Retention, detention, and groundwater recharge are at the heart of a stormwater management system installed at a new medical office building that is part of an assisted living facility in Newtown, Connecticut.
The two-story, 2415-m2 (26,000-sf) structure sits on a 1.3-ha (3 ¼-acre) site at Maplewood Medical Center.
Engineers originally designed the project to include solid-wall concrete units, but later choose proprietary plastic underground stormwater chambers to decrease costs and to offer adequate infiltration to the site.
The chambers—which provide the largest volume possible between the groundwater and the cover requirement, while using the smallest footprint—are situated beneath the center’s parking lot to save space for a conventional detention pond. The chambers’ ability to withstand the weight of heavy-duty equipment was also a key component in choosing this system, as heavy trucks would be driving over them.
The stormwater management system features 159 chambers arranged in seven rows beneath the parking lot. Each chamber measures 813 mm (32 in.) high and 1524 mm (60 in.) wide and has a bare chamber capacity of 0.75 m3 per linear m (8.68 cf per linear ft). The bed of chambers provides the site with a total of 446.7 m3 (15,777 cf) of storage.
In addition to the chambers, other stormwater management solutions onsite include:
- suspended solids separators, which provide initial pre-treatment by removing fine particles from runoff;
- catch basins, water-quality separators, manholes, and high-density polyethylene (HDPE) and concrete pipes that remove up to 44 per cent of total suspended solids (TSS) from runoff before it is directed into the chambers units, eliminating 80 per cent of TSS; and
- rain gardens that provide final treatment, soaking runoff from the impervious surface area into the ground, rather than allowing it to flow into storm drains and surface waters.
This last measure in particular is designed to help prevent erosion, water pollution, flooding, and diminished groundwater.
