SEWERS, WASTEWATER & COMBINED SEWER OVERFLOWS

Wastewater is used water. In our homes, it comes from sinks, showers, baths, toilets, washing machines, and dishwashers. Other chemicals and debris get into wastewater from everyday household activities, like food scraps, oils, soaps, human waste, and chemicals. 

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Overview

In most homes or businesses in urban or suburban areas, wastewater enters an underground sewer. There are three types of sewers: sanitary sewers, storm sewers, and combined sewers. A sanitary sewer is designed to carry waste away from homes and businesses to wastewater treatment plants. From wastewater treatment plants, the waste is treated before exiting into an outlet, i.e., Boston Harbor, Massachusetts Bay, etc. Combined flows (a mixture of sanitary wastes and stormwater) are usually routed into a much larger pipe that transports the combined flows to a wastewater treatment plant. Heavy rains can overflow combined sewers, sending untreated wastewater to Combined Sewer Overflows (CSO), which then drains that raw mixture directly into nearby waterways. These systems are specifically designed to handle human waste and easily degradable manufactured solids such as toilet paper and tissues. Storm sewers, also known as surface or runoff sewers, are designed to collect and carry rainwater, snowmelt, and irrigation runoff into storm drains located in parking lots, streets, and gutters. These drains are connected through a series of underground pipes that carry this water directly to rivers, lakes, and other bodies of water without having been treated at a treatment plant.  This runoff is called stormwater runoff, and is the number one source of water pollution in Massachusetts. 

Boston uses both combined and separated sewer systems. Storm drains transport only stormwater, while sanitary sewers transport sewer flow. In contrast, combined systems transmit both sanitary sewer water and stormwater runoff through a single pipe that carries it to the Massachusetts Water Resources Authority (MWRA) for treatment. In older cities like Lowell, New Bedford, Springfield, and Chicopee, this type of system is common. 

How Water Moves 

Before returning to the ecosystem, sewage from residential, commercial, and industrial sources is routed through a sewage treatment system. Sewage from about half of Massachusetts' residents is sent to MWRA's treatment plants near Boston Harbor. Water for domestic or commercial uses is flushed through the building's pipes until it reaches the local sewers, which are owned and maintained by the city/town sewer departments. Three different sets of pipelines are used to transport the sewage. A total of 5,100 miles of local sewers deliver wastewater to MWRA interceptor sewers, which then take it to treatment facilities. The Deer Island Treatment Plant receives primary and secondary wastewater treatment from MWRA. After treatment, any remaining effluent is disinfected before being released into Massachusetts Bay.

The Town of Palmer's wastewater treatment facility, sited along the Ware River, provides another, more compact example. This facility discharges treated wastewater directly to the Chicopee River.

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Who is Responsible for Maintaining the Infrastructure?

The EPA's National Pollutant Discharge Elimination System (NPDES) regulates wastewater systems. Stormwater permit regulations apply to water discharges to the Boston Water and Sewer Commission's (BWSC) municipal storm sewer systems. BWSC owns and operates the city's wastewater and storm drainage collection and transportation system. This system serves about 20,500 acres or about 70% of the total land area. The Operations Division of the BWSC oversees smaller sewer and drain repair, maintenance, and cleaning jobs. In 2021, the BWSC's crews and contract personnel conducted televised inspections of 102.43 miles of sewer and drain pipe to evaluate where structural issues existed and where repairs were needed. The BWSC cleans debris from 11 brook inlets and outlets throughout Boston as part of storm drain and catch basin cleaning initiatives.

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Affects on Water Cycle

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Areas where water can soak directly into the ground, like forests, fields, and wetlands, have been replaced by impermeable surfaces like buildings, roads, and parking lots as developments across Massachusetts expand. On these surfaces, water cannot sink into the ground, and instead flows across the surface until it meets a waterway or natural area, picking up chemicals and debris along the way. Creating more impermeable surface has a significant impact on how water moves through ecosystems: more stormwater pollution, and less groundwater recharge. The transition to developed, impermeable surfaces has altered the hydrological cycle that preserves water purity and the wellbeing of the natural environment.

When rainwater falls and "runs off" rather than permeating the ground, stormwater runoff is produced. As this water moves, runoff collects a variety of pollutants, such as metals, pathogens, fertilizers, pesticides, debris, oils, minerals, and germs. These pollutants are discharged into urban drainage systems, where they endanger wildlife and damage water quality before being dumped into rivers and the ocean. Traditional stormwater management systems including catch basins, storm drains, and pipes that transport wastewater can become overwhelmed during larger rainstorms. Climate change delivers more frequent and extreme precipitation events as development grows, raising the risk of overtaxing existing infrastructure. Stormwater runoff that is generated in bigger quantities moves faster and transports more contaminants at higher flow

rates. Localized floods caused by these poor drainage systems result in water contamination and land erosion. To be resilient to climate change and accommodate our growing development needs, we must support infrastructure upgrades statewide.

Sustainable Options

Green infrastructure is a low-cost alternative to traditional infrastructure with many extra benefits. These projects use plants, soil, and permeable surfaces to store and filter rain, allowing the water to soak back into the ground where it lands. Green infrastructure reduces the amount of runoff that enters sewage systems and our waterways, making our pipes last longer.

Green infrastructure filters and reduces excess nutrients and bacteria in stormwater runoff. These projects also create green space that reduces urban heat, improves wildlife habitat (especially for pollinators!) and naturally protects people from flooding. The green infrastructure filters air, and purifies water by harnessing the power of nature. Boston Water and Sewer Commission has undertaken several projects to help demonstrate “green” alternatives to traditional “gray” stormwater management. These projects include:

  • Central Square in East Boston

  • Audubon Circle

  • Green Infrastructure at 5 Boston Public Schools

  • Rain Garden at South Street + Bussey Street

  • Tree Trenches on Harrison AveCodman Square

In order to advance the construction of green infrastructure in the county, the Worcestershire Green Infrastructure Partnership created the Worcestershire Green Infrