Lake of the Woods TMDL: Update and Next Steps November 21, 2017
Outline Where we ve been (2016) HSPF Bathtub Internal loading estimation Progress in 2017 Development of TMDL load allocation table Next steps
Watershed Model, Lake Model, Internal Loading REFRESHER
Watershed Model: HSPF (Hydrological Simulation Program Fortran) 9 Linked HSPF models 70,000 km 2 >615 HUC12s >30,000 Waterbodies Completed in September 2016
Lake Model: Bathtub Input based on HSPF quantity and water quality for each tributary and lakeshed Improved internal loading estimate Calibrated to monitoring data
Internal Loading: Past Work Bill James (2012) Dissolved oxygen-mediated sediment P release Aerobic release: 0.2 to 0.6 mg P m -2 d -1 91 to 272 tons/yr from Big Traverse Anaerobic release: 8.3 to 12.5 mg P m -2 d -1 Bill James (2015) Aerobic release: 0.12 mg P m -2 d -1 53 tons/yr from Big Traverse (based on monthly bottom water temp.) Anaerobic release: 7.3 mg P m -2 d -1 (assumed T = 17 ⁰C) 9 tons/d from Big Traverse Sediment P release is very sensitive to anoxia
Internal Loading: Past Work Science Museum of Minnesota Observed Bottom Dissolved Oxygen Concentration (mg/l) Dissolved oxygen measurements 50cm above lake bottom Depletion (0.4 to 0.5 mg L -1 d -1 ) during calm periods No anoxia observed Unknown if/how often anoxic conditions occur 12 10 8 6 4 2 Bottom Dissolved Oxyen Concentration, 2015 0 6/21/2015 6/26/2015 7/1/2015 7/6/2015 7/11/2015 7/16/2015 7/21/2015 7/26/2015 7/31/2015 MPCA Muskeg Big Traverse
RESPEC s TP Mass Balance Approach Δ Σ Σ Unexplained residual internal loading : Net of TP release, resuspension, and settling Approach to determine long-term mean annual water and TP budgets Corresponds to Bathtub: mean annual Q and loading
Water & TP Mass Balance Approach Data Water Balance TP Balance Volume/surface area by bay X HSPF tributary and lakeshed runoff/loading X X Precipitation X X Atmospheric deposition X Evaporation X Observed in-lake TP concentrations by month X Outflow at Kenora X X
Entire Lake Water Balance 4,000 Lake of the Woods Overall Monthly Water Balance Summary 3,000 Monthly Inflow/Discharge (hm 3 ) 2,000 1,000 0 1,000 2,000 3,000 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Total Inflow Total Outflow Change in Volume
Entire Lake TP Budget 140,000 Monthly TP Inflow and Outflow 120,000 100,000 TP Flux (kg) 80,000 60,000 40,000 20,000 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec TP Inflow TP Outflow
TP Mass Balance Pathway Mean Annual TP Load (t) Atmospheric deposition 69 Tributary inflow (includes lakeshed & PS loading) 440 SSTS (septic) direct to lake 0.6 Bank erosion 72 Total external load 582 Internal loading??? Outflow at Kenora 320
Monthly TP Budget 200,000 Entire Lake Monthly TP Budget Net P release 150,000 100,000 50,000 Monthly TP Flux (kg) - (50,000) (100,000) (150,000) (200,000) (250,000) (300,000) Net sedimentation May Jun Jul Aug Sep Oct Total Surface Inflow (kg) Total Outflow Net Inflow Unexplained Residual Observed Change in In-Lake TP
Internal Loading Summary Performed detailed hydrologic and nutrient mass balance with HSPF outputs Monthly mass balance compared to observed in-lake TP mass Mean annual internal loading: 282 tons
Draft TMDL Components and Load Allocation Table PROGRESS
2017 Progress Development of complete draft TMDL load allocation table Boundary conditions Wasteload Wastewater Industrial stormwater Construction stormwater Load Tributaries Lakeshed SSTS (septics) Shoreline erosion Atmospheric deposition Internal loading
Overview/Primer Overall in-lake P goal: 30 ppb P Overall current P loading (all sources):886.9 Overall P reduction required: 176.3 t/yr Only 2 reductions from Canada 1 Abitibi (reduction occurred after TMDL listing) 2 Lake of the Woods Internal loading (reduction prorated based on % area in Canada) All other reductions from United States
Existing Loads by Country Source Country Existing Load (t/y) Percent of Total Load Canada 326.5 37% USA 560.4 63% Total 886.9 - DRAFT MATERIALS 11/20/2017
Existing Loads by Source and Country Source Country Wasteload (t/y) Load (t/y) Total Load (t/y) Canada 44.7 281.8 326.5 USA 45.4 515.0 560.4 Total 90.1 796.8 886.9 DRAFT MATERIALS 11/20/2017
Reductions at a glance Source Existing Load (t/y) Proposed Load (t/y) Reduction (t/y) % Change Wasteload 90.1 33.1 56.9-63% Load 796.8 677.4 119.4-15% Total 886.9 710.5 176.3-20%
Existing vs. Proposed Loads (by source) Existing Loads by Source Proposed Loads by Source 33.1 90.1 796.8 677.4 Wasteload Load Wasteload Load DRAFT MATERIALS 11/20/2017
Existing Phosphorus Budget 10.1% Point Sources All Tributaries 31.8% Lakeshed Septic Systems 5.8% 0.1% 1.9% 8.1% 42.2% Shoreline Erosion Atmospheric deposition Internal load DRAFT MATERIALS 11/20/2017
