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• No petroleum hydrocarbons were detected in the shallow soil samples collected beneath the <br /> unlined storm water retention pond; <br /> • Hydrocarbon-impacted soil was encountered near the receiving end(south side) of the three <br /> stage clarifier at a depth of five feet below ground surface (bgs). Soil in one sample from <br /> boring B3 was impacted by 350 parts per million(ppm) TPH-gasoline, 10,000 ppm TPH- <br /> diesel,and 0.094 ppm tetrachloroethene(PCE). These constituents were not detected in the <br /> sample collected at a depth of 10 feet in the same boring. TPH-diesel was detected in one <br /> other boring at 1.6 ppm. PCE was detected in one boring at 0.045 ppm. <br /> The concentrations of TPH-gasoline and TPH-diesel detected at 5 feet exceed the California <br /> Regional Water Quality Control Board's typical"action level"of 100 ppm. The 100 ppm <br /> action level is commonly used as guidance for removing impacted soil encountered during <br /> UST removals. <br /> • No detections were reported for the two samples collected adjacent to the lined truck wash <br /> evaporation pond. Samples were not collected beneath the pond to avoid further damage to <br /> the liner. <br /> • Groundwater was not encountered to a depth of approximately 10 feet bgs. <br /> The report concluded that the lateral extent of impacted soil adjacent to the clarifier was not defined <br /> on the south, but was probably limited to an area not more than 10 feet from the receiving end of the <br /> clarifier and not more than ten feet deep. Additional sampling directly beneath the evaporative pond <br /> was recommended to evaluate potential impacts from the wastewater containing PCE that was <br /> discharged to the pond. <br /> I <br /> R:\MN\98JCM.013 9 <br /> DAMES&MOORE <br />