2014-06-04_REVISION - C1980005 - Laserfiche WebLink

Home Browse Search

Seneca 11 Mine SL -6 Phase 111 Bond Release Request June 2014 soils. In alkaline soils, as are found in the Seneca II Mine region, a more appropriate (EPA, 1976) standard would be 10 mg /1. The CDPS and CDRMS sample data from the Seneca II Mine, 2011 through 2013, support a finding that the mine is not causing exceedances of the instream standards as measured at the downstream site on lower Bond Creek (SSB12) or at the lower Fish Creek stream site (SSF13). Selenium receiving stream excursions noted above at Outfall 008 are not CPDS permit limit excursions, and the receiving stream, Fish Creek, is in compliance with the receiving stream standard. The CDPHE uses the 85`h percentile of dissolved selenium values over the past five years to determine stream attainment of the selenium standard. At Fish Creek Site SSF13, the sample data value is 0.5 ug /1, which is well below the standard of 4.6 ug /1. Lower Bond Creek Site SSB12, as well as Outfall 008, are also in compliance of the stream standard using the five year, 85h percentile, with values of 2.40 and 3.91 ug /1, respectively. Seneca used PD selenium values in these calculations, as dissolved values were typically not measured. Permit Requirements of the Colorado Discharge Permit System (CDPS) The Seneca II Mine maintains one outfall, Pond 008 (NPDES8) that is monitored under the CPDS Permit No. CO- 0000221. Parameters monitored are provided in Table 4 for that outfall. Sample analysis has included testing for Whole Effluent Toxicity. Sample data has been reported quarterly in discharge monitoring reports (DMRs) filed with the CDPHE and the CDRMS. These DMRs indicate that no exceedances of permit limits (as discussed in the previous section) have occurred in the past three years (2011 — 2013). Clean WaterAct E (tent Limitations (40 CFR Part 434) Monitoring data for the past three years provided in Table 4 indicates the mine has not caused exceedances of either limitation identified in 40 CFR Part 434 that is applicable to reclamation areas on coal mines (settleable solids (STS) of 0.5 ml /1 and pH of 6.0 to 9.0). Seneca records STS values that it measures monthly for Outfall 008 (NPDES8) in its field notebook. Only values that are at or above the detection limit, 0.4 ml /1, are entered in to Seneca's water quality database. The absence of those values on Table 4 for NPDES8 indicates that no samples were measured at or above the detection limit.