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Soil Suitability&Nitrate Loading Study Page 10 Proposed starts winery, 17521 Davis Rd,Lodi CA Project No. 670.1 B Julv 22.2013 Denitrifrcadon Denitrification of raw sewage occurs from solids settling in the septic tank and from the action of certain bacteria in the leach field, which convert dissolved nitrates into nitrogen gas. The denitrification effect is expressed as a percentage, and it varies with septic system design, soil type,and pH conditions. The denitrification that occurs through solids settling is accounted for in estimating the nitrate concentration of septic tank effluent. The denitrification that occurs in the leach field from bacterial activity typically is between 10 and 35 percent. In this case, it is assumed to be 25 percent as suggested by Hantzsche and Finnemore(1992). Other Nitrate Sources Since the site is in agricultural use to raise grapes, nitrogen fertilizer is applied to the crop. Approximately 4 acres are expected to be developed as vineyard. An employee of Delta Buildings, h r. John Vierra, reports that twice each year 40 gallons of 4 percent nitrate solution will be applied to each acre of vineyard by drip irrigation. Calculation suggest this amounts to slightly less than 180 pounds of nitrate (or 40 pounds of nitrogen) per acre per year. In general, any nitrate that penetrates below the root-zone can be expected to leach to the groundwater. Crops, however, have the capacity to remove a limited amount of nitrate from the soil. The actual amount of nitrate applied that becomes available for leaching is the applied amount less the amount taken up by the crop. According to the California Water Board, the average nitrate uptake rate for vineyards is about 200 pounds of nitrogen per acre per year. Since the uptake exceeds the application, the net effect is that the entire fertilizer nitrate load is taken-up by the vineyard and there is no net nitrate leaching. Flow Rates The average daily flow rate of the proposed septic system on the site must be estimated based, in part, on guidance available from Table 6.1.15 of the Wastewater Standard (EHD, 2003). The single restroom on the site will be used by several classes of people. The proposed facility will produced estimated flow rates as follows: Perwmnel Na Pereorts Flow Rate Schedule Annual Output Caretaker Residence 5 60 GPD per Person 355 s(Yr 106,5000a Full Time Em levees 4 15 OPD per Person 260 s'Yr 15,600 salt Part Time Employees- 5 8 GPD per Person 260Days/Yr 10,400 gals Tasting Room Visitors•' 71 71 X4 GPD 355 Da arl'r 100,820 gals Marketing Mxtin '•• 150 8GPD per Person 30 srYr 36,000 gals Comm']Kitchen 150 3 GPD per Person 8 Days/Yr 3,600 tads Total Annual Emueat 272,920 prals • Assumes pan timers work approx.half time. •' Assumes 500 visitors per 7-day week •'• Assumes 4 restroom visits each day per person at 2 gals,per use. 2937 Venertem Ave..#6240 Ge Phase Environmental Inc. Phone: (209)569-0293 Modesto.CA 95356 Fax: (209)569-0295