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Calculation of Alkalinity Requirement for Nitrification \' The nitrate-nitrogen loading to the underlying groundwater 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 on-site domestic well water, in addition to the introduction of wastes,which was determined to be 616 mg/L total alkalinity. Nitrification consumes approximately 7.1 mg of alkalinity for every mg of ammonia-nitrogen (NH4-N) oxidized. Nitrification of the average Total Nitrogen(TN) concentration of 90 mg/L, as determined from an on-site septic tank effluent sample, would require: 90 mg/L NH4 N x 7.1 mg CaCO3 =639 mg/L. The alkalinity concentration in the wastewater effluent is 616 mg/L. Therefore, sufficient alkalinity may exist in the wastewater for nitrification to proceed. E. SURFACE WATER INFORMATION Storm water drainage management will be by on-site retention. Percolating rainwater will theoretically provide an indeterminable water table dilution effect to percolating wastewater effluent since the disposal area is cross-gradient to the rainwater retention basin. However, 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 potentially 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 Stockton 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. Evapotranspiration data was obtained from the California Irrigation Management Information System(CIMIS): TABLE 4 PRECIPITATION AND Eto DATA FOR STOCKTON, CA Month 2 Years in 10 will have more Lto Average Potential Deep precipitation than: (in/mo) Percolation (in/mo) (in/mo) (in/day) 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 1 0.50 6.82 0.22 -- i Page -5- Chesney Consulting