2002-07-08_GENERAL DOCUMENTS - M2002004 (4)

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urden characterization. The average variation hese properties must also be known since suffi- t Boll materials must be replaced over the entire to ensure optimum postmine productive levels those spoil sites which have the least desirable ropertles. If site - specific soil replacement guide- Wm are to be utilized, reliable estimates for depth 1 soil replacement must be made before initial temoval of topsoil and subsoil materials. At sites on which the available soil materials are not adequate in either quality or quantity for restora- tion of optimum productivity, some soil and/or spoil materials may be available which have less than op- timum properties for use in reclamation. Research is needed to develop methods for the most effective utilization of marginal soil and spoil materials; all possibilities for restoration of better postmine pro- ductivity by proper utilization of submarginal materials need to be investigated. Methods to relate the potential productive capaci- ty (productivity index) of both undisturbed and reclaimed soils to soil properties and characteristics need.to be adapted for use in reclamation planning and evaluation. Current soil productivity indexes are based upon the correlation of field classification with laboratory measurements of chemical, physical and mineralogical properties and with landscape position. Discussions of the relation of soil types (field classification) to chemical and physical pro- perties have been given by Omodt et al. (1975) and Patterson and Schroer (1980). Refining and adapting these productivity indexes for use in reclamation will facilitate the most effective use of available soil and spoil materials for restoring optimum postmine productivity. SUMMARY Restoration of stripmined lands to a level of pro- ductivity equal to or better than existed before min- ing is required by law in North Dakota. Reclamation costs are a significant part of the cost of mining coal and these costs are passed on to the consumers. These costs can be minimized if the chemical and physical properties of available soil and spoil materials are well characterized and then used to determine the needed depth of soil replacement to restore acceptable levels of productivity. Initial research showed that respreading of soil materials was the fastest and most practical method of restor- ing soil productivity. Postmine productivity was governed by the amount and quality of soil materials available for respreading and to the chemical and physical characteristics of the reshaped spoil. In many instances, more soil needed to be replaced to restore premine productivity than was available as topsoil, so subsoil materials also needed to be removed and respread. When the underlying spoil 20 was of good quality with desirable properties, lesser amounts of subsoil materials needed to be respread for restoration of optimum productivity. When the underlying spoil has undesirable properties, larger amounts of subsoil were needed. If soil and spoil properties are to be used as a basis for determining needed depths of soil replace- ment, the properties which govern the productive capacity of the most productive soils in the area need to be identified and quantified. These criteria could then be used as a "standard" to assure the most effective utilization of all available soil and spoil materials at any specific site. Research cited in this report indicates that the most productive soils in western North Dakota have an effective root zone at least 4 feet in depth which is medium or finer in texture. The topsoil is nonsaline and nonsodic, con- tains less than 10 percent free carbonates, and has an organic matter content of 2 percent or more. The subsoil is no more than slightly saline or moderately sodic. The most productive soils are located at the base of concave slopes or in well- drained depres- sional areas which receive runon water from sur- rounding higher areas; however, available research data are not sufficient to justify adjusting the depth of soil replacement to topographic location. The most important soil and spoil properties to be con- sidered in reclamation planning are 1) water - holding capacity (texture) and 2) soluble salts and sodium levels. During soil development, the topsoil ( "A" horizon) develops into the most favorable medium for plant growth; at least 1 foot of topsoil should always be respread when soils are reclaimed. The subsoil, that portion of the rooting zone below the topsoil, serves mainly as a reservoir for nutrients and moisture. Sub- soil replacement serves two purposes. First, if the underlying spoil is coarse - textured with a low water - holding capacity, finer - textured second lift materials will increase the available water - holding capacity within the root zone. Second, if the underlying spoil has undesirable properties for plant growth, replac- ed subsoil serves as a buffer by placing the undesirable spoil materials below the root zone. If the properties of the underlying spoil are such that it is a suitable plant growth material, it can serve as the lower portion of the root zone. When the supp- ly of suitable soil and spoil materials is plentiful, replacement of excess soil materials over spoil with desirable properties will not increase postmine pro- ductivity. If the underlying spoil has undesirable properties, more than 4 feet of soil materials may need to be replaced to provide an effective rooting zone depth of 4 feet. Therefore, the depth of subsoil, or second lift, that must be replaced to restore op- timum productive levels depends upon the charac- teristics of the underlying spoil. Frequently the amount and quality of soil materials available for replacement is not adequate to meet the criteria established for soils of optimum productivity. In these cases, available suitable materials, possibly in