webcast 3: seeking, designing, and implementing stormwater
TRANSCRIPT
Webcast 3: Seeking, Designing, andImplementing Stormwater Retrofits
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Welcome to the Webcast• To Complete the Webcast Survey – After the webcast, we
will have a short multiple choice survey to get feedback on your experience. Please take a few minutes to fill the survey out so we can identify areas for improvement.
• Continuing Education Credits – We are offering CEUs for our watershed and stormwater management webcast series. A total of 1.0 CEU can be earned for attending five webcasts. Only the registered attendee is eligible to earn the CEU. The registered attendee must watch the entire webcast. Email [email protected] if you are interested in earning CEUs and did not indicate this during the registration process. Two PDUs are also available for certified professionals (CPESC, CPSWQ) for this webcast.
• Resources – After the webcast, we will email a resources sheet, speaker contact information, and the presentation.
Upcoming Webcasts
• Urban Watershed Forestry
November 18, 2009, 12:00 – 2:00 PM EST
• Erosion and Sediment Control
December 15, 2009, 12:00 – 2:00 PM EST
• Register at http://www.cwp.org/Webcasts
Webcast Outline• The Basics of Retrofitting• Case Studies
– Developer wants to retrofit – Fredericksburg, VA– City wants to retrofit – Weymouth, MA– County has to retrofit – Montgomery County, MD
• Retrofit Accounting• Summary• CEUs, Certificates, Evaluations
Webcast Team
Doug Beisch, Williamsburg Environmental Group
Steve Shofar, Montgomery County, MD
Rich Claytor, Horsley Witten Group
David Hirschman, CWP
Manual 3: Urban Stormwater Retrofit Practices
• Key resource for stormwater retrofitting
• Information on:– Retrofit locations– Stormwater retrofit practices
• Pollutant removal performance• Cost
– Retrofit processwww.cwp.org/postconstruction
EPA Webcasts on Retrofitting: http://cfpub2.epa.gov/npdes/outreach.cfm?program_id=0&otype=1
What Are Stormwater Retrofits?• Stormwater retrofitsare stormwater management practices in locations where stormwater controls did not previously exist or were ineffective
Rolling Stone Retrofit Montgomery Co., MD
Levels of Complexity
The Importance of Scale
Retrofit Accounting
•Cost
•Pollutant Load Reductions
Case Study #1
Developer wants to do “incentive”retrofitting
Doug BeischWilliamsburg Environmental Group
Project Information provided courtesy of Silver Companies (Developer)
Central Park Commercial Development Retrofit Program
• Allow for infill development/redevelopment within existing retail complex
• Developer‐driven ‐ Coordinated with City and FOR
• 300+ acre Commercial/Retail Complex• > 40 Retrofit Candidate Sites• Small Scale Retrofitting(<2 ac drainage area)• Voluntary program to facilitate additional infill development in retail complex
Retrofit Planning• Initial Retrofit Screening Developed
• Walkover Level
• Prioritization Matrix
• Photo‐documentation/Mapping
• Short List of Practices identified for implementation
Retrofit ImplementationRetrofit Implementation
•• Schematic Designs Schematic Designs DevelopedDeveloped
•• City Approval Received City Approval Received for eachfor each
•• Retrofit projects Retrofit projects associated with infill associated with infill development (typical 2development (typical 2‐‐3 retrofits per new 3 retrofits per new development)development)
•• Field coordination with Field coordination with contractor contractor
Types of Retrofits• Commercial Area treated by wet ponds and constructed wetlands– Bioretention/”Rain Gardens”
– Amended Soils/Filter Strips
– Engineered Swale Systems
– Forebay Improvements/Pre‐treatment
Important Field Coordination Milestones
• Stakeout
• Rough Grading
• Underdrain/Gravel Sump Installation
• Final Grading
• Landscaping and Stabilization
• Post‐Construction Follow‐up
Bioretention and Engineered Swales
Small Rain Garden
Amended Soils/Filter Strip
Forebays/Pretreatment Measures
Challenges Encountered• Design Challenges
• Utilities !!!!
