Bioretention Designs to Meet Different Goals. Jay Dorsey & John Mathews ODNR-DSWR June 18, PDF Free Download

Bioretention Designs to Meet Different Goals Jay Dorsey & John Mathews ODNR-DSWR June 18, 2014

Goals for Presentation Sizing Requirements for WQv New Development Redevelopment Base Design Design Modifications to Address Location Specific Conditions/Limitations or Meet Watershed Specific Goals Basic Design Example

Sizing Requirements for WQv - New Development - From NPDES Construction Stormwater Permit

Sizing Requirements for WQv - New Development - Target Drawdown Time, T d = 24 hr

Design Drawdown Assumption - K fs of settled filter bed media (planting soil) is between 0.5 to 2.0 in/hr [Maintenance required when K fs < 0.5/in/hr] Td = d WQv /K fs = (12 in)/(0.5 in/hr) = 24 hr Where: T d drawdown time d WQv equivalent depth of WQv K fs saturated hydraulic conductivity

Filter Bed Sizing Requirement If impervious area exceeds 25% of contributing drainage area, filter bed area shall be a minimum 5% of contributing impervious area.

Filter Bed Sizing Requirement Example 1 Total contributing drainage area = 0.82 Ac Impervious percent = 45% (>25%) Contributing impervious area = (0.82 Ac)(0.45) = 0.37 Ac = 16,073 ft 2 Minimum filter bed area = (16,073 ft 2 )(0.05) = 803 ft 2

Filter Bed Sizing Requirement If impervious area exceeds 25% of contributing drainage area, filter bed area shall be a minimum 5% of contributing impervious area. If impervious area makes up less than 25% of contributing drainage area, filter bed area shall be at least equal to the WQv divided by the one foot maximum ponding depth.

Filter Bed Sizing Requirement Example 2 Total contributing drainage area = 0.82 Ac Impervious percent = 15% (<25%) For 15% impervious, C = (0.858)(0.15) 3 (0.78)(0.15) 2 + (0.774)(0.15) + 0.04 = 0.141 WQv = C*P*A = (0.141)(0.75 in)(0.82 Ac)(1 ft/12 in) = 0.007 Ac-ft = 315 ft 3 Minimum filter bed area = (315 ft 3 )(1 ft) = 315 ft 2

(%) Filter Bed Area

What about Redevelopment? For redevelopment projects, the full WQv must be captured for all new/additional impervious area, but for existing impervious area the volume that must be captured is 20% of the WQv.

What about Redevelopment? A rule of thumb based on research shows an optimal 10:1 to 20:1 ratio for contributing impervious drainage area to bioretention filter bed area (i.e. hydrologic loading ratio). If all best practices are used (pretreatment, energy dissipation, construction, etc.) a hydrologic loading ratio of 25:1 is probably okay for most sites. The filter bed area of the bioretention cell should not be less than 4% of the contributing impervious area.

Redevelopment BRC Options For straight redevelopment (no new impervious), capture and treat the full WQv from 20% of the site For mixed redevelopment and new development, match the size of your bioretention cell to your contributing impervious area Build a bioretention practice capable of capturing the full WQv from the entire site, and use the rest as credit toward reduction of stormwater fees or as mitigation

Bioretention Cell Components

Bioretention Decisions Base Design 30-36 depth; IWS Layer HSG A Soils Temperature Nitrogen Treatment Depth Limitations (e.g., Shallow Outlet, High Water Table) HSG D Soils (depending on limitations) If Kfs > 1 in/hr, may not require underdrain, aggregate, filter 36+ media depth; IWS Layer (>18 ); 48 depth to drain 36 media depth; IWS layer (>18 ), outlet raised >6 into planting media 24 media depth Underdrain w/ 3 of cover & 3 of bedding High Water Table, Karst, Shallow Bedrock or High Pollution Loads Impermeable liner

Base Bioretention Configuration

Base Bioretention Configuration 30-36 Planting Soil 6 Filter 12 Aggregate

Base Bioretention Configuration 24 Planting Soil above Invert 6 (min) Planting Soil in IWS

