Larry Coffman, President Stormwater Services, LLLP lcoffman ...

Larry Coffman, President
Stormwater Services, LLLP
lcoffman@filterra.com
301-580-6631

The first Rain Garden in Virginia, located in a turning
circle in front of St. Stephens School, Alexandria.

St. Stephens Rain Garden- 5 years later.

What is Bioretention?
Filtering and/or infiltrating stormwater runoff through a terrestrial
aerobic (upland) plant / soil / microbe complex to remove
pollutants through a variety of physical, chemical and biological
processes.
The word “Bioretention” was derived as a technical term to
describe the process of the “biomass” (plant / microbe complex)
“retaining” pollutants of concern such as N, P and heavy metals.
The term “Rain Garden”
“Rain Garden” was derived to market Bioretention to
the general public.

“CULTIVATING
HARMONY IN A
THEMED
GARDEN”

Rain Gardens in OR

Rain Gardens in Australia

Rain Gardens in S. CA

Rain Gardens in FL

Rain Gardens in Auckland, NZ

Rain Gardens in Bose, ID

Rain Gardens in WI

Rain Gardens in MA

Rain Gardens in MN

Rain Gardens in MD

Village Homes
Davis, CA

1992 Somerset, Maryland - Rain Gardens
First Residential Application

2008 Somerset, Maryland - Rain Gardens

1992 Somerset, Maryland - Rain Gardens
First Residential Application

2008 Somerset, Maryland - Rain Gardens

• Education
Responsibility
Function
O & M
• Enforcement
Easements
HOA
Community Standards
• Economics
Property Values
Added Value
Ease of Maintenance

Bioretention Advantages
• Universally applicable
• Economically sustainable
– Lower construction, maintenance & operation costs
• Ecologically sustainable
• Multiple benefits
– Water Quality
– Water Quantity
– Air, Energy, Heat Island, Carbon Sequestration …
• Added value (nature sells!)
• Encourages public stewardship

THE BIORETENTION CONCEPT
Original Design P.G County 1993

What were the drivers for change?
• Problems with ponds (performance and
liabilities).
• Maintenance / inspection of private onsite
systems.
• Costs of growing infrastructure.
• Urban retrofit.
• Restoring ecological integrity of receiving
waters.

Limitations
• Safety / Health
Maintenance
• Inspection / Maintenance
• Inefficient Pollutant Removal
• Temp / Sediment / Frequency /
Volume
Pond Liabilities
Safety

Number in 90 Meter Station
60
50
40
30
20
10
0
16
39
29
20 20
11
10
5
7
20
11
31
19
28
Good Hope Tributary To Paint Branch
15
43
13
10
7
Population Estimates
Adults YOY
28
13 13
17
20
11
15
9
19
10
51
27
22 22
17
16
28
27
34
21
17
15
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
Year of Survey
22
5
14
8
15
4
11
4
0

45
40
35
30
25
20
15
10
5
0
B-IBI w/BMPs B-IBI w/o BMPs
0 10 20 30 40 50 60 70
Watershed Urbanization (%TIA)
Figure 2: Showing the lack of mitigating influence of
structural BMPs on biologic conditions in Puget Sound
lowland streams (Horner and May, 2000).

Maintenance Burdens

Issues
• Outdated / Inflexible Regulations & Design
Guidance
• Construction Inspection / Enforcement

THE BIORETENTION CONCEPT
Original Design P.G County 1993

X
2’
Under Drain
Bioretention
Shallow Ponding - 4” to 6”
• Mulch 3”
• Soil Depth 2’ - 2.5’
• Sandy Top Soil
• 65% Sand
• 20% Sandy Loam
• 15% Compost
• Under Drain System
• Plants

New York State
Stormwater Management Design Manual
April, 2008
Examples of Outdated
Information

Why shouldn’t there be a preference for
better performing technology?

