2020-12-09_REVISION - C1994082 (11)

Home Browse Search

Suspended Solids Demonstration In addition to the pond effluent sample data submitted by SPL,the operator submitted sediment level data (pond capacity)in the Annual Reclamation Report(ARR), submittal (Illustration I, labeled Table 13-3 in SPL's 2019 ARR), for the ponds receiving run off from the proposed release area. The data show, as per the illustration below and monthly DRMS inspections that the ponds possess ample water capacity and that sediment levels in the ponds have stabilized since revegetation activities began in 2006. None of the ponds have required cleaning since Pond 10 was dredged in 2002 and Pond 11 in 2003. TABLE 13.3 SENECA SEDIMENT PONDS-WATER CAPACITY TRENDS Requ'rej TrCumn Decision d ID Capacity'(11 t Remaining Water Capacity2(ac- Reference 6, 'I YEAR 1 2008 2009 1 2010 2011 2012 2013 2014 2015 Y-010* 3.08 7.6 7.6 7.8 8 8 7.7 9.2 9.2 TR-37 Y-011 0.99 3.6 3.6 3.6 3.6 3.6 3.7 3.6 3.6 TR-37 Y-011A 0.633 NA NA NA NA NA NA NA NA TR-37 Y-012* 0.767 0.7 0.7 L I 0.83 1.2 1.3 1.3 1.3 TR-37 Y-012A 6.3 6.3 6.1 5.6 5 4.6 4.4 4.4 Y-013 1.325 4.5 4.4 4.5 4.4 4.3 4.5 4.5 4.5 TR-37 Y-014 1.6 10.5 7.5 7.6 7.5 7.5 7.5 7 7 TR-37 (*) Required every Syrs-next survey 2020 (1) Based on SEDCAD results for a 10yr/24hr storm event. (2) Remaining capacity below principal spillway or orfce. (3) TK 37,page 13-4A.1 A9(stock pond) Illustration 1: Pond Capacity from SPL's 2019 ARR The operator submitted pond discharge sample data for all of the ponds receiving discharge from the proposed release area, as well as receiving stream sample data for the Grassy Creek(YSGF5,YSG5), and Sage Creek(YSSF3 and YSS2) stream points in Attachment G of this application. Pre mine and post mine TSS (total suspended solids), are compared in Table 5 of Attachment G. Analytical results from monitoring points upstream and downstream of the 5 NPDES outfalls comprise Tables 6 through 10 of Attachment G. The pond outfall data indicate that total suspended solids(TSS) contributions do not exceed the limits set forth by the Colorado Department of Public Health and Environment. Monitoring data of the upstream and downstream receiving stream sites indicate that TSS is reduced from the upstream site at the downstream site, and TSS at outfalls 12, 13 and 14 are below pre mine average. Further comparison of pre mine and post mine NPDES TSS concentrations are available in revised the pages of the SL8 application dated 24 November 2020. This updated information was requested as part of DRMS's adequacy questions of August 2020. The sediment ponds receiving runoff from the proposed release area comprise Ponds 12, 12A, 13, and 14 and the operator demonstrated that the quantity and quality of impounded water is appropriate for their intended use. Permit Number C1994 082 Page 13 of 15