Special Designs Pollutant Load Reduction Goals Temperature Mitigation Nitrogen Removal Phosphorus Mitigation Site Conditions or Limitations High Permeability Soils (> 1 in/hr) Very Low Permeability Soils (<0.05 in/hr) Depth Limitations Groundwater Pollution Potential

High Permeability Soils If measured subgrade infiltration rate exceeds 1.0 in/hr, the underdrain, and aggregate and filter layers, can be eliminated

High Permeability Soils

Source: Bill Hunt, NCSU-BAE

Temperature Mitigation Planting soil media depth - minimum 36 Underdrain/outlet configuration minimum 48 depth to drain; more is better upturned elbow with internal water storage (IWS) layer, minimum 18 sump

Temperature Mitigation Planting Soil 36 Minimum 48 Drain Depth Min. 18 IWS Min.

Nitrogen Removal Planting soil media depth - minimum 36 Underdrain/outlet configuration upturned elbow with internal water storage (IWS) layer, minimum 18 sump with at least 6 IWS in planting media if necessary, orifice on drain outlet to control discharge rate

Nitrogen Removal Planting Soil 36 Minimum 6 Min. in Planting Soil 18 IWS Min.

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

Source: Bill Hunt, NCSU-BAE

Depth Limitations

Low Permeability Soils or Impediments to Infiltration If subgrade infiltration rate is less than 0.05 in/hr, or if shallow bedrock or seasonal high water table is present, there may be limited benefits and potential issues from the IWS; a level drain with 3 sump allows limited exfiltration

Low Permeability Soils or Impediments to Infiltration

High Groundwater Pollution Potential In Karst areas or areas with shallow groundwater aquifers, water supplies are susceptible to contamination use an impermeable liner In sites with contaminated soils or pollution hot spots, bioretention cells should use an impermeable liner Alternative configurations can still be used to mitigate temperature and nutrient impacts

GW Pollution Potential Add Liner

Base Bioretention Configuration

Design Example Holden Arboretum

Watersheds North Wshed DA = 0.67 Ac %Imp (est) = 58% ImpArea = 0.39 Ac ABRC = 0.0195 Ac = 850 sq ft ~ 23 x 40 ft South Wshed DA = 0.48 Ac %Imp (est) = 59% ImpArea = 0.28 Ac ABRC = 0.014 Ac = 610 sq ft ~ 20 x 30 ft

Watersheds North Wshed DA = 0.67 Ac %Imp (est) = 58% ImpArea = 0.39 Ac ABRC = 0.0195 Ac = 850 sq ft ~ 23 x 40 ft proposed bioretention locations South Wshed DA = 0.48 Ac %Imp (est) = 59% ImpArea = 0.28 Ac ABRC = 0.014 Ac = 610 sq ft ~ 20 x 30 ft

Design Example Holden Arboretum North Bioretention Cell Drainage Area = 0.67 Ac Imperviousness = 58% Impervious Area = 0.39 Ac ABRC = 0.05*0.39 Ac = 0.0195 Ac = 850 sq ft C = 0.394 WQv = C*P*A = 0.394*(0.75 in)*(0.39 Ac) = 0.016 Ac-ft = 719 ft 3

Platea HSG-D Pierpont HSG-C Soil Map

proposed bioretention locations measure infiltration rate at proposed depth of excavation ~48-54 other potential sampling locations sample at ground surface

Infiltration Tests Measured Kfs (in/hr) BRC1(N): 0.02, 0.02 BRC2(S): 0.02, 0.08

Target Bioretention Configuration 36 Planting Soil 6 Filter 12 Aggregate

Bioretention Cell 1(N) - Section Lowest Pavement = 99.3 existing pavement existing 15 outlet Outlet Invert = 94.0 All Elevations are Relative, Not MSL Not to Scale

Bioretention Cell 1(N) - Section Lowest Pavement = 99.3 freeboard = 0.5 max ponding depth = 1.0 existing pavement drain outfall ~36 bioretention soil Outlet Invert = 94.0 All Elevations are Relative, Not MSL existing 15 outlet drain 3 filter clean concrete sand 3 filter - clean gravel (#8) 12 clean gravel (#57) Not to Scale

