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Climatic Data: Rainfall versus Evapotranspiration NLS§3.2. It is generally and scientifically accepted that when precipitation exceeds evapotranspiration (Eto), deep percolation of surface rainwater may occur. Evapotranspiration refers to water evaporation that takes place both at the soil surface and transpiration by plants. e The following Table illustrates rainfall and evapotranspiration for the Stockton area. Precipitation data was obtained from the Soil Survey of San Joaquin County. The conservative"2 years in 10"data was used and not the"average rainfall"data. Evapotranspiration data was obtained from the California Irrigation Management Information System (CIMIS): TABLE 3 PRECIPITATION AND Eto DATA FOR STOCKTON, CA Month 2 Years in 10 will have more Eto Average Potential Deep precipitation than: (in/mo) (in/mo) (in/day) Percolation (in/mo) January 4.42 1.24 0.04 3.18 February 3.20 1.96 0.07 1.24 March 3.43 3.41 0.11 -- April 1.92 5.10 0.17 May 0.50 6.82 0.22 -- June 0.25 7.80 0.26 -- July 0.23 8.06 0.26 -- August 0.40 7.13 0.23 -- September 0.76 5.40 0.18 -- October 1.39 3.72 0.12 -- November 3.31 1.80 0.06 1.51 December 3.67 0.93 0.03 2.74 TOTALS (in.) 18.92 53.4 ------ 8.67 This chart illustrates that evapotranspiration far exceeds precipitation, even when using higher rainfall data that exceeds normal rainfall data by 56%. Only in the months of January, February, November and December would deep percolation potentially occur. This data illustrates a relatively high potential for there to be significant evapotranspiration (or bare soil surface evaporation) from a wastewater disposal system design that may take advantage of evapotranspiration during favorable months of the year, specifically summertime. I Page -5- Chesney Consulting