Bioretention Pollutant Removal
University of Maryland
Box Experiments
Cumulative
Depth
Phos-
(ft) Copper Lead Zinc phorus TKN Ammonia Nitrate
Removal Efficiency (%)
1 90 93 87 0 37 54 -97
2 93 99 98 73 60 86 -194
3 93 99 99 81 68 79 23
Field 97 96 95 65 52 92 16
Dr. Allen Davis, University of Maryland

Stage 1. Capture
Pollutant Removal Mechanisms
“Physical Physical / Chemical / Biological”
Processes
Sedimentation
Filtration
Adsorption
Absorption
Cation Exchange Capacity
Stage 2. Sequester
Microbial Action (aerobic / anaerobic)
decomposition / nitrification /
denitrification
Evaporation / Volatilization
Cycling Nutrients / Carbon / Metals
Biomass Retention (Microbes / Plant)
System Components
Storage
Mulch
Media
Surface Area
Organics
Microbes
Plants

Pollutant Removal - Plant Microbe
• Phytoremediation
– Translocate
– Accumulate
– Metabolize
– Volatilize
– Detoxify
–Degrade
• Exudates
• Bioremediation
• Soils
– Capture / Immobilize
Pollutants

Burnsville, MN
Rainwater Gardens
• Urban Retrofit
• 90% Runoff Reduction
• 85% Participation
For more information, contact
Barr Engineering Company,
4700 W. 77th St., Suite 200,
Minneapolis, MN 55435,
(952)832-2600 or (800)632-
BARR or Fax (952)832-2601.

Interesting Study Findings
• Mulch and Metals
• Plants and Metals
•P Uptake
• Capacity / Longevity
• Time For Reactions (Residence Time)
• Oil and Grease 95% Removal
• 90% Bacteria Removal

Don’t use filter fabric use a bridging stone (pea gravel)
No Need for stone diaphragm!

Pretreatment doesn’t extend the life of the system.
The issue is to ensure proper maintenance!

Criteria severely restrict the use of bioretention.
Flexibility is key!

Division Street Planters

Buckman Heights courtyard with infiltration garden

• Depth should vary based on type of plants, target
pollutants, site constraints, etc.
• Generally 2 to 2.5 feet.

No soils are the same!

Sizing should be based on actual “K” factors

City of Portland , OR
Low Flow – 0.5” to 1” / Hour
“Soaker”
Sand / Municipal Compost
Ocean City, MD
High Flow - + 100”-120 ” / Hour
Filterra
Corse Sand / Peat

Low Flow Media
2 to 10 inches / hour
Peat / Sand / Aggregate Matrix - PSD
Peat 15 to 20% by volume
Clay

High Flow Media
10 to 50 inches / hour
Peat Sand / Aggregate Matrix - PSD
Peat 5 to 10% by volume
Clay

Louisburg Bioretention Cells
• Soil Media:
– Nominally 0.75 m Deep
– 60% Sand
– 40% “Ballfield Mix”
• Low PI (1-2) (1 2) fill
– 85% Sand
– 10% Fines
– 5% Organics
• Constructed Spring 2004

US Army Corps
of Engineers®
Engineers
Darryl J. Calkins
Nov 6, 2003
US Army Cold Regions Research and Engineering Laboratory
Hanover, New Hampshire

State of VT Stormwater Management
Manual-Comments
• Infiltration systems & ground freezing
– The moisture content of the soil at freeze-up is critical
as it occupies air void space and during freezing takes
up space that could be available for infiltration

Bioretention Cold Weather
Climate Considerations
• Good Drainage!
• Sandy Course Media
• Combination Filtration / Infiltration
• Provide Extra Surface Storage
• Selection of Plants
• Proper Location and Use
• Reduced Salt or use Alternative Deicers
• Ground Water Levels
• Maintenance

Wilmington, NC

Lessons Learned
Failures Due to:
• Use of Old Design Standards
- clay / organic / K factor
• Poor Drainage
- Under drain design / Geo-fabrics / Saturated soils
• Media Variability
- Reliable Sources
• Contractor Substitutes
• Contamination
- P, N and Heavy Metals
• Sizing / Space
• Maintenance
- Can be high