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recoverable iron measured at Outfall 005 in April 2016 was within the temporarily modified Yampa <br /> Segment 13d chronic water quality standard. There were no other exceedances of the NPDES limits at <br /> these six outfalls during the last five years. <br /> All NPDES samples met the CDPHE Yampa Segment 13d and 13e instream standards except for a single <br /> manganese result at Outfall 006. The manganese sample, collected on 1/2/2018, was analyzed for the <br /> potentially dissolved fraction rather than the dissolved fraction, which is the fraction the surface water <br /> quality standards are based on. This is an important distinction because the potentially dissolved analysis <br /> is run after the sample is treated with nitric acid to a pH less than 2.0 and left to stand for 8 to 96 hours <br /> before its filtered. This promotes artificial leaching of metals from sediment and organics present in the <br /> sample prior to filtration, something that would not occur in the alkaline surface waters of this region. No <br /> other samples exceeded any of the Yampa Segment 13d or 13e water quality standards. See the Seneca <br /> 11-W Annual Hydrology Reports from 2015 through 2019 (2019 to be submitted in 2020) for additional <br /> discussion of the frequency of discharge. <br /> D. Clean Water Act Effluent Limitations(40CFR Part 434) <br /> Monitoring data from the past five years indicate the mine has not caused exceedances of the 40 CFR Part <br /> 434 settleable solids and pH limits that are applicable to reclamation areas on coal mines (settleable solids <br /> limit: 0.5 ml/1; pH limit: 6.0 - 9.0 S.U.). See the Seneca II-W Annual Hydrology Reports from 2015 <br /> through 2019 (2019 to be submitted in 2020) for additional discussion of the frequency of discharge and <br /> analytical data. Note that the results of the monthly settleable solids analysis for these outfalls are <br /> documented in the SCC field notebook and only values that are at or above the detection limit(0.4 ml/1) <br /> are entered in to the water quality database. The absence of those values in the Tables within the Annual <br /> Hydrology Reports indicates that no samples were measured at or above the detection limit. <br /> E. Impacts to Alluvial Valley Floors(AVFs) <br /> No lands satisfying the geomorphic and flood or subirrigation criteria for an Alluvial Valley Floor were <br /> located within the Seneca 11-W mining permit boundary. <br /> Two AVF areas were identified downstream of Seneca 11-W mining operation. A flood irrigated field <br /> located within the Dry Creek drainage in Section 16 and 21, TSN,R88W and a flood irrigated field within <br /> the Sage Creek drainage in Section 30, T6N, R87W. Two subirrigated fields in Section 9, TSN, R88W of <br /> the Dry Creek drainage were originally identified as AVF's however subsequent assessments of these <br /> fields in 2005 by ESCO Associates (Dr. David L. Buckner) determined that these parcels do not meet the <br /> AVF criteria. A more detailed discussion of these findings can be found in Tab 17 Probable Hydrologic <br /> Consequence section of the mine permit. <br /> Impacts to the Alluvial Valley Floors were addressed in the Probable Hydrologic Consequences section of <br /> the mine permit (Tab 17). Projected TDS concentrations in the receiving streams were estimated from <br /> geochemical models that evaluated potential salt loads from spoil/groundwater interactions. This <br /> information was then used to evaluate the potential impacts to the AVF crops. The impact analysis <br /> projected a 270%(1088 mg/L)increase in TDS within Hubberson Gulch near WSH7(SW-S2W-SG7)and <br /> a 95%increase(1303 mg/L)within Dry Creek near WSD5 (SW-S2W-SG5). These increases equated to a <br /> 20 <br />