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January 17,2023 Rania Zabaneh Page 3 of 4 Reference:Transmittal of Supplemental Site Investigation Work Plan and Response to Comments-South Pointe Property-701, 705,833,&855 West Weber Avenue,Stockton,California below grade from boreholes 32, 36, 38, and 40 (advanced along the southwest border of the property) will be analyzed for pentachlorophenol. Comment #3 - Historical operations at the site included steam boilers, which often used descaling chemicals, such as hexavalent chromium. Any elevated chromium detections from soil sample analyses should be further assessed for hexavalent chromium. Stantec response: Historical data indicate that chromium is not a site-related chemical of concern.The previous investigator (Wallace Kuhl) analyzed 189 samples for chromium. Concentrations ranged from 18 to 68 mg/kg, with an average and mean concentration of 42 mg/kg. Although no human health-based screening level exists for total chromium (among DTSC SLs, USEPA RSLs, and RWQCB ESLs), the concentrations do not exceed the terrestrial habitat ESL of 160 mg/kg, and the mean concentration of 42 mg/kg is below the mean benchmark for background chromium in California soils of 69 mg/kg established by Kearney Foundation of Soil Science (March 1996). Total chromium has been added to the list of 'additional soil COCs' whereby 20% of primary samples will be analyzed for additional COCs, including total chromium. Additionally, soil samples from boreholes 35 and 36, advanced in the vicinity of the historical boiler, will be analyzed for chromium. The samples containing the two highest and the two lowest reported concentrations of total chromium will be additionally analyzed for hexavalent chromium to evaluate the potential presence of hexavalent chromium at the site. Comment #4-According to the GeoTracker website database, "fertilizers" have been identified by the State Water Resources Control Board as a contaminant of concern. Site documents indicate the presence of a former fertilizer mixing area. It should be determined if the on-property wells, MW-34 and MW-35, associated with the adjacent McCormick & Baxter Superfund site, have been assessed for nitrogen and perchlorate. If not, the analysis of the proposed grab groundwater samples should include these contaminants. Stantec response: Existing onsite groundwater monitoring wells MW-34 and MW-35 are associated with the upgradient L&M Operable Unit site. Based on our review of historical data for these wells, nitrogen and perchlorate have not been sampled in these wells. Therefore, grab groundwater samples will be additionally analyzed for these compounds. Comment #5 -Tables 1 and 2 indicate that some soil samples collected from the surface and from very shallow depths are to be analyzed for volatile organic compounds (VOCs). Surface and very shallow soil, exposed to sunlight and atmospheric effects, will contain little to no VOCs. For the proposed sampling event at this site, the soil samples submitted for VOC analysis should be collected from depths no shallower than 3.5 feet below surface. Stantec response: The sampling matrix has been adjusted so that VOC analysis is conducted on samples located 3.5 feet or greater below ground surface. Comment #6 - In contrast to VOCs, soil samples for PCB analysis should be collected from surface soil. Aside from the samples proposed to be collected from the soil pile, which contains mixed material, soil samples for PCB analysis should be collected from surface material, or the material Design with community in mind