The Washington State Department of Ecology has mandated that Seattle adopt additional stormwater control regulations as a condition of the City’s National Pollution Discharge Elimination System (NPDES) permit for its stormwater systems. To be compliant, the City’s regulations must be equivalent to Ecology’s Stormwater Management Manual for Western Washington. To meet these requirements, Seattle is revising the existing Stormwater, Grading and Drainage Control Code (SMC 22.800-22.808) and its associated Directors’ Rules. The Directors’ Rules contain more detailed requirements specifying the methods to be used to comply with the code. These Directors’ Rules will be administered jointly by DPD and Seattle Public Utilities (SPU).

Stormwater regulations are needed to protect people, property and the environment from damage that could be caused by rain water running off of our urban land surfaces. This stormwater runoff can cause flooding, landslides, erosion and other potential hazards. It can also carry pollutants into our creeks, lakes, bays and other receiving waters.

Seattle’s stormwater code includes these requirements:
1. To practice stormwater pollution prevention during construction
2. To reduce the introduction of pollutants into stormwater runoff as close to the source as possible
3. To install flow control and/or stormwater treatment facilities, depending on the size and nature of a project

Seattle’s stormwater regulations will consist of the Stormwater Code (SMC 22.800-22.808) and four Joint DPD/SPU Directors’ Rules. The Directors’ Rules provide specifications, guidelines, and additional information for meeting the requirements of the Stormwater Code. The four Directors’ Rules are:

• Volume 1: The Source Control Technical Requirements Manual
• Volume 2: The Construction Stormwater Control Manual Technical Requirements Manual
• Volume 3: The Stormwater Flow Control and Water Quality Treatment Best Management Practices Technical Requirements Manual
• Volume 4: The Stormwater and Side Sewer Code Enforcement Manual

Seattle last updated its Stormwater Code in 2000 to comply with its 1995 NPDES Municipal Stormwater Permit. A new NPDES Municipal Stormwater permit was issued January 17, 2007, which requires our Stormwater Code to be changed to be equivalent to the Stormwater Management Manual for Western Washington (Ecology 2005).

The Stormwater Code Revision Project is an SPU-led project, conducted in close collaboration with DPD, the Department of Transportation, and many other City departments and external stakeholders.

The objectives of the project are to produce a set of requirements and technical standards that:
1. Protect – to the greatest extent practicable – life, property, and the environment from loss, injury and damage by pollution, erosion, flooding, landslides and other adverse impacts of urban stormwater runoff.
2. Meet the requirements of state and federal law, including the City’s municipal stormwater NPDES permit.
3. Obtain a determination from the Washington State Department of Ecology that Seattle’s Stormwater Code is equivalent to Ecology’s Stormwater Management Manual for Western Washington (February 2005).
4. Provide a clearly-written, cohesively-formatted set of requirements and standards that are consistent with other City regulations, policies and procedures.
5. Reflect the latest advances in management techniques designed to reduce the adverse impacts of stormwater runoff in an urban environment.

Major Changes
The Stormwater Code and its associated Joint SPU/DPD Directors’ Rules have been completely rewritten in order to provide a more consistent and cohesive set of regulations, requirements, and standards. Of all the changes incorporated into the revised Stormwater Code and Directors’ Rules, the three most significant involve:
1. Revising how the Stormwater Code is enforced
2. Incorporating requirements to install green infrastructure
3. Changing thresholds and performance standards for development projects.

The revised Stormwater Code will modify the existing code in order to meet the following goals:
1. Empower the Directors of SPU and DPD to issue penalties administratively as an additional option, while retaining current provisions regarding referral to Municipal Court in the Code.
2. Ensure the penalty is better matched to the nature of the violation and the actions by the responsible party. The assessed penalty, which can range from $250 to $5,000 per day of violation, will be determined by using a matrix-based set of criteria and guidelines.

Green infrastructure are best-management practices that use infiltration, evapotranspiration, or stormwater reuse to manage stormwater runoff. The revised Stormwater Code will contain design criteria for a suite of these stormwater flow control and treatment facilities, including bioretention, landscaping, permeable paving, rainwater harvesting, and vegetated roofs. Additionally, the revised Stormwater Code will require development projects in Seattle above a specific threshold to implement green infrastructure to the maximum extent feasible.

Significant changes in treatment and flow control are being proposed for all development projects, based on Ecology’s minimum requirements and Seattle’s unique development patterns. In general, thresholds and performance standards for flow control and treatment will be a function of:
1. The five project types defined in the revised Stormwater Code: Single-family residential project, Parcel-based project, Roadway project, Joint project, and Trail/Sidewalk project.
2. The requirement for a project to install a flow control facility, a water quality treatment facility, or both, depending on the drainage basin in which the project is located.A project located in a creek basin (a “flow critical receiving water”) will be required to meet a flow control requirement based on a flow-duration standard, which is more protective than the flow requirements in the current Stormwater Code.
3. The amount of impervious surface on a site. As is true with the current Stormwater Code, the thresholds that trigger a requirement to install a flow control or treatment facility depend on the amount of new plus replaced impervious surface (for flow control) or the amount of new plus replaced pollution-generating impervious surface (for treatment). Among the changes to the existing thresholds are the following:

• Treatment: The new threshold for treatment will be lowered from the current one acre to 5,000 square feet of new plus replaced pollution-generating impervious surface. This change is based on both Ecology’s minimum requirements and, for roadways, the need to reduce the amount of pollutants entering our receiving waters.
• Flow Control: The new threshold triggering flow control for projects discharging to the public combined sewer will be raised from the current 2,000 square feet to 10,000 square feet of new plus replaced impervious surface. This change is intended to reduce the number of small flow control facilities.

The Draft Stormwater Code and associated Directors’ rules can be found online at: www.seattle.gov/dpd/Planning/Stormwater_Grading_and_Drainage_Code_Revisions/
Overview/default.asp
The Stormwater Code revisions are anticipated to go into effect in early 2009.