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0 Work Plan for Groundwater Investigation and Groundwater Monitoring Well Installation Field Maintenance Shop #24, Stockton, California internal surface of the membrane, carrying volatile constituents for analysis to a series of gas - phase detectors. The detectors used are a photo -ionization detector (PID), a flame -ionization detector (FID), and an electron -capture detector (ECD). In addition to the gas -phase detectors, the rate of push, exact depth, in-situ temperature, and electrical conductivity are measured and continuously recorded to the total depth of each boring. The drilling contractor will prepare 2-D and 3-D visualizations of the petroleum hydrocarbon plume from the data generated by the membrane interface probe. The primary COPCs at FMS 24 are petroleum hydrocarbons and VOCs. These contaminants are generally highly volatile and therefore amenable to investigation using MIP techniques. A soil conductivity probe will also be deployed to assess soil permeability with depth. These data will yield insights into the delineation of the horizontal and vertical extents of residual contamination from the former USTs, and will be utilized to determine the locations for two new groundwater monitoring wells within the primary source area for petroleum hydrocarbons and related constituents (Figure 4). Borings will be advanced using DPT drilling equipment fitted with membrane interface probe tooling. Drilling equipment will be operated by a C-57 licensed well drilling contractor under the direct oversight of a qualified geologist/hydrogeologist working under the supervision of a California Professional Geologist (PG). The first 5 feet of each boring will be advanced using a hand auger prior to implementation of drilling using the direct push rig/MIP. After each use, drive rods and other reusable components will be properly decontaminated to prevent cross contamination. Decontamination methods will include a 3 -stage wash and rinse (e.g., wash equipment with a nonphosphate detergent, rinse with tap water, and finally rinse with distilled water); and/or a steam cleaning process. Each borehole will be abandoned according to SJCEHD's regulations with neat cement, the top 3 feet backfilled with clean native materials (SJCEHD, 2005), and the surface restored to its original condition. 3.3.1 Data Evaluation OTIE will evaluate the MIP data on a daily basis in order to optimize the sampling program to meet data quality objectives. Subsequent to the MIP activities and prior to the well installation activities, OTIE will integrate all MIP data with previously collected data and evaluate it using traditional 2-D interpretation methods as well as 3-D modeling software. These data visualization tools will be used to optimize subsequent MIP boring locations and the proposed permanent well locations and screening intervals, and to further delineate plume geometries and distribution of COPCs in the subsurface. 3.3.2 Confirmation Sampling The MIP sampling system is quantifiable to the extent that it detects and counts ions. In order to calibrate the ion counts with a VOC concentration, corroborative soil and groundwater sampling will be performed at the MIP locations chosen for well installations. Soil samples will be obtained by a split spoon sampling device using a HSA drill rig during borehole advancement for well installation, and analyzed as described below. The groundwater samples will be collected during the baseline sampling once the wells have been installed and developed, also as described below. The monitoring wells will be co -located with MIP locations so as to correlate qualitative data on lithology and soil/groundwater chemistry from the MIP study, with sample descriptions and laboratory analysis of soil and groundwater samples collected during well installation. Soil sample intervals analyzed for VOCs may be pre -selected by evaluating the MIP data at the selected locations, or at approximately 5 foot depth intervals. Each of the 11 OTIE