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` January 14,2003 <br /> Job Number: LG02460 <br /> Page 8 <br /> second dwelling unit(SDU) up to 1,500 SF could also be placed on the site at some time in the <br /> future. Three(3)people are estimated to occupy the SDU should one ever be built. The <br /> ` following table presents the anticipated daily usage for each parcel. <br /> Table 4. <br /> Total Estimated Daily Usage of Septic System. <br /> Category Effluent usage People Effluent quantity per category <br /> for each per day <br /> category <br /> Future 3-bedroom home 75 gals 4 4 people*75 gal/person-day=300 gal/day <br /> Future 2-bedroom,second 75 gals 3 3 people* 75 gal/person-day=225 gal/day <br /> dwelling unit <br /> IL Average Daily Flow: 525 gals/day <br /> Denitrification is an important process in septic systems that normally occurs in the leach line <br /> trench whereby certain bacteria utilize the oxygen in the nitrate(NOO and release nitrogen gas <br /> (NZ) to the atmosphere. Denitrification is expressed as a percentage, and the normally accepted <br /> �. range is 10 percent to 35 percent. Soils with higher clay content, moist soil conditions, high pH, <br /> and organic material denitrify about 35 percent and soils with very high sand content and fast <br /> percolation rates are estimated to denittify at a lower rate, about 10 percent to 15 percent. The <br /> �- denitrification factor for the soils is estimated to be about 25 percent. <br /> An estimate of the quantity and quality of rainfall was required for the analysis. The average <br /> deep percolation of rain was estimated to be 1.85 inches per year for the Tracy area. The deep <br /> percolation of rain is the water which may actually recharge ground water originating surface <br /> rain after evapotranspiration losses occur. The calculation for deep percolation of rain is shown <br /> on Plate 4. The nitrate concentration of rain fall was estimated to be I mg/L-N.' <br /> 6.2 Nitrates from Agriculture <br /> Leaching losses of nitrate fertilizer occur when soils have more incoming water(rain or <br /> irrigation) than the soil can hold. As water moves through the soil,the nitrate(NO3)that is in <br /> soil solution moves along with the water. Ammonium(NH4 ) forms of N have a positive charge <br /> •. and are held by the negative sites on the clay in the soil; therefore,NH4*forms of N leach very <br /> little. In sands where there is very little clay, ammonium forms of N can leach. Coarse-textured <br /> OE4t0 <br /> Z <br /> O <br /> t,SOC\ <br /> L <br />