SITE INFORMATION AND CORRESPONDENCE_2001-2018

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Ms. Devra Lewis February 20, 2003 Page 2 of 6 Upon receipt of analytical data from the testing lab, specific locations for additional groundwater monitoring wells will be identified. Wells will be located in areas outside of the leading edge of the plume in areas not impacted by petroleum hydrocarbons. Once the locations are determined and approved, a truck-mounted hollow stem auger (HSA) rig will be mobilized to the site to install monitor well(s) at specific locationdowngradient of MW-33. Once the new wells are installed, they will be developed, surveyed, and added to the groundwater monitoring network. s A completion report documenting the investigation and well installation activities would then be provided to the CVRWQCB. The wells would then be sampled at the next scheduled quarterly event. The following sections discuss the methodologies to be employed during the investigation. Proposed Direct Push Locations Direct push sampling locations have been selected based on recent groundwater plume information and locations of existing monitoring wells. Approximately 10 direct push sampling locations will be completed to a depth of approximately 5 feet below the water table. Figure 1 provides these proposed areas, although exact locations will be determined in the field based on site conditions and other visual information collected during the geoprobe program. Each soil core will be logged by a RETEC Field Geologist by ASTM Method D-2488, Standard Practice for Description and Identification of Soils (Visual-Manual Method). Soils will also be field screened for volatile constituents with a photoionization detector(PID). Groundwater Sampling Using Direct Push Methods Groundwater sampling using direct push methods is discussed briefly in SOP 212, Procedures for Direct Push Technology Probe System, provided in Appendix A. Additional detail is provided below. When using the direct push technology for groundwater sampling, the lead drilling rod section is fitted with a retractable rod tip, which prevents any solids from entering the sampler. When the desired depth is reached, the rod is pulled back to expose 3 feet of slotted screen for groundwater sampling. The procedures for groundwater sampling are as follows: 1) Position the drill rig at the sampling location 2) Attach the sampling tool to the end of the drive rods 3) Advance the rods into the soil, adding sections of blank pipe as necessary 4) When the desired groundwater sampling depth is reached, unscrew the inner rod 5) Pull the rod up to expose the screen 6) Using clean, new polyethylene tubing, pump groundwater from inside the screen. Purging will be accomplished by lowering the sampling tubing to approximately the center of the screen and pumping from this location at a rate of 0.1 to 0.5 liters per minute. A small volume of water will be purged to initiate flow through the screen