Town Center Subbasin Study Report - Bellingham Massachusetts

Recommended Stormwater ControlsBIORETENTIONBioretention systems collect and filter stormwaterthrough layers of mulch, soil and plant root systemswhere pollutants such as bacteria, nitrogen,phosphorus, heavy metals, oil and grease are retained,degraded and absorbed. Treated stormwater is theninfiltrated into the ground or, if infiltration is notappropriate, discharged into a traditional stormwaterdrain system through under-drains.Vegetated bioretention systems have a high aestheticvalue, and are an attractive option in developedlandscapes.INFILTRATION BASINAn infiltration basin is a large depression thatis designed to infiltrate stormwater into thesoil. Infiltration basins can be quite efficient inremoving pollutants, and can also help rechargethe groundwater, thus restoring low flows to streamsystems.Because Bellingham has predominantly well-drainedsoils, infiltration basins are a practical and costeffectivealternative. Infiltration basins are most costeffectivewhen there is ample space available.RAIN GARDENSRain gardens look similar to traditional gardens, butthey differ in design and function. Rain gardens canbe planted with a variety of perennials, grasses, shrubsand small trees, with native plants typically preferred.Rain gardens add asthetic value to any site and can beinstalled at large or small sites.Rain gardens use shallow detention and infiltrationto reduce the volume, flow rate and temperature ofstormwater runoff, increase groundwater infiltrationand recharge and improve water quality in localsurface waterways.INFILTRATION TRENCHInfiltration trenches are constructed like infiltrationbasins, but can cost more than infiltration basins andare used predominantly when space is at a premium.Trench systems capture and infiltrate water throughgravel and stone, recharging the groundwater supply.Infiltration trenches are particularly effective at filteringstormwater and removing heavy metals, phosphorus,nitrogen and bacteria and also have the potential tosignificantly reduce peak flows and runoff volume.Rain gardens provide a cost effective way of treatingstormwater as the ratio of cost to volume of runofftreated is lower than many other stormwater controls.17