The Miscellaneous Permanent Best Management Practices on Oahu project, which will help reduce pollutant contribution to the storm water system, is currently underway along Interstate H-3 near Kaneohe. The $2 million project includes the construction of a Nutrient Separating Baffling Box treatment system and will replace existing concrete drainage channels with 16 bioswales. The bioswales will convey storm water runoff from the roadway into the storm water system and will include several layers of treatment to help filter the runoff from the roadway and promote its infiltration into the soil. Construction of the project began in the spring of 2015 and will be completed in approximately six-months.
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First the old concrete channel is removed and in its place a trench is dug and filled with several layers of permeable rock. A perforated drain pipe is installed near the top of the trench to collect excess water that does not infiltrate into the ground. A layer of soil and grass provide a cap over the rock filled trench and provide the first layer of storm water treatment for the new bioswale.