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Achieving Stormwater NPDES Compliance Through New Development Strategies

Explore the goals, compliance requirements, and actions involved in stormwater NPDES compliance for new developments. Learn about the importance of Low Impact Development (LID) techniques, biotreatment, and hydromodification management to protect the environment and public health. Understand how municipalities can implement LID practices, regulate projects, and ensure long-term sustainability. Discover the thresholds, criteria, and monitoring measures needed for successful compliance with stormwater regulations. Enhance your knowledge of bioretention, infiltration, and treatment feasibility tests to improve water quality and reduce pollutant loadings. Take steps towards achieving environmental goals through innovative stormwater management practices.

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Achieving Stormwater NPDES Compliance Through New Development Strategies

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  1. Background and Overview Stormwater NPDES Compliance For New Developments

  2. Let’s talk about… • Goals • Compliance • Actions

  3. Research shows… • Impairment • Impacts from runoff • Effectiveness of LID • To mimic pre-development hydrology • To reduce pollutant loadings • To protect against dumps and spills GOALS

  4. Why target new development? • Think long-term • Demonstrate LID techniques and technologies • Improve livability of increasingly urban areas GOALS

  5. Municipalities must… Page4 • Use planning authorities to require LID • Regulate Projects • Implement LID on public projects COMPLIANCE

  6. Threshold Arcana • What if the project reduces the amount of impervious surface? • What about a 6,000 SF project with two parking spaces? • Does pervious pavement count? • Does pavement replacement count? • Are public improvements included? • The old 50% rule and the new 50% rule • Flow-control on already developed sites COMPLIANCE

  7. Low Impact Development • Source Control • Site Design • Treatment COMPLIANCE

  8. LID Treatment Criteria • 80% of Average Annual Runoff • Volume-based criteria • Flow-based criteria

  9. Treatment Infiltration/ Evapotranspiration ● Harvesting /Reuse COMPLIANCE Biotreatment(Bioretention) High-Rate Biofilter●Vault-Based Filter

  10. Bioretention Overflow COMPLIANCE Underdrain

  11. Volume-based Criteria: Derivation Vary V until 80% is detained and 20% overflows One Acre COMPLIANCE V 48-hourdrawdown • Largest storm retained • 85th percentile, 24 hour •  0.5" - 1.0" storm depth

  12. Bioretention Overflow COMPLIANCE Underdrain

  13. Bioretention flow-based criterion • MRP Provision C.3.c.i.(2)(b)(vi) • Maximum surface loading rate COMPLIANCE i = 0.2 inches/hour BMP Area/Impervious Area = 0.2/5 = 0.04 Surface Loading Rate i = 5 inches/hour

  14. Treatment Feasibility Tests COMPLIANCE Page60

  15. Alternative Compliance • Treat runoff from an equivalent impervious area offsite • At another site • Within a project site • On a road project • Within a Capital Improvement Program • Payment of in-lieu fees • Net environmental benefit COMPLIANCE

  16. Bioretention Overflow COMPLIANCE Underdrain

  17. Bioretention Soil Mix Criteria • Soil Mix Specification • 60%-70% sand • 30%-40% compost • MRP Attachment L • GuidebookAppendix B • Now available from local suppliers COMPLIANCE

  18. Hydromodification Management COMPLIANCE Stream Discharge

  19. Flow Duration Control COMPLIANCE

  20. 250,000 hours COMPLIANCE This flow exceeded during 2 hours/250,000 hours (0.0008%) This flow exceeded during 7 hours/250,000 hours (0.0028%)

  21. Flow Duration Control COMPLIANCE

  22. Bioretention Overflow COMPLIANCE Underdrain

  23. Bioretention Monitoring • Three bioretention facilities in Pittsburg • Clay soils (Hydrologic Soil Group “D”) • Underdrain discharge near top of gravel layer • Tipping buckets below each underdrain discharge • Pressure sensors at bottom of monitoring wells to measure saturated depth of gravel layer • Continuous monitoring during WY 2011-2012 COMPLIANCE

  24. Some Initial Monitoring Results COMPLIANCE

  25. Ensure Operation & Maintenance • Initial inspection within 45 days • Inspect 20% of facilities each year • Inspect every facility once every 5 years COMPLIANCE

  26. Achieving Goals and Compliance • Consistent implementation • LID Design to maximize retention • Documentation • Construction • Innovation • Harvesting and Reuse • Green Roofs • Bioretention • Multi-use landscapes • Retrofits • Fact-based advocacy ACTION

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