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