With 382 apartments, Mile High Apartments is just minutes from downtown Denver. The project had a number of challenges, including a limited footprint, corrosive soils and a high degree of treatment needed to meet water quality standards from the city of Denver.
To address these issues, engineers from Harris, Kocher & Smith designed a storm water detention system consisting of 388 ln ft of 120-in. polymer-coated corrugated metal pipe (CMP) in a double-manifold, three-barrel configuration. The system contains five 120-in. weir plates, two trackracks, five 36-in. risers, 24 120-in. bands or gaskets, and five stubs.
To meet the treatment requirements, an 8-by-11-ft storm water management StormFilter vault with 24 27-in. cartridges was placed downstream of the detention system. The StormFilter cartridges were filled with ZPG media, a proprietary blend of zeolite, perlite and granulated activated carbon that targets organics, soluble metals and other pollutants.
In this part of Colorado, storage and treatment typically is managed using aboveground ponds with biofiltration swales. The lack of space for such elements meant engineers had to manage these requirements below ground. Using a 120-in.-diameter pipe allowed for a large volume of storage in a small footprint.
Contech Engineered Solutions designed the detention system with a series of internal orifice plates and weirs to control targeted release rates and drain down times specified by local drainage requirements. Using the detention system to control release rates in this way allowed Contech to place the StormFilter in a downstream configuration, which provided the most economic treatment option.
The limited footprint was a unique element of this project. The detention system underwent multiple design iterations until the final layout was acceptable. Pipe material requirements also were an element of this project, but having a poly-coated CMP option allowed Contech to provide an underground detention system in an area where soil conditions sometimes prohibit the use of aluminized pipe. Contech also provided a long-term life-cycle analysis for the StormFilter system to give the owner a better understanding of long-term maintenance costs of the system.