LID Case Studies

“Complete restoration efforts for an additional 20 percent of the County's impervious, urban surfaces not currently restored to the maximum extent practicable”

4,300 acres

Montgomery County MS4 Program Management – Massive investments, accelerated schedule • $320 million CIP

• 4 years to implement

• Low Impact Development

• Stormwater infrastructure retrofits

• Stream restoration

• Dashboard – BI/DV to track

progress

2

Seattle’s Integrated Plan Jeff Herr, PE, D.WRE, Brown and Caldwell

Puget Sound, Duwamish Waterway, Lake Washington, Lake Union, Ship Canal, creeks

Stormwater

from MS4

Outfalls

Stormwater from

combined system

and POTW

Combined

Sewer

Overflows

Sewage from

combined system

and POTW

584,000 Kg TSS/Year

174,000 Kg TSS/Year

514,000 Kg TSS/Year

Annual Total Suspended Solids (TSS) to Receiving Waters

Stormwater is major source of pollutant

loading to local water bodies

5,560,000 Kg TSS/Year

• Extended detention basin

• Drain inlet inserts (2 types)

• Infiltration basin and trench

• Oil / Water separator

• Media filters (3 types)

• MCTT

• Vegetated controls

• Wet Extended Detention Basin

• CDS

CalTrans BMP Retrofit Pilot Program

Brown and Caldwell 5

The study evaluated 37 BMPs at 33 sites with 12 types of technology.

Approved Treatment BMPs

Brown and Caldwell 6

1. Biofiltration: Strips/ Swales

2. Infiltration Devices

3. Detention Devices

4. Traction Sand Traps

5. Dry Weather Flow Diversion

6. Media Filters

7. Multi-Chambered Treatment Trains

8. Wet Basins

9. Gross Solids Removal Devices (GSRDs)

Brown and Caldwell 7

Biofiltration Strips and Swales

Infiltration Basins and Trenches

Brown and Caldwell 9

Brown and Caldwell 11

Brown and Caldwell 13

Pilot Studies

Brown and Caldwell 15

BMP Consideration – in ROW

Brown and Caldwell 17

City of Portland Green Streets GI Design and Construction

Brown and Caldwell 18

• Large-scale application of GI/Low Impact Development (LID)

Partnered to achieve their goal to be a top-tier sustainable city:

• Opportunistic

• Aesthetic improvement/ economic revitalization

• Flooding relief

• Standard GI details

• Partnering and outreach

• Data tracking and technical analysis

• Development on-site volume reduction required

City of Atlanta

Metro Atlanta (Roswell, GA)

Developed lessons learned from program to reduce impervious area:

• Permeable paver installations on public streets

• Working with mature trees close to the roadway, utilities, soft soil conditions

• Supporting with Public Outreach

21

Stormwater Credits in Roswell How do the Credits Work?

Brown and Caldwell 22

Property owners and developers may purchase stormwater credits to meet some or all of their stormwater treatment requirements. Aesthetic improvement/revitalization

• A credit is a unit of stormwater treatment that can purchased to partially or fully meet the WQ treatment required for site development

• Credit units are sold by impervious acre treated

• Credit costs are determined by fair market value of similar on-site treatments or by the full project cost borne by City

• Credit costs will vary by location and stormwater facility

• Credits are available on a first come/first serve basis

• The City tracks available credits per facility, what has sold, and what is available

Permeable Paver Transition Critical

Brown and Caldwell 23

Paver aggregate specifications (strength and durability) also critical.

Underground utilities and existing soils and groundwater.

Worked on their Green Streets Program, our focus included:

• Flexibility in Standard Details

• Site Specific Designs to Match Surface Features

City of Portland

Brown and Caldwell 24

Oregon City

Developed their BMP Design Standards, which included:

• O&M Plan

• What to look for

• What to do

• Implementation schedule

Helped city address BMP implementation challenges by developing:

• 3rd Party Property Management Model

• One-stop shopping for large regional sites

• Vegetative and non-vegetative

• Inspection and testing

• Community engagement

• Approx. $1/sq. ft of surface area

City of Cleveland

Develop with the City a BMP design to eliminate SSOs and remove storm drainage from sanitary laterals • Create linear bioswale in sidewalk median

• Capture roof and area drainage in bioswale

• Enhance neighborhoods and improve ROW drainage

City of Columbus, OH

City of Boston

Developed a screening process including non-cost factors to: • Achieve 65% of TP reduction in Charles River

• Cost effective, large–scale urban retrofits

• Maximize TBL

Columbus, OH

Issue

• Eliminate SSOs

• Remove storm drainage from

sanitary laterals

Opportunity

• Create linear bioswale in

sidewalk median

• Capture roof and area

drainage in bioswale

• Enhance neighborhoods and

improve ROW drainage

Boston, MA

Issue

• TMDL - 65% TP reduction in Charles River

• Cost effective, large–scale urban retrofits

• Maximize TBL

Opportunity

• Screen alternatives

• Non-Cost factors such as O&M requirements

Improve Treatment Through BMP Maintenance and Expansion - Lake Claiborne Restoration

Removed 40,000 cy sediment;

restored original volumes.

Increased flood storage/WQ benefit.

Stream restoration.

Constructed 2 off-line treatment

ponds for future sediment capture.

31

DWR Main Facility

• County Property

• Public Access/Education Opportunity

• Training for Developers

• Long Term Monitoring

Gwinnett County Opportunities Demonstration Projects

33

Stream Restoration and GSI Stormwater Retrofit

Pre and Post Comparison

Brown and Caldwell 34

Pre-project

Pre-project

Post-project

Post-project

Brown and Caldwell 35

Design and Construction – Bankston Creek • In-stream structures • J-hook

• Compound cross-vane

• Root wad

• Wetland and stormwater outfall channel

• Bank grading

• Low-flow benches

• Seating area and path

AWRA | November 3, 2010

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