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SWMU O-1 Interim/Stabilization Measures and Partial Facility Closure Report

Section 1 - Introduction

On May 5, 1999 an Administrative Consent Order was issued to Camp Stanley Storage Activity (CSSA) pursuant to §3008(h) of the Solid Waste Disposal Act, as amended by the Resource Conservation and Recovery Act (RCRA), and further amended by the Hazardous and Solid Waste Amendments of 1984.

In accordance with the Interim/Stabilization Measures (IM) requirements of the Consent Order, this IM report has been prepared to document the environmental condition and site partial facility closure requirements of Solid Waste Management Unit (SWMU) O-1. The work documented in this report fulfills the requirements of paragraph C.2(d) of the 3008(h) Order Scope of Work for implementation of Interim/Stabilization Measures which specifies that “Respondent shall expedite the closure of the oxidation pond under state closure requirements. In order to expedite closure of the oxidation pond, previous investigation data and results shall be used.”

In order to expedite closure of the oxidation pond, (SWMU O-1), CSSA is seeking a partial facility closure of the surface soil zone located within the boundaries of SWMU O-1. The underlying limestone and the groundwater are not included as part of this partial facility closure. The limestone/groundwater zone will be addressed when a final remedy solution is available for these operable units.

This specific IM was performed under the U.S. Air Force Air Mobility Command (AMC) Prime Contract F11623-94-D0024, Delivery Order RL74. The Air Force Center for Environmental Excellence (AFCEE) provided technical oversight for the delivery order. Based upon the AMC pre-defined Scope of Work (SOW) dated September 30, 1998, a set of work plans to govern the fieldwork were established. These include:

For this IM report, Section 1 provides the site-specific background, criteria for judging the functioning of the IM, and a closure standard for SWMU O-1. Section 2 summarizes the IM actions, field actions, and partial facility closure evaluation. Section 3 presents the conclusions regarding the IM actions. Finally, Section 4 contains the references. The content of this report meets both the U.S. Environmental Protection Agency (USEPA) requirements specified in paragraph C.3(b) of the 3008(h) Order Scope of Work for IM implementation, and the Texas Natural Resource Conservation Commission (TNRCC) requirements for closure reports specified in 30 Texas Administrative Code (TAC) 335.553.

1.1 - Background

Generalized facts regarding the history and environmental setting of CSSA can be found in the CSSA Environmental Encyclopedia (Volume 1-1, Background Information Report). In that report, data regarding the geology, hydrology, and physiography are available for reference.

Background information regarding the location, size, and known historical use of the site is also included in the Environmental Encyclopedia (Volume 1-2, SWMU O-1). This volume includes a Chronology of Actions and an IM Work Plan Addendum for SWMU O-1.

Results for both geophysical and soil gas surveys are also included as part of the Environmental Encyclopedia (Volume 1-2, SWMU O-1). As part of a groundwater source assessment, “Groundwater and Associated Source Characterization Report” (Parsons ES, 1996a), an area-wide study was conducted to define potential areas which may have released contaminants to groundwater. The presence of chlorinated hydrocarbons in soil gas implicated SWMU O-1 as a potential source area for the contamination detected in Well 16.

1.2 - Site Description

SWMU O-1, also referred to as the oxidation pond, was reportedly constructed in 1975 (Parsons ES, 1993b). Reportedly, the pond measured 42 feet by 60 feet with a depth of 2.5 feet and was lined with vinyl plastic. Wastes from Building 90-1 (spillage, change-out, etc.) were trucked to the unit from an exterior 1,000-gallon settling tank. In 1982, an estimated 24,000 gallons were contained in the oxidation pond.

The Texas Department of Health conducted sampling efforts of the oxidation pond material (liquid and sludge) in April 1984. The samples were delivered to Brooks Air Force Base (AFB) for analysis. Results from this sampling event indicated that the material was non-hazardous for metal concentrations; however, no data were available to assess the tetrachloroethene (PCE) concentrations.

