retrofitting revisited: a post-expert panel...
TRANSCRIPT
Retrofitting Revisited:A Post-Expert Panel Perspective
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Poll Question #1
How many people are watching with you today?
• Just me
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• > 10 people
Poll Question #2
Tell us a little about yourselves…who are you representing today?
• Local government
• Private sector
• Regulatory agency
• Non-profit
• Academia
• Other…tell us in the chat box
Poll Question #3
Tell us what YOUR role in retrofitting is:
• I design them
• I construct them
• I record/track/account for them to meet my permit/restoration/TMDL requirements
• I conduct retrofit/watershed assessments
• What is a retrofit?
Tom SchuelerChesapeake Stormwater
Cecilia LaneChesapeake Stormwater
Speaker Info
1964
My Early Retrofitting Years
Wiggle-tail
Today’s Agenda
1. Retrofit Classification
2. Envisioning Restoration
3. The Retrofit Discovery Process
4. Tom’s Short Cut Process
5. Retrofit Evaluation: Removal and Costs
6. Some FAQs for Retrofits
7. Some Other Options
8. Discussion
Why Retrofit?
~ 10 to 30% TP and TN load reductions needed from existing development
Massive Increase in Retrofitting
15 Years to Get It Done
Stormwater Retrofit Classification
Category 1
RETROFIT EXISTING BMPS
1. BMP Conversions
2. BMP Enhancements
3. BMP Restoration
Can be the most cost effective type of retrofit since it represents existing stormwater infrastructure that you already own or control
EXISTING RETROFITS
BMP CONVERSION
DRY POND
CONSTRUCTEDWETLAND
Retrofit Existing Stormwater Basins
1. Excavate Storage
– Wet pool
– Sand filter
2. Raise Embankment
Retrofit Existing Stormwater Basins
3. Modify Riser
Retrofit Existing Stormwater Basins
4. Trade Storage
OTHER BMP CONVERSIONSAdding Bioretention or Sand Filters to Dry Ponds
EXISTING RETROFITS
BMP ENHANCEMENT
Increase treatment volume, hydraulic residence time or other design elements to improve pollutant removal *
* Expert panel did not provide a lot of specifics
EXISTING RETROFITS
BMP RESTORATION
DREDGING AN UNDERPERFORMING POND TO RESTORE FULL PERFORMANCE
Retrofit Category 2: NEW BMPs
Near Existing Stormwater Outfalls
Source: CWP
NEW BMPs
Within the Existing Conveyance System *
Source: CWP
* Impervious Cover Disconnection EP provides new design methods for this kind of retrofit
Wet Pond
Bioretention
NEW BMPs
Adjacent to Large Parking Lots
Source: CWP
NEW BMPs
Green Streets
NEW BMPs
Residential Stewardship Practices
A lot of resources, design tools, tracking systems and incentive programs have been developed for this class of
retrofits in recent years
Questions ?
Envisioning Restoration
Retrofitting requires:
Sleuthing skills to determine what can work at highly constrained sites
Simultaneously envisioning restoration possibilities and anticipating potential
problems
What would you do here?
Activity
The Retrofit Discovery Process
Source: USRM 3, CWP
Step 1. Retrofit Scoping
• Purpose
– Define a retrofit strategy to meet local restoration objectives
• Key tasks
– Review local stormwater management infrastructure and practices
– Define restoration objectives
– Define preferred retrofit practices and locations
Step 1. Retrofit Scoping
•Consult with stakeholders
•Understand watershed conditions and develop restoration objectives
•Select subwatersheds
•Identify target land usesto treat
Step 2. Desktop Retrofit Analysis
• Purpose
– Rapidly search for and identify potential retrofit sites across the subwatershed
– Save time in the field
• Key tasks
– Secure GIS layers and other mapping data
– Conduct a structured desktop search for retrofit sites
– Prepare base maps for field investigation
Step 2. Desktop AnalysisAnalyze mapping and metrics to find prospective sites
• Aerial photos
• Topography
• Hydrology
• Ownership
• Land cover
• Storm sewers
• Existing BMPs
• Outfalls
• Road
Good Desktop Search Targets
• Publicly owned property
• Institutional property
• Existing stormwater ponds
• Stormwater outfalls
• Large impervious cover with adjacent open land
• Conveyance system intersected with open space
• Where roads cross ditches
• Streets that meet width and slope criteria and include a nearby storm drain.
Step 3. Field InvestigationCharacterize drainage patterns and retrofit potential at each parcel
• Take photos, measurements, notes
• Sketch retrofit and drainage area.
Look at Existing Stormwater Infrastructure & Feasibility Factors
Understand the Plumbing at the Site
Rooftop Connections
Follow the Runoff
Weep Hole Drainage Chute
Eroded Conveyance Grass Channel
Storm Drain
Pipe Invert
Available Hydraulic Head
Detention Areas
2-year
10-year100-year
Storm drain Storm drain Manholes
Curb Drop Inlet
GAS
Sanitary Sewer
Utilities!Cable
Water line
Stream Impacts
Our friend the beaver….
