Maryland’s new General Permit for Stormwater Discharge Associated with Construction Activity (20-CP) will be effective on April 1, 2023. The reissuance has been long anticipated; the previous General Permit for Stormwater Discharge (14-GP) expired December 31, 2019¹ and a draft of the new permit was issued in September 2020.

Wetland Studies and Solutions, Inc. (WSSI) has reviewed the 20-CP, and has summarized key points below in order of appearance in the permit. Links to the permit and other resources from the Maryland Department of the Environment (MDE) are provided at the bottom of this page. WSSI staff are available to discuss what these changes mean for your projects.

Notable in the 20-CP

  • Projects operating under the 14-GP will need to apply for authorization via a Notice of Intent (NOI) under the new 20-CP by September 30, 2023.
  • Under the new 20-CP, the 14-day public notice will begin after a Stormwater Pollution Prevention Plan (SWPPP) has been fully prepared and the Erosion and Sediment Control (ESC) plan fully approved, where previously the 14-day public comment period started immediately once the NOI had been submitted without the need for a completed SWPPP and approved ESC plan.
  • NOI application requirements reflect increased focus on pollution prevention; some examples include:
    • Site Information, Responsible Person, Proof of Workers Compensation Insurance Coverage
    • Project & Watershed information
    • Approved Erosion and Sediment Control Plan and associated information (RCNs, BMPs, Area of Disturbance, Impervious Cover) and a vicinity map
    • Tier II Antidegradation Checklist (if applicable)
    • Completed SWPPP
    • Indication if known contaminated soils are being disturbed (if applicable)
    • Indication if chemical additives are used for flocculation (if applicable)
    • Rare, Threatened or Endangered species or designated critical habitats and if they are addressed in the E&SC Plan or SWPPP
    • Indication if dewatering benchmarks are applicable
  • Use of chemical additives for sediment control is addressed for the first time in the CGP (Part I.C.3).
    • When chemical additive use is anticipated, the permittee must disclose it in the NOI application and provide details in the project’s SWPPP.
    • Chemical additives not on the 20-CP’s pre-approved list will require review per the protocol provided in the 20-CP. Cationic polymer use requires additional review with residual testing.
  • The 20-CP mandates that permittees meet new Stream Protection Zone requirements. “The Stream Protection Zone consists of a natural buffer from the site’s earth disturbances to edge of stream of at least 50 feet for Tier I watersheds, or an average of 100 feet and not less than 50 feet at any point for Tier II watersheds, or other appropriate E&SCs in addition to, or instead of, a Stream Protection Zone. Additional requirements may also apply based on State regulations or local criteria (e.g., wetlands and waterways, forest conservation, and critical area).” Specifics for implementation are in Part III.A.2.a, Appendix B, and Appendix C.
  • Pollution prevention requirements have been added to the 20-CP in Part III.A.3 to detail the controls required to prevent pollutant discharges and to minimize the discharge of pollutants from spilled or leaked materials.
  • Inspection timing has been refined in Part III.C.2 & Part III.C.3. These changes provide a more prescribed inspection schedule, in contrast with the 14-GP’s requirement for weekly inspections paired with post-rain inspections within 24 hours of a runoff producing event; rainfall quantity was not specified.
    • Permittees will now have the option to choose from two regimens:
      • Once every four business days or
      • On a weekly schedule that also requires ¼” rain event inspections.
      • Projects that discharge to Tier II waters have a more demanding inspection schedule of twice weekly.
  • A SWPPP will now be required if the operator has any of the following conditions at their site, as noted in Part III.F.1:
    • The use of chemical additives or polymers for sediment control
    • Construction activity that calls for disturbing material or soils with known contamination by toxic or hazardous substances (Part I.D.6 and Part III.B.3)
    • Dewatering activity requiring turbidity benchmarks (Part III.B.4)
    • MDE requirements for using additional controls to meet water quality standards (Part III.B.1)
    • Use of controls associated with any of the pollution prevention activities referenced in Part III.A.3 (some projects smaller than five acres are exempt)
    • Sharing permit-related functions between and among operators on the same site
    • Where coverage under this permit is required but Title 4 provides grounds to exempt E&SC or SWM plan requirements or both
  • Turbidity benchmark monitoring is now required for sites where the dewatering effluent discharges to sensitive waters (Tier II or Impaired Waters) or there is a sediment or a sediment-related parameter. Details are in Part III.B.4.

¹ In May 2020, the U.S. Environmental Protection Agency deemed the expired permit unacceptable and requested MDE require all permittees who had permits issued after December 31, 2019 to sign a Declaration of Intent (DOI) that committed the permittee to following the requirements of the permit, regardless of its expiration, while MDE worked on finalizing the 20-CP.



  • Matt Elliott, CPESC, CESSWI

    Environmental Compliance Manager - Northern Region

    Gainesville, VA

  • Joshua Howard, CPSEC, CESSWI

    Environmental Compliance Specialist

    Millersville, MD