ARCHIVED REPORTS XR0001860 - Laserfiche WebLink

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Mr Kenneth Earnest Ultramar Inc May 21, 1996 Page 2 A soil vapor extraction system was in operation at the site between July 1991 and February 1996 The system was shut down in February 1996, due to low influent soil vapor concentrations As of February 1996, 85,402 pounds (13,863 gallons) of vapor equivalent gasoline was extracted from the soil underling the site The soil vapor extraction system's EVAX catalytic oxidizer was removed from the site in March 1996 Ultramar is currently evaluating the results presented in this report, along with alternative remediation technologies to assess if further site remediation is warranted Soil Boring Results Between March 20 and 27, 1996, six soil borings were drilled to a depth of 71 5 feet below surface grade (bsg) Soil samples were collected from each boring at approximately 5 foot intervals for classification and possible laboratory analysis A copy of the drilling permit issued by the San Joaquin County Division of Environmental Health (County) is included in Enclosure B Locations of the borings are shown in Figure 2 Soils encountered during drilling generally consisted of weakly to well indurated silty sand and silt with sand from the surface to depths of approximately 20 to 30 feet, poorly graded sand and/or hard silt from 30 to 45 feet, hard clay with sand from approximately 45 to 55 feet, poorly graded sand from approximately 55 to 60 feet, clayey sand/sandy clay from 60 to 65 feet, and silty sand and/or • poorly graded sand from 65 feet to the bottom of the boring (71 5 feet) Ground water was first encountered in each boring at a depth of approximately 67 feet bsg Boring logs are included in Enclosure C While drilling SB-5, a void space was encountered at the location shown in Figure 2 The void space was encountered at a depth of approximately four feet bsg, and extended to a total depth of approximately ten feet bsg The top of the void space was covered with a wood and soil mixture from three to four feet bsg The extent of the void to the north, east, and west could not be assessed The southerly edge of the void was visible and appeared to be a smooth, vertical concrete wall The County was notified of the discovery and made a site visit to inspect the void space Upon further inspection, Delta and County personnel concluded that the void was most likely an old mechanics pit With the County's approval, the void space was backfilled with approximately six cubic yards of controlled density fill The backfilling operations were conducted under the supervision of Delta and County personnel No permits were required by the County for backfilling Soil Sam le Anal cal Results Selected soil samples collected from each of the borings were submitted for laboratory analysis of benzene, toluene, ethylbenzene, xylenes (BTEX), total petroleum hydrocarbons (TPH) as gasoline, and TPH as diesel using the methods described in Enclosure A The soil samples submitted for analysis were selected based on their photoionization detector (PID) readings and depth correlation to soil samples collected during previous investigations Soil sample analytical results are summarized in Table 1, and copies of the analytical laboratory reports are presented in Enclosure D . Benzene was only reported in the soil samples collected from SB-1 at a depth of 61 5 feet bsg and SB-6 at depths of 24 and 66 5 feet bsg, concentrations ranged from 0 82 (SB-1) to 18 (SB-6) milligrams per kilogram (mg/kg) Total petroleum hydrocarbons (TPH) as gasoline and as diesel were reported in soil samples collected from each of the soil borings Detectable concentrations of