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File No. 20-3941-01.E01 KLEINFELDER August 20, 1996 The results of the chemical analysis conducted on selected soil samples were much lower than the PID readings. In fact, the results were primarily non-detect except for a concentration of 820 mg/kg TPH-Gas at 21.5 feet in Boring B-24. However, samples obtained at depths of 6 feet and 26.5 feet in the same boring were non-detect for TPH- Gas. One possible explanation for the discrepancy between the PID and the analyses is that the PID screens the soil sample for "vapor phase" contaminants, whereas, the chemical analyses performed screens the soil for hydrocarbon residues which are adsorbed onto the soil particles. In instances where vapor contamination exists and absorbed hydrocarbon contamination does not (e.g., the edge of a volatile hydrocarbon contaminant plume) said conditions may occur. High vapor phase contamination, with an isolated sample of high absorbed concentration at depth, may likely indicate the edge (horizontally) of the contaminant plume. In this scenario, the high PID readings may be indicative of volatilization of the absorbed phase hydrocarbons within the granular soils. 14. Kleinfelder's services were limited in scope. Therefore, we recommend that asbestos/lead paint surveys be conducted prior to any building demolition. Kleinfelder can supply the City of Escalon with a proposal for said services upon request. 15. Because Kleinfelder's scope of services were limited in nature, the City of Escalon must realize that contamination may also exist in areas not investigated. In the event that discolored soil, contaminant odors, or other environmental concerns are encountered during demolition or earthwork, our office should be notified immediately. 16. A copy of this report should be submitted to the County of San Joaquin Public Health Services Department Environmental Health Division and the State of California Regional Water Quality Control Board by the City of Escalon for their review and consideration. 3 t i ,. 20-3941-OLE011MR960163 Page 19 of 21 ©1996, Kleinjelder,Inc.