Minimum Control Measure #5: Post-Construction Runoff Control

Bioswales are a structural BMP that can help mitigate the effects of stormwater once a site has been developed. 

Post-Construction Runoff Control is one of the six (6) Minimum Control Measures (MCM) required under the Small MS4 program*.  The goal of the Post-Construction Runoff Control MCM is to avoid increased stormwater runoff problems and increased non-point source pollution that often accompanies the development of land and associated increase in impervious surfaces.    Six (6) best management practices (BMPs) are required under this MCM.

Under Chapter 102, Erosion and Sediment (E&S) Control, County Conservation Districts and/or DEP must issue a permit for earth disturbance activities greater than 1 acre.  If the small MS4 permittee elects to use their participation in the Chapter 102 program as a Qualifying Local Program (QLP)  under their MS4 permit requirements, then MCM #5 BMPs 1 -3 are automatically accounted for.  BMPs 1-3 include:  1) Develop a written procedure that describes how the permittee will address all required components of this plan, 2) Require the implementation of a combination of structural and/or non-structural BMPs, and 3) Ensure that controls are installed that will prevent or minimize water quality impacts.   Read below to learn more about each of the 6 BMPs required under this MCM. 

BMP #1 – Develop a written procedure that describes how the permittee will address all required components of this plan.  Guidance can be found in the Pennsylvania Stormwater Best Management Practices Manual, which can be accessed at  The plan should be developed within the first year of permit coverage and be annually reviewed and updated where necessary. Minimum requirements of the plan include:

  • Minimum requirements for use of structural and/or non-structural BMPs in plans for development and redevelopment,
  • Criteria for selecting and standards for sizing stormwater BMPs, and
  • Implementation of an inspection program to ensure that BMPs are properly installed.

BMP #2 – Require the implementation of a combination of structural and/or non-structural BMPs that are appropriate to the local community, the minimize water quality impacts, and that are designed to maintain pre-development runoff conditions.  Ensuring that the BMPs required by the ordinance that must be enacted and enforced under BMP #4 of this MCM will satisfy this requirement.   All qualifying development or redevelopment projects should be reviewed to ensure that their post-construction stormwater management plans and selected BMPs conform to the applicable requirements.  A tracking system should be used to record qualifying projects and their BMPs. 

BMP #3 – Ensure that controls are installed that will prevent or minimize water quality impacts.  Qualifying development or redevelopment projects should be inspected during construction to ensure proper installation of the approved post-construction stormwater management (PCSM) BMPs.  A tracking system should be used to track inspections and results.  Permittees that do not rely on Chapter 102 as a QLP to fulfill these requirements must summarize construction inspections and results in periodic reports.

BMP #4 – The permittee should enact, implement, and enforce an ordinance or other regulatory mechanism to address post-construction stormwater runoff from new development and redevelopment projects, as well as sanctions and penalties associated with non-compliance, to the extent allowable under state law.  An ordinance must be adopted within the first year.   

What is a Post Construction Stormwater BMP (PCM BMP)?

PCM BMPs are practices that are put in place to prevent and mitigate stormwater runoff after the site is developed.  PCM BMPs include non-structural and structural BMPs.  Non-structural BMPs include practices that  aim to avoid and/or minimize damages associated with stormwater volumes and runoff from development.  Structural BMPs are engineered systems that are designed to mitigate the impacts of stormwater.

Examples of Non-Structural BMPs

Examples of Structural BMPs

BMP #5 – Develop and implement measures to encourage and expand the use of Low Impact Development (LID) in new and redevelopment.  Measures also should be included to encourage retrofitting LID into existing development.  DEP’s Pennsylvania Stormwater Best Management Practices Manual provides guidance on implementing LID practices.  An inventory of development and redevelopment projects that discharge stormwater to your regulated MS4 must be kept.  In this inventory, note which projects that have been authorized for construction since 3/10/2003 that incorporated LID practices (and specifics on what LID practices were used).  Additionally, ordinances should be enacted that are consistent with LID practices.  Sections of existing ordinances that conflict with LID practices should be repealed.     

BMP #6 – Ensure adequate operation and maintenance of all post-construction stormwater management BMPs installed at all qualifying development or redevelopment projects (including those owned or operated by the permittee).  Within the first year of permit coverage, permittees should develop and implement a written inspection program to ensure that BMPs are properly operated and maintained.  This program should be reviewed annually and updated accordingly.  An inventory of PCSM BMPs should be developed and updated regularly.  The inventory should include all PCSM BMPs installed since 3/10/2003 that discharge to your regulated MS4.  Information required in inventory includes but is not limited to: owner, location, type of BMP, installation date, required maintenance, inspection activities, and an assessment by the permittee to determine if proper inspection and maintenance of BMP has been taking place.

Explore the links below to learn more about MCM #5, Post Construction Stormwater Best Management Practices, view educational webinars, and more. 

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