Best Management Practices for Stormwater Quality Treatment in Urban Settings. Lower Mississippi River WMO September 2017

Transcription

1 Best Management Practices for Stormwater Quality Treatment in Urban Settings Lower Mississippi River WMO September 2017

2 Stormwater 101 Impervious surfaces (pavement, parking lots, etc.): quickly produce large volumes of runoff, causing erosion and flooding Runoff carries pollutants (e.g., sediment, phosphorus) to surface waters First flush runoff contains higher concentrations of pollutants

3 Common stormwater runoff-related water quality impairments Nutrients (phosphorus, nitrogen) Can cause excess algae growth Total suspended solids (particulate material such as sediment) Impacts water clarity Chloride (salt) Can affect aquatic life

4 BMP family tree Not all best management practices (BMPs) work for every site; not all BMPs created equal Wet Ponds Stormwater Wetland Underground Infiltration Traditional Engineering Infiltration Basins Swales Structural BMPs Stormwater BMPs Filtration/ Sedimentation Rain Gardens Bioinfiltration Basins Green Roofs Green Infrastructure Good Housekeeping Tree Trenches Permeable Pavement Stormwater Planters Vaults Chambers Perforated Pipes In-Catch-Basin Devices Sedimentation Filtration Media Beds Iron-Enhanced Sand Spent Lime Systems

5 Good housekeeping (pollution prevention) Non-structural programs/action Street sweeping Salt/chemical storage practices Training and education Maintenance/operation procedures

6 Traditional engineering Wet Ponds Stormwater Wetlands Traditional Engineering Infiltration Basins Swales Proven design techniques that provide effective water quality treatment Often requires significant footprint Easy to implement at time of development Difficult to retrofit

7 Traditional engineering: wet ponds Popular in early 1990s Proven design techniques (NURP) ~50% total phosphorus reduction ~85% total suspended solids reduction Easy to implement at time of construction Provide water quantity benefits Large footprint Image: Minnesota Pollution Control Agency

8 Traditional engineering: stormwater wetlands Image: Minnesota Pollution Control Agency Constructed BMP (not discharge to existing wetland) Treatment concept/performance similar to wet ponds Education and habitat value Pretreatment is recommended Water quantity benefits Large footprint

9 Stormwater pre-treatment Reduce maintenance and preserve long-term functionality Remove trash, debris, and coarse sediments, organic materials Various pretreatment types: Sediment Forebays Screens Sump Manholes Vegetated Filter Strips Images: Minnesota Pollution Control Agency

10 Traditional engineering: infiltration basin and swales Various types Dry pond Trench Swale Pretreatment is recommended Requires permeable soils Limited water quantity benefits Image: Minnesota Pollution Control Agency

11 Green infrastructure Rain Gardens Bioinfiltration Basins Green Roofs Green Infrastructure Tree Trenches Permeable Pavement Stormwater Planters Mimics natural hydrology Science is still developing Retrofit opportunities Lower impact/more sustainable

12 Green infrastructure: raingardens and bioinfiltration Variety of applications Small scale Retrofit potential Visually appealing Treat small volumes Requires permeable soils Maintenance often delegated Image: Living Streets project, Maplewood

13 Green infrastructure: raingardens and bioinfiltration Images: Burnsville and Minneapolis

14 Green infrastructure: green roofs Image: Minneapolis College of Art and Design Layered substrate supporting plant growth Volume reduction through evapotranspiration Filtration through substrate Retrofit opportunities Maintains usable space

15 Green infrastructure: tree trenches and tree boxes Often use engineered substrate or structural cells Filtration through substrate with underdrain Pretreatment recommended Maintains usable space Aesthetically pleasing Image: Green Line tree trenches, St. Paul

16 Green infrastructure: permeable pavement Image: Minnetonka Civic Center Many types Pervious concrete Porous asphalt Permeable pavers Reduces runoff by replacing impervious surface Maintains usable space Requires frequent maintenance

17 Structural BMPs: underground infiltration Structural BMPs Underground Infiltration Vaults Chambers Image: Minnesota Pollution Control Agency Perforated Pipes

