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4 Field Operations <br /> 4.1 Pre-field Activities <br /> Prior to the commencement of field activities, Roux will perform the following action items: <br /> • Develop a Site-Specific Health and Safety Plan (HASP)in compliance with 29 CFR Section 1910.120 <br /> and CCR Title 8, Section 5192. The HASP will address the health and safety aspects of all activities <br /> related to subsurface investigation at the Site (included as Appendix A). <br /> • Roux will mark out proposed boring locations (two temporary groundwater wells and five soil gas <br /> probes) at the Site in white paint and call Underground Service Alert (USA) at least two business <br /> days prior to the subsurface investigation work at the Site; <br /> • Roux will contract with a private utility locator to perform clearance of each boring location for <br /> potential utilities, including utilizing ground penetrating radar(GPR)as appropriate; and <br /> • Roux will apply for and obtain a boring permit from the San Joaquin County Environmental Health <br /> Department (SJCEHD). <br /> 4.2 Investigation Activities <br /> The following methodology for conducting groundwater, soil vapor and indoor air sampling will be applied in <br /> order to address previously identified data gaps for Site environmental conditions. Roux will document soil <br /> vapor probe, sub-slab vapor pin, and temporary well installation and sample collection using field forms as <br /> shown in Appendix B. <br /> 4.2.1 Temporary Monitoring Well Installation <br /> Roux proposes the analysis of groundwater grab samples collected from two temporary, pre-packed, nested <br /> monitoring wells at two depth intervals (TW-1 S/D and TW-2S/D in Figure 3). Borings will be advanced to <br /> approximately seven feet below the observed groundwater table and a temporary polyvinyl chloride (PVC) <br /> prepacked well screen will be placed in the boreholes to facilitate groundwater sampling. <br /> The boreholes for the prepacked monitoring wells will be constructed using a hollow-stem auger rig with <br /> 6 inch diameter augers. Upon completion of the borehole, a 2-inch diameter Schedule 40 polyvinyl chloride <br /> (PVC)prepack well with 10-slot screen (0.010-inch slots)will be constructed within the borehole.The shallow <br /> prepack well will be constructed with a 10-foot screen interval placed between approximately 6 and <br /> 16 feet bgs and an associated riser pipe between approximately 0.5 and 6 feet bgs. The deeper prepack <br /> well will be constructed using similar methods upon encountering the water bearing zone below the shallow <br /> groundwater at approximately 10 ft bgs. <br /> The prepack monitoring wells will be developed after installation to remove any fine- grained material from <br /> the filter pack and to establish communication with the aquifer prior to sample collection. The monitoring <br /> wells will be developed by mechanical pumping until the turbidity of the purged water is reduced. <br /> 4.2.2 Groundwater Sampling <br /> Following installation and development of the temporary groundwater monitoring wells, groundwater samples <br /> will be collected from the two temporary wells and the five existing groundwater monitoring wells using low <br /> flow purging and sampling techniques using a bladder pump and disposable polyethylene tubing. During <br /> purging activities, the polyethylene tubing will be connected to a flow-through cell and water quality <br /> 3989.0001S101/R Revised Data Gap Investigation Work Plan I ROUX 18 <br />