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the surface spoil layer, on both pit backfill and out-of- pit spoil areas. We assume that this <br />surface replacement layer would exceed 4 feet in thickness, but merely requested <br />clazification in the handling plan text. We were not requesting placement of a "special <br />lift", just confirmation that the approved plan does result in a surface layer of weathered <br />overburden at least 4 feet thick. In the South Taylor and Lower Wilson project areas, <br />placement of the weathered material from the upper overburden zone at the surface of the <br />spoils would appear to be important, primarily due to the presence of strata with unsuitable <br />SAR levels within deeper "unweathered" overburden zones. <br />Please amend the "Overburden Monitoring Program" narrative to state that the <br />thickness of weathered material placed as the surficial layer of spoil on reclaimed pit <br />spoils and out of pit permanent overburden disposal areas will be a minimum of four <br />(or more) feet. <br />74. The operator response was that Table 2.04.6(2) was submitted in error, and that the <br />parameters and suspect levels listed on page 2.05-5 would continue to be used for the spoil <br />monitoring plan for South Taylor and Lower Wilson project areas. The Division does not <br />believe this is appropriate. The PR-2 overburden baseline assessment was conducted <br />based on the parameters and suspect levels listed in Table 2.04.6(2). Suspect levels in the <br />table were From the current Wyoming DEQ Soil and Overburden Guidelines, and the <br />values are based on published reseazch referenced in the guidelines. We believe it is <br />logical and appropriate that the suspect levels employed in the spoil monitoring program <br />for South Taylor and Lower Wilson, be consistent with the suspect levels employed in the <br />baseline assessment. Please amend the spoil monitoring plan parameters and suspect <br />levels as requested, or provide valid technical justi£cation for any modifications. <br />75. The operator response indicates that Colowyo has demonstrated suspect levels have not <br />been reached after the homogenous mixing of overburden seams, and as such, "the need to <br />special handle weathered overburden appeazs to be negated". <br />As previously stated, the Division is not familiaz with the "homogenous mixing <br />demonstrations" referenced. Many constituents exhibiting marginal or unsuitable levels do <br />occur in such a low percentage of the strata that sufficient dilution is likely to occur as a <br />result of normal operations. However, drill hole data referenced in our original adequacy <br />letter do indicate some potential for concern, due to the relative thickness of certain <br />overburden zones exhibiting suspect levels of particular parameters. On page RZ-36 of the <br />revision application, narrative states that "Saturation % and SAR are the primary physical <br />properties of overburden that may prohibit their use as root zone or aquifer restoration <br />material." Further down on the same page, narrative states that "unsuitable overburden <br />materials that represent a considerable portion of the overburden to be mined will be <br />identified, selectively handled and isolated from aquifer and root zone areas within the <br />backfilled pits and out-of--pit disposal facilities using the methods specified in the mine <br />plan." <br />From our review of the drill hole data, it appears that strata with suspect levels of SAR and <br />Saturation % are primarily concentrated in relatively deep overburden zones (particulazly <br />10 <br />