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1117 Lone Palm Avenue <br /> Suite B <br /> Modesto CA 95351 <br /> 209 579 2221 <br /> Fax 209 579 2225 <br /> A S S O C I A T E S I N C <br /> HPCEIVI=17 <br /> July 9, 1999 <br /> 13099 JUL 12 1999 <br /> ENVIRONMENTAL HEALTi--� <br /> PERMIT/SERVICES <br /> Mr Harlin Knoll <br /> San Joaquin County Public Health Services <br /> Environmental Health Division <br /> 304 E Weber Street, Tlurd Floor <br /> Stockton, California 95202 <br /> Subject Monitoring Report Second Quarter 1999, Ripon Unified School District, 304 <br /> North Acacia Avenue, Ripon, California <br /> i <br /> Dear Mr Knoll <br /> This report presents the results of quarterly groundwater monitonng and sampling performed on <br /> June 1, 1999 by ATC Associates Inc at the site located at 304 North Acacia Avenue, Ripon, <br /> California (Figure 1) Monitoring was performed to determine the groundwater flow direction <br /> and the hydraulic gradient in the uppermost aquifer Sampling was performed to monitor the <br /> distribution of petroleum hydrocarbons in groundwater at the site <br /> BACKGROUND <br /> In February 1991, one 500-gallon underground storage tank (UST) of unknown fuel type was <br /> removed, in August 1991, one 550-gallon unleaded gasoline UST was removed, in October 1991, <br /> 47 feet of single wall piping was removed, and, in December 1991, one 7,500-gallon unleaded <br /> gasoline UST was removed Laboratory analysis of soil samples collected from beneath the <br /> former USTs and piping locations indicated the presence of detectable concentrations of total <br /> petroleum hydrocarbons Discoloration of soil and petroleum hydrocarbon odors were noted in <br /> the field After the tanks were removed, the areas of the former tanks were backfilled with the <br /> stockpiled material <br /> On April 23, 1998, a geologist from ATC Associates supervised the advancement of six soil <br /> borings, SBI through SBb, to 21 feet below ground surface (bgs) A site plan showing soil <br /> boring locations is included as Figure 2 Soil samples were collected at five-foot intervals and <br /> grab groundwater samples were collected from each boring Samples were analyzed for <br /> petroleum hydrocarbons and elevated concentrations of petroleum hydrocarbons were detected in <br /> soil and groundwater samples The April 1998 subsurface investigation results are detailed in <br /> ATC's Summary Report of Subsurface Investigation, dated June 17, 1998 <br /> W 1130991quartly\2gr-1999 doc 1 <br />