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Fort Belvoir Main Post Infrastructure Improvements

Fairfax County, Virginia

Stormwater Detention


Fort Belvoir Directorate of Public Works


Shirley Contracting Co., LLC


Summer 2010 - September 2011

Technical Description:

CMP Detention 11 systems 72” , 108” diameter

Fort Belvoir is one of the oldest military bases in the country and is located 8 miles south of the Washington D.C. beltway in Fairfax County, Virginia. The base is an ‘open’ base, situated in the heart of an urban area. BRAC (Base Realignment and Closure) improvements to the base required that the access and through roads on Fort Belvoir be widened to increase their capacity and this project was awarded to Shirley Contracting Co., LLC to construct.

The Fort Belvoir Directorate of Public Works (DPW) and the United States Army Corp of Engineers (USACE) were faced with the challenge of choosing a design to meet the Virginia and Fairfax County stormwater management regulations as a result of these improvements. The design needed to provide stormwater management for both the existing and proposed site areas. The available site footprint was limited due to base development and environmental constraints. Consequently, aboveground stormwater management in a pond was quickly eliminated as a viable option and 11 underground stormwater management detention facilities were chosen to meet the project’s requirements. As a result, Shirley selected Contech Construction Products Inc. to design and provide the aluminized steel type 2 (ALT2) underground stormwater management detention facilities. During final design and preparation for construction, Shirley conducted extensive geotechnical analysis of the existing soils.

During this process, it was determined that there were pockets of acidic and possibly contaminated soils within the project area. To address this challenge, Contech designed each detention system to be backfilled with clean graded stone and then encapsulated in EPDM liner. This design served to isolate the existing soils from the 11 systems to ensure that they would not be introduced into the environment through the underground system.

Contech, working very closely with Shirley, was also able to provide additional savings to the project by increasing the diameter of the originally proposed 60” system to 72” and 108”. This increase in diameter significantly decreased the footprint of the 11 systems and enabled Shirley to eliminate some extensive sheeting and shoring required to support the 60” system design. In order to accommodate this increase and support the approval process, Contech provided complete Hydrocad and Water Quality computations for each system.

“Contech partnered with the project team to come up with the most efficient and effective solution to meet a critical schedule and reduce the overall footprint and environmental impact of the systems, helping to make this component of the project a success,” said a Shirley representative.

Technical Description:

CMP Detention 11 systems 72” , 108” diameter

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