REV07929 - Laserfiche WebLink

Home Browse Search

West Elk Mine B Seam longwall experience indicates that some inflows confinue past "one to two weeks," but these inflows generally drop to levels of less than 10 gpm, except as noted from the fault system inflows. 9. CDMG staff quantified the maximum mining impact on the North Fork and the probable mining impact on the North Fork for total dissolved solids (TDS), using conservative assumptions. The conclusions reached from this analysis were: "The worst case impact with regards to TDS in the North Fork during the irrigation season would be to raise the TDS level from 130 to 189 mg/L. This is understandable since the total discharge from all the mines, as used in the calculation, is only 7 percent of the flow of the North Fork." • "With the maximum, worst-case impact for TDS being only 189 mg/L, there is no need to calculate the more realistic impact." (p. 16) WWE has reviewed the cited TDS computations. The methodology is reasonable and provides a conservative projection of what could occur in the azea. This analysis can be translated to the South of Divide pemmit revision area. As discussed in Surface Water Quality Effects, W WE has revisited the TDS loading analysis conducted by CDMG and found that, even under the extreme conditions of 1996 and eazly 1997, when MCC was forced to discharge lazge quantities of mine water without adequate treatment (in response to lazge inflows from the BEM and 14HG fault inflows), TDS levels in the North Fork were well below those considered to be a concern. 10. "Mine inflows aze not normally significant when ephemeral or intermittent streams are undermined. Mine inflows are seldomly, if ever, correlated to the undermining of ephemeral or intermittent streams. Most of the streams to be undermined in the SOD permit area are ephemeral and intermittent. Flow in these streams is concentrated in periods of snowmelt and high intensity precipitation events. The stream gradients aze steep and their channels contain little alluvium." (p. 20). In both the current permit and South of Divide mining area, all of the streams aze ephemeral, except a portion of the Deep Creek channel in Section 35. Their steepness is characterized in Exhibit 55 and SSA, which contrasts pre- and post-mining sediment transport. As described in the section Groundwater Quantity Effects, neither the BEM Fault nor the 14HG Fault inflows aze directly linked to surface inflows. Probable Hvdrologic Consequences - 2.05.6 (3)(b)(iii & viii) With the fmdings and observations provided above as background information, the pemut document now turns to site-specific evaluation of probable hydrologic consequences (PHCs), based on data from the current permit azea. PHCs are projected based on past experience, expected rates of water use and water dischazge, location and extent of mining (and subsidence) relative to basin geology and hydrology, and hydrogeologic conditions of the mined interval and its overburden. 1.03-154 Revised June 1003 PRIG