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Alliance for the Chesapeake Bay Stormwater Management Projects

Dynamic partnership provides water quality treatment to protect the bay from pollution.
  • Meandering rain garden lined with river rock outside St. Margaret’s Episcopal Church - Gannett Fleming.

    A rain garden at St. Margaret’s Episcopal Church captures and treats runoff from a downspout.

Alliance for the Chesapeake Bay

Anne Arundel County, Maryland

Our Role
Design, Construction Management.

2 acres
Construction Cost
New Construction
  • Runoff pollutants reduced by up to 40 percent, helping protect the Chesapeake Bay
  • Program showcases stormwater treatment for congregations and communities
  • Partnership with interfaith program provides countywide water treatment.

Church congregations throughout Anne Arundel County, Maryland, participated in an ambitious program to protect the Chesapeake Bay from stormwater pollution. In partnership with the nonprofit Alliance for the Chesapeake Bay (ACB), they installed best management practice (BMP) features on church properties to naturally remove harmful nutrients from runoff before it reaches the bay. The projects improve water quality by reducing the runoff’s nitrogen and phosphorus content by an estimated 20 to 40 percent, decreasing the source of toxic algae blooms.

Gannett Fleming worked hand-in-hand with the ACB and representatives from two congregations to design and build BMP features that effectively treat stormwater runoff on two church properties. The projects were funded by a Maryland Department of Natural Resources grant obtained by the ACB as part of RiverWise Congregations, a collaborative program to protect the bay and highlight the importance of stormwater quality to the community.

What We Did

BMP features were custom designed to fit the constraints of each individual site and achieve goals established by the congregations. A 60-foot-long rain garden outside the nave at St. Margaret’s Episcopal Church in Annapolis includes a lined, brick planter that collects and treats stormwater from the building’s downspout. A weir allows overflow to enter a bed of river rock and native plantings, where water is filtered naturally to remove pollutants.

St. John Lutheran Church in Linthicum faced a different challenge—a half-acre, sloped parking lot that directed untreated stormwater straight into a storm drain. The solution was a trench along the lot’s lowest edge, topped with rock cobble and lined with permeable soils to capture and filter runoff before it reaches the drain. Two separate rain gardens capture stormwater from the parsonage roof and a neighboring 1-acre lot, providing natural filtration. The team’s work at both churches included construction oversight to ensure that the features were built as specified.

Key Features

  • Modified planter with weir treats church roof runoff and directs overflow into a rain garden
  • Rain gardens provide natural filtration to remove pollutants from runoff
  • Trench system collects and treats parking lot runoff before it enters the storm drain.

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