A new 119,000 square foot school will serve as many as 850 students in sixth through eighth grade in Newcastle, Washington. The new school, which will be the district’s fourth middle school, was made possible because of overwhelming voter support of an April 2012 bond measure which also includes improvements at many other schools across the district.
Engineers needed to develop a stormwater management system to provide treatment and a large infiltration vault per King County regulations. Engineers with Coughlin Porter Lundeen worked with Contech to design the stormwater system which utilized a CDS® hydrodynamic separator, a Stormwater Management StormFilter® , and a CON/SPAN® O-Series® infiltration vault.
Water from impervious surfaces will first be pretreated with the CDS which uses swirl concentration and continuous deflective separation to screen, separate and trap trash, debris, sediment, and hydrocarbons from stormwater runoff. Pretreating the stormwater with the CDS will reduce the maintenance needed in the downstream structures.
Stormwater is then conveyed to an 8’x18’ StormFilter vault that contains 38 cartridges that trap particulates and absorbs pollutants. The filter media in the StormFilter cartridges can be customized to target site-specific pollutants. On this project, ZPG™ media, a proprietary blend of zeolite, perlite, and granular activated carbon, was selected to remove organics, soluble metals, and other pollutants.
The treated stormwater is then directed to a 48’ x 13’ CON/SPAN O-Series concrete infiltration vault. CON/SPAN is a modular, precast concrete arch system designed to provide economical, large volume stormwater detention or infiltration below grade. The 48’ open span allows for easier maintenance because there are no walls or posts in the center of the vault.The open bottom vault houses a sand filter and provides infiltration before draining into nearby Lake Washington.
Fast installation, wide span availability (48’), and Contech’s ability to provide a stamped structural design for the CON/SPAN vault were all factors in selecting the Contech solution. The original design was a cast-in-place sand filter vault. The city requested the change to the current configuration to speed up installation. The county also required the vault have a 5 x 10' access grate to allow for a bobcat to enter the vault for maintenance, and Contech was able to accommodate this request.
Installation was quick. After the contractor had poured the foundation for the CON/SPAN vault, the entire system was installed in five days. The CDS, StormFilter, and a several CON/SPAN units were all installed on the first day. On the second day, the remaining CON/SPAN sections were installed. By the third day, they had taped all the seams and began to backfill around the structure.