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colm PEA Work Plan Martin Metals Finishing Inc. (Former) Stockton, California 2.5.2 Sampling Activities and Results Analytical results for historical samples of various media at the Site are presented in Table 1. Historical sampling events completed at the Site to date are summarized below. • On July 25, 1984, a previous consultant for the Site (Kleinfelder & Associates [Kleinfelder]) collected three sediment samples beneath the storm drain outfall to Mormon Slough. • Between 1987 and 1989, CA DHS conducted the following events: o The July 30, 1987 sampling of water and sludge from the chromic acid tank area inside the MMF building; o The November 2, 1988 sampling of sludge from the storm drain trench and Mormon Slough; o The December 2, 1988 sampling of soil, water, sludge, and solids from the storm drain and Mormon Slough; o The December 7, 1988 sampling of sludge in Mormon Slough; and o The February 22, 1989 sampling of liquid, sludge, and solids from the MMF building and storm drain trench. Samples were analyzed for metals including chromium, lead, and zinc. Several samples were analyzed for other Title 22 metals and soluble metals. CDIM compared historical analytical results for sludge and soil samples to DTSC Human Health Risk Assessment(HHRA) Commercial/Industrial Screening Levels (DTSC-SLs; DTSC, 2020) for soils. If no DTSC-SL was established for a constituent, the USEPA Industrial Soil Regional Screening Levels (RSLs; USEPA, 2022) for soils were used. A summary of sampling results is presented by medium and/or location below. • Solid Samples: Soil samples collected from onsite filter cake material (1989), the storm drain (1988), and a paint chip found near the old storm drain outfall (1988)contained concentrations of total chromium ranging from 63.1 to 13,800 milligrams per kilogram (mg/kg), copper ranging from 29.5 to 47.4 mg/kg, and lead ranging from 12.5 to 12,200 mg/kg. Results of solid samples were not compared to screening criteria, as the materials have been removed from the Site and/or are not representative of sludge or soil concentrations. • Liquid Samples: Liquid or water samples collected from onsite processing equipment, the floor of the MMF building, and standing water in Mormon Slough were collected between 1987 and 1989. Concentrations of total chromium ranged from less than 0.02 mg/kg (Mormon slough near old storm drain outfall) to 24,600 mg/kg (drippings from extrusions). Copper and lead were only detected in the sample collected from the extrusion drippings at concentrations of 52.7 mg/kg and 2,000 mg/kg, respectively. Concentrations of zinc ranged from less than 0.04 mg/kg (water on building floor) to 5,360 mg/kg (drippings from extrusions). Results of liquid samples were not compared to screening criteria, as the liquids have been removed from the Site and/or are not representative of surface water or groundwater concentrations. CDIM—Fairgrounds Industrial Park Page 5