Describing the recently installed 72 Bishop Street project in Portland, Maine, Robert Woodman, P.E., senior storm water engineer for ACF Environmental, said, “Urban infill development begs for space-efficient innovative solutions when looking for function [and] feature and meeting rigorous state storm water standards.”
The problems for Ransom Consulting and Mitchell & Associates of Portland, Maine—the project’s design team—were trying to account for the 4,600 cu ft of storm water runoff that needed to be accounted for on this tight site and protecting the curvilinear segmental big block retaining wall that was on the back side of the property.
To protect the big block wall, the entire system was wrapped in a 30-mil PVC liner to prevent migration of stored storm water into the wall. In order to address the volume of storm water, the R-Tank system was selected due to its 95% void space. The system also serves as a subsurface detention area so that the runoff is slowly released through an outlet control structure controlling the 2-, 10- and 25-year storms before being released to Capisic Brook.
Approximately 2,400 sq ft of the PaveDrain system was installed and served as the paving, drainage and conveyance of surface sheet flow down into the tanks below. An 18-in. sand filter course was provided between the pavement and the storage system to provide water quality treatment in accordance with Maine Department of Environmental Protection (DEP) criteria. The permeable pavement system qualifies as a “modular, removable, maintainable surface,” and as such, Maine DEP allows it to be used in a “run-on” condition with 80% regular pavement and only 20% PaveDrain. Other permeable surfaces would have needed to be installed over 100% of the area.
Peters Construction (site contractor) and Great Falls Construction (general contractor) installed all system components.
