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' Diamond Lumber Manteca Quarierly Groundwater Montionng Page d April 1992 Quarterly groundwater samples were collected from the three monitoring wells installed by SRK The existing monitoring wells installed by BEI were not sampled Analytical groundwater samples included volatile hydrocarbons, BTEX and total lead The constituents of BTEX or volatile hydrocarbons were not detected in groundwater samples collected from SRK-MW1 and SRK-MW3 ' Analyses of the groundwater sample collected from SRK-MW2 detected elevated levels of volatile hydrocarbons and the constituents of BTEX Lead concentrations were detected in each of the monitoring wells ' 3.0 SCOPE OF SERVICES The scope of work for the Quarterly Groundwater Monitoring includes ' • Purging and sampling the wells according to PHS/EHD guidelines • Shipping the groundwater samples under correct chain-of-custody procedures to a California licensed laboratory for analyses • And measuring the static water level relative to the top of casing 4-0 GROUNDWATER GRADIENT Prior to the April 1992 quarterly groundwater monitoring event, SRK retained the services of Cella Barr Associates to provide elevations at the top of well heads relative to a known datum, and the locations of the wells relative to on-site structures This information is provided on Figure 1 (located in the pocket at the back of this report) Static water levels were measured in the monitoring wells installed by SRK on November 24, 1991, April 6, 1992, and August 31, 1992 using a Solnist water level meter Water levels were measured in the BEI monitoring wells on October 15, 1991 and August 31, 1992 The static water levels are provided on Table 1 The locking caps were removed from each of the monitoring wells, and the water level in each well was allowed to equilibrate approximately 230 minutes before the groundwater levels were measured An estimate of the groundwater gradient was made by using the most recent static water elevations ' to complete an orthogrdphic, c.onstruc.tion 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 casings) from the elevations of the well heads (referenced to the USGS Bench Mark D- 83, Brass Cap on the top step of Legion Hall, south tide of Yosemite Avenue, 1-1/2 blocks east of Main Street Elevation 38 051 tect) It should be noted that because the groundwater gradient is extremely flat (the difterence in static, groundwater elevations between the highest and lowest points is less than 0 2 feet), it was difficult to determine the true gradient 1 Steffen Robertson and Kirsten