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4.3.4.2 Minimum and Maximum Root Potentials <br />The minimum root potential is the minimum potential at which plant roots can <br />remove water from a soil and should be within range of the wilting point <br />(estimated around —1500 Kilopascals (Kpa )) and the hygroscopic water of a soil <br />(estimated around —3100 Kpa) (Brady and Weil, 1996). The maximum root <br />potential is associated with the force required by plants to access capillary water <br />(estimated to be around 0 to —30 'Kpa). <br />Calculated net flux through several modeled profiles varied significantly when <br />completing sensitivity analysis using minimum root potential values between <br />-1000 and -3000 Kpa and only slightly when using maximum root potential values <br />between —30 Kpa and 0 Kpa. As a result, it is concluded that the minimum root <br />potential is a sensitive parameter and system performance will be enhanced by <br />incorporation of relatively high suction and region plant communities. In <br />anticipation of the use of high suction and plant types, a reasonably conservative <br />minimum root potential of -2000 Kpa (relatively low for and plant types) was <br />selected for long-term analyses. <br />Though not considered a sensitive parameter, a conservative maximum root <br />potential of -15 Kpa, were selected for the analyses included to simulate the water <br />extraction capabilities of the average grass and shrub vegetative cover anticipated. <br />0 4.3.4.3 Crop Cover Fraction <br />Selection of crop cover fraction coefficients ranging from 0 to 60 percent resulted <br />in significant changes in the calculated net flux and as a result, crop cover fraction <br />is considered a sensitive parameter. Since undisturbed areas of the native <br />landscape adjacent to the FSL currently support a sturdy vegetative growth of at <br />least 60 percent, this value was selected for subsequent long-term analyses. <br />4.3.4.4 Root Distribution <br />Root distributions were incorporated in the analyses completed for this study by <br />simulating native shallow rooting grasses with only a few deeper rooting shrubs. <br />As modeled in the long-term analyses of the alternative design, roots were limited <br />to the upper three feet of the proposed four foot final cover profile, with 87 <br />percent of the roots assigned to the upper one foot (3 05 mm) interval, 10% in the <br />middle 2-3 foot layer and 3% for the bottom foot. As shown in Table 3, variations <br />in root distribution did yield significant variability in system performance <br />however and this parameter is therefore considered a critical variable for system <br />performance. As a result, incorporation of an intermediate root depth shrub into <br />the low-lying grass vegetation is considered an important component of long-term <br />system performance. <br />C:UO05.00S2\FOR W ARD/ForwardCO VER.DOC17/13/2005 <br />Geologic Associates <br />