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Water Quality Improvements at Manchester Farm

As part of Montgomery County’s responsibility to ensure the proper functioning of stormwater management facilities and reduce pollutants in our local streams and rivers, the County’s Department of Environmental Protection will upgrade several poorly functioning, existing stormwater management ponds that have reached the end of their functional lifespan. By installing upland stormwater best management practices, including submerged gravel wetlands, stormwater quantity management can be realized along with improvements to water quality.  Impaired and deeply incised outfall channels associated with existing stormwater facilities will also be stabilized. Native tree and shrub planting will follow construction to promote a vegetative buffer. 

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PROJECT DETAILS

Submerged Gravel Stormwater Management System (SGSMS)

Typical SGSMS at full maturity, in the Spring/Summer.

Typical SGSMS, immediate post-construction.

Typical SGSMS at full maturity, in the Winter.

Retrofitting the existing dry ponds to SGSMSs will add water quality treatment function while expanding the facility’s stormwater storage volume to reduce flows downstream.

  • The existing dry ponds provide limited water quality treatment.
  • Various components within the existing facility are failing and in need of maintenance or replacement.
  • Structural deficiencies include sediment accumulation, failing and rusting pipes, and drains clogged with debris and sediment.
  • Converting the existing dry ponds to SGSMSs will improve water quality and expand the facility’s stormwater storage volume.
  • Project design will include excavating gravel media and sloping both pond bottoms. A flow splitter will be used to divert a portion of water quality volume to one of the ponds in the existing facility.
  • Native herbaceous plant materials will be sourced specifically for this area and planted within an organic layer at the base of the SGSMS, overlaid on a gravel media. No exotic or invasive plant material will be used.
  • Flowering plants will attract and serve as habitat for pollinator species, improving plant growth and biodiversity in the region by facilitating a key step in plant reproduction processes.
  • Construction is currently scheduled to begin in Spring 2025 and will last approximately five months. Most excavation and truck traffic will occur within a 10-12-week window in the middle of construction.
  • Community members will have the opportunity to review plans before construction at various points in the planning process and will be invited to walk the site with the GreenVest team before and after construction.

  • Construction parking, staging and stockpiling for the SGSMS retrofit will occur along Steeple Road, near the existing access point in place to maintain the existing facility.

  • Limited tree removal will occur to facilitate access and construction or in cases where a tree is dying or at risk of falling. Material from trees will be used on site for in-stream structures and for wildlife habitat. Trees that are removed will be replanted. The intent of the design is to minimize tree loss to the maximum extent practicable.

  • Open space will remain available informally for public access, as under current conditions.
  • The project must pass through rigorous review processes established by County, State and Federal agencies developed to maximize safety, minimize environmental impacts and ensure modern design standards are met.

Submerged Gravel Stormwater Management Systems are small- scale filters that mimic natural hydrologic and ecological processes to capture and treat stormwater runoff, filtering sediment and pollutants through a combination of wetland plants and gravel media.

PROJECT DETAILS

Stream Restoration and Outfall Stabilization

Stabilizing approximately 1,250 linear feet of actively eroding channels that convey runoff from existing stormwater outfalls into the existing stormwater management facility before flowing to the Germantown Estates Tributary, which drains to Little Seneca Creek, which flows into Seneca Creek, and eventually into the Potomac River.

  • Several outfall channels which flow into and through the existing dry ponds are actively eroding and contributing to sediment and pollutant loading downstream.
  • Under current conditions, streams and outfall channels have unstable vertical banks which undermine large trees, posing a safety risk.
  • Uncontrolled runoff from upstream, steep slopes and erodible soils have contributed to the extensive stream erosion.
  • Structural improvements will reduce erosion, improve water quality and preserve upstream habitat and infrastructure.
  • Outfall channels are major contributors to sediment and nutrient loading in downstream waters due to steep slopes, exposed and non-cohesive soils and/or inadequately controlled stormwater runoff.
  • Project design will restore approximately 1,250 feet of degrading stream and outfall channels that are incised, vertically unstable and actively eroding
  • Native vegetation, including grasses, trees and shrubs will be planted within the riparian buffer to reduce soil compaction, stabilize erodible soils, and filter storm flows. The riparian buffer will be permanently protected by an easement.
  • Construction is currently scheduled to begin in Winter 2025 and will last approximately five months. Most excavation and truck traffic will occur within a 10-12 week window in the middle of construction.
  • Community members will have the opportunity to review plans before construction at various points in the planning process and will be invited to walk the site with the GreenVest team before and after construction.
  • The stream and outfall channels will be used as primary access points for stream restoration work in this area to minimize clearing and tree removal, and preserve existing residential viewshed to the greatest extent possible.
  • Limited tree removal will occur to facilitate access and construction or in cases where a tree is dying or at risk of falling. Material from trees will be used on site for in-stream structures and for wildlife habitat. Trees that are removed will be replanted. The intent of the design is to minimize tree loss to the maximum extent practicable.
  • The project must pass through rigorous review processes established by County, State and Federal agencies developed to maximize safety, minimize environmental impacts and ensure modern design standards are met.
  • Stream Restoration is a set of techniques used to protect property and infrastructure by reducing stream bank erosion, minimizing the downcutting of stream beds and restoring natural stream ecosystems.
  • Outfall Stabilization is the practice of implementing a stable channel that extends from an upland stormwater pipe outfall to a receiving stream channel. It provides a permanently stable stormwater conveyance through engineering practices such as grading, step-pools, cascades and/or rock stream bank protection.

