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Questions to answer

Questions to answer. What is the overall modeling approach (after calibration and background scenarios)? What are the WLA assumptions? How will Avista’s requirement be determined? Misc. considerations (policy) How TMDL WLA’s are translated into permits Others?.

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Questions to answer

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  1. Questions to answer • What is the overall modeling approach (after calibration and background scenarios)? • What are the WLA assumptions? • How will Avista’s requirement be determined? • Misc. considerations (policy) • How TMDL WLA’s are translated into permits • Others?

  2. Overall Approach: Step 0 (Scenario #1) • Establish riverine assessment point nutrient criteria • 2001 flows 10 ug / L Phosphorus Riverine Target

  3. Overall Approach: Step 1 • (Scenario #1) • Set tributary phosphorus for nonpoint source reductions. • Hangman: 30% (Apr.-May); 35% (Jun.-Oct.) • Little Spokane: 35% (Apr.-May); 38% (Jun.-Oct.) • Coulee Cr.: Same as Hangman 10 ug / L Phosphorus Riverine Target LSR CC HC

  4. Overall Approach: Step 2 • (Scenario #1) • Set point source TP to Flat 50 ug/L • March to October • Monthly average permit limit • Scenario #2: Lower Level of Treatment= <50 ppb for WA • Scenario #3: Account for reuse at HARSB and PF (variable TP) 10 ug / L Phosphorus Riverine Target TP = Flat 50 ug/L

  5. Overall Approach: Step 3 • (Scenario #1) • Set point source CBOD and Ammonia values • CBOD = 5 mg/L • See handout for ammonia values 10 ug / L Phosphorus Riverine Target TP = Flat 50 ug/L CBOD = 5 mg/L Ammonia = variable

  6. Overall Approach: Step 4 • (Scenario #1) • Run model to determine if riverine target is met. • TP = 30 day rolling average • DO = daily minimum • Ammonia = daily max 10 ug/L phosphorus Riverine target Run Model TP = Flat 50 ug/L CBOD = 5 ppm Ammonia = Variable

  7. Overall Approach: Step 5 • (Scenario #1) • If target is met, run model through reservoir to analyze dissolved oxygen • DO processed into volume-weighted average for each 2 week period (>8 m depth) • Segment 157 (LL5) to 188 (LL0) analyzed Run Model 10 ug/L phosphorus Riverine target TP = Flat 50 ug/L CBOD = 5 ppm Ammonia = Variable

  8. NO SOURCE scenario in model environment Model Segment

  9. Compare NO SOURCE with TMDL scenarios, compare volume weighted average of vertical cells over 2 week periods Volume weighted average across profiles

  10. Additional considerations • Foundational Concepts delta management will be retained to achieve WLA’s • Can be addressed during implementation: • Off season P limits • Effects of stormwater • Effects of high flows from Hangman Creek • Bioavailability of phosphorus • Nonpoint source impacts to river mainstem • Avista water quality attainment plan • SOD in Lake Spokane • Etc.

  11. Average = 467.5

  12. Monthly Average (95th %tile) = 1,072 Average = 467.5

  13. Daily Maximum (99th %tile) = 1,502 Monthly Average (95th %tile) = 1,072 Average = 467.5

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