The construction of a Sheetz gas station, restaurant, and convenience store in Strongsville, Ohio, necessitated the need for a stormwater management system. Although this was a re-development project, the local stormwater regulations required Sheetz to address both storm water detention and treatment of the first flush.
The site had three challenges: 1) a shallow outlet to the existing storm sewer system 2) flat site topography and 3) a small horizontal footprint for underground stormwater management. Because of these factors, a relatively short vertical envelope was available to place an underground detention system.
The engineer of record, GPD Group, selected the Terre Arch TA48 from Contech Engineered Solutions for underground stormwater management, including both volume detention and stormwater quality. Terre Arch is a modular, multi-chambered, precast concrete stormwater storage system that is engineered especially for underground installation.
One reason the engineer selected Terre Arch is it only required 12 inches of cover, including the asphalt pavement. This allowed the engineer to fully utilize the 48” rise of the Terre Arch and still connect to the existing storm sewer system. Other solutions would have required a significantly shorter vertical rise in order to meet minimum cover requirements. As a result, the Terre Arch solution provided the smallest horizontal footprint compared to other available options. In addition, the engineer required a special design for the inlet distribution boxes which included a sump to help address storm water quality requirements.
Besides meeting the design constraints, the Terre Arch also provided the lowest total installed cost among available solutions. “The Terre Arch TA48 provided the best possible solution for this particular site,” said Jesse Rufener, PE, Project Manager at GPD Group. “Contech’s engineering design staff was helpful in establishing the optimum layout to obtain the smallest possible horizontal footprint using this solution. In light of the shallow cover, this affordable precast open-bottom arch provides a long-term confidence that the structure will continue to support vehicle live-loads throughout its expected service life."
The site utility contractor installed all of the precast concrete components of the Terre Arch system in a total of ten hours over a two-day period. Standard equipment was used to excavate and prepare the trench for receiving the precast Terre Arch units. All precast components were installed using a crane. Once all the precast elements were installed, the site contractor commenced with the backfill operation using standard site construction equipment.
Leon Tang, Estimator/Project Manager at JTO, had this to say about installing Terre Arch. “Our company is very experienced at installing various types of open-bottom underground detention systems, including plastic chambers and other types of precast concrete. Terre Arch is far and away the easiest system we have installed to date. Although it is made from precast concrete, it is extremely “contractor friendly” and allows for high production rates while maintaining the correct alignment. Contech’s on-site support throughout the entire installation was very helpful in maintaining an orderly approach for the placement of the Terre Arch system.”
Terre Arch was the ideal solution for all stakeholders in this project. Terre Arch provided quick approval and acceptance by the local review agency; easy, problem-free installation from the contractor, and a permanent and sustainable stormwater management solution for the project owner.