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AOC 37 Soil Gas Survey Results

December 1999

Introduction

A soil gas survey was performed at Area of Concern (AOC) 37 located in the north-central portion of Camp Stanley Storage Activity (CSSA). This report contains a summary of the analytical results from the AOC 37 survey. A detailed description of the methodology is included behind the Soil Gas Surveys tab in Volume 3-1. This work was performed in conjunction with adjacent soil gas surveys at AOCs 41 and 66, and the entire survey area encompassed approximately 25 acres just north of Well 16 in the outer cantonment area.

Implementation

Sampling locations at AOC 37 are shown on Figure AOC37-1. Because of the limited size of the site (less than 0.5 acres), only 6 samples were collected at AOC 37. All samples were collected and analyzed for BTEX compounds (benzene, toluene, ethylbenzene, m/p/o-xylenes), tetrachloroethene (PCE), trichloroethene (TCE), and cis-1,2-dichloroethene (DCE) on December 15, 1999 by Parsons ES personnel. The soil gas samples were analyzed on-site at a field laboratory established within the CSSA Environmental Office. Work plan protocols presented Section 1.1.3 behind the Field Sampling Plan tab in Volume 1-4 were used to plan the soil gas survey. Specific procedures for the December 1999 surveys are presented behind the Soil Gas Surveys tab in Volume 3-1. 

Soil Gas Survey Results

The distribution, concentrations, and contaminant associations are discussed below for the compounds detected in 6 soil gas samples collected at AOC 37. The sampling depths varied from 2 feet to 6 feet, and were usually determined by the refusal of the probe advancement. The average soil thickness was 4.2 feet. PCE was the only target compound detected in soil gas samples from AOC 37. PCE was detected at location AOC37-6 with a concentration of 0.01 mg/L, or close to the detection limit. The singular occurrence of PCE at AOC37 appears to be related to a PCE detection reported at AOC66. Otherwise, the data suggests that a source of VOCs was not present in the area. The soil gas survey data for AOC 37 is presented in Table AOC37-1 and illustrated in Figure AOC37-2. The gas chromatograms from the field analyses are presented in Appendix A.

The results of this soil gas survey combined with results from previous soil gas surveys performed on the land adjacent to AOC 37 suggest that the PCE plume terminates as it approaches the southern boundary of the north pasture. The PCE results from all soil gas surveys conducted by Parsons ES at CSSA were consolidated and the concentration gradients are illustrated in Figure AOC37-3.