Rhode Island Stormwater Design and Installations Standards Manual - PowerPoint PPT Presentation

Rhode Island Stormwater Design and Installations Standards Manual Public Workshop Acceptable Water Quality BMPs and S election Criteria January 13, 2011 Horsley W itten Group, I nc. Horsley W itten Group, I nc.

Water Quality BMPs Larger Conventional Community Planning BMPs LID BMPs LID Site Design Receiving Waters Horsley W itten Group, I nc. Horsley W itten Group, I nc.

3.2.3 Minimum Standard 3: Water Quality • The WQv must be treated by at least one of the structural BMPs listed in Chapter Five at each location where a discharge of stormwater will occur. • Minimum average pollutant removal efficiencies: 85% removal of total suspended solids (TS S ), 60% removal of pathogens, 30% removal of total phosphorus (TP) for discharges to freshwater systems, and 30% removal of total nitrogen (TN) for discharges to saltwater or tidal systems. • Excludes LID credits allowed under S ection 4.6 Horsley W itten Group, I nc. Horsley W itten Group, I nc.

Acceptable BMPs • 5.2 Wet Vegetated Treatment S ystems (WVTS ) • 5.3 S tormwater Infiltration Practices • 5.4 Permeable Paving • 5.5 Filtering S ystems • 5.6 Green Roofs • 5.7 Open Channel S ystems Horsley W itten Group, I nc. Horsley W itten Group, I nc.

Minimum Design Criteria • Required Elements and Design Guidance – If required elements can’ t be met, select a different BMP • S ix Categories – Feasibility – Conveyance – Pretreatment – Treatment – Landscaping – Maintenance Horsley W itten Group, I nc. Horsley W itten Group, I nc.

Wet Vegetated Treatment S ystems • Designed t o st ay wet ! • Veget at ion –key component • S ome rest rict ions near coldwat er st reams Horsley W itten Group, I nc. Horsley W itten Group, I nc.

Gravel WVTS Horsley W itten Group, I nc. Horsley W itten Group, I nc.

Gravel WVTS Horsley W itten Group, I nc. Horsley W itten Group, I nc.

Infiltration • S oil t est ing required • S eparat ion t o S HGT and bedrock • Rest rict ions in fill Horsley W itten Group, I nc. Horsley W itten Group, I nc.

Horsley W itten Group, I nc. Horsley W itten Group, I nc. Permeable Paving • Two main cat egories

Porous Pavements Horsley W itten Group, I nc. Horsley W itten Group, I nc.

Permeable Pavers Horsley W itten Group, I nc. Horsley W itten Group, I nc.

Filtering Practices Sand/organic filters Bioretention areas/Tree filters Horsley W itten Group, I nc. Horsley W itten Group, I nc.

Sand Filters Horsley W itten Group, I nc. Horsley W itten Group, I nc.

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Bioretention Horsley W itten Group, I nc. Horsley W itten Group, I nc.

Bioretention Schematic Runoff Vegetation on Surface Vegetation on Surface Planting Soil - Primarily Sand Underdrain System Horsley W itten Group, I nc. Horsley W itten Group, I nc.

Bioretention Planting Soil and Mulch • Loamy S and to a S andy Loam – 85-88 % sand – 8-12 % silt – 0-2 % clay • Well-aged graded compost (25% of soil mix) • Layer of well-aged, shredded hardwood mulch (aged 6 months, if possible) Horsley W itten Group, I nc. Horsley W itten Group, I nc.

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Bioretention –Many Applications Horsley W itten Group, I nc. Horsley W itten Group, I nc.

Tree pits Horsley W itten Group, I nc. Horsley W itten Group, I nc.

Green Roofs Extensive Intensive Horsley W itten Group, I nc. Horsley W itten Group, I nc.

Open Channels Horsley W itten Group, I nc. Horsley W itten Group, I nc.

Dry Swale Horsley W itten Group, I nc. Horsley W itten Group, I nc.

Wet Swale Horsley W itten Group, I nc. Horsley W itten Group, I nc.

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Swales Horsley W itten Group, I nc. Horsley W itten Group, I nc.

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Practices Approved for Other Criteria • Pretreatment Practices – Chapter 6 � Grass Channel � Filter S trips � S ediment Forebay � Deep S ump Catch Basins � Proprietary Devices • S torage Practices – Chapter 7 � S tormwater Basins � Underground S torage Devices Horsley W itten Group, I nc. Horsley W itten Group, I nc.

II. S electing the Most Effective and Appropriate S tormwater Practices Horsley W itten Group, I nc. Horsley W itten Group, I nc.

Five Selection Factors to Consider 1. Land Use 2. Physical Feasibility 3. Watershed 4. S tormwater Management Capability 5. Community and Environmental Horsley W itten Group, I nc. Horsley W itten Group, I nc.

#1. Land Use The land use of the contributing drainage area influences the stormwater strategy: • Rural areas • Residential sites • Roads/ highways • Commercial sites • LUHPPLs • Urban sites (e.g., redevelopment) Horsley W itten Group, I nc. Horsley W itten Group, I nc.

Cul-de-Sac Application Horsley W itten Group, I nc. Horsley W itten Group, I nc.

Commercial Application Horsley W itten Group, I nc. Horsley W itten Group, I nc.

Municipal Application Horsley W itten Group, I nc. Horsley W itten Group, I nc.

Retrofit Application Horsley W itten Group, I nc. Horsley W itten Group, I nc.

# 2. Physical Feasibility S ome Practices Cannot Be Used Because of S ite Constraints: • S oils • Groundwater • Drainage Area • Minimum S urface Area • S lope Restriction • Head Horsley W itten Group, I nc. Horsley W itten Group, I nc.

Wet Swale • Used when water table is close to surface Horsley W itten Group, I nc. Horsley W itten Group, I nc.

#3. Watershed Factors Different Receiving Water Management Obj ectives S hape S tormwater S trategies: • Groundwater (Aquifer protection) • Freshwater streams and Rivers • Other Freshwaters (Ponds/ Lakes/ Wetlands) • Coastal Waters (shellfish/ beach areas Horsley W itten Group, I nc. Horsley W itten Group, I nc.

#4. Stormwater Management Capability No single practice achieves all stormwater management obj ectives. A combination of practices is often needed to provide desired level of: • Groundwater recharge • Water quality treatment • Channel protection • Flood control • Ability to treat LUHPPLs Horsley W itten Group, I nc. Horsley W itten Group, I nc.

To Offline Facility for Water Quality Treatment To Discharge Pipe

#5. Community and Environmental Impacts Other community and environmental impacts should be considered when selecting BMPs: • Ease of maintenance • Affordability • Community acceptance/ aesthetics • S afety • Habitat Horsley W itten Group, I nc. Horsley W itten Group, I nc.

S tormwater Practice Maintenance Burden Maintenance Burden is a function of the type of facility as well as the design and implementation • WVTS ---------- Medium to Easy • Infiltration* --------- Medium to Difficult • Filters -------------- Medium to Difficult • Green Roofs --------- Medium • Open Channels ------------ Medium to Easy *Except drywells - Easy Horsley W itten Group, I nc. Horsley W itten Group, I nc.

Pollutant Removal Capability Important when higher removals are required (see list in S ection 3.2.3). Table H-3/H-4 compares removal efficiencies for: • Total S uspended S olids • Total Phosphorus • Total Nitrogen • Bacteria Horsley W itten Group, I nc. Horsley W itten Group, I nc.

Questions? Horsley W itten Group, I nc. Horsley W itten Group, I nc.