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1 tSttiited Hydrogeok40 Assessmerd WoflioM 1399 E Yosemite Avenue Manteca California • Groundwater is present in both confined and unconfined conditions in the basin In the area of the subject site, groundwater occurs in unconfined aquifers, characteristic of formations composed of alluvial fan, floodplain, and stream channel deposits The direction of regional groundwater flow ,s toward the Sacramento River Delta from the surrounding mountain ranges Development of pumping wells in the area has created a depression in the groundwater surface, and has caused the gradient to be toward the central portion of the valley (Department of Water Resources, 1967) On the basis of measurements collected from existing wells in January 1992, the estimated depth to groundwater is approximately 25 feet below surface and the direction of flow is to the northwest PROPOSED WORKPLAN Site Safety Plan A site safety plan (SSP) has been prepared and will be on site during all field activities A copy of the SSP is included as Appendix B All work on site described herein will be conducted according to the SSP The SSP contains information on the properties of the hazardous materials determined to be on site (by previous investigation) This information is equivalent to that contained within the material safety data sheets Soil Boring and Soil Sampling Two soil borings will be drilled to approximately 35 feet below surface at the locations shown on Figure 2 The borings are to be completed as 4-inch-diameter groundwater monitoring wells The borings will be drilled, using 10-inch-diameter hollow-stem augers, to a maximum of approximately 15 feet into the first water-bearing zone Drilling into a confining layer, if encountered, will be done so as to avoid its complete penetration and maintain the layer's integrity The total depth of each boring will be determined in the field, but may be as deep as 35 feet below surface Aegis may elect to continuously core one or more of the borings to more completely evaluate the subsurface sedimentary and/or lithologic conditions During drilling, the subsurface soils and alluvial materials of the unsaturated zone will be sampled at 5-foot intervals The sampling interval may be shortened where subsurface conditions warrant The deepest sample in each boring will be collected 10 feet below first water or within the low-estimated permeability confining layer The sod samples will be screened in the field, using a portable photoionization detector, for possible laboratory analysis 90-098A WPN 4