Be st Ma na g e me nt Pra c tic e s fo r Sto rmwa te r Qua lity T re a tme nt in Urb a n Se tting s Lower Mississippi River WMO – September 2017
Sto rmwa te r 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
Co mmo n sto rmwa te r runo ff-re la te d wa te r q ua lity impa irme nts • 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
Stormwater BMP fa mily tre e BMPs Green Traditional Engineering Infrastructure Not all best Wet Infiltration Tree management Rain Gardens Ponds Basins Trenches practices (BMPs) Stormwater Bioinfiltration Permeable Swales work for every Basins Pavement Wetland site; not all BMPs Stormwater Green Roofs Planters created equal Structural Good BMPs Housekeeping Filtration/ Underground Infiltration Sedimentation In-Catch-Basin Vaults Media Beds Devices Iron-Enhanced Chambers Sedimentation Sand Perforated Spent Lime Filtration Pipes Systems
Go o d ho use ke e ping (po llutio n pre ve ntio n) • Non-structural programs/action • Street sweeping • Salt/chemical storage practices • Training and education • Maintenance/operation procedures
T ra ditio na l e ng ine e ring • Proven design techniques that Traditional provide effective water quality Engineering treatment • Often requires significant footprint Wet Ponds Infiltration Basins • Easy to implement at time of Stormwater Swales development Wetlands • Difficult to retrofit
T ra ditio na l e ng ine e ring : we t po nds • 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 Image: Minnesota Pollution Control Agency • Large footprint
T ra ditio na l e ng ine e ring : sto rmwa te r we tla nds • Constructed BMP (not discharge to existing wetland) • Treatment concept/performance similar to wet ponds • Education and habitat value • Pretreatment is recommended • Water quantity benefits Image: Minnesota Pollution Control Agency • Large footprint
Sto rmwa te r pre -tre a tme nt • Reduce maintenance and preserve long-term functionality • Remove trash, debris, and coarse sediments, organic materials • Various pretreatment types: Sediment Sump Vegetated Screens Forebays Manholes Filter Strips Images: Minnesota Pollution Control Agency
T ra ditio na l e ng ine e ring : infiltra tio n b a sin a nd swa le s • Various types • Dry pond • Trench • Swale • Pretreatment is recommended • Requires permeable soils • Limited water quantity benefits Image: Minnesota Pollution Control Agency
Gre e n infra struc ture Green Infrastructure • Mimics natural hydrology Rain Gardens Tree Trenches • Science is still developing Bioinfiltration Permeable • Retrofit opportunities Basins Pavement • Lower impact/more sustainable Stormwater Green Roofs Planters
Gre e n infra struc ture : ra ing a rde ns a nd b io infiltra tio n • Variety of applications ‒ Small scale ‒ Retrofit potential • Visually appealing • Treat small volumes • Requires permeable soils Image: Living Streets project, Maplewood • Maintenance often delegated
Gre e n infra struc ture : ra ing a rde ns a nd b io infiltra tio n Images: Burnsville and Minneapolis
Gre e n infra struc ture : g re e n ro o fs • Layered substrate supporting plant growth • Volume reduction through evapotranspiration • Filtration through substrate • Retrofit opportunities • Maintains usable space Image: Minneapolis College of Art and Design
Gre e n infra struc ture : tre e tre nc he s a nd tre e b o xe s • 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
Gre e n infra struc ture : pe rme a b le pa ve me nt • Many types • Pervious concrete • Porous asphalt • Permeable pavers • Reduces runoff by replacing impervious surface • Maintains usable space Image: Minnetonka Civic Center • Requires frequent maintenance
Struc tura l BMPs: unde rg ro und infiltra tio n Structural BMPs Underground Infiltration Vaults Chambers Image: Minnesota Pollution Control Agency Perforated Pipes
Unde rg ro und infiltra tio n syste ms • Variety of shapes and sizes ‒ Vaults ‒ Chambers ‒ Perforated pipe networks • Can store/infiltrate large volumes • Requires permeable soils Image: Minnesota Pollution Control Agency • Relatively expensive • Allows for land use above
Unde rg ro und infiltra tio n: va ults • 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
Unde rg ro und infiltra tio n: c ha mb e rs 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
Struc tura l BMPs: filtra tio n/ se dime nta tio n In-catch-basin device Structural BMPs • Inserted into or replaces stormwater catch basin Filtration/ • Uses a variety of treatment mechanisms Sedimentation ‒ Filtration (screens/cartridges filter suspended pollutants) In-Catch-Basin ‒ Settling (water movement/detention used to Devices settle/capture pollutants) Sedimentation • Best used for retrofit/where space is limited Requires regular inspection and maintenance to remain effective! Filtration
Se dime nta tio n: Hydro dyna mic se pa ra to rs • Several proprietary technologies • Stormceptor • Downstream Defender • Used as pretreatment for downstream infiltration BMPs • Alternative to sump catch basins Image: Hydro International
Se dime nta tio n: Hydro dyna mic se pa ra to rs • Effective at removing large particles • Ineffective at removing dissolved nutrients/very fine particulates • Requires yearly inspection and regular maintenance • Relatively expensive Images: Hydro International
Se dime nta tio n: Hydro dyna mic se pa ra to rs • 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
F iltra tio n: E c o Sto rm Plus b y Wa te rte c to nic s • 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
F iltra tio n: E c o Sto rm Plus b y Wa te rte c to nic s • 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
F iltra tio n: SAF L Ba ffle b y Upstre a m T e c hno lo g ie s • 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
F iltra tio n: Me dia b e ds Iron-Enhanced Sand Filter Structural BMPs 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
F iltra tio n: I ro n-e nha nc e d sa nd • 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 Iron-enhanced (to prevent ground Filter media drain tile sand filter media water intrusion) to outlet structure Image: MPCA
F iltra tio n: I ro n-e nha nc e d sa nd • 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
F iltra tio n: Spe nt-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
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