Natural Treatment System Revisited

Storm basin pump station performs during wet California winter.

Folks at Irvine Ranch Irrigation District (IRWD) in Orange County, Calif. are pleased with the performance of the El Modena Park storm basin, part of the San Diego Creek Natural Treatment System (www.naturaltreatmentsystem.org), a regional approach to treating urban runoff. In the first wet winter experience with the storm basin, some lessons have been learned while achieving nitrate removal.

During precipitation, runoff in the nearby flood control channel is diverted into the park’s man-made wetland. Besides reducing the direct flow into San Joaquin Marsh in the upper reach of Newport Bay, the constructed wetland is designed to naturally cleanse urban runoff before it reenters the channel. Plants at the perimeter of the basin help remove nitrates and other pollutants from the water. Keeping the water at just the right level for these plants to thrive, a key factor in  biofiltration system’s success, is the job of the Romtec Utilities duplex submersible stormwater pumping system installed in 2008.

When the water in the basin reaches a certain level, the lift station starts one of its pumps. At the same time, the control panel sends a radio signal to the basin’s 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-gallon pond is sized so the water is cycled about every 14 days, thus providing optimum time for biofiltration to occur.

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

The natural treatment system has been in place for just over a year. Unusually heavy rains during the 2009-’10 winter caused some unexpected erosion around the basin’s inlet structure, but the pumping equipment at the other end of the basin was not affected.

In general, the system has performed well. “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,” says Lou Denger, IRWD’s wetland field operations supervisor. “Over the last year, we have seen a 79% nitrate removal rate, with a total number of 1,200 pounds removed. That definitely meets our expectations.”

Click here to read more about this project in WaterWorld online.

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4. Fish Love Pump Stations