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December 22, 1998 Harding Lawson Associates 4034405 Margaret Lagorio, Supervising RENS San Joaquin County Public Health Services Environmental Health Division Page 3 FIELD INVESTIGATION The scope of work was developed after discussions with Ms Margaret Lagorio of PHS/EHD Boring permits were issued by PHS/EHD on February 12, 1998 The objectives of the investigation included the following • Assess further the lateral and vertical distribution of petroleum hydrocarbon-impacted soil • The purpose of boring SB-1 was to assess the maximum concentrations of TPH-impacted soil and the vertical extent of impacted soils near the source 1 • The purpose of boring SB-2 was to assess the lateral extent of impacted soil to the east of the USTs/sump location • Assess whether impacted soils present pose a potential threat to groundwater quality by collecting data on the soluble fractions of TPHd and BTEX present in soils with the maximum concentrations of petroleum hydrocarbons • If groundwater was encountered during drilling collect a grab sample with a Hydropunch sampling tool • Assess the feasibility of insitu passive bioremediation of impacted soils Prior to commencement of work, a site specific Health and Safety Plan (HSP) (HLA, 1998) was prepared that was consistent with the requirements of Title 8 CCR 5192 During all field work, procedures outlined in the HSP were followed Prior to onsite sampling activities, Underground Service Alert (USA) was notified to mark existing utilities present at the site, and a private utility locator surveyed the drilling locations and marked additional subsurface utilities Soil Borings and Soil Sampling On April 28, 1998 two soil borings (SB-1 and 513-2) were drilled to depths of 20 5 feet bgs at the locations shown on Plate 3 Boring S13-1 was moved approximately thiee feet from its proposed location due to the presence of a subsurface utility line and was drilled as close as possible to the sump to assess the 1 maximum concentrations and vertical extent of impacted soil at the former source area Boring SB-2 was drilled east of the USTs/sump location to assess the lateral extent of impacted sail All borings were drilled with skid-mounted Diedrich D-25 drill rig equipped with four-inch diameter, solid-stem augers and I operated by PC Exploration Incorporated, a C-57-licensed driller fiom Roseville, California Soil samples were collected at minimum 5-foot inteivals for lithographic description, volatile organic compound (VOC) screening, and potential laboratory(chemical) analysis The samples were collected using a 2 0 inch (inside diameter) California Modified split-spoon sampler lined with thiee clean 6-inch long brass tubes The sampler was driven with a 140-pound hammer The number of blows required to drive the sampler each six-inch interval was recorded and used as a qualitative measure of soil density The lowermost tube from each sample interval was removed from the sampler and immediately capped with Teflon-lined plastic end caps, labeled, and placed in an ice-chilled cooler for transport to a state- certified analytical laboratory Samples were recorded on a standard HLA chain-of-custody form to document sample identification and handling The remaining sod sample from each interval was checked for hydrocarbon stains and monitored for VOC vapors using a photoionization detector (PID) to indicate the relative concentrations of volatile compounds The PID was equipped with a 10 2 electron-volt lamp • and calibrated to a 100 pait per million (ppm) isobutylene standard