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w CLEARWATER <br /> G R O U P, I N C <br /> 4 1.0 INTRODUCTION <br /> This report presents' the results of groundwater monitoring performed by <br /> Clearwater Group, Inc (Clearwater) on March 8, 1995 at 1002 North Yosemite Street <br /> in Stockton, California (Figure 1). The tasks performed during this phase of work <br /> ' included groundwater gauging, well purging and groundwater sample collection <br /> 2.0 BACKGROUND <br /> Records indicate that the subject site was utilized as a gasoline service station from <br /> 1961 to 1978, and that the underground fuel storage tanks were removed in 1980 <br /> An environmental assessment conducted in 1990 by ,Evax Technologies, Inc <br /> consisted of a limited soil gas survey The purpose of this investigation was to <br /> identify any potential subsurface contamination in the vicinity of the three former <br /> underground storage tanks. The soil gas survey indicated the possible presence of <br /> petroleum hydrocarbons in the soil <br /> ' Following this initial discovery, GeoAudit was retained to conduct ` a more <br /> comprehensive subsurface investigation The investigation consisted of drilling six <br /> soil borings to depths from between 29 5 and 36 5 feet below ground surface (bgs), <br /> with soilsamples collected at five foot riritervals , Lab analysis of soil samples <br /> collected during thus'phase ,of`the project indicated the presence of low levels of <br /> ethylbenzene in the soil 'around,the western'edge of the property, Subsequently, San <br /> oar um County Public Health Services,Environmental Health Division. (PHS/EHD)' <br /> directed 'the property owner to install monitoring well's and to ,bein quarterly ' <br /> sampling <br /> d <br /> In accordance with, PHS/EHD directives, GeoAudit completed installation an , <br /> sampling of three nrionitoring wells m October 1993 The highest concentrations of <br /> volatiles 'were found in ground ,collected from MW-2, located near the ; <br /> ' former Ftank area 'A detailed presentation of the preliminary stage of,site assessment <br /> can' be''found in GeoAudit's November 1993 ""Monitoring Well Installation and <br /> Quarterly Report".',' <br /> r' , �I I I l <br /> li ]I I ,',I f l Vi l ' I I I' ` I I ' I ki Ii <br /> As part' of an effort to `evaluate the extent) of h dr'ocarbgn distribution` in <br /> y <br /> groundwater, Clearwater`installed MW-4 and MW-5 on August 31,r 1994, ,MW-5 was <br /> 3{ installed approximately 50 feet downgradient from MVII,-2:', E At the request 1of the�I <br /> ' PHS/EHD, MW-4 was installed in order to evaluate' the possibility of periodic <br /> groundwater flow direction fluctuation. Water level and surveying data com sled Il <br /> over the course of the last year, has indicated) a fairiconsistent northwestern 1 <br /> ' <br /> r groundwater flow direction ' , I <br /> ll' <br /> �J [ <br /> I 3 F r t <br /> I I I I <br /> I��firI I I I I J4'+ 9'I Ill'ippit f I <br /> 1II�,i "4l 21{1/J <br /> J <br /> D-101 41 " I Ill I <br /> i <br /> I r <br /> fr <br /> IlA ' {l, <br /> �I�`'� I �I _ dl �'f�f� EV ^I ll I �IiFM{w i Sp�If1� del �irtlldl it � tt "a �I I r r���wVnlr ,II IlV l�I�ul I��' � <br /> I ' qrt <br />