ARCHIVED REPORTS XR0005816 - Laserfiche WebLink

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Groundwater flow direction at the site has generally been to the northeast, but the most recent quarterly monitoring round, conducted at high groundwater elevations, shows flow to the south PREVIOUS WORK AT THE SITE The certified analytical laboratory results from soil samples collected from seven strata probe test holes and five monitor wells have partially established the lateral and vertical extent of soil contamination at the site The deepest soil sample from the site that was analyzed by a certified laboratory was collected from 26 feet below ground surface (bgs) at SP-E, located between the two product dispenser islands This sample did not contain TPH-G or BTEX constituents above the laboratory detection limits Soil samples collected from 16 feet bgs and 21 feet bgs at the same test hole showed TPH-G concentrations of 14, 000 and 2, 000 mg/kg respectively These samples contained the highest TPH-G concentrations in soil observed at the site The five monitor wells at the site are screened to a maximum depth of 34 feet bgs at MW2 The San Joaquin County EHD noted in their letter dated October 21, 1997 that historical drought groundwater elevations may have extended to 40 feet bgs in the site vicinity and raised the possibility that significantly high levels of soil contamination may remain below the current top of groundwater at those depths In order to verify if those conditions existed at the site they required that soil and groundwater samples be collected at these historical drought groundwater elevations I COLLECTION OF SOIL AND GROUNDWATER SAMPLES,3126/98 DRILLING AND COLLECTION OF SOIL SAMPLES FROM TH1 Woodward Drilling Company (C57# 710079), under the supervision of a WEGE geologist, drilled one soil boring (TH 1) to a total depth of 40 feet bgs at the site on March 26, 1998 The soil boring was drilled with a mobile rig equipped with 8-inch diameter hollow stem augers TH1 was drilled between the two product dispenser islands and near the previous strataprobe test hole SP-E, which had exhibited the highest levels of soil contamination at depth (see Figure 3) The drilling and sample collection were observed by Mr Mike Inf ima, representing the SCEHD The soil boring was advanced without sample collection to a depth of 25 feet bgs Groundwater level in the boring at the time of first soil sample collection rose to approximately 15 feet bgs Representative soil samples were collected at 5 foot depth intervals beginning at 25 feet bgs in 2"X6" clean brass sleeves with the aid of a 140 pound slide hammer and split spoon sampler that contained three metal sleeves The geologist selected the soil sample contained in the middle sleeve of the split spoon sampler for laboratory analysis to help prevent cross contamination from shallow groundwater that had entered the hollow stem augers Soil samples for laboratory analysis were collected at 25 5, 30 5, 36 0, and 40 5 feet bgs During the drilling and sampling operations the WEGE geologist maintained a log of the materials encountered (see Appendix B) The geologist screened the soil samples from the two sleeves immediately above and below the sample point for Total Volatile Organic (TVO) vapors with a Photo Ionizing Detector (PID) equipped with a 10 2 EV lamp The PID was calibrated immediately prior to sample collection with a 100 ppm standard provided by the manufacturer The TVO vapor concentrations from the four soil sample intervals ranged from a maximum of 64 • ppm at 25-26 5 feet bgs to 8 3 ppm at 30-315 feet bgs (see borehole log, Appendix B) 2 SANCHEZ SRPT 5111198