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Article in Stormwater magazine edition with SuperTank used at Virginia Capitol.
Citation preview
January/February 2013 | www.stormh2o.com
THE JOURNAL FOR SURFACE WATER QUALITY PROFESSIONALS
Also in this issue:• A supersized BMP• Daylighting a river• Greening the Twin Cities
Also in this issue:• A supersized BMP• Daylighting a river• Greening the Twin Cities
STREET SWEEPING
STREET SWEEPINGENHANCING OVERALL BMP PERFORMANCEENHANCING OVERALL BMP PERFORMANCE
January/February 2013 | www.stormh2o.com
55January/February 2013 www.stormh2o.com
Last summer, the Virginia Department of Conservation and Recreation, the Department of General Services, the city of Richmond, and the Alliance for the Chesapeake Bay completed
a green stormwater retrofit of Virginia’s Capitol Square. As have other states in the Chesapeake Bay watershed, Virginia has paid increasing attention to the quality and quantity of its run-off in recent years. With this project, the state government has taken the lead, demonstrating that low-impact development can be an effec-tive retrofit tool in urban areas.
The Greening Virginia’s Capitol project included fi ve phases designed to preserve the character of the Capitol Square while reducing runoff. The project includes rain gardens, bioretention plant-ers, porous pavers, and a rainwater harvesting system. This rainwater harvesting system is one
of the fi rst to be installed on a state capitol site and provides a valuable public example of a rain-water harvesting system. As with most retrofi t projects, the design and installation of the system had to be modifi ed from the original plans and
PROJECT PROFILE
Retrofi tting Virginia’s Capitol SquareRetrofi tting Virginia’s Capitol Square
System installation
56 January/February 2013www.stormh2o.com
adapted to the site.The initial plan for the rainwater
harvesting system involved a large preexisting underground detention tank. Unfortunately, runoff was not fi ltered before entering the tank. Pre-tank fi ltration is a crucial but often-ignored component of a rainwater harvesting system. Without fi ltration, leaves and other organic debris build up and decompose in the tank, which can create anoxic conditions and support extensive bacterial growth. A partition wall to create a settling area was considered, but the cost of routine maintenance (i.e., clean-ing out the settling area) and the cost of fabricating the partition wall made this option cost prohibitive. In addi-tion, because the tank was designed as a detention tank, the rainwater could be stored for only short time periods, reducing the amount of water the rainwater harvesting sys-tem would supply.
The second design option involved intercepting the existing stormwater
drainage system at a manhole near the capitol building and routing this water to a new storage tank. This plan was ideal because the water
system would have collected most of the water from the roof of one wing of the capitol building. Roof sur-faces are ideal for rainwater harvest-ing because roof runoff is typically cleaner than runoff from ground sur-faces. In addition, in urban settings, the roof area often makes up a large portion of the total site impervious area. Unfortunately, during site inves-tigations, the civil engineer, Chris Sonne of Civil and Environmental Services LLC, discovered that the manhole did not exist. As is common when retrofi tting a stormwater sys-tem at an existing site, particularly a site that has undergone multiple renovations, verifying the plans with site surveys is crucial.
Finally, installation of a new rainwa-ter storage tank to collect some site runoff and water from the underdrains of nearby rain gardens was selected. Sonne sized the rainwater harvesting system using the new rainwater har-vesting spreadsheet provided by the Virginia Department of Conservation and Recreation and available on the Virginia Stormwater BMP Clearing-house. Optimizing rainwater harvest-ing systems to provide a consistent water supply and maximize storm-water benefi ts is frequently a chal-lenge. This spreadsheet uses mea-sured daily rainfall data for a 30-year
Underground storage tank (above) and rain garden from which runoff is collected
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57January/February 2013 www.stormh2o.com
window to model the rainwater har-vesting system based on anticipated inputs from the catchment area and expected demand. The spread-sheet summarizes these results into a table that lists the percentage of runoff reduction for storms 1 inch or less and the percentage of the water supply demand met by the rainwa-ter harvesting system for a variety of tank sizes. Larger tank sizes are able to supply more water and a
greater runoff reduction. However, the results typically show a point of
diminishing returns beyond which increases in tank storage volume have little effect on the overall volume of water stored. Using this spreadsheet, an 8,000-gallon storage tank was selected. According to Sonne, the rainwater harvesting sys-tem should save $1,500 per month in water bills.