Bioretention Cell 1(N) - Section Lowest Pavement = 99.3 Proposed Overflow = 98.8 Filter Bed Surface = 97.8 freeboard = 0.5 max ponding depth = 1.0 existing pavement drain outfall ~36 bioretention soil Drain Outfall = 95.1 Filter Bed Bottom = 94.8 Sand/Gravel Filter = 94.3 Outlet Invert = 94.0 Bottom of Excavation = 93.3 All Elevations are Relative, Not MSL existing 15 outlet drain 3 filter clean concrete sand 3 filter - clean gravel (#8) 12 clean gravel (#57) Not to Scale

Scarifying Bottom of Cell

Underdrain w/upturned Elbow Creating 21 Internal Water Storage (IWS) Zone or Sump

Waterproof Connection Hydraulic Cement

12 #57 gravel Water Table Monitoring Well

3 #8 gravel filter

3 clean C-33 sand filter

36 bioretention planting soil

Holden Bioretention Configuration 36 Planting Soil 6 Filter 12 Aggregate

Holden North Cell Drawdown Data North Cell Well Drawdown Rates Drawdown Begin Date/Time Drawdown End Date/Time Beginning Stage (ft) Ending Stage (ft) Delta Stage (ft) Delta time (days) Drawdown Rate (ft/day) Drawdown Rate (in/hr) Infiltrated Volume (ft3) 10/7/2013 17:22 10/16/2013 0:30 2.099 1.17 0.929 8.30 0.112 0.056 261 10/17/2013 6:42 10/17/2013 15:38 2.085 1.97 0.115 0.37 0.309 0.154 32 10/18/2013 2:48 10/19/2013 12:20 2.084 1.721 0.363 1.40 0.260 0.130 102 10/20/2013 12:12 10/21/2013 20:30 2.052 1.624 0.428 1.35 0.318 0.159 120 10/22/2013 14:16 10/23/2013 7:02 2.07 1.783 0.287 0.70 0.411 0.205 81 10/26/2013 18:36 10/26/2013 21:12 1.923 1.894 0.029 0.11 0.268 0.134 8 10/27/2013 12:56 10/31/2013 4:00 1.892 1.352 0.54 3.63 0.149 0.074 151 11/2/2013 3:48 11/2/2013 9:22 1.883 1.815 0.068 0.23 0.293 0.147 19 11/4/2013 1:30 11/6/2013 17:18 1.847 1.344 0.503 2.66 0.189 0.095 141 11/9/2013 10:00 11/11/2013 17:46 1.851 1.355 0.496 2.32 0.213 0.107 139 11/15/2013 7:16 11/17/2013 18:46 1.794 1.491 0.303 2.48 0.122 0.061 85 11/19/2013 4:14 11/21/2013 21:28 1.789 1.279 0.51 2.72 0.188 0.094 143 11/23/2013 21:28 12/9/2013 9:06 1.811 1.165 0.646 15.48 0.042 0.021 181 Avg drawdown rate: 0.125 ft/day TotalExfiltrated Volume: 1463 Avg drawdown rate: 0.062 in/hr Standard Deviation: 0.0507

Holden North Cell Drawdown Data

References ODNR. Rainwater and Land Development Manual. NCDENR Stormwater Manual. 2009. Hunt, Davis, and Traver. 2012. Meeting Hydrologic and Water Quality Goals through Targeted Bioretention Design. J. Env. Eng. 138(6): 698-707. 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. Brown, Hunt, and Kennedy. 2009. Designing Bioretention with an Internal Water Storage (IWS) Layer. NCSU-CE. CWP. 2012. West Virginia Stormwater Management and Design Guidance Manual.

Questions: Jay Dorsey Water Resources Engineer ODNR, Soil & Water Resources (614) 265-6647 jay.dorsey@dnr.state.oh.us

Bioretention Designs to Meet Different Goals. Jay Dorsey & John Mathews ODNR-DSWR June 18, 2014