ARCHIVED REPORTS_WELL INSTALL AND QUARTERLY GROUNDWATER MONITORING REPORT 2008

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' Well Installation and Quarterly Groundwater Monitoring Report Second Quarter 2008 1950 West Fremont Street, Stockton, California ' 3.0 SUMMARY OF RESULTS ' 3.1 SUBSURFACE LITHOLOGY ' The native soil in the vicinity of the site apparently consists of flood basin deposits, generally clay and silt with some sand. Lithologic logs obtained during the monitoring well installation activities in June 2008 generally show that the asphalt or concrete surface is underlain by a clay and clayey silt layer ' extending to the depth 20 feet bgs. Silty sand was observed in the three borings at depth ranging from 12.2 feet bgs to 14.5 feet bgs. A very thin sand interval was observed in boring MW-1 at a depth of 12.0 ' to 12.2 feet bgs. ' 3.2 GROUNDWATER ELEVATIONS Depth to water measurements during the June 16, 2008 monitoring event were between 6.03 feet bgs and ' 7.62 feet bgs. Ground water elevations ranged from -1.70 feet MSL in well MW-3 to -0.33 feet in well MW-1. Depth to water measurements and groundwater elevations for June 16, 2008 are summarized in ' Table 1.A contour map of groundwater elevations are shown on Figure 4. The direction of flow at the site is approximately toward the north. The horizontal hydraulic gradient is approximately 0.004 feet/feet,based on the June 16, 2008 data. ' 3.3 SLUG TESTING Slug test data files were pre-processed in Microsoft Excel®to adjust the data for the start time of the test ' and to determine the change in water level from initial static level. The hydraulic conductivity was calculated from slug-out tests using the AQTESOLV® for Windows aquifer test analysis software. The ' data were analyzed using the method of Bouwer and Rice. (1976 and 1989) for confined aquifers. Based on conditions encountered during drilling and subsequent groundwater sampling, it was determined that confining conditions hold at wells MW-1 through MW-3. Due to transducer malfunction, the slug-out test for well MW-3 was calculated using data recorded manually during slug testing. The water level was within the well-screen interval at each of the wells. Having the water level in the well-screen interval created a significant response (double straight-line effect) as the filter pack filled ' with water during slug-in testing or drained of water during slug-out testing. Bouwer (1989) developed a correction for the filter pack response. This correction was made in AQTESOLV® for Windows, and the ' curve was matched to the later data that reflect the aquifer response rather than the filter pack response. Project 102790 9 July 2008