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®:M PEA Work Plan Martin Metals Finishing Inc. (Former) Stockton, California • Onsite Process-Related Sludge Samples: Onsite samples of sludge collected from inside and beneath the former chromic acid tank contained concentrations of arsenic (3.85 to 75.7 mg/kg), antimony (766 mg/kg) and thallium (237 mg/kg) exceeding DTSC-SLs or RSLs. Total chromium concentrations ranged from 182 to 33,900 mg/kg, exceeding California hazardous waste criteria of 2,500 mg/kg.5 In each exceedance case, samples obtained inside the former chromic acid tank had higher analyte concentrations compared to samples collected beneath the tank. MMF cleaned and removed these materials and associated liquids from the Site in 1990. • Storm Drain Sludge Samples: Samples of sludge collected from the storm drain trench contained concentrations of arsenic (less than 5 mg/kg) and lead (369 to 641 mg/kg) exceeding DTSC-SLs. Lead concentrations were greatest in samples collected from the storm drain line just north of the MMF building. Total chromium concentrations from the trench ranged from 74 to 4,440 mg/kg, exceeding California hazardous waste criteria of 2,500 mg/kg. Concentrations of zinc ranged from 323 mg/kg (storm drain south of MMF building)to 2,650 mg/kg (trench at storm drain discharge from MMF building). • Mormon Slough Samples: Samples of sludge, soil, and sediment from Mormon Slough contained concentrations of arsenic6 (5.3 mg/kg) and lead (545 to 765 mg/kg)exceeding DTSC- SLs. Total chromium concentrations from Mormon Slough ranged from 22.2 to 3,380 mg/kg, exceeding California hazardous waste criteria of 2,500 mg/kg. The greatest concentrations of total chromium and lead were observed directly beneath the old and new storm drain outfalls, although exact historical sampling locations are difficult to discern. Hexavalent chromium,copper, and zinc detected at the Site and in Mormon Slough did not exceed the respective screening criteria. Based on maximum concentrations detected between 1988 and 1989, the worst-case scenario storm drain trench plating-related contaminant concentrations are: 4,444 mg/kg of total chromium, 104 mg/kg of copper, 641 mg/kg of lead, and 2,650 mg/kg of zinc. Based on maximum concentrations detected between 1984 and 1988, the worst-case scenario Mormon Slough plating-related contaminant concentrations are: 3,380 mg/kg of total chromium, 855 mg/kg of copper, 765 mg/kg of lead, and 1,260 mg/kg of zinc. 5 California Code of Regulations Section 66261.24, Characteristic of Toxicity. s The average background concentration of arsenic in the Central Valley is approximately 3.5 mg/kg (University of California [Riverside], 1996). CDIM—Fairgrounds Industrial Park Page 6