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FiSeptember 30, 2007 NOA Project Number: E07141A 3.0 SOURCES AND IMPACT OF NITRATE TO GROUND WATER 3.1 Current Off-Site Sources of Nitrate Septic systems, agriculture, and dairies in the area may be the most significant sources of nitrate. Septic tank use in the vicinity discussed in Sectio and to be low. A water sample was taken from the on-site well. Nitrate was fou at 28.0 mg/L-N 3, below the maximum contaminant level (MCL) of 45 mg/L-NO3 set by the Unite tates PA. A discussion of issues related to Fit, potentially high nitrates in the area is included in Section 4.4 of the SSS. 3.2 Contribution of Rainfall An estimate of the quantity and quality of rainfall was required for the nitrate loading analysis. The estimate of deep percolation of rain is based on the average monthly precipitation of rain fall and evapotranspiration for the West Tracy area of California. An estimate of potential deep percolation of rain water recharge into the ground is required for the nitrate loading calculation. hSince the site had rapid percolation rates,we will make the assumption that nearly all the rainfall will infiltrate the ground fairly rapidly. Based on this method,we estimate the deep percolation of rain is based on 80 percent of the long-term average total rain fall for the Tracy area (San Joaquin Soil Survey). The 20 percent reduction is toallow or serne��v oration and transpiration of plants. Runoff is not expected: 12.18 inches x 0.8 = 9.74 inches. his method is not appropriate for sites Fwhich do not have relatively high infiltration ra The nitrate concentration of rainfall was estimated to be 1 m L-N ntzsche and Finnem F1992). g/ ( ore, 3.3 Current On-Site Sources of Nitrate Nources of nitrates be des rainfall are recognized for the parcels. F o s 3.4 Future On-Site Sources of Nitrate --� F! 3.4.1 Quantity and Quality ofDomestic Wastewater From Proposed Project The following discussion is for determining the long-term waste water flow generated from the 1 proposed residences for the nitrate loading analysis and should not be used for septic system design purposes. Typically, use estimates for the sizing of septic systems include a peak use factor,whereas the numbers discussed here are based on long-term averages. Development for the commercial parcel is not yet known. Therefore, for this parcel,we wi1L sh9 the maximum flow the parcel could produce to stay below the MCL of 10 mg/L-N, assuming/an 80� mg/L-N total nitrogen (Nw) concentration. F 4 P