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Exchangeable Sodium Percentage (ESP) (Tables 2.7-7 and 2.7-8 and Maps M41 and <br />M42) <br />Sodium in soil and overburden materials can have a pronounced influence on the <br />success of revegetation efforts. It has a dispersing effect on soil and if pre- <br />sent in high concentations, water permeability can be reduced, thereby promoting <br />runoff and decreasing water availability for plant uptake. Erosional problems <br />may be increased also due to the increased runoff. Soils that are high in sodium <br />also exhibit poor structural stability and a low hydraulic conductivity. <br />Sodium was evaluated in the overburden on the basis of the "exchangeable sodium <br />percentage" (ESP) which is calculated from the sodium fraction of the total <br />cations held on the cation exchange sites. It is essentially a measure of the <br />amount of sodium compared to the number of elements on the exchange sites of a <br />soil colloid. <br />• Various desirable limits have been defined for the ESP in soils but most fall <br />within a narrow range. Olsen (1974) and many other researchers suggest a maximum <br />acceptable ESP value of 15 while others have recommended a maximum ESP of 10 for <br />effective revegetation (Cook et.al., 1970). <br />As is shown in the cross sections on Map M41, higher ESP values were found in <br />connection with shale-siltstone layers where values ranged up to as high as 31.0 <br />before weathering and 26.7 after weathering (Tables 2.7-7 and 2.7-8). In con- <br />trast, sandstone strata in the overburden are associated with lower ESP figures <br />(<1 to 15.6). This indicates that a mix of the shale-siltstone layers with sand- <br />stone layers would be likely to result in a material with acceptable ESP values <br />(Map M42). <br />In the eastern portion of the proposed permit area, high ESP values can poten- <br />tially cause problems in the weathered overburden from the areas represented by <br />holes CR220, 222 and 223 where ESP values ranged from 5.5-26.7. ESP values were <br />low (<1) in the overburden from holes CR219 and 221. The high ESP values are <br />associated with high clay contents as indicated by data in Table 2.7-8 from the <br />weathered samples. Estimates of clay content from water percentage at 0.33 bar <br />2-388 <br />