Apr 13, 2010

Urban Treatment Goes Organic

What do you get when you combine an urban pond with some carefully selected vegetation, a healthy dash of sunshine and a pump station to help make it all work? With the El Modena Park Natural Treatment System, the people of central Orange County, Calif., got a recipe for success.

El Modena Park incorporates several storm water solutions.

Irvine Ranch Water District’s (IRWD) innovative water treatment project, located in the city of Orange’s El Modena Park, cleans urban runoff by filtering it through wetland plants and exposing it to the sun. The naturally treated water is then pumped into a storm drain, where it makes its way to upper Newport Bay and eventually into the Pacific Ocean.

“The focus of the system is to remove nitrates from the water—to treat it in the watershed before it goes down to the ocean,” said Lou Denger, IRWD’s wetland field operations supervisor.

Site Solutions

The El Modena project is one of the first wetland treatment sites completed for the ambitious San Diego Creek Natural Treatment System (NTS), a $41-million regional approach to treating urban runoff.

The treatment site is located in urban El Modena Park near a flood control channel. Workers regraded an existing basin to create a pond with sloping sides and areas of open water 6 ft to 8 ft deep, and connected it to the channel.

Naturally treated water drains to upper Newport Bay.

The regrading improved a walking trail and created four flat areas suitable for picnickers––features much appreciated by park patrons. Workers also installed flood control gates at one end of the pond, and, at the other end, a lift station from Romtec Utilities Inc., Roseburg, Ore.

The pre-engineered pump station, which arrived at the site pretested and ready to install, features a 6-ft-diameter wet well that is nearly 20 ft deep. The pump station, which controls the level of water in the wetland area, is located alongside the NTS basin.

The treatment system uses the power of Mother Nature to clean the water. Urban runoff is redirected from the concrete flood control channel into the shallow basin, where plants such as bulrush and cattails help remove harmful compounds from the water.

When the water reaches a certain level, the lift station’s pumps start and its control panel sends a radio signal to the slide gate, instructing it to stay open. The pumps move the “clean” water out of the basin and into the nearby drainage channel, while the pond’s water level is maintained. The 1.2-million-gal pond is sized so that the water is cycled about every 14 days.

During a large storm event, the pond and the area around it are allowed to be flooded completely as the water level rises. The pump station is designed to be flooded during these occasions as well, and the pumps automatically shut down. After the storm, the pumps resume standard operation, draining the wetland to its “normal” level so the biofiltration function can continue.

A Natural Fit

The natural treatment system has been in place for a little more than a year. Unusually heavy rains over the winter caused some unexpected erosion that damaged the inlet structure, but in general, the system has performed well.

“Over the last year, we have seen a 79% nitrate removal rate, with a total number of 1,200 lb removed,” Denger said. “That definitely meets our expectations.”

About the author

Megan Monson is a writer for Romtec Utilities. Monson can be reached by e-mail at [email protected].

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