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�� March 2006 5 053-2442 2.2 Monitoring Wel[ Installation We propose to install four shallow and two deep monitoring wells on-site to facilitate the following: • Determination of groundwater flow direction and seasonal variations in flow direction; • Determination of the vertical extent of VOC-affected groundwater; and • Documentation of temporal variations in VOC concentrations in groundwater. Proposed monitoring well locations are shown on Fig�'e 2. Prior to installing the monitoring wells, �r... we will advance push probe borings at five locations to characterize geologic conditions and document the vertical distribution of VQCs in groundwater. This work, referred to as "hydroprofiling," will involve collecting groundwater samples from borings at predetermined depths � based on lithologic conditions. Lithologic conditions will be determined by first collecting continuous soil core from ground surface to bedrock (estimated to be present at approximately 90 feet) or probe refusal. Lithologic characterization borings will be grouted with a bentonite slurry � immediately a£�er the boring is completed. ' Soil core will then be exammed in the field to identify features such as high permeability zones or � clay layers that would act as either preferential pathways for VOC migration or barriers to vertical flow. A push probe horing will then be ad�anced immediately adjacent to lithologic characterization borings and groundwater samples will collected from the dual tube drill string at depths predetermined, as described above. Employment of this sample technique will enable better � characterization of the vertical distribution of VOC-affected groundwater. Groundwater samples will be analyzed on-site in a mobile laboratory. Ten percent of the groundwater samples will also be submitted to a fixed laboratory for confirmation analysis. Table 1 lists parameters and reporting I limits for a fixed laboratory and Table 2 lists parameters and reporting limits for the mobile laboratory. � Geologic and water quality data obtained from the hydroprofiling work will be used to determine screened intervals for monitoring wells. We intend to install deep monitoring wells near probe GP-31 and GP-20 (Figure 2) at depths coincident with the deepest indication of VOC affected water. � Shallow water table wells will he installed adjacent to the deep wells, and two additional shallow wells will be installed to the north and south of probe GP-20, to delineate the width of the VOC plume near the downgradient property boundary. � All monitoring wells will be installed using a hollow-stem auger drill rig. Borings for the wells will be drilled using 4.25-inch inside diameter hollow-stem augers. Borings for the shallow wells will be drilled to approximately 18 feet below ground surface. Split spoon samples will be collected at Z,5- � foot intervals while ad�ancing the horing. Once the target depth of the well is achieved, shallow wells will be constructed by placing 2-inch diameter, flush threaded, Schedule 40 polyvinylchloride (PVC) casing in the hollow-stem drill string. The bottom of the well will include a ten-foot section of � 0.01-inch slot screen. The screened section of the monitoring well will be filter packed using inert 30-40 silica sand. The sand pack will he added to the annular space between the borehole wall and the PVC casing as the augers are removed fromthe horing to a depth of approximatelyone to two feet � above the well screen. Emplacement of the filter pack will be verified by probing the annular space with a PVC rod or weighted measuring device as the sand is added and the augers removed. The remaining annular space will he backfilled using granular bentonite. Deep monitoring wells will be � constructed with a five foot section of stainless steel well screen and black iron riser pipe. � �