ARCHIVED REPORTS_WELL INSTALL AND QUARTERLY GROUNDWATER MONITORING REPORT 2008

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1 Well Installation and Quarterly Groundwater Monitoring Report Second Quarter 2008 1950 West Fremont Street, Stockton, California ' 2.2 FIELD ACTIVITIES ' The field activities performed at the site included the following primary tasks: • Drilling three 8-inch diameter boreholes to approximately 20 feet below surface ground(bgs); • Converting each of the three boreholes into 2-inch diameter groundwater monitoring wells; • Development and groundwater sampling of the newly-installed wells; • Laboratory analysis of groundwater samples. 2.2.1 Soil Borings All drilling activities were performed by Resonant Sonic, International (RSI) of Woodland, California, a licensed C-57 driller, on June 9 and 10, 2008, under the oversight of an Earth Tech Professional Geologist. The three borings (MW-1, MW-2 and MW-3) were advanced utilizing a Geoprobe 6620 DT limited-access track-chassis combo rig equipped with a combination direct push technology (DPT) drive head and HSA drive head (combo rig). DPT was used to advance a pilot boring and collect soil samples using a 2.125-inch diameter dual-tube sampler and rods. The borings were over-drilled using 8.25-inch diameter HSAs for installation of 2-inch diameter wells. Soil samples were collected continuously from the soil borings using the dual-tube sampler lined with acetate sleeves. Soil samples were collected for lithologic logging purposes only; soil samples were not submitted for laboratory analysis.Based on depth to water observed during previous investigations, all boring depths were 20 feet below ground surface (bgs).Boring logs are presented in Appendix B. 2.2.2 Well Installation The monitoring wells (MW-1 through MW-3) were installed to approximately 20 feet bgs and constructed with 2-inch diameter schedule 40 polyvinyl chloride (PVC) flush thread casing. The wells were constructed with 15-foot long, 0.010-inch slot, schedule 40 PVC well screen placed from ' approximately 5 to 20 feet bgs. Blank casing was installed from the top of the well screen to approximately 0.5 feet bgs. All wells were installed using a filter pack of Lonestar #2/12 sand placed to 1 foot above the top of the screen interval. The filter pack was periodically sounded to monitor the depth and to locate points of bridging between the well casing and the borehole wall. After placement of the filter pack, a 1 to 2-foot- thick zone of bentonite chips was added. The bentonite chips were hydrated with a minimum of 5-gallons ' of potable water for no less than 30 minutes. The remainder of the annulus was sealed with a cement Project 102790 4 July 2008