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+r • PHS/EHD, part of the stockpile was used to backfill the excavation in April 1996 It is our understanding that Valley Motors arranged for the removal of the remainder after July, 1996 In July 1996, three soil borings were drilled and two were converted to monitoring wells Contaminated soil was encountered in two of these, and one or more hydrocarbon contaminants were detected in water samples from all three, as well as in the previously drilled well (VM-1) The resulting data helped to partially define the limits of soil contamination, but the limits of groundwater contamination were not reached Groundwater samples were collected again in December, 1997 Concentrations of most petroleum hydrocarbons exceeded those detected in previous monitoring events, and several new solvent compounds were detected for the first time In written communication in March, 1997, PHS/EHD recommended that Valley Motors conduct a soil-vapor survey in an effort to identify areas of contaminated soil that may be impacting groundwater PHS/EHD also reccommended that an additional monitoring well be installed to determine the eastern limit of groundwater contamination In response, Upgradient submitted a work plan in October 1997 Upgradient proposed to survey the northwest portion of the site, including the sidewalk and street areas bordering the property, drill two soil borings to collect soil samples to confirm the results of the vapor survey, and install one monitoring well PHS/EHD approved this plan with additions in October 1997 • 3.0 SOIL VAPOR SURVEY 3.1 Procedures The soil vapor sample points were laid out in a grid pattern on 15-foot centers Approximately 35 sample points were originally planned, but several of these could not be drilled because they were located too close to gas and water lines in the parking lane on Main Street Several others could not be dnlled because they were located in traffic lanes, and the City of Stockton encroachment permit allowed drilling only in parking lanes A few others were eliminated when it became apparent during the survey that they were located beyond the limits of contamination or because of auger refusal Hence, of the planned 34 vapor borings, only 16 were actually drilled and sampled (Figure 3) A Geoprobe direct-push drilling rig was used to drill borings that were 1-314-inches in diameter Seven borings were drilled to a depth of 12 feet, 7 borings were drilled to approximately 14 5 feet, and 2 borings were drilled to 20 feet Four borings had auger refusal at 4 feet and were abandoned After drilling the boring, a 15-foot length of copper pipe with several perforation holes drilled near the bottom end was lowered into the boring and driven 12-18 inches into the soil using a slide hammer A vacuum pump was then connected to the top end of the pipe to create a vacuum and withdraw air from the soil at the sample depth After evacuating the ambient air from the pipe for several minutes, a portable photo-ionization detector (PID) was connected to the vacuum pump 4