February 2010, Vol. 22, No. 2

Problem Solvers

Handling Stormwater One Company at a Time

Problem: Stormwater runoff contaminating local waterways.
Solution: Installing a runoff containment and filtration system.

As the owners of Shaw & Son Concrete Contractors LLC (Costa Mesa, Calif.), an architectural concrete construction company, grew more concerned about pollutants entering the ocean from areas they paved, they decided to build a solution. After 2 years of research and development, the company created the patented Oceansafe system to contain stormwater runoff from paved urban areas.

Stormwater containment and management in urban areas, such as Los Angeles, have been ineffective because rapid growth and increases in property prices have led to a lack of affordable open land for agencies to use to mitigate runoff, said James Taylor, vice president of Shaw & Sons. Catchment basins and water-retention ponds require land, which is not always affordable or viable in metropolitan areas, he said.

Stormwater Solution

Shaw & Sons created a different solution that can handle heavy traffic loads, treat the stormwater before it seeps into the ground, and look good.

“In order for our streams, rivers, lakes, and ocean to be safe, we must start to clean up the pollution at the source, and that means tackling the problem one site at a time and taking the time to understand each case on its own merits,” Taylor said.

The Oceansafe system employs onsite horizontal and vertical aggregate-gravel water-storage basins. Surface drains carry stormwater through passive and active filters down to a network of polyvinyl chloride (PVC) piping that sits in an aggregate base below a reinforced concrete slab. The PVC piping is perforated to let the stormwater seep out into the aggregate. Layers of filtering fabric above and below the aggregate help form a horizontal storage basin and provide another layer of filtration. Water that remains in the PVC pipe is carried to a vertical storage basin, which is built deep enough to conduct the water down below clay layers to the pervious layer of soil. The pipes, drains, and aggregate base are all sized to meet local rainfall conditions.

The system includes two sets of filters, the first being passive screen filters that capture solid debris. Next, the active filters use polypropylene pellets or activated charcoal to adsorb hydrocarbons and other toxins. The active filters must be sized to handle the projected stormwater flow for the local area.

Polypropylene pellets turn black when they are exhausted, alerting maintenance staff that they should be changed. Small access drains allow for cleaning and replacement of the filters and access and inspection of the pipes.

The top layer of the system can be asphalt or reinforced concrete, which then can be topped with decorative finishes.

Starting at Home

Shaw & Sons installed the first Oceansafe system at its headquarters. The system has been in place through two storm seasons. The 204-m2 (2200-ft2) system was installed under the parking area to handle runoff.

To install the system, the company excavated and compacted the site, then installed a layer of the special filtering fabric. Next, a hole was drilled deep enough to pass through the clay layer in the soil — in this case, 3 m (10 ft). A perforated pipe 450 mm (18 in.) in diameter was placed in the hole and filled with 25-mm (1-in.) rock to form the vertical storage basin. The perforated pipes and aggregate were laid in the area to create the horizontal aggregate storage field — the top layer of filtering fabric was sandwiched within the aggregate material above the PVC pipes. Finally, steel reinforcing bar was placed over the site and concrete poured.

The system accommodates heavy vehicle traffic with 150-mm (6-in.) reinforced concrete and is topped with a decorative specialty finish. The installation handles 90% of hydrocarbons and 95% of silt and debris from the site. At capacity, the system can contain more than 57 m3 (15,000 gal) of filtered water.

Since installation, the system has contained all stormwater from the facility’s 1115-m2 (12,000-ft2) headquarters, preventing it from entering the city’s stormwater system.

“It has proved reliable and easy to maintain,” Taylor said. “Most people coming to the company facility do not recognize that a stormwater containment system is even installed in the parking lot.”

Taylor and his colleagues have deemed the system effective because it contains 100% of the runoff from a storm that dumps 25 mm (1 in.) of rain in 1 hour.

They also call the system economically viable, requiring a small amount of land area; structurally sound; and able to carry heavy traffic loads. The system also is easy to maintain and architecturally and aesthetically pleasing, they say.

“In the long term, it must meet the demands of all the constituents involved, including federal, state, and municipal agencies; environmental advocates; facilities engineers and maintenance staff; and finally the architects and owners,” Taylor said.

Personalizing the System

Oceansafe systems are designed to meet the specific needs of each client’s location and facility, Taylor said.

“The design criteria must address the square footage of the runoff area, the projected worst-case stormwater runoff, the soil report for the site, the percolation rate, the contaminants that are present, the traffic loads that are projected, and finally the architectural finish desired by the client,” Taylor said.

For companies looking to obtain the Leadership in Energy and Environmental Design, or LEED, certification from the U.S. Green Building Council (Washington, D.C.), the system can qualify for as many as 14 points in three categories.

 

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