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71tappearts that the maximum mound height.that may occur under the flter bed, and above the current satic water table depth is 1,8 feet. This would leave a marginal distance of approximately five feet between the soilleffluent interface and the top of the mound (soiUeffluent interface z2 ft below grade + 5 ft separation distance= 7 ft, which the mound may rise to this depth: 9.0 ft minus 1.8 ft rise of mound z 7 ft.) For wastewater treatment to occur, the distance effluent must travel under unsaturated conditions through the soil environment is generally regarded to be five feet. Wastewater treatment in this respect is taken to be destruction of bacteria and viruses. If it is determined at some point in the future that mounding effects are preventing proper effluent treatment and disposal, the area designated as 100%replacement area may have to be activated. This may occur prior to attaining 1;050 gpd effluent flow volumes,but is unlikely. The nitrate concentration of the water table is over twice the MCL Drinking Water Standard. Total Dissolved Solids is over saline water, which is generally accepted to be 1,000 mg/L. Total alkalinity plays a significant role in nitrate formation. A concentration of 444 mg/L can be considered high for groundwater. It is normally the domestic water supply and the alkalinity in the wastewater effluent that determines nitrification potential. E. SURFACE WATER INFORMATION The surface water retention pond for the existing and future development of the project is located at the west and'south areas of the project. There should be no impact to impoundment water from the proposed new filter bed. The south pond is upgradient and somewhat crossgradient to the proposed filter bed and the addition of runoff water-percolating into the top aquifer mixing layer may create a dilution effect. Climatic Data: Rainfall versus Evapotranspiration It is generally regarded that when precipitation exceeds evapotranspiration (Eto), deep percolation of surface rainwater impoundment may occur. Evapotranspiration refers to water evaporation that takes place both at the soil surface and transpiration by plants, and is defined as water loss from a large field of 4-to-7 inch tall, cool-season grass that is not water stressed. A number of factors determine deep percolation and ultimately groundwater recharge, primarily domestic irrigation volumes and stormwater subsurface storage. The following chart illustrates rainfall and evapotranspiration for the Tracy area. Precipitation data was obtained from the Soil Survey of San Joaquin County. The "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): 7 Chesney Consulting