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-46- Given the above discussion, the Division is not requiring the applicant to restore the essential hydrologic functions in the area of the waste piles. The following findings, therefore, are presented only for the surface facilities (excluding waste piles) and mining impacts on the Stonewall Valley AYF. Stonewall Valley Findings 1) The proposed operation would not interrupt discontinue or preclude farming on the alluvial valley floor. No additional disturbance of the AYF is planned at the Allen Mine. Portions of the Stonewall Valley have been undermined. No additional mining under the Stonewall Valley is planned during this five year permit term. The applicant has predicted no subsidence related impacts on the Stonewall Valley based on previous mining under the Stonewall Valley at the Allen Mine. The surface disturbance related to facilities in the Stonewall Valley at the Allen Mine occurred prior to August 3, 1977. Therefore, this area is exempted from this finding. 2) The proposed operation would not cause material damage to the quantity and quality of surface and ground water that supply the alluvial valley floor. As previously discussed, all coal mining related surface disturbance in the Stonewall Valley occurred prior to August 3, 1917, therefore, this area is exempted from this finding. The applicant has provided an assessment of the effect of undermining the alluvial valley floor upon flow in the stream/alluvial aquifer system (See discussion of probable hydrologic consequences). This potential effect was shown to be minimal and would not cause material damage. The applicant also assessed the effects of discharging water from the underground workings to the receiving stream and the effects of additional disposal of coal processing waste on the stream/alluvial aquifer system. These activities were shown to have a minimal effect upon water quality, and would not cause material damage. 3) The proposed operation would preserve (or restore) the essential hydrologic functions of the alluvial valley floor. The valley fill material along the Middle Fork of the Purgatoire River was assumed to be significant to agriculture. Therefore, its essential hydrologic functions must be preserved throughout the mining operation. Its essential hydrologic functions are those geologic, hydrologic, and topographic characteristics which make surface and ground water usefully available for flood irrigated and subirrigated agriculture. A portion of the Stonewall Valley has been disturbed by mining activities which started at the Allen Mine in 1951. The area has been determined to be eligible fora "grandfathering" exemption under Rule 2.06.8(5)(a)(c)(e)(I), therefore, in this area, the applicant is required to restore the essential hydrologic functions of the alluvial valley floor.