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systems. Mixing and dilution in the aquifer as well as adsorption and adhesion in the soil substantially P � Y reduce the concentration of percolating effluent. 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 from on- site septic systems. 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 Figure 3. Mass Transport Soil Properties Preliminary percolation tests at the site have revealed that the soils are permeable.The soil will allow moderate infiltration of water through the surface soils. Effluent remaining near the ground surface provides more opportunity for biologic processes to occur. In addition, soil borings at the site consistently show the presence of numerous lenses of sandy clays in the 0'to 50' depth range. Although it is not expected that the sandy clays will act as impermeable barriers, it will reduce the rate of transport and greater dispersion of nitrate. 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 proposed project will add nitrate to the groundwater through use of an on-site septic disposal system. Although there are no data to determine groundwater gradients at the site, it is likely to follow the slope of the ground,generally from south to north. The distance between the property and a groundwater boundary(coastal hills) is short,so areas/activities that may contribute a nitrate load upgradient are limited. According to satellite photography, agrarian use is minor,and there are only 5 to 10 houses on large AR zone lots that are assumed to have on-site septic systems. The project consists of commercial warehousing,so the septic load will include bathrooms(toilets,sinks, urinals),and small breakroom area (sinks, dishwasher). Since the sewage characteristics are not the same as residential (which would include wastewater from showers, clothes washing, additional food preparation, hygiene activities),the nitrate concentration is greater. Thus, a value of 70 mg/I as N was used for the study. 51