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Re-evaluation of the Mid-Snake/Upper Snake Rock Subbasin TMDL: Data - - PowerPoint PPT Presentation
Re-evaluation of the Mid-Snake/Upper Snake Rock Subbasin TMDL: Data - - PowerPoint PPT Presentation
Re-evaluation of the Mid-Snake/Upper Snake Rock Subbasin TMDL: Data Summary, Evaluation, and Assessment Mid-Snake Watershed Advisory Group Meeting September 17, 2014 TMDL Data Assessment Discussion Overview Background 2013 Report --
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Mid-Snake TMDL
Activity to Date
Initial TMDL in 1997, followed by …
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1997 ► Initial Phosphorus TMDL
Placeholder for aquaculture facilities Established TP & nuisance algal growth targets
2000 ► Phosphorus and Total Suspended Solids (TSS) TMDL
WLAs established for municipalities Industry-wide WLA established for aquaculture (970.2 pounds /day) Assessed low flow, high flow, & baseline years
Mid-Snake TMDL
Activity to Date
Defined six TMDL study segments WLAs set for municipalities
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Activity to Date
Mid-Snake TMDL
Past decade flows substantially lower than TMDL assumptions TMDL did not employ a low flow assumption
2010 ► DEQ Five-year Data Review
Discussion of water quality trading
2014 ► Current Issues
WLA revision for Jerome Cheese, City of Jerome TSS & E. coli targets achieved. TP targets not met. Aquaculture general permit expired in 2012
2005 ► Phosphorus and TSS TMDL Modification
WLAs established for aquaculture facilities WLAs set for municipalities Population & economic growth in the area
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Scope of Current Task
Integrated analysis of available data
Total phosphorus conditions
- Concentrations relative to
0.075 mg/L target
- Loading patterns
(sources, in-stream response)
- Attenuation & uncertainty
Role of hydrology
- Flow conditions over past decade
- Comparison to TMDL assumptions
Data Assessment
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Mid-Snake TMDL
WHY the Concern
Excessive Algal Growth
! ! ! ! ! ! ! ! ! ! ! ! ! !
Twin Falls Lincoln Cassia Owyhee Elmore Gooding Jerome Blaine Camas Min
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Eden Buhl Filer Bliss Hansen Jerome Wendell Murtaugh Kimberly Hazelton Hagerman Hollister Twin Falls King Hill Snake River (Middle) Upper Snake Rock Subbasin (HUC 17040212)
NAD_1983_StatePlane_Idaho_Central_FIPS_1102_Feet Map produced 01-09-2012 - C. Carter±
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Legend
! City Upper Snake-Rock Subbasin Major Road River/Stream Water County Boundary
10 20 5 Miles 10 20 5 Kilometers§ ¨ ¦
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Mid-Snake TMDL
Parameter Target 2001-2010 Average Total Suspended Solids (mg/L) 52
1
22.6
3,4
Total Phosphorus (mg/L) 0.075
2
0.091
3
Notes:
1 Monthly average (Daily maximum: 80 mg/L) 2 0.1 mg/L for tributaries 3 Gridley Bridge monitoring site 4 Maximum monthly average (June)
First TMDL established: March 1997
(EPA approval: April 1997)
WHAT are the Targets
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Comments and Additional Data
2013 Report
Idaho Power Twin Falls Canal Northside Canal Clear Springs Food University of Idaho Watershed Advisory Group
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Adaptive Management
Mid-Snake TMDL
Data Driven Approach
! H ! H ! H ! H ! H
# * # * # * # * # * # * # *
Twin Falls Lincoln Cassia Owyhee Elmore Gooding Jerome Blaine Camas Minidoka Box Canyon (SR05) Milner pool (SR08) Pillar Falls (SR07) Buhl (13094000) Gridley Bridge (SR04) Crystal Springs (SR06) King Hill Bridge (SR01) Shoestring Bridge (SR03) Kimberly (13090000) King Hill (13154500) Milner Dam (13088000)
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Snake River (Middle) Upper Snake Rock Subbasin (HUC 17040212)
NAD_1983_StatePlane_Idaho_Central_FIPS_1102_Feet Map produced 05-06-2013 - C. Carter±
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Legend
Upper Snake Rock Subbasin Major Road River/Stream Water County Boundary Monitoring Station
# * IDEQ
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USGS Study Segments Milner Dam to Pillar Falls Pillar Falls to Crystal Springs Crystal Springs to Box Canyon Box Canyon to Gridley Bridge Gridley Bridge to Shoestring Bridge Shoestring Bridge to King Hill Bridge
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Lower Salmon Falls (13135000)
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Stakeholder sampling DEQ & USGS monitoring
