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' GW&SW Monitoring Report COE-WDR Project No. 894.2 September 1,2011 This report documents the groundwater monitoring event that was performed at the site on ' August 2, 2011. The sampling protocol followed the July 28 and August 24, 2000, Groundwater Monitoring Work Plan and Addendum prepared by Geological Technics Inc. as well as the January 8, 2001, Work Plan Addendum #2: Disinfection of Groundwater Monitoring Wells. 3.0 GROUNDWATER MONITORING On August 2, 2011, GTI personnel mobilized to the site to purge and sample the site's ten ' monitoring wells for the 3rd quarter 2011 monitoring event. The following sections present a discussion of the data collected during the monitoring event. ' 3.1 Site Hydrology Groundwater flow at the site is complex and may be affected by pumping wells, the Stanislaus River, and regionalSroundwater flow patterns. Overall groundwater flow trends ' to the southwest. For the 3r quarter 2011 groundwater monitoring event, groundwater gradient and bearing were not calculated due to the uneven nature of the groundwater surface below the site, however, a groundwater contour map was produced (Figure 3). It is believed ' that the water found in wells MW-7 and MW-8 is confined between two fine grained stiff layers of silts estimated to be present at a depth of approximately 25 feet bgs and 46 feet. The low rate of recharge that may have contributed to the well having historically gone dry from past monitoring events corroborates the above interpretation. The average elevation of groundwater under the site was 67.55 feet AMSL. The elevation of the main portion of the site is approximately 100 ft AMSL. Table 1 of Appendix A provides a summary of historical groundwater elevations, gradients and bearings of flow. Individual groundwater elevations in the site's wells ranged from 65.37 (MW-6) to 70.56 (MW-7) feet AMSL. Depth to groundwater ranged between 25.12 (MW-6) to 41.82 (MW-1) feet below grade surface (bgs) depending where on the site the wells are located. The average ' groundwater elevation was measured to have increased 1.35 ft from the May 3, 2011 event, and increased 5.21 ft from the 3rd quarter 2010 (July 26, 2010) event. ' 3.2 Groundwater Sampling Procedure Sampling for General MineralAnalysis Upon arriving on site on August 2, 2011, GTI staff personnel first opened all of the ' monitoring wells and took depth to water measurements. The monitoring wells were purged and sampled according to the procedure detailed below. Purging was started using the Waterra® purging system with dedicated tubing that has been installed in each monitoring well. Purging continued until the temperature, electric conductivity and pH of the groundwater had stabilized (<10% variation for three consecutive ' readings) indicating that formation water representative of aquifer conditions was entering the well. These water quality parameters were measured at intervals of each well volume ' Geological TecWCS Inc. 3 894 3rd QMR l l.doc