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a total decrease of .8% might be experienced with a soil salinity of <br />2.0 mmhos/cm. <br />Concerning the Trout Creek alluvial region, the percent vegetative cover of <br />moderately sensitive species is 15.3%. Within Pasture 11, the cover of <br />moderately sensitive grasses is 19.2% (21.9% relative composition) and the <br />percentage of production supplied by these plants is 32.6%. The cover of <br />clover is 5.3% of 6.1% relative cover and production is 2.0%. Using the <br />assumptions presented for Pasture 2, the expected yield decrease might be <br />1.1%. <br />Within the irrigated land of Fish Creek, moderately sensitive species <br />comprise only .5% of the total cover (.7% of relative composition). <br />Concerning the Sagebrush/Meadow vegetation type, moderately sensitive species <br />cover 3.3% (or 3.7% relative composition). <br />Based on site specific data and irrigation practices, Twentymile Coal Company <br />contends a material damage standard of 2000 umhos/cm is applicable for the <br />Foidel Creek Mine. This proposed standard is consistent with the crops and <br />vegetation growing in the area. Moderately sensitive plants do not dominate <br />the area; the current material damage standard appears to be based on that <br />concept. Moderately tolerant species, which are economically important for <br />both hay production and grazing, grow in a greater percentage of the area <br />(21.8%) than do moderately sensitive species (5.8%). <br />At the proposed standard of 2000 umhos/cm, the yield reduction of moderately <br />sensitive plants would not exceed more than 3.1% for grasses (using values for <br />orchard grass) and 6.0% for forbs (using values for clover). For a pasture to <br />experience a yield decrease of even 5%, moderately sensitive grasses would <br />have to provide about 33% of the production and moderately sensitive forbs <br />would have to provide the remaining 675 In such a pasture, the vegetative <br />cover of moderately sensitive species would approach 100%. None of the <br />pastures studied indicate such a situation exists. <br />Additionally, the areas which contribute to the crop productivity of the <br />region are irrigated with waters diverted from Middle, Trout, and Fish Creeks. <br />10 <br />Revised 10/1/86 <br />