Laserfiche WebLink
33503 S Koster Road Project No. 2021-00073 P a g e | 6 <br />average monthly potential evapotranspiration. If so, then the difference is potential deep <br />percolation. This method does not consider runoff. See Plate 7 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 Tracy station (Station 048999) used in the analysis. The average <br />rainfall for the area, as well as the average evapotranspiration data, was obtained from CIMIS <br />(https://cimis.water.ca.gov/) where the average rain fall for the Tracy area was found to be <br />9.88 inches per year for years 1906 to 2016. <br />Based on this method, the average deep percolation of rain for Tracy area is estimated to be <br />1.28 inches. The nitrate concentration of rain fall was estimated to be 1 mg/L-N (Hantzsche <br />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 2-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 />Table 3. <br />Typical Quantity of Effluent <br />Category Total <br />Bedrooms <br />Average <br />Quantity <br />per <br />Bedroom <br />per Day <br />(gal) <br />Days of <br />Use per <br />Year <br />Average Daily Flow <br />Per Facility