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~. -43- The Picketwire Value Two types of unconsolidated streamlaid deposits, valley floor deposits, and strath terrace deposits have been identified along the main stem of the Purgatoire River I;Plate 6 of the permit application). Valley floor deposits include the current floodplain and low-lying terraces, up to 50 ft. above the river. These deposits contain alluvial ground water that is hydrologically connected to the river and supports hydrophytic vegetation. The applicant has also identified strath terraces with a thin alluvial veneer. The terraces are confined to the main stem of the Purgatoire in the Maxwell permit area and downstream. Strath terrace deposits are located 100 to 200 feet above the Purgatoire River. Field investigations, including backhoe pits and drill holes, provided no evidence of a saturated ground water zone in the deposits on which the Maxwell Mine surface structures are located. The deposits are not in direct hydrologic contact with the river and do not support hydrophytic vegetation. Areas of historic flood irrigation have been identified in and adjacent to the proposed permit area (Plate 6A of the permit application). Areas of flood irrigation are found along the North Fork of the Purgatoire River, the Picketwire Valley, and the Stonewall Valley. In the mine area, flood irrigation is confined to the valley floor deposits found adjacent to the river. The water is directly diverted from the river through ditches. The most common flood irrigation method is wild flooding, although border and furrow irrigation are practiced in some areas. The dominant crop is grass-hay consisting of a mixture of clover, alfalfa, timothy, brome, and other grasses. Downstream of the Maxwell Mine, flood irrigation is practiced on the strath terraces. Based on the information provided in the application, the Picketwire Valley is found to be an alluvial valley floor. The valley floor deposits have essential hydrologic functions supporting both flood irrigation and subirrigation, and the strath terrace deposits have the capability for flood irrigation. Picketwire Valley Findings 1. The proposed mining operations would not interrupt, discontinue, or preclude farming on the Picketwire Valley alluvial valley floor. Other than the existing access road and the existing sediment control and main water intake systems, no surface disturbance would occur on the valley floor deposits. The applicant has proposed to undermine portions of the alluvial valley floor. However, in this area, mining would be limited to 50X extraction to avoid subsidence effects (Map 17 of the permit application). Mining would not alter the surface topography or affect the overlying fanning operations. 2. The proposed mining operations would not cause material damage to the quantity and quality of surface and ground water that supply the Picketwire Valley alluvial valley floor; provided that the refuse pile expansion is not constructed until the effects of the refuse pile on the alluvial valley floor are assessed and it is demonstrated that the water emanating from the refuse pile will not cause material damage.