Inside the National Mall's new irrigation system

The Mall’s new irrigation system is a mix of the usual and the unusual.

Photo courtesy of Irrigation Consultants

With more than 25 million visitors and 3,000 events every year, the National Mall turf takes a beating. And after years of heavy use, one of the nation’s most iconic green spaces needed an overhaul. But this wasn’t going to be your average irrigation job.

Spanning three years of planning, four years of construction and covering more than 300 acres of turf, it was a big undertaking, but there were additional challenges to overcome to renovate the irrigation system.

“The word they liked to use is ‘compromised,’” says Brian Vinchesi, president of Irrigation Consulting. “It really didn’t work at all.”

The Mall irrigation system had hundreds of holes from tent stakes and compacted soil. The historic landmark designation meant that nothing new could be built on the grounds. On top of that, the National Park Service wanted to reduce the amount of potable water used for three main reasons.

“One, it’s very expensive, two, they wanted to be sustainable and three, there’s a big move in D.C. to reduce stormwater going into the Potomac,” Vinchesi says.

Thanks to the new irrigation system, the National Mall is now irrigated by 40 percent stormwater runoff.

Less maintenance.

To avoid damage from tent stakes, the National Park Service has set up stake-free areas. To protect the new irrigation, Irrigation Consulting switched from the original PVC pipe to HDPE pipe because it has a thicker wall. They also buried the pipes 5 feet underground to keep them safe from harm.

The National Park Service wanted as few sprinklers as possible because they wanted to minimize maintenance issues, Vinchesi says. So, Irrigation Consulting found a way to place sprinklers on an 85-foot by 85-foot basis. It’s also a two-wire system instead of a conventional one wire per sprinkler system.

“Because they wanted to minimize the number of sprinklers, we put golf sprinklers on it, so that’s basically a golf system on a commercial project,” he says. “And because it’s a golf system, it has a golf control system and it’s basically a central control system.”

Catch and release.

To alleviate soil compaction, contractors replaced the first 6 to 18 inches of soil with a mixture enhanced with sand and compost, and added a drainage system. That system, along with surface drains along the walkways, feeds stormwater from about 1 million square feet into the filtration system.

After the solid particles are filtered out, the system uses three 25-micron filters in order to prepare it for disinfection. “Under Washington, D.C., code, if you spray stormwater in the air, it has to be disinfected,” Vinchesi said.

From there, water flows into four separate 250,000-gallon tanks held underground.

“We modeled it based on projection,” Vinchesi says. “We have basically a million square feet that we get stormwater from which is lawns, walkways and some other areas. We just modeled it, looked at the cost and came up with something somewhat economical. We had to kind of look at it from the client’s view of what they wanted to spend.”

Water is only pumped out of one cistern into the sprinkler system, while the other three transfer water into that one as needed.

“We have a sophisticated logic system where we take water out of the cistern that has the most water in it first,” Vinchesi says. “The problem with that is you never know how much room you’re going to need if it’s going to rain and you don’t want to put potable water in if it’s not going to get used.”

To get around that problem, Irrigation Consulting put a flow meter on the station that syncs to the flow meter on the water supply. That way, the only time the system is using potable water is when there’s no stormwater left in the tanks. “We only put as much potable water into the tank as we’re pumping out,” Vinchesi says. “We never have excess potable water.”

Historic landmark.

Since contractors couldn’t place any new construction above ground on the lawn, Irrigation Consultants had to get creative. “We couldn’t put a controller out there, which we got around pretty quickly,” Vinchesi says. “The problem was we couldn’t put antennae up there.”

The pump station was another problem since they couldn’t build a station for it, so it’s located in a large underground station with the controls.

With the control system located a mile and a half away, the company would usually use radio to monitor, but since antennae weren’t allowed, Irrigation Consultants went with wi-fi to communicate. “That was one of the first ones to do that,” Vinchesi says.

April 2018
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