Forest Buffers
Trees in general
High quality wetlands Low quality wetlands
Soil Indicators
Soil Depth
Saturated Soils
Compacted Soils
Develop Conceptual DesignDevelop conceptual designs
Step 4. Compile Retrofit Inventory
Retrofit Inventory CompilationUpdate parcel-based database with field data
• Input into master database –spreadsheet or similar format
Step 5. Evaluation and Ranking
• Consult with stakeholders
• Use ranking factors based on predetermined subwatershed objectives
• Assign weights to ranking factors
• Develop system to assign scores to individual sites
• Create a prioritized list
Step 6. Subwatershed Analysis
Step 7. Final Design and Construction
• More realistic
construction costs
come to light
• Convert concept to a
construction drawing
• Requires site analysis
and construction plan
Step 8. Inspection, Maintenance and Verification
Questions ?
Initial Verification of Retrofit Installation
• Localities to verify that retrofits:– Installed properly– Meets/exceeds design
standards– Functions hydrologically as
designed
• Initial verification should be provided by the designer or inspector as condition of project completion
Retrofit Verification
• CBP emphasizing verification of BMPs installed for the TMDL
• The Retrofit Removal Rate is not perpetual
• Good for 10 years, and can be renewed based on field inspections (5 years for on-site LID retrofits)
• Use of simple visual indicators
Performance Verification
Ensure BMP still exists and is providing the
pollutant removal it was designed to achieve or if
it requires major restoration
MS-4 Permit/Bay TMDL
Once every 9 -10 years
Trained evaluator
Facility BMP
Inventory
State BMP
Reporting for Bay TMDL
73
Retrofit Tracking
Tom’s Short Cut Method
• Evaluate the condition of your legacy stormwater ponds to optimize the nutrient reduction, safety and habitat value of your existing stormwater infrastructure
Retrofit Evaluation
• Defining Retrofit Pollutant Removal
• Evaluating Retrofit Cost
– Individual Retrofits
– Administering a Local Retrofit Program
Retrofit Removal Rates
BMP removal rates are a function of runoff depth captured and the amount ofstormwater treatment (ST) or runoff reduction (RR) achieved by the practice
Classification of BMPsRunoff Reduction Practices
(RR)
Stormwater
Treatment Practices
(ST)
Bioretention Constructed Wetlands
Dry Swale Filtering Practices
Infiltration Wet Swale
Permeable PavementWet Ponds
Green Roof
All practices sorted into 2 categories: Runoff Reduction (RR) &
Stormwater Treatment (ST)
Achieve at least 25% reduction of annual runoff volume
Traditional Practices
Design Examples – New Retrofit Facility Constructed Wetland
• A constructed wetland is built on a federal facility as a retrofit, classified as a ST practice
• The retrofit storage is estimated to be 1.67 acre-feet• Treats runoff from 50 acre residential neighborhood
with 40% impervious cover
Design Examples – New Retrofit Facility Constructed Wetland
• Using the Standard Retrofit Equation:
• RS = Retrofit Storage ≈ 1.67 ac-ft
• IA = Impervious Area = 20 acres
X = (RS x 12) / IA
(1.67 x 12) / 20 = 1.0 inch
TP TN TSS
55% 35% 70%
Design Examples – New Retrofit Facility Constructed Wetland
Pollutant Removal Efficienciesof the practice
Retrofit Example 1 – Constructed Wetland
Total
Nitrogen
Total
Phosphorus
Suspended
Sediment
Pounds/acre/year Tons/acre/year
IMPERV PERV IMPERV PERV IMPERV PERV
MDE
Loading
Rates
10.85 9.43 2.04 0.57 0.46 0.07
Area
(acres)20 ac 30 ac 20 ac 30 ac 20 ac 30 ac
Baseline
Load500 lbs/yr 57.9 lbs/yr 11.3 tons/yr
Removal
Rate35% 55% 66%
Load
Removed175 lbs/yr 31.85 lbs/yr 7.91 tons/yr
* Example using MDE guidance loading rates
Questions ?
The Costs of Retrofitting
Retrofit Construction Costs for Existing BMPs (per impervious acre treated)
BMP Conversions: 5 to 15 K
BMP Enhancements: 5 to 10 K
BMP Restoration: 2 to 5 K
Less excavation, modify plumbing, own or control land, strong neighborhood support
Comparative New Retrofit Construction Costs * (per impervious acre treated)
New Retrofits: 12 to 30 K
Non-residential LID: 40 to 80 K *
Residential LID: 80 to 120 K *
Green Streets: 100 to 150 K *
* Demonstration project phase, should drop
• Enormous variation within each retrofit category depending on site conditions
• These estimates represent the “25% easiest”
• Major influence of the “prototype effect”
Caveats on Retrofit Cost Numbers
1. Discovery Costs2. Project Evaluation Costs 3. Design, Engineering and Permitting4. Contracting5. Construction6. Retrofit Maintenance
Breakdown of Retrofit Costs
• Cost to identify candidate sites for potential retrofits
• Involves desktop GIS analysis and subsequent field investigation
• Two options: 1. Comprehensive subwatershed evaluation 2. Limited assessment of existing BMP
inventory
Discovery Costs
Usually done by consultant, but can be done in house
For a ten square mile subwatershed, plan on:• 200 hours for comp subwatershed eval.• 40 hours for BMP inventory assessment
Discovery Costs
• Cost to: • evaluate project feasibility• develop concept design • compute reductions and
cost • Rule of Thumb: 10 to 20
hours per site• May requires some
engineering review and neighborhood consultation
Project Evaluation Costs
What is Fixed•Wetland permitting•Off-site haul of excavated materials•Sewer or utility relocation•Need easements or contested ROW•Complicated plumbing (flow splitters)•Parking, maintenance of traffic•Amenity landscaping
Take care in the stream corridor !
