Specifications include, but are not limited to: This project will address stormwater drainage over a 27.4-acre area which includes the aforementioned municipal properties as well as portions of the adjacent residential area bounded by Maplewood Ave, Burns St, Johnson St, and parts of Sheridan St and Merchant St. More than one-third (10 acres) of the drainage is classified as impervious. Currently, stormwater is collected in a series of storm lines that outlet directly to Gunners Brook on Seminary St. The Project Partners seek a State licensed Professional Engineer to provide a 100% design for a subsurface sand filter to treat stormwater for the 27.4- acre drainage area described above. The 30% design, completed as part of the stormwater master planning process, called for rerouting existing storm lines to an underground sand filter system located in the northwest corner of the parking lot. The design standard used for this retrofit was detention and slow release of the Channel Protection volume (CPv, 2.02 inches of rain in a 24-hour period), equal to 55,190 ft3 of runoff. Further design will involve refinement of the retrofit design with respect to size, outlet design, and routing to ensure that the CPv can be completely filtered and slowly released, and that larger storms bypass the system safely. A retrofit of this site has the potential to prevent more than 24,000 pounds of total suspended solids and 8.7 pounds of total phosphorus from entering receiving waters annually.
