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CVYATC 1117 Lone Palm Avenue, Suite B Modesto, CA 95351 www.atc-enviro.com 209.579.2221 ti ASSOC IATES I N C . Fax 209.579.2225 May 4, 2004 54.14981.0001 MAY 0 6 2004 Ms. Margaret Lagario ENVIRONMENT HEALTH Joaquin County, Environmental Health Division ENV' 304 E. Weber Street, Third FIoor PERMIT/SERVICES Stockton, California 95202 Subject: Groundwater Monitoring Report - First Quarter 2004, N & S Irrigation Property, 215 West Main Street, Ripon, California Dear Ms. Lagorio: This report presents the results of quarterly groundwater monitoring and sampling performed on March 2, 2004 by ATC Associates Inc. (ATC) at the site located at 215 West Main Street, Ripon, California (Figure 1). Monitoring was performed to determine groundwater flow direction and the hydraulic gradient in the uppermost aquifer. Sampling was performed to monitor dissolved petroleum hydrocarbon concentrations in the groundwater at the site. BACKGROUND INFORMATION In March 1990, one 1,500-gallon unleaded gasoline underground storage tank (UST), one unleaded gasoline UST of unknown size, and associated piping and dispensing equipment were removed and transported off-site. Laboratory analyses of soil samples collected from beneath the farmer 1,500-gallon UST location indicated the presence of detectable concentrations of total petroleum hydrocarbons. Discoloration of the soil and a petroleum hydrocarbon odor were noted in the field. After the tanks were removed, the areas of the former tanks were backfilled. On November 14, 1997, a geologist from ATC supervised the advancement of two soil borings to 30 feet below ground surface (bgs). Analytical results of soil samples indicated the presence of petroleum hydrocarbons. One groundwater sample was collected from each boring at the depth groundwater was first encountered, approximately 30 feet bgs. Groundwater samples indicated the presence of petroleum hydrocarbons. Results are summarized in ATC's Summary Report of Subsurface Investigation, dated January 14, 1998. On July 13, 1998, a geologist from ATC supervised the advancement of four soil borings to 26 to 31 feet bgs. Analytical results of soil samples indicated the presence of petroleum hydrocarbons. One groundwater sample was collected from each boring at the depth groundwater was first encountered. Groundwater samples indicated the presence of petroleum hydrocarbons. Results are summarized in ATC's Summary Report of Additional Subsurface Investigation, dated September 9, 1998. On February 18, 1999, a geologist from ATC supervised the installation of three groundwater monitoring wells from 39 to 41 feet bgs. Soil borings MW 1, MW2, and MW3 were completed as two-inch monitoring wells. One soil sample from each boring was collected and after the ENVIRONMENTAL, GEOTECHNICAL AND MATERIALS PROFESSIONALS saenvironmental1149811Reportsll QR-04.doc ]