Reductions by Sector 40% Internal load Wastewater 6% 33% Little Fork River Watershed Shoreline Erosion All other watershed sources Other Source Reductions Big Fork River WS 11% Rapid River WS 0% Lower Rainy WS 21% LOW HUC 8 65% Lakeshed 0% Septic Systems 3% Atmospheric Dep. 0% 7% 15% DRAFT MATERIALS 11/20/2017
Boundary Conditions
Boundary Conditions Lower Boundary Condition (Rainy River at 4 Mile Bay ) Upper Boundary Condition (Rainy River at International Falls)
DEVELOPING WASTE LOAD ALLOCATIONS DRAFT MATERIALS 11/20/2017
Wastewater Existing loads are from the calibrated HSPF model, which integrates monitoring data from US/Canadian sources Additional existing minor loads were supplied by MPCA Proposed loads US wasteloads supplied by MPCA Canadian sources set equal to existing loads Abitibi/Resolute (Fort Frances paper mill) is yet to be determined as it is expected to remain closed for the foreseeable future Existing load = 90.0 t/y; proposed load = 33.1 t/yr
Industrial Stormwater No reduction proposed Categorical wasteload allocation Excludes sites upstream of I-Falls/FF boundary condition Total area: 798 ha (1972 ac) Assumed annual loading of 1 kg/ha Assumed 100 percent delivery to Lake of the Woods Provides implicit margin of safety Total load = 798 kg/ha/y
Construction Stormwater No reduction proposed Categorical wasteload allocation Based on construction stormwater permits from eight counties in Basin Area from each county prorated based on portion in Basin Mean annual area 389 ha (962 ac) Assumed annual loading of 1 kg/ha Assumed 100 percent delivery to Lake of the Woods Provides implicit margin of safety Total load = 389 kg/ha/y
DEVELOPING LOAD ALLOCATIONS DRAFT MATERIALS 11/20/2017
Tributaries: Rainy River Analysis Analysis of HSPF data (2005-2014) Goals: Quantify loads by source Point sources Tributaries Local drainage to Rainy River Determine delivery ratios to estimate loading to Lake of the Woods
Rainy River Analysis Lower Boundary Condition (Rainy River at 4 Mile Bay ) Upper Boundary Condition (Rainy River at International Falls)
Rainy River Analysis Outcomes Produced TP/OP delivery ratios for: Rainy Lake outflow Point sources discharging directly to Rainy River Direct runoff to Rainy River Tributaries to the Rainy River (Big Fork, Pinewood, etc.) Point sources discharging to Rainy River tributaries Delivery ratios allow for full accounting of reductions at both the source and the lake For example, 26.1 t/y reduction at Little Fork River mouth Equivalent to 21.8 t/y reduction at 4-Mile Bay
Tributaries Reductions based on assumption of meeting water quality standards River eutrophication standard (TP 50 ppb) Reduction proposed for all tributaries with HSPF flowweighted mean TP concentration > 50 ppb
Tributaries: Reductions by HUC8 Existing Load Proposed Load Reduction % Watershed (t/y) (t/y) (t/y) Change Rainy Lake (US/CAN) 148.3 148.3 0.0 0% Little Fork River (US) 73.4 47.7 25.7-35% Big Fork River (US) 48.5 47.3 1.2-2% Rapid River (US) 20.9 20.9 0.0 0% Lower Rainy River (US/CAN) 142.6 82.6 60.0-42% Lake of the Woods (US/CAN) 453.2 363.7 89.5-20% Total 886.9 710.5 176.3-20%
Lakeshed Loading No reduction proposed Existing loading taken from HSPF Existing load = 17.1 t/y
SSTS (septics) Existing load from HSPF Existing load = 0.7 t/y Proposed reduction are based an assumption of 100% compliance from US septic systems Proposed load = 0.4 t/y Reduction = 0.3 t/y
Shoreline Erosion Existing load = 72 t/y Houston Engineering study (2013) Shoreline between Warroad River and 4-Mile Bay Proposed reduction = 16% based on replacement/maintenance of recent shoreline protection projects Proposed load = 60.5 t/y
Atmospheric Deposition No reduction proposed Existing load = 51.4 t/y
Internal Loading Existing load = 282 t/y Researchers at the Science Museum of Minnesota s Saint Croix Watershed Research Station have estimated the lake s internal loading is declining by 1 percent per year Proposed reduction = 25 % over 25 years Reduction = 70.5 t/y Proposed load = 211.5 t/y
Margin of Safety Total allowable load = 710.5 t/y Margin of safety = 33.5 t/y Based on robust data and calibrated models Several reductions include additional implicit margin of safety Construction and industrial wasteload allocations
Reserve Capacity Evaluating potential growth areas Evaluating potential for unsewered communities to connect to municipal wastewater systems Evaluating potential future discharge from Fort Frances paper mill site
Continue writing TMDL document Reasonable assurance Monitoring plan Implementation strategy WHAT S NEXT?
Thank you! Questions/Comments? Julie Blackburn: Julie.Blackburn@respec.com Geoff Kramer: Geoff.Kramer@respec.com DRAFT MATERIALS 11/20/2017