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i <br /> <br />acceptable and stable condition is defined as removal of any and all barriers, stockpiles, or <br />structures that aze at or above the original ground elevation and regrading all disturbed slopes to <br />a grade of 3:1 or less. Please address. <br />4. The Division strongly recommends that the applicant commit to baseline and annual channel <br />cross sectional surveys (or other such methods as offered by the applicant) at both [he upstream <br />and downstream permit boundaries to help isolate natural changes within the Colorado River <br />channel such as aggredation or degradation vs. mining related changes. The surveys (or other <br />such methods) will also help [o verify the absence of any possible offsite impacts due to mining. <br />Please address. <br />5. In order to evaluate the potential for offsite impacts due to flooding during mining and <br />reclamation, the applicant must commit to providing a detailed assessment of the possible <br />impacts expected during a "worst case" flooding event along with any necessary mitigation <br />measures to be employed. Such an assessment will need to be reviewed and approved by the <br />Division prior to any site disturbance. The assessment may be submitted as a technical revision <br />to the permit if not available at the time of the Division's recommended decision. (It should be <br />emphasized that the intent of the assessment is to predict or assess any impacts to the river <br />channel both within the permit area and and the upstream and downsteam areas during flooding <br />that may be excacerbated due to mining related disturbed slopes). At a minimum, the assessment <br />will need to include the following infornration: <br />a. predicted flood elevation or "stage" above disturbed slopes <br />b. predicted flood flow velocities in the disturbed pit areas & in-pit stockpile areas <br />c. extent of pit disturbance during such time, ie: pit slopes, slope heights, size or diameter of pit <br />wall materials, size or diameter of stockpiled/processed materials <br />d. potential for headcutting of pit walls and movement/saltation of stockpiled materials <br />e. extent of potential headcutting and/or erosion, ie: will headcutting/erosion be contained within <br />the permit area or will headcutting/erosion extend beyond the permit boundaries <br />f. mitigation measures to be employed to minimize potential for predicted impacts <br />headcuttinglerosion <br />6. The depth of mining not to be exeeded in the RRA is projected to be an average of 5 feet with <br />excavation varying from 1 to 7 feet. The applicant has proposed a "phased approach" for mining <br />in the RRA and annual surveys to verify compliance with the maximum allowable depth of <br />excavation as well as to evaluate changes within the river channel and the feasibility of future <br />excavation. Although the Division is not opposed to such an approach, we highly recommend <br />that the applicant consider a minimal depth of excavation over the entire area during the first few <br />seasons of mining, such as I or 2 feet, and [hen evaluate the ability the river channel to fill in and <br />reclaim itself. A commitment toward a minimal depth of excavation over the entire area during <br />the first few seasons of mining will better enable the applicant to demonstrate a minimal impact <br />to the river channel and will also enable the applicant to mine at a deeper depth in the future (via <br />a technical revision to the mine plan) once the ability of the river to reclaim itself is better known <br />from on-going channel surveys and monitoring. Please respond. <br />