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E. SURFACE WATER INFORMATION Storm water management will be on-site containment as required by SJC planning and public works departments. There should be no impact from on-site containment to percolating effluent water from the septic system. Since the groundwater directional flow is to the west, percolating rainwater west of the disposal area into the top aquifer mixing layer may create a dilution effect to the upgradient percolating septic system effluent. Groundwater dilution effects can only be truly discerned with complicated groundwater monitoring and modeling. According to a scientific paper authored by Shaw and Turyk(1994),reduction of nitrate concentrations in groundwater can occur primarily through dispersion,or by percolating rainwater recharge. Climatic Data: Rainfall versus Evapotranspiration NLS§3.2. It is generally and scientifically accepted that when precipitation exceeds evapotranspiration �3 3J (Eto),deep percolation of surface rainwater may occur. Evapotranspiration refers to water evaporation that takes place both at the soil surface and transpiration by plants. The following chart illustrates rainfall and evapotranspiration for the Stockton area,which is the closest data to Lodi available. Precipitation data was obtained from the Soil Survey of San Joaquin County. The conservative"2 years in 10"data was used and not the"average rainfall'data. Evapotranspiration data was obtained from the California Irrigation Management Information System(CIMIS): TABLE 4 PRECIPITATION AND Eto DATA FOR STOCKTON, CA (Closest Data) Month 2 Years in 10 will have more Eto Average Potential Deep precipitation than: (in/mo) (in/mo) (in/day) Percolation(in/mo) January 4.42 1.24 0.04 3.18 February 3.20 1.96 0.07 1.24 March 3.43 3. 41 0.11 -- April 1.92 5.10 0.17 May 0.50 6.82 0.22 - June 0.25 7.80 0.26 - July 0.23 8.06 0.26 - August 0.40 7.13 0.23 -- September 0.76 5.40 0.18 - October 1.39 3.72 0.12 - November 3.31 1.80 0.06 1.51 December 1 3.67 0.93 0.03 2.74 2� TOTALS(in.) 18.92 53.4 ------ 8.67 6