ARCHIVED REPORTS_2019-MAY 15 SITE ASSESSMENT REPORT

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15 May 2019 AGE Project No. 14-3002 Page 16 of 17 were provided in the Clean Closure Plan, dated 20 June 2018 prepared for 17100 Murphy Parkway, Lathrop. Furthermore, arsenic has historically been detected above the MCL in shallow and deep groundwater throughout the City of Lathrop. The Louise Avenue Water Treatment Facility (LAWTF) was constructed in 2007- 2008 primarily to remove arsenic from the city’s drinking water. • It’s AGE’s opinion that dissolved arsenic detected in shallow grab groundwater samples collected from the subject property are more likely attributed to a combination of naturally occurring background concentrations and industrial activities throughout the City of Lathrop than to historical site activities at the subject property. Additionally, the subject property is within the City of Lathrop services area and drinking water will be provided by the City. And under the current law, a public water well systems cannot be installed at the subject property for any use or reason. Therefore, water will be provided by the City of Lathrop, as primacy for public water in the area is held under the authority of the City of Lathrop. • A low concentration of dioxin/furan was detected in the grab groundwater sample collected from B35 in Waste Cell No. 2 (2.10 pg/l). The concentration was significantly below the MCL of 30 pg/l for dioxin/furans and the congener 2,3,7,8- TCDD was not detected in the sample. The glass processing waste is likely the source of the dissolved dioxin/furans (Table 6). • Elevated concentrations of nitrates and TDS are likely attributed to historical and current industrial activities being performed at surrounding properties, and possibly to the historical agricultural use of the subject property. However, shallow groundwater is not used for drinking water and as discussed above, water will be provided by the City of Lathrop, as primacy for public water in the area is held under the authority of the City of Lathrop; and under the current law, a public water well systems cannot be installed at the subject property for any use or reason. • Shallow groundwater beneath the site is not impacted with dissolved SVOCs, PAHs, PCBs, TPH or VOCs (Table 6). • The historical use of the property as a power plant and solid waste disposal facility likely contributed to the PCB, TPH and dioxin/furan impact encountered at the site However, with the exception of one detection of dioxin/furan, all analytes were below their respective environmental screening levels and below hazardous waste limits. Additionally, the dioxin/furan ESL exceedance did not include the congener 2,3,7,8-TCDD. 7.0. RECOMMENDATIONS Based upon data reviewed and collected at the site, AGE recommends: • Defining the limits of the PCB- and TPH-impacted soil in the former power plant area.