SITE INFORMATION AND CORRESPONDENCE

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Ms. Karen McLaughlin 03 March 2016 City of Manteca Page 2 0f 4 Former Police Firing Range assessed by trenching with a backhoe and screening the trench walls with the XRF and metal detection equipment. Four samples were analyzed by EPA Method 6010B/7471A for the CAM 17 metals, six samples for the soluble threshold limit concentration (STLC) for lead by waste extraction test (WET), and thirteen samples for the toxicity characteristic leaching procedure (TCLP) for lead to characterize site soil as either a Resource Conservation Recovery Act (RCRA) waste or a California Hazardous waste, or as nonhazardous. This information was derived to determine the masses of each lead waste category that will be subjected to different treatment and disposal methods for proper i disposition. The correlation between XRF readings, in mg/kg, and total lead analytical data was statistically determined as were the correlations between total lead data and the WET and TCLP data. The correlation coefficient between the XRF data and total lead analytical data was 0.809, which seems reasonably good, but GCI noted that the equation of correlation between the two variables underestimated the total lead concentrations when such concentrations exceeded 2,000 mg/kg. GCI determined the correlation coefficient between total lead and WET lead to be 0.915, and between total lead and TCLP lead to be 0.879; leading to the determination that total lead concentrations exceeding 50 mg/kg correlate to STLC concentrations that exceed 5 milligrams per liter (mg/1), which would define a California hazardous waste, and total lead concentrations exceeding 135 mg/kg correlate with TCLP concentrations exceeding 5 mg/l, defining a RCRA waste. GCI mapped the area of lead-impacted soil inferred to exceed the TCLP lead concentration of 5 mg/I (RCRA waste) based on total lead concentrations exceeding 135 mg/kg and/or XRF lead concentrations exceeding 50 mg/kg; soil inferred to exceed the STLC concentration of 5 mg/I (California hazardous waste) appears to have been mapped primarily on the density of XRF concentrations ranging between 50 mg/kg and 135 mg/kg and with sparse analytical total lead data. The resulting distribution of California hazardous waste soil appears to follow a natural decline with increasing distance from the highly impacted RCRA waste area. Soil mapped as not impacted to either waste classification is characterized by XRF concentrations and total lead concentrations less than 50 mg/kg. Soil on the firing range floor was found to be impacted by excessive lead concentrations to a depth of one foot and to extend as much as three feet horizontally into the berm. Using these findings, GCI calculated that approximately 490 cubic yards (785 tons) of impacted soil would be profiled as California hazardous, and 660 cubic yards (1,050 tons) of soil would be profiled as RCRC hazardous waste. GCI found no significant lead impact to groundwater. The EHD concurs with GCI's estimate of the volume of soil impacted to RCRA hazardous waste characteristic as the data sets utilized for the statistical analysis are fairly robust and the area can virtually be mapped solely on the total lead data. The EHD is of the opinion that the estimated distribution, volume and mass of soil impacted to the California hazardous waste classification is less certain than that for the RCRA waste as a correlation of XRF data to the total lead concentration data in the concentration range of interest (50 to 135 mg/kg) was not demonstrated and there is only one analytical total lead concentration data