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 2 SOIL SAMPLING ACTIVITIES Luke Castle (CA Professional Geologist number 9945) observed drilling and collected samples at the subject property on August 19 through August 21, 2024. All drilling was conducted by Confluence Technical Services, Inc. (Confluence), a California licensed drilling contractor (C57-1035255), under Permit #AP2400851 issued by EHD (Appendix F). A total of twenty-two (22) direct push borings were advanced to a depth of 15 feet below ground surface (bgs), designated DP-1 though DP-22. Eight (8) hand auger borings were advanced to 4 feet bgs designated HA-1 though HA-8. Soil samples were collected at depths of approximately 5 feet bgs, 10 feet bgs, and 15 feet bgs from the direct push borings. Soil samples were collected at 4 feet bgs from the hand auger borings. Figures showing the proposed and actual boring locations are included in Appendix A. The direct push borings were advanced using a Geoprobe 6600 direct push drilling rig equipped with a 2-inch diameter conical bit, which was driven using a hydraulic hammer. Continuous core soil samples were collected from the borings with a 2.25-inch outside diameter (O.D.), 5-foot long core barrel fitted with a clean, single use, polyethylene liner. During the sampling, the core barrel was driven in 5-foot intervals. The sample liner was extracted from the core barrel and used for geological logging and field observations. Geological logs were prepared containing field observations including soil type and the presence of staining or odor (Appendix E). At each direct push boring location, soil samples collected for laboratory analyses were cut from the liners. The liners were sealed at the ends with Teflon® sheeting and capped. Upon completion of drilling and sampling, all borings were grouted to the ground surface with neat cement grout. A stainless-steel hand auger was used to advance each hand auger boring to the sampling depth of 4 feet bgs. Due to the unconsolidated nature of the material at HA-2 and HA-4, a Shop-Vac was utilized to remove the upper 2 feet of soil. The sampled soil was collected into brass tubes, sealed at the ends with Teflon® sheeting and plastic caps. Prior to and after advancing boring each boring location. dedicated sampling equipment was decontaminated by washing the equipment in a non-phosphate detergent and tap-water mix and triple rinsed (repeated twice). At areas of suspected contamination, decontaminated procedures included an additional tap-rinse and nitric acid rinse with a double rinse in de-ionized water. Nitric acid rinse water was contained in a 5-gallon bucket and kept onsite pending laboratory analytical results. Collected soil samples were immediately labeled and placed in chilled coolers. The samples were transported under chain-of-custody procedures to Enthalpy Analytical (ELAP 1338) on a daily basis. Sample depths were labeled on the sample identification in feet bgs. For example, sample DP-1-10 was collected at soil boring DP-1 from a depth of 10 feet bgs. The soil cuttings were placed in a 5-gallon bucket and transferred to a 55-gallon drum. The drum remained onsite pending laboratory analytical results. FIELD OBSERVATIONS Apparent fill material was observed at each sampling location, comprised of light to dark brown fine soils, gravel, and sand. Dark staining was observed at DP-3 between approximately 4 and 10 feet bgs containing organic (sewage) odors. Concrete debris was noted in borings DP-8 (~2 to 5 feet bgs), DP-10 (~3 feet bgs), DP-19 (~5 to 10 feet bgs), and DP-22 (~10 to 15 feet bgs). Broken glass debris was observed in borings DP-13 (~5 to 10 feet bgs), DP-14 (~10 to 15 feet bgs), and DP-18 (near surface to 15 feet bgs). More varied debris was noted in borings DP-15 (burned material near surface to 10 feet bgs, plastic trash ~5 to 10 feet bgs, concrete ~5 to 15 feet bgs) and DP-16 (concrete and brick debris near surface to 15 feet bgs). Daily field summaries and field boring logs are included in Appendix E.