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Water: Best Management Practices

Ordinances for Post-construction Runoff

Minimum Measure: Post-Construction Stormwater Management in New Development and Redevelopment

Subcategory: Municipal Program Elements


A vital step in controlling the harmful effects of development on urban water-quality is managing post-construction stormwater runoff.  Land development creates roads, sidewalks, parking lots, rooftops and other impervious surfaces that can have detrimental effects on aquatic systems.  Impervious cover has been linked with stream warming and the loss of aquatic biodiversity in urban areas.  Stormwater runoff from impervious areas can contain sediment, nutrients, road salts, heavy metals, bacteria, petroleum hydrocarbons, and other pollutants detrimental to water quality.     

An ordinance promotes the public welfare by guiding, regulating, and controlling the design, construction, use, and maintenance of any development or other activity that disturbs or breaks the topsoil or results in the movement of earth on land. The goal of a stormwater management ordinance for post-construction runoff is to limit surface runoff volumes and reduce water runoff pollutant loadings.


These ordinances apply to all major municipal subdivisions.  Post-construction stormwater runoff management applies to developments of varying sizes, but many communities opt for a size threshold of at least 5,000 square feet.  Such details should be addressed in the ordinance itself.  All plans must be reviewed by local environmental protection officials.  This is to ensure that established water quality standards are preserved during and after construction, and that post-construction runoff levels are consistent with any local and regional watershed plans.

Several resources are available to assist in developing an ordinance. EPA's (2000)  post-construction model ordinance website provides a model ordinance and examples of programs currently being implemented. The EPA has also developed a website that features model ordinance language. In addition, the Stormwater Managers Resource Center Exit EPA Site, which was created by the Center for Watershed Protection (no date) and is sponsored by the U.S. Environmental Protection Agency, provides information to stormwater management program managers in Phase II communities that helps them meet the requirements of the National Pollutant Discharge Elimination System Phase II regulations.

Siting and Design Considerations

The purpose of the post-construction ordinance is to establish stormwater management requirements and controls to protect and safeguard the general health, safety, and welfare of the public residing in watersheds within a jurisdiction. The following paragraphs provide the general language and concepts that can be included in your ordinance.

General Provisions

This section should identify the ordinance's purpose, objectives, and applicability. Post-construction runoff controls apply to sites of varying sizes, but as was mentioned above, many communities opt for a threshold of at least 5,000 square feet.  This section can also discuss the development of a stormwater design manual.  This manual can include a list of acceptable stormwater treatment practices and may include the specific design criteria for each stormwater practice. In addition, local communities should select the minimum water quality performance standards they will require for stormwater treatment practices and place them in the design manual.


It is important to define the terms that will be used throughout the ordinance to assist the reader and prevent misinterpretation.

Permit Procedures and Requirements

This section should identify the permit required, the application requirements, procedures, and fees, and the permit duration. The permit's intent should ensure that no land-disturbing activities are issued permits prior to review and approval. Communities may elect to issue a stormwater management permit separate from any other land development permits required, or, as in this ordinance, to tie the issuing of construction permits to the approval of a final stormwater management plan.

Waivers to Stormwater Management Requirements

This section should discuss the process for requesting a waiver and to whom this waiver would be applicable. Alternatives, such as fees or other provisions for those requesting a waiver, should also be addressed.

General Performance Criteria for Stormwater Management

The performance criteria that must be met should be discussed in this section. Performance criteria can include the following:

  • All sites must establish stormwater practices to control the peak flow rates of stormwater discharge associated with specified design storms and to reduce the generation of stormwater.

  • New developments may not discharge untreated stormwater directly into a jurisdictional wetland or local waterbody without adequate treatment.

  • Annual groundwater recharge rates must be maintained by promoting infiltration through the use of structural and non-structural methods.

  • For new development, structural sewage treatment plants must be designed to remove a certain percentage of the average annual post-development total suspended solids (TSS) load.

Basic Stormwater Management Design Criteria

Rather than place specific stormwater design criteria into an ordinance, it is often preferable to fully detail these requirements in a stormwater design manual. This approach allows specific design information to be changed over time as new information or techniques become available without requiring the formal process needed to change ordinance language. The ordinance can then require those submitting any development application to consult the current stormwater design manual for the exact design criteria for the stormwater management practices appropriate for their site. Topics in the manual can include minimum control requirements, site design feasibility, conveyance issues, pretreatment requirements, and maintenance agreements.

Requirements for Stormwater Management Plan Approval

The requirements for a stormwater management plan should be addressed in this section. This can be accomplished by including a submittal checklist in the stormwater design manual. A checklist is particularly beneficial because changes in submittal requirements can be made as needed without revisiting and revising the original ordinance.

Construction Inspection

This section should include information on the notice of construction commencement, as-built plans, and landscaping and stabilization requirements.

Maintenance and Repair of Stormwater Facilities

Maintenance agreements, failure to maintain practices, maintenance covenants, right-of-entry for inspection, and records of installation and maintenance activities should be addressed in this section.

Enforcement and Penalties

This section should include information on violations, notices of violation, stop work orders, and civil and criminal penalties.


Site inspections are required for a post-construction stormwater ordinances. In addition, an adequate staff must be available to review permit applications and proposed plans.

Maintenance Considerations

A stormwater ordinance's operation and maintenance language can ensure that designs facilitate easy maintenance and that regular maintenance activities are completed. In the "Maintenance and Repair of Stormwater Facilities" section of your ordinance, it is important to include language regarding a maintenance agreement, failure to maintain practices, maintenance covenants, right-of-entry for inspection, and records of installation and maintenance activities.


If a stormwater management ordinance for existing development is properly implemented and enforced, the community can effectively achieve the following:

  • Minimize increases in stormwater runoff from any development to reduce flooding, siltation, and streambank erosion, and to maintain the integrity of stream channels.

  • Minimize increases in water quality-degrading stormwater pollution caused by runoff from development.

  • Minimize the total annual volume of surface water runoff that flows from any specific site during and following development, so as not to exceed the pre-development hydrologic regime to the maximum extent practicable.

  • Reduce stormwater runoff rates and volumes and soil erosion through stormwater management controls, and ensure that these management controls are properly maintained and pose no threat to public safety.
Cost Considerations

Municipalities that implement and enforce post-construction ordinances must budget for the drafting and enforcement of the regulation.


Center for Watershed Protection (CWP).  Stormwater Manager's Resource Center.  [www.stormwatercenter.net Exit EPA Site].  Accessed May 24, 2001. 

USEPA. 2000. Model Ordinances to Protect Local Resources: Post-construction Controls. U.S. Environmental Protection Agency, Washington, DC. [www.epa.gov/nps/ordinance/postcons.htm]. Last updated July 12, 2000. Accessed October 3, 2000.

USEPA. Model Ordinances Language.U.S. Environmental Protection Agency, Washington, DC. [www.epa.gov/owow/nps/ordinance/mol4.htm#topofpage]. Last updated September 23, 2003. Accessed May 23, 2005.

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