Technical Description:
- The Stormwater Management StormFilter®
- Storm Screen
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Over the past several years, Baby Beach has been closed more than it’s been open. Tucked in the back of Dana Point Harbor in
Dana Point Calif., the 200-yard stretch of sand ranks among the state’s most bacterially polluted ocean beaches. “No one is sure
why the bacteria thrive there,” said Jim Volz, senior civil engineer of Orange County’s Watershed and Coastal Resources Division.
The Challenge
When Headlands Reserve LLC, a corporation wanting to build a resort and custom residential housing development at Dana Point, worked closely with the city and county to manage its runoff well.
Now called the Strand at Headlands, the 121-acre property rests about a quarter mile from the beach. Sixtyeight acres of open space will hold a wildlife conservation park, four other parks and walking trails. A key feature of the development is its best management practice (BMP) water quality treatment system to help mitigate the existing conditions at Baby Beach and insure no water quality issues would impact the beach.
“While no treatment train for stormwater runoff addresses bacteria, managing the runoff has an impact on the beach,” said Darnall. “We wanted to work with Orange County to provide the best solution to address the problem from the start.”
The Solution
Under different conditions, a sand filter could work. But there were concerns about disturbing the landscape to create one, the area it would take up and its ease of maintenance. Instead Headlands Reserve chose the StormScreen and Stormwater Management StormFilter from Contech Engineered Solutions to manage and treat runoff and storm flows.
Mike Trumble, president, Kennedy Pipeline, said installation took about three days to prepare the holes and one day to set the vaults in place. “Our biggest challenge was pumping out the groundwater from the ocean,” he said. “At high tide there was about four feet of water in the holes.” Installing the systems under a parking lot left more land available for other uses, such as parks and housing.
To install the system, workers dug a hole in the parking lot and removed a small section of storm drain installed in 1969. They constructed a manhole containing an 18-inch high concrete diversion dam in a gap of the storm drain. When runoff exceeds the first flush storm flow, its runs up and over this concrete dam and into the existingstorm drain to the beach. The fixed concrete dam directs all urban runoff and first-flush storm flows out of the storm drain and into a six by 12 foot StormScreen vault.
A four-inch diameter PVC pipe downstream of the StormScreen vault delivers urban runoff to the sanitary sewer. The valve between the StormScreen vault and the sanitary sewer is opened and closed at least twice a year. During the dry season, a county worker opens the valve so the urban runoff, after it has been cleaned of debris by the StormScreen, flows into the sanitary sewer. In the rainy season, the valve is closed so the outflow runs from the StormScreen into the StormFilter vault.
With an average rainfall of just over 12 inches a year, it’s rare to close the valve during the dry season, unless rain is forecast. When rain is expected, the county closes the valve to filter the stormwater flow and capture as much particulate matter as possible in the StormFilter before emptying at the beach. “A recent dry season flow test showed about 300 gallons of runoff a day,” said Volz. “We don’t expect the Headlands development to add much to that.”
The StormScreen captures any debris pea-sized (2.4 millimeters) or bigger from the flows before it enters the sanitary sewer during the dry season. It’s a passive siphon-activated cartridge and assures the entire surface area of the screen is used evenly during every storm. Directing the dry season nuisance flows into the sanitary sewer prevents any bacteria in the flow from making it to the beach.
Downstream from the StormScreen are two large precast-concrete StormFilter vaults containing 154 filter cartridges for filtering stormwater runoff during rain storms. Each filter cartridge contains three kinds of media, perlite, zeolite and activated carbon. These media target a full range of pollutants carried by runoff, such as total-suspended solids (TSS), soluble heavy metals, oil and grease, and nutrients. A 24-inch diameter, reinforced concrete pipe joins the StormFilter to an existing storm drain that empties runoff onto the beach at low tide and into the sea at high tide.
The Result
“Headlands Reserve completed the design, installation and provided water quality improvements more quickly than Orange County could have,” said Volz.
Darnall said that it’s unusual to put the stormwater treatment system in before the development, but that’s what Headlands Reserve did to make sure it did everything to help address the existing pollution and lessen the project’s impact on Baby Beach. Grading for custom home sites and the infrastructure has started and lot sales will begin in September he said. During this work, the company is using temporary measures such as sandbags, detention basins and matting for runoff control. Darnall also noted that an additional stormwater management system for the residential phase of the development will be installed. The homeowners and the city will be responsible for the long-term maintenance, he said.
Technical Description:
- The Stormwater Management StormFilter®
- Storm Screen
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