1986-12-08_GENERAL DOCUMENTS - M1977493 (2)

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gg ;, 23 Each plot was planted with a tomato and crested wheatgrass , alfalfa, and rye grain seeds. The plants were allowed to grow for 13 months, by which time most of the wheatgrass, alfalfa, and rye had matured and died and then the �L ' plots containing living tomato plants were dismantled and examined. The exam- ii P it. ; ination showed the following: (1) The root systems of all plants were princi- pally located in the pelletized portion of the tailings, and (2) placing the sewage sludge layer at 3 inches prevented to a great extent the oxidation of ';; i.� i pyrite in the tailings as witnessed by an average tailings pH range of 3.9 to -inch-deep layer as compared with a tail 6.1 and a sludge pH of 6.8 for the 3 ings pH range of 1.7 to 2.0 and a sludge pH range of 3.6 to 4.0 for the sludge ;'1,' layer at 15-inch depth. A comparison of figures 3 and 4 shows the difference , r in pH change and moisture content within the tailings materials. Proper place- in ent of the sewage sludge layer to control water and gas movement appears excep- tionally promising for controlling JJ ' , acidification of pyrite-bearing tailings. fi iii 111 Costs of Methods Using Sludge as Pellets As previously noted, several tested physical , chemical, vegetative, and 1 combined vegetative methods have been evaluated as to stabilization effective- ness, required maintenance, and cost. The costs for the preferred vegetative methods have ranged from $100 to $1,750 per acre. Based upon the success of laboratory testing, costs were also estimated for the buried sludge layer, nelletization, and a combination method by the Bureau of Mines. The cost eval- p,# :ions were made utilizing laboratory data and after consultation with firms 1J ' having land-moving, transportation, and pelletizing capabilities. The follow- ing figures were basic to the Bureau evaluations : Cost of sludge, $1 per ton; hauling of sludge, $0.42 per cubic yard, based on a 7-mile haul; amount of sludge per acre, 130 tons for buried layers and 11 tons for pellets ; and a cost of seeds, fertilizer, and planting of $50 per acre. Calculations on lay- ing of the buried sludge were made using the following criteria : (1) An agri- culturally developed method using a broad flat plow for lifting the soil and a device for spreading a layer of buried material under the long plow, and then allowing the lifted soil to drop back and bury the layered material; and (2) use of a conventional wheel scraper and spreader method. The mixture of pelletizing consisted of, in percent, 92.4 tailing, 6.6 sludge, and 1.0 chemi- cal binder. Pelletizing was calculated as being done in place on the tailings II 1 using a recently designed high-speed light-compaction roll pelletizer which I can produce pellets at an estimated cost of $0.80 per ton. All sewage layer costs were based on application to flat pond areas only. These costs, although ( " ' broadly generalized, provide comparison for the different methods and are pre- sented in table 6. TABLE 6. - Cost comparison of auxiliary stabilization methods Approximate i Type of stabilization Effectiveness Maintenance cost per acre, dollars Buried sludge layers.. . . . Excellent. . . . Minimal. . . . $405- 810 ' kllet cover (1-1/2 inches). . .. . . . . . . . .do. . . . . . . . . .do. . . . . 330- 660 "ombined buried sludge plus pellet cover. . . . . . . . . . .. . . . .. . . . . . . . . . . . . . . . .do. .. . . . . . ..do. . . . . 735-1,470