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4.4 Monitoring Wells <br /> Four monitoring wells will be installed after the extent of impacted soils has been <br /> delineated. The monitoring wells will be installed to evaluate hydrogeologic characteristics (such <br /> as the groundwater depths, flow direction, and gradient) and sampled to assess the presence of <br /> dissolved petroleum hydrocarbons. The actual well locations will be determined after review of the <br /> soil analytical results from the soil borings. <br /> On the assumption that the water table is approximately 30 feet below ground <br /> surface, the wells will be installed to a depth of 40 feet. The soil borings in which the wells will <br /> be installed will be drilled using hollow-stem augers. Soil samples will be obtained at five-foot <br /> intervals using the same equipment and procedures described in Section 4.3. <br /> The monitoring wells will be constructed with 2-inch diameter, Schedule 40 <br /> polyvinyl chloride (PVC) casing connected with flush-threaded joints. The actual well depth and <br /> screen interval placement will be determined in the field after the static groundwater level is <br /> measured. The well screen will have a maximum length of 15 feet; the screen will extend 10 feet <br /> below and 5 feet above the water table. The well screen slot size and filter pack size will be <br /> specified at the time of drilling and will be based on the lithology encountered. Our review of the <br /> site-specific conditions described in the previous reports leads us to anticipate that the screen slot <br /> size will be 0.010 inches and that the filter pack will consist of Lonestar 2/16 sand. <br /> The well casing and screen will be installed through the hollow-stem augers. The <br /> hollow-stem augers will be simultaneously removed from the borehole as the filter pack, bentonite <br /> pellet seal, and grout seal are emplaced. The annular space around the well screen will be packed <br /> with the filter pack to a height of two feet above the top of the well screen. Above the filter pack, a <br /> two-foot-thick bentonite pellet seal will be emplaced. On placement and hydration of the bentonite <br /> pellet seal, the remaining annular space will be grouted to about one foot below grade with a <br /> Preliminary Site Investigation Work Plan-Final July 9, 1998 <br /> Roberts Property(Former Vernalis Pump Station) <br /> Vernalis,California <br /> 11 <br />