Island Detention

The Makena residential development is located above one of Hawaii’s ecological treasures, Makena Bay. The highest level of storm water treatment was sought to protect this precious resource.

The development’s engineer, Austin Tsutsumi & Associates, selected a treatment train concept that combines a number of storm water BMPs into one integrated system to both improve the quality and manage the quantity of runoff. The treatment train uses a Contech Stormwater Management StormFilter, followed by CON/SPAN detention vaults and an infiltration basin.

Storm water drains convey storm water to a Contech Stormwater Management StormFilter, a passive media filtration system that removes fine solids, soluble heavy metals, oil and total nutrients from urban runoff. The site called for four StormFilter vaults and a total of 30 filter cartridges.

Filtered water is then conveyed to two CON/SPAN detention vaults used to reduce the quantity of storm water runoff flowing into the retention basin by temporarily storing the runoff and releasing it slowly over time. CON/SPAN is an economical, modular precast system designed to provide economic concrete below-grade storm water detention.

Lastly, the filtered water flows to the retention basin, where it infiltrates the soil.

This system, the first of its kind installed in Hawaii, is now favored by the low impact development regulations recently adopted by the City and County of Honolulu. The project is being certified under the Leadership in Energy and Environmental Design (LEED) Green Building Rating System.