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Mt. Soma Reservoir Design

Pioneering water infrastructure provides Maryland community with a critical storage facility.
  • Aerial view of partially filled impoundment in rolling, wooded landscape - Gannett Fleming.

    The impoundment can hold 90 million gallons of raw water for drought or other water emergency.

  • Closeup view shows bituminous geomembrane liner, pictured during installation - Gannett Fleming.

    The project marks the first time a BGM liner has been used for a water reservoir on the East Coast.

  • Worker installing an array of man-made wetlands units that float on the water’s surface - Gannett Fleming.

    Floating wetlands reduce algae-promoting nutrients in stored water to preserve its clean taste.

Maryland American Water

Bel Air, Maryland

Our Role
Design, Permitting, Construction Services.

90 million gallons
Construction Cost
$6.2 million
New Construction
  • Reliable backup water supply for 20,000 residents of Harford County
  • Enough raw water maintained to last as long as the 100-day drought of record
  • Exposed liner system saved an estimated $450,000 in construction costs
  • Substantial completion seven weeks early exceeded client expectations

The largest Maryland dam project in the past 30 years blazes a new trail for the design of water storage reservoirs in the U.S. The 90-million-gallon Mt. Soma Reservoir, featuring a 62-foot-high earthen embankment with a 20-foot-wide crest, secures a reliable backup water supply for 20,000 residents of Harford County. Gannett Fleming served as lead designer for the project, which draws and stores water from a nearby stream. The facility allows Maryland American Water to maintain enough raw water to provide service to its Bel Air-area customers in the event of drought or other water emergency.

The design team selected a bituminous geomembrane (BGM) liner to create a watertight barrier inside the dam embankment and impoundment floor. The project marks only the second time that a BGM liner has been used to line a water supply reservoir in the U.S., and the first time on the East Coast. Sustainable water-quality improvement systems maintain water quality in the impoundment and inhibit the growth of algae, which can affect water’s taste. Natural wetlands and chemical-free algae control systems help mitigate environmental concerns by reducing chemical usage and related costs by an estimated 20 percent.

What We Did

Because it does not require a soil cover, the BGM liner reduced construction costs by approximately $450,000. The project showcases the benefits of using a BGM liner in an exposed liner system: The liner has a friction angle of 34 degrees, making it suitable for most embankment slopes. Its dimensional stability provides permanent contact with substrate, making it ideal for differential soil settlement, which is common during embankment construction.

The team designed the facility to maximize sustainability. It features man-made floating wetlands to reduce algae-promoting nutrients in stored water, as well as ultrasonic algae control and water mixing systems that eliminate up to 90 percent of existing algae. The impoundment was positioned so that gravity conveys raw water to a nearby treatment plant, eliminating the need for an electric-powered pressure system. Extensive materials testing allowed the team to set acceptable parameters for using on-site soil that accounted for extreme variations in the soil’s composition, eliminating the need for costly soil disposal or hauling.

Key Features

  • BGM liner provides watertight barrier inside 2,025-foot embankment and impoundment bottom.
  • Highly durable, resistant to punctures and ultraviolet radiation, and textured to provide traction, the liner demonstrates an optimal solution for an exposed liner system.
  • Ultrasonic algae control and water mixing systems reduce existing algae by up to 90 percent, maintaining water’s clean taste.

Sustainability Features & Outcomes

  • Artificial floating wetlands reduce nitrogen and phosphorus by approximately 30 percent, lessening the environmental concerns of chemical algae control.
  • Wetland units contain 4,000 native aquatic plants, creating a welcoming habitat for birds, fish, and other wildlife.
  • Gravity system delivers raw water to treatment plant, eliminating the need for an electric-powered pressure system.

Awards & Recognition

  • Best Project, Water/Environment, 2019, Engineering News-Record (ENR) Mid-Atlantic, Regional Best Projects
  • Outstanding Project Award, 2019, American Council of Engineering Companies (ACEC) Maryland, Engineering Excellence Awards
  • National Recognition Award, 2019, American Council of Engineering Companies (ACEC), Engineering Excellence Awards

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