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Minrec, Incorporated Water Quality Assessment CO- 0048233 Data collected at the Divison Station 133 (Thompson Creek @ Hwy 133), located approximately 6 miles downstream from the Minrec facility, were determined to be representative of fully mixed condition downstream from the facility, and thus this data was used to determine the BWQ concentrations. Since the data was collected downstream of the discharge, it takes into account the contribution of the facility. Currently, it is the Division's approach to evaluate five years of ambient water quality data, if available, for the five years prior to September 30, 2000 when determining the BWQ. However, data from this location was only available for a period of record of August 2006 through April 2007 for dissolved manganese and dissolved zinc and March 2001 through August 2006 for total and dissolved arsenic. Although these data were not collected during the five years prior to September 2000, the Division has determined that, absent data available during the AD period, the available data are considered representative of the BWQ during the AD period. The BWQ concentrations based on these data, represented by the 50'h percentile for total recoverable metals and total metals and the 85h percentile for dissolved metals and other pollutants, are summarized in Table A -6. There was no water quality data for trivalent chromium, boron, and sulfide. Note that the AD requirements outlined in The Basic Standards and Methodologies for Surface Water specify that chronic numeric standards should be used in the antidegradation review; however, where there is only an acute standard, the acute standard should be used. Chronic standards were available for all pollutants except total recoverable arsenic and total recoverable trivalent chromium. Bioaccumulative Significance Test For mercury, which is a bioaccumulative toxic pollutant, the bioaccumulative significance test can now be completed with some minor additional calculations for the baseline water quality load (BWQload), the threshold load (TL), the new load based on the WQBELs, and the threshold load concentration (TL conc). These terms are defined by the following equations: BWQload = BWQ (from Table A -6) * AD low flow (chronic) * 8.34 Threshold Load (TL) = 0.1 * BWQload Threshold Load Concentration (TL Conc) = TL - new design flow - 8.34 WQBEL Load = new WQBEL (concentration) * new design flow * 8.34 The discharge is considered to be insignificant if the new load (WQBEL load) is less than the threshold load (TL), or if the new WQBEL (concentration) is less than the TL Conc. The results of the calculations and the comparisons are shown in Table A -11. Table A -11 Bioaccumulative Significance Test Parameter Threshold Load Threshold Load WQBEL Cone WQBEL Load Concentration (TL Cone) (TL) Mercury, Total 0 0 0.032 0.002 Appendix A (WQa v 7.0) Page 20 of 25 Last Revised Sept 14, 2009 /ES