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Manteca Unified School District 2901 E. Louise Ave., Lathrop, California Remedial Excavation Report Page: 3 mobile lab or transported by their couner in a cooler with ice Chain of Custody records were maintained at all tunes 32 Groundwater Sampling The de-watering groundwater that was stored in a surface tank and the in-situ groundwater were sampled with Teflon bailers and carefully poured into clean glass vials with Teflon-lined screw caps and one liter amber glass containers provided by the ' laboratory Care was taken to ensure that no air space existed in the vials by inverting to check for bubbles and re-sampling if necessary All water samples were collected ' under the direction, supervision and approval of San Joaquin County Health Department personnel The samples were analyzed or extracted within 14 days according to their EPA methods Water samples collected for analysis were analyzed ' by EPA method 602 for BTEX compounds and method 8015 modified for diesel and gasoline hydrocarbons All analyses were conducted by Sparger Technology, Inc, Sacramento, CA, a State certified laboratory 4.0 Soil Conditions The subsurface geology of the Manteca Unified School District site in Lathrop, California is characterized by interbedded inorganic rrucaceous silty sands and clayey, sandy silts This is typical of the valley fill deposits in the region (Figure 5) A notable bed of cross-bedded fluvial ' sand is continuous throughout the site from a depth of 8 0 to 12 5 feet It is a clean, loose, well-sorted sand that caves easily Analysis of soil samples show residual ccntaminnation in the walls below 12 feet and the floor of the excavation to the north and west(Table 1, Figure 3) S.0 Groundwater Conditions The water table was approximately 16 feet below ground level at the time of the excavation No data exists for a gradient calculation, but indications are that the gradient was to the northwest at the tune of the fuel leak This is supported by 1 ) no contamination in the south wall of the original tank excavation, 2 ) no contamination in the south half of the east wail of the original tank excavation, 3 ) no contamination in the floor samples adjacent to the south and east walls of the original tank excavation, 4) no contamination in the groundwater pumped into the surface tank from the southeast corner of the original tank excavation and 5 ) the contamination levels extending and continuing to the west and north of the original tank excavation This may also be affected by the irrigated fields to the south and east of the site, dormant land to the west and north, and the regional westerly gradient toward the delta