Evaluation of Proposed New Point Source Discharges to a Special Resource Water and Mixing Zone Determinations: Thompson Creek Mine facility, Upper Salmon River Subbasin, Idaho Idaho Department of Environmental Quality December 2000 EVALUATION OF PROPOSED NEW POINT SOURCE DISCHARGES TO A SPECIAL RESOURCE WATER AND MIXING ZONE DETERMINATIONS: THOMPSON CREEK MINE, UPPER SALMON RIVER SUBBASIN, IDAHO NPDES PERMIT APPLICATION ID-002540-2 Prepared by: Christopher Mebane Idaho Division of Environmental Quality Contents SUMMARY ..........................................................................................................................................................1 Existing and Proposed Discharges ................................................................................................................2 Regulatory Classification and Status of Receiving Waters.............................................................................3 Critical habitats for threatened or endangered fish species and mixing zone determinations....................................... 3 NEW DISCHARGES TO SPECIAL RESOURCE WATERS...............................................................................................8 Introduction ..................................................................................................................................................8 Precedence for measures to protect Special Resource Waters..................................................................................... 8 Relationship of Policies on Antidegradation and Special Resource Waters............................................................ 8 Specific recommendations to protect Special Resource Waters......................................................................9 a. Working Definitions for Special Resource Waters Protections............................................................................... 9 Rationale for Special Resource Waters Requirements..................................................................................11 a. Analytical variability and precision of chemical analyses near detection limits.................................................... 11 b. Sampling and natural variability in upstream concentrations............................................................................... 12 c. Significance of pollutants to beneficial uses........................................................................................................ 12 Aquatic Life Beneficial Uses.............................................................................................................................. 12 Total suspended solids ....................................................................................................................................... 13 pH ..................................................................................................................................................................... 13 Metals ............................................................................................................................................................... 13 d. Ambient Monitoring Data Needs........................................................................................................................ 15 Biological Monitoring........................................................................................................................................ 15 Chemical monitoring.......................................................................................................................................... 15 Statistical considerations in ambient monitoring................................................................................................. 15 Sample Size Determination (Power Analysis) and Testing for Differences..........................................................16 MIXING ZONE ANALYSIS ...................................................................................................................................18 Introduction ................................................................................................................................................18 Mixing Zone Analysis Methods....................................................................................................................19 Chemical Evaluation...................................................................................................................................19 Water hardness values............................................................................................................................................. 21 Biological Evaluation..................................................................................................................................25 a. Macroinvertebrate Community Analyses............................................................................................................. 25 b. Thompson and Squaw Creek conditions ............................................................................................................. 26 c. Fish Populations................................................................................................................................................. 29 d. Toxicity Testing.................................................................................................................................................. 36 i Significance of whole effluent toxicity results to beneficial uses ......................................................................... 36 Review of the accuracy of whole effluent toxicity testing for predicting instream effects ..................................... 37 e. Comparison of toxicity literature on sensitive species to existing and predicted chemical discharges................... 41 f. Potential for bioaccumulative effects from mercury and selenium in the mixing zone.......................................... 44 Mercury............................................................................................................................................................. 46 Mercury in Sediments ................................................................................................................................... 47 Selenium............................................................................................................................................................ 51 Recent lentic-lotic and water-sediment selenium exposure pathway controversy ............................................ 54 Potential wildlife exposure to bioaccumulative substances in mixing zones ........................................................ 60 g. Zone of passage for migratory fish through the mixing zone................................................................................ 61 Concentrations of Metals Shown to Cause Avoidance......................................................................................... 62 Arsenic ......................................................................................................................................................... 62 Cadmium...................................................................................................................................................... 62 Chromium..................................................................................................................................................... 63 Copper.......................................................................................................................................................... 63 Lead ............................................................................................................................................................. 63 Mercury........................................................................................................................................................ 63 Nickel........................................................................................................................................................... 63 Selenium....................................................................................................................................................... 64 Silver............................................................................................................................................................ 64 Zinc.............................................................................................................................................................. 66 Comparisons of fish avoidance response to chemicals in lab and field conditions................................................ 66 Zone of Passage Thresholds Conclusions............................................................................................................ 70 Other views on avoidance thresholds.................................................................................................................. 72 Necessary width for migratory stream fish passage ............................................................................................. 73 Physical Evaluation ....................................................................................................................................75 Biological significance of physical features of the mixing zones..............................................................................