Laserfiche WebLink
These two NRCS reports were used to evaluate the mapping with the <br />Colowyo Mine area. There are no hydrologic group A soils within the <br />area, and hydrologic group B and D soils are rare. The general <br />conclusion from this analysis was that for the premining case, all soils <br />should be assumed to be hydrologic soil group C. This statement has <br />been added to Table 1, and the curve numbers adjusted accordingly. <br />It is the Colowyo Mine's position that this is a very conservative <br />assumption, particularly for soils that have been rehandled and respread <br />on the reclamation. The principal reason for lower infiltration rates in our <br />soils is based on a limiting soil layer rather than a moderately fine soil <br />texture, and this limiting layer is obviously not present once a soil has <br />been stripped and rehandled. <br />In response to item b, we have modified the percent cover values <br />presented in Table 1 based on discussions with Steve Viert of Cedar <br />Creek Associates Inc. It should be noted that the cover values shown are <br />only used to support the appropriate curve number. For example, <br />footnotes in Table 8 provide a basis for a "good" or `fair" category based <br />on the ground cover. A wealth of sampling vegetation sampling data for <br />existing reclamation has been provided. <br />It should also be noted that the "ground cover" discussed in the footnotes <br />would include both the vegetative cover (living plants) plus the litter <br />component. The litter portion is at least 10 percent for the early <br />reclamation and at least 15 percent for the older reclamation areas. <br />3. The Division noted a discrepancy between Table 6 and the narrative in Section 1.9. Section 1.9 <br />Base Flow, of the revised materials states "A base flow of 0.15 cfs was used for the Streeter Pond <br />design. A base flow of 0.03 cfs was used for the West Pit pond design. Base flows were not used <br />in any other pond design." Table 6 shows three ponds with a base flow. <br />Second, Colowyo deleted the statement in Section 1.9 that said, "Discharge of collected water from <br />the open pits, as a result of pumping, will not be permitted during a storm event equal to or greater <br />than the 10-year, 24-hour storm event". In our 12 June 2008 letter we asked that the language in that <br />sentence be revised, not removed. <br />The Division's original question was related to the pumping of pit water, through outfalls as approved <br />under the CDPS permit and the implications of this pumping for those pond treatment systems where <br />a constant base flow was not included in the design. That was the reason for the original language <br />that has been removed by Colowyo in this response. The currently approved CDPS permit allows pit <br />water to be pumped to Streeter, Work Area, Gossard, Gulch A, Stoker Siding, Rail Loop, West Pit, <br />Section 16, and East Taylor. <br />According to Table 6, Sediment Pond Summary Proposed Plan, of the revised materials, a base flow <br />was used for the Prospect Pond design (0.15 cfs). A check of the currently approved design for <br />Prospect Pond confirms a base flow of 0.15 cfs was used in the pond design. Please note that the <br />currently approved CDPS permit does not approve pit pumpage through the Prospect Pond.