The new site had its challenges as well, one of which was managing the stormwater runoff. The new stadium sits adjacent to San Tomas Aquino Creek, which flows into San Francisco Bay less than six miles away. Considering that a venue capable of seating 70,000 people requires large parking areas and other impervious grounds, it posed a challenge for the construction.
During the rainy season, rainwater can turn a football field into a muddy swamp and a parking lot into a floodplain. Runoff from parking lots typically includes trash, debris and petrochemical pollutants that drip or leak from vehicles. The site is located on land with a high-water table, and existing storm drain lines are shallow so a stormwater infiltration system would not work.
To handle stormwater runoff from the parking lots, access roads and other hardscape surrounding the stadium, project manager GHD Engineering selected the BioMod biofiltration system, a precast modular stormwater collection and natural treatment system manufactured by Oldcastle Infrastructure, A CRH Company. Biofiltration is one of the simplest, most natural, and most cost-effective ways to collect runoff and treat it onsite, and it is considered a best practice under U.S. Environmental Protection Agency (EPA) guidelines for low impact development.
Today, the stadium has six biofiltration systems to manage stormwater runoff from the site. In total, about 2,500 linear feet of BioMod cells, or approximately 14,000 square feet of bioretention area, currently treat stormwater runoff from the stadium complex. A big win for the new stadium.