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conditions, namely the present continuous flow of snowmelt water, <br /> would make culvert replacement, required to complete abatement of <br /> NoV C-90-050, environmentally harmful . The specific circumstances <br /> are these: <br /> C-90-049 . <br /> The abatement required for pond 4-1 is to install a secondary <br /> spillway. The design in the permit indicates a pipe in the <br /> embankment as the spillway. This design was prepared by Morrison <br /> Knudsen (MK) over a decade ago, as part of the drainage and <br /> sediment control plans prepared for all the mine portals. <br /> Several spillways do not now conform to the recent MLRD requirement <br /> of separate secondary spillways. Accordingly, Mid-Continent has <br /> applied for a technical revision (TR-18) to allow for construction <br /> of rip-rapped channels on those sediment pond embankments, in order <br /> to comply with the requirement. <br /> Mid-Continent has determined that a rip-rapped spillway would be <br /> the better alternative for the No. 4 Mine pond. The MK design <br /> would require digging into the embankment to install pipe, then <br /> replacing embankment material. We have some concern about then re- <br /> compacting the embankment because the pond location is such that <br /> access by equipment is very difficult, if not infeasible. For that <br /> reason, we have included the No. 4 Mine pond in the technical <br /> revision request. <br /> We are in turn asking for an extension to allow us to install the <br /> secondary spillway, as a rip-rapped channel, when the technical <br /> revision is approved. Preparation of the technical revision <br /> request, and the determination that the rip rapped spillway is <br /> preferable for the No. 4 mine pond, were delayed by the late <br /> snowpack, which prevented on-the-ground review of the ponds until <br /> quite recently. <br /> The abatement work required for the No. 3 Mine Bin Pad, namely <br /> widening of the embankment, has been completed. This pond is also <br /> included in the TR-18 request. Although the violation did not <br /> relate to the spillway of this pond, the certification of the pond <br /> should be done after completion of the additional spillway. <br /> C-90-050 <br /> Mid-Continent's request for an extension is to allow replacement of <br /> culvert C-3 during low flow. This culvert is presently receiving <br /> a continuous flow of snowmelt runoff from the higher elevations, <br /> and these flows will continue beyond the time presently allowed for <br /> abatement. It seems to us to be advisable to replace the culvert <br /> when there is the least amount of water to contend with. This is <br /> 2 <br />