2022-09-29_PERMIT FILE - C1980007 (2)

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West Elk Mine (SAR) is an indicator of the risk that soils may have low permeability. Thus, waters high in sodium and low in calcium and magnesium (the constituents used to calculate SAR) may impose a risk to soils that are used for agriculture. If the SAR is less than 3, there is little to no risk of soil "swell". Water with SAR values ranging from 3 to 6 slightly increase the risk for detrimental impacts to soils, and those with values greater than 6 aze cause for concern. WWE calculated the values of sodium, calcium, and magnesium for the combined flow of the North Fork and the fault inflow effluent and found the new SAR to be 3.6 during low flow conditions. These results aze shown in Table 56, below. Table 56 SAR Values at Various Locations Location Flow cfs Sodium m /L Calcium m /L Magnesium m /L SAR N. Fork u stream 69 6.6 20.1 3.4 0.36 Fault water dischar e 5 87.2 3.1 1.6 99.6 Mixed downstream 74 65.1 19.0 3.3 3.6 It is important to note that the increase in SAR will be temporary, due to sodium exchange with calcium and magnesium on sediments and additional downstream inflows. Also, the analysis assumes that the pond discharges consist solely of fault water. Other water reaching the ponds, such as runoff, will have a lower SAR, thereby reducing the SAR of the pond dischazges. WWE has reviewed the salinity (TDS) loading analysis in the 2001 Cumulative Hydrologic Impacts Analysis (CHIA) for the North Fork in the context of MCC's 1996 discharges. In the CHIA, CDMG calculated the cumulative TDS (salinity) loading to the North Fork from coal mines located in the North Fork valley. The assumptions used for MCC's contribution were a discharge rate of 5,520 gpm (12.3 cfs) and a TDS concentration of 2,500 mg/L. When assessing calendaz yeaz 1996, the total volume discharged from ponds MB-1 and MB-2R was approximately 433 acre feet, which translates to an average continuous dischazge rate of approximately 270 gpm. Additionally, the TDS concentration of the B East Mains fault water was typically around 2,000 mg/L. Consequently, the annual salinity loading to the North Fork from West Elk Mine for 1996 was 3,290 tons, well below the value assumed in the CHIA as shown in Table 57. The analysis for 2002 results in a salt load of 1,922 tons per year, or 6 percent of the values assumed in the CHIA. Furthermore, even considering the "worst case" scenario, the annual salinity load is just 11 percent of the value calculated in the CHIA. This result stems primarily from the discontinuous nature of the pond dischazges. While dischazge rates from the ponds aze commonly above 2,000 gpm, the dischazges occur roughly one quarter of the time. The TDS concentration was assumed to be equivalent to that of the 14HG Fault water. This is extremely conservative for an annual calculation when considering that imported water, with a much lower TDS concentration, comprises a major component of the dischazge volume. `.J 2.05-238 Revised June 2005 PRl0; Rev. MarcH 1006; Rev. May 1006 PR/0