LOS ANGELES, CA -- Major renovations have already begun at LAX's South Airfield including installing the Grasspave2 porous paving system to allow the maintenance roads to be used as infiltration swales between the runways. The unique design, at the world's fifth busiest passenger airport, reflects a growing trend for permeable pavement design as a stormwater runoff mitigator.
Improvements to the airfield included runway, taxiway and over-roadway construction. The renovation, the first major project in twenty years, was necessary to provide enhanced safety on the south airfield as well as will be the primary runway for the arrival and departure of the new Airbus A380.
Over 438 thousand square feet (40,700 square meters) of Grasspave2 is being placed at strategic locations throughout the South Airfield runway and taxiway system. The porous pavement will collect the stormwater coming off of the concrete runways/taxiways, filter out major pollutants (hydrocarbons and other airport waste) and either deliver the stormwater to an underground detention system or let the water infiltrate naturally back into the ground. A section of the Grasspave2 system will be graded as an infiltration swale and deliver the stormwater to inlet grates connected to the underground detention system. Grasspave2 will also serve as service roads between the taxiway and runway.
The Engineering Design Firm, HNTB, had to meet the Standard Urban Stormwater Mitigation Plan (SUSMP) set by the Los Angeles Region of the California Regional Water Quality Control Board. Stormwater runoff has to be cleaned and treated before it reaches the ocean and the tributaries.
HNTB, whose experience in aviation work, airport planning, transportation, and bridge engineering, has led them to collect a catalog of stormwater BMP products, including Grasspave2. "Grasspave2 was perfect for what we needed, especially in the sandy soil, " says Ryan Damery an Aviation Engineer and Project Manager for HNTB. According to Damery, the Grasspave2 sits on 12 inches of PMB material. Additionally, 18 inches of soil were removed outside of the units to provide sand filtration for the runoff, enough to filter out bacteria from the stormwater before it infiltrates into an underground storage unit or reaches ground water supplies.
The Grasspave2 system is the primary method of providing a drivable maintenance road surface as well as an infiltration swale on top of the loose sand that is found at LAX, according to Damery. For runoff that will exceed the infiltration rates that the existing soil conditions can handle, HNTB deigned a cyclonic filter to treat the water before it reaches the city storm drain. These devices will collect debris, pollutants, sediment, oils, and grease. The cyclonic filters are primarily used in the east side of the airport where the clay soil conditions would not allow high enough infiltration rates to satisfy SUSMP requirements with the infiltration swale alone
Porous pavers, such as Grasspave2, provide a drivable surface suitable for H-20 rated maintenance roads and also allow rainwater to flow into the ground, instead of sheet flowing off site carrying pollutants to fresh water supplies. Impermeable surfaces, such as asphalt and concrete, create pollution, temperature, and velocity problems as rainwater collects on the surface and overwhelms a cities water infrastructure.
Grasspave2 is a flexible ring and grid system made from 100% recycled high-density polyethylene plastic. The units are manufactured into rolls for easy transport and installation. Grasspave2 installs over an engineered road base, is filled with clean sand, and topped with grass. Grasspave2 provides 100% grass coverage with an engineered strength to support extremely heavy loads -- at 5,721 psi, Grasspave2 has nearly twice the compressive strength as two inches of concrete (3,000 psi). Any street legal vehicle can park or drive on the system.
Other notable Grasspave2 installations include The Pentagon helicopter landing pads, Miami's Orange Bowl Stadium parking lot, Reliant Stadium and the Astrodome -- parking lot and access road, and The World's Fair Park in Knoxville.
Since 1982, Invisible Structures Inc. has been a manufacturer of environmentally friendly surfacing and stormwater containment systems including Gravelpave2, Rainstore3, Slopetame2, Draincore3, and Beachrings2.
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