1. Low Impact Development for Compliance with NPDES Treatment and Hydrograph Modification Management Requirements in Contra Costa County Tom Dalziel, Assistant Manager Contra Costa Clean Water Program Dan Cloak, Principal Dan Cloak Environmental Consulting CASQA Pre-Conference Workshop, 10 September 2007

2. Topics 1.Brief history of LID in California 2.Contra Costa Approach: What’s been working for us Planned improvements

3. A Brief History of LID in CA Contra Costa Approach Hydrograph Modification Mgt. SWRCB Bellflower Decision Portland Stormwater Manual Low Impact Development Manual Imperviousness and flow-control Start at the Source Stormwater NPDES Permits Village Homes, Davis 1978 1994 1999 2003 2000

4. Village Homes Narrow streets Surface drainage Swales as an amenity

5. Stormwater NPDES—Early Years Characterization of urban runoff Focused on demonstrating reductions of pollutant loads End-of-pipe treatment vs. BMPs Design criteria for conventional treatment facilities “Do what you can, where you can.”

6. Start at the Source Preceded by San Francisco Bay RWQCB “Staff Recommendations” (1993) Emphasis on reducing imperviousness to reduce pollutant loading Addressed need to identify site-design alternatives Integrates urban design and site design No regulatory mandate

7. Imperviousness Importance of Imperviousness (1994) Empirical relationship between watershed imperviousness and stream degradation Awareness of the effects of small storms and increased runoff frequency Peak flow control over a range of storm sizes Continuous simulation Before After

8. Low Impact Development Developed as an alternative to treatment detention basins Addressed preserving site hydrology and natural functions Site design and bioretention (“rain gardens”) Included hydrologic criteria based on matching curve numbers

9. Portland Stormwater Manual

10. Bellflower Decision and HMPs Bellflower made the L.A. RWQCB’s treatment criteria a statewide “maximum extent practicable” standard San Francisco Bay Board added “Hydrograph Modification Management” Before After

11. Contra Costa’s Approach LID is a means to achieve compliance with NPDES treatment and flow-control requirements Focus Program resources on helping small developments, infill, and redevelopment to comply with NPDES requirements Be pro-active

12. Things that are working Collaborative Problem Solving Development Review Process Regulatory Compliance Approach Prescriptive Flexible Continuous Improvement

13. The Bathtub Theory of Government Organize across disciplines and levels Engage top decision-makers Learn from developers and development professionals Collaborative Problem-Solving

14. Development Review Process Pre-Application Meeting Completed Application “Deemed Complete” Section Review CEQA Review Conditions of Approval Planning Commission Detailed Design Plan Set and Permit Application Construction

15. Development Review Process Pre-Application Meeting Completed Application “Deemed Complete” Section Review CEQA Review Conditions of Approval Planning Commission Detailed Design Plan Set and Permit Application Construction Discuss design, O&M responsibility Prepare and submit a Stormwater Control Plan Respond to questions and revise plan Stormwater requirements are attached to COAs Incorporate facilities in plans and specifications Submit draft Stormwater Facilities O&M Plan Lay out the site and stormwater facilities Transfer Maintenance Responsibility Construct facilities. Submit Final O&M Plan prior to end of construction

16. Regulatory Compliance Approach Ordinances reference Guidebook Countywide consistency Empowers municipal reviewers Ability to update requirements Options and flexibility Design criteria and specifications

17. Swale

18. Planter Box

19. Dry Well

20. Showing Treatment Compliance NPDES Permit sizing criteria for treatment control: “collect and convey” drainage design Conventional “end of pipe” treatment Composite “C” factors to determine design inflow or volume

21. Sizing criterion for treatment Planting medium 0.2 inches/hour i = 5 inches/hour BMP Area/Impervious Area = 0.2/5 = 0.04

22. Application of sizing factor

23. LID for flow control Can LID facilities mitigate increased peaks and volumes of flows from impervious areas? How would we demonstrate that? What are the design criteria? Before After

24. Analysis for flow control 33 years hourly rainfall Pre-project condition 100% impervious condition Hydrologic soil groups A, B, C, D Swales, Bioretention Areas, In-ground and Flow-through Planters Underdrain with flow-restrictor in C&D soils Dry wells, infiltration trenches and basins

