Silver Lake, in the northern suburbs of Boston, is heavily used for recreational purposes such as swimming, fishing, wildlife viewing, and boating. However, the lake is degraded from nutrients, sediment, and bacteria from the surrounding conventional stormwater systems (which include several direct discharge outlets to the lake) and nonpoint source runoff. Beach closures due to high bacteria counts had become a repeated occurrence. The Ipswich River basin in which Silver Lake sits is a heavily stressed watershed. American Rivers named the Ipswich River the third most endangered river in the country in 2003, reflecting the severe and chronic reductions in flow the river has experienced, mainly due to evapotranspiration rates from development and increased groundwater withdrawals. Long sections of the river had even occasionally dried up altogether.
The Massachusetts Department of Conservation and Recreation (DCR) received a demonstration grant from the U.S. EPA's Targeted Watershed Program to demonstrate an integrated approach to addressing the multiple problems facing the Ipswich River. Their goal was to employ innovative techniques to help increase groundwater recharge and base flow. The Town of Wilmington, working with the DCR, wanted to look into ways to minimize polluted stormwater runoff entering Silver Lake, improve the lake's water quality, and minimize the number of beach closings each summer due to bacteria violations. Low impact development (LID) strategies, such as landscaping and design techniques that capture stormwater and recharge it to the groundwater before it enters a surface water body, if employed widely, could potentially assist in meeting these multiple goals.
Geosyntec's Scope of Services
The Town of Wilmington and the DCR selected Geosyntec for the demonstration project to develop and implement innovative designs to reduce the amount of stormwater runoff entering Silver Lake, improve water quality in the lake, and to increase groundwater recharge. Geosyntec designed and implemented a number of LID stormwater management techniques at Silver Lake, including porous paving systems, bioretention cells and rain gardens, vegetated water quality swales to replace piped stormwater outfalls near the town beach, and a "pocket wetland" to provide a natural filter where a stormwater pipe had been discharging directly to Silver Lake.
Geosyntec also designed and installed a series of rain gardens and porous pavers in a nearby residential area in order to decrease stormwater runoff there before it got to the area of the town beach, and to encourage groundwater recharge and improve water quality.
Since this was meant to be a demonstration project, Geosyntec also installed four different types of pervious surfaces, in addition to conventional asphalt, to demonstrate the varying effectiveness of these techniques at infiltrating stormwater runoff.
The Town of Wilmington anticipates fewer beach closings as result of the LID techniques employed at Silver Lake, and will conduct routine maintenance of the systems that Geosyntec developed here to ensure their continued effectiveness. In fact, for the first time in recent years, the town beach was not closed at all in the summer of 2006 due to bacteria violations.
The U.S. Geological Survey has also begun monitoring both the quality and quantity of groundwater beneath this site. The data will be used to support a basin-wide recharge model to simulate future flows in the Ipswich River. The model will also estimate how many areas of similar LID stormwater techniques would be required to improve base flow in the river and restore the Ipswich River to a more sustainable flow condition.