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PRELIMINARY ASSESSMENT SUMMARY DIAMOND WALNUT GROWERS, INC; COUNTY OF SAN JOAQUIN April 1993 L Site Information A. Location and Description of Site - 1050 Diamond Street; Stockton; APN 155- 320-19; located northeast of the intersection of Charter Way and South Diamond Street in Stockton. The facility has been operating as a walnut processing plant since the 1950'x. Five underground concrete vaults are located north and east of the main processing building and formerly contained refrigerants used in the plant cooling systems. Vaults 1, 5, (1,200 gallon capacity) and 6 (500 gallon capacity) were installed between 1974 and 1976, and contained 1,2-Propanediol (aka: Niagara No-Frost KY Liquid, PM-6534) . Vaults 7 and 8 (3,000 and 5,000 gallon capacities, respectively) were constructed with poured concrete and line fiberglass and asphalt, and stored calcium chloride and sodium dichromate solution. Four underground storage tanks storing petroleum products (gasoline and diesel) have been removed at the site over the last 6 years. Soil sample test results from each of the tank excavations indicated no petroleum hydrocarbon contamination. One 550 gallon diesel tank was removed in 1986; one 125 gallon gasoline tank was removed in 1987; and two tanks were removed in 1991, 1-5,000 gallon unleaded gasoline and 1-500 gallon leaded gasoline. B. Description of Hazardous Wastes and Substances - Proovlene glycol (1,2-Propanediol, CAS#57-55-6) ; a colorless liquid, practically odorless. An eye and human skin irritant; slightly toxic by ingestion and skin contact. Sodium dichromate (Cr207.2Na) ; irritant, caustic to skin, poison by ingestion; chromate salts are considered to be carcinogens. C. Threat to Public Health and Environment- Primary drinking water standards known as Maximum Contaminant Level (MCL) have been established through the State of California, Department of Health Services (DHS) , in Title 22 of the California Code of Regulations (CCR) , Division 4, chapter 15, and the U. S. Environmental Protection Agency (EPA) , under the Safe Drinking Water Act. It. Site Status A. Status of Site Activity Several phases of subsurface soil and groundwater investigation have been conducted at the site since December 1988. The Central Valley Regional Water Quality Control Board maintained the lead regulatory authority until December 1990, at which point Public Health Services, Environmental Health Division (PHS/EHD) placed the site into a local oversight program to provide expeditious regulatory guidance.