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percolation ponds, additional subsurface flow is induced to Oakwood Lake which <br /> would increase the amount of pumping from the Oakwood Lake to maintain the lake <br /> level at -14.0 feet. To mitigate any impact to the lake, it is recommended that <br /> discharge wells be installed at the pond site to pump groundwater at a rate equal to the <br /> pond recharge to maintain groundwater at the existing levels. These discharge wells <br /> will also add a degree of reliability to the system and will allow the system to perform <br /> adequately under extreme hydrologic conditions. The model was modified to simulate <br /> groundwater levels while groundwater pumping occurs at a rate equal to the ultimate <br /> buildout of 600,000 gpm. <br /> IV. POND PERFORMANCE UNDER CONTROLLED GROUNDWATER OPERATION <br /> While the modeling was to assess the impact of the San Joaquin River on a site <br /> previously determined to be suitable for the percolation ponds, the importance of <br /> maintenance of the area's groundwater levels became apparent. The same wells <br /> utilized to mitigate groundwater flow impact on Oakwood Lake could be used to <br /> artificially control or regulate local groundwater levels to maintain the 5 foot separation <br /> between the bottom of the pond and the top of the groundwater mound. A review of <br /> the historical groundwater level data obtained from the Department of Water Resources <br /> (1990) and the San Joaquin County Flood Control and Water Conservation District <br /> (1983-1992) showed that the groundwater elevations in the area can be expected to rise <br /> approximately 10 feet from present day conditions. <br /> Additional model simulations were performed to judge performance of the ponds when <br /> the groundwater levels are 5 feet and 10 feet higher than the current -2.0 feet; i.e., at <br /> 3.0 to 8.0 feet above mean sea level and wells are used to control the groundwater. In <br /> these simulations, two discharge wells, each operating at 300,000 gpd flow rate, were <br /> located approximately 350 feet from the center of the pond area. The results obtained <br /> after one year of normal river stage and six months of flood condition are given in <br /> Figures 6 and 7, when groundwater elevation is 3.0 feet, and in Figures 8 and 9, when <br /> groundwater elevation is 8 feet. The results show that the groundwater mound <br /> APRIL 1994 CCIP/SIMULATION OF PERCOLATION POND PERFORMANCE PAGE 7 <br />