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The possibility still exists that very shallow wells (<100 ft in depth with a pump set high in elevation) in the Valpico Section locale may be affected by this recharge volume removal. It must be recognized,however,that the proposed housing development will also provide an indeterminable volume of recharge from domestic irrigation,wastewater treatment percolation ponds,on-site septic systems and stormwater runoff ponds. POTENTIAL DRAWDOWN EFFECTS The only well that may be affected by drawdown created from the CSA-44A well is the Fairoaks well-CSA-44 No.2,since it is also screened in the lower zone. Bookman-Edmonston Engineering completed a Theis Analysis for a Single Pumping Well(See pg.6-17). The Theis equation was used to evaluate drawdown for a well pumping 1,500 gallons per minute which is similar to the production rate for the City of Tracy wells, and may be applicable for CSA-44A. Figure 25 in the Bookman-Edmonston Report illustrates the drawdown at various distances from the pumping well. The data in this Figure was used to determine possible influence to the Fairoaks wells from the CSA- 44A well. The Fairoaks well is approximately 1,250 feet from CSA-44A. Interpolating the distance (1,250 ft) from the pumping well (CSA-44A), it is determined from this graph that the drawdown would be 22.5 feet at the Fairoaks well, after 365 days of pumping at 1,500 gpm. From the well schematic for the Fairoaks well located in the Appendices,the upper well screen is located 486 feet bgs or-368 feet MSL. The standing water level was measured in July 1998 and found to be 158 ft bgs (40 ft MSL). Therefore, the drawdown effect from the CSA-44A well should not influence production from the Fairoaks well. Additional data was obtained from Groundwater and Wells' to illustrate the potential for well interference. The Table below shows interference in wells at the referenced distances from a production well. The time of pumping for this data was 7 days with a calculated well yield of 1,000 gpm. These numbers are correct when all of the assumptions for the Theis equations are satisfied and offer an approximate guide to anticipated drawdowns. Aquifer Transmissivity Drawdown Drawdown Drawdown Drawdown Drawdown Type gpd/ft in at 100 ft at 500 ft at 1,000 ft at 10,000 ft Production Well ft ft ft ft Unconfined 100,000 16.7 6.1 2.4 0.9 0 50,000 31.8 10.7 3.3 0.1 7 0 25,000 60.4 18.2 3.4 0 0 Confined 100,000 22.8 12.2 8.5 6.9 1.6 50,000 43.9 22.8 15.4 L.3 1 .7 25,000 1 84.7 j 42.5 j 27.7 21.3 0.2 Page -5- Vaffey Ag Research