ARCHIVED REPORTS_ENVIRONMENTAL SITE ASSESSMENT

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from 26 vapor locations (SV-21 was saturated and no vapor or soil matrix samples were collected), and four groundwater grab samples. See Figure 3 for boring locations. The initial proposed scope included only 20 soil vapor locations with no soil matrix samples collected from the soil vapor locations. Six soil vapor locations were added to better evaluate the railroad spur along the western border of the property (SV-11 to SV-14) and to evaluate concrete patches discovered inside the building (SV-24 and SV-25). Soil matrix samples were collected from the soil vapor locations because the vapor samples were deemed to be of"poor quality" due to the high vacuum created by the dense clayey silt that underlies the Site to a depth of at least 50 feet bgs. In addition, shallow soil sampling from soil vapor probe borings along the railroad right-of-way (SV-10 to SV-14) sufficed for the shallow soil sampling included in the proposed scope of work. All down-hole drilling equipment was decontaminated using a three-stage process of a non- phosphate grade detergent (Alconox) mixed with potable water, a potable water rinse and a de- ionized water rinse. After collection of samples, each borehole was backfilled to near-surface with Portland cement grout, then sealed with a plug to match the existing ground cover. D. SOIL VAPOR SAMPLING Soil vapor sampling was conducted to assist in the location of areas of potential environmental concern. Twenty-six locations were located for soil vapor and soil matrix sample collection. Soil vapor sampling was conducted in accordance with the protocols developed by the California Department of Toxic Substances Control(DTSC) and the California Regional Water Quality Control Board Los Angeles Region (Advisory-Active Soil Gas Investigations, January 28, 2003). Soil vapor sampling probes were installed initially at 5 feet bgs but adjusted to 2 feet bgs or less because the native clayey silt created a vacuum such that no soil vapor (at 5 ft) could be collected. Almost all soil vapor samples were collected from what could be termed "sub-slab". Twenty-six soil vapor samples were collected for analysis. Polyethylene tubing was used for the probes. Probe tips were embedded within a minimum one-foot section of sand pack and sealed from surface ambient air by hydrated granular bentonite. At the surface, the tubing was marked with the probe depth and capped. After completion of soil vapor probe installation, 30 minutes of elapsed time was allowed for the soil vapor to reach equilibrium prior to sampling. A purge volume test was conducted in the SV-1 adjacent to the septic system. (See Figure 3 for location.) Isopropanol tracer gas was used as a leak check compound during soil vapor sample extraction and was analyzed and reported. Purge and sample rates were maintained between 100 to 200 milliliters per minute. Samples were collected in stainless steel and glass syringes. Sample containers were decontaminated per DTSC protocol prior to use. Soil vapor samples were analyzed in a certified on-site mobile laboratory (Environmental Support Technologies [EST], ELAP #2772) for VOC target analytes via modified USEPA Method 8260 analysis. Limited Phase II Environmental Site Assessment Report Pinnacle Environmental,Inc. 248 Industrial Avenue,Stockton,CA 95206 Page 12