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Million-gallon McNamara Pond more than just aesthetics 
8/13/2013 
By Amanda Neumann 

The pond and fountain located at the rear of the McNamara Headquarters Complex is the bubbling focal point of the facility grounds. Besides aesthetics, few realize the pond also serves a more economical purpose: irrigation.

The man-made pond, created during the complex’s construction in 1995, was dug to be a stormwater retention basin, said Greg Pruiksma, chief of building operations and maintenance at HQC Installation Management, part of DLA Installation Support.

“All along the roof and all through the parking lot are stormwater inlets which capture water from rain, snow and hurricanes,” he said. “All that water is channeled to this pond. The pond was designed to slow down the amount of water that enters into the Chesapeake Bay through Dogue Creek and the Potomac River because you’ve now removed the foliage and trees that would have normally slowed it down. It’s a way to help nature.”

Built to collect excess water, the pond’s odd-shape and design is on purpose, Pruiksma said, noting that the pond’s levels vary due to the weather and season.

“It was built very similar to the way they build a dump,” he said. “They hollowed out the ground, put a plastic liner in and covered it with special clay called bentonite, which stops the water from leaking back into the ground. The pond is well over a million gallons, and the center, where the fountain is, is about 27 feet deep. If we’re getting a lot of rain, the level can come up significantly. In the summer or in a drought, the level will come down significantly as we use the water for the irrigation system.”

The pond’s sloped sides have a natural overflow, allowing water pressure to push water to the complex’s “outfall structure,” which discharges the water. It’s then pumped out to the rest of the grounds for irrigation, Pruiksma said.

“It was engineered so that as water rises in the pond, the water pressure pushes water through a pipe to the outfall structure,” he said. “In that room, there is a standing reserve of water, the same height as the pond, with an irrigation pump. The pump picks the feed up from the water level and pumps it out through the irrigation pipes, which reach out to the edge of the parking lot, the front islands and the front and back of the building. Sometimes storms fill up the pond. … As the pond fills up, it will naturally drain back down and, within 24-48 hours, it is self-leveling.”

The irrigation watering system, which uses timers and sensors for plants and grass on the complex, automatically switches off if rainfall is detected. It also allows the complex to adjust the amount of water it uses to treat different areas, Pruiksma said.

“The timers start late in the evening and run until early in the morning,” he said. “Each area is a zone, so they don’t all come on at once, and it’s timed specifically. As we look at the grass, we can adjust those times if we need more water in a specific zone. We typically irrigate from April to October. In the late fall, we shut the system down to keep from freezing the pipes.”

By using the pond, the agency is able to cut costs on water usage, said John Holwick, Fort Belvoir site director in DLA Installation Support.

“For every square of pavement, you have to have retention for the water run-off because it has light amounts of oil and fuel,” he said. “To keep it from going straight into the storm drains, it goes into the retention pond and it’s basically filtered as it seeps through. Because we use the pond’s gray water for watering, which is free, versus using metered water that is treated, it is one of the reasons we were able to cut our water consumption costs by 20 percent.”

There are also fish in the pond: Israeli carp to be exact, although estimates of how many fish vary, said Tamberly Averett, division chief at HQC Installation Management.

“Absolutely there’s fish,” she said, noting the pond was stocked with a dozen fish to begin with. Introduced to cut down on algae growth, the fish quickly grew in size and population, Pruiksma said, attributing part of their success to the installation’s supplemental feeding of barley.

“Besides aeration from the fountain, there was nothing in the pond to stop algae so we added the fish,” he said. “The carp were chosen because they are particularly known for their ability to eat algae. We supplement the carp by adding submerged barley bales that we replenish twice a year. As the barley decays, it gives off enzymes that stop the growth of algae. It doesn’t get rid of algae that have already bloomed. But the fish eat the algae, so do frogs, snakes, turtles. And the carp have gotten huge, there’s some fish out there that are 20 pounds.”

For Pruiksma and his team, the fun part comes when it’s time to clean the pond.

“We do preventative maintenance on the fountain periodically,” he said. “We go out there on a boat, with all our safety gear, scrape the algae off and replace the light bulbs. And boy, do we get a lot of phone calls when people see us out there. The first thing we do is we shut the fountain off. As soon as the fountain goes off, we get the first calls asking, ‘What’s wrong with the fountain?’ and ‘Have we lost power?’ It always causes quite the stir.”

Photo: pond behind building
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The stormwater retention pond, which holds over a million gallons of water, is an aesthetically pleasing focal point of the McNamara Headquarters Complex. The man-made pond was designed to slow water flow into the Chesapeake and allow for irrigation of the complex’s grounds. Photo by Teodora Mocanu