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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?

Questions to answer

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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?. - PowerPoint PPT Presentation

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Page 1: 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?

Page 2: Questions to answer

Overall Approach: Step 0 (Scenario #1)

Establish riverine assessment point nutrient criteria

• 2001 flows

10 ug / L PhosphorusRiverine Target

Page 3: Questions to answer

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 PhosphorusRiverine Target

HC

CC

LSR

Page 4: Questions to answer

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)

TP = Flat 50 ug/L

10 ug / L PhosphorusRiverine Target

Page 5: Questions to answer

Overall Approach: Step 3(Scenario #1)Set point source CBOD and Ammonia values

• CBOD = 5 mg/L• See handout for ammonia values

TP = Flat 50 ug/L

10 ug / L PhosphorusRiverine Target

CBOD = 5 mg/LAmmonia = variable

Page 6: Questions to answer

10 ug/L phosphorus Riverine target

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

TP = Flat 50 ug/LCBOD = 5 ppmAmmonia = Variable

Run Model

Page 7: Questions to answer

10 ug/L phosphorus Riverine target

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

TP = Flat 50 ug/LCBOD = 5 ppmAmmonia = Variable

Run Model

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NO SOURCE scenario in model environment

Model Segment

Page 10: Questions to answer

Compare NO SOURCE with TMDL scenarios, compare volume weighted average of vertical cells over 2 week periods

Volume weighted average across profiles

Page 11: Questions to answer

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.

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Average = 467.5

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Average = 467.5

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

Page 15: Questions to answer

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

Average = 467.5

Daily Maximum (99th %tile) = 1,502

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