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Kennedy/Jenks/Chilton Attachment to Kennedy/Jenks/Chilton's letter to San Joaquin Local Health District dated 23 March 1989 AMENDED WORK PLAN FOR PRELIMINARY SITE ASSESSMENT CAL-FARM SUPPLY STOCKTON FACILITY The following is the amended work plan for conducting a preliminary site in- vestigation of the Cal-Farm Supply Stockton warehouse facility located at 2040 West Washington Street, Stockton, California. BACKGROUND INFORMATION Table 1 summarizes the results of soil and water analyses performed by Roy F. Weston, Inc. during their previous investigation of the site. These results are presented in their letter of 14 and 15 July 1987. The letters provided to Kennedy/Jenks/Chilton did not describe sample locations or method of collec- tion; thus, it is difficult to accurately interpret the results. The results were somewhat contradictory in that nitrates and Total Petroleum Hydrocarbons were only detected in shallow soils to a depth of three feet below the ground surface. However, analysis of a water sample, WP-2, detected 1350 mg/L of nitrates and 30.4 mg/L of Total Petroleum Hydrocarbons. It is assumed that water sample WP-2 represents a grab sample of groundwater collected either from a soil boring or a reconnaissance probe. Thus on the basis of the water sample these two chemicals may be present in groundwater at this site, although none of the soil samples indicate a source area. The nitrate concentration in the water sample exceeds the 45 mg/L level set by the EPA for Drinking Water Standards and may therefore be a concern to regula- tory agencies. Although there are currently no standards for acceptable levels of Total Petroleum Hydrocarbons in groundwater, the primary concern with petroleum fuels is generally with the gasoline constituents benzene, ethylbenzene, toluene, and xylenes, and not with petroleum hydrocarbons as a class of chemicals. City of Stockton records indicate that a 2000 gallon underground diesel storage tank is present on the site, and the constituents listed above may be present from tank leakage. At the time of our visit, the warehouse appeared empty, although, several labels remained on the storage shelves. The labels referenced the chemical products listed on Table 2. However, as Cal-Farm supply was a registered pesticide dealer, it was decided to take wipe samples from shelves, flooring, and walls in the warehouse area also. PROJECT APPROACH On the basis of the above understanding of site conditions, both groundwater and soil sampling will be conducted. Four groundwater wells will be installed to evaluate the local groundwater gradient. Three of the wells will be located near the property perimeters to provide an indication of possible offsite sources for the nitrate detected in the water sample. The fourth well will be located near the center of the site. Based on the levels of nitrates 1