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]~ Letter from Jeffrey Torrence <br />It should be emphasized that this amendment addresses only the mining of the adjacent <br />lake, although the permit for river mining has been revised to show much more detail. <br />Erosion shall not increase for the amendment since all embankment work can only be <br />done during a low flow period in the river and extra precautions have been taken to keep <br />all river flows in the original eastern channel for this work. <br />We also point out that river mining will not cause increased erosion since mining is now <br />limited to a certain level, providing a grade which has been the historic grade in this area. <br />Cross-sections have been shown which are to be strictly measured year after year. If Four <br />Corners Materials mines below this level, they will be in violation. Currently, river <br />mining has not resumed due to the approval from the COE, however, when lean flow <br />years occur (such as 2002), Four Corners can only mine to the pre-determined healthy <br />level of the river at this location (6645'). This means that mining may not occur in a given <br />year if the upper San Juan Basin has not deposited any significant gravel. <br />Since this location is one of the most extreme depositional stretches of river in the United <br />States, river mining here is not detrimental, as long as it is done within these safe <br />extraction levels. The problem with past mining in the river is that the hydrology of the <br />river was not well understood and all parties involved were learning what effects occurred <br />from certain practices. When mining occurred too deeply, negative effects were <br />experienced. With the current controls in place, this can no longer happen. Any <br />hydrologist at the DMG or the local COE office will substantiate this information. <br />2) Letter from Marion Rau <br />This letter's main concern is the stability of the embankment separating the lake from the <br />river. This embankment has been well-thought out and has been designed to handle the <br />100 year flood, as shown on the maps generated by the Corps of Engineers and used by La <br />Plata County. These maps are located in Appendix C of the permit application. <br />Overall, a number of design features ensure the stability of the embankment: <br />a) The jetty will divert some water from the embankment. It will also slow the velocity of <br />the water that does reach the embankment. <br />b) The large concrete blocks cabled together will provide a heavy, durable beam so that <br />all the blocks will act as one piece and will likely not move for a storm far greater than <br />the 100 year event. <br />