1998-10-15_REVISION - M1977378 - Laserfiche WebLink

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File No. M- 77-378 Page 3 Observed flows have been less than 0.5 cfs. This drainage was not addressed in the Consolidated Permit, 1987 (probably because it skirts the outside fringe of the property and no tailings erosion issues would be applicable from this drainage). The outfall from the pipe will be rock armored and lined with 40 mil PVC to prevent erosion. The existing upland diversion ditch that will carry this intercepted water off site will be enlarged to carry a minimum flow of 40 cfs and lined with 40 mil PVC covered with rocky subsoil material. The proportions of rock in the liner cover material will be increased with increasing gradient. The open drainage to the upland diversion ditch will be cleaned and defined where applicable to allow improved flow direction definition. Tailings Pond No. 4 Surface Drainage Modification The current drainage plan allows for surface runoff from the slopes of Tailings Pond No. 4, Hwy. 110 bordering Tailings Pond No. 4, and the Hwy. 110 drainage ditch from the last culvert up- gradient from Tailings Pond No. 4 to travel and/or infiltrate along the toe of Tailings Pond No. 4 to a topographic low where the collected water ponds and evaporates or infiltrates. In heavy flow condition, this ponded water could also be pumped into Tailings Pond No. 4 to prevent an overflow across Hwy. 110. While this arrangement was preferable when the tailings embankment was uncapped tailings and secondary containment was desirable as a precaution for spill containment while operating. Sunnyside does not believe this configuration (ie. no drainage) is desirable under present or future conditions (ie final reclamation). The embankments are capped with subsoil material and vegetation has been established. Surface runoff will not contact tailings material but infiltrating water has the potential to contact tailings. Therefore to minimize the potential for water to contact tailings and provide a positive drainage path for a future final reclamation configuration, Sunnyside proposes the following: 1) Installation of a 40 mil PVC liner in the toe drain invert to minimize infiltration. This liner will be covered with subsoil material and planted with Sunnuside's Mountain Mix since this is a low velocity pathway with intermittent flows. 2) At a topographic low, install a 24" culvert under Hwy. 110 to allow surface drainage to exit the site through drainage channels existing on the other side of Hwy. 110. This culvert installation will require a Colorado Department of Transportation(CDOT) Utility Permit and be installed to CDOT specifications. Sunnyside held a Utility Permit for this purpose in 1997 that has since expired and will require renewal. The installation was not made in 1997 because of weather and a TR submittal had not been made.