18 Underground infiltration systems Variety of shapes and sizes Vaults Chambers Perforated pipe networks Can store/infiltrate large volumes Requires permeable soils Relatively expensive Allows for land use above Image: Minnesota Pollution Control Agency

19 Underground infiltration: vaults Large pre-cast concrete vaults Customizable sizes, modular design Used for infiltration, storage, reuse Requires pretreatment chambers Images: StormTrap Stormwater Management; 37 th Avenue, Minneapolis

20 Underground infiltration: chambers Triton Stormwater Chamber Plastic dome chambers of various sizes Grid pattern with multiple layers possible to accommodate large storms Requires header row for sedimentation and clean-out Images: Triton Stormwater Solutions

21 Structural BMPs: filtration/sedimentation In-Catch-Basin Devices Structural BMPs Filtration/ Sedimentation Sedimentation Filtration In-catch-basin device Inserted into or replaces stormwater catch basin Uses a variety of treatment mechanisms Filtration (screens/cartridges filter suspended pollutants) Settling (water movement/detention used to settle/capture pollutants) Best used for retrofit/where space is limited Requires regular inspection and maintenance to remain effective!

22 Sedimentation: Hydrodynamic separators Several proprietary technologies Stormceptor Downstream Defender Used as pretreatment for downstream infiltration BMPs Alternative to sump catch basins Image: Hydro International

23 Sedimentation: Hydrodynamic separators Effective at removing large particles Ineffective at removing dissolved nutrients/very fine particulates Requires yearly inspection and regular maintenance Relatively expensive Images: Hydro International

24 Sedimentation: Hydrodynamic separators Several proprietary technologies Stormceptor Downstream Defender Effective at removing large particles Ineffective at removing dissolved nutrients/very fine particulates Images: Hydro International Requires yearly inspection

25 Filtration: EcoStorm Plus by Watertectonics Large pre-cast concrete chamber with multiple removal mechanisms Uses gravity, hydrodynamic separation, adsorptive filtration Filtration accomplished via porous concrete elements that last approximately 5 years Proven effective for TSS, heavy metals, and dissolved nutrients Image Credit: Watertectonics

26 Filtration: EcoStorm Plus by Watertectonics Effective, but relatively expensive Requires a small footprint, but can be scaled to treat a larger watershed Removal Efficiency Total suspended solids (TSS) >80% Zinc (Zn) >90% Lead (Pb) >95% Copper (Cu) >80% Phosphorus >60% Image: Watertectonics

27 Filtration: SAFL Baffle by Upstream Technologies Perforated screen inserted in to catch basin Prevents resuspension and wash out of sediments previously captured by sump catch basin Allows for the retrofitting of most existing sump catch basins Designed to be maintained twice per year Image: Upstream Technologies

28 Filtration: Media beds Structural BMPs Iron-Enhanced Sand Filter Filtration/ Sedimentation Image: Minnesota Pollution Control Agency Media Beds Spent-Lime Filter Iron-Enhanced Sand Filter Spent-Lime Filter Image: Ramsey-Washington Metro Watershed District

29 Filtration: Iron-enhanced sand Filtration basin similar to rain garden or modified wet pond Employs underdrains embedded in sand mixed with iron (filings or granular) Overflow outlet structure to storm sewer Perimeter underdrain to outlet structure (to prevent ground water intrusion) Iron-enhanced sand filter media Filter media drain tile to outlet structure Image: MPCA

30 Filtration: Iron-enhanced sand Numerous local examples in several configurations Dissolved phosphorus bonds to iron as it passes through the filter Research shows up to 90% removal of dissolved phosphorus Critical that water level draws down within 48 hours to prevent conditions that can release bound phosphorus (filter needs to dry out) Iron enhanced sand filter, Maplewood Image: Ramsey-Washington Metro Watershed District

31 Filtration: Spent-lime New technology using available waste material granular lime previously used to treat drinking water Highly effective at removing dissolved phosphorus up to 95% Effective lifespan being researched Wakefield Lake Spent Lime Filter, Maplewood Image: Ramsey-Washington Metro Watershed District

32 Questions?