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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. z Thus, a value of 75 mg/I as N was used for the analysis. Groundwater Gradient CASGEM data indicate the groundwater gradient is west to east, as could be expected due to municipal and agrarian groundwater pumping. Water from the Delta (approximately mean sea level) creates a recharge boundary for lowering groundwater tables to the east. CASGEM well data located immediately west of 1-5 and Highway 12 indicate groundwater is approximately-2' msl and relatively consistent, whereas approximately 2 miles east (Highway 12 and N. Deveries Road), groundwater is-12' msl and declining over time. 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 adverse nitrate impacts to the aquifer. It is assumed that not all rainfall will percolate to the aquifer, as some water may be lost to evaporation or transpiration. However, most of the rainfall in California is during the cooler months when evaporation is less. Hence, if water is held in detention for long periods, and the holding basin soils are permeable, much of the water will percolate. Rainfall recharge (or deep percolation of rain) is a significant factor in the nitrate loading estimate in the Hantzsche and Finnemore model. There are a variety of rainfall data that span various timeframes for the Lodi, California area. For analysis, both 30 year and 5 year averages were used to estimate annual precipitation, resulting in values of 19.02 inches/year and 16.78 inches/year. For purposes of this report, the more conservative value of 16.78 inches was used for calculating nitrate loading. Due to requirements for new developments to detain site runoff, some of the storm water will be held and either percolate into the groundwater or evaporate. Only peak flows will need to be pumped off- site, as they will exceed the capacity of the detention basins. For purposes of determining nitrate loading, an estimated 50%of the rainfall will be retained.The nitration concentration for rainfall was estimated to be 1 mg/L-N (Hantzsche and Finnemore). Denitrification Reductions Denitrification is a process that occurs in the septic system drain field whereby certain bacteria metabolize the oxygen in nitrate (NO3) in the wastewater and release nitrogen gas (N2)to the atmosphere. Due to the biologic processes in the shallow soils, nitrogen in the leach field may undergo a 2 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. 51 Page