Procedures to Implement the Texas Surface Water Quality Standards Prepared by Water Quality Division RG-194 June 2010 1 Contents Introduction................................................................................................. 12 Determining Water Quality Uses and Criteria........................................ 14 Classified Waters .......................................................................................................... 14 Unclassified Waters ...................................................................................................... 14 Presumed Aquatic Life Uses......................................................................................... 14 Assigned Aquatic Life Uses...................................................................................... 16 Evaluating Impacts on Water Quality...................................................... 20 General Information...................................................................................................... 20 Minimum and Seasonal Criteria for Dissolved Oxygen............................................... 21 Federally Endangered and Threatened Species ............................................................ 21 Screening Process ..................................................................................................... 22 Additional Permit Limits .......................................................................................... 22 Edwards Aquifer ....................................................................................................... 23 Bacteria ......................................................................................................................... 24 Recreational Uses and Criteria.................................................................................. 24 Assigning Recreational Uses .................................................................................... 25 Wastewater Permitting.............................................................................................. 26 Nutrients........................................................................................................................ 26 Introduction............................................................................................................... 26 General Screening Approach for Nutrient Impacts .................................................. 26 Nutrient Screening for Main Pool Effects in Reservoirs with Numerical Nutrient Criteria ...................................................................................................................... 30 Nutrient Screening for Local Effects in Reservoirs.................................................. 38 Nutrient Screening for Streams and Rivers .............................................................. 47 Nutrient Screening for Estuaries............................................................................... 53 Other Applicable Rules................................................................................................. 53 Antidegradation .......................................................................................... 55 Policy ............................................................................................................................ 55 General Applicability.................................................................................................... 55 Tier 1—Protecting Uses................................................................................................ 56 Protecting Impaired Waters under Tier 1...................................................................... 57 Definitions................................................................................................................. 57 General Provisions.................................................................................................... 58 Applicability to Specific Parameters ........................................................................ 58 Procedures for Discharges to Listed Water Bodies .................................................. 59 Applicability of Pollution Reduction Programs........................................................ 60 Examples of Permitting to Listed Water Bodies....................................................... 60 2 Tier 2—Protecting High-Quality Waters...................................................................... 61 Applicability ............................................................................................................. 61 Evaluating the Potential for Degradation of Water Quality...................................... 63 Examples Where Degradation Is Unlikely to Occur................................................. 65 Examples Where Degradation Is Likely to Occur .................................................... 66 Evaluation of Alternatives and Economic Justification............................................ 66 Agency Review of Degradation................................................................................ 67 Tier 3—Outstanding National Resource Waters .......................................................... 67 Watershed Protection Rules.......................................................................................... 68 Public Notice................................................................................................................. 69 Mixing Zones and Critical Conditions...................................................... 70 General Information...................................................................................................... 70 Mixing Zones and ZIDs for Aquatic Life Protection.................................................... 70 Critical Conditions for Aquatic Life Protection............................................................ 72 Determining the 7Q2..................................................................................................... 75 Determining Critical Low-Flows for Streams and Rivers that are Dominated by Springflow..................................................................................................................... 77 Mixing Zones and Critical Conditions for Human Health Protection .......................... 78 Determining the Harmonic Mean Flow ........................................................................ 80 Diffusers........................................................................................................................ 82 Modeling Dissolved Oxygen....................................................................... 83 General Information...................................................................................................... 83 Model Selection and Inputs .......................................................................................... 83 Screening Level Methods ............................................................................................. 84 Nontidal Streams and Rivers .................................................................................... 84 Tidal Water Bodies, Ponds, and Lakes ..................................................................... 87 Critical Low-Flow Values for East and South Texas Streams ..................................... 88 Regression Equation Relating Dissolved Oxygen, Flow, and Bedslope .................. 91 Calculating Bedslope ................................................................................................ 92 Guidelines for Adjusting the Regression Equation................................................... 92 Regression Equation for Establishing Critical Low-Flows in Specific Water Bodies in the Cypress Creek Basin....................................................................................... 93 Water Bodies with a Dissolved Oxygen Impairment ................................................... 94 Whole Effluent Toxicity Testing (Biomonitoring)................................. 102 Applicability ............................................................................................................... 102 Chronic and 48-Hour Acute Tests .............................................................................. 104 Test Types............................................................................................................... 104 Test Acceptability Criteria...................................................................................... 105 Statistical Interpretation of Test Results................................................................. 107 Test Frequencies ..................................................................................................... 108 Dilution Series, Dilution Water, and Type of WET Test ....................................... 110 Reasonable Potential Determination....................................................................... 113 3 Toxicity Reduction Evaluations (TREs)................................................................. 115 24-Hour Acute (100% End-of-Pipe) Tests ................................................................. 118 Test Types............................................................................................................... 118 Test Acceptability Criterion.................................................................................... 119 Test Frequencies ....................................................................................................