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CLEARWATER <br /> G R o f U P, I IAF C , <br /> 1.0 INTRODUCTION <br /> ' This report presents` the results of groundwater monitoring performed by <br /> Clearwater Group, Inc (Clearwater) on December 28, 1994 and January 4, 1995 at 1002 <br /> North Yosemite Street in Stockton, California (Figure 1). The tasks performed <br /> ' during this phase of work included groundwater gauging, well purging and <br /> groundwater sample collection <br /> ' h 2.0 BACKGROUND <br /> Records indicate that the subject site was utilized as a gasoline service station from <br /> r1961 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 `soil samples collected at five foot intervals Lab analysis of soil samples <br /> collected during this phase of the project indicated the presence of low Ilevels of <br /> r E ethylbenzene in the soil around .the western edge of"the property "Subsequently, San <br /> 'Joaquin' County Public Health Servxces Environmental Health`Division (PHS/EHD) <br /> ' directed the, property owner to install monitoring wells and `to begin quarterly <br /> sampling <br /> E , ' <br /> II <br /> ' In' accordance with PHS/EHD directives, GeoAudit completed installation and , <br /> sampling of three,monitoring wells in October 1993' The highest concentrations of <br /> { volatiles were Mound in groundwater samples collected from MW-2, located near the , <br /> former tank area Aldetailed-presentation of the preliminary stage of site assessment <br /> can bet found' in GeoAudit's Novembetr 1993 `"Monitoring,Well 'Installation and <br /> E ! ' � ' <br /> Quarterly Report" t E " <br /> (, "'� t I ' 4 , I I I � l ' y' r , ,! it <br /> I; As part ofF 'an' leffor`t to 'evaluate the' extent of 'hydrocarbon distribution in <br /> groundwater, ,Clearwater installed MW-4 and MW-5 on August 31<, 1994 I MW-5 was <br /> installed approximately 50 feet downgradient from MW-2 At the request Iof the <br /> PHS/EHD, MW-4 was installed in order to evaluate the possibility of periodic I <br /> groundwater flow direction fluctuation , Water level and surveying data,compiled <br /> 1r ', <br /> over the course of the last year has indicated a fairly consistent northwestern „ <br /> II 'groundwater flow direc, tion <br /> , <br /> I + © 101'I4Q94 �',i1 r <br /> J4!"'I IiFebruary <br /> ebruary II+1I5,,,,1n9r 9rf5 <br /> Ij!f '6Ir 1{11 1 1.1 1 1 ' 1� <br /> u; <br /> ! i <br />, I h <br /> 4 i r tr 4 t + 1 _ e !`,{ 1„ I ' ' "Iru l L <br /> I� <br /> till�c'� t I I II' �I i6 �� irk : r trt ,� ,r��ql P� ,l � ° �,I � r rl . Ir r llaf �I `'I !I <br />