In 1985, Red River Army Depot (RRAD) prepared a “recommended procedure” for closure of SWMU O-1 (RRAD, 1985). During Fall of 1985, bulldozing of the oxidation pond resulted in the destruction of the pond liner prior to being filled in with surrounding soils. No records are available to indicate whether or not disposal of the sludge or residue contained in the oxidation pond occurred before destruction of the liner. A chronology of activities at SWMU O-1 is provided in Volume 1-2, SWMU O-1.

1.3 - Previous Investigations

Several investigations were conducted to assess groundwater contamination detected in Well 16 located north of SWMU O-1. Most of these investigations focused on identifying possible source areas that could have contributed to contamination of the groundwater. Results of those previous studies are discussed in the Environmental Encyclopedia (Volume 1-2, SWMU O-1), and in “Groundwater and Associated Source Characterization Report” (Parsons ES, 1996a). A general overview is presented below.

Chlorinated hydrocarbons were first detected in Well 16 in 1991 at concentrations above drinking water standards, prompting investigations of the possible contaminant source areas. Source characterization began with surface geophysical surveys performed during January through March 1995 at seven potential source areas. A large anomalous area was detected at SWMU O-1 during the electromagnetic and ground penetrating radar surveys.

Based on this geophysical data, four soil borings were drilled within SWMU O-1 to investigate the portions of each area exhibiting apparent geophysical anomalies. Results of analytical data gathered from the investigation indicated levels of PCE, chromium, and cadmium above background level concentrations.

A subsequent soil gas survey of SWMU O-1 during Summer and Fall 1995 identified PCE concentrations as high as 80,000 parts per billion volume (ppbv). Depths of sampling were 1.0 to 3.5 feet below ground surface (bgs). Distribution of PCE in soil gas at the oxidation pond in 1995 is shown in Figure SWMU O-1-1. Additional surface soil sampling was accomplished during subsequent periods following 1995.

A treatability study was performed on SWMU O-1 soils to test the efficacy of electrokinetic remediation of contaminants identified in SWMU O-1 surface soils. Test methods employed and results of the treatability study are included in the Environmental Encyclopedia (Volume 4-2, Electrokinetic Treatability Study). In general, use of the electrokinetic remedial technology was found not to be cost effective due to the large buffering capacity of the soils.

1.4 - Interim Measures and Closure Standard Criteria

The TNRCC promulgated the Texas Risk Reduction Program (TRRP) under Chapter 30 of the TAC, Section 350 (30 TAC §350) in September 1999. The effective date of the TRRP rule is May 1, 2000. However, in the interim, the regulated community has the right to choose whether their response action will be reviewed under the TRRP or under the former Risk Reduction Rule (RRR) (30 TAC §335). CSSA submitted a letter of closure notification to the TNRCC on February 20, 1996 stating it intended to close the site under 30 TAC, §335.554, risk reduction standard (RRS) 1. Under the TRRP, CSSA still maintains the same decision of closing SWMU O-1 under RRS1.

The partial facility closure of SWMU O-1 includes only the surface soil zone located within the defined boundary of SWMU O-1. The underlying limestone and groundwater are considered as a separate operable unit that will be addressed when a final remedy is specified for the underlying limestone/groundwater zone.

The IM and partial facility closure criteria are specified in 30 TAC §335, Subchapter S, and the approved Work Plan developed for the IM corrective actions. The IM actions included removal of all contaminated soils and placement of a clay cap to mitigate, control, and minimize spread of contamination into the underlying groundwater unit.

Closure criteria for the surface unit of SWMU O-1 is RRS1 specified in 30 TAC 339.§554. Removal of contaminated material to background levels or practical quantitation limits (PQLs) is specified in 30 TAC §335.554. There are no requirements for post closure care or operation and maintenance (O&M) or deed recordation. However, as part of the IM effort, O&M is required for the clay cap until a final solution is applied. Therefore, this report is intended to provide details of the IM corrective action which results in SWMU O-1 meeting the requirements of a partial facility closure to RRS1.

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