Non-point Source POLLUTION Management: Alewife Brook Watershed
Through the Massachusetts Department of Environmental Protection (DEP), the Town of Arlington was awarded a 604(b) Water Quality Management Planning Grant in 2013.
The intent of 604(b) grants is to perform nonpoint source assessment and planning projects leading to the: 1) determination of the nature, extent and causes of water quality problems; 2) assessment of impacts and determination of pollutant loads reductions necessary to meet water quality standards; 3) green infrastructure projects that manage wet weather to maintain or restore natural hydrology; 4) development of designs and implementation plans that will address water quality impairments; and 5) development of assessment and remediation strategies in impaired watersheds in areas that are not regulated under Municipal Separate Storm Sewer Systems (MS4) permits.
Project partners include the Towns of Arlington and Belmont, MyRWA and Bioengineering Group. The Alewife Brook sub-watershed is the target area of this work – a watershed shared by the two towns as well as Cambridge and Somerville. MyRWA and BioEngineering Group worked on a similar 604(b) project in 2010-2012 with the cities and towns of Woburn, Winchester, Reading and Burlington – as part of this work, four conceptual designs were completed for ‘green’ Best Management Practices (BMPs) in the Aberjona River sub-watershed to promote rain water infiltration and address pollution.
WHAT IS THE PROBLEM BEING ADDRESSED?
The problem that the project is trying to address is a problem shared by almost every community in the watershed, state and country: non-point source pollution. Non-point source pollution is the mixture of pollutants picked up by rainfall as it moves through the soil and built environment. These pollutants include fertilizers (nutrients), herbicides, oil, grease, sediments, salt and bacteria (e.g. dog waste). When the pollutants reach the waterbody, they contribute to the degradation of these waterways for recreation and wildlife habitat. Degradation can include elevated bacteria levels that make recreation unsafe, high nutrient levels that yield development of algal blooms and invasive plants and a long-term decline in habitat quality.
The Towns of Arlington and Belmont will work to identify the highest sources of stormwater runoff within their communities and begin planning for solutions to mitigate this impact. The municipalities, along with MyRWA, are taking a proactive approach toward identifying pollution sources and reducing pollutant loading through an examination of solutions with a focus on “green” structural Best Management Practices (BMPs).
Conceptual designs of five BMPs – three within Arlington and two in Belmont– will be developed to reduce pollutant loading from their respective sites to water bodies in the Alewife and Mill Brook sub-watersheds. The collaborative approach among the municipalities will allow the teams to share key expertise at a reduced cost, foster communication on the shared Alewife Brook and provide opportunities to learn from the projects completed in bordering towns.
Green BMPs represent an approach to wet-weather management that utilizes small-scale facilities, distributed throughout the watershed, to slow down, cleanse, infiltrate, and reuse rainwater where it falls. Specific BMPs that may be considered during our project include vegetated swales, bio-retention structures, permeable pavement, street trees and rainwater harvesting. Green BMPs – based on Low Impact Design (LID) principles - have demonstrated performance, cost effectiveness, and broad community benefits.
- GIS Analysis – One analysis will identify key sub-basins within each community where pollutant loading is highest, targeting phosphorus; an additional analysis will focus on the priority drainage basins to identify which sites are feasible for BMP implementation and are optimally located to reduce downstream sediment and nutrient loading.
- Site Prioritization – Arlington and Belmont will create a list of potential sites for BMP retrofits. These sites will be compared to municipal goals and possible synergies with town activities, such as planned infrastructure work.
- Water Quality Monitoring - MyRWA will perform monitoring at one of the final BMP sites in each of the communities to estimate pollutant loading pre-installation.
- Final Conceptual Designs - Bioengineering Group will prepare conceptual designs for the BMP retrofits at each of the five top priority sites. The conceptual design report for each BMP will verify the engineering feasibility of the proposed BMP; estimate drainage and water quality benefits of the retrofit; provide conceptual level site plans and typical details for the BMP; and estimate construction and maintenance costs.
By the end of this project, Arlington and Belmont will be armed with conceptual designs and water quality data for key BMP retrofit locations. At this point, the project partners can then move on to pursuing implementation funds from local, state, federal and private sources, in addition to using their new skills in future work around town.