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tia Field Sampling Report For San Joaquin County Leaking Underground Storage Tank Site Investigation Stockton, California 1.0 Introduction A site investigation was conducted by Roy F. Weston, Inc. (WESTON) at the Human Services Building site near the corner of Sutter and Washington Streets, Stockton, California, to evaluate the presence of petroleum hydrocarbons and fuel related compounds in the soil and groundwater. From December 5, 1988 through December 15, 1988, twelve boreholes were completed and three shallow groundwater monitor wells were installed and developed. Sampling and surveying of the vertical well elevations were conducted concurrently on December 30, 1988. The location of the wells and boreholes is shown in Figure 1. " 2.0 soil Borehole Drilling " Borehole drilling began on December 5, 1988. Twelve exploratory boreholes were drilled between December 5 and December 12, 1988 with the last of these being grouted to the surface on December 15, 1988. A table depicting the scheduleof work completed is presented as Table 1 with a location map Figure 1 exhibiting the " locations of boreholes. An Acher-AD2 drill rig using 6 inch outer diameter, 3 inch inner .- diameter hollow stem augers was used to drill all boreholes. Cuttings returned to the surface by to auger flights were con- tainerized in 55 gallon drums and left on site pending receipt of the soil analytical results. All holes were then grouted with a 5% bentonite-cement grout mixture to within 1 foot of the current s ,.. surface. All augers were steam cleaned prior to use in each borehole. A description of the depth of the 12 boreholes, the estimated elevation of the ground surface at the time of drilling, and estimated depth of boreholes below current sidewalk level is presented in Table 2. 2.1 Soil Sampling During the drilling of the boreholes, soil samples were collected from each location at 5 foot below ground surface (BGS) and at 5 foot intervals thereafter down to groundwater. All samples were examined for any staining and odors which would indicate the presence of hydrocarbons compounds. Additionally, all samples were screened with a photoionizer. The instrument used was an HNu model P101 equipped with an 10.2 eV bulb. Before first use, the unit was allowed to warm up for approximately 5 minutes, zeroed, calibrated to isobutylene as benzene at a span setting of