SU0006613 SSNL - Laserfiche WebLink

Home Browse Search

r �1 n - Soil Suitability&Nitrate Loading Study Page 10 St.Patrick's Church, Escalon, CA : Project No- 607.1 August 31, 2009 based, in part of the long-term average annual precipitation and on the average U evapo-transpiration rate (ET). The rate at which precipitation exceeds evapo- transpiration is the rate at which percolating meteoric water is available to leach nitrates to groundwater. According to the National Weather Service (http://cdo.ncdc.noaa."ovn, the mean annual rainfall at the Stockton Airport.(the r, nearest reporting station) is 13.84 inches. The rate of evapo-transpiration is available from the website of the California Irrigation Management Information System (CIMIS) (http:llwwwcimis.water.ca.gov/cimisD. California has been ' divided into zones, and Escalon falls in Zone 12. The average annual evapo- transpiration rate for Zone 12 is 53.3 inches. In recognition of the fact that most of the precipitation falls during the winter months, while most of the { evap o-transpiration occurs during the summer, the following table was prepared k to provide a month-by-month breakdown. Month Mean Precip. Mean ET Percolation �s (in.) (in.) (in. I Jan. 2.71 1.24 1.47 *` Feb. 2.46 1.96 0.50 Mar. 2.28 3.41 - Apr. 0.96 5.10 May 0.50 6.82 Jun. 0.09 7.80 " Jul. 0.05 8.06 Aug. 0.05 7.13 - ;�+ Sep. 0.33 5.40 - Oct. 0.82 3.72 - Nov. 1.77 1.80 - �, Dec. 1.82 0.93 0.89 2.86 ' Based on these data, all of the percolation occurs between December and F11 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. n I 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 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 1 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). j +_.. 2937 Veneman Ave.,#B240Geo-Phase Environmental Inc. Phone: (209) 569-0293 ( Modesto, CA 95356 Fax: (209) 569-4295 iI