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• <br />for the irrigated land downstream of the Foidel Creek Mine. The amount of <br />irrigation water applied to the pastures is more than sufficient to supply <br />both the consumptive demands and the amount of water necessary to effectively <br />leach the soil profile. Sufficient leaching exists to maintain the electrical <br />conductivity of the soil at the level of the applied water. For example, if <br />the applied water EC was 1000 umhos/cm, the soil profile EC would be <br />maintained at 1000 umhos/cm. ~ <br />(STS-i3 D~~ G::~~,~jD~,.. <br /> The vegetative data collected by TCC does not support the assumption that <br /> moderately sensitive species dominate the irrigated lands of the alluvial <br />1~ valley floors. In the Middle Creek region, the percentage of cover of <br /> <br /> moderately sensitive plants is 5.6%. The Trout Creek moderately sensitive <br />~ ,~~i species cover is 15.3% and the cover of Fish creek is 3.1%. <br />~ <br />~~y~/ <br />~ 7 <br />Y <br />1 Based on site specific conditions, Twentymile Coal Company contends a <br />- <br />„~Q/~ ~~ <br />~~~ material damage standard of 2000 umhos/cm is applicable and reasonable for <br />QQQ the areas downstream of the Foidel Creek Mine. <br />• <br /> Projected yield decreases were calculated for Pastures 2 and 11. As indicated <br /> by the data of Pasture 2, the vegetative cover of moderately sensitive grasses <br /> and clovers is 4.2%. Moderately sensitiv grasses comprise 11.2 grams of the <br /> production (24.0%) and clovers supply .6 grams (1.4%). Using the relative <br /> yield calculations as presented in the article of Maas and Hoffman <br />Y = 100 - B (EC -A) <br />Y = expected relative yield <br />A = salinity threshold (millimhos per centimeter) <br />B = percent yield decrease per unit salinity increase <br />ECe = specific conductance of saturated soil extract <br />the expected yield decrease at an ECe of 2.0 mmhos/cm (2000 umhos/cm) for the <br />production of Pasture 2 would only be .8%. The published expected yield <br />decrease of orchard grass (6.2% at 1.5 mmhos/cm) was used to represent the <br />grasses end the decrease of clover (12.0% at 1.5 mmhos/cm) was used for the <br />genera of clover. Thus, concerning Pasture 2, the moderately sensitive <br />• grasses might decrease .7% of 24.0% and clovers might decrease .1% of 1.40% or <br />9 <br />Revised 10/1/86 <br />