Sustainable Expansion: Stormwater Detention and Reuse

By Luke Carothers

San Jose State University (SJSU) is currently in the process of initiating a new campus master plan (CMP) that addresses the physical development of both the main and south campuses as well as their various off-campus properties.  As a part of the South Campus plan, SJSU hired McCarthy Building Companies to design-build a four-level parking facility.  This new facility–located adjacent to athletic fields–has 1,500 parking spaces that serve both the student population and visiting spectators.  

The use of reclaimed water was one of the major factors in the project’s design and development.  Cameron Moon, a project manager at McCarthy, notes that the project’s location in California makes the use and reuse of water a paramount concern.  In this manner, Moon says the team worked from the perspective of using as much reclaimed water as possible for as many uses as possible.  The structure’s reclaimed water is currently used in its bathrooms as well as on the rotors to keep the athletic field wet.  In addition, reclaimed water is used by the maintenance team on several levels.   In fact, the only two uses of domestic water in the structure are for fire hydrants and drinking water.  

With numerous uses for reclaimed water being scheduled for potential use, the structure had to not only be capable of collecting water, but doing so in a manner that makes it safe for reuse.  Completed in September 2020, SJSU’s new parking structure is equipped with a stormwater detention system under the lower level that significantly reduces the pressure on city storm sewers.  The biggest challenge in incorporating stormwater management into the site design was space, says Courtney Rousseau.  Rousseau is a project manager for Verde Design who led the civil and landscape architecture aspects of the project.  There were several spatial challenges that the project had to consider during the design process such as the number of parking spaces outlined by the University and the dimensions of the surrounding athletic fields.  

Working with such confinements, Rousseau says that the team had to think creatively to meet stormwater detention goals.  This precipitated the decision to house the detention tanks for stormwater management beneath the lower level of the parking facility.  Rousseau also points out that the project was located in an older area of San Jose, which meant that the stormwater infrastructure wasn’t necessarily sized to facilitate the growth the area was experiencing.  As such, Rousseau and her team incorporated hydro modifications to the detention design.  These modifications were essential to mitigating any inundation of the city’s infrastructure.  

A major part of the retention system in the new facility is water filtration.  With the collected water being used for multiple purposes, it was imperative that the water be free of any harmful contaminants.  The lower levels of the structure are outfitted with a filter on the final manhole before the water is discharged.  These filters are not only designed to stop larger contaminants such as trash and sediments, they filter out things like gas and oil as well.  However, another large component of the project’s filtration compacities is located outside of the structure itself.  The adjacent athletic field is covered in synthetic turf with 5 inches of permeable material beneath.  This surface acts as a natural filtration system as the water is forced downward through this layer and travels along the sloped subgrade.  To ensure this natural filtration system worked properly, there was considerable work put into the field’s grading and percolation.  Moon notes that this process was greatly improved through testing developed by Verde.  

This project is significant in its impact on how we design for stormwater in a way that has positive environmental impacts.  Although significantly more frequent in places like California, the conversation about how we use water in the built environment is impacting the design of current projects and will continue to do so.  This project represents a benchmark moving towards a more sustainable understanding of our use of water.

Luke Carothers is the Editor for Civil + Structural Engineer Media. If you want us to cover your project or want to feature your own article, he can be reached at lcarothers@zweiggroup.com.