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Additional Groundwater Investigation Work Plan 419 S.Main Street,Manteca.,CA June 25,2003 Page 4 Condor anticipates that 16 groundwater samples (four samples from each CPT boring pair) will be collected during the deep groundwater investigation. Groundwater samples will be collected using a push-type groundwater sampler. The sampler has a sealed, retrievable stainless steel screen. The sampler will be pushed in a closed position to the desired sampling interval. The sampler push rod will then be retracted exposing the inlet screen. Groundwater will flow hydrostatically from the formation into the inlet screen. The groundwater sample will be collected by lowering a stainless steel bailer through the hollow push rods and into the sample screen. The groundwater will be gently emptied from the bailer into the appropriate laboratory supplied containers. The sample containers will be sealed, labeled, placed in a cooler chilled with ice, and delivered under chain-of-custody Now procedures to a California certified laboratory for analyses. The piezocone, associated push rods, groundwater sampler, and stainless steel bailer will be thoroughly cleaned before each boring is advanced using laboratory-grade, non-phosphate detergent and deionized water and double rinsed with deionized water. Upon completion of the boring and sampling, the borings will be backfilled with neat cement. The cement will be tremied into the borehole to avoid bridging. low 3.3 DIRECT PUSH BORING PROCEDURES Five shallow direct push borings (hydropunch) will be advanced to approximately 25 feet bgs. The proposed depths are considered sufficient to collect a groundwater grab sample to provide data on the lateral extent of contamination in shallow groundwater. One groundwater sample will be collected from each direct push boring for a total of five groundwater samples collected during the shallow groundwater investigation. The proposed direct push boring locations are shown in Figure 3, Appendix A. Although not anticipated, it is possible that the borings will be terminated at refusal before encountering groundwater. The locations for the shallow direct push borings were chosen to assist in evaluating the lateral extent of shallow groundwater contamination in the predominant down-gradient direction, which is to the west. Four of the shallow direct push borings are sited within the Wetmore Street public right-of-way (Figure 3, Appendix A); three borings are proposed adjacent to the southern margin of Wetmore Street and one boring is proposed on the northern edge of Wetmore Street near the intersection with Stockton Street. One shallow direct push boring is proposed adjacent to the eastern edge of Stockton Street within the public right of way near the intersection with Wetmore Street(Figure 3, Appendix A). The direct push borings will be hydraulically advanced using a 2-inch diameter conical bit. Upon completion of the boring and sampling, the borings will be backfilled with neat cement. The cement will be tremied into the borehole to avoid bridging. One groundwater sample will be collected from each boring with the hydropunch-type groundwater sampler. The sampler has a sealed,retrievable stainless steel screen. The sampler will be pushed in a closed position to the desired sampling interval. The sampler push rod will then be retracted exposing the inlet screen. Groundwater will flow hydrostatically from the formation into the inlet screen. The groundwater sample will be collected by lowering a stainless steel bailer through the hollow push rods and into the sample screen. The groundwater will be gently emptied from the bailer into the appropriate laboratory supplied containers. The sample containers will be sealed, labeled, placed in a cooler chilled with ice, and delivered under chain-of-custody procedures to a California certified laboratory for analyses. 1 j �./� CONDOR