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rainfall and evapotranspiration for the Tracy area. Precipitation data was obtained from the Soil <br /> Survey of San Joaquin County. The"2 years in 10" data was used and not the "average rainfall' <br /> data. Evapotranspiration data was obtained from the California Irrigation Management <br /> Information System (CIMIS): <br /> TABLE 6 <br /> PRECIPITATION AND Eto DATA FOR TRACY, CA <br /> Month 2 Years in 10 will have Eto Average Potential Deep <br /> more precipitation than: Percolation (in/mo) <br /> (in/mo) (in/mo) (in/day) <br /> January 2.93 1.55 0.05 1.38 <br /> February 2.21 2.24 0.08 -- <br /> March 2.38 3.72 0.12 <br /> April 1.51 5.10 0.17 <br /> May 0.71 6.82 0.22 <br /> June 2.09 7.80 0.26 <br /> July 0.28 8.68 0.28 <br /> August 1.05 7.75 0.25 <br /> September 0.84 5.70 0.19 - <br /> October 1.06 4.03 0.13 <br /> November 2.10 2.10 0.07 <br /> December 2.38 1.55 0.05 0.83 <br /> TOTALS (in.) 13.18 1 57.0 ------ 2.21 <br /> The chart illustrates that evapotranspiration far exceeds precipitation, even when using higher <br /> rainfall data that exceeds normal rainfall data by 28% (10.33 in. vs. 13.18 in.) Only in the months <br /> of December and January, and possibly November and February would deep percolation <br /> potentially occur. <br /> The following Worksheet is found in A Guide to Estimating Irrigation Water Needs of Landscaae <br /> Plantings in California and contains the calculations necessary for estimating the water <br /> requirements of the wastewater disposal area landscaping. It is assumed that only effluent from <br /> the drip irrigation, and not the conventional leachfield, will supply a percentage of the total <br /> volume of water required by the landscape grass during the spring and summer months. <br /> Therefore, the total volume of water to be applied to maintain the grass must be known. <br /> Page -10- <br /> Chesney Consulting <br />