This technical note is for Best Practices for Under-Structure Detention Systems. Structure types, specifications, project conditions and design layout explained.

Site development in urban settings continues to have challenges due to population growth and increasing water containment requirements. When site constraints don’t allow for retention/detention systems to be placed outside of a building structure, designers are looking to place these systems within the structure’s foundation system. This application raises many questions related to system & foundation installation, adverse effects due to the presence of water and ability of the system to be inspected & maintained.

Structure types for ADS detention system can be installed under building structures, provided the level directly above the system is dedicated to parking. Multi-use structures, where the bottom level(s) are for parking and the upper levels are for office/retail/residential space are acceptable.

StormTech chamber for use under parking structures meet ASTM F2418 and ASTM F2787 standards. To facilitate access, inspection and maintenance, pipe manifolds and connections are recommended.

Project conditions dictate that no loads exert pressure on the foundation system. Groundwater elevation is above the detention system. Soil conditions must be suitable for the foundation and bearing capacity.

The design layout may include a base stone depth recommendation for the configuration of the project. ADS can provide a CAD layout to aid the engineer.