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F , Cealagica[Te hnics 2nc. %—/ N"04 Page 3 &B Equipment Additional Site Characterization WP Addendum Project No. 336.2 April 7, 1997 ' 3.0 VERTICAL DEFINITION OF THE GROUNDWATER PLUME .. The following work is proposed to define the vertical extent of the groundwater plume at C & B Equipment. Except where noted all drilling and sampling will be conducted as per the ` Geological Technics Inc. June 15, 1996 Monitoring Well Installation and Groundwater Monitoring Work Plan. We have proposed the following construction for the deep monitoring well. However, its •- design may need to be modified during drilling depending on geologic information obtained during drilling. An extensive search was conducted for well logs for wells located on the property and nearby properties to no avail. Records from both SJCPHSEHD and the State of ,. California Department of Water Resources were checked. 3.1 Well Location We propose to install one deep, discretely screened monitoring well (MW-101) north of the point of release. This location was selected based on its proximity to the point of release (Figure 2) and in consideration of compiled project information (Summary Tables-Appendix B). 3.2 Drilling and Sampling Because of the proximity to the point of release the following modified well construction technique will be used to minimize the potential for cross contaminating the deeper zones. The well boring will be drilled using a 12.25 inch outside diameter continuous flight hollow stem auger owned and operated by V&W Drilling (C57# 720904) to a depth of 30 feet (10 feet deeper than the "shallow" MW's). An 8 inch diameter auger will then be used to advance �. from 30 feet to the total depth. In this manner we can reduce the possibility for dragging contaminated soil from the vadose zone into the deeper zone. Soil samples will be collected for geological and possible analytical evaluation at five foot intervals and continuously below 20 feet. In addition we propose to use the SimulProbe sampling tool to collect soil and water samples �- at three intervals below 20 feet. The SimulProbe allows a soil sample to be collected at the exact interval from which the water sample is collected thus providing correlative information on the sorbed portion of the contaminated zone. Furthermore the SimulProbe's design reduces the possibility of cross contamination from shallower borehole waters. After the SimulProbe groundwater sampling tool is advanced into the saturated zone the tool is retracted to expose the screen. The sample collection chamber is allowed to fill under ambient hydrostatic pressure. Once full the chamber is sealed with an pneumatically actuated (N, gas) solenoid valve and the apparatus is brought to the surface. The sample chamber is carefully emptied using a bottom emptying device thus reducing the possibility of sample agitation and volatilization. Once the sample container (40 ml VOA) is filled and capped, the bottle will be inverted, tapped, and checked for head space bubbles. The sample container is identified and labeled with a unique designation, inserted into foam holders and placed in an ice chest cooled to 4°C for transport to the laboratory. V V