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NITRATE LOADING STUDY Because of concerns of nitrate leaching into ground water from septic systems, a nitrate loading analysis was required by the San Joaquin County Environmental Health Department for approval of the proposed project. The study estimates the potential concentration of percolating effluent produced by the project over the long term. Where percolating effluent leaches into the ground, ground water quality may be impacted to some degree should the effluent reach ground water. The method utilized for the nitrate loading analysis is based on a simple and convenient mass balance formula, discussed in a published paper by Hantzsche and Finnemore (1992). Hantzsche and Finnemore have found from investigations conducted in Chico, California, and other areas, that 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 would tend to 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 percolating recharge waters. The equation and method is for estimation of long-term effect ground-water quality, and is not intended for prediction of seasonal changes (Hantzsche and Finnemore, 1992). For the purpose of the Hantzsche and Finnemore equation, only septic effluent is included in the nitrate loading calculation; no other potential sources of nitrate are considered. The method takes into account the development area, soil denitrification factor, rate of recharge from percolating waters, waste effluent quantity, and waste effluent nitrate concentration from on-site septic systems, and predicts the nitrate concentraticn of percolating effluent. Mass Transport Soil Properties The percolation test has revealed that the surface soils are moderately permeable and will allow some infiltration of water. The longer the effluent remains near the surface, the more biologic treatment may occur. If permeable soils exist to the depth of the ground- LOGE 1910 Page 7