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Phase II Environmental Site Assessment Manteca Multimodal Station Project, Southeast of Moffat Boulevard and Main Street Manteca, California • Lead: The concentration of lead in RB4 (86.5 mg/kg) slightly exceeds the CHHSL for lead in residential soil of 80 mg/kg, but not the commercial/industrial CHHSL for lead of 320 mg/kg. Because the site is proposed for industrial/commercial land uses,the exceedance of the residential CHHSL does not indicate that a health risk to future occupants of the site (commercial/industrial setting) is likely. However, if residential use of the site is planned, further risk assessment of the detected lead in soil in the vicinity of RB4 would be warranted. Zinc: Although the detected the detected concentration of zinc in RB 14 (601 mg/kg) exceeds naturally occurring background levels of zinc found in California soils,the detected concentration of zinc in RB 14 falls well below the SLs and CHHSLs for zinc in soil as follows: • SLs for zinc are 23,000 mg/kg(residential)and 31,000 mg/kg(industrial). • CHHSLs for zinc are for 23,000 mg/kg(residential) and 100,000 mg/kg(industrial). Comparison to TTLCs and STLCs Furthermore, the metal concentrations were also compared to TTLCs and STLCs to determine if the soil would be classified as a hazardous waste. None of the detected levels of metals exceeded their respective TTLCs. However, because the detected concentrations of lead in RB4 and RB 14 at 0.5 feet below grade (86.5 and 68.1 mg/kg,respectively) exceeded 50 mg/kg,these two soil samples were further analyzed for soluble lead by STLC. The results of the STLC soluble lead analyses are as follows: • STLC analyses: 11.5 mg/L soluble lead in RB4 and 1.41 mg/L soluble lead in RB 14. The STLC threshold for soluble lead is 5 mg/L. Because soluble lead in RB4 using the STLC method exceeded the STLC threshold, RB4 was further analyzed for soluble lead by TCLP analysis. The result of the TCLP analysis is as follows: • TCLP analysis: 0.051 mg/L soluble lead in RB4 The TCLP threshold for soluble lead is 5 mg/L. Soluble lead in RB4 using the TCLP method did not exceed the TCLP threshold. Because the soil sample collected from RB4 at 0.5 feet exceeded the STLC threshold of 5 mg/L, if soil is excavated from this area, it would be classified as a California Hazardous Waste, however, because the soil sample did not exceed the TCLP threshold of 5 mg/L, soil excavated from this area would not be classified as a RCRA Hazardous Waste. Conclusions Regarding Metals in Soil Arsenic: The detected concentrations of arsenic in soil samples collected from the site (1.15 to 5.68 mg/kg) fall within the range of normal background concentrations of arsenic found in California soils (0.6 to 11.0 mg/kg), however,the detected concentrations of arsenic exceed the SLs and CHHSLs for arsenic in residential and commercial/industrial soil. Even though the concentrations of arsenic exceed the SLs and CHHSLs, because regulatory agencies typically consider the use of local or regional background concentrations as the threshold concentration, the concentrations of arsenic do not appear to warrant further assessment or remediation of arsenic at the site. Zinc: Even though the concentration of zinc in RB 14 is above the naturally occurring background range of zinc found in California soils, because the elevated zinc concentration in Rincon Consultants 13