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minor variability when using application rates between 10 and 60 mm/day (Table 3). Recognizing the nature of typical storm events in the area, a reasonably conservative application rate of 60 mm/day was selected for long-term modeling of final cover performance. 4.3.4 VEGETATION CONDITIONS The sensitivity of model results to vegetation coefficients ranging from transpiration, root potentials, root distribution, root lengths and root flow resistance are discussed below and are also summarized in Table 3. 4.3.4.1 Maximum Actual Transpiration/Evaporation Sensitivity analyses for this parameter included stipulation of maximum actual transpiration/evaporation values slightly greater or less than 1.0 and these analyses resulted in only minor changes to the calculated net flux through the modeled soil profile. This suggests that with site soils in this environment this is not a critical parameter. However, since selection of values greater than 1.0 may not be conservative (in that it allows transpiration to compensate for an evaporative deficit), a value of 1.0 was selected for the long-term analyses completed as part of this study. 4.3.4.2 Minimum and Maximum Root Potentials The minimum root potential is the minimum potential at which plant roots can remove water from a soil and should be within range of the wilting point (estimated around —1500 Kilopascals (Kpa )) and the hygroscopic water of a soil (estimated around —3100 Kpa) (Brady and Weil, 1996). The maximum root potential is associated with the force required by plants to access capillary water (estimated to be around 0 to —30 Kpa). Calculated net flux through several modeled profiles varied significantly when completing sensitivity analysis using minimum root potential values between -1000 and -3000 Kpa and only slightly when using maximum root potential values between —30 Kpa and 0 Kpa. As a result, it is concluded that the minimum root potential is a sensitive parameter and system performance will be enhanced by incorporation of relatively high suction and region plant communities. In anticipation of the use of high suction and plant types, a reasonably conservative minimum root potential of -2000 Kpa (relatively low for and plant types) was selected for long-term analyses. Though not considered a sensitive parameter, a conservative maximum root potential of -15 Kpa, were selected for the analyses included to simulate the water extraction capabilities of the average grass and shrub vegetative cover anticipated. -8- C:\2003-033\EDOM HILL ALTERNATIVE COVER.D006/1612005 v n Geologic Associates