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• NITRATE LOADING STUDY The method utilized for the nitrate loading analysis is based on a simple and convenient mass balance formula, discussed in a published article by Hantzsche and Finnemore (1992). Hantzsche and Finnemore have found from investigations conducted in the Chico, California area, the water quality in the upper saturated ground-water zone closely approximates the quality of percolating effluent from septic systems. They have developed a simple method that could be used to estimate the quality of the percolating effluent from septic systems. The quality of the percolating effluent may represent the potential worst-case condition the upper aquifer would ever experience from the use of on-site septic systems. Mixing and dilution in the aquifer as well as adsorption and adhesion in the soil substantially reduce the concentration of percolating effluent. The Hantzsche and Finnemore equation is a conservative approximation of ground- water nitrate-nitrogen concentration resulting from the combined effect of on-site sewage disposal systems and precipitation of rain. The equation and method are for estimation of long-term effect ground-water quality, and are not intended for prediction of seasonal changes (Hantzsche and Finnemore, 1992). The method takes into account the development area, soil denitrification factor, rainfall recharge rate, rainfall nitrate concentration, waste effluent quantity, and waste effluent nitrate concentration from on-site septic systems. On-Site Sources of Nitrate The current sources of nitrate to the Site are the septic systems from the existing three employee housing units. The future on-site sources of nitrate will be the new septic systems for the proposed employee housing units. No contribution from any irrigation or soil amendment is considered for the Hantzsche/Finnemore method. It is reasonably assumed that any irrigation or soil amendments would be applied at close to agronomic rates for a net balance of plant irrigation and nutrients. Contribution of Rainfall An estimate of the quantity and quality of rainfall was required for the nitrate loading analysis. The Hantzsche and Finnemore method utilizes the "average recharge rate of rainfall' in calculating potential nitrate impacts to the aquifer. Not all rainfall will percolate into the aquifer; evapotranspiration, the sum of evaporation and plant transpiration, will reduce percolating effluent, especially in summer months. • LOGE 1833 Page 5