SM Retrofit: Countywide (P808726)

  • Category: Conservation of Natural Resources
  • Sub Category: Stormwater Management
  • Administering Agency: Environmental Protection (AAGE07)
  • Planning Area: Countywide
  • Date Last Modified: 4/21/14
  • Required Adequate Public Facility: No
  • Relocation Impact: None
  • Status: Ongoing





This project provides for the design and construction of new and/or upgrades of existing underperforming stormwater management facilities and devices under the County's Municipal Separate Storm Sewer System (MS4) permit as detailed in the draft Montgomery County Coordinated Implementation Strategy (CCIS). Compliance with the MS4 permit requires controlling 20 percent of impervious surfaces, or approximately 4,300 impervious acres, not currently treated to the maximum extent practicable to address the approved Total Maximum Daily Loads (TMDLs). Inventories of candidate projects have been conducted under the Facility Planning: SM project (PDF No. 809319) for the County's ten watersheds (Paint Branch, Rock Creek, Cabin John Creek, Hawlings River, Watts Branch, Great Seneca, Muddy Branch, Sligo Creek, Little Paint Branch, and Northwest Branch). Some of the most complex projects constructed under this project are assessed, and the preliminary plans are completed in the Facility Planning: SM project (No. 809319). Where feasible, the projects integrate wetland and habitat features consistent with the goals of the Chesapeake Bay 2000 Agreement. In small drainage areas, retrofit projects may also include biofiltration, bioretention, or stormwater filtering devices.

Cost Change

Increase due to the addition of FY19 and FY20 to this ongoing project and adjustments for prior project delays. Costs have also been offset by capitalization of prior expenditures.


This project is needed to comply with the new MS4 permitting requirements outlined in the County Coordinated Implementation Strategy (CCIS) and to implement the County's adopted water quality goals (Chapter 19, Article IV) and protect habitat conditions in local streams. In addition, the project supports the goals of the Chesapeake Bay tributary strategy initiatives and the Anacostia Watershed Restoration Agreement


Projects in design and construction include projects located in the Rock Creek Watershed, Watts Branch Watershed, Great Seneca Creek Watershed, Muddy Branch Watershed, Cabin John Creek Watershed, and Anacostia River Watershed.

Fiscal Note

While the State of Maryland has indicated a desire to provide funding, all indicated State Aid is preliminary and not committed. Funding may need to be revised based on actual State Aid commitments.


Expenditures will continue indefinitely.

The Executive asserts that this project conforms to the requirements of relevant local plans, as required by the Maryland Economic Growth, Resource Protection and Planning Act.


Department of Transportation, Maryland National Capital Park and Planning Commission, Department of Permitting Services, Maryland Department of the Environment, Natural Resources Conservation Service , U.S. Army Corps of Engineers, Facility Planning: SM (No. 809319), Maryland Department of Natural Resources.