The stormwater treatment system was designed to project nearby Whittier Lake.Click here to enlarge imageThe Whittier site is comprised of a retirement assisted living facility which is 19,151 square feet, a retirement medical care facility which is 26,950 square feet, a handicapped accessible walk system, courtyards and exercise paths, and a 47 space parking lot.
The project fell under the EPA's Stormwater Management Phase I requirements. To meet those requirements and the special design considerations, initial stormwater management plans included the use of grading, swales, catch basins, and an underground single manhole gravity separator.
The separator was to be used as pre-treatment to runoff through a system that would eventually reach the lake. However, after some research Fox & Associates found the underground stormwater treatment system offered by BaySaver® leveraged the advantages of a two manhole system and provided more effective treatment at a better cost per treated cubic feet per second (CFS).
Ensuring that pre-treatment of the stormwater met the minimum 80 percent removal requirement of total suspended solids (TSS), the BaySaver® Separation System was sized based on flow rate. Rainfall data used during the design process was provided by local National Weather Stations (Technical Paper No. 40 Rainfall Frequency Atlas of the United States). This ensured that local data was being used to determine design. The design also took into consideration site conditions, area, and rainfall intensity.
Based on the site layout plan and calculated flow rate, it was determined that two separate underground treatment systems would be used to pre-treat the storm water runoff. The east side of the site includes a system which treats a drainage area of 1.3 acres, and the west side includes a system which treats a drainage area of 1.6 acres.
Both underground systems included installation of the BaySaver® Separator Unit with two standard pre-cast manholes for each. The primary manhole for each system is designed for inline collecting and retaining of larger particulates while the second or "storage" manhole is situated offline to collect and retain fine particulates, oils and floatables.
In this project, the underground BaySaver® Stormwater Treatment System was used as a pre-treatment in the stormwater plan. These systems are also used as a stand alone BMP in a variety of applications. Whether pre-treatment or stand alone, underground storm water treatment systems are becoming necessary to improve surface water quality.
