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1.0 INTRODUCTION <br /> 1.1 Purpose & Scope <br /> Upgradient Environmental Consultants (Upgradient) has been retained by Gillies Trucking to <br /> continue the assessment of soil and groundwater contamination at the Gillies Trucking yard on <br /> Newton Road in Stockton, California The scope of work is to install two groundwater monitoring <br /> ' wells to a depth of 100 feet and collect soil and groundwater samples for laboratory analysis of <br /> petroleum hydrocarbons, calculate the groundwater gradient, and present recommendations <br /> 1 regarding future site investigation <br /> 2.0 BACKGROUND INFORMATION <br /> 2.1 Site Location and Description <br /> The project site is located at 3961 Newton Road, Stockton, California The location of the site is <br /> shown in Figure 1, and the site facilities are shown on Figure 2 The site is located in a <br /> commercial area on the northeast outskirts of Stock-ton near U S Highway 99 Topography in the <br /> area is flat and the property covers an area of about 3 5 acres <br /> 2.2 Previous Work <br /> Onginally agricultural property, the site has reportedly been used only as a truck terminal for <br /> loading and unloading of freight and as a small repair shop and office for the trucking business <br /> since approximately 1973 The fuel tanks were reportedly installed at about that time <br /> According to the assessment report prepared b <br /> P P P Y Ric hesin& Associates in 1990, Iwo underground <br /> storage tanks (UST's) were removed from 3931 Newton Road in January 1989 by SEMCO, 1:ic <br />' (Figure 1) Petroleum hydrocarbons in the gasoline and diesel ranges were de •, <br /> g detected in soil samplt5 <br /> at a depth of 15 feet, indicating that unauthorized releases had occurred from both the <br /> 1 2,000-gallon unleaded gasoline tank and the 10,000-gallon diesel tank SEMCO deepened the <br /> excavation to 35 feet in July, 1990 and collected eight additional soil samples, all of which <br />' contained moderate concentrations of hydrocarbons Historically, the depth to groundwater has <br /> been as high as 50 or perhaps 40 feet, implying that hydrocarbon contaminants had percolated <br /> downward to at least 15 feet above the water table Therefore, San Joaquin County <br /> •Environmental Health required a groundwater investigation to determine whether groundwater had <br /> been impacted <br /> Richesin& Associates supervised the dr)Ming of two bonngs in November, 1990, and collected soil <br /> and groundwater samples for analysis One boring(TB-2, Figure 2) was terminated at 70 feet and <br /> eiu,ountered diesel-contaminated soil from the surface to total depth The other boring was <br /> terminated at 100 feet and completed as monitoring xvcll MW-1, and encountered <br /> diesel-contaminated soil to s;5 feet and gasoline-contaminated soil from .15 to 60 feet Low <br />