1. An overview and critique of methods
Como Lake TMDL
An overview and critique of methods

2. Capital Region Watershed District
Formed in 1998 in response to a citizen initiative to protect Como Lake
Community continues to play an active role in watershed management

3. Como Lake Strategic Management Plan
Prior to 303d listing of Como Lake, CRWS undertook a study of the lake to develop a management plan.
The resulting management plan was completed in 2002 and formed the basis for the later TMDL.
Source: 2009
CRWS survey

4. Scope of 2002 Management Plan
Review and evaluate available watershed & water quality information
Prioritize management concerns
Identify management goals and objectives
Enumerate implementation activities
Evaluate citizen agency roles

5. Background on Como Lake
Area (acre)
Located in the north-central portion of the Capitol Regional Watershed District (CRWD)
Roughly 1783 acre watershed (not including the lake area)
Defined as a shallow lake by the MPCA.
Mostly used for recreation (fishing, boating and aesthetics)
City
Saint Paul
1205
Falcon Heights
230
Roseville
420
Total
1,855

6. Background Cont.
Majority of the watershed's water contribution to Como Lake is delivered through 22 storm sewers discharging directly into the lake.
Gottfried's Pit collects the drainage from parts of Roseville, Flacon Heights, Ramsey County right-of-ways, and the City of St. Paul.

8. Permitted Point Sources
MS4's (stormwater program for municipal separate storm sewer systems) are designed to reduce the amount of sediment and pollution that enters the surface and ground water from storm sewer systems to the maximum extent predictable.

9. Beneficial Uses Como Lake is classified as:
Como Lake is classified as:
2B – Cool and warm fisheries
3B – Industrial consumption
4A - Agricultural use, irrigation
4B – Agricultural use, livestock and wildlife watering
5 – Aesthetic enjoyment, navigation
6 - other
← most stringent

10. 303d Listings First year listed: 2002 Impairment: Aquatic Recreation
Pollutant or stressor: Nutrient/Eutrophication
Biological Indicators

11. Pollutants of Concern
Phosphorus loading is the main concern in Como Lake.
Related to Chlorophyll-a concentration, which is negatively correlated to Secchi depth.
Standards in this ecoregion are 60 ug/L
Total [P] growing season means ranged from ug/L from

12. Water Quality Standards
To be listed as impaired, monitoring data must show BOTH:
WQS for TP violated AND Chlorophyll-a WQS violated OR
Secchi Depth WQS violated
Parameter
Eutrophic Standard, Shallow Lake
Lake Como, GSM
Trophic Status Index
TP (µg/l)
TP > 60
173 78
(hypereutrophic
Chlorophyll-a (µg/l)
chl < 20 25 62
(eutrophic)
Secchi depth (m)
SD > 1.0
1.6 53
(eutrophic)
High TP/chl-a or Secchi suggests that phosphorus does not limit algae growth. (Some other factor limits growth).

13. Total Mean Phosphorus

14. Chlorophyll-a v. Total P

15. Secchi Depth v. Total P

16. Secchi Depth v. Chlorophyll-a

17. Modeling Source Loads
P8 (Program Predicting Polluting Particle Passage thru Pits, Puddles, and Ponds)
Pro’s
simulates flow conditions and pollutant transport in urban environments.
Discretely model BMP’s.
Model set-up, calibration, and validation requirements are moderate.
Con’s
The initial model was set up by Barr Engineering in 2000.
Only minor (insignificant) changes in hydrology do to installation of BMP’S.
Recalibration with more recent data may yield somewhat different results.

18. Existing Load Allocations
Watershed Load
34% of total load
All permitted sources (all MS4’s)

19. Existing Load Allocations
Internal Load
65% of the total load
Result of years of Phosphorus accumulation!
Anoxic conditions at sediment-water interface causes phosphorus release from sediment.
Bottom-feeding fish disturb sediments
Decaying curly-leaf pondweed.
Physical disturbance due to wind mixing
Atmospheric Deposition = 1% of total load

20. Estimate of Assimilative Capacity
WiLMS (Wisconsin Lake Modeling Suite, Version )
Empirical Model, input parameters minimal
Chosen for ability to predict response of in-lake loading to changes in external load
Walker 1987 Reservoir Model
Addition modeling of lake sediment
Allows of chlorophyll and transparency
Lake Area
(acres)
Volume (ac-ft)
Mean Depth (ft)
Drainage Area (ac)
Total Unit Runoff (inches)
Watershed TP load to Lake (lbs/yr)
TP, GSM, (µg/L) 72
525.6
7.3
1767
5.4
625
173

21. Estimate of Assimilative Capacity
Model calibrated unsing GSM averages
TP standard (60 µg/L) used as endpoint
Loads adjusted until model prediction = WQS
Assimilative Capacity found to be 306 lbs/yr
Overall Reduction of 83% from existing load!

