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PRELIMINARY REPORT <br />Underground Fuel Storage Tank Site Investigation <br />J.R. Simplot Company Facility <br />Lathrop, California <br />1.0 INTRODUCTION <br />The following preliminary report presents a soil and shallow <br />groundwater investigation program designed by Roy F. Weston, Inc. <br />(WESTON) to assess the extent of hydrocarbon residues at the J.R. <br />Simplot Company (Simplot) facility located at 16777 Howland Road, <br />Lathrop, California (Figure 1). Simplot has been the owner and <br />operator of this facility since 1983, with the primary contact <br />for this program being John J. Pallen. <br />The program addresses the installation and sampling of three <br />shallow groundwater wells and the gathering and analysis of soil <br />samples from several locations. All of these activities are to <br />occur within the vicinity of the recently removed gasoline and <br />diesel storage tanks. All of the work detailed within this <br />report will be conducted under the supervision of a registered <br />geologist. <br />2.0 BACKGROUND <br />During removal of two underground fuel storage tanks at a refuel- <br />ing area within the J.R. Simplot Company's facility (Figure 2), <br />it was discovered that some leakage had occurred from the diesel <br />tank. The analysis of soil samples taken from beneath the two <br />removed tanks indicated that concentrations of hydrocarbon <br />related chemicals were present in the excavated area. <br />While BTX compounds were found to be highest in the area of the <br />gasoline tank, the amount of total petroleum hydrocarbons ob- <br />served were approximately equal to those observed beneath the <br />diesel storage tank (see Section 4.0 of this Report for addition- <br />al details). <br />3.0 SETTING <br />3.1 Topography <br />The study area is in the Central Valley of California on the <br />southeast margin of the low-lying Delta region, where the San <br />Joaquin and Sacramento Rivers join in a maze of channels before <br />discharging into San Francisco Bay. Elevations in the study area <br />range from 8 feet above mean sea level near the San Joaquin River <br />to 40 feet near Manteca. The land is almost level, with a slope <br />of 5 feet per mile rising from west to east. The most notable <br />topographic features are artificial levees, and railroad and <br />