Stormwater Treatment and Flow Control

Dan CloakPresentation to the Citizens Advisory Committee

November 13, 2006

Options for implementingnew Phase II NPDES regulations

Outline

Effects of runoff from new developments

Stormwater regulations for new development in Marin

Low Impact Development Possible Next Steps

Effects of New Development

Runoff Before DevelopmentRunoff After Development

Effects of increased runoff

Increased flows and more frequent flooding leads to…

Increased streambank erosion, which leads to…

“Hardening” to prevent erosion, which leads to…

Loss of Stream Functions

Regulatory History

1987

Congress adds Section 402(p) to Clean Water Act

1990

USEPA regulations require states to issue stormwater NPDES permits to large municipalities

1993

Marin County municipalities begin implementing “baseline” stormwater pollution prevention activities

1999

USEPA promulgates “Phase II” stormwater regulations applicable to smaller municipalities.

2000

State Water Resources Control Board “Bellflower decision” confirms municipalities must require new developments to treat runoff

2001

Regional Water Board begins adding “Provision C.3” requirements to permits in Santa Clara, Alameda, Contra Costa, and San Mateo Counties

2003

State Water Board adopts General Permit for Small Municipal Separate Storm Sewer Systems (MS4s), including “Attachment 4”

2003

MCSTOPPP files a Notice of Intent for coverage under the statewide General Permit

2008

Implementation of all “minimum control measures” required

Regulatory History

Which areas? What projects?

All municipalities● “Enforce a program to address

stormwater runoff”● Projects disturbing an acre or more

San Rafael, County, Novato● “Attachment 4”—design standards for

• Single-family hillside residences• Subdivisions with 10 or more units• Repair shops, gas stations, restaurants• Commercial developments > 100,000 sq.

ft.• Parking lots with 5,000 sq. ft. or 25

spaces Or a “functionally equivalent

program”

Ideas to Consider

Involve the community in planning an approach for compliance

Create our own “functionally equivalent program” and get Regional Water Board approval

Seek countywide consistencyActively assist developers to

use “Low Impact Development”

Low Impact Development

Design the site to mimic natural drainage.

Disperse runoff to landscape where possible.

Use Integrated Management Practices distributed around the site.

Example of an engineered Integrated Management Practice

“Dry” swale detains and filters runoff

Fitting IMPs into landscaping

Portland, Oregon Albany, California

Fitting IMPs into landscaping

Seattle, Washington

Spokane, Washington

Reservoir, 12" min. depth

Reverse bend trap or hooded overflow

18" sandy loam, minimum infiltration rate 5" per hour

12" open-graded gravel, approx. ½" dia.

Perforated pipe

Downspout

Building exterior wall

Cobbles or splash block

Filter fabric

Concrete or other structural planter wall with waterproof membrane

Additional waterproofing on building as needed

Drain to storm drain or discharge; bottom-out or side-out options

Planter Box

Integrated Management Practices

Detain and treat runoff

Typically fit into setbacks and landscaped areas

Accommodate diverse plant palettes

Low-maintenance Don’t breed

mosquitoes Can be attractive

Soil surface must be 6-12" lower than surrounding pavement

Require 3-4 feet of vertical “head”

Can affect decisions about placement of buildings, roadways, and parking

Advantages Challenges

Implementing “LID”

IMPs can be effective, attractive, and accepted by developers

Incorporate IMPs in preliminary site, landscaping and drainage design drawings

In-ground planter boxes under construction

Residential subdivision

Clayton, May 2006

Some Possible Next Steps

Discuss options with public works directors

Sponsor a public workshop with developers and land development engineers

Convene a group of municipal attorneys to develop a model revised stormwater ordinance

Develop more specific guidance for implementing new design standards