• Contractor Education– Function of Facilities
– Field Modifications
– Proper Materials Handling/Installation
• Soil Testing
• Long‐Term Maintenance/Upkeep
Retrofit Cost Data
• Bioretention Retrofits– $30+/s.f. of bioretention surface area
– Costs higher than for new construction
– No Economy of Scale
– Different Contractors for Different Facilities
• Overall– Approximately 7 ac IC retrofitted
– Estimated total cost $300,000 ($40K + per impervious acre treated)
Lessons Learned1. Cast a wide net on inventory opportunities2. Flexible approaches that allow for field
modifications are essential for cost‐effective small‐scale retrofits
3. Educate Contractor/Owners on all aspects of design, implementation and maintenance
4. Strong soil testing, quality control and quality assurance needed
5. Follow‐up and adjust after “establishment period”
Q&A
Case Study #2
City wants to retrofit for habitat improvement
Rich ClaytorHorsley Witten Group
Herring River RetrofitWeymouth, Massachusetts
• Herring Brook ‐ Fisheries
• Ultra Urban Watershed
• Watershed Assessment
• Retrofit Assessment
• Innovative Design
Herring Brook
Whitman’s Pond
Weymouth, MA
Herring Brook Watershed• 550‐acres of urbanized area• Herring Run via fish ladders and resting pools to spawn in Whitman’s Pond
• Lower portion of Brook used for smelt spawning
• Div. of Marine Fisheries has identified brook as impacted due to excessive sediment loading
• Downstream shellfish beds
• Limited space
• Closed drainage system
• Large amount of impervious area draining to each outfall
Urban Watershed Retrofit Challenges
Herring Brook
Whitman’s Pond
Watershed Assessment
Drainage Area = 24; 42% ImperviousDrainage Area = 24; 42% Impervious
Municipal Parking Lot• Design Challenges
– 24 acre Drainage Area (10.1 Imp. Acres, 42%I)
– Soil test pits reveal layers of peat;
– Original concept of infiltration not appropriate;
– Public Parking lot serving local businesses, every space a premium;
– Design incorporates gravel wetland design in linear chambers in the existing parking lot islands
Project Elements• Utilize the existing islands for gravel wetlands
– Sized to treat 0.5 inches of runoff;
– Flow diversion of upland drainage area;
– Up‐flow filter with wetland plants (sedges/rushes);
– High pollutant removal;
– No standing water;
– Limited space required – no loss of parking spaces;
– Highly visible for maintenance.
BypassBypass
Diversion Diversion ManholeManhole
Diversion Diversion ManholeManhole
BypassBypass
Diversion Manhole
Septic Tank
Gravel Wetland Chambers
Gravel Wetland Site Plan
Gravel Wetland Details
ExamplesExamples
Design and Operations• Design:
– Gravel Wetland sized to store (in permanent pool and above) 50% of WQv, with minimum surface area = .35% of Drainage Area;
– Off‐line septic tank for pre‐treatment sized for 25% of WQv;
– Diversion MH’s sized to divert WQv peak flows, bypass larger storms.
• Maintenance– Vactor pretreatment unit annually (preferably after spring‐melt);
– Landscape maintenance of wetland (replacement plantings/pruning/etc);
– Vactor “muck” from wetland annually, through cleanouts.
Project Cost and Other Considerations
• Capital Construction Cost ~ $425,000 ($42,000/impervious acre)
• Concerns– Landscaping/trees impacted;
– Lost parking during construction;
– Aesthetics and long‐term maintenance.
Lessons Learned1. The first retrofit alternative is not always the best
2. Use of public property often involves multiple interests
3. Ultra urban landscapes require innovative alternatives (don’t be afraid to think out of the box)
4. New practices/approaches are viewed with great skepticism (show me where this has been done before)
Q&A
Case Study #3
County HAS to retrofit as condition of MS4 permit
Steven ShofarMontgomery County, MD
Watershed Management DivisionWatershed Restoration Program
Montgomery County’s Stream Restoration Program
• Program began in 1991
• Focused on stream restoration and stormwater retrofit (including new facilities)
• 17 miles of stream restoration
• 33 retrofit projects with a total drainage area of approximately 4,000 Acres and an impervious area of approximately 1,000 Acres.
• Total cost approximately $24 million.
NPDES MS‐4 Permit Requirements• New permit requires providing SWM control for 20% of the uncontrolled impervious area in the County (~5,200 impervious acres) to the maximum extent practicable (MEP).
