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SWMU B-20 Investigation Report Addendum Appendix G - Preliminary Evaluation of Remedial Alternatives
Section 1 - Introduction
This preliminary evaluation of remedial alternatives has been developed for the B-20 Former Open Burn/Open Detonation (OB/OD) area at Camp Stanley Storage Activity (CSSA). This evaluation was performed by Parsons Engineering Science, Inc. (Parsons ES) under contract with Armstrong Laboratory/OEB (AL/OEB).
CSSA is located in northwestern Bexar County, approximately 19 miles northwest of downtown San Antonio in south-central Texas. The B-20 site is a 33.5-acre field surrounded by wooded areas in the northeastern portion of CSSA. The area is vegetated with grasses and cedar shrubs. Site features include an inactive bunker, a standpipe used for firing of rocket motors, a junction box, a broken aboveground conduit, and inert scrap metal debris. The site also includes three small arms ammunition disposal areas.
According to a 1950 memorandum on file at CSSA, CSSA started using the B-20 area for demolition activities on March 4, 1946. Approximately 200 tons per year of ammunition were destroyed at the site from 1946 to 1950. The operations at the site included detonation of conventional explosive ordnance and other ordnance items, static firing of one rocket motor (nose down), disposal of scrap metal from detonation activities, and disposal of small arms ammunition.
Additional explosives were detonated in 1984, 1986, and 1987. There was no reported detonation use of the site from 1951 to 1983, in 1985, and after 1987.
Based on the nature of its operation, the B-20 site is considered a thermal treatment unit (40CFR 265 Subpart P) by state regulators. As a hazardous waste treatment unit, B-20 site is regulated under both federal and state regulations. The U.S. Environmental Protection Agency (EPA), Region VI, Resource Conservation and Recovery Act (RCRA) Enforcement, Texas Section, issued a Compliance Order which was sent to CSSA on June 30, 1993. This order required that CSSA immediately cease operation of the unit and prepare a closure plan for the unit in accordance with the applicable regulations.
In accordance with the compliance order, a Remedial Investigation (RI) Report was prepared by Parsons ES under contract with AL/OEB (Parsons ES, 1995). The RI was a broad investigation, the objectives of which were to assess the effect of past waste disposal actions on the environment and to recommend a standard to be applied for site closure. The RI found the following:
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Surface soil (i.e., 0-2 feet) was contaminated with heavy metals including arsenic, barium, cadmium, lead, and mercury at concentrations above background or RRS1 in approximately 30 percent of the site area and above RRS2 in less than 1 percent of the site area. One surface soil sample contained explosive compounds (i.e., nitroaromatics and nitroamines) at concentrations exceeding both the background level (RRS1) and RRS2. |
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Subsurface soil was generally not contaminated with heavy metals or explosive compounds. Only three out of the total 22 subsurface soil samples collected had arsenic or mercury concentrations slightly exceeding the background levels (RRS1). Several samples had arsenic and mercury concentrations exceeding RRS2 for soil-groundwater cross-media protection. However, the second phase of the RI indicated that arsenic and mercury did not leach concentrations greater than maximum contaminant levels (MCLs). |
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Surface water in ponds at the site was not impacted. However, surface water in three craters contained lead and cadmium at concentrations above RRS2 or Texas fresh water criteria (30 TAC 307). No background levels (i.e., RRS1) were available for comparison. |
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Groundwater was not contaminated based on one grab sample taken from a boring. No metals were detected above MCLs. No explosive compounds were detected. |
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Most of the sediment samples collected at the site did not show contamination levels above RRS1 (background) or RRS2. One sediment sample collected from within a crater contained cadmium at a concentration above the background level. |
1.3 - Project Goals and Objectives
The goal of the evaluation is to preliminarily identify and evaluate possible remedial alternatives for the B-20 site. The primary objective of the evaluation is to identify remediation alternatives that would provide cost-effective protection of human health and the environment. This is achieved by performing a preliminary screnning of remedial technologies followed by a detailed analysis of the remedial alternatives. In the preliminary screening, the technologies selected for formulation of alternatives are those applicable to the B-20 site based on three factors:
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the nature and extent of contamination at the site as described in the RI Report (Parsons ES, 1995); |
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the closure options and recommendations proposed by Parsons ES in the RI Report; and |
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the effectiveness of the technology in achieving the Risk Reduction Standard 1 (RRS1) of the Texas Risk Reduction Rules (30 TAC 335 Subchapter S). |
Based on the RI Report, the primary contamination at the site includes heavy metals such as lead and cadmium associated with firing and disposal of ammunition. A very small portion of the site soil is contaminated with explosives residue. Nearly all of the contamination is limited to shallow depths of 0 to 1 foot. The volume of the metals contaminated soil is estimated at 17,885 cubic yards.
The groundwater pathway is not of concern, because no contamination above MCLs was detected. Except in a few bomb explosion craters at the site, surface water is not contaminated either on or off site.
Based on the above, the remedial action objective (RAO) for the B-20 site is to prevent human contact over the long-term with surface soils contaminated with heavy metals and explosive residue.
Per requirements of the Texas Risk Reduction Rules, the remediation for the B-20 site may be conducted under one of the three Risk Reduction Standards (RRS1, RRS2, and RRS3).
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Remediation under RRS1 would require site clean-up to background levels. |
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Remediation under RRS2 would require clean-up to risk-based levels. Deed recordation information must be filed, but post-closure is generally not required. For teh B-20 site, the RRS2 used in the RI Report was based on the assumption of industrial land use. |
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Remediation under RRS3 would allow engineering controls to achieve protection of human health and the environment. The clean-up criteria are then based on site specific information. Post-closure care and deed recordation are required. |
At this time, CSSA prefers RRS1 closure or remediation.