COMPLIANCE INFO_10/7/24 SITE CHARACTERIAZTION RPT

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Site Characterization Report Former Riverbank City Dump City of Riverbank Waste Water Treatment Plant Riverbank, California Page 3 LABORATORY ANALYTICAL RESULTS The three collected soil samples at each boring location were composited at the laboratory at a ratio of 3:1 and the composite samples were analyzed for pH by EPA Method 9040, CAM 17 Metals by EPA Method 6010, total petroleum hydrocarbons (TPH, carbon chain) by EPA Method 8015M, semi volatile organic compounds (SVOCS) by EPA Method 8270, polychlorinated biphenyls (PCBs) by EPA Method 8082, and polycyclic aromatic hydrocarbons (PAHs). The samples collected from the hand augered borings were analyzed discretely for the analyses summarized above. In addition, the discrete sample DP-15-10 was analyzed for dioxins and furans by EPA Method 8290 due to burned material noted in boring DP-15 from approximately 5 to 10 feet bgs, and the discrete sample DP-16-10 was analyzed for asbestos due to insulation-like debris noted from approximately 5 to 10 feet bgs. Analytical results are summarized in Table 1, Appendix B. The final laboratory analytical reports, including chain-of-custody documentation, are included in Appendix F. DISCUSSION OF RESULTS Analytical results of detected analytes in soil samples were compared to remediation screening levels (SLs) for industrial/commercial settings, as established by California Department of Toxic Substances Control (DTSC). Results were compared to SLs established in DTSC’s Human Health Risk Assessment (HHRA) Note 2, April 17, 2017, for dioxins/furans and to DTSC’s HHRA Note 3, June 2020 update, for other potential constituents of concern (PCOCs). The DTSC SLs are concentrations for selected chemicals with a target threshold of a 1E-06 risk for carcinogens, and a hazard quotient of one for noncarcinogens, using updated exposure and toxicity factors. PCOCs for which no DTSC SLs were developed were compared to SLs established by the U.S. EPA Region 9 (May 2024). The detected concentrations of arsenic were compared to the Interim Guidance for Sampling Agricultural Properties (Third Revision), August 7, 2008, (the Guidance) established by the DTSC, California Environmental Protection Agency (Cal-EPA). Comparison of results indicated: • CAM 17 metals: No metals were detected at concentrations exceeding their respective SLs for commercial/industrial settings. • Fuel Fingerprint Organics (TPH): No SLs for TPH are included in HHRA Note 3. Relatively low level concentrations of TPH in the diesel and/or oil range were detected in the composite samples from DP-11, DP-12, DP-13, DP-14, DP-17, DP-18, DP-19, DP-21, and hand auger boring HA-8. • PCBs: No PCBs were detected in any sample except for the composite from DP-13. The detected concentration of Aroclor-1260 was below the SL for that analyte. • PAHs: No PAHs were detected in any sample except for the composite from DP-1. The detected concentrations of PAHs constituents were all below their respective SLs, when established in HHRA Note 3. • SVOCs: No SVOCs were detected in any sample except for the composite from DP-1. The detected concentrations of SVOCs constituents were all below their respective SLs, when established in HHRA Note 3. • Dioxins/Furans: the sample collected from DP-15-10 contained several detectable dioxins/furans PCOCs. The most toxic compound in the chemical group of dioxins/furans is 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD). Since seven other dioxins and ten furans are considered to have 2,3,7,8-TCDD-like toxicity, toxic equivalency values (TEQs) are used to estimate toxicity from a mixture of these compounds. The industrial DTSC SLs for dioxins is 220 picograms per gram (pgkg). It should be noted that the DTSC SLs for outdoor workers who may come in contact with soil is 22 pg/g. Since the TEQ for dioxins was calculated at 28.6, workers that