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Calculation of Alkalinity Requirement for Nitrification The nitrate-nitrogen loading from the wastewater effluent and the indigenous soil nitrogen is contingent upon the environmental factors required for nitrification to occur. These conditions include soil pore-space oxygen content, soil temperature, pH, electrical conductivity, organic matter, cation exchange capacity, and alkalinity. Alkalinity in wastewater effluent is derived from the City of Tracy well water, in addition to the introduction of wastes. Nitrification consumes approximately 7.1 mg of alkalinity for every mg of ammonia-nitrogen (NH4-N) oxidized. Nitrification of the Total Kjeldahl Nitrogen(TKN) concentration of 146 mg/L, from a septic tank sample that serves the existing Holly Commerce Center as discussed below, would require: 146 mg/L NH4-N x 7.1 mg CaCO3 = 1,037 mg/L alkalinity. The alkalinity concentration in the City water is unknown. The level found in the water table was 15 mg/L. Therefore,there is an insufficient alkalinity concentration for complete nitrification to readily proceed without the introduction of wastes and the alkalinity that may be derived from the soil environment. E. SURFACE WATER INFORMATION Storm water drainage management will be by on-site retention as engineered by Siegfried. Rainwater storage will theoretically provide a water table dilution effect to percolating wastewater effluent although this effect is indeterminable since the water table elevation and directional flow is variable throughout the entire project site. As referenced in the next Section, rainfall.in comparison to evapotranspiration is minimal. Climatic Data: Rainfall versus Evapotranspiration NLS§3.2. It is generally and scientifically accepted that when precipitation exceeds evapotranspiration(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 Table illustrates rainfall and evapotranspiration for the Tracy area. 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. . TABLE 4 PRECIPITATION AND Eto DATA FOR TRACY, CA Month 2 Years in 10 will have more Eto Average Potential Deep precipitation than: (in/mo) (in/mo) (in/day) Percolation(in/mo) January 2.93 1.55 0.05 1.38 February 2.21 2.24 0.08 -- March 2.38 3.72 0.12 - April 1.51 5.10 0.17 May 0.71 6.82 0.22 -- Page -5- Chesney Consulting