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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 The full list of analytes is shown on Table 1. Grab groundwater samples will be labeled with a unique sample designation identifying the location and depth, in that order(e.g., GW-1-40'). Sample designations, collection times, and analysis information will be recorded in the field notebook and on the COC form(s). Field duplicate samples will be collected at a frequency of 10% or one field duplicate sample per 10 groundwater samples collected. MS/MSD samples will be collected at a frequency of 5%, and trip blank and equipment rinsate blank samples (for non-disposable sampling equipment) will be collected once per day of sampling and accompany all groundwater samples sent to the laboratory. 3.3.2 Soil Gas Survey Stepping out no more than 5 feet from each grab groundwater sampling location, a second direct-push boring will be advanced for the purpose of collecting soil gas samples. One or more samples may be collected from the vadose zone from each of the approximately 30 proposed locations. All soil gas samples will be collected in accordance with the California Environmental Protection Agency (CaIEPA) March 3, 2010, Advisory—Active Soil Gas Investigations (ASGI Advisory). 3.3.2.1 Soil Gas Probe Depth Soil gas sample depths will be based upon the lihtologies encountered (logged in the field), PID readings, and the field experience of the on-site geologist. As stated above, encountered soils (i.e. borings) will be screened with a PID for VOCs. Boring depths with elevated levels of VOCs (as compared to all boring intervals screened) will be noted. These values, in combination with other logistical criteria, will contribute to the depths at which soil gas samples are collected. At a minimum, one sample will be collected from each borehole above the top of the groundwater table and capillary fringe at a depth determined by the lithologies encountered in each borehole. Based on the CSM, the upper 20 feet bgs beneath the site is generally characterized by fine sediments consisting of predominantly silts and clays less conducive to soil gas migration. Coarser materials (sands and silty sands) from approximately 20 feet bgs to the top of groundwater are more conducive to potential soil gas migration. In the case of soil gas samples planned within a suspected source area (inferred by location or elevated PID readings) possessing what appear to be impermeable soils, one sample attempt per discrete location will be made, prior to attempting a sample at a more feasible (i.e. more permeable) sample depth. All soil gas sample depths will be chosen to minimize the effects of changes in barometric pressure, temperature, or breakthrough of ambient air from the surface; and to ensure that representative samples are collected. 3.3.2.2 Soil Gas Probe Emplacement Soil gas samples will be collected from soil borings advanced using a direct-push drill rig. Soil gas samples will be collected using an expendable point and point holder, which is attached to the drilling drive rod. Following advancement of the soil gas sampler to the desired depth, the expendable point holder will be retracted, separating the expendable point and point holder and creating a void in the soil at that depth. New Teflon"A or similar tubing will be placed inside the drive rods and secured to the expendable point holder. Given the thickness of the clay and silt OTI E 9