An innovative pollution-fighting trench under the Hermosa Beach sand appears to be operating exactly as it was meant to, encouraging officials that the same technology could be used in other beach cities that are awaiting the outcome of the Hermosa experiment.
Officials stressed that a yearlong monitoring is not yet complete, but preliminary results for dry summer months show that bacteria released from the permeable, 1,000-foot storm-water trench are being shredded and killed before they reach the ocean.
“I’m very hopeful, but I’m cautious. I don’t want to over-promise the results,” consultant Kathleen McGowan said of the city-engineered trench.
The trench design is so cutting-edge that officials could find only one similar storm drain project nationwide, a filtration trench in the sand dunes of North Carolina that had not yet yielded enough data to fully gauge its usefulness.
The Hermosa trench, completed in April 2010, lies three feet under the sand and runs from the city pier south, parallel to the Strand wall, ending at Eighth Street. A pump at the base of the pier diverts urban storm-water runoff – a leading cause of ocean pollution – from a huge storm drain into the trench, which is made of interlocking plastic boxes like milk crates, with fabric wound around them to let the water filter downward into the beach sand.
As the runoff moves through the dry sand and into the groundwater table, it decomposes, and is eaten by friendly microorganisms. City engineers believed that the bacteria would be killed before they reached the ocean, and the monitoring results so far indicate just that.
The monitoring involves “hydro punching,” in which a track-mounted rig pushes PVC pipe about four inches wide into the sand until it hits groundwater, which is pumped up and tested for bacteria.
The PVC wells are punched into the sand in three rows parallel to the trench, one five feet to the west, another row 50 feet further westward, and the last row another 50 feet westward.
“We haven’t detected any [of the bacteria] 50 feet out, so somewhere between five and 50 feet it is filtering out,” McGowan said. “That’s what we found last summer. In the winter there is more water coming through the system,” she added, and it is not yet known if the filtering held up under those more demanding conditions.
The PVC wells had to reach down seven to 10 feet to reach groundwater near the trench, and did not have to go as deep to reach groundwater closer to the ocean.
A final report on the trench system’s effectiveness is expected in the fall, after monitoring ends about June.
“We don’t have a final report, we have not gathered all the data, but so far it is looking very promising,” McGowan said.
National honor
The U.S. Environmental Protection Agency has recognized the trench system, officially named the Strand Infiltration Trench Project, with a 2010 Performance and Innovation in the State Revolving Fund Creating Environmental Success Award, and the Southern California Chapter of the American Public Works Association gave it last year’s B.E.S.T. Project of the Year Award.
“We are pleased and gratified to have this recognition of the hard work and innovative efforts of our public works departments and the team responsible for the Strand Infiltration Trench Project,” Mayor Pete Tucker said following the EPA recognition. “This project exemplifies the city’s commitment to making Hermosa Beach a greener place to live, work and play.”
Funding for the project came from a number of sources. California’s Proposition 50 Clean Beaches Initiative paid for planning and pre-construction work. The Los Angeles County Flood Control District funded design of the project, and construction and monitoring was funded by the EPA with federal stimulus money.
“The whole project was funded by grants. That’s what made it possible,” said Rick Morgan, then the city’s public works director, during a seaside ribbon-cutting for the project last year, on the nation’s 40th annual Earth Day.
Looking on were City Council members, public works commissioners and officials of the U.S. Environmental Protection Agency, the environmental group Heal the Bay, the California Water Board and Los Angeles County public works.
Morgan hailed a handful of lifeguards stationed at the pier building who were watching the proceedings, and one of them called to him, “You’re cleaning up our water, thank you.”
Mark Gold, president of the prominent environmental group Heal the Bay, praised the “great leadership” of Hermosa officials. ER
