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Diamond Lumber-Lodi Quarterly Groundwaler Monitoring Page 5 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 City of Lodi Bench-Mark 710, Brass Cap at the southeast corner of Stockton Street and Locust Street: Elevation 49.74 feet). It should be noted that the groundwater elevations varied by only a few tenths of feet. Based on calculations using data collected during the April sampling event, the trend of the groundwater gradient was estimated to be N27.5°E, with a nearly horizontal gradient. Trend refers to the bearing of a line on a horizontal plane. Bearing is measured in degrees east or west from north or south. It should be noted that because the groundwater gradient is extremely flat (the difference in static groundwater elevations between the highest and lowest point is approximately 0.15 feet) it was difficult to determine the bearing. Our calculations indicate that the gradient is from S27.50W to N27.5°E. Because the Mokelumne River is located north of the Diamond Lumber facility, it was assumed that the natural groundwater gradient would mimic the surface water flow direction, an assumption which is qualified by our calculations. SRK is currently gathering subsurface groundwater information from private, municipal and irrigation wells Iocated within 2,000 feet of the site, pursuant to the request of the San Joaquin County PHS/EHD (Correspondence dated September 14, 1992). This information was not available at the time of this report, and will be provided as an addendum to this quarterly monitoring report upon receipt. Recent communication with Mr. F. Biehler (City of Lodi) indicates that a generally horizontal groundwater table with minor local variations exists in this area. Mr. Biehler is forwarding i further information which will be included in forthcoming monitoring reports, i5.0 GROUNDWATER SAMPLING Three additional casing volumes were purged from well SRK-MW1 and SRK-MW3 before analytical samples were collected. Monitoring well SRK-MW2 was bailed dry after one casing volume was removed. This well was allowed to recharge for approximately one hour, however, there was not a sufficient volume of water in the well to sample. The analytical groundwater samples were collected after the pH, temperature, and conductivity had stabilized. "Stabilized" was defined as three consecutive readings within 15% of one another. Copies of the Field Groundwater Purging/Sampling Logs are provided in Appendix A. Copies of the Geologic Logs and Monitoring Well Construction Diagrams are provided in Appendix B. Dedicated pre-cleaned tellon bailers and nylon rope were used to retrieve the water samples. The water samples were carefully poured into laboratory grade sample containers equipped with teflon lined lids, then placed in an iced cooler. The analytical parameters include volatile hydrocarbons (by EPA 8015M, GC/FID Purge & Trap), benzene, toluene, ethlybenzene, and xylene (BTEX) i (Aromatics by EPA 60218020, GC/PID Purge & Trap); and total lead (EPA Method 239.2 GFAA). The analytical groundwater samples were placed in a cooler containing additional frozen blue ice packets and shipped following strict chain-of-custody procedures to a California certified laboratory (ACZ Laboratories) for analysis. �� T` `•W ., Steffen Robertson and Kirsten 3zw..1 \3-oLr I Y.LM