Typical channel at full maturity, in the Spring/Summer.

Tagline: Typical channel, immediate post-construction.

Typical channel at full maturity, in the Fall/Winter.

PROJECT UPDATES

News & Updates

Check back regularly for up-to-date project news and information, including construction alerts and opportunities to meet with the project team.

December 5, 2025
Site Walk on December 16, 2025
With the construction of the Manchester Farm Stream and Stormwater Management Project complete, we invite all interested residents and stakeholders to a post-construction site
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September 10, 2025
September, 2025 Construction Update
Work is progressing steadily at the Manchester Farm Stream and Stormwater Management Project. Crews have been focused on stream restoration, stormwater management infrastructure installation,
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June 25, 2025
Construction Update
With tree work complete and construction access paths near completion, construction has begun at both the stormwater management facility and outfall channel locations.  
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Frequently Asked Questions

Montgomery County holds a Municipal Separate Storm Sewer System Permit (“MS4 Permit”) issued by the Maryland Department of the Environment under authority delegated from the U.S. Environmental Protection Agency which imposes several water quality improvement requirements and goals on the County. This project will support the County’s efforts to achieve water quality requirements by addressing failing stormwater infrastructure, retrofitting two existing dry stormwater management ponds, and stabilizing eroding streams and outfall channels.

  • The two existing dry ponds serving the Manchester Farm community have various deficiencies including failing and rusting pipes and inlets clogged with debris and sediment.
  • Several outfall channels which flow into and through the existing dry ponds are actively eroding and contributing to sediment and pollutant loading downstream. Eroding banks are undermining large trees, which poses a safety risk and impacts the health of the forest.
  • The project will enhance the geomorphic and hydraulic function of the stabilized stream reach improve water quality and help protect adjacent properties from continued bank erosion and storm flows. Specifically:
    • Retrofitting the existing two dry ponds to a Submerged Gravel Stormwater Management System (SGSMS) will treat sediment, nutrients, and other pollutants, thereby improving water quality.
    • Increasing active stormwater storage volume will reduce storm flows.
    • Restoring approximately 1,247 linear feet of actively eroding channels will reduce erosion, improve water quality, enhance habitat and protect infrastructure.
    • Storm drain outfall channels at the terminus of the existing storm drain network are actively eroding. These outfall channels will be stabilized which will reduce erosion and protect infrastructure.
  • Construction is currently scheduled to begin in Winter2025 and will last approximately five to six months. Most excavation and truck traffic will occur within a 10-12-week window in the middle of construction.
  • Construction parking, staging and stockpiling for the SGSMS retrofit will occur along Steeple Road, near the existing access point in place to maintain the existing facility.
  • The stream channels will be used as primary access points for stream restoration and outfall stabilization work to minimize tree removal and preserve existing residential viewsheds to the greatest extent possible.
  • All project work will follow strict soil erosion and sediment control requirements set by both the State and the County to minimize dust during construction.
  • Techniques such as wetting throughout the day, street sweeping, dust screens, and stabilized construction entrances will be utilized to minimize dust and dirt during construction.
  • There will be some noise disruption during construction. In addition to compliance with standards set forth in the Montgomery County DEP’s Noise Control Law, GreenVest will use noise mitigation techniques to minimize impacts to adjacent property owners. Night work is not anticipated.
  • Most of the excavation work will occur below foundation elevations, which will make vibration unlikely for adjacent residents. However, it is possible that homeowners within 50 feet of the project could feel minimal vibration during excavation.

 

  • GreenVest provides a 1-year guarantee on the completed project which includes providing required maintenance. After this time and into the future Montgomery County will be responsible for structural maintenance of the SGSMS facility, including:
    • Removal of sediment accumulation and debris, if necessary, after major storms.
    • Semi-annual removal of sediment, invasive plant species and replanting in any poorly established areas.
    • Removal of accumulated vegetation and replanting, if necessary, every 2-3 years.
  • Stream restoration and outfall stabilization is designed to be maintenance free.
    • The County will monitor and maintain if needed the streams for a period of five years. This includes ensuring that riparian and floodplain plants are successful and established.
    • After five years, the County will only perform limited maintenance to address concerns that may impact the function of the project.
  • The HOA will continue to be responsible for non-structural maintenance in this area, as it is currently.

For a full list of FAQs, click here.

Fact Sheets
Montgomery County Resources

PROJECT CONTACTS

Contact the Project Team

Residents can sign up to receive email updates and/or text alerts and ask questions of the project team through the contact information below and the form on the right.

Call or Text :

301-960-5355

Email :

info@GreenManchesterFarm.com

Translation Services :

If you would like project information in another language or format, or if you require the services of an interpreter, please contact hilary@GreenManchesterFarm.com.

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