• Make progress toward meeting TMDLs• Meet Potomac Trash Treaty commitments• Use Environmental Site Design (ESD) / Low Impact Development (LID) techniques to the Maximum Extent Practicable (MEP)
Watershed StudiesWatershed Studies•• DEP has watershed DEP has watershed studies that identify studies that identify >300 potential retrofit >300 potential retrofit projects projects
•• Projects are ranked Projects are ranked within evaluated within evaluated subwatershedssubwatersheds
•• Developing inventories Developing inventories of LID retrofits for public of LID retrofits for public property (roads, property (roads, schools, libraries, etc)schools, libraries, etc)
Types of Retrofits• Construction of new ponds
• Retrofitting of existing ponds
• Create Pocket Wetlands at Storm Drain Outfalls
• Retrofit with LID
• Retrofit using conventional stormwater devices (sandfilters, underground storage, etc.)
Construction of New Stormwater PondsConstruction of New Stormwater Ponds
Piping Rock Drive Pond Piping Rock Drive Pond -- Good Hope Good Hope Tributary of Paint BranchTributary of Paint Branch
Retrofit of Peppertree SWM Pond• Modify control structure to improve control
• Remove concrete channels and extend flow path
• Create wetland habitat
Peachwood II SWM RetrofitPeachwood II SWM Retrofit
•• Retrofit of pond to improve quantity controlRetrofit of pond to improve quantity control•• Install berm to increase flow path and improve Install berm to increase flow path and improve pollutant removalpollutant removal
Before AfterPaint Branch WatershedPaint Branch Watershed
Intercept Storm Drains Before Storm Drain Intercept Storm Drains Before Storm Drain Outfall DischargesOutfall Discharges
to improve stormwater controlto improve stormwater controland create new wetlands habitatand create new wetlands habitat
Sligo Creek Parkway at Forest Glen RoadSligo Creek Parkway at Forest Glen Road Sligo Creek Parkway at the BeltwaySligo Creek Parkway at the Beltway
Sligo Recreation Center• Added bioretention to existing building & parking lot
Paint Branch Road Retrofit• Conversion of road ditches to bioretention
Challenges Encountered• Putting 10 pounds in a 5 pound bag• Citizen Concerns
– Flooding concerns– Tree removal– Aesthetics of retrofitted pond– Concerns about mosquitoes & snakes– Construction noise and dust
• Existing utilities• Permitting• Changing regulatory climate• Interagency coordination
Costs for Stream Protection in Developed Urban/Suburban Watersheds
• Stormwater Management Retrofits Cost– $1,000 ‐ $4,000 / drainage acre to retrofit existing pond
– $4,000 ‐ $6,000 /drainage acre for a new pond
– $12,000 / per impervious acre treated
• LID Costs– $100,000 ‐ $200,000 per impervious acre treated
Stormwater Fee Water Quality Protection Charge
• Current rate $45.50. Approximately $8,500,000
• Funds stormwater facility inspection and maintenance, water quality monitoring, Rainscapes, and part of CIP program.
• Evaluating new incentives to promote installation of stormwater facilities on residential and commercial property.
Lessons Learned1. Anticipate and address permitting issues early in
the project design2. Prioritize projects to mitigate the greatest damage3. Evaluate benefits vs environmental impacts (this
requires involving ecologists in the project goals and concept)
4. Solicit community support5. Don’t give up on a project because you hit a
problem, but know when the problems are insurmountable and be prepared to kill the project
MS4 Bean Counting• Working with consultant to prepare implementation plans for MS4
• Developing method to track progress using CWP Watershed Treatment Model
• Tracking TMDL progress and retrofit progress
Q&A
Retrofit Accounting
Measuring retrofit benefits at the site and watershed scales
I need to know the costs AND benefits
of your retrofit
Important Metrics• Pollutant removal & runoff reduction• Cost• Community values
– Drainage– Outreach & Education– Habitat– Recreation/Open Space– Tree Canopy– Trash Reduction– Community Spaces
Benefits: How Much Treatment?90th percentile rainfall event (water quality goal)
1.2” in Washington D.C.
1.0” in Columbus, OH
0.6” in Salt Lake City, UT
1.3” in Los Angeles, CA
(Table 1.4 in Manual 3)
Depth of 1‐year, 24‐hour storm (resource protection goal)2.6” in Washington, D.C.
2.2” in Columbus, OH
1.1” in Salt Lake City, UT
1.6” in Seattle, WA
(Table C.3, Appendix C, Manual 3)
Channel protection storm
Costs!!!
Which Retrofits Will Survive the Budget Axe?
