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Soil Suitability&Nitrate Loading Study Page 13 ~ St. Patrick's Church, Escalon, CA Project No. 607.1 October 14, 2009 Based on these data, all of the percolation occurs between December and February, and the total annual percolation rate is 2.86 inches. The assumption is also made that rain water contains 1 mg/L of nitrate as N. Denitrification 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 4 = nitrates into nitrogen gas. The denitrification effect is expressed as a ,r., 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' e and F nne_m-ore-(1992) _ Othe Nitrate Sources Since the site is in agricultural use to raise corn, nitrogen fertilizer is applied to ' the crop. One of the St. Patrick's parishioners, Mr. Danny Costa is managing the corn crop. Based on a telephone interview with Mr. Costa, 150 units (pounds per acre of nitrogen) are applied each year. This use is expected to continue- or thenex -0`to 15 years until the parcel is developedas described above. 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 Reeves and Touchton (1989), at least 160 pounds of nitrogen per acre can be taken up by corn crops each year. The net effect is that substantially the entire fertilizer nitrate load is taken-up by the corn crop and there is no net nitrate leaching. The existing septic sewage system on the property also contributes to the nitrate r� load, and must be considered. The average daily flow rate of the existing and proposed septic systems ms on the site must be estimated based, in part, on guidance available from Table 6.115 of the Wastewater St n a-d D, 2003). As discussed above, the chapel is expected to produce 00 GPD raw sewage five eek, and the existing k residential system is a so expected to produc 200 GPD f sewage. The other proposed facilities will produced estimated flow ollows: r 2937 Veneman Ave.,#B240 Geo-Phase Environmental Inc. Phone: (209) 569-0293 FModesto, CA 95356 Fax: (209)569-0295