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3 Feasibility StudylCorrective Acton Plan The Drake Properly 26485 Thornton Road Thornton Calsfornia November 26 139fi concentration of 510 milligrams per kilogram (mglkg equivalent to parts per million, or ppm) Sample T2b, collected at 9 feet BGS, contained 100 mg/kg of a compound qualified by the laboratory as non-typical TPH-G Sample SW-1, obtained at 4 feet BGS on the excavation sidewall, contained 4 1 mg/kg TPH-G Samples were not analyzed for total petroleum hydrocarbons-as-diesel (TPH-D) or motor oii (Wallace- Kuhl, 1993) Soil samples collected by Wallace-Kuhl during the November 1993 excavation activities did not contain benzene concentrations at or above laboratory detection limits (MDLs) All samples collected did not contain TPH-G, with the exception of sample EX6-7 (28 mg/kg) in addition, samples EX4-7 and EX8-7 were analyzed for TPH-D and motor oil, these compounds were not detected (Wallace-Kuhl, 1994) Soil samples collected by Wallace-Kuhl during drilling and installation of monitoring wells MW-1, MW-2 and MW-3 in November 1993 contained no detectable benzene concentrations Hydrocarbons in the range of TPH-G, but not typical of TPH-G,were detected only in the sample collected at 10-feet BGS from boring MW-2 at 39 mg/kg Samples collected at 10-feet BGS from borings MW-1, MW-2 and MW-3 contained no detectable concentrations of TPH-D or motor old (Wallace-Kuhl, 1994) • Additional soil samples were collected by Groundwater Technology during advancement of soil borings B-1 through B-10 in February 1995 All of the soil samples submitted to the laboratory for analysts were below laboratory reporting limits for benzene, toluene, ethylbenzene and total xylenes (BTEX) and TPH-G with the exception of the 6-foot BGS sample from boring B-3 [ethylbenzene at a concentration of 5 2 micrograms per liter (pg/L, equivalent to parts per billion, or ppb)] Laboratory analysis detected the presence of a matrix interferant in several borings, which chromatograph patterns indicated was a heavier-end fuel such as kerosene or diesel fuel However,TPH-D analysis was not performed on soil or groundwater samples collected because hydrocarbons in this range have historically not been detected on site, all known petroleum hydrocarbon sources had already been removed, and diesel had never been stored or dispensed at the site Based on the data collected during previous environmental investigation, and data collected during January and February 1995, it appears that gasoline-range hydrocarbons in soil are concentrated in the area previously defined by Wallace-Kuhl (Wallace-Kuhl, 1994) However, it appears that other compounds not specified by the TPH-G analysts may be present in soil near sampling locations B-4, B-5, B-8, B-9 and B-10, as well as MW-2 MW-3 and the southern former UST area 24 Results of Groundwater Assessment Table 2 presents analytical results of groundwater samples collected from the excavated UST pit by Wallace-Kuhl during June 1993 excavation activities These samples did not contain detectable levels of benzene, but contained a maximum TPH-G concentration of 2 300 uglL (Wallace-Kuhl, 1993) 0191 PEA APT(Mmc 15) r4� FLUOR DANIEL GTI