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Groundwater Monitoring Plan 4 <br /> During drilling, soil samples will be collected at selected intervals using a California modified split- <br /> spoon sampler lined with sample sleeves. The samples will be examined for lithologic <br /> characterization and described using the Unified Soils Classification System (USCS). Select samples <br /> may be analyzed for physical and chemical characteristics. <br /> Groundwater monitoring wells will be installed using hollow-stem auger drilling methods and will <br /> extend to a maximum depth of 45 feet bgs. The actual well depth and screen length will be <br /> determined based on the geologic conditions. The wells will be constructed of 2- diameter PVC <br /> casing with a maximum of 20 feet of 0.01-slot screen. The slot size of the well screen may be <br /> modified based on observations of subsurface soil encountered during installation. The filter pack <br /> will extend from the base of the borehole to at least two feet above the top of the screen. A <br /> minimum two-foot thick bentonite transition seal will be placed on top of the filter pack. The <br /> remainder of the borehole to within one foot of the surface will be backfilled with cement grout. <br /> Groundwater well depth, sand pack height, and bentonite thickness may vary based on the depth of <br /> groundwater. Each well will be completed with a locking well cap. A protective steel casing or flush <br /> mounted well box will be set in concrete around the wellhead. The type of surface completion will <br /> be determined in the field for each well location. <br /> 3.3 Monitoring Well Development <br /> Initial well development will be conducted immediately after placing the filter pack by surging to <br /> settle the filter pack prior to placing the bentonite transition seal. Additional well development will <br /> completed after well installation by surging and pumping or bailing until physical parameters such as <br /> pH, temperature, and conductivity stabilize and the water appears clear or the well goes dry. If the <br /> subsurface soil is comprised primarily of fines,it may not be possible to achieve low levels of <br /> turbidity. <br /> 3.4 Monitoring Well Locations and Site Survey <br /> A California licensed surveyor will survey the top of casing of each monitoring well for horizontal <br /> and vertical control. The horizontal control will be tied into the California coordinate system and <br /> the vertical control will be tied into a county benchmark. The ground elevation will also be <br /> determined at each well location. <br /> 3.5 Well Gauging and Groundwater Sampling <br /> 3.5.1 Water Level Gauging <br /> Groundwater levels in all wells at the site will be measured with an electric water level meter prior to <br /> sampling. The probe will be decontaminated before gauging each well. Measurements will be taken <br /> from the surveyed reference point marked on the top of the PVC risers. Water level measurements <br /> will be taken within 0.01 foot and recorded. <br /> PAwp\jobs\20587\CAO GW Workplaa.doc—DCN 12495 January 2002 <br />