Stormwater Retrofitting Demystified!
A training for local governments to cost effectively implement retrofits to
meet MS-4 permit and Chesapeake Bay TMDL requirements.
Workshop Agenda9:30 – 9:40 Welcome and Learning Objectives for the Day
9:40 – 10:00 State Perspectives on Stormwater Retrofitting
10:00 – 10:45 Session 1. Basics of Stormwater Retrofitting
10:45 – 11:15 BREAK
11:15 – 12:30 Session 2. Strategies to Consider Prior to Retrofits
12:30 – 1:30 LUNCH
1:30 – 2:30 Session 3. The Retrofit Discovery Process
2:30 – 3:45 Session 4. Retrofit Costs, Delivery and Maintenance
3:45 – 4:00 Concluding Remarks
4:00 Evaluations!
To learn how you can have access to: Discounted Webcasts
Free One-day design workshopsIntensive master stormwater design seminars
Direct On-site technical assistance Self guided web-based learning modules
Visit: www.chesapeakestormwater.net
Chesapeake Bay Stormwater Training Partnership
Session 1Basics of Stormwater Retrofitting
1. Where do Nutrients and Sediment Come From?
2. Retrofit Categories 3. Envisioning Retrofits
Session 1 Agenda
Where do Nutrients and Sediment Come From?
There are many sources of N and P in the urban environment
The main sources of nutrients to the Bay Watershed are:
•Runoff from Forests •Wastewater•Atmospheric Deposition to Open Water•Urban and Suburban Runoff•Agricultural Runoff •Septic Systems (N only)
Relationship of Atmospheric Deposition to Urban Runoff Quality
NutrientAtmospheric Deposition 1
Stormwater Runoff Load 2
Pounds per impervious acre per year
Total Phosphorus
0.7 2.0
Total Nitrogen 13 to 17.0 3 15.41 measured rates during Washington NURP Study (MWCOG, 1983)2 Simple Method annual stormwater runoff loads for one acre of impervious cover (Schueler, 1987)3 About 40% of nitrogen deposition occurs through wetfall, which would presumably be quickly converted into runoff. 60% of nitrogen deposition occurs via dryfall, which is available for washoff in future storms, or may be blown over to pervious areas
Much of the nitrogen in urban runoff is derived from atmospheric deposition, either in the form of dryfall or wetfall
Other sources of nitrogen in urban runoff include:
•Washoff of fertilizers•Nitrogen attached to eroded soils and streambanks •Organic matter and pet wastes on IC
Nitrogen EMCs for different urban land covers
Urban Land Cover Total N (mg/l) Lawns 9.70Highway 2.95Streets (Variable) 1.40 Parking Lots 1.94Rooftops 1.50
Source; CWP, 2003
Runoff sampling shows that lawn runoff is very high in nitrogen. Also, rooftop runoff concentration shows effect of atmospheric deposition
Many sources of TP in urban runoff
• Blow in of organic matter onto impervious surfaces (leaves, pollen, clippings, flowers, etc.)
• Phosphorus attached to eroded soils and streambanks
• Fertilizer washoff• Atmospheric deposition
Phosphorus EMCs for different urban land covers
Urban Land Cover Total P (mg/l) Lawns 1.90Highway 0.60Streets (Variable) 0.50 Parking Lots 0.16Rooftops 0.12
Source; CWP, 2003
The sources of phosphorus are more complex. While lawn runoff is high in nitrogen, atmospheric deposition is less important as a source of TP
Phosphorus EMCs for different urban land uses
Urban Land Use Total P (mg/l) Residential 0.30Commercial 0.22Industrial 0.26Freeway 0.25Source: Pitt et al 2004
Residential runoff is slightly higher in TP concentration, which reflects the effect of vegetation and fertilization
Total Phosphorus Loads By Sector in Maryland Portion of Bay WatershedSector
2009Load
Target Load % Reduction Needed to Meet Target
Million pounds per yearForest 0.34 0.34 0Atm. Deposition 0.04 0.04 0Wastewater 0.67 0.70 0Urban and Suburban
0.68 (22%) 0.39 43%
Agricultural 1.37 1.25 9%Septics -0- -0- 0TOTAL 3.10 2.72 12%Source: US EPA Chesapeake Bay Program, 2010
Sources of Urban Sediment
• Urban stream channel erosion• Wash-off from impervious areas• Erosion from pervious areas• Construction sites
