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Climatic Data: Rainfall versus Evapotranspiration <br /> NLS§3.2. It is generally and scientifically accepted that when precipitation exceeds evapotrans- <br /> piration (Eto), deep percolation of surface rainwater may occur. Evapotranspiration refers to water <br /> evaporation that takes place both at the soil surface and transpiration by plants. <br /> The following chart illustrates rainfall and evapotranspiration for the Stockton area, which is the <br /> closest data to Escalon available. Precipitation data was obtained from the Soil Survey of San <br /> Joaquin County. The conservative "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 4 <br /> PRECIPITATION AND Eto DATA FOR STOCKTON, CA <br /> Month 2 Years in 10 will have more Eto Average Potential Deep <br /> precipitation than: (in/mo) (in/mo) (in/day) Percolation (in/mo) <br /> January 4.42 1.24 0.04 3.18 <br /> February 3.20 1.96 0.07 1.24 <br /> March 3.43 3.41 0.11 -- <br /> April 1.92 5.10 0.17 <br /> May 0.50 6.82 0.22 - <br /> June 0.25 7.80 0.26 <br /> July 0.23 8.06 0.26 - <br /> August 0.40 7.13 0.23 <br /> September 0.76 5.40 0.18 -- <br /> October 1.39 3.72 0.12 -- <br /> November 3.31 1.80 0.06 1.51 <br /> December 3.67 0.93 0.03 2.74 <br /> TOTALS(in.) 18.92 53.4 ------ 8.67 <br /> This chart illustrates that evapotranspiration far exceeds precipitation, even when using higher <br /> /rainfall data that exceeds normal rainfall data by 56% (8.30 in. vs. 18.92 in.) Only in the months of <br /> January, February, November and December would deep percolation potentially occur. This data <br /> illustrates a relatively high potential for there to be significant evapotranspiration (or bare soil <br /> surface evaporation) from the leachfield. <br /> 7 <br /> Chesney Consulting <br />