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• In a subsequent study involving overburden cores and regraded mine <br />spoil, IGmble and Temple (1980) reported that the populations of sulfur and <br />iron oxidizing bacteria were widely distributed in all of the materials they <br />examined. They stated that T. ferrooxidans isolated from regraded soil, which <br />was not aged, from the Western Energy Mine had lowered the pH of the spoil <br />to 1.84 and had oxidized 99 percent of the ferrous iron. They concluded that <br />the formation of acidic mine spoils 'would be a problem only in the <br />arcumstance when a potentially aad-forming strata is so placed during spoil <br />reclamation that it drains directy into a surface stream.' <br />The occurrence of acidification in three spoil types, including acidic pyrRe- <br />rich waste coal were evaluated by Olson et. al. (1980). They determined that <br />the occurrence of acidophitic iron and sulfur oxidizing bacteria was related to <br />the availability of water in the spoil. Waste coal was reported to have <br />weathered to a pH of 2.6, while the pH of the "halo' surrounding this coal had <br />a pH of 5.4 and the alkaline spoil had a pH of 7.7. They reported that <br />although pyritic rich coal refuse materials might be readily available, <br />oxidization of the sulfur in these materials might never occur due to the low <br />water potentials during the dry summers. In instances where oxidization of <br />the waste coal had occurred, they reported that the oxidization of pyritic iron <br />produced sulfuric aad which reacted with calcium carbonate to form a halo <br />of gypsum crystals. Gypsum crystals were also reported by Schafer et. al. <br />(1979) to form upon the oxidization of pyrites in waste coal. <br />• TOPSOILING STUDIES CONDUCTED ON SODIC SPOIL <br />More work relative to the characterization of sodic mine spoils and their <br />reclamation potential has been conducted in North Dakota than in any other <br />area of the west. Sandoval et. al. (1973) was among the first to document <br />the high sodium content of western mine spoil and implement research <br />directed at overcoming this recamation problem. Subsequent research by <br />these scientists (Sandoval and Gould 1978), documented that upward <br />migration of sodium into respread topsoil was a major potential problem that <br />needed to be properly addressed for long term reclamation. Upward sodium <br />migration following application of 30 cm of topsoil was reported to reduce <br />plant yields from 4,020 kg/ha the first year to 1,890 kg/ha four years after <br />reseeding. This study and its associated implications largely became the <br />driving force for implementing cover soil requirements on sodic spoil. The <br />initial OSM regulations required a four foot cover on all sodic spoil. This <br />specfic requirement has been changed but regulatory policy still largely <br />depends on this standard. <br />Subsequent research in North Dakota (Merrill at. al. 1980), documented <br />that upward migration of sodium and other soluble sales from spoil into <br />respread mine soil was a complex and variable process. Two of four sites <br />studied had measurable upward sodium migration while the other sites had <br />signficantly less saR movement. They reported.that the ultimate suitability of <br />. materials in the rooting zone could not be defined on the basis of sodicity <br />level alone. Clay fraction mineralogy, texture, degree of aggregation, <br />aggregate stability and organic matter needed to also be considered. The <br />dominant mechanism of sodium migration was suggested to be due to <br />diffusion. Capillary rise was not considered to be involved. The greatest <br />9 <br />