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Page 3 <br />Carol Russell <br />April 8, 1981 <br />When resolution of the exempted geographic areas is completed an appropriate <br />program for monitoring the subsidence affects upon the no;i-exempted portions <br />of the affected alluvial valley floors will have to be sui~mitted by the <br />applicant. At this time a review of this issue cannot be completed. <br />4.6.2,11 Yampa River <br />Empire Energy proposes to conduct room and pillar production mining beneath <br />the Yampa River in the future utilizing limited extraction procedures <br />without pillaring. Such extraction should be limited to areas outside the <br />area in which subsidence could possibly affect the hydrologic properties of <br />the river, until monitoring results have verified that the operator's <br />subsidence projections within the Number 9 mine workings zire correct. An <br />appropriate panel scheduled for early extraction within tl~e Number 9 mine <br />should be instrumented and monitored to accomplish this tusk. <br />4.6.2.12 Williams Fork River <br />The applicant indicates that no additional mining is proposed beneath the <br />Williams Fork River within the Number 5 mine. The applicant further <br />indicates that: "Any mining adjacent to the river will be' conducted so <br />that the river is outside the area of influence of mining and subsidence." <br />(Page IV-106) The applicant should specify how the area of influence has <br />been determined, including discussions of the definitions of the appropriate <br />river boundaries and the projected angle-of-draw. <br />4.6.2.13 Sandstone Aquifers <br />The applicant is of the opinion that the performance stanc'ards of Rule 4.20.4, <br />which regard the protection of aquifers which serve as significant sources <br />of water supply to public water systems, limit the definition of renewable <br />resource lands [Rule 1.04(110)] to aquifers which serve as significant sources <br />of water supply to public water systems. The Division disagrees with that <br />opinion. The application of specific performance standarc's within Rule 4.20.4 <br />does not modify the definition of renewable resource Lands. Rule 1.04(14) <br />clearly defines "aquifer" as "a zone, stratum, or group of'strata that can <br />store and transmit water in sufficient quantities for beneficial use." This <br />is a generic definition which includes all aquifers capable of providing any <br />beneficial use recognized by Colorado Law, rule and regulation. <br />The application recognizes three major bedrock aquifers within the mine <br />permit area: the Trout Creek sandstone, the Twenty-Mile sandstone and the <br />Middle sandstone. The Middle sandstone is described in the narrative as <br />being located from 50 feet to 60 feet stratigraphicaZly above the F seam. <br />Nowever, the geologic cross-sections included within the application (drawing <br />III-I) indicate a location approximately 250 feet stratigraphically above <br />the F seam, in which the Number 5 mine is developed. Furthermore, examination <br />of the strati graphic boring logs included within the application (figures <br />III-1 through III-11) fail to indicate the stratigraphic position of the <br />Middle sandstone. <br />(cont'd) <br />