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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 wastewater disposal systems. Mixing and dilution in the aquifer, as well as adsorption and adhesion in the soil, substantially reduce the concentration of percolating effluent. Irrigating plants and trees with treated effluent will also remove some of the nitrogen. The Hantzche 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. The equation and method is for estimating long-term effect on 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 recharge area, rainfall nitrate concentration, waste effluent quantity, and waste effluent nitrate concentration of the wastewater effluent. The equation for calculating the project's potential to adversely impact local groundwater by increasing nitrate concentrations, also defined as long term average concentration of percolating effluent, Nc, shown in Table 3.1. Mass Transport Soil Properties Preliminary percolation tests at the site have revealed that the soils have low permeability. The soil will allow limited infiltration of water through the surface soils due to the high clay content. Effluent remaining near the ground surface provides more opportunity for biologic processes to occur. Since the Project will use the tertiary treated effluent for irrigation of plants, grasses, and trees associated with the development, a significant portion of the effluent volume and nutrients will be absorbed and/or transpired. Sources of Nitrate Septic systems and dairies are significant sources of nitrate found in ground water. Farming activities using soil fertilization where sandy soils are present may also contribute to nitrate contamination, especially in shallow unconfined aquifers. The main source of nitrogen in domestic wastewater is urine (urea), which will be a primary waste product from the proposed Project. Hence, the proposed project will add nitrate to the groundwater through use of an on-site septic disposal system. The project consists of commercial warehousing, so the septic load will include bathrooms (toilets, sinks, urinals), and small breakroom area (sinks, dishwasher). The wastewater characteristics of the proposed Project will not be identical to residential wastewater, as greater nitrate concentrations are expected due to less dilution. 1 Thus, a value of 75 mg/I as N was assumed for influent nitrogen concentrations. However, the WWTP process proposed for the Project will reduce effluent nitrogen to 10 mg/I or less. 1 Residential wastewater is commonly found to have total nitrogen concentrations of 30 mg/I to 40 mg/I, which includes water from showers, clothes washing, additional food preparation, hygiene activities, etc. 5 1 P a 2 e