New Green Stormwater Infrastructure Completed in Hinesburg Lewis Creek Association, December 2014 At the beginning of October, the Lewis Creek Association completed the construction of a stormwater treatment project known as the Silver Street Rain Garden. The project represents a continuation of the work completed as part of a Townwide hydrology study completed in 2011 and 2012, which targeted the Silver Street site as a potential location for a stormwater treatment system. The project site is located at the intersection of VT Route 116 and Silver Street in the Town of Hinesburg, was initiated and managed by the Lewis Creek Association with funding provided by Vermont’s Department of Environmental Conservation Ecosystem Restoration Program. The stormwater treatment system was designed to fit within the sloping site along Silver Street between an existing drainage swale and the Hinesburg Masonic Lodge Building on Townowned land. The site was selected because it is the location of three storm drainage outfalls that drain a portion of the Village. Prior to constructing the rain garden, runoff from the three outfalls was conveyed directly to the Laplatte River by an existing swale and culvert system with little treatment. The rain garden will treat stormwater runoff from a 6.7acre subwatershed collected by the existing storm drainage systems, with approximately 2.6 acres or 39% of the contributing watershed consists of impervious surfaces. The primary design objective is to capture the runoff from a 1inch rainfall event, which generally represents 90 percent of the rainfall events occurring annually. Treatment goals are to remove 80% of the average annual total suspended solids (TSS) and to remove 40% of the total phosphorus (TP) load present in the contributing stormwater runoff. The stormwater treatment system was designed in a twotiered configuration. The upper treatment cell collects all of the stormwater from the existing drainage outfalls, transfers stormwater to the lower treatment cell using a perforated riser structure, and bypasses larger storms to the swale along Silver Street. The roadside swale was reshaped, revegetated, and stone check dams were installed as part of the overall project. The lower treatment cell was Figure 0: Completed Upper Treatment Cell