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Soil Suitability&Nitrate Loading Study Page 10 Proposed Oak Farm Vineyards Expansion,Lodi CA Pmjcct No- 670.1C June 17,2013 St_•stem Effluent Nitrate Cont oij Employees 60 m !L Tasting Room Visitors 80 m Marketing Mtg Attendees 80 m 4, Meteoric Water Rainwater percolating through the soil is the primary leaching agent carrying nitrates to the groundwater. The estimate of the amount of deep percolation is based in part of the long- term average annual precipitation and on the average evapo-transpiration rate(ET). The rate at which precipitation exceeds evapo-transpiration is the rate at which percolating meteoric coater is available to leach nitrates to groundwater. According to the National Weather Service (http://cdo.ncdc.noaa.govn, the mean annual rainfall at Lodi (the nearest reporting station) is 13.84 inches. The rate of evapo-transpiration is available from the website of the California Irrigation Management Information System (CMS) (htto://wwwcimis.water.ca.gov/cimisil. The average annual evapo-transpiration rate for the Lodi station 12 is 503 inches. In recognition of the fact that most of the precipitation falls during the winter months, while most of the evapo-transpiration occurs during the summer, the following table was prepared to provide a month-by-month breakdown. Month Mean Precip.(hr.) Mean ET Percolation in. to Jan. 3.48 0.79 2.69 Feb. 3.31 1.55 1.76 Mar. 2.87 3.28 -Apr. 1.36 5.17 - Mav 0.67 6.58 Jun. 0.14 7.51 Jtil, 0.0 7.87 -Aug .03 - 0.31 5.11 Oct. 1.15 3.29 Nov. 2.36 1.54 0.82 Dec. 3.34 0.76 2.58 7.85 Based on these data, all of the percolation occurs between November and February, and the total annual percolation rate is 7.85 inches. The assumption is also made that rain water contains I mg1L of nitrate as N. 2937 Veneman Ave.,i1B240 Ge Phase Environmental Inc. Phone: (209)569-0293 Modesto.CA 95356 Fax: (209)569-0295