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• SAR. The most deleterious property of the refuse materials in this <br />comparison centers on the elevated sodicity associated with the new refuse <br />materials. The mean SAR value of the refuse is 18.21, which would be <br />considered to be a sodic material. However, as previously discussed, this <br />material is very dynamic in its properties. The mean SAR of fresh refuse <br />materials averaged 34.0, three year old refuse had an average SAR of 16.1, <br />the refuse 5 years old had an average SAR of 29.6, the refuse 7 years old <br />had a mean SAR value of 12.07 while the mean SAR of the refuse over 30 <br />years old is 0.79 and the SAR of the coal contaminated soil averages 0.95. <br />Upon considering the reclamation techniques that were used, the data appear <br />to follow somewhat of a consistent Vend. Wdh the exception of the five year <br />old sample all of the SAR values show a consistent decrease in sodicity over <br />time. Recognizing that the five year old sample lies very near the end of the <br />1984 reclamation and thus was topsoiled in a relatively "fresh" and <br />'unweathered' condition the values make much more sense. A statistical <br />analysis of these data document that the SAR values of the refuse decrease <br />over time. Upon excluding the "fresh' and 'unweathered" refuse samples <br />from the suitability comparison no differences in overall suitability exist <br />between the soils and refuse materials aS shown by the second SAR line in <br />Table 12. <br />Using the NMMMD suitability guidelines for topsoil substitutes, the SARs <br />• of the fresh refuse would all be unsuitable, the three year old refuse would <br />have a "good' to "marginal' suitability while the old refuse materials would all <br />possess a 'good" sutability. The question then becomes one of at which <br />point in time is the suitability standard and the applicable thickness of topsoil <br />established. The answer to this question will be explored in the following <br />discussion. <br />The previous discussion on the processes of sodification of mine soils <br />spread over sodic spoil reveals that the mere presence of elevated levels of <br />sodium in the spoil does not automatically mean that the processes of <br />diffusion will occur and reduce the quality of respread topsoil applied to these <br />sites. One attempt to quantify the potential upward migration of sodium was <br />presented by Daugherty (1982) wherein he presented a numeric formula to <br />determine the relative potential of the reapplied topsoil to become sodic. His <br />'sodicity index' is S=((SAR-5) % CLAD 1/2. Upon applying this formula to <br />the published data on the upward migration of sodium several very interesting <br />trends appear. In Merrill et. al. (1980) it was reported that upward migration <br />of salt occurred at sites having a calculated sodicity index values greater than <br />24.5 while essentially no upward sodium migration occurred on the two field <br />sites having sodicity index values less than 16.4. Subsequent research by <br />Merrill et. al. (1983a) reported no upward migration of sodium occurred on <br />sites having sodicity index values less than 14.2 while sites with sodicity index <br />values greater than 23.5 were characterized as having upward migration of <br />sodium. At the Decker Mine in southeastern Montana, Dollhopf et. al. (1985) <br />reported no upward migration of sodium two years following retopsoiling, but <br />. after seven years, upward migration of sodium had occurred on spoil having <br />a calculated sodicity index of 21.2. At two sites in the Northern Great Plains, <br />Barth and Martin (1982) confirmed the upward migration on two sites having <br />sodiciry index values of 22.6 and 46.8, respectively. The data of Berg et. al. <br />(1983) and Pendleton (1981) on TOSCO II retorted oil shale having a sodicity <br />38 <br />