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Rationale for Approval Recommendation May 20, 2002 <br />Four Corners Materials, Inc. <br />AM-01. Thomas Pit. Permit No. M-1976-020 <br />they will comply with DWR requirements. The application satisfies the requirements of <br />Rule 6.4.13. <br />DMG has not received notice from agencies with jurisdiction to enforce water rights, of <br />conflict with the application for AM-01. The application satisfies the requirements of Rule <br />3.1.611)(a), which requires that disturbances to the prevailing hydrologic balance of the <br />affected land and of the surrounding area and to the quantity or quality of water in <br />surface and groundwater systems both during and after the mining operation and during <br />reclamation shall be minimized by measures, including, but not limited to compliance with <br />applicable Colorado water laws and regulations governing injury to existing water rights. <br />10. Comments indicating a history of adverse impact to river and riparian <br />vegetation from previous operator. Excess grave/ has been removed by the <br />previous operator resulting /n reduction of a/evation of river channe% acce/erated <br />bank erosion, reduction in water tab/e and death of flees. (Ritz, Mayo, Torrence/ <br />DMG records do not support these allegations. <br />The Thomas Pit permit area is located within a reach of the Animas River where an abrupt <br />reduction in the channel grade occurs as the river transitions from the steep upland <br />topography to the relatively flat floodplain of the Hermosa/Durango area valley. The steep <br />upland topography imparts high flow velocity to the river. Rivers with high flow velocity <br />can carry great quantities of sediment, to include cobbles and boulders, along its channel <br />bed. However, where flow velocity is reduced, the river's capacity to carry heavy <br />bedload materials is also reduced. The Thomas Pit is located within an aggrading reach of <br />river where excess bedload materials are deposited in response to a reduction in flow <br />velocity. <br />Aggrading rivers, such as this reach of the Animas River, often form several <br />interconnecting channels, separated by unvegetated gravel bars or sparsely vegetated <br />islands. The active floodplain is wide and sparsely vegetated, and contains several high- <br />water channels. The location and configuration of the interconnecting channels are often <br />altered by the seasonal deposition of excess bedload. Thus, the lateral stability of the <br />interconnecting channels are quite low within the boundaries of the active floodplain. <br />When such areas become developed, landowners typically attempt to fortify river banks <br />on their property to restrict the wandering river to a defined channel. DMG records <br />indicate that such actions, by the landowners or on behalf of the landowners, may have <br />resulted in adverse impact to the Wallace irrigation ditch. <br />As clarified in AM-01, various types of mining activities have occurred at the site from at <br />least the 1930's, and prior to the enactment of the Act and Rules. Mining type <br />extractions have also occurred upstream and downstream from the Thomas Pit permit <br />area. DMG records indicate that the river channel has been modified by a variety of <br />8 <br />