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The hydrologic balance, previously discussed, will be protected through a number of <br />• procedures designed to mitigate any potential impact from mining. Temporary and permanent <br />diversions will route runoff away from disturbed areas to minimize erosion and sediment <br />loss. Temporary channels are designed to safely pass the runoff from a 10-year, 24-hour <br />precipitation event and, where necessary, will be constructed using bank stabilization <br />methods including energy dissipators, sediment traps, and dug outs or a combination of these <br />methods. Drainage culverts will also use energy dissipators at the outlets if necessary so that <br />runoff will not cause additional erosion and subsequently increased total suspended solids <br />(TSS) levels. Detention ponds will be used to detain runoff water from the disturbed areas to <br />allow the TSS to settle out and to attain acceptable concentrations for other parameters <br />consistent with the requirements of the NPDES Permit. Any Small Area Exemptions (SAE'S) <br />employed will be designed to minimize contributions of TSS to the hydrologic balance. <br />Infiltration and percolation of precipitation in the mine area may be enhanced by the <br />reclamation techniques of contour furrowing on hillsides and the continued excellent <br />revegetation success at Colowyo. Infiltration rates for the pre-mined and post-mine condition <br />of the land were presented earlier. Striffler and Rhodes (1981) showed through field <br />measurements, using an intense rainfall simulation, that infiltration capacities of the mulched <br />and revegetated areas were much greater than the pre-mine estimates. Runoff from the <br />revegetated and contour-furrowed areas has been minor to date, as documented by Colowyo <br />Mine personnel. Flows from Streeter Gulch will be moderated with the detention pond. <br />Moderated flows will continue to pass through the historic drainages. Recharge of the limited <br />groundwater systems in the mine will not be inhibited and may be enhanced through the use <br />• of the above techniques. <br />Groundwater protection, per se, is not necessary in the permit area as essentially no <br />continuous groundwater system exists. Perched aquifers of limited nature will be impacted <br />only in the mine area property. This water will be evaporated. The quantity of groundwater is <br />minimal as evidenced by the lack of water in test holes and the dry active pit. <br /> <br />2.05-74 Revision Date: 6/7/01 <br />Revision No.: TR-51 <br />