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• ease of access, <br />• potential remediation that might be applied, <br />• potential effectiveness of remediatioq <br />• rough estimate of cost of remediation. <br />The proximity of receiving stream is rated relatively: instream, near, medium, or far. <br />Biological potential of the receiving stream is rated high, medium or low. Ease of access <br />has a relative scale of 1-4 with 1 meaning easy access. <br />As with mine waste, the potential remediation technique for each site was based on <br />professional judgement of the ARSG Prioritization Committee. The techniques are <br />categorized as bulkhead seals, source controls, passive treatment and active treatment. <br />Hydrologic controls like bulkhead seals and source controls aze more desirable because <br />there is minimal operating and maintenance costs. Source controls aze means of <br />inhibiting water from leaching metals from underground workings, either by preventing <br />water from entering mines (e.g. re-routing surface waters, pressure grouting inflows) or <br />by collecting in-flowing water before it reaches mineralized surfaces and transporting the <br />water back to surface in an inert conveyance. <br />~'~fiere conditions are perfect, such as in deeply situated mine workings where water <br />is entering far from the surface and when the rock has only minimal, small fractures, <br />complete reduction of loading to streams might be expected using bulkhead seals. But <br />this is an unusual situation since many adits aze shallow in depth, and the surrounding <br />rock is often highly fractured, naturally or from mining activities. Then water will find <br />alternatit=e pathvs~ays around the bulkhead seal. <br />Finding and gathering in-flowing water can be difficult and expensive. First the i~ <br />flow must be located by geophysical methods, tracer dye injections, or visual <br />examination from the surface and within the mine. Seldom can all in-flowing water be <br />accounted for, particularly if the underground workings include abandoned slopes and <br />raises. As result of these difficulties, ARSG has determined that on the average, 50'/0 <br />reductions for these two methods would be optimistic for the typical mines and <br />conditions presently knov~~n in the tipper Animas Basin. <br />The other two remediation categories are passive and active treatment. Passive <br />treatment generally requires corninued long xerm maintenance and, on average, will be <br />less effective than hydrological controls. There is a wide range of passive treatment <br />methods available and often two or more methods can be built into the treatment of a <br />single mine drainage. Some treatment methods (e.g. settling ponds) may only remove a <br />small percentage of a single metal whereas a complex system may remove varying <br />amounts of several metals. Given the high elevation, severe wieners, high precipitation, <br />steep slopes, and need for continued maintenance and medium renewal, it is estimated <br />that passive treatment systems may average 30% reductions over an extended (20 year) <br />period. <br />There are several methods of active treatment available. All require lazge initial <br />capital outlays and annual expenditures for operation and maintenance in perpetuity. <br />This category• is consider the least desirable approach, although potentially the most <br />effective at reducing metal loading. Active treatment plants are generally designed for <br />reduction of specific metals. As such, they can be very effective for the metal of concern. <br />But it is to be expected that there will be lower percentage reductions for other metals. <br />An 85% average reduction of all metals is anticipated using active treatment methods. <br />lb <br />