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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 Environmentai Health Department for approval of the proposed development. The study estimates the potential concentration of percolating effluent produced by the proposed 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 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 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 precipitation of rain. 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). The method takes into account the development area, soil denitrification factor, rainfall, rainfall nitrate concentration, waste effluent quantity, and waste effluent nitrate concentration from on-site septic systems. No contribution from the vineyard irrigation or any soil amendments is considered for the Hantzsche/Finnemore method. It is reasonably assumed that the irrigation and soil amendments would be applied at close to agronomic rates for a net balance of plant irrigation and nutrients. Mass Transport Soil Properties The percolation tests have revealed that the surface soils are very permeable. The soil will allow infiltration of water through the surface soils. The longer the effluent remains near the surface, the more biologic treatment may occur. If permeable soils exist to the Z1 depth of the ground water aquifer, it is possible that any remaining surface contaminants may be transported to the first saturated zone of the aquifer. `— LOGE 1402 Page 9