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sensitive species. However, in this region, the only area which could be <br />directly affected by water from the Foidel Creek Mine is area 18. This small <br />area, 9.3 acres, supports 42.2°L of moderately sensitive species. The area is <br />undeveloped rangeland which does not contribute significantly to the hay crop <br />production. The remaining area which does contribute to the crop <br />productivity has a moderately sensitive species coverage of 13.3%. However, <br />the water used for irrigating this area is either diverted from Middle Creek <br />above the Foidel Creek confluence or Trout Creek above the Middle Creek <br />confluence. Thus, the water from Foidel Creek would not be utilized. The <br />Trout Creek alluvial valley floor region has a 11.7% cover of moderately <br />sensitive species. The majority of this amount can be found in Pastures 14, <br />15N, and 155, all of which are irrigated by Trout Creek waters below the <br />confluence of Fish Creek. Therefore, the contribution of moderately <br />sensitive species for the Middle Creek and Trout Creek areas is not <br />significant to this discussion. <br />Twentymile Coal Company does not feel the material damage standard of <br />1000 umhos/cm is applicable for the crops and vegetation growing in alluvial <br />valley floor regions which may be affected by water from the Foidel Creek <br />Mine. For the entire area of study, the moderately tolerant species cover <br />12.2°,6 and moderately sensitive species cover 5.7%. The moderately tolerant <br />species which are currently growing in the area are valuable in terms of hay <br />crop production and grazing. According to the Agricultural Research Service <br />(pers. comm. August 1986), smooth brome is the most preferential grass for <br />hay production. Concerning grazing use, livestock forage preferences have <br />been documented by Marquiss, et. al (1974) to include, in descending order, <br />smooth brome, intermediate wheatgrass, desert wheatgrass and western <br />wheatgrass. All of these species were found in the area of study and are <br />considered moderately tolerant. The moderately sensitive species timothy, <br />orchard grass, alfalfa and clover are used in this region to complement hay <br />production and pasture forage. A rg ostis contributes significantly to the <br />percentage of moderately sensitive species, but its economic importance is <br />limited. In the study area a major component of the moderately sensitive <br />species percentage is timothy and clover. By extrapolation of the table <br />depicting yield decrease in the Maas and Hoffman article, the yields of these <br />plants would not decrease more than 30% if the soil extract ECe measures 3.0 <br />mmhos/cm (3000 umhos/cm). An ECe of 3.0 mmhos/cm would correspond to a 2000 <br />umhos/cm ECe for the irrigation water. <br />Twentymile Coal Company contends a material damage standard of 2000 <br />umhos/cm for the irrigation waters is applicable and reasonable for the site <br />specific conditions of the Foidel Creek Mine. This proposed standard is <br />consistent with the crops and vegetation growing in the area. Moderately <br />sensitive pants do not dominate the area; the current material damage <br />standard appears to be based on that concept. Moderately tolerant species, <br />which are economically important for both hay production and grazing, grow in <br />a greater percentage of the area (i2.2%) than the moderately sensitive plants <br />(5,7%). <br />At the proposed standard value of 2000 umhos/cm, the yield reduction of <br />moderately sensitive plants, which would not exceed 30%, would be compensated <br />by the competitive nature of other economically important species, namely <br />smooth brome. Furthermore, the areas which contribute to the crop <br />productivity of the region are irrigated with water diverted from Middle and <br />Trout Creeks. <br />4 <br />