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Bioretention Design Specification Updates
1. Rainwater and Land Development Manual
Bioretention Design
Specification Updates
Jay Dorsey & John Mathews
ODNR-DSWR
April 16, 2014
2. Why Change?
Improved Design -> Better Performance,
Fewer Failures; Based on:
Bioretention Practice Inspections/Observations
Research – Scientific Knowledge Base
Ability to Target Specific Pollutants or
Stormwater Management Goals
• Temperature, Nitrogen, Phosphorus
Facilitate Design, Review and Inspection
Runoff Volume and Peak Discharge
Reduction Credits (under Development)
3. Primary References
Hunt, Davis, and Traver. 2012. Meeting Hydrologic and
Water Quality Goals through Targeted Bioretention
Design. J. Env. Eng. 138(6): 698-707.
Hunt and Lord. 2005. Bioretention Performance, Design,
Construction and Maintenance. NCSU-CE.
Brown, Hunt, and Kennedy. 2009. Designing
Bioretention with an Internal Water Storage (IWS) Layer.
NCSU-CE.
NCDENR Stormwater Manual. 2009.
Wardynski and Hunt. 2012. Are Bioretention Cells Being
Installed per Design Standards in North Carolina? A
Field Assessment. J. Env. Eng. 138(12): 1210-1217.
CWP. 2012. West Virginia Stormwater Management and
Design Guidance Manual.
4. Third Federal Bank, North Olmstead
Source: Dan Bogoevski, Ohio EPA
Grassed Bioretention
aka Dry Enhanced Water Quality Swale
11. Planting Soil (Filter Bed Media)
PARAMETER OLD NEW
Texture Class
Sandy Loam, Loamy Sand
>72% Sand, <10% Clay
Loamy Sand
>80% Sand, <10% Clay
pH Range 5.2 – 7.0 5.2 – 8.0
Organic Matter
5-20% (no specification
whether by weight or volume)
3-5% by Weight
Phosphorus Content Soil P-Index between 15 and 40 15-60 mg/kg P by Mehlich3
Soil Test Certification
Soil mixes must be certified by
a qualified laboratory
(1 test/100 yd3 soil)
Soil mixes must be certified
by a qualified laboratory
(1 test/100 yd3 soil)
12. Planting Soil Mix or Recipe
To get the appropriate planting soil mix
(loamy sand; >80% sand, <10% clay when
considering only mineral fraction; 3-5%
OM by weight) a good place to start is a
5:1:1 mix (70% sand, 15% topsoil, and
15% organic matter by volume).
The sand shall be clean and meet AASHTO
M-6 or ASTM C-33.
Good (lower P) sources of “aged” organic
matter include leaf compost, pine bark fines,
or mulch fines.
21. Underdrain Configuration
For Basic BRC Installation 30”–36” Media Depth
Elevated outlet recommended for all
HSG-A, B, C soils with Kfs > 0.1 in/hr
- 18”+ for Temp, N & Volume Reduction
D soils – 3” gravel
bedding acts as sump
23. Temperature Mitigation
Planting soil media depth - minimum 36”,
48” preferred
Underdrain/outlet configuration - upturned
elbow with internal water storage (IWS)
layer, minimum 18” sump
24. Nitrogen Removal
Planting soil media depth - minimum 36”
Underdrain/outlet configuration
upturned elbow with internal water storage
(IWS) layer, minimum 18” sump
if necessary, orifice on drain outlet to control
discharge rate
25. Phosphorus Removal
Planting soil media depth - minimum 36”
Planting soil phosphorus content – 15-40
mg/kg P by Mehlich3
Recommend adding water treatment
residuals (WTR) or other iron or aluminum
rich amendment
27. Sizing and Drawdown Requirements
Assumptions
Kfs of settled filter bed media (planting soil) is
between 0.5 to 2.0 in/hr [Maintenance
required when Kfs < 0.5 in/hr]
20% of WQv sediment storage requirement
will be met with excess bowl volume