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City of Stockton Draft Amended Report of Waste Discharge(AROWD) Austin Road Landfill Work Plan r These data requirements will be filled by undertaking a soil boring and aquifer sampling program using Hydropunch®technology and by conducting aquifer pumping and recovery(interference) testing on the existing extraction wells and potentially the California Youth Authority water supply wells. To comply with CVRWQCB requirements for a Corrective Action Monitoring Programing, the field work will also include the installation and sampling of additional monitoring wells beyond the downgradient limit of the plume. 2.2.1 Plume Delineation Sampling The field investigation program consists of collection of soil samples and groundwater samples along three north-south trending transects located to the north,or downgradient,of the site. As depicted in Figure 2,one transect will be located along the northern limit of the contaminant plume, with the two other transects placed at the plume's leading edge. A single boring,identified as Hydropunch Location 4,will be placed at a central point in the contaminant plume between MW-11 and MW-13. Two permanent well clusters consisting of a shallow and deep well,MW-15 S,D and MW-16 S,D; are proposed outside the contamination limits. The purpose of these wells is to provide a monitoring location along the leading edge of the plume to track plume movement. These wells will be incorporated into the Correction Action Monitoring Program,designed to monitor the effectiveness of the remedial system in containing the plume. It is anticipated that two borings will be drilled at each transect,with a single boring at Hydropunch Location 4. Sample collection will consist of soil cores(collected at 5-foot intervals below the water table) and groundwater samples collected using the Hydropunch®method. Groundwater samples will be obtained for both the shallow aquifer(approximately 80 to 100 feet below grade),and deep aquifer (approximately 150 to 170 feet below grade)with only a deep aquifer sample taken from Location 4. Depending on the results,deep samples may not be collected at every location in a transect. The borings will be installed with a hollow-stem auger rig in accordance with EPA guidelines. Drilling and installation of the borings will be performed by a qualified subcontractor. The following subsections describe the sampling approach to be used. 2.2.1.1 Groundwater Sample Collection ■ The initial boring of each of the plume transects will be sited along the approximate position of the inferred edge of the PCE plume based on existing groundwater data. ■ Subsequent borings for each transect will be located based on the following criteria: 1. If groundwater sampling results from the initial boring for each transect indicate detectable concentrations of PCE (greater than 0.5 ug/L),a subsequent boring will be sited downgradient(northward direction). The second boring will be located where the PCE concentrations are likely to be non-detect(i.e.,less than 0.5 ug/L)based on the analytical results of groundwater samples from the first boring. If the groundwater sampling result from this subsequent boring shows non-detectable concentrations,then the plume edge has been defined. Otherwise,a third boring will be located farther downgradient based on the analytical results as previously stated. Greater than two borings per transect will be needed only if analytical results for the second boring indicate detectable PCE concentrations. W:\REPORTS\STOCKTON\AUSTIN\WORKPLAN.DOC Page 4