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• index of 20.2 failed to confirm the upward migration of sodium. Additional <br />studies performed by CSU and reported on by Redente and Cook (1984) <br />failed to document appreciable upward sodium migration from retorted oil <br />shales having calculated sodicity index values less than 16.2. <br />These data suggest that upon applying the sodiciry index value proposed <br />by Daughtery (1982) upward migration of sodium occurred on sites with <br />sodicity index values greater than approximately 21 while sites with lower <br />sodicity values have not experienced any problems with upward migration of <br />sodium. Examination of the Southfield Mine refuse data reveals an overall <br />sodicity index of 12.5, suggesting that upward migration of sodium would be <br />highly unlikely at this site and iF it occurred it would be a situation unique to <br />all of the previous examples of sodium migration reported in the scientific <br />literature. <br />The influence of saturation percentage as a mechanism closely connected <br />with the upward migration of sodium has been discussed by Merrill et. al. <br />(1987). They reported that on field sites where the SP was less than 92 <br />percent, the downward leaching of moisture reduced the upward movement <br />of sodium while on sites with SP greater than 113, sodium and salt <br />accumulation in the cover soil was more stable and potentially more <br />deleterious. They suggest using an SP value of 95 percent as a guideline for <br />°separating more deleterious from less deleterious sodic mine spoils." It must <br />• be pointed out that the maximum SP value for the Southfield Mine refuse is <br />56, with an overall average of 47.9 percent. Using the criteria recommended <br />by Merrill et. al. (1987) the Southfield Mine refuse materials with an SP value <br />this low would not require any special handling. <br />Another important factor in the upward migration of sodium relates to the <br />hydraulic conductivity of the soil and spoil materials. Merrill et. al. (1980) <br />reported that when the hydraulic conductivity of the spoil "is great enough <br />that some leaching into the spoil occurs, upward migration of sodium is not <br />expected to be a problem.' Similar findings were reported by Merrill et. al. <br />(1983a), wherein they found that two of four field sites having sodic spoil <br />showed no upward migration of sodium. They stated that at such sites the <br />leaching of salts, due to higher hydraulic conductivities, in the reapplied <br />topsoil was more effective in abating sodium accumulation than on sites <br />where I'dtle or no movement of water across the spoil-topsoil interface <br />occurred. North Dakota sites where signficant sodium accumulation <br />occurred were reported to have HC values of 0.1 to 0.2 cm/d for mine spoil <br />below the soil-spoil interface. Conversely, using the HC values calculated <br />using the USDA-SCS (1983) methods, the HC for the Southfield Mine refuse <br />averages 55.5 cm/d with a range of 0.61 to 85.34 cm/d. Upon comparing <br />the very lowest HC value for the Southfield Mine refuse materials it can be <br />concluded that these materials are at a minimum, 30 times more permeable <br />than the materials in North Dakota where upward migration of sodium was <br />determined to be a problem. <br />• pb, The second area where the overall average of the refuse material is lower <br />than that of the soil material is pH. A total of four refuse samples have pH <br />values below the WDEQ suitability cutoff value of 5. These four samples were <br />collected from abandoned refuse piles that are upwards of 52 years old and <br />from the harshest sites available for sampling. These sites contained more <br />39 <br />