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Design Standards

Design Standards. for Bioretention Facilities. Dan Cloak Environmental Consulting May 23, 2011. Topics. Why such emphasis on bioretention ? Criteria for hydrologic performance and NPDES compliance Area and volume requirements Discharge orifice requirements and outlet design

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Design Standards

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  1. Design Standards for Bioretention Facilities Dan Cloak Environmental ConsultingMay 23, 2011

  2. Topics • Why such emphasis on bioretention? • Criteria for hydrologic performance and NPDES compliance • Area and volume requirements • Discharge orifice requirements and outlet design • Soil specification • Additional Design Specifications • Gravel and underdrain • Plantings • Structural

  3. Why Bioretention?

  4. Area and Volume Criteria • Sizing Factor for Treatment Only • A ≥ 0.04 • Sizing Factors for Treatment + Flow Control • 3 factors • Vary with soil type and rainfall record (location) • A is the wetted surface area of the bioretention soil mix • V1 is the surface storage at overflow stage • V2 is the free volume within the gravel layer

  5. Treatment-Only Criterion i = 0.2 inches/hour BMP Area/Impervious Area = 0.2/5 = 0.04 Surface Loading Rate i = 5 inches/hour

  6. Section –Treatment Only A 18"

  7. Flow-Control Criteria

  8. Sizing Factors Page 44

  9. Standard Section A 2" Overflow V1 10" Soil Mix 18" Gravel V2 18" Φ = 0.4

  10. V1 by flooding pavement A 2" V1 10" 6" Soil Mix 18" Gravel Page 70 V2 18" Under drain

  11. V2 by large diameter pipes 2" 10" Soil Mix 18" Page 71 18"

  12. Outlet Design Page 76 Overflow elevation

  13. Soil Specification Page B-3 • See Appendix B – Use Mix “B” • 60-70% Sand • ASTM C33 for fine aggregate • 30-40% Compost • Certified through US Composting Council Seal of Testing Assurance Program • Issues since initiating a design specification • Suppliers may still be using a performance specification • Performance of non-spec materials starts out OK, then falls off with repeated wettings • Failures seem to correlate with observable presence of clays

  14. Gravel and Underdrain Pages 71-72 • Class 2 permeable • Caltrans spec 68-1.025 • Typical to be slightly off gradation spec on delivery • No filter fabric • Underdrain • PVC SDR 35 or equivalent • Holes facing downward • Solid pipe for 2' closest to outlet structure • Cleanout

  15. Plantings Page B-7 • List in Attachment B-1 • Use experienced professionals • Trees • Incorporate into bioretention facility • Account for surface roots • Consider multi-purpose • Lawns or working gardens • Flooding is brief and only in winter Page 73

  16. Call out elevations Page 94 • Outlet structure • Top of overflow grate • Invert of subdrain • Inlet • Flow line at inlet • Top of curb • Top of adjacent paving • Soil layers • Top of soil layer • Bottom of gravel layer • Bottom of soil layer

  17. Structural 15"

  18. Structural

  19. Inlets

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