Contra Costa Approach I: Initial Implementation of LID

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Contra Costa Approach (I)Initial Implementation
of LID

• Tom Dalziel, Assistant Program Manager
• Contra Costa Clean Water Program
• Dan Cloak, P.E., Principal
• Dan Cloak Environmental Consulting

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Contra Costa Approach Afternoon Presentations

• Experience So Far with LID(Tom Dalziel and Dan
  Cloak)
• Sizing IMPs to manage hydrograph modification
  (Tony Dubin, Brown Caldwell)
• Stream Classification Methodology (Andy
  Collison, Philip Williams Associates)
• Next Steps in Implementation(Dan Cloak)

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NPDES Permit New Development requirements

• Treat runoff before discharge from site.
• Match runoff peak flows and durations to
  pre-project conditions.
• Cover or control sources of stormwater
  pollutants.
• Maintain treatment facilities in perpetuity.

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Cities, Towns, and County must

• Incorporate requirements into their policies and
  processes for development review
• Verify that on-site treatment devices are
  maintained
• Prepare a Hydrograph Modification Management Plan
  to control future increases in runoff peaks and
  durations

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Program Objectives

• Comply with NPDES permit requirements.
• Achieve reasonable protection of beneficial uses.
• Minimize staff time required for additional
  project review.
• Minimize costs to applicants.
• Encourage smart growth and maintain economic
  competitiveness.
• Adopt a flexible approach.
• Encourage participation and consensus among
  interested parties.

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Key Implementation Steps

• Update to Model Stormwater Ordinance
• Requires Stormwater Control Plan with Planning
  and Zoning Application
• Adopted by each municipality countywide
• Stormwater C.3 Guidebook
• Workshops for municipal staff and land
  development professionals
• Assistance with initial projects and preparation
  of examples

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Stormwater C.3 Guidebook

• Step-by-Step Approach to Compliance
• How to Prepare a Stormwater Control Plan
• Guidance for Selecting Treatment Facilities
• Design Checklists and Standard Details for LID
  IMPs
• Spreadsheet for Sizing BMPs and presenting
  calculations
• Sample Outline and Examples
• How to prepare an Operation and Maintenance Plan
  for treatment facilities
• References and Hyperlinks to Design Resources

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Stormwater Control Plan
Contents

• Project Setting
• Measures to Limit Imperviousness
• Selection Design of Treatment BMPs
• Source Control Measures
• Permitting and Code Compliance Conflicts
• BMP Maintenance
• Construction Plan C.3 Checklist
• Certification

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Development Review
Pre-Application Meeting
Completed Application
Deemed Complete
Section Review
Conditions of Approval
Planning Commission
CEQA Review
Detailed Design
Plan Check
Permits to Build
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Stormwater C.3 Compliance
Section staff may review planning zoning docs
for C.3
Pre-Application Meeting
Completed Application
Deemed Complete
Planning staff may determine if C.3 reqts are
addressed
Staff identifies general C.3 requirements
Section Review
Conditions of Approval
Planning Commission
CEQA Review
C.3 requirements attached to COAs
Detailed Design
Plan Check
Permits to Build
Staff reviews C.3 implementation in drawings
specs
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Operation Maintenance
General descriptionof OM requirements
Detailed description and maintenance plan for
each facility
Certification of inspection continued
operation
Stormwater Control Plan
Stormwater Facilities Operation Maintenance
Plan
Stormwater Facilities Compliance Certificate
Submitted with Planning Zoning Application
Draft submitted with construction documents
Renewedeachyear
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Results so far

• Development community has responded positively
  to
• Consistent ordinances countywide
• Usability of Stormwater C.3 Guidebook
• Workshops
• Biggest Challenges
• LID requires a different approach to drainage
  design
• Resolving conflicts with public works standards
• IMP ownership and maintenance responsibility

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Low Impact Development in Contra Costa
CountyProblems and Solutions

• Dan Cloak, P.E.
• Dan Cloak Environmental Consulting

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Implementing LID

• Showing compliance with NPDES permit criteria for
  treatment
• Designing effective IMPs
• Residential Subdivisions
• Street and drainage design
• IMP operation and maintenance
• Integrating with the HMP

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Showing Compliance

• NPDES Permit sizing criteria for treatment
  control
• collect and convey drainage design
• conventional, end of pipe treatment
• use of runoff factors to determine design inflow
  or volume

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Accounting for Pervious Areas
Conventional
LID

• Self-treating areas
• Zero discharge or self-retaining areas
• Reduced runoff areas

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Zero discharge areas
Conventional grading
Zero-discharge area
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Zero-discharge areas
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Example LID Site Design
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Example LID Site Design

• Make landscaped areas self-retaining

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Example LID Site Design

• Delineate areas that drain to each IMP
• Decide where roofs will drain
• Divide paved areas along grade breaks

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Example LID Site Design

• Fit IMPs into landscaping at low points of each
  drainage area

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Example LID Site Design

• Show each IMP is sized to treat runoff from its
  tributary area

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IMP Design Gallery

• Flow-through Planter
• In-ground Planter
• Bioretention Area
• Vegetated or Grassy Swale
• Infiltration Basin
• Dry Well
• Infiltration Trench

Indirect Infiltration

Direct Infiltration
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Indirect Infiltration
Turf or planting
Planting medium
Gravel or drain rock
Perforated pipe
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Sizing Criterion
0.2 inches/hour
BMP Area/Impervious Area 0.2/5 0.04
Planting medium
i 5 inches/hour
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Flow-through Planter
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Vegetated (Dry) Swale
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Design Checklists

• Vegetated Swale
• Setbacks from structures
• Sizing criteria
• Minimum depth
• Side slopes
• Specification for imported soil
• Specification for underdrain
• Irrigation

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Direct Infiltration
Dry Well
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Residential Subdivision
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Residential Subdivision

• Suitably sized infiltration basin would require 3
  of 80 lots
• Roofs, driveways, and landscaped areas drain to
  front yard swales
• Streets drain to same swales

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Seattle SEA Streets
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Swales in Front Yards

• Some jurisdictions prefer monolithic curb
  gutter
• Access to parked vehicles
• Avoid trip hazards
• Standard location for public utilities
• Still developing standard designs and
  maintenance responsibility

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Curb and sidewalk
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HMP Requirements

• NPDES permittees must propose a plan
• Manage increases in flow and volume where
  increases could
• Increase erosion
• Generate silt pollution
• Impact beneficial uses
• Post-project runoff may not exceed pre-project
  rates and durations
• Option Equivalent Limitation
• Account for expected stream change
• Maintain or improve beneficial uses

37
Contra Costa HMP

• Succinct standard, with four compliance options
• Encourage Low Impact Development Integrated
  Management Practices (LID IMPs)
• Allow proposals for stream restoration in lieu of
  flow control where benefits clearly outweigh
  potential impacts
• No exemptions for
• Project size (gt1 acre impervious area must
  comply)
• Infill projects in highly developed watersheds
• Project cost

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Four Compliance Options

• Demonstrate project will not increase impervious
  area
• Implement pre-designed hydrograph modification
  IMPs
• Use a continuous simulation model to compare
  post- to pre-project flows
• Demonstrate increased flows will not accelerate
  stream erosion