Stormwater Water Quality Treatment Options

Alvin Shoblom, P.E.Hydraulics Engineer

Options

Low Impact Development (LIDs) Engineered

Low Impact Development (LIDs)

Definition:

LID is the concept of designing projects to minimize the effect of natural hydrology and water quality.

This is primarily accomplished by minimizing impervious surface area and providing opportunities for filtration of stormwater by vegetation and infiltration into the soil.

For highway projects, LID refers to the treatment of highway runoff within the linear highway right of way using techniques and facilities that generally require minimal hydraulic engineering.

LID Options

Minimizing impervious area Preserving or restoring adjacent roadside

landscaping Mimicking natural drainage patterns (e.g. using

sheet flow, dispersion, infiltration, and existing open channels)

Incorporating/retrofitting vegetated shoulders and drainage channels with soil amendments

Soil Amendment

Example of maintaining existing vegetated shoulder (sheet flow)

Engineered Treatment Facilities

Stormwater Ponds Biofiltration Swales Filter Strips Bioslopes Proprietary Structures

Bioretention Pond

Bioretention Pond

Bioretention Pond

Bioretention Pond Sizing Example

Given: Salem Oregon Project Contributing ODOT impervious area (CIA) for

project is 1 acre

Determine: Water Quality Design Storm to size the pond.

The design storm is a percentage of the 2-year, 24 hour event for the project site.

Bioretention Pond Sizing Example (Cont.)

Results: Volume calculated is 3755 cubic feet using

an appropriate hydrology method. Therefore, the volume in the pond would

need to be 3755 cubic feet or greater.

Bioretention Pond

Biofiltration Swale

(with soil amendment)

Biofiltration Swale

Filter

Strip

Filter Strip

Bioslope

Bioslope

Downstream Defender

(Separation unit)

Stormwater Management Stormfilter

(Filtration unit)

Treatment Solution SelectionFor project with identified water

Issues and treatment goals

Incorporate LID techniques suchas soil amendments, impervious

surface reduction, preservingor restoring adjacent roadway landscaping

Submit hydraulic Design Deviation for other BMP

not listed in WaterQuality Guidance/Tech Bulletin with supporting

documentation

Select appropriatetreatment based on:

• BMP removal capabilities• Constructability• Cost and maintenance• Site constraints (steep Slopes, high groundwater, Bedrock, etc)

Go to StormwaterManagement Tech

Bulletin and attachedWater Quality Guidance

Sufficient LIDs Incorporated?

Water Quality SelectionComplete

YN

BMP selected from Recommended listFrom Water Quality

Guidance/Tech Bulletin?

N

Y

LIDs and/or EngineeredTreatment option used

To meet treatmentgoals

Sufficient design?

Y

Re-Submit deviation for for other BMP

not listed in WaterQuality Guidance/Tech Bulletin with supporting

documentationN

Design Guidance

Stormwater Management Program Technical Bulletin Provides Selection and Design Guidance Technical Bulletin #GE09-02B Available online

Hydraulic Design Deviation Requests Directive Process for design not adhering to ODOT guidance Directive #TSB08-01(D) Available online