2020-06-25_REVISION - C1981019 (6)

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RULE 2 PERMITS Geomorphic Characteristics The investigation was initiated by mapping unconsolidated deposits in the general area, using published and unpublished geologic maps and ground reconnaissance. These deposits, their associated stream channels and the general topography of the floodplain areas are shown on Map 10. The watersheds of Good Spring Creek, Wilson Creek, and Taylor Creek are also delineated on Map 10. From field reconnaissance, it was determined that many of the mapped floodplains in the general area are extremely narrow, have been severely down-cut (Wilson and Jubb Creeks), and/or contain too much topographic relief in the form of slopes to be considered capable of being irrigated. Agricultural Activities Section 2.04.3 contains a description and map of agricultural activities in the permit and adjacent area. The Land Use Map (Map 17) shows that the historic pre-mining land use of the area has been generally undeveloped rangeland. The description under Section 2.04.3 documents crops in the permit area. Historically, there has not been a developed water supply for agricultural activities to expand upon; however, some limited irrigation is conducted in the floodplains of Good Spring Creek and Wilson Creek. Flood Irrigation — The areas that are currently or were historically flood irrigated are shown on Map 17, Land Use. Irrigation diversion points, irrigation canals, and topography are shown on Map 10. A small area of Wilson Creek above the mine permit boundary is irrigated, and some areas near the Gossard Loadout have historically been irrigated. No irrigation has occurred in West Fork Good Spring Creek. Subirrigation — The channel fill of the floodplains in the canyon areas is generally comprised of unconsolidated deposits in a clay matrix. The clay soil texture will minimize the transmission of water to or from the overlying stream and root zone. Due to the narrow area in the floodplains,the overall slope of the drainage and expected clay soil, the likelihood of a developed subirrigation in the canyon areas is questionable. The West Fork Good Spring Creek does not meet the criteria of an AVF based on field reconnaissance. It has areas with flat topography and clayey soil where surface water occasionally accumulates after precipitation. This allows the valley bottom to support lush vegetation without subirrigation. Monitoring wells A-7 and A-8 reveal a water table that is at least 10 feet below ground surface. Based on field and monitoring data,the West Fork Good Spring Creek is not an alluvial valley floor. The area of Wilson Creek below the Lower Wilson Mine and extending north about four miles is an area that was formerly described as a potential AVF and was mapped as such by some (OSM, 1985). This area was subjected to a flooding and mass-wasting event that downcut the alluvium 20 to 30 feet below the former surface and left two narrow terraces 20 to 30 feet above Wilson Creek on either side of the creek. These terraces are generally no wider than 100 feet and in many places are much narrower than 100 feet. A monitoring well in this section (well MW-95-03) was installed to the base of the alluvium at the mouth of the unnamed drainage holding the Lower Wilson expansion area. This well, installed during the summer of 2005, is 57.34 feet deep and encountered angular "clinkers" and no stream-rounded alluvium. The well had 3 feet of water in August 2005, but contained only a few tenths of a foot of water in September and October 2005. This indicates that the alluvium in the terraces is dry and is not sub- irrigated. The narrow width and fragmented nature of the minimal flat land, depth to groundwater, and impracticality of irrigating or mechanically farming this stretch of Wilson Creek indicates that it does not South Taylor/Lower Wilson—Rule 2,Page 87 Revision Date: 6/22/20 Revision No.: MR-220