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Overburden Char•acterisi;ics • <br />In general, the physical and chemical data general:ed by the testing regime <br />was typical for Williams Fork, Iles, and Lewis overburden formations which <br />form the htesaverde Group. Stratigraphic units predominantly consist of <br />fine-grained, interbedded sandstones and shales with lesser amounts of <br />sandy shale, siltstone, and coal. The overburden particle distribution <br />showed a high silt and very fine sand contf~nt which reflects the <br />fine-grained nature of the depositional units. Salt levels were low while <br />pH ranged from acidic to alkaline. SAR levels were low in the overburden <br />section but were occasionally quite high in the underburden. Generally, <br />trace elements were at normally expected background levels. Significant <br />concentrations of iron and nickel exist on the exchange sites. <br />The criteria used for assessing the suitability of overburden material are <br />listed in Table 6-3. The suspect limit for each parameter is documented <br />by current literature citings. All cores that have poor quality strata are <br />documented further in the Overburden Mixing and Mitigation of • <br />Inhibitory Material Section. <br />The following techniques were used to analyze the overburden and <br />underburden core data. Initially, statistical analyses including range <br />(maximum and minimum), arithmetic mean, standard deviation, and <br />sample frequency were completed to determine the variability between <br />strata, between overburden and underburden, and from core to core. <br />This statistical summary is shown in Tables 6-4 and 6-5. Second, since <br />overburden sampling increments varied with depth, weighted means were <br />calculated for all physiochemical parameters across all lithology types, <br />excluding topsoil (Table 6-6). These means are representative of the <br />physiochemical concentrations that will be present in the spoil pile <br />(Dollhopf, July 18, 1980). In this manner, select overburden zones of <br />poor quality material will, with mathematical reasoning, be acceptable <br />• <br />6-16 Revision 8-17-90 <br />