2020-06-08_REVISION - C1982057 (20)

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6/30/2023 (see CDOH Regulation 33).The temporary modification includes a chronic total recoverable iron standard of 1.11 mg/L for May— February and a standard of 3.04 mg/L for March—April. Although the Water Quality Control Division acknowledges that this modification is in place they have been unable to incorporate it into permit CO-0000221 while the permit is under Administrative Extension. The total recoverable iron measured at Outfall 005 in April 2016 was within the temporarily modified Yampa Segment 13d chronic water quality standard.There were no other exceedances of the NPDES limits at these six outfalls during the last five years. All NPDES samples met the CDPHE Yampa Segment 13d and 13e instream standards except for a single manganese result at Outfall 006. The manganese sample, collected on 1/2/2018, was analyzed for the potentially dissolved fraction rather than the dissolved fraction, which is the fraction the surface water quality standards are based on.This is an important distinction because the potentially dissolved analysis 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 before its filtered.This promotes artificial leaching of metals from sediment and organics present in the sample prior to filtration, something that would not occur in the alkaline surface waters of this region. No other samples exceeded any of the Yampa Segment 13d or 13e water quality standards. See the Seneca II-W Annual Hydrology Reports from 2015 through 2019 (2019 to be submitted in 2020)for additional discussion of the frequency of discharge. D.) Clean Water Act Effluent Limitations(40CFR Part 434) Monitoring data from the past five years indicate the mine has not caused exceedances of the 40 CFR Part 434 settleable solids and pH limits that are applicable to reclamation areas on coal mines (settleable solids limit: 0.5 ml/l; pH limit: 6.0 -9.0 S.U.). See the Seneca II-W Annual Hydrology Reports from 2015 through 2019 (2019 to be submitted in 2020)for additional discussion of the frequency of discharge and analytical data. Note that the results of the monthly settleable solids analysis for these outfalls are documented in the SCC field notebook and only values that are at or above the detection limit (0.4 ml/1) are entered in to the water quality database.The absence of those values in the Tables within the Annual Hydrology Reports indicates that no samples were measured at or above the detection limit. E.) Impacts to Alluvial Valley Floors(AVFs) No lands satisfying the geomorphic and flood or subirrigation criteria for an Alluvial Valley Floor were located within the Seneca II-W mining permit boundary. Two AVF areas were identified downstream of Seneca II-W mining operation. A flood irrigated field located within the Dry Creek drainage in Section 16 and 21,TSN, R88W and a flood irrigated field within the Sage Creek drainage in Section 30,T6N, R87W.Two subirrigated fields in Section 9,TSN, R88W of the Dry Creek drainage were originally identified as AVF's however subsequent assessments of these fields in 2005 by ESCO Associates (Dr. David L. Buckner) determined that these parcels do not meet the AVF criteria. A more detailed discussion of these findings can be found in Tab 17 Probable Hydrologic Consequence section of the mine permit.