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Groundwater dilution effects can only be truly discerned with groundwater monitoring and modeling. According to a scientific paper authored by Shaw and Turyk (1994), reduction of nitrate concentrations in groundwater can occur primarily through dispersion, or by percolating rainwater, or a water source including effluent water recharge. Climatic ta: Rainfall versus Evapotranspiration NLS§3.2. It is generally and scientifically accepted that when precipitation exceeds evapotrans- piration (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, and is defined as water loss from a large field of 4-to-7 inch tall, cool-season grass that is not water stressed. The following Table illustrates rainfall and evapotranspiration for the Tracy 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): E TABLE 6 PRECIPITATION AND_Eto_DATA#0k1TRACY;,CA Month 2 Years in 10 will have more Eto Average Potential Deep precipitation than: (intmo) Percolation(in/;no) (in/mo) (in/day) January 2.93 1.55 0.05 1.35 February 2.21 2.24 0.08 -- March 2.38 3.72 0.12 -- April 1.51 5.10 0.17 May 0.71 6.82 0.22 -- June 2.09 7.80 0.26 -- July 0.28 8.68 0.28 -- August 1.05 7.75 0.25 -- September 0.84 5.70 0.19 -- October 1.06 4.03 0.13 -- November 2.10 2.10 0.07 -- December 2.38 1.55 0.05 4.83 r TOTALS(in.) 13.18 57.0 ------ 2.21 The Table illustrates that evapotranspiration far exceeds precipitation, even when using higher rainfall data that exceeds normal rainfall data by 28% (10.33 in. vs. 13.18 in.) Only in the months of December and January, and possibly November and February would deep percolation potentially occur. This data 11 illustrates a relatively high potential for there to be significant evapotranspiration(or bare soil surface evaporation) frorr a mound system disposal area,particularly around the edges of the mound. 10 �jj Chesney Consulting i.