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_. ~,. . The applicant's monitoring program proposes to monitor genn_ra1 constituents, inclu- ding total dissolved solids, electrical conductivity, temperature, pN, and total suspended solids on a monthly basis. Other paramr_ters will be monitored according to the plan on pages 4.6-140 and 141. The applicant's statement of probable hydrologic consequences has not discussed possible effects to Oak Creek. .1l though no mining occurs within the Oak Creek water- shed, minor effects could potentially result From the rlrainage control system or Fzom water quality changes resulting from coal fines at the loadout facilities. Data from two monitoring stations on Oak Creek which are located upstream and downstream from the loadout show very little difference in water quality (see p. 2.5-28 to 2.5-32 and 2.5-38 to 2.5-39 in the permit application). Changes in quantity resulting from the total containment sediment control system are expected to be insignificant. (The sediment ponds provide 0.72 acre-feet of storage compared to Oak Creek's annual yield of 10,800 acre-feet of water.) The cumulative hydrologic assessment for the Edna mine (on file with the Division) has identified no significant cumulative effects to surface water in the general area There is some potential for a long-term degra c'a ti on of surface water quality. How- ever, the applicant's analysis of probable hydrologic consequences has shown that the Edna mine is expected to increase the mean annual concentration of total dis- solved soilds by 12 ng/1. 14onthly concentrations may show additional concentrations as high as 39 mg/1. These increases would be diluted downstream and are not expected to limit use of surface Boa to r. Ground Water Cumulative Fludrolonic Effects M assessment of the probable hydrologic consequences of the proposed mining operation and an assessment of the probable cumulative impact of all anticipated mining in the area on the hydrologic balance have been made. ':'ith the above hydrologic stipu- lations, including those found in the alluvial valley floor determination, the proposed operation has been found to be designed to prevent material damage to the hydrologic balance outside the permit area. The proposed permit area for the Edna mire is located on the southeastern edge of Twenty Mile Park. Twenty h1i1e Park. contains an enclosed ground ~.•ater basin formed by several synclinal folds. There are two types of aquifers which occur in the basin: confined bedrock aquifers and unconsolidated alluvial aquifers. The major bedrock aquifers of the Twenty Flile Park basin are the Twenty hlile and Trout Creek Sandstones of the [dilliams Fork Formation. h(inor aquifers include thin layers ~c' of fine- azed sandstone, silt'stone, and, where locally Fractured, coal beds. These units are largely laterally discontinuous. That is, they do not occur over a wide geographic area. For a more detailed description of the hydrogeology of the Williams Fork Formation, see the Geology and Ground [dater portions of this document.