Como Lake TMDLAn overview and critique of methods

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

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.

http://www.capitolregionwd.org/documents/Wilder_Report.pdf

Source: 2009CRWS survey

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

Background on Como Lake

City Area (acre)

Saint Paul 1205

Falcon Heights 230

Roseville 420

Total 1,855

• 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)

Background Cont.

• Majority of the watershed's water contribution to Como Lake is delivered through 22 storm sewers discharging directly into the lake.

• 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.

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.

Beneficial Uses

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

http://www.historicalartforum.com/catalog/images/IceComo16x22.jpg

← most stringent

303d Listings

• First year listed: 2002• Impairment: Aquatic Recreation• Pollutant or stressor: Nutrient/Eutrophication

Biological Indicators

http://nonizamboniblue.blogspot.com/2009_08_01_archive.html

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 100-400 ug/L from 1993-2007.

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 1998-2007

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).

Total Mean Phosphorus

Chlorophyll-a v. Total P

Secchi Depth v. Total P

Secchi Depth v. Chlorophyll-a

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. http://www.extension.umn.edu/projects/nre/Stormwater/images/InstallationInstructionsforP8ModelingSoftware.pdf

Existing Load Allocations

Watershed Load• 34% of total load

o All permitted sources (all MS4’s)

Existing Load AllocationsInternal Load• 65% of the total load

o 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

http://www.lmvp.org/Waterline/spring2005/algae2.htm

Estimate of Assimilative Capacity

WiLMS (Wisconsin Lake Modeling Suite, Version 3.3.18)• 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

Estimate of Assimilative Capacity

• Model calibrated unsing 1998-2007 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!

Margin of Safety

Implicit MOS incorporated into TMDL• Based on conservative assumptions for :

o Sedimentation rates likely under-predict rate for shallow lakes.

o Model results reflect meeting MQS while lake is still in the turbid phase = underestimate of the lake’s loading capacity under clear-water phase.

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

TMDL Load Allocations

TMDL = Load Allocation + Wasteload Allocation

306 lbs/yr = 57 lbs/yr + 249 lbs/yr0.83 lbs/day = 0.15 lbs/day + 0.68 lbs/day

Total = Internal Load + Watershed Loading

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 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

Implementation Strategy: External Load

REDUCE WATERSHED LOAD FIRSTStructural BMP’sEx. Pascal-Arlington Stormwater Improvement Project• Eight raingardens,• Eight underground infiltration trenches,• An underground stormwater storage and

infiltration facility• A regional stormwater pond.

o Sub-watersheds 7 & 8 have reached targeto Sub-watershed 3 is underway

http://sustainablestormwater.org/2007/05/23/infiltration-trenches/

Non-Structural BMP’s• Increase street sweeping from 2x to 4x/year• Stormwater education• Support for raingardens, citizen involvement

Implementation Strategy: Internal Load

ADDRESS INTERAL LOAD AFTER REDUCTION FROM WATERSHEDManagement Options:• Fisheries management • reduce benthivorous/increase piscivorous• Shoreline management• Waterfowl management• Optimize aeration practices• Consider addition of phosphorus stabilizer (alum, CuSO4)

http://www.phoslock.com.au/about.php

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

TMDL Critique 

• The TMDL is a formatted version of an earlier water quality management plan.o Focus of TMDL: Excess nutrients, is on TP.o Focus on reducing the "turbid, algal-dominated state

to clear state".

• Implementation plan focuses on reductions in external loading.

o 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

TMDL Critique - cont.

• Categorical wasteload allocation approach. o 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.o No significant change to land use 

• Time and effort spent on converting the early WQ mgmt plan to a TMDL format.o Additional strain on limited resourceso Potential confusion of stakeholderso danger of focusing on assessment and not implementation

Como Lake TMDL Public Outreach Work Group

City of Falcon HeightsCity of RosevilleCity of Saint PaulCity of Saint Paul, Div of Parks and RecreationCity of Saint Paul Public WorksCRWD Board of ManagersCRWD Citizens Advisory CommitteeCommunity Council District 6Community Council District 10Como Northtown Credit UnionComo Shoreline Interests

Neighborhood Energy ConsortiumMetropolitan Council Environmental ServicesMinnesota Department of Natural ResourcesMinnesota Pollution Control AgencyMinnesota State LegislatureRamsey County Ramsey County Public WorksRamsey Soil and Water Conservation DistrictEmmons & Olivier ResourcesLynch AssociatesUniversity of Minnesota Water Resources Center

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.

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.