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15999 W CORRAL HOLLOW RD Project No.2019-00027 Page 15 <br /> 4.2 Contribution of Rainfall <br /> An estimate of the quantity and quality of rainfall was required for the nitrate loading analysis. The <br /> estimate of deep percolation of rain is based on the average monthly precipitation of rain fall for <br /> Tracy, California, based on the nearest weather station to the site available. The estimate first <br /> determines whether the average monthly precipitation exceeds average monthly potential I-- <br /> evapotranspiration. If so,then the difference is potential deep percolation. This method does not <br /> consider runoff. See Plate 1 for the data and calculation. <br /> Average potential evapotranspiration was obtained from the California Irrigation Management <br /> Information System (CIM1S).The Tracy site is located within evapotranspiration zone number 12,as <br /> well as the Tracy station used in the analysis. The average rain fall for the area was obtained from <br /> the Western Regional Climate Center(www.wi-cc.dri.edu)and was found to be 12.18 inches per year <br /> for the years 1955 through 2004. <br /> Based on this method, the average deep percolation of rain for the site area is estimated the 2.52 <br /> inches. The nitrate concentration of rain fall was estimated to be 1 mg/L-N (HAfantzsch:e_an <br /> Finnemore, 1992). <br /> 4.3 Current On-Site Sources of Nitrate <br /> The site is currently used for operations as a experimental test facility. As such existing facilities <br /> related to this use are considered to be a potential source of nitrate. In particular, a number of <br /> bathroom and septic facilities are in use on the site.As mentioned in our concurrent SSS report,and <br /> now shown below in Table 2,there are 33 septic systems currently onsite. <br /> Table 2-Onsite Septic System Information <br /> Summary of Site 300 Septic Systems <br /> System Location Septic System Type Size- <br /> (Building) <br /> 801 A&D Septic tank w/Leach field 10009, (1) 125',(1) 100',(1) 75' <br /> 802 Septic tank w/2 Leach fields 1000g,75'4" Pipe <br /> 805 2 Septic tanks w/Cesspool 12009 and 350g,460 sq.ft., 141 sq.ft. l <br /> 806 A Septic tank w/2 Cesspools 1000, 115 sq.ft. <br /> 807 Septic tank w/2 Leach fields 1000g,75'4"Pipe <br /> 809 Septic tank w/Cesspool 500g,315 sq.ft <br /> 810 Septic tank w/Leach field 500g,25'x4" <br /> 812 A&B Septic tank w/2 Leach fields 1000g,75'4"Pipe <br /> 813 Septic tank w/3 Cesspools 14809 - <br /> 817 Septic tank w/4 Leach fields 1000g,55'Pipe <br /> Petralogix Engineering,Inc. <br /> 26675 Bruella Road,Galt,Ca 95632 <br /> (209)-400-5729 <br /> www.petralogix.com <br />