SITE INFORMATION AND CORRESPONDENCE

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Letter to Mr.Ross Atkinson • Regional Water Quality Control Board February 20,2002 ` Page 3 of 4 Results of the Investigation Based on the investigation,the following conclusions were indicated: Soils • Petroleum Hydrocarbons. Soil below the pad is slightly impacted with petroleum hydrocarbons (TPH-d and TPH-m) to varying depths of 1.5 to 3.0 feet below the pad. The TPH-d levels are slightly higher(maximum of 25 mg/kg) than the ambient Site soil levels (maximum concentration of 3.5 mg/kg), and the TPH-m levels are lower than ambient soil levels. Soil underlying the pad and stockpile contain low levels of TPH (mainly below the pad) and alkaline pH levels, which may,in part be associated with the leaching of these constituents from the overlying material. The low levels TPH seen in soil may naturally biodegrade after the pad is removed and may not require any further action. The petroleum hydrocarbons in soil are several orders of magnitude lower then the LA-RWQCB Site Assessment and Cleanup Guidelines for Petroleum Sites for TPH-d at 100 mg/kg(diesel) and TPH-m 1,000 mg/kg(motor oil). The low levels of TPHs found in soil may naturally degrade. Extractable petroleum hydrocarbons found in soil are similar in concentration to ambient Site soil. With the exception of toluene and MTBE,no other BTEX compounds were found in the pad and stockpile samples, or the soil underlying these areas. The toluene and MTBE detected do not appear related to the pad materials.A summary of results is provided in Tables 2 through 6. • Iron.In most cases, the total Fe concentrations in soil below the pad and stockpile were similar to that found in ambient Site soil. As such, the Fe detected in the soil at the Site may be associated with native Site conditions in the shallow fine-grained unit. A summary of results is provided in Table 7. Metals. The pad material contained a distribution of metals and the concentrations of these metals are below the TTLC, and ten times the STLC. Soil underlying the pad contained a similar suite of metals at concentrations less than California background levels for metals in soil. Arsenic (As) was found in ambient Site soil at similar concentrations found in soil underlying the pad and may be associated with pre-existing Site conditions. Summaries of the results are provided in Tables 8 and 9. Groundwater Five monitoring wells were installed around the pad in order to evaluate potential impacts from the pad location (Figure 3). Groundwater at the site appears to flow from east to west(Figures 4 and 5). Therefore,MW-4 is upgradient of the pad,MW-3 and MW-5 are to the side;however seasonally may be downgradient,and MW-2 is downgradient. MW-1 is located inside the pad itself with some apparent seasonal mounding in that area. • Petroleum Hydrocarbons. Based on the initial sampling results,groundwater directly below the pad (MW-1) contains petroleum hydrocarbons (TPH-d and TPH-m),Fe, and MTBE, and aromatic hydrocarbons benzene and toluene. The TPH-d may be related to the pad,while the Fe may be related to native soil conditions at Site (Fe-oxide staining was observed at all boring locations,etc.). With the exception of Fe these constituents were not detected in monitoring wells MW-2,MW-3, and MW-4, and appear to be limited in lateral extent. The MTBE and aromatic hydrocarbons benzene and toluene do not appear to be related to the pad materials and may be related to other fill on the facility site. Based on the initial sampling results,groundwater at MW-5 located south of the pad and west of the Stockpile also contains MTBE. This compound appears to be limited in lateral extent to the area of MW-5 and as noted previously, does not appear to be related to the pad materials. Summaries of the results are provided in Tables 10 and 11. • Metals. Total and dissolved metals were detected in groundwater at the Site,including the water supply well as summarized below. Summaries of the results are provided in Tables 12 through 14.