Engineering & Mining Journal

JUL 2018

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ENVIRONMENTAL MANAGEMENT JULY 2018 • E&MJ 29 a new water treatment plant at Gladstone. The old dry hydrated lime-feed system was replaced with a milk of quick lime and liquid flocculent system with an ef- fluent pH control loop. The improvements resulted in a modern, efficient operation with greatly reduced environmental im- pacts. As a result of SGC's efforts, on Feb- ruary 29, 1988, the Colorado Mined Land Reclamation Division awarded SGC the 1987 Mined Land Reclamation Award in the classification "Most Improved Sites." SGC's Primary Reclamation Activities: Historic Mayflower Impoundment No. 1—SGC moved the im- poundment toe back from Boulder Creek and the highway to min- imize the potential for erosion and migration. SGC flattened the side slopes to increase stability and potential for revegetation, regraded to promote drainage, capped with subsoil and seeded. Historic Mayflower Impoundment No. 2—SGC moved the im- poundment toe back from Boulder Creek to minimize erosion and migration potential. SGC flattened the side slopes to in- crease stability and the potential for revegetation, regraded the top to promote drainage, capped with subsoil and seeded. Historic Mayflower Impoundment No. 3—SGC regraded the top to promote drainage, capped with subsoil and reseeded. Mayflower Impoundment No. 4—SGC excavated and relocated ap- proximately 80,000 tons of mostly historic mine waste and histor- ic tails to Mayflower Impoundment No. 4, regraded the area and re-seeded. SGC improved the intercept and diversion drains and placed a concrete diversion wall to divert groundwater to surface and around the tailings material. SGC also installed a lined toe ditch. Mayflower Mill Area—SGC cleaned the site, contoured and seed- ed. SGC ultimately donated the mill to the San Juan Historical Society along with $120,000 and nearby property. The mill is now on the National Register of Historic Sites and operated as a historical tour by the San Juan Historical Society. Eureka Tailings—SGC removed 112,000 yd 3 of historic finely ground tailings, which are more geochemically active, from the banks and floodplain of the Animas River and its tributaries and relocated them to the Mayflower Impoundments. American Tunnel mine waste and tailings—SGC removed 80,000 tons of mostly historic mine waste and tails. Longfellow-Koehler Project—SGC opened a caved adit and removed 32,000 yd 3 of mine waste and pond sediments, consolidated other waste to reduce footprint, added neutralizing materials to the area, covered the area with overburden, seeded, and constructed surface water diversion to divert upland flow around the site. Boulder Creek Tailings—SGC removed 5,700 yd 3 of tailings from the Boulder Creek and Animas River flood plain. Pride of the West Tailings—SGC excavated 84,000 yd 3 of his- toric tailings and relocated 45,000 cubic yards to an on-site tailings impoundment and the remainder to the Mayflower Tail- ings Impoundment No. 4. SGC conducted a geotechnical study, installed a toe drain and contoured to the slope. SGC capped the impoundment with overburden, fertilized and seeded. SGC partially rebuilt and planted a wetland. Lead Carbonate Tailings Impoundment Removal—SGC relocat- ed 27,000 yd 3 of tailings to Mayflower Impoundment No. 4, regraded, neutralized and reseeded the area. Lime injection—SGC injected approximately 1.3 million lb of hydrated lime into the interior workings of the Sunnyside mine to increase alkalinity. Gold Prince Mine Waste and Tailings—SGC installed two clo- sure bulkheads, relocated historic tails and ash piles into lined containment within a consolidated waste pile that was relocated away from stream flows, covered removal areas with overburden, and seeded. Ransom adit drainage—SGC opened the caved in adit, designed and installed a bulkhead to eliminate drainage, graded the por- tal area, and seeded. Mayflower Hydraulic Controls—SGC designed and installed three interception structures to capture and transport stormwa- ter and groundwater around Mayflower Impoundment No. 1 and the Mayflower Mill area to prevent contact and infiltration with tailings and waste rock. Sunnyside Basin—SGC placed 240,000 yd 3 of clean fill to cover the Lake Emma subsidence area and to create positive drainage, contoured the area and seeded. American Tunnel portal—SGC removed surface facilities, con- structed a diversion ditch, stabilized the bank of Cement Creek, recontoured and seeded. Mogul adit and Koehler Tunnel Bulkheads—SGC funded the placement of bulkheads in the Mogul Adit and Koehler Tunnel. Mayflower Passive Treatment Wall—SGC constructed a pas- sive treatment wall for groundwater, leaving a wetland near the southwest corner of the historic lower deposits in Tailings Im- poundment No. 4. Power Plant Tailings—SGC picked up tailings previously re- claimed along the Animas River in the vicinity of the old power plant and consolidated these into Tailings Impoundment No. 4. Bulkhead Installation—With oversight and approval of all rele- vant agencies, between 1992 and 2002, SGC installed a series of nine engineered concrete bulkheads in the Sunnyside mine, and the Terry and American tunnels to isolate the mine work- ings from other workings in the area and to prevent water flow from the Sunnyside mine workings into the Animas River. The bulkheads were always expected to return the local water table toward its natural, pre-mining level.

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