ARCHIVED REPORTS XR0011704 - Laserfiche WebLink

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Previous Work Previous work on the subject property consisted of an investigation performed by GHH Engineering, Inc. in January of 1989. The investigation included soil sampling in the area of the former underground tank and product tine. Results of the investigation indicated the presence of small concentrations of toluene, xylene and ethyl benzene in the soils, as stated in our Work Plan for Subsurface Soils Evaluation dated December 3, 1990. FINDINGS Soil Conditions Soils encountered during our drilling of borings 81 and B2 included a gravelly sand extending from the surface to a depth of 12 feet. The gravelly sand was determined to be the backfill material for the former tank excavation. A 1.5400t-thick concrete slab was discovered directly beneath the backfill. The slab was part of an underground tank anchor apparatus. The anchor was used to counter-react buoyant effects of the underground tank caused by a high ground water table. Underlying the slab is a silty sand, which grades to a clean sand at the ground water table. Borings 61 and B2 were terminated at ground water, which was encountered at a � depth of 15 feet. Borings B3 and B4 revealed a gravel-clay-silt mixture extending four to five feet below a 2-Inch- thick asphalt surfacing. The gravel-clay-silt mixture contained foreign debris including asphalt �..- pieces and broken plastic piping. Samples were obtained from an underlying clayey silt layer. Laboratory Testing Laboratory test results revealed non-detectable concentrations of BTX&E in all samples. TPH as diesel was detected in the soil sample from boring 84 only (130 mg/kg). All soil samples, however, indicated motor oil concentrations ranging from 1.1 mg/kg to 440 mg/kg. The water sample from boring B1 revealed a motor oil concentration of 900 mg/L. Complete laboratory test results and chain-of-custody documents are appended. CONCLUSIONS Laboratory testing and field observations indicate that subsurface soils on the subject property are impacted with petroleum hydrocarbons. The diesel contamination detected in Boring B4 is possibly a result of a leak in the former product line. The motor oil concentrations detected in all samples, including the ground water sample, is probably the result of asphalt debris present in the fill material used to elevate the building pad. ' RECOMMENDATIONS i Based on our findings and conversations with the San Joaquin County Environmental Health Division, we recommend that a site-specific workplan for a proper site characterization be prepared so that an appropriate, cost-effective remedial treatment can be implemented for the property. 1