A redevelopment project for a medical clinic office building in Cobleskill, N.Y., required a new storm water management solution that required the engineer to address three major challenges: First, space at the site was limited, so an underground solution was needed. Second, the site had shallow limestone bedrock, limiting the available depth of an underground system. Third, the project had to meet the redevelopment water quantity and quality requirements of the New York State Department of Environmental Conservation. 

To meet these challenges, the engineer chose an underground detention system and a hydrodynamic separator from Contech Engineered Solutions. 

Storm water from the site is first directed to the Terre Arch underground detention system, a modular precast concrete storm water storage system engineered for underground installation and providing a load-bearing rating of HS-25—which was critical, as the land above the system will be used as a parking lot. The system called for 10 Terre Arch-26 units and two distribution manifolds, providing a total storage capacity of 5,064 cu ft in a total footprint that was only 18 ft 11½ in. by 88 ft ¼ in. The engineers included 12 in. of stone over the top of the system for frost heave, and the system was placed on an HDPE impervious liner for limestone erosion protection. The entire system was installed in less than two hours, dramatically reducing labor and installation costs. 

Water stored in the system exits the distribution boxes and flows into a Vortechs, a hydrodynamic separator that provides flow control and removes fine sediment, oil, and floating and sinking debris. The system was an ideal choice for the site because of the shallow bedrock; the horizontal profile of the system results in a shallower depth of excavation. The treated storm water exits the separator and flows into the existing storm water infrastructure.