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Work Plan for Groundwater Monitoring Well Installation, Soil Gas and Groundwater Investigation, and Groundwater Monitoring Army Aviation Support Facility, Stockton, California 3.6 WELL DEVELOPMENT A minimum of 48 hours after installation, to allow sufficient time for well materials to cure, the wells will be developed. The purpose of developing new monitoring wells is to remove the residual materials remaining in the well after installation has been completed. Development procedures will include pumping compressed air into the water column (at a depth of 2-3 feet below static water level), and flushing water up and out of the well and into waste containers. This procedure will be continued until water removed from the well is clear and free of any visible sediment, and the physical parameters of temperature, pH, and conductivity have stabilized. At this time, the total depth of the existing wells (MW-1 to MW-3) will be measured, and the wells re-developed if a significant amount of sediment has accumulated within the well screen, as recommended in the URS SI report (2008). Development water will be containerized and stored onsite until properly characterized and transported offsite for disposal. 3.7 GROUNDWATER MONITORING WELL SAMPLING At least 48 hours after the monitoring wells have been developed, groundwater samples will be collected from all site wells (existing wells MW-1 to MW-3 and proposed wells MW-4 through MW-7) and submitted for laboratory analysis. Prior to sampling, water levels will be gauged to ±0.01 foot for purposes of evaluating groundwater elevations. If light non-aqueous phase liquid (LNAPL) is suspected to be present based on findings during well installation, an electronic interface probe will be used to gauge one or more of the wells. After gauging, samples will be collected using a two-inch diameter monsoon pump to continuously pump water at a low-flow (250 - 500 milliliters/minute depending on well recharge). The sampling procedures will follow USEPA guidance for low stress (low flow) purging and sampling for groundwater monitoring wells (USEPA, 1996). Low-flow purging minimizes turbidity in samples, thereby eliminating an objective for removal of a specified number of well volumes. As a result, this technique tends to minimize the volume of purge water that needs to be managed and disposed. The depth of the low-flow pump intake will be based on the expected site contaminants and the site-specific hydrostratigraphy identified during the monitoring well installation, and the rationale will be presented in the associated groundwater monitoring report, as addressed in Section 4.0 below. Samples will be collected only after field- measured water quality parameters have stabilized indicating the presence of formation water. Water quality parameter stabilization will be documented separately for each well on a project- specific Monitoring Well Purge/Sample Log, which will be incorporated with reporting documentation as addressed below. Once water quality parameters have stabilized, groundwater samples will be collected in sterile, laboratory supplied containers, submitted to a California-certified laboratory under appropriate COC documentation, and analyzed for the following: • TPH-g and TPH-d using USEPA Method 8015-Modified; • VOCs, including Naphthalene, BTEX, and Fuel Oxygenates using USEPA Method 82606; and • Total Lead using USEPA Method 6010B. The full list of analytes is shown on Table 1. The first groundwater sampling event will be performed within approximately one week of well installation and development, and will OTI E 13