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January 17,2023 Rania Zabaneh Page 2 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 Other SLs include screening levels that may be appropriate for some chemicals and/or some media are the Environmental Screening Levels (ESLs) published by San Francisco Bay Regional Water Quality Control Board (see example in item #3 below). Stantec response: Tables included in Appendix D of the Work Plan include selected screening levels for analytes. Comment #3 -Screening levels for petroleum hydrocarbon mixtures reported as TPH: DTSC often uses the ESLs for the evaluation of petroleum data reported as gasoline, diesel and/or motor oil range TPH. If you plan on having your petroleum results reported as "TPH", please make sure that the samples for petroleum hydrocarbon mixtures are not treated with silica gel cleanup. Silica gel cleanup (SGC) is not part of a normal sample prep for petroleum hydrocarbon analysis. Most of the petroleum present in water is in the form of hydrocarbon oxidation products (HOPS) and SGC removes the HOPS. Petroleum hydrocarbons themselves are not very soluble, especially the larger ones. Also, there is no SGC-step in the TPH method (USEPA method 80156). Detailed explanations of analysis methods and screening levels for petroleum mixtures can be found in the ESLs User's Guide, in the ITRC TPH Risk guidance and in DTSC's HHRA Note 12. In this context I would like to note that on page 3 of the Supplemental Work Plan under "Further Assessment of groundwater conditions is not necessary ..." the second paragraph starts with "Low concentrations of motor oil in groundwater ...". Since motor oil-range hydrocarbons are not soluble in water, this statement raises questions. Therefore, collecting current groundwater (GW) water samples and making sure they are properly analyzed may help to better understand the level of GW contamination. Stantec response: Grab groundwater samples will be analyzed for total petroleum hydrocarbons (TPH) as gasoline, diesel, and motor oil, and results compared to ESLs established by the San Francisco Bay RWQCB. Comments from Peter Cooke, DTSC geologist. Comment #1 - Polychlorinated biphenyls (PCBs) were detected at sampling location PL-9 at 3' bgs (66 mg/kg). This location should be further characterized during the upcoming Supplemental Work Plan field work. Stantec response: Boreholes 27a, 27b, and 27c have been added to further investigate historical detections of PCBs at location PL-9. Comment #2 - Pentachlorophenol has been released from the adjacent McCormick & Baxter Superfund site. It should be determined if the soil of the South Pointe property could have been impacted. If so, the analysis of the proposed soil samples should include pentachlorophenol. Stantec response: The McCormick & Baxter creosoting site is located at 1214 Washington Street West, across Interstate 5 and approximately 2,000 feet southwest of the project site. Based on this distance, it seems unlikely that airborne contaminants such as pentachlorophenol would have reached the site at appreciable concentrations. Soil samples from ground surface and 4 feet Design with community in mind