Post-construction Stormwater Management


This measure focuses on mitigating stormwater impacts from new and re-development by requiring practices that treat, store, and infiltrate stormwater onsite. Towns should use the minimum disturbance size they normally regulate (whether it's 0.5 acres per the Erosion Sediment Control Act or smaller if your town uses a lower threshold) for the stormwater retention standards in this section.

Relevant terms

  • Redevelopment: means any construction activity (including, but not limited to, clearing and grubbing, grading, excavation, and dewatering) within existing drainage infrastructure or at an existing site to modify or expand or add onto existing buildings or structures, grounds, or infrastructure.
  • Low impact development (LID): means a site design strategy that maintains, mimics, or replicates pre-development hydrology through the use of numerous site design principles and small-scale treatment practices distributed throughout a site to manage runoff volume and water quality at the source.
  • Runoff reduction practices: means those post-construction stormwater management practices used to reduce post-development runoff volume delivered to the receiving water, as defined by retaining the volume of runoff from a storm up to the first half inch or one inch of rainfall in accordance with sections 6(a)(5)(B)(i) or (ii) respectively. Runoff reduction is quantified as the total annual post-development runoff volume reduced through canopy interception, soil amendments, evaporation, rainfall harvesting, engineered infiltration, extended filtration or evapotranspiration.
  • Water Quality Volume (WQV): means the volume of runoff generated by one inch of rainfall on a site as defined by the Connecticut Stormwater Quality Manual.


Task list

Where the deadline for new MS4 permittees differs from the deadline for exisiting permittees, the second deadline in parenthesis applies to new permittees.



Permit page

Maintenance plan for stormwater ponds and treatment structures

Jul 1 2019
(Jul 1 2020)


Determine baseline DCIA

Jul 1 2020


Review regulations for LID barriers

Jul 1 2021
(Jul 1 2022)


Establish legal authority for site stormwater retention standards

Jul 1 2021
(Jul 1 2022)