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Development the Right Way

A commitment to Low Impact Development overcame constrained site challenges and environmental limitations to deliver a new Post Exchange shopping center at Fort Belvoir that maximizes aesthetic, practical and sustainable elements.

 

By Emily C. Murphy Siem, CPSM, Kristine L. House, P.E., LEED AP, and Gregory V. Murphy, P.E., ARCSA AP, M.SAME 

  


 

The new Post Exchange (PX) at Fort Belvoir, Va., on the outskirts of Washington D.C., exemplifies the federal government’s commitment to providing sustainable proj­ects and the ability of its industry partners to deliver projects that meet the goals of sustainable design.

With the comprehensive implementa­tion of Low Impact Development features within the site engineering design, the Fort Belvoir PX shows that a commitment to sustainability can extend far beyond the installation of solar panels and building insulation. It can mean incorporating sustainable elements on virtually all of the land occupied, or disturbed by, the facility.

In the years leading up to the 2012 ground-breaking of the project, the govern­ment had identified the need to replace the aging, existing shopping center . It wanted a more modern center, comparable to the shopping experience seen in neighbor­hoods across America—a PX that would meet, even exceed, the quality of other new facilities around the country. As the target construction date approached, policies and standards aimed at providing sustainable projects were being implemented by the federal government. The project’s contract­ing and management team determined that the design and construction team should be selected in part based on their experience in sustainable projects.

 

Fort Belvoir PX project

The 25-acres allotted for the new Fort Belvoir Post Exchange were situated in the midst of a heavily forested area, compacting the site and adding considerations with regard to tree preservation, habitat restoration and wildlife preservation. IMAGE COURTESY CALIBRE ENGINEERING


 

In early 2012, the government selected Walbridge Construction as general contrac­tor and Calibre Engineering as civil engi­neer in charge of designing the Low Impact Development site engineering features for the $42 million, 250,000-ft² complex. Under the contract the work would include a garden center, military clothing store, and a Post Exchange building with nine food concepts and 20 concessions.

The site, complete with native forests, lush plant life and an active biosphere, presented several challenges. Additionally, construc­tion limitations because of the sensitive woodlands environment and a proximity to wetlands had to be addressed by the project team with solutions that would maximize the principles of Low Impact Development.

Thoughtful design considerations were necessary to provide a final product that overcame environmental challenges and met LEED goals. The 25-acres allotted for the PX were situated in the midst of a heavily forested area, compacting the site and adding considerations with regard to tree preservation, habitat restoration and wildlife preservation. The team carefully designed the site layout, reduced the footprint to avoid sensi­tive areas, and utilized underground deten­tion to ensure that the buildings would fit within the constraints—without losing critical elements or quality enhancements of the design.

 

HEAT ISLAND EFFECT

The design team was required to meet parking goals (958 spaces) to maximize visitation to the center. However, both the government and the design team desired to minimize the impact of developed impervi­ous areas on microclimate and human and wildlife habitat by incorporating efforts to reduce Heat Island Effect.

To actualize the reduction of Heat Island Effect on the parking areas, the team maxi­mized the use of porous pavement, pave­ment with high Solar Reflectance Index, along with hardscape areas that will be shaded within the next five years.

 

STORMWATER MANAGEMENT

The stormwater management approach was complicated by the adjacent forested and protected biosphere elements. To meet the stringent water quality and mitigation requirements onsite, the team incorporated a variety of controls and strategies to miti­gate the impacts of the development on the quantity and quality of stormwater.

Stormwater quality is being managed by a combination of four bio-retention areas, vegetated swales, fields of porous pave­ment, a mechanical filter, and an existing dry detention basin. All of these remove pollutants generated within the parking lot and other hardscape areas prior to releasing runoff into the existing sensitive areas. The water quality volume being treated is equal to the first 1-in of rainfall over the impervi­ous areas of the site. For best management practices utilizing a flow rate-based design (the mechanical filter), the water quality volume is approximated by half of the two-year rainfall event. The cartridge for the mechanical filter operates at a flow rate of 2-gpm/ft² at 27-in of driving head with a radial media depth of 7-in.

 

Fort Belvoir PX project

Native, naturalized species and hardwood mulch eliminate the need for a permanent irrigation system. Planting bed areas at the entry of the building use native or adaptive shrubs, groundcover plantings and trees. PHOTO COURTESY CALIBRE ENGINEERING


 

Two fields of porous paving allow storm­water runoff to be filtered through the system before it is released, providing water quality control by adsorption, sedimenta­tion, biological action, and infiltration into the underlying soils. The design perme­ability of the porous pavement is 4-in/hr, which was field verified before acceptance. The site has a maximum ratio of 7:1 for impervious area tributary to the porous pavement, and the maximum drain time for the system is 48 hours.

The stormwater infiltration design achieves 65 percent phosphorous removal at vegetated swales, 50 percent phospho­rous removal at the mechanical filter, and a theoretical total phosphorous removal of 59 percent, as well as a greater than or equal to 80 percent suspended soil removal.

Stormwater quality criteria implemented by the government in an effort to promote sustainable design includes a requirement that the post-development release rate not exceed historic rates for the 10-year storm event and the volume of post-development runoff from both the one-year and two-year 24-hour storm events is less than pre-development values. Detention volumes are provided via underground storage facilities and open-graded stone storage depths under the porous concrete and bio-retention areas. Stone storage depths on the project range from 2.5-ft to 4.5-ft. Due to suitable existing site soils, it was possible to incorporate infiltration into the stormwater facilities. Observation wells onsite verify if runoff is not draining properly.

The work met federal requirements of the Energy Independence and Security Act, Section 438, commonly referred to as EISA 438. This provision requires that the project use site planning, design, construction and maintenance strategies that maintain or restore (to the maximum extent technical feasible) the pre-development hydrology of the property with regard to the tempera­ture, rate, volume and duration of flow.

 

POTABLE WATER REDUCTION

The landscape design was developed to exist and perform in harmony with the architecture and the environment.

Existing trees were preserved as much as possible. Removed trees were replaced per the Fort Belvoir Tree Conservation Program. Native, naturalized species and hardwood mulch eliminate the need for a permanent irrigation system. Planting bed areas at the entry of the building use native or adaptive shrubs, groundcover plantings and trees. During the establish­ment period of the turf grass (one growing season), temporary irrigation and natural precipitation provided sufficient water to initiate and sustain growth.

 

SUSTAINABLE AND MODERN

Through the incorporation of sustainable enhancement, the design team was able to help the federal government implement sustainable strategies for the entirety of the site while constructing a modern facility to meet the needs of service members past and present, and their families.

The project demonstrates great technical skill and care for the natural environment, as well as the in-action commitment of all stakeholders to providing sustainable design and construction. Through the execution of projects like the Fort Belvoir PX, government and industry can help shape the built and horizontal landscape to ensure a sustainable and environmentally friendly future.

 


 

Emily C. Murphy Siem, CPSM, is Marketing Manager, Kristine L. House, P.E., LEED AP is Project Engineer, and Gregory V. Murphy, P.E., ARCSA AP, M.SAME, is President, Calibre Engineering. They can be reached at 303-951-8941, or This email address is being protected from spambots. You need JavaScript enabled to view it.; 303-951-8942, or This email address is being protected from spambots. You need JavaScript enabled to view it.; and 303-339-5401, or This email address is being protected from spambots. You need JavaScript enabled to view it., respectively.