Commuters and neighbors can see that the I-405 uses a sophisticated system of lanes, ramps and signage to move hundreds of thousands of vehicles each day. What few see is the comprehensive drainage system beneath the I-405 road surface.
Miles of drains under the I-405 carry runoff from rain falling on cars, trucks, motorcycles and the highway itself. Where that water flows is closely monitored by state and federal environmental agencies, because as the water drains off the highway, it sweeps up oil and other debris from the road surface.
Within the I-405 Sepulveda Pass project boundaries, for example, drains run along the center median of the northbound and southbound lanes. They are also strategically placed along the outside shoulders.
Treating that water and debris properly, before it joins the stormwater system that runs to the ocean, requires that the drains channel the runoff for treatment. To accomplish this, the drains must be clear and undamaged.
To check the condition of the drains, workers use a tiny closed circuit television (CCTV) camera to photograph the drains and see real-time images of debris. To reduce their effect on I-405 traffic, the workers inspect the drains at night, so it is common to see a worker staring at a video monitor in the back of a truck long into the wee hours of the morning.
Sediment constitutes a large part of the debris found in the drains, as does non-hazardous material such as concrete chips and general trash. That sediment and debris is blown out by a jet of high-pressure water and sucked out by vacuum. The water and debris are taken to the Mulholland Yard, where water is separated from the trash.
Governed by regulations of the federal Environmental Protection Agency and the State Water Resources Control Board, the I-405 construction team must keep construction debris from the stormwater system as well, as part of the project’s Stormwater Pollution Prevention Plan (SWPPP).
To meet SWPPP standards for the 121 acres that constitute the construction area, workers use a variety of tools, such as adding fabric filters to the drains where they are working or placing gravel bags to create a debris barrier. Commuters might also notice silt fences placed around construction areas to prevent debris and sediment from entering the stormwater system.
These photographs, taken south of the Getty Center Dr undercrossing, show workers gaining access to the drain system by removing welded steel grates along the freeway median barriers, recording the condition of the drainage system (for later evaluation by a hydraulic engineer) and vacuuming debris from the drains.
“Our goal is to minimize any pollution reaching the stormwater system from our project,” explains Dania Almordaah, a Caltrans segment engineer and lead for the project’s SWPPP compliance.