ARCHIVED REPORTS_2019-MAY 15 SITE ASSESSMENT REPORT

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15 May 2019 AGE Project No. 14-3002 Page 15 of 17 arsenic range from 0.31 mg/kg (ESL) to 3.0 mg/kg (RSL). The maximum concentration of arsenic in soil was 3.5 mg/kg and the maximum concentration in waste was 13.5 mg/kg. The maximum arsenic concentration detected in soil was the only detection that exceeded the RSL of 3.0 mg/kg, and all concentrations were significantly below the hazardous waste limit of 500 mg/kg (Table 2). Additionally, the DTSC has determined that background concentrations of arsenic in California soils are commonly high, ranging anywhere from 0.6 mg/kg to 11 mg/kg - Background Concentrations of Metals, a Progress Report, Geological Services Unit, Glendale (Arsenic in California Soils). • A total of five soil and waste samples were analyzed for specific metals by the STLC method due to elevated TTLC concentrations. All STLC concentrations were below hazardous waste limits (Table 3). • The only SVOC/PAH detected in soil and waste samples was bis (2-ethylhexyl) phthalate (B18-5 at 2.33 mg/kg); the concentration was significantly below the ESL (Table 4). • PCBs were detected in four soil samples (B30-3, B31-5, B35-5, and B43-5) at concentrations above the ESL of 0.94 mg/kg, but below the hazardous waste limit of 50 mg/kg (Table 4). Concentrations of PCBs in soil above the ESL do not extend to 10 feet bsg, but the lateral extent is undefined (Table 4; Figures 5, 8, and 9). • TPH-d was only detected at concentrations above the ESL in soil samples collected from B40 at 13 and 17 feet bsg. Glass processing waste extends from approximately 5.0 feet to 12.5 feet bsg in boring B40. A potential surface or subsurface release of petroleum hydrocarbons may have migrated through the permeable waste materials to 17 feet bsg. TPH-d impacted-soil is undefined (Table 4; Figures 8 and 9). • Dioxin/Furans were detected in the waste samples at TEQ concentrations ranging from 0.238 pg/g in mixed waste/soil sample B35-14 to 52.2 pg/g in waste sample B36-6. Congener 2,3,7,8-TCDD was not detected above the ESL of 22 pg/g in sample B36-6. Significantly lower concentrations were detected in the soil samples analyzed. The data indicates that the glass processing waste is the source of the dioxin/furan impact. Additionally, dioxin/furans concentrations were substantially below the hazardous waste limit of 1,000,000 pg/l (Table 4; Figures 4, 8, and 9). • Except for the groundwater sample collected from B13, arsenic concentrations in the grab groundwater samples were above the MCL of 0.01 mg/l (0.014 mg/l to 0.094 mg/l). However, the maximum regional background concentration of dissolved arsenic in shallow groundwater in the vicinity of the subject property and in the Central Valley Delta Region is 0.095 mg/l. The background concentration was determined by a study performed at the Rough and Ready Island (RRI) site located in the Delta Region of Stockton, California by Environmental Risk Services Corporation (Draft Central Island Area Ground Water Monitoring 2010 and 2011 Annual Report). Additional information and discussion about the study, other potential sources of dissolved arsenic, and background concentrations of arsenic