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Diamond Lodi,CA-November 1993 Groundwater Monitoring Page 2 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 City of Lodi Bench Mark 710, Brass Cap at the southeast corner of Stockton Street and Locust Street: Elevation 49.74 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 allowed to equilibrate approximately one hour before the groundwater levels were measured and recorded. Static water level data has been collected from each of the three monitoring wells during quarterly sampling events (performed by SRK)on November 25, 1991, April 7, 1992, September 1, 1992, February 4, 1993, June 28, 1993, and November 29, 1993. Table 1 contains static water level information collected to date by SRK, and most recent data qualify earlier results. The static water levels contained in Table 1 are the depths below ground surface (top of casing) at which groundwater was encountered. These depths were measured using a Solnist Water Level Meter. TABLE 1: Static Water Level Depths Measured From Top of Casing Nov 25, 1991 Apr,7, 1992 Sep 1, 1992 Feb 4. 1993 Jun 28,1993 Nov 29,1993 (feet) (feet) (feet). (feet) .(feet) ([eet} F-MW 5' Screened Interval(50' -65') 51.15 49.75 53.95 50.05 49.65 51.12 0' Screened Interval(45'-60') 51.40 50.00 54.15 50.30 49.90 51.34 SRK-MW3 Well Depth= 59' Screened Interval (44' -59') 51.50 50.17 54.30 50.40 49.90 51.48 NOTES: Static water levels measured from top of well casing using a Solinst Water Level Indicator Top of well casing elevations referenced to City of Lodi MB##710 The static water level elevations collected November 29, 1993, were on the average 1.5 feet lower than the previous sampling event (June 28, 1993), and comparable with the water levels collected during the November 25, 1991 sampling event. SRK contacted the Western Regional Climate Center to obtain precipitation data for the Lodi area. Precipitation data was obtained for the Lodi weather station (Station Number 045032). A copy of this information gathered from 1985 through July 1993, is provided in Appendix A. The SRK series monitoring wells were installed during November 1991 under the direct guidance of PHS/EHD when the Lodi area received a monthly accumulation of 0.48 inches of precipitation. An estimate of the groundwater gradient was made using the most recent static water level elevations to complete an orthographic construction known as a 3-point problem (Davis, G.H., 1984, Structural Geology { of Rocks and Regions: John Wiley & Sons, pp 210). Solving a 3-point problem requires elevation control for at least three points that lie on a common plane, in this case the groundwater surface. The elevation control was obtained by subtracting the static water levels (measured from the top of well casing) from the elevations of the well heads (referenced to the City of Lodi Bench-Mark 710: 49.74 feet). 1t should be 325a4.1AV QtdyLd Steffen Robertson and Kirsten