Retrofit Costs(Manual 3, Figure 1.10 & Appendix E)
Retrofit Costs(Manual 3, Figure 1.10 & Appendix E)
Ponds = $3/cf
Infiltration = $15/cf
Small Bioretention = $30/cf
Intensive Green Roof = $360/cf
Combine Cost, Runoff Reduction, Pollutant Removal
• Cost per cubic foot reduced
• Cost per pound treated (e.g., TSS, TP, TN)
Retrofit Spreadsheet12345678910111213141516171819
A B C D E FPROJECT NAME
DATEDESIGNER/USER
Practice #1 Practice #2 Practice #3 TotalBioretention Filtering Practice Rooftop Disconnection
70131 20037 1089070131 20037 10890 101058
100 100 1001.0 1.0 1.0
5552 1586 862 80005333 1667 920 7,92096% 105% 107%40% 0% 25%55% 60% 25%64% 30% 25%70% 60% 60%
$10.50 $20.00 $1.00$0.80 $1.66 $0.08 $38,904
$55,997 $33,340 $920 $90,257
Runoff Reduction (%)Total TP Reduction (%)Total TN Reduction (%)
Total TSS Reduction (%)Unit Cost ($/cubic foot)
Cost per Impervious AcreCost Estimate
Percent Provided/Needed
Site Parameters
Impervious Cover of CDA (sq. ft.)Impervious Percent of Combined Treatment Areas (whole #)
Storage (Water Quality) Volume Provided (cubic feet)
Contributing Drainage Area (CDA) (sq. ft.)Type of Practice
Storage (Water Quality) Volume "Needed" (cubic feet)Target Rainfall Depth for Capture & Treatment (inches)
Retrofit To‐Do List• DO a front‐end desktop and field survey for candidate projects & create a priority list
• DO use retrofits as opportunity to educate stakeholders & gain community support
• DO provide flexibility & quality control in the field & be diligent about utilities
• DO account for costs and benefits
• DO have fun
Resources• Manual 3: Urban Stormwater Retrofit Practices ‐ Detailed guidance on
how to effectively retrofit urbanized subwatershedshttp://www.cwp.org/postconstruction
• EPA Webcast: The Art and Science of Stormwater Retrofitting (presented by CWP), April, 2008 (scroll down to “Training Resources, Archived Webcasts” – Post Construction). http://cfpub2.epa.gov/npdes/outreach.cfm?program_id=0&otype=1
• Other Resources on the downloadable Resources Page
Post Webcast Information• To Complete the Webcast Survey – We will be providing you with
a short multiple choice survey to get feedback on your experience. Please take a few minutes to fill the survey out so we can identify areas for improvement.
• Continuing Education Credits – We are offering CEUs for our watershed and stormwater management webcast series. A total of 1.0 CEU can be earned for attending five webcasts. Only the registered attendee is eligible to earn the CEU. The registered attendee must watch the entire webcast. Email [email protected] you are interested in earning CEUs and did not indicate this during the registration process. Two PDUs are also available for certified professionals (CPESC, CPSWQ) for this webcast.
• Participation Certificate – Participation certificates are also available. If you have multiple attendees, please save the certificate to your computer. You can type the attendees name inthe name field and then print the certificate.
Webcast Archive• We will make every effort to post the archive as quickly as possible. The archive should be available on the first Monday following the webcast, pending any edits.
• Registered participants will receive email instructions for accessing the archived webcast.
• The archive will be downloadable and can be saved on your local machine.
Next Webcast
• Urban Watershed Forestry
November 18, 2009, 12:00 – 2:00 PM EDT
• $99
• Register at http://www.cwp.org/Webcasts
Upcoming Webcasts
• Erosion and Sediment Control
December 15, 2009, 12:00 – 2:00 PM EST
• Register at http://www.cwp.org/Webcasts
Speaker Contact InfoDoug Beisch, P.E.Program Manager – Water ResourcesWilliamsburg Environmental Group, [email protected] Center Street Williamsburg, VA 23188757-220-6869www.wegnet.com
Richard A. Claytor, Jr., [email protected] Witten Group90 Route 6A, Sandwich, MA 02563508-833-6600www.horsleywitten.com
Steven ShofarDivision Chief, Watershed Management DivisionMontgomery County Department of Environmental [email protected]://www.montgomerycountymd.gov/dep
David J. HirschmanProgram DirectorCenter for Watershed Protection, [email protected]
Webcast 3: Seeking, Designing, andImplementing Stormwater Retrofits