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June 2 1. 2000 Job Number: LG00-173 Page 4 A DWR water well driller's report for a well located near the site was reviewed at the San Joaquin County Environmental Health Division office. The drillers log indicated that generally the shallow water-bearing deposits in the area are most likely combosed of several thin layers of sand bounded by relatively thin and thick confining clay layers. (Please note: DWR Water Well Driller Reports are confidential and cannot be copied or disbursed to the public). Ground water samples were collected from the agricultural well at 22111 North Lower Sacramento Road on May 30, 2000, submitted to the FGL Environmental Laboratory, and tested for the presence of dibromochloropropane (DBCP) and Nitrate (NO3) per County requirements. The test results indicated that DBCP was found to be 0.03 ug/I and nitrate as NO3 found to be 2.1 mg/I (or 0.47 mg/1-N). Both tests indicated the ground water sample was below the maximum contaminate level set by the United States Environmental Protection Agency of 0.2ug/I for DBCP and 45 mg/L as NO3(or 10 mg/L-N). The presents of nitrates and DBCP are not uncommon in shallow ground-water aquifers in San Joaquin County and other parts of the Central Valley. Nitrate in ground water originates from agricultural fertilizers, livestock waste, and untreated septic tank waste. Nitrate is mobile and often accumulates in the shallow ground-water zones. In the early 1900's, natural levels of nitrate in ground water were measured in 43 wells throughout the Sacramento Valley by Bryan.' It was thought that ground water at that time was close to "natural"conditions. Based on the work by Bryan it is estimated that under natural conditions,groundwater concentration of nitrate is no more then about 3 mg/1-NO3 (about 0.67 mg/L-N). Areas having 5.5 mg/1-NO3 (about 1.2 mg/L-N) or more are those in which nitrate concentrations may be increasing.3 DBCP is a nematocide and soil fumigant for vegetables, and grapes. It is thought to cause health problems consisting of kidney damage, liver damage, and cancer. The use of DBCP was discontinued in 1979. VI. GEOLOGY, SOILS, AND PERCOLATION TEST The surficial geology of the site is reported to be the Pleistocene age(11,000 years to about 2 million years old)Modesto Formation. This formation consists of arkosic alluvium .� 'Bryan K, 1923, Geology and ground-water resources of Sacramento Valley of California:U.S. Geological Survey Water-Supply Paper 495,285p. r, 3 Hull,L.C., 1984,Geochemistry of Ground Water in the Sacramento Valley,California:U.S. Geological Survey Professional Paper 1401-B. pEMtO i 1 4 O