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I Sampling Plan - 152 East 11th Street, Tracy, CA � Ft�; I ra ` Wage 3 fig ' Ly v i, MAY 14 1993 ENVIRONMENTAL HEALTH ' GEOLOGY AND HYDROGEOLOGY PERMIUSERVICES The subject property and the surrounding area are situated on level terram on the distal, northern slope of an alluvial fan The underlaying alluvial sediments are of Quaternary to Recent age Logs of the monitoring well bormgs indicate that the soils beneath the site includes clays, silty clays, sandy clays, clays with gravel, sands, silty sands and sands with gravel These clastic materials are distributed in a complex lenticular structure with little continuity of facies from boring to boring Areas beneath the streets adjacent to the property have been extensively excavated and backfilled for installation of sewers and other utilities The depth to groundwater is in the range 7 to 9 ft and vanes seasonally The general direction of the groundwater gradient is northward across the 152 East 11th Street property Local and seasonal variations occur whereby the direction of the gradient varies from northwesterly to north-northeasterly depending upon seasonal rainfall with the downgradient direction shifting towards the northwest as flow progresses from the south to the north side of 11th Street Typical groundwater table contours are shown on Figure 3 These contours were interpreted from measurements made in the Navarra and Ultramar monitoring wells on April 13th 1988 The slope of the groundwater gradient is typically about 0 005 ft/ft with minor seasonal variations PREVIOUS INVESTIGATIONS Monitoring Wells and Groundwater Sampling In March 1988, following a request from the RWQCB, the Navarra's arranged for WaterWork of Sacramento, California to perform a site investigation The investigation included installation of four groundwater monitoring wells These wells are shown on Figure 2 and are designated NAV 1 through NAV 4 In April 1988 WaterWork recovered samples from these wells The samples were analyzed for hydrocarbon fuel components The results of the investigation were reported to the RWQCB Another round of groundwater sampling from the Navarra wells was performed in January 1983 by The San Joaquin Company Inc and the results reported to the SJCPHS Directly north of the subject property (i a 152 East 11th Street), and across 11th Street, there is a Beacon Station located at 153 East lith Street The station is owned by Ultramar Inc of Hanford, California (Ultramar) In connection with investigations of a release of hydrocarbon fuels at the Beacon station, a total of rime ground water monitoring wells have been installed on an around that property The locations of these wells are also shown on Figure 2 where they are designated as ULT . 1 through ULT 9 Well ULT 9 is located in the sidewalk along the lith Street frontage of the Navarra property The Ultramar monitoring wells were installed subsequent to