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Work Plan for Groundwater Monitoring Well Installation at the California Army National Guard Stockton Field Maintenance Shop, Stockton, California • • TPH-g and TPH-d using USEPA Method SW8015-Modified; • BTEX and Fuel Oxygenates using USEPA Method 8260B; and • Total Lead using USEPA Method SW6010B. 3.5 GROUNDWATER SAMPLING No less than 48 hours after monitoring wells have been developed, groundwater samples will be collected from each well and submitted for laboratory analysis. Prior to sampling, water levels will be gauged 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). Consistent with USEPA guidance for low stress (low flow) purging and sampling procedures for groundwater monitoring wells, the low flow pump intake will be placed in approximate middle (or just above) of the screen interval (USEPA, 1996). 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. 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. Once water quality parameters have stabilized, groundwater samples will be collected in sterile containers, submitted to a California -certified laboratory under appropriate COC documentation, and analyzed for the following: • TPH-g and TPH-d using USEPA Method SW8015-Modified; and VOCs, including BTEX and Fuel Oxygenates using USEPA Method 82608. The first groundwater sampling event, to be performed within approximately one week of well installation and development, will constitute the first of four planned quarterly groundwater monitoring events. A report documenting groundwater monitoring activities and findings, as described below, will be submitted following the monitoring event. The first quarterly report will also include documentation for groundwater monitoring well installation. 3.6 GROUNDWATER MONITORING WELL SURVEYING Following completion of groundwater well installation, a California -registered land surveyor will be contracted to survey the horizontal and vertical locations of each well. Horizontal control will be established for the center of the well vault, and vertical control will be established at the top north side of the inner PVC casing. Adjacent land surface elevation and top of monument elevation will also be surveyed. Horizontal datums will be in accordance with the appropriate California State Plane Coordinate System, and elevations will be in accordance with mean sea level per NAVD88. Horizontal and vertical survey accuracies will be ±0.5 feet and ±0.01 feet, respectively. All surveying activities will be in complete accordance with standards for • uploading Geo Tracker data. OTI E