Watershed-Wide Modeling for TMDL/MS4 Permit Compliance. Greg Wilson, Barr Engineering

Transcription

1 Watershed-Wide Modeling for TMDL/MS4 Permit Compliance Greg Wilson, Barr Engineering

2 Acknowledge City of Golden Valley Eric Eckman Heather Hegi Laura Jester and BCWMC Technical Advisory Committee members

3 Objectives for Bassett Creek Watershed- Wide Modeling Update water quality modeling, watershedwide, for tracking progress towards TMDL implementation goals P8 Urban Catchment Model Current/future water quality impairments Provide a tool for evaluating the effect of proposed projects Such as those that come under Commission review and CIP projects Determine treatment effectiveness for permit requirements and prioritize BMP maintenance

4 Pond assessment procedures and schedule MS4 Permit Pollution Prevention/ Good Housekeeping for Municipal Operations Develop procedures and a schedule for determining TSS and TP treatment effectiveness of permittee s ponds constructed/used for stormwater treatment Schedule (which can exceed permit term) based on measurable goals and priorities established by permittee

5 Watershed- Wide Modeling

6 P8 Urban Catchment Model Used for watershed-wide water quality modeling and all of the TMDLs in BCWMC Used in more than 20 TMDL studies in the TCMA Applications range from watershed-scale down to site planning and compliance evaluations using continuous simulation Design and evaluate effectiveness of detention, retention, infiltration/filtration practices, constructed wetlands and street sweeping Evaluation of extended detention and outlet configuration

7 Can be used to evaluate a network of BMPs P8 Urban Catchment Model (cont d.) Hourly precipitation and daily temperature inputs allow for calibration to observed monitoring data Build-up/washoff of pollutants is simulated along with BMP treatment Constituents include sediment, nutrients (including dissolved and particulate phosphorus), and heavy metals More powerful for comparing relative BMP treatment efficiencies than absolute pollutant load predictions

8 Sweeney Lake Watershed Modeling TMDL calls for 15% TP load reduction from watershed

9 Sweeney Lake Watershed Modeling ~60 ponds in watershed FWM TP Conc. leaving Schaper Pond = mg/l

10 Sweeney Lake Watershed Modeling

11 Sweeney Lake Watershed Modeling

12 Limitations Modeling/analysis assumes Pond design corresponds with ideal settling conditions Fully mixed conditions Ponds do not experience sediment phosphorus release P8 doesn t account for Scour/resuspension/erosion Short-circuiting Particle interactions Winter sanding Reduced effectiveness from sediment accumulation over time

13 Sweeney Lake Watershed Modeling

14 Pond assessment procedures and schedule MS4 Permit Pollution Prevention/ Good Housekeeping for Municipal Operations Develop procedures and a schedule for determining TSS and TP treatment effectiveness of permittee s ponds constructed/used for stormwater treatment Schedule (which can exceed permit term) based on measurable goals and priorities established by permittee To counteract model limitations Assess pond size mean depths, potential for scour, sediment accumulation rate as % of assumed size Evaluate pond inlet and outlet locations

15 Watershed- Wide Modeling

16 Watershed- Wide Prioritization ~600 ponds throughout the watershed can be prioritized to manageable number

17 Summary Consistent, watershed-wide modeling provides method for Watershed organizations and MS4s to properly account for stormwater management effects on impaired waters measurable goals Track progress and prioritize BMP implementation capital improvements planning Benefits of modeling for pond assessments Identifies BMPs with limited treatment effectiveness and/or vulnerability to deterioration over time Enables permittees to prioritize or schedule maintenance activities

18 Questions?