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Declining Trends
Data Driven Approach
Total Suspended Solids
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Declining Trends
Data Driven Approach
Total Phosphorus
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Role of Hydrology
Data Driven Approach
Flow Patterns
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Seasonal Patterns
Role of Hydrology
Critical Conditions
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Effect on Water Quality
Role of Hydrology
Seasonal Patterns
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Year-to-Year Variation
Role of Hydrology
Shift over Past Decade
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Attenuation
Data Assessment
Permanent Removal – e.g., deep burial or chemical change Temporary Retention – e.g., plant uptake Dilution
Defining what we mean by “Attenuation” TMDL assumptions can directly affect loading capacity and allocations
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Attenuation
Data Assessment
2005 TMDL assumed removal occurs 2014 Assessment
Retained nutrient load is likely re-suspended and transported downstream during high flow events Plant uptake and die-off is likely resulting in temporary retention of phosphorus in aquatic plant bed sediments
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Key Questions
Mass Balance
Examine loading changes between segments
What are areas of uncertainty? What are the data gaps? What is the relative magnitude of source inputs?
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Draft Report Approach (2013)
Mass Balance
Assumed no attenuation
Gaged tributaries Irrigation return drains Gaged springs (discrete GW) Baseflow (diffuse GW) Point sources (direct & indirect)
Baseflow contributions did not account for potential year-to-year variability Source Load Estimates
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Total Phosphorus
Trend Analysis
Revised Approach
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Total Phosphorus
Trend Analysis
LOWESS Analysis
Compared to critical probability value to determine significance Data smoothing to account for seasonal and flow variability
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Mass Balance and Loads
LOADEST Analysis
LOADEST Analysis
LOAD estimation based on statistical analysis of flow and concentration data
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Flow-weighted Concentrations
Declining TP trends
LOADEST Analysis
Monthly and annual average values based on flow weighting Daily concentrations calculated from load estimates
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LOADEST Analysis
Flow-weighted Concentrations
Buhl concentrations remain highest Declining trend in TP at all stations
LOADEST Analysis
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General Observations
Buhl Trends
Largest allocations above Buhl
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Twin Falls POTW
Buhl Trends
Effect of existing discharge
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Nutrient Cycling
Macrophytes
Plays an important role
Relationship between bed sediments, macrophytes, and non-rooted algae critical
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Key Findings
Data Assessment
Concentrations remain highest at Buhl
Declining TP concentration trends (all stations)
Flow basis of current TMDL exceeds average and current flow conditions
Declining trends in river flow
Twin Falls POTW Reduced assimilative capacity
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Key Findings
Data Assessment
however Point sources generally in compliance with WLAs Significant macrophyte growth continues
Likely minimal long-term nutrient attenuation Numerous factors likely affect their growth
- Nutrients (phosphorus and nitrogen)
- Substrate (sediment)
- Flow
Quantitative data on macrophyte levels is lacking Both water column and sediment are nutrient sources Intense local nutrient cycling
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Next Steps
Mid-Snake TMDL
Implementation Discussion
Further evaluation of NPS controls where data indicate tributaries / drains not meeting 0.100 mg/L target Address data gaps for tributaries / drains
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Next Steps
Mid-Snake TMDL
Implementation Discussion
Quantitative analysis of macrophyte levels Investigation of other factors controlling macrophytes (flow shaping, nitrogen, etc) Data collection of periphyton / chlorophyll-a may aid in determining what is happening in the system
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