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� • i <br /> ' December 5, 2005 <br /> NOA Project Number: E05132C <br /> 3.4 Discussion of Results <br /> ' Eight organochlorine pesticide constituents were detected in on-site soils: DDD,DDE, DDT, <br /> alpha-chlordane, dieldrin, endosulfan II, endosulfan sulfate, and toxaphene. However, all eight <br /> chemicals were detected at levels well below the Preliminary Remedial Goals (PRGs) and California <br /> ' Human Health Screening Levels (CHHSLs). All eight constituents were identified in sample S-2, <br /> collected near the domestic well,indicating either that this location may have been used for chemical <br /> mixing or that the soil surface was less disturbed at this location than elsewhere on the site. DDT <br /> and DDE were detected in all nine samples analyzed,indicating widespread use of DDT across the <br /> Site. <br /> ' Except for arsenic,none of the metals detected in the four samples analyzed were present above the <br /> PRGs or CHHSLs. Arsenic was detected in seven of the nine samples analyzed at levels above the <br /> cancer endpoint PRG and CHHSL. It has been NOA's experience,however,that regulators may <br /> ' consider 5 mg/Kg an acceptable level of arsenic in soil, dependent upon background levels of <br /> arsenic in the area. Background levels of arsenic found by the Kearney Foundation Special Report12 <br /> support this choice of a threshold value. Levels of arsenic were found to be below 5 mg/Kg in all <br /> ' nine samples analyzed. <br /> Sample S-10, a composite sample of soil from all four sides of the existing residence,was found to <br /> ' have a concentration of lead well below the PRG and CHHSL. Based on this result,it does not <br /> appear that the soil has been impacted by any potential lead-based paint use on that structure. <br /> ' Based on the non-detect results for diesel and motor oil in sample S-1,it appears that the stain <br /> observed may be old and the constituents may have naturally attenuated. <br /> 4.0 UNDERGROUND STORAGE TANK INVESTIGATION <br /> One boring was advanced to a total depth of ten feet below ground surface (bgs) for the purpose of <br /> ' investigation into possible impacts to soil on the Site from the adjacent former underground storage <br /> tank. <br /> 1 <br /> 12KearneyFoundation of Soil Science,Division of Agriculture and Natural Resources,University of California, <br /> 1996,Background Concentrations of Trace and Major Elements in California Soils. <br /> 7 '004 <br />