Stormwater Quality Treatment

Drainage pipe with water gushing out

Unincorporated Johnson County has adopted regulations that require development projects that disturb more than one acre to treat stormwater for pollutants before releasing it into storm drain system and eventually into our streams and rivers. The requirements of this regulation can have a significant impact on site designs for both private and public development.

Questions regarding this information should be directed to the Johnson County Public Works Department at 913-715-8300.


The purpose of this regulation is to comply with the County's National Pollution Discharge Elimination System (NPDES) permit that is issued by the state of Kansas. This page is a summary of the new requirements and is intended for use by Developers, Project Designers, Plan Reviewers, Contractors, and Inspectors to aid in the development of post-construction stormwater quality treatment plans.

These guidelines apply to both private development projects and municipal capital improvement projects. Development projects that disturb more than one acre and have the potential to negatively impact stormwater quality are required to mitigate impacts through the implementation of Best Management Practices (BMPs). BMPs can include both non-structural measures, such as site planning to preserve open space or native vegetation; or structural measures, such as extended wet detention ponds or engineered wetlands.

If site planning is not enough to mitigate the effects of the development, then the project must include structural post-construction BMPs.

Section 2: Standards

The March 2008 version of the MARC BMP Manual has been adopted as the County's stormwater treatment standards.

The APWA Design Criteria Section 5600 has been adopted as the County's stormwater conveyance standards.

Section 3: Design Spreadsheets

Design Spreadsheets from the APWA/MARC Stormwater BMP Manual (March 2008 version) for calculating design parameters for commonly used BMPs.

These design spreadsheets are provided as an aid to the design engineer who is responsible for checking calculations and designs to meet all applicable regulations. It should also be noted that spreadsheets by their nature can be modified which could lead to errors if not properly coded and checked. The Johnson County Stormwater Management Program and/or CDM (provider of the spreadsheets) does not express or imply any warranty for the use of the spreadsheets.

What Are Your City's Regulations?

The regulations on this page pertain only to the unincorporated area of Johnson County, Kansas. If you plan to build within a City of Johnson County, contact your city to learn more about their regulations