ARCHIVED REPORTS_XR0013116 - Laserfiche WebLink

Home Browse Search

4.1.4 Volatile Organic Compounds A total of 11 soil samples were analyzed for VOCs using EPA Method 8260/5035. With the exception of one acetone detection, which could be a potential laboratory contaminant, in the B 1 quadrant (Figure 11), the only detections of VOCs in soil samples were those collected in the A3 quadrant, adjacent to the location of the former gasoline UST. As expected, the detected constituents were those typically associated with residual impacts from USTs, including: BTEX, methyl tertiary butyl ether (MTBE), trimethylbenzenes, butylbenzenes and isopropylbenzenes. Additional constituents detected included 2-butanone, acetone and naphthalene. Concentrations of these constituents were relatively low, with the exception of naphthalene. A3-2A-1 and its duplicate sample A3-2A-1D had elevated concentrations of naphthalene (6,100 ug/kg and 8,800 ug/kg, respectively) as compared to all other soil VOC concentrations. VOC analytical data in soil is presented in Table 16. As a note, soil samples collected for VOC analysis were based on the highest PID headspace readings collected in the field during sampling operations and to provide a representative distribution of VOCs in soil across the Site. The headspace VOC readings are presented in Table 17. 4.1.5 Geotechnical Investigation A total of eight samples were analyzed for specific geotechnical parameters including: moisture content [American Society for Testing and Materials (ASTM) Method D2216], dry bulk density [American Petroleum Institute (API) RP 40 Method], grain density (API RP 40 Method), total porosity (API RP 40 Method], and fraction of organic carbon (Walkley-Black Method). Moisture content ranged from 16.67 to 20.82 percent by weight. Dry bulk density ranged from 1.49 to 1.67 grams per cubic centimeter (g/cc). Grain density ranged from 2.68 to 2.71 g/cc. Total porosity ranged from 38.34 to 44.51 percent bulk volume. Fraction of organic carbon ranged from 0.00073 to 0.00875 grams of carbon content versus grams of total sample. Complete geotechnical analytical data for soil is presented in Table 18. Analytical results for geotechnical samples are provided in Appendix L2. 4.1.6 Background Investigation As part of the RI/SSI, background data was obtained in order to facilitate the HRA and determine baseline COPC concentrations for metals. At total of five background sampling locations, presented in Figure 10, were reviewed by DTSC and approved for sampling. At each location, a sample was collected from a depth of approximate 0.5 feet bgs and analyzed for the following constituents: PAHs using EPA Method 8310, TPH using EPA Method 8015 Modified and Title 22 Metals using EPA Method 6010/7000 Series. Analytical data for background soil samples are provided in Tables 19 through 21 and laboratory analytical reports are available in Appendix L 1. 4.2 SOIL GAS As mentioned in Section 3, soil gas probes were installed to identify the extent of VOCs on-site due to historical MGP related operations and/or residual impacts associated with the former gasoline UST. Sampling procedures and analysis were conducted in accordance with the Cal/EPA Advisory—Active Soil-Gas Investigations (DTSC, 2003) and revisions to the Advisory that were being promulgated between the RI and SSI events at the Site. The following section provides an overview of VOC findings in on-site soil gas. PARSONS 34 FINAL RI REPORT-FORMER TRACY MGP APRIL 2010