SITE INFORMATION AND CORRESPONDENCE

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Mr. Thomas J. Bois March 13, 1997 Page 3 cleaners located at the Site. 3. The PCE values detected in the deeper soils are consistently higher than the levels detected in shallow soils. The presence of elevated levels of PCE in deeper soils indicates that the PCE contamination has migrated vertically into deeper soils and may have caused groundwater contamination beneath the Site. As a preliminary screening tool to determine the significance of the levels of PCE detected in soils beneath the City, DTSC has developed the PCE cleanup goals (maximum allowable PCE contamination level) in soils, based on the guidance document entitled "Interim Guidance for Remediation of VOC Impacted Site"published by the Los Angeles Regional Water Quality Control Board. Using the equations and mean values of the soil data specified in the guidance document, and an average of 45 feet vadose zone depth beneath the City, DTSC obtained the cleanup goal for PCE in soils at 5 feet bgs is 9.4 ug/1, and in soils at 15 feet is 6.8 ug/l. PCE detected at levels exceeding the corresponding cleanup goals indicate that the levels of PCE detected may pose threats to the groundwater beneath the site and that soil remediation may be necessary. Based on the cleanup goals developed, DTSC concludes that one sample collected in soils at 5 feet bgs (VP 11) has exceeded the PCE cleanup goal at 5 feet bgs of 9.4 ug,/1; and that all three samples collected in soils at 15 feet bgs have exceeded their PCE cleanup goal of 6.8 ug/1. CONCLUSIONS - Soil gas sampling results indicate that PCE was released from past operations conducted by the two former dry cleaners and has caused soil contamination, in areas adjacent to the Building,the sewer laterals, and the sewer lines that serviced the Building. Furthermore,the PCE released to soils may have impacted the groundwater beneath the Site. Only one sample was collected beneath the Building and one sample in areas west of the Building. Therefore, additional soil gas samples need to be collected beneath the Building and in areas west of the Building to determine extent of the PCE contamination beneath the building, and that if PCE had been discharged into the branch line identified by Pinyon. Depth-discrete soil gas sampling should be conducted in the high and medium PCE contaminated areas. Soil gas sampling is necessary to determine (1) the vertical extent of the PCE contamination beneath the contaminated areas; and (2) if soil remediation using vapor extraction system is needed. Site specific soil gas cleanup goals for the PCE detected in soils should be established. Site-