Design Standards Dan Cloak Environmental Consulting May 23 2011 Why such emphasis on bioretention Criteria for hydrologic performance and NPDES compliance Area and volume requirements ID: 717035
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Slide1
for Bioretention Facilities
Design Standards
Dan Cloak
Environmental Consulting
May 23, 2011Slide2
Why such emphasis on bioretention?Criteria for hydrologic performance
and NPDES complianceArea and volume requirements
Discharge orifice
requirements and outlet designSoil specificationAdditional Design SpecificationsGravel and underdrainPlantingsStructural
TopicsSlide3
Why Bioretention?Slide4
Sizing Factor for Treatment OnlyA
≥ 0.04Sizing Factors
for Treatment +
Flow Control3 factorsVary with soil type and rainfall record (location)A is the wetted surface area of the bioretention soil mixV1
is the surface storage at overflow stage
V
2
is the free volume within the gravel layer
Area and Volume CriteriaSlide5
Treatment-Only Criterion
Surface Loading Rate
i
= 0.2 inches/hour
i = 5 inches/hour
BMP Area/Impervious Area =
0.2/5 = 0.04Slide6
Section – Treatment Only
A
18"Slide7
Flow-Control CriteriaSlide8
Sizing Factors
Facility Design
Soil Group
Area A (
ft
2
/ft
2)
Volume
V1
(ft
3
/ft
2
)
Volume
V
2
(ft
3
/ft
2
)
Rainfall Adjustment for Surface Area
Rainfall Adjustment for Storage Volume
Maximum Release Rate
Bioretention
Facility
A
0.07
0.058
No min.
Eq. 4-6
Eq. 4-6
No orifice
B
0.11
0.092
No min.
Eq. 4-7
Eq. 4-7
No orifice
C
0.06
0.050
0.066
Eq. 4-8
Eq. 4-8
Eq. 4-10D0.050.0420.055Eq. 4-9*Eq. 4-9Eq. 4-11Flow-through PlanterANot permitted in “A” soilsBNot permitted in “B” soilsC0.060.0500.066Eq. 4-8Eq. 4-8Eq. 4-10D0.050.0420.055Eq. 4-9*Eq. 4-9Eq. 4-11Dry WellA0.050.130N/AEq. 4-6Eq. 4-6No releaseB0.060.204N/AEq. 4-7Eq. 4-7No releaseCNot permitted in “C” soilsDNot permitted in “D” soilsCistern + BioretentionA0.0200.193N/AEq. 4-13Eq. 4-6Eq. 4-17B0.0090.210N/AEq. 4-14Eq. 4-7Eq. 4-12C0.0130.105N/AEq. 4-15Eq. 4-8Eq. 4-10D0.0170.063N/AEq. 4-16Eq. 4-9Eq. 4-11Bioretention + VaultA0.04N/A0.096N/AEq. 4-6No releaseB0.04N/A0.220N/AEq. 4-7Eq. 4-12C0.04N/A0.152N/AEq. 4-8Eq. 4-10D0.04N/A0.064N/AEq. 4-9Eq. 4-11
Page 44Slide9
Standard SectionSoil Mix
Gravel
18
"
18
"
10
"
2
"
Overflow
A
V
1
V
2
Φ
= 0.4Slide10
Soil Mix
Gravel
18
"
18
"
10
"
2
"
Under drain
6
"
V
1
by flooding pavement
A
V
1
V
2
Page 70Slide11
V2 by large diameter pipes
Soil Mix
18
"
18
"
10
"
2
"
Page 71Slide12
Page 76Outlet Design
Overflow
elevationSlide13
Soil SpecificationSee Appendix B – Use Mix “B”
60-70% SandASTM C33 for fine aggregate
30-40% Compost
Certified through US Composting Council Seal of Testing Assurance ProgramIssues since initiating a design specificationSuppliers may still be using a performance specificationPerformance of non-spec materials starts out OK, then falls off with repeated wettingsFailures seem to correlate with observable presence of clays
Page B-3Slide14
Class 2 permeable
Caltrans spec 68-1.025Typical to be slightly off gradation spec on delivery
No filter fabric
UnderdrainPVC SDR 35 or equivalentHoles facing downwardSolid pipe for 2' closest to outlet structureCleanout
Gravel and
Underdrain
Pages 71-72Slide15
List in Attachment B-1Use experienced professionals
Trees
Incorporate into
bioretention facilityAccount for surface rootsConsider multi-purposeLawns or working gardensFlooding is brief and only in winterPlantings
Page B-7
Page 73Slide16
Outlet structureTop of overflow grate
Invert of subdrain
Inlet
Flow line at inletTop of curbTop of adjacent pavingSoil layersTop of soil layer
Bottom of gravel layer
Bottom
of soil layer
Call out elevations
Page 94Slide17
Structural
15"Slide18
StructuralSlide19
Inlets