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V � <br />f <br />UT:3 <br />A S S O C I A T E$ I N G <br />August 19, 2002 <br />54 13099 0001 <br />Mr Harlin Knoll <br />San Joaquin County Public Health Services <br />Environmental Health Division <br />304 E Weber Street, Third Floor <br />Stockton, California 95202 <br />AI.1�1 <br />i i r 4i �''—ter if <br />� lF <br />1 #M 1: 30 <br />1117 Lone Palm Ave, Suite B <br />Modesto, California 95351 <br />www atc-envlro com <br />209 579 2221 <br />Fax 209 579 2225 <br />Subject Monitoring Report Third Quarter 2002, Ripon Unified School District, 304 North <br />Acacia Avenue, Ripon, California <br />Dear Mr Knoll <br />This report presents the results of quarterly groundwater monitoring and sampling performed on <br />July 3, 2002 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 <br />1991, 47 feet of single wall piping was removed, and, in December 1991, one 7,500 -gallon <br />unleaded gasoline UST was removed Laboratory analysis of soil samples collected from <br />beneath the former USTs and piping locations indicated the presence of detectable concentrations <br />of total petroleum hydrocarbons Discoloration of soil and petroleum hydrocarbon odors was <br />noted in the field After the tanks were removed, the areas of the former tanks were backfilled <br />with the stockpiled material <br />On April 23, 1998, a geologist from ATC Associates supervised the advancement of six soil <br />borings, SB 1 through S136, to 21 feet below ground surface (bgs) Soil samples were collected at <br />five-foot intervals and grab groundwater samples were collected from each boring Samples <br />were analyzed for petroleum hydrocarbons and elevated concentrations of petroleum <br />hydrocarbons were detected in soil and groundwater samples The April 1998 subsurface <br />investigation results are detailed in ATC's Summary Report of Subsurface Investigation, dated <br />June 17, 1998 <br />w 1130991quar11yl3gr-2002 doc <br />1 <br />ENVIRONMENTAL, GEOTECHNICAL AND MATERIALS PROFESSIONALS <br />