Edge of Stream Unit Loading Rates for MD Using CBWM v. 5.3.2
Pounds/acre/year Total N Total P TSS
IMPERV PERV IMPERV PERV IMPERV PERVUrban 15.3 10.8 1.69 0.43 1116 175Forest 3.16 0.13 60
Source: CBPO, 1/4/2012
Discussion
1964
My Early Retrofitting Years
Wiggle-tail
Why Retrofit ?• Local Watershed restoration • Meet IC Treatment Targets in MD • Comply with Bay-wide TMDLs
(and local ones too)• Improve local stream habitat
and diversity• Fix old mistakes/drainage
problems• Improve performance of existing
stormwater infrastructure
Why Retrofits Are DifferentUrban Retrofit Practices New Stormwater Practices Construction costs are 1.5 to 4 times greater
Designers seek least costly options
Assessment and design costs are higher
Focus on low cost design and construction
Sized to meet watershed restoration objectives
Sized to meet local stormwater design standards
Typically installed on public land Installed at new development projects
Urban soils often cannot support infiltration Soils may support infiltration
Fingerprinted around existing development
More flexibility on where to locate practices
Why Retrofits Are DifferentUrban Retrofit Practices New Stormwater Practices Must be acceptable to adjacent neighbors
Aesthetics are not always a major design factor
Most are publicly maintained Most require private maintenance
Not all candidate sites are feasible
Nearly all sites are made to work
Tied into existing conveyance system
Usually creates new conveyance system
Integrated with other restoration practices Stand-alone practice
Public investment in watershed infrastructure
Private investment in stormwater infrastructure
Caution: The “rules” are in flux
• MDE 2011 Guidance• CSN Technical Bulletin 9• Roll out of New MS4 Permits• 6 New Urban BMP Expert Panels• New BMP Verification Protocols• Updated editions of MASTBad news: the numbers will changeGood news: the numbers will improve
Advice: use them for general planning and evaluation of alternatives
Stormwater Regs: Final ESD regulations issued in May 2009 with local implementation to start in May of 2010.
MS4 Permits: Phase 1 and Phase 2 backlog
Dual BMP Reporting in MD
• For MS4 Permits:• Report BMPs implemented **• Report “Treated Acres” of Existing Impervious Cover
*
For Bay TMDL/Local WIPs: • Report BMPs implemented **• Report TSS, TN, and TP reductions
** both are done using Appendix A of MS4 BMP Reporting * ESD to MEP for existing IC defined as minimum site
WQv
Stormwater Regs: Final ESD regulations issued in May 2009 with local implementation to start in May of 2010.
MS4 Permits: Phase 1 and Phase 2 backlog
Best Opportunities for Retrofitting in the Urban
Landscape
Retrofit CategoriesA.NEW RETROFIT FACILITIES
1. Near Existing Stormwater Outfalls2. Within the Conveyance System3. Adjacent to Large Parking Lots4. Green street retrofits 5. On-site LID retrofits
B.EXISTING BMP FACILITIES1. BMP Conversions 2. BMP Enhancements3. BMP Restoration
NEW RETROFITSNear Existing Stormwater Outfalls
Source: CWP
NEW RETROFITS Within the Existing Conveyance
System
Source: CWP
Wet Pond
Bioretention
NEW RETROFITSAdjacent to Large Parking Lots
Source: CWP
NEW RETROFITS Green Street Retrofits
NEW RETROFITS On-Site LID Retrofits
Retrofit Categories
B.EXISTING BMP FACILITIES1. BMP Conversions 2. BMP Enhancements3. BMP Restoration
EXISTING RETROFITS BMP CONVERSION
DRY POND CONSTRUCTEDWETLAND
BMP CONVERSIONSRehabilitating Failed Infiltration Practices
BMP CONVERSIONSAdding Bioretention/Filtering to Ponds
EXISTING RETROFITS BMP ENHANCEMENT
INCREASE IN HYDRAULIC RETENTION TIME
EXISTING RETROFITS BMP RESTORATION
DREDGING AN UNDERPERFORMING POND TO RESTORE FULL PERFORMANCE
Discussion
Retrofitting requires:Sleuthing skills to determine what can
work at highly constrained sitesSimultaneously envisioning restoration possibilities and anticipating potential
problems
Activity: Envisioning Restoration
Activity
Activity
Questions?
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