25. Results: Control of Peak Flows

26. Results: Flow Duration Control

27. Sizing Factors for Flow Control IMPSizing Factors In-Ground Planter Group A: 0.08 Group B: 0.11 Group C: 0.06 Group D: 0.05 Flow- Through Planter Group C: 0.06 Group D: 0.05 Vegetated/ Grassy Swale Group A: 0.10 to 0.14 Group B: 0.14 to 0.21 Group C: 0.10 to 0.15 Group D: 0.07 to 0.12 Bioretention Basin Group A: 0.13 Group B: 0.15 Group C: 0.08 Group D: 0.06 IMPSizing Factors Dry WellGroup A: 0.05 to 0.06 Group B: 0.06 to 0.09 Infiltration Trench Group A: 0.05 to 0.06 Group B: 0.07 to 0.10 Infiltration Basin Group A: 0.05 to 0.10 Group B: 0.06 to 0.16

28. Adjustment to annual rainfall

29. LID Site Design 1.Divide the site into Drainage Management Areas 2.Use landscape to disperse and retain runoff where possible 3.Route drainage from remaining areas to bioretention facilities 4.Check facility locations for available space and hydraulic head

30. Four Types of Areas 1. Self-treating areas 2. Self-retaining areas 3. Areas draining to a self-retaining area 4. Areas draining to a treatment facility Only one surface type within each area Many-to-one relationship between drainage areas and facilities Drainage Management Areas

31. Self-treating areas Must be 100% pervious Must drain offsite Must not drain on to impervious areas Must not receive drainage from impervious areas Must not drain to treatment facilities No treatment or flow control required No further calculations required

32. Self-retaining areas

33. Berm or depress grade to retain 1" rain Set area drain inlets above grade Amend soils Terrace mild slopes Have limited applicability in Dense developments Hillsides

34. Areas draining to self-retaining areas Impervious areas can drain on to self-retaining areas Example: Roof leaders directed to lawn or landscape Maximum ratio is 2:1 for treatment; 1:1 for flow control No maintenance verification required

35. Areas draining to self-retaining areas

36. Tabulating Areas Self-Treating Areas DMA NameArea (SF) Self-Retaining Areas DMA NameArea (SF) Areas Draining to Self-Retaining Areas DMA Name Area (SF) Post- project surface type Runoff factor Receiving Self-retaining DMA Receiving DMA Area (SF)

37. Areas draining to Bioretention Facilities Areas used to calculate the required size of the bioretention facility Where possible, drain only impervious roofs and pavement to bioretention facilities Delineate any pervious areas as separate Drainage Management Areas

38. DMA Name DMA Sq. Ft Surface Type Runoff Factor Area x runoff factor Sizing Factor Min. Size Size Planned Facility A-----  DMAs draining to facilities

39. Calculating Facility Size A-2: Paving 10,000 SF A-3: Turf 20,000 SF A-1: 5,000 SF Roof Bioretention Facility A

40. DMA Name DMA Sq. Ft Surface Type Runoff Factor Area x runoff factor A-1 5000Roof1.05000 A-210000Paved1.010000 A-320000Grass0.12000Sizing Factor Min. Size Size Planned Facility A-----  170000.04680800 DMAs draining to facilities

41. Treatment Effectiveness Policy Maximum Extent Practicable Remove small particles Biological action/multiple pathways Withstand shock loadings and deferred maintenance Visibility and ease of inspection Future availability and cost of materials Special Site Conditions—under one acre and: Zero lot line development Redevelopment subject to “50% rule” Ranked Selection—Prescriptive and Flexible 1. Bioretention facilities served by gravity 2. Bioretention facilities served by pumps 3. Conventional detention basins or sand filters 4. High-rate biofilters 5. Vault-based filtration systems

42. Improvements for 4 th Edition Compliance for subdivision maps Operation and maintenance responsibility in small residential subdivisions Treatment effectiveness policy Improved facility designs and specs Better integrated design guidance Emphasize landscape choices Emphasize need to coordinate developer’s design team

43. One hot afternoon in Contra Costa

47. tdalziel@pw.cccounty.us www.cccleanwater.org/construction/nd.php dan@dancloak.com www.dancloak.com