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1 ' dDiamond Manteca,CA-November 1993 Groundwater Monitoring Page 2 �txs s 3.0 GROUNDWATER GRADIENT Prior to the April 1992 quarterly monitoring event, SRK retained the services of a registered California Land Surveyor to provide elevations at the top of well heads relative to a known datum (referenced to the USGS Bench-mark D083, Brass Cap on top step of Legion Hall, South side of Yosemite Avenue Elevation 38 051 feet), and the locations of the wells relative to on-site structures This information is provided on Figure 1 The locking caps were removed from each monitoring well and the static water levels were allowed to equilibrate approximately one hour before the groundwater levels were measured and recorded Static water Ievel data has been collected from each of the three monitoring wells during quarterly sampling events(performed by SRK)on November 24, 1991,April 6, 1992,August 31, 1992, February 5, 1993,June 29-30, 1993, and November 30, 1993, using a Solinst water level meter Table 1 contains static water level information collected to date by SRK TABLE 1: Static Water Levels 1 Oct 15, Nov 25, April 7, Aug 31, Feb 5, Jun 29-30 Nov 30 1991 (ft) 1991 (ft) 1992(ft) 1992(ft) 1993(rt) 1993(ft) 1993(tt) SRK-MW I Well Depth=38' Screened Interval(23'-38') NI 2345 2120 2545 2125 2255 2090 SRK-MW2 Well Depth=39' Screened Interval(24' -39') NI 2375 2152 2580 2155 2285 2120 ' SRK-MW3 Well Depth=39' Screened Interval(24' -39') NI 2375 2210 2570 2145 2276 21 10 BEI -MW4(Assumed to be MW2 to BEI Reports) Well Depth=30' Screened Interval(15' -30') 2567 NS NS 25 55 214 2260 21 10 BEI - PAW (Assumed to be MW_ in BEI Reports) Well Depth=30' Screened Interval(15' 30 ) 2508 NS NS 2590 21 55 2300 2120 BEI -MW6(Assumed to be MW l in BEI Reports) Well Depth=30' Screened Interval(15' -30) 2508 NS AIS 2585 2111 2110 2121 NOTES Static water levels measured from top of well casing using a Solmst Water level Indicator Top of casing elevations referenced to the USGS bench marls D-83,which is a brass cap on the top step of Legion Hall, south side of Yosemite Avenue Elevation 38 051 feet NI=No sample collected because monitoring well had not yet been installed NS=No sample collected ' The static water level elevations collected November 29, 1993, were on the average 1 5 feet to 1 8 feet higher than the previous sampling event (June 29-30, 1993) SRK contacted the Western Regional Climate Center to obtain precipitation data for the Manteca area Precipitation data was obtained from the nearest weather station(Stockton, California) A copy of this information gathered from 1985 through July 1993, is provided in Appendix A The BEI series monitoring wells were installed during August 1989 No precipitation was recorded during this month, which typically is one of the driest The SRK series monitoring wells were installed during November 1991 under the direct guidance of the PHS/EHD, and during that month 0 34 inches of precipitation was recorded Pre-1988 precipitation levels for November were between 1 and 2 inches By comparing monthly precipitation data in Appendix A with static water level information in Table 1, it can be deduced that static water levels are influenced by seasonal precipitation patterns Steffen Robertson and Kirsten