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?