Selecting a tank size and location is only a small part of the design of a rainwater harvesting system. Sonne
worked with Rainwater Manage-ment Solutions to design the fi ltration and pumping system. Before water enters the storage tank, it is fi ltered through four WISY vortex fi lters. These self-cleaning fi lters prevent any debris larger than 280 microns from entering the tank, protecting the water quality and removing the costly maintenance demand of cleaning a tank. The fi ltered water then enters the tank through a smoothing inlet. With the smoothing inlet, new, oxy-genated water can be introduced near the bottom of the tank, prevent-ing a stagnant layer, without disturb-ing any settled sediment.
This system is one of the fi rst to be installed on a state capitol site and provides a valuable public example of a rainwater harvesting system.
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age to the pump, which limits the amount of usable storage space in the tank. The cooling jacket allows the pump to be laid at approximately 15 degrees and provides appropri-ate cooling. Because the harvested rainwater will supply the fountain and some irrigation needs, the pump is controlled by a variable frequency drive. This drive will maintain water pressure and energy effi ciency across a wide range of fl ow rates without fre-quent pump starts and stops.
The rainwater harvesting system and the other low-impact-devel-opment projects were installed by Messer Contracting of Richmond, VA, with oversight from the Vir-ginia Department of General Ser-vices. Because of the design pro-cess, only minor modifi cations were required during installation. As with design, installation of retrofi t proj-ects includes additional challenges. The most signifi cant challenge when installing a rainwater harvesting sys-tem into an existing storm drainage system is ensuring the inverts to the tank are all installed to allow grav-ity overfl ow. The tank also had to be carefully sited to avoid damage to existing trees.
The installation of a rainwater har-vesting system on the Virginia Capitol Square demonstrates how rainwater harvesting can work as part of a low-impact-development treatment train. Until recent years, rainwater harvest-ing was considered only a water con-servation practice. With the devel-opment of sites such as the Virginia Capitol Square, rainwater harvesting is gaining attention as a stormwater management practice, particularly because of the ability of rainwater harvesting to reduce total runoff vol-ume. The combination of water con-servation and stormwater benefi ts helps make rainwater harvesting a cost-effective option for many sites.
For related articles: www.stormh2o.com/project-design
While water is introduced near the bottom of the tank, it is drawn from near the top of the water column for use. A fl oating fi lter sits approxi-mately 6 inches below the water sur-face. Water at this depth is often the cleanest in the tank because buoyant debris fl oats above the intake and
heavier debris sinks below the intake. The water is pressurized with a sub-mersible pump in a cooling jacket at the bottom of the tank. Submersible pumps are often installed vertically in rainwater harvesting tanks. However, the pumps must be fully submerged to cool appropriately and avoid dam-
Some of the harvested rainwater will supply a fountain.
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Rainwater Harvesting Case Study:
Virginia Capitol Achieves “Sustainable Sites” Pilot
Project with SuperTank™
Water Reclama on Solu ons, LLC Sales@wrs‐solu ons.net Phone: 910‐340‐0552
OO n this project, the Commonwealth of Vir‐
ginia applied to the Na onal Fish and
Wildlife Founda on in conjunc on with
the James River Founda on for a grant
to “...implement a variety of innova ve storm water
management approaches in a high‐profile urban envi‐
ronment.” Addi onally, the “Greening of Virginia’s
Capitol” Project has been selected by The Sustainable
Sites Ini a ve™ (SITES™)as a Pilot Project. The SITES™
program “…is an interdisciplinary effort by the Ameri‐
can Society of Landscape Architects, the Lady Bird
Johnson Wildflower Center at The University of Texas
at Aus n and the United States Botanic Garden to cre‐
ate voluntary na onal guidelines and performance
benchmarks for sustainable land design, construc on
and maintenance prac ces.”
“We looked at fiberglass, plastic, and several other options and the SuperTank was
just the best value.” -Tony Griffen Deputy Chief of Maintenance & Operations for the Bureau of Facilities Management, Virginia Department of General Services
Project: Greening of Virginia’s Capitol
Location: Capitol Square, Richmond, Virginia
Owner: Department of General Services, Virginia
Description: Design and Build rainwater harvesting and Storm water Reuse system capable of Supplying water to historic fountain and irrigation to the Grounds of Virginia’s State capitol
Water usage: Fountain Water, Irrigation
General Contractor: Messer Contracting
Engineer: Civil & Environmental services, LLC
Rainwater Design: Rainwater Management Solutions, Inc
Installer: Messer Contracting