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2.7.2 HYDROPUNCH GROUNDWATER SAMPLING After soil sampling is performed, hydropunch groundwater grab samples will be collected at 11 of the 25 borehole locations. Hydropunch samples will be collected at an additional two (2) locations along Van Buren Street and an additional one (1) location along Washington Street as indicated in Table 4 and Figure 5. The exact location of the sampling points will depend on subsurface utilities and other surface or subsurface obstructions that may be present. The purpose for obtaining groundwater grab samples along the eastern and western boundaries is to evaluate whether impacted groundwater, if present, has migrated on and/or off-site. Groundwater samples will be collected in the middle of the Stockton UPRR Project area to provide data for evaluating the distribution of impacted groundwater. If impacted groundwater is identified, groundwater- monitoring wells may be installed. It is anticipated that four (4) groundwater monitoring wells will be installed as described in Section 2.8. Sample collection will be accomplished by replacing the soil-sampling tool with a hydropunch groundwater-sampling tool, and advancing it to a depth of approximately four (4) feet below the water table. An expendable drive point is then removed from the end of the tool as the entire drive rod assembly is extracted upward approximately four (4) feet, exposing a temporary well screen that allows water to enter for sampling. After allowing sufficient time for water to enter the screen, Tygon tubing will be lowered into the center of the drive rod to the bottom of the screen and attached to a peristaltic pump. Water will then be pumped up from the screen and placed into sample containers for analysis. Samples for VOC analysis will be collected using a disposable bailer. Due to the temporary nature of this kind of sampling point, measurement of groundwater parameters (temperature, pH, conductivity, turbidity) will not be performed. Following collection, samples will be analyzed for: TPHg, in accordance with Modified EPA Method 8015; TPHd and TPHo, in accordance with Modified EPA Method 8015B; VOCs, in accordance with EPA Method 8260B; and Total metals, (no hexavalent chrome), in accordance with EPA Method 7470/7471. Groundwater samples to be analyzed for TPHg and VOCs will be placed into four (4), 40 ml VOA vials with zero headspace maintained. The VOA vials will be inverted after the cap is secured to verify that bubbles are not present. If bubbles are present, the sample will be discarded and a new water sample will be collected. The groundwater samples, to be analyzed for TPHd and TPHo, will be placed into appropriate containers; maintenance of zero headspace conditions is not required. Groundwater samples to be analyzed for metals will be filtered onsite prior to placement in the sample container. This will be accomplished by placing the water from the bailer into a clean container, then using a peristaltic pump and disposable Tygon tubing, pumping the water through a disposable 0.45-micron filter into the sample container. After collection, the groundwater samples will be labeled and placed into temporary storage in an insulated chest filled with ice pending transport to a California certified laboratory for Golden State Environmental, Inc. - 20 - Los Angeles, San Diego and Houston Revised Work Plan — Soil and GW Characterization July 2006