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476 N Patton Avenue Project No. 2021-00084 Page 16 <br /> 5.2 Contribution of Rainfall <br /> An estimate of the quantity and quality of rainfall was required for the nitrate loading <br /> analysis. The estimate of deep percolation of rain is based on the average monthly <br /> precipitation of rain fall for South Stockton, California, based on the nearest weather station <br /> to the site available. The estimate first determines whether the average monthly <br /> precipitation exceeds average monthly potential evapotranspiration. If so, then the <br /> difference is potential deep percolation. This method does not consider runoff. See Plate 7 <br /> for the data and calculation. <br /> Average potential evapotranspiration was obtained from the California Irrigation <br /> Management Information System (CIMIS).The site is located within evapotranspiration zone <br /> number 12, as well as the South Stockton station (Station 048558) used in the analysis. The <br /> average rainfall for the area, as well as the average evapotranspiration data, was obtained <br /> from CIMIS (https://cimis.water.ca.gov/) where the average rain fall for the South Stockton <br /> area was found to be 13.78 inches per year for years 1948 to 2016. <br /> Based on this method, the average deep percolation of rain for South Stockton area is <br /> estimated to be 3.21 inches. The nitrate concentration of rain fall was estimated to be 1 <br /> mg/L-N (Hantzsche and Finnemore, 1992). <br /> 5.3 Current On-Site Sources of Nitrate <br /> The current onsite 3-bedroom residence, and associated septic system and rainfall are <br /> recognized as potential current on-site sources of nitrate. <br /> 5.4 Future On-Site Sources of Nitrate <br /> 5.4.1 Quantity and Quality of Domestic Wastewater from Proposed Project <br /> The following discussion is for determining the long-term wastewater flow anticipated from <br /> the planned residential house for the site,to be incorporated into the nitrate loading analysis. <br /> The anticipated wastewater flow determined is not intended to be used for septic system <br /> design, because septic system sizing includes a peak use factor, whereas the numbers <br /> discussed herein are based on a long-term conservative measure of estimated effluent <br /> volume. <br /> There is currently a 3-bedroom residence with associated septic system onsite. In addition, <br /> a proposed 3-bedroom, 2-bath secondary dwelling unit with a separate septic system is <br /> planned for the site. Per San Joaquin County Environmental Health requested guidelines <br /> based on previous nitrate loading studies, an average daily flow of 100 gallons for the first <br /> bedroom and 50 gallons for each additional bedroom per residence per day is estimated for <br /> the site. The following table presents the nitrate contributing septic wastewater flow rates <br /> anticipated for the site. <br /> Petralogix Engineering,Inc. <br /> 26675 BruelIa Road,Galt,Ca 95632 <br /> (209)-40o-5729 <br /> www.petralogix.com <br />