Retrofit Cost Inflators
• Typically run be 30 to 50% of retrofit construction cost
• High end: “demonstration” projects, refiguring plumbing, unfamiliar practices
• Low end: Conversion, enhancement or restoration of existing BMPs
Design, Engineering and Permitting Costs
Contract Administration Costs
• Assume that 1 FTE is needed for every 1 to 2 million contracted in retrofit capital budget
• Project bundling, design/build, call contracts, bid incentives and other project management tools can reduce costs and improve quality
Tip 1. Develop multiple revenue streams and delivery mechanisms
• Capital Improvement Budget
• Stormwater Offset Fees
• Stormwater Utility Discounts
• Stormwater Maintenance Budgets
• Maintenance Enforcement
• Street Reconstruction
• Piggyback on Municipal Construction Projects
• Public/Private Partnerships
Another slice of restoration
A slice of restoration
Frequently Asked Questions
Q: Are Regenerative Stormwater Conveyance practices considered retrofits?
• Yes! Dry RSC practices can be treated as an upland BMP or as a retrofit for treating stormwater runoff
• Use the “RR” curve for determining removal rates
• Wet channel RSC practices are considered to be a stream restoration practice
Cabin Branch RSC project
Q: What about a Floating Treatment Wetland in an existing Wet Pond?
• Good question!
• Currently the focus of a CBP Urban BMP Review Panel
Floating Treatment WetlandPhoto credit: Sarah White, Clemson University
Q: What happens if my project has a mix of runoff reduction and stormwater treatment
practices ?
Answer: Use the curve associated with the practices that provide a majority of the runoff capture or storage volume for the site as a whole
For example, Site C has RR practices providing 60% of the runoff capture volume and ST practices provide the rest. Use the RR curve
Q: I have trouble reading the curves…can you provide the actual equations for them so I can plug them into a spreadsheet and calculate the removal
rates directly?
• A brilliant idea! While they are shown here, they are also in the FAQ document.
TPRR y = 0.0304x5 - 0.2619x4 + 0.9161x3 - 1.6837x2 + 1.7072x - 0.0091
ST y = 0.0239x5 - 0.2058x4 + 0.7198x3 - 1.3229x2 + 1.3414x - 0.0072
TNRR y = 0.0308x5 - 0.2562x4 + 0.8634x3 - 1.5285x2 + 1.501x - 0.013
ST y = 0.0152x5 - 0.131x4 + 0.4581x3 - 0.8418x2 + 0.8536x - 0.0046
TSSRR y = 0.0326x5 - 0.2806x4 + 0.9816x3 - 1.8039x2 + 1.8292x - 0.0098
ST y = 0.0304x5 - 0.2619x4 + 0.9161x3 - 1.6837x2 + 1.7072x - 0.0091
Q: What if I want to use a retrofit practice that is does not fall into the current retrofit
classification ?
• Good question!
• Two possibilities:– Determined by future
expert panels based on the priority assigned by the USWG
– Practice can be mapped into existing urban BMP credit
CMAC Outfall RetrofitPhoto credit: Marcus Quigley, OptiRTC
Prerequisites
• Cannot be a proprietary practice
• Represents a real change on the ground that occurs in the present day (e.g., no historic BMP finds)
• Have verification procedures that are as stringent or more stringent than their “parent” BMP
Process
• Proposer provides supporting documentation for consideration by USWG
• USWG can accept, accept w/ modification, reject or require a full blown expert panel
• States can individually opt out if they are not comfortable with the technical basis for the decision, reporting requirements and/or verification protocols
• Modelers will be consulted prior to any decision
Other CBP-Approved Urban BMPs to Meet the Bay Pollution Diet
1. New State Performance Standards
2. Redevelopment Credits
3. Residential Stewardship Practices
4. Urban Nutrient Management
5. Stream Restoration
6. Enhanced Erosion and Sediment Control
7. Illicit Discharge Removal
8. Street and Storm Drain Cleaning
9. Shoreline Management
10. Septic System Upgrades
11. FTWs and UTC (this summer)
Resources
• U-1 Urban Stormwater Retrofits Fact Sheet
• USRM 3: Urban Stormwater Retrofit Practices
• CWP Stormwater Retrofitting Reconnaissance Videos:
– Part 1: https://youtu.be/tHvuzReiDHQ
– Part 2: https://youtu.be/Q-9j2RgLW3I
– Part 3: https://youtu.be/vmjyskDxzuU
• Retrofit Expert Panel Report
• Retrofit FAQ Document
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