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,F <br /> Cl1ARTERLY GROUND WATER MONITORING REPORT <br /> 420 W.KeWtmdn.Leal.Caldorma <br /> r <br /> i <br /> 1.0 INTRODUCTION <br /> This report documents the results of the first quarterly groundwater monitoring program <br /> for 1991 conducted by Aegis Environmental, Inc. (Aegis), at the Shell Service Station <br /> located at 420 W. Kettleman Lane, Lodi, California (Figure 1). The quarterly monitoring <br /> involved collection of groundwater samples, submittal of samples to a state-certified <br /> laboratory for analysis and water level measurements for the three on site wells. The field <br /> activities took place on January 16, 1991. This report presents the first <br /> sampling/measurement interval since installation of the three wells. <br /> 2.0 SELECTIVE SUMMARIZAND INFORMATION <br /> In September 1989, a total of fifteen soil borings were advanced and sampled at the site <br /> ("Pre-Tank Replacement Site Assessment Results Report' (Aegis 1989)). The borings <br /> ranged in depth from 11-1A to 21-1h feet below grade (bg). Soil samples collected and <br /> analyzed from one boring along the south edge of the existing underground storage <br /> tanks,at 15 feet tag,reported low concentrations of toluene and total xylenes. Laboratory <br /> analysis of the soil samples for the remaining borings adjacent to the existing dispenser <br /> islands and underground storage tanks indicated concentrations of total petroleum <br /> m hydrocarbons as gasoline (TPH as gasoline) and benzene, toluene, total xylenes, and <br /> ethylbenzene(STEX) below detection limit. Low concentrations of toluene were detected <br /> at approximately five feet bg in the northwest quadrant of the site in the location of the <br /> formerly proposed tank basin. However, one boring in the northwest quadrant reported <br /> TPH as gasoline at 1,060 ppm at 10 feet bg. The source of the petroleum hydrocarbons <br /> concentrated in this one soil boring has been attributed to a "thief port' present in the <br /> existing underground storage tank system. <br /> installation of the three on site groundwater monitoring wells, MW-1 through MW-3, <br /> occurred on October 3 and 4, 1990, in pursuant to a request by the San Joaquin County <br /> Public Health Services Environmental Health Division to perform further subsurface <br /> - investigations. The laboratory analysis for the soil and groundwater samples collected <br /> of the wells reported concentrations below <br /> during the construction and completion <br /> detection limit for petroleum hydrocarbons volatile as gasoline and benzene,toluene,total <br /> a xylenes, and ethylbenzene per the Tri-Regional and LE1Ff guidelines and <br /> recommendations. Water level measurements in the three groundwater wells for <br /> __. _ .... <br /> November and December 1990, are included in the results report for the monitoring well <br /> _._......_......... <br /> installation. —­­ <br /> 93-0OB.RPr - <br />