2010-12-17_REVISION - C1981019 (109)

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RULE 2 PERMITS canyon walls near the mine on a seasonal basis, and in some of the unconsolidated valley fill. Little Collom Gulch is ephemeral, and did not produce measurable flow during the baseline hydrologic monitoring efforts described in Section 2.04.7. Very little water is found in the current active mine; and, based on existing geological and hydrological evidence, the areas to be mined provide no or only minor amounts of recharge to local surface water features. Geomorphic Characteristics Tetra Tech's (2005) investigation included mapping unconsolidated deposits in the Collom permit expansion area, using published and unpublished geologic maps and ground reconnaissance. These deposits are shown in Figure 1 of Exhibit 7, Item 24. Much of the mapped deposits contained substantial proportions of colluvium and /or sheetwash. Valley bottoms elsewhere within the permit expansion area were very narrow and historically uncultivated, or contained significant amount of colluvium or sheetwash. The source material for the valley fills was primarily erosion and deposition of loess, leading to a loamy soil texture which supports more lush vegetation than adjacent uplands, even absent sub - irrigation. Most floodplains in the area are generally extremely narrow (less than 20 feet), have been severely down -cut, and/or contain too much topographic relief in the form of slopes to be considered capable of being irrigated. Due to downcutting, flooding does not extend beyond the limits of the incised channel. Flood Irrigation and Agricultural Activities Section 2.04.3 contains a description and map of agricultural activities in the permit and adjacent area. The Premining and Postmining Land Use Map (Map 17) shows that the historic pre- mining land use of the area has been generally undeveloped rangeland. Based on repeated field investigations, there is no evidence of historical flood irrigation in the Collom permit expansion area. However, documentation exists indicating several small parcels totaling approximately 2.4 acres and located along the West Fork of Jubb Creek were historically used for hay production. Additional exceptions to undeveloped range land in the permit area include the presence of equipment staging areas, small structures, reservoirs, roads, and stream crossings. Historically, there has not been a developed water supply for agricultural activities in the potentially- affected drainages; however, some limited irrigation is conducted in the floodplain of Wilson Creek, outside the proposed southern permit boundary above areas downcut during the mid - 1980's. Prior to the mid 1980's, flood irrigation did occur northeast of the current Gossard Loadout factilities across Highway 17, outside Colowyo's permit boundary, away from any prior mine related activities or planned disturbance associated with the Collom Access Road. The area of concern surrounding the Gossard Loadout Facility was bypassed historically in order to apply irrigation water downstream in the bottom lands outside the current permit boundary. There is no evidence the area around the Gossard Loadout Facility was ever irrigated in the past. Irrigation diversion points, irrigation canals, and topography are shown on Map IOB. These areas are well outside the subject drainages of Collom Gulch, Little Collom Gulch, and Jubb Creek. Subirrigation Depths to groundwater for the area have been reported to occur in valley fill (floodplain) materials anywhere between 9 feet below ground surface (bgs) along West Fork Jubb Creek, to greater than 47 feet bgs within Little Collom Gulch. The historical average Depth to Water at the Gossard Well directly Northeast of the Gossard Loadout Facilitites is approximately 21 feet (2009 Annual Reclamation Report) Tetra Tech (2005) concluded that such depths to groundwater are too great to allow for agriculturally significant subirrigation. Further information on groundwater occurrence is provided in Section 2.04.7. Collom — Rule 2, Page 132 Revision Date: 1/23/09 Revision No.: PR -03