portion of the selected remedy for the S-1 Site is LTM of the VOC contamination in the groundwater and, as a contingency, alternate water supply will be supplied to the property owner and other area residences as needed. This is the most practical and cost-effective remedy that is protective of human health and the environment.

2.11.6 Five-year Reviews

Five-year reviews are required to ensure that the selected remedy is protective of human health and the environment and the remedy is meeting RAOs. Five-year reviews will be conducted until the final cleanup levels are achieved.

2.11.7 Significant Changes

The Proposed Plan was released for public comment from April 11, 2016, to May 13, 2016, with a public meeting held on May 11, 2016. The Proposed Plan identified Alternative 2 as the Preferred Alternative for remediation. No comments were received from the public during the comment period or at the public meeting. No significant changes to the remedy, as originally identified in the Proposed Plan, were deemed necessary or appropriate.

Bennington, Kansas

3.0 RESPONSIVENESS SUMMARY

This Responsiveness Summary provides responses from USACE to comments received during the public comment period for the Proposed Plan. USACE sponsored a public meeting at the Minneapolis Public Library on May 11, 2016.

3.1 Summary of Comments and Responses

No comments were recorded from the public during the public comment period or during the public meeting.

4.0 REFERENCES

EPA A Guide to Preparing Superfund Proposed Plans, Records of Decision, and Other Remedy Selection Decision Documents, EPA 540-R-98-031, OSWER 9200.1-23P, PB98-963241, July 1999.

USACE Final Site Inspection for Schilling Air Force Base Atlas Missile Facility S-1, United States Army Corps of Engineers, Kansas City District, March 2012.

USACE Final Remedial investigation Report Former Schilling Air Force Base

Atlas F Missile Facility S-1 Bennington, Kansas , United States Army Corps of Engineers, Kansas City District, December 2013.

USACE Final Feasibility Study Report Former…