22. Margin of Safety Implicit MOS incorporated into TMDL
Based on conservative assumptions for :
Sedimentation rates likely under-predict rate for shallow lakes.
Model results reflect meeting MQS while lake is still in the turbid phase = underestimate of the lake’s loading capacity under clear-water phase.

23. Critical Condition TP levels peak and clarity is worst in Jul-Aug
WQS based on growing season averages
Load reduction designed so lake will meet WQS over entire growing season

24. TMDL Load Allocations TMDL = Load Allocation + Wasteload Allocation
306 lbs/yr = 57 lbs/yr lbs/yr
0.83 lbs/day = 0.15 lbs/day lbs/day
Total = Internal Load + Watershed Loading

25. Wasteload Allocations
Source
Existing Load (lbs/yr)
Load Allocation (lbs/yr)
Required Load Reduction (lbs/yr)
Percent Reduction
Internal Load
1190 37
1153
97%
Atmospheric Load 20 20 0%
Watershed Load
625
249
376
60%
Total
1835
306
1529
83%
Watershed Load = Wasteload allocation for MS4’s
WLA is shared by all NPDES permitted entities
Load reduction will met by the group as a whole
For implementation, assessments made at sub-watershed level

26. Implementation Strategy: External Load
REDUCE WATERSHED LOAD FIRST
Structural BMP’s
Ex. Pascal-Arlington Stormwater Improvement Project
Eight raingardens,
Eight underground infiltration trenches,
An underground stormwater storage and
infiltration facility
A regional stormwater pond.
Sub-watersheds 7 & 8 have reached target
Sub-watershed 3 is underway
Non-Structural BMP’s
Increase street sweeping from 2x to 4x/year
Stormwater education
Support for raingardens, citizen involvement

27. Implementation Strategy: Internal Load
ADDRESS INTERAL LOAD AFTER REDUCTION FROM WATERSHED
Management Options:
Fisheries management
reduce benthivorous/increase piscivorous
Shoreline management
Waterfowl management
Optimize aeration practices
Consider addition of
phosphorus stabilizer
(alum, CuSO4)

28. Why Target External Load?
Internal Load is the result of accumulation from watershed load
Measures taken to addressing Internal Load will be temporary at best unless External Load is decreased

29. TMDL Critique Focus of TMDL: Excess nutrients, is on TP.
The TMDL is a formatted version of an earlier water quality management plan.
Focus of TMDL: Excess nutrients, is on TP.
Focus on reducing the "turbid, algal-dominated state to clear state".
Implementation plan focuses on reductions in external loading.
currently evaluating switching attention from external to internal load reductions solutions (Como Lake implementation audit underway soon)
Existing Load (lbs/yr)
Allocated Load (lbs/yr)
% Reduction
Permitted sources (watershed runoff)
Non-permitted sources (atm. and internal load)
625
249 60
1210 57 95
Total
1835
306 83

30. TMDL Critique - cont. Categorical wasteload allocation approach.
Requires the participation and shared responsibility to achieve reductions between 3 municipalities, various government agencies and residents. 
Data used in analysis dates to late 1990's.
No significant change to land use 
Time and effort spent on converting the early WQ mgmt plan to a TMDL format.
Additional strain on limited resources
Potential confusion of stakeholders
danger of focusing on assessment and not implementation

31. Como Lake TMDL Public Outreach Work Group
City of Falcon Heights
City of Roseville
City of Saint Paul
City of Saint Paul, Div of Parks and Recreation
City of Saint Paul Public Works
CRWD Board of Managers
CRWD Citizens Advisory Committee
Community Council District 6
Community Council District 10
Como Northtown Credit Union
Como Shoreline Interests
Neighborhood Energy Consortium
Metropolitan Council Environmental Services
Minnesota Department of Natural Resources
Minnesota Pollution Control Agency
Minnesota State Legislature
Ramsey County Ramsey County Public Works
Ramsey Soil and Water Conservation District
Emmons & Olivier Resources
Lynch Associates
University of Minnesota Water Resources Center

32. Feasibility of Proposed Goals
There are Federal, State, Watershed and Local authorities in place to ensure that the plan for Como Lake is moving forward. 
Estimated cost of the plan is ~$2.5 million.
Considerable input from the watersheds stakeholders.
Addressing the needs of the public.

33. This leads us to believe that…..
The emphasis on public policy and checks and balances elicited by various governmental policies, along with a coherent budget makes the goals put forth by the Como Lake TMDL lofty, but overall, attainable.