Transcript Tom Dalziel and Dan Cloak - Contra Costa Clean Water Program

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
Contra Costa Approach:
Afternoon Presentations
1. Experience So Far with LID
(Tom Dalziel and Dan Cloak)
2. Sizing IMPs to manage hydrograph
modification (Tony Dubin, Brown &
Caldwell)
3. Stream Classification Methodology
(Andy Collison, Philip Williams &
Associates)
4. Next Steps in Implementation
(Dan Cloak)
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.
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
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.
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
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
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
Development Review
Pre-Application
Meeting
Planning
Commission
Detailed
Design
Completed
Application
Conditions of
Approval
Plan Check
“Deemed
Complete”
Section
Review
CEQA
Review
Permits
to
Build
Stormwater C.3 Compliance
Pre-Application
Meeting
Staff identifies
general C.3
requirements
Planning
Commission
Detailed
Design
Completed
Application
Planning staff
may determine if
C.3 req’ts are
addressed
Conditions of
Approval
C.3
requirements
attached to
COAs
Plan Check
Section staff
“Deemed may review
Complete” planning &
zoning docs
for C.3
Section
Review
CEQA
Review
Permits
to
Staff reviews C.3
Build
implementation in
drawings & specs
Operation & Maintenance
General
description
of O&M
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
Renewed
each
year
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
Low Impact Development
in Contra Costa County:
Problems and Solutions
Dan Cloak, P.E.
Dan Cloak Environmental Consulting
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
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
Accounting for Pervious Areas
Conventional
LID
 Self-treating
areas
 “Zero
discharge”
or “selfretaining”
areas
 Reduced
runoff areas
Zero discharge areas
Conventional grading
Zero-discharge area
Zero-discharge areas
Impervious
2
Pervious
Example LID Site Design
Example LID Site Design
 Make
landscaped
areas “selfretaining”
Example LID Site Design
 Delineate
areas that
drain to
each IMP
 Decide
where roofs
will drain
 Divide
paved areas
along grade
breaks
Example LID Site Design
 Fit IMPs
into
landscaping
at low
points of
each
drainage
area
Example LID Site Design
 Show each
IMP is sized
to treat
runoff from
its
tributary
area
IMP Design Gallery
}
Flow-through Planter
In-ground Planter
Bioretention Area
Vegetated or Grassy Swale
Infiltration Basin
“Direct
Dry Well
Infiltration”
Infiltration Trench
}
“Indirect
Infiltration”
Indirect Infiltration
Turf or planting
Planting medium
Gravel or drain rock
Perforated pipe
Sizing Criterion
0.2 inches/hour
BMP Area/Impervious Area =
0.2/5 = 0.04
Planting medium
i = 5 inches/hour
Flow-through Planter
Reservoir,
12" min. depth
Reverse bend
trap or hooded
overflow
Building
exterior wall
Downspout
Cobbles or
splash block
18" sandy loam,
minimum
infiltration rate
5" per hour
Filter fabric
Concrete or other
structural planter wall with
waterproof membrane
12" open-graded
gravel, approx.
½" dia.
Perforated pipe
Additional
waterproofing on
building as
needed
Drain to storm drain or discharge;
bottom-out or side-out options
Vegetated (“Dry”) Swale
18" sandy loam,
min. infiltration rate 5"/hr
grasses or landscape plant
1% min
4
1
6" min. depth
12" curb cut
native soil; no
compaction
6“ perforated pipe
18" x 12"; ½" gravel
or drain rock
6' min. overall
Design Checklists
Vegetated Swale
● Setbacks from structures
● Sizing criteria
● Minimum depth
● Side slopes
● Specification for imported soil
● Specification for underdrain
● Irrigation
Direct Infiltration
Dry Well
Residential Subdivision
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
Seattle “SEA” Streets
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
Curb and sidewalk
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
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 (>1 acre impervious area must comply)
● Infill projects in highly developed watersheds
● Project cost
Four Compliance Options
1. Demonstrate project will not
increase impervious area
2. Implement pre-designed
hydrograph modification IMPs
3. Use a continuous simulation model
to compare post- to pre-project
flows
4. Demonstrate increased flows will
not accelerate stream erosion