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xrt �--. Site Assessment Report April 5, 1991 W 139 South Center,'Stockton,CA Page 7 well from the botrom of the well bore up to 5-feet above the top of the well screen. A 2-foot-thlck layer of hydrated bentonfte pellets was placed above each sand filter pack and a cement surface seal was set w. to grade love]above the bentonite. A traffic-rated BVK O Wheaton box was pla—d over the cap. The _ vrellheads were sealed with locking plugs. Well construction details are presented on the drill togs In Appendix B. Well k>cation photographs are presented as Figure 3. Before the rement seal for monitoring well MW-4 had set oompletely,a gasoline delivery truck passed over it and over the red waming cane that had been placed atop the traffic cover. Consequently, Groundwater Technology staff personnel had to return to the site and rebuild the surface m protection for this well. ftnitoring Well v"Ipmeal Standard Groundwater Technology well development Procedures require new wells to be developed using a combination of bailing,surging and pumping. Groundwater Technology employed a truck-mounted surge block and bailer system to develop the four new wells on March 8, 1991. Development of the monitoring wells entailed the extraction of between 60- and 100-gallons of well water. The well was sampled when the well volurra had recovered to at least 80 percent of Its original static water level. During development,the casing for monitoring well MVI'-4 was found to be bent slightly,so that ,., the metal surge block could not pass down tt. Therefore,a PVC bailer was used to develop this well. GROUNDWATER MONITORING AND SAMPLING On F=ebruary 15, 1991, monitoring wells MW-1,MW-2 and MW-3 were professionally surveyed to a common datum to determine wellhead elevations. The depth-to-groundwater was then measured using an Interface Probe, to make a preliminary determination of the groundwater gradient direction prior to the Installation of MW4 near the waste-oll tank.On the basis of this preliminary determination of r groundwater-gradient direction,monitoring well MW-4 was sited to the north of the waste-oil tank,In a downgradlent direction from the waste-oll tank, On March 8, 1991,the elevation of the wellhead of MW-4 and the horizontal position of the four monfhxfr g wells were professionally surveyed and referenced to a common United States Geological Survey datum. GRouND"ATER i TECHNOLOGY;INC,