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In addition to these passive and semi-passive techniques, there are active systems that operate in much the same manner but have more mechanical mechanisms and need more maintenance_ I~%. REMEDIATION IN THE UPPER ANIMAS BASIN Of the 3 ~+ projects completed or in progress in the Upper Animas Basin as listed in Appendix B, 21 are surface hydrologic control projects. There are also four subsurface hydrologic co~rol projects, all using bulkhead seals. Five different passive techniques are in use or have been used in the- Upper Animas Basin including injection of a neutralizing agent, anoxic drains, a wetland, a bioreactor, and settling ponds. At some sites a combination of techniques have been used. Sunnyside Gold's treatment plant at the American Tunnel is the only active treatment facility_ It consists of mechanical injection of a neutralizing agent followed by a series of settling ponds. The plain has recently been purchased by Silver Wing Co. Currently Silver Wing Co. is treating what little discharge remains from the American Tunnel and discharge from the Gold King Mine. Challenges in Doing Remediation Remediation is site specific and most of the sites in the Upper Animas Basin offer substantial challenges. Many sites lie on steep slopes at elevations 10,000 to 13,000 feet above sea level where it can snow any day of the year, and snow depths can reach 12 to 15 feet in winter. The construction season may last only three to fow months. Avalanches are a constant hazard for at least half of the yeaz and some sites lie directly in avalanche paths. Some sites have no vehicle access so that helicopters may be needed to transport equipment. Areas around the sites are fragile mournain tundra where heavy equipment can do substantial damage. Few sites have electric power needed for some types of treatment. Hydrologic controls are the preferred method of remediation because they are frequently less expensive and need less maintenance than treatme~. Drainage diversions around mine waste piles can be a good, inexpensive partial remediation method, yet it is difficult to totally isolate piles from water. Removal of mine waste piles can be a very effective remediation measure, but where does one put the material? In the Upper Animas Basin, some piles have been scooped up, consolidated, and then capped with clay or soil to reduce water infiltration. However, there are few lazge, flat areas in San Juan County that could be used as repositories for significant amounts of material. Trucking the wastes outside the region to a landfill would be prohibitively expensive. Another alternative is to mill the mine wastes to remove the offending metals_ This alternative is currently being explored. Many mine waste piles occur on steep slopes. As material was dumped from a portal, the piles themselves became conical with steep sides and small flat tops. Their shape makes them difficult to cap or amend with neutralizing agents. Sub-surface hydrologic comrols can be very effective, if the underground mine workings are accessible. Most mines in the Upper Animas Basin have not seen any 11