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-45- 3) The proposed mining operation would preserve the essentiaY hydrologic functions of the alluvial valley floor. The Picketwire alluvial valley floor is located downstream from the proposed permit area and would not be disturbed by the proposed mining operations. The assessment of probable hydrologic consequences has not identified any significant change in the stream/alluvial aquifer system. Stonewall Valley The applicant has identified unconsolidated streamlaid deposits along the Middle Fork of the Purgatoire River, in the Stonewall Valley. Valley floor deposits include the current floodplain and low-lying terraces. These deposits contain alluvial ground water that is hydrologically connected to the river and supports hydrophytic vegetation. Areas of historic flood irrigation have been identified in the Stonewall Valley in and adjacent to the proposed permit area (Plate 6A and Map 8 of the permit application). Based on the information provided in the application, the Stonewall Valley is found to be an alluvial valley floor. The valley floor deposits have essential hydrologic functions supporting both flood irrigation and subirrigation. No information has been provided concerning the significance of the Stonewall Valley alluvial valley floor to farming operations. Therefore, the Division conservatively assumes that the valley floor deposits of the Stonewall Valley are significant to farming. A portion of the Stonewall Valley has been disturbed by surface operations at the Allen Mine. This includes the area within the disturbed area boundary as shown on Maps 13 A-C. The disturbed area has been determined to be "grandfathered" from the requirements of Rule 2.06.8(5)(a)(i)(A). Therefore, the Division is required to make a finding that the proposed operation will restore the essential hydrologic functions of the alluvial valley floor far that area contained within the disturbed area boundary. A large portion of the Stonewall Valley adjacent to the Allen Mine has been previously impacted by the disposal of coal processing waste. The alluvial valley floor in the disposal area has been largely covered by the waste piles. The waste piles were in existence prior to the enactment of the Colorado Mined Land Reclamation Act, C.R.S. 1973, as amended, and the Division has evidence that the areal extent of the waste pile disturbance was identical to the present extent as early as November 5, 1911. Therefore, the areal extent of the disposal area is pre-law. The applicant does not propose to impact any additional area of the Stonewall Valley AVF. Portions of the waste piles will be increased vertically, but the impacts associated with the additional refuse material will not significantly increase impacts to the AVF. Based on analyses by the applicant and the Division, the Division finds that allowing a vertical increase in the waste pile is preferable to the disturbance of new areas for refuse piles. All presently active portions of the waste piles will be reclaimed consistent with the performance standards of the Rules and Regulations.