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Hydrolow Data Interpmaum and Impact Asremnmt fw Pmnft Ana and Adjacmt Am= <br /> Because of the small quantity of mine water since they were constructed. MB-4 sometimes <br /> anticipated, any discharge from ponds would catches hydraulic oil spills from the Unit Train <br /> normally be dominated by water quality charac- Loadout.When this occurs,the pond is pumped by <br /> teristics of disturbed area runoff as described in a licensed contract hauler or the WECC vacuum <br /> the following section. truck. The pumped oil is deposited in the shop <br /> waste oil tank which is in turn pumped by a h- <br /> Runoff from Disturbed Area tensed waste oil recycling firm. This standard <br /> procedure was unnecessary during 1989. <br /> Overland runoff from snowmelt and precipitation <br /> within the disturbed areas is routed to one of six Flowmeters are installed on all discharge points <br /> sediment ponds on the mine site.The six sediment from sediment ponds which discharge intermittent- <br /> ponds are designed to contain the predicted runoff ly to continuously record flows. Information on <br /> from a statistically determined 10 year, 24 hour flows, sampling points, and quality of water dis- <br /> , precipitation event as well as a calculated sediment charged from the mine site sediment ponds during <br /> storage volume. The ponds are also designed to 1989 is included in Appendix J. All water dis- <br /> ' pass the overflow from a 25 year, 24 hour precipi- charged was in compliance with NPDES permit <br /> tation event safely. effluent limitations. During spring runoff condi- <br /> tions, as well as some precipitation events,quality <br /> The Mi. Gunnison Mine site receives much of its of water in the North Fork of the Gunnison is <br /> annual precipitation from snowfall during the much worse than the quality of discharges from <br /> winter months. When warmer weather begins in WECC sediment ponds. It is also well outside <br /> late February, March or April, most runoff to the NPDES effluent limitations. During winter base- <br /> sediment ponds is from snowmelt. It is entirely flow and summer conditions water quality in the <br /> possible for a volume of runoff greater than the 10 North Fork is better and is within NPDES effluent <br /> year, 24 hour precipitation event to result from limitations. However, this is the time of year when <br /> snowmelt or snowmelt coupled with a small precip- WECC's ponds are rarely discharged. <br /> itation event. <br /> The sediment ponds are treated with cationic Flowvolumes from WECC sediment ponds are low <br /> flocculent when necessary to speed clarification relative to the North Fork of the Gunnison flows. <br /> and settling of suspended solids.The ponds MB-I, Even during low Dow conditions on the North <br /> Fork WECC discharges represent an imperceptible <br /> MB-2, MB-5, and MB-6 have manually controlled <br /> difference in stream quality. <br /> dewatering devices. Ponds MB-3 and MB-4 have <br /> automatic dewatering capability. Ponds MB-1, <br /> MB-2, MB-5 and MB-6 are dewatered intermit- Based on the analyses, sediment pond discharges <br /> tently with most discharges coming during early have had no adverse impact on the North Fork of <br /> spring runoff. Dewatering procedures take usually the Gunnison River. The quality of discharges <br /> less than one day for all ponds except MB-5. Pond usually exceeds the quality of the North Fork. In <br /> MB-5 is responsive to a high spring groundwater addition, pond discharge flows are so small that <br /> table and sometimes has to be dewatered more incremental changes in concentrations in the North <br /> often. Fork are imperceptible. <br /> Ponds MB-3 and MB-4 did not discharge during Discharges of surface runoff in 1990 are expected <br /> 1989 and records indicate they have not discharged to be similar to 1989. <br /> • <br /> 14 <br />