With four approaches and both sides of the main span, the Bridge Project has more than 15,000 feet of road surface that will collect stormwater during a rain event. Drainage grates are located up and down the roadway in both directions. Water runoff will enter these capture points and travel via pipes inside the approach structures down to large basins at ground level called Austin Vault sand filters.
The photo above shows one of the vaults under construction. This one is directly below the abutment on Terminal Island where the eastbound incline and westbound decline will connect with Ocean Boulevard. With the vehicle inside, you can get a sense for just how large these Austin Vault sand filters are, and there are several of them below the approach structures of the Bridge Project.
Austin Vault sand filters of this kind are designed to handle runoff from drainage areas up to 20 hectares (i.e. 50 acres), so there is more than enough capacity to handle even the heaviest downpours onto the new bridge structure.
These types of Austin Vault sand-filter systems are highly effective stormwater best management practices (BMPs) that achieve high removal rates for common roadway pollutants, such as Total Suspended Solids (TSS), which are inorganic (e.g., sand, concrete, metals) and organic (e.g., vegetative and animal waste) particles and debris, as well as hydrocarbons (e.g., oil and grease). These elements are trapped in the sand as water seeps through it, then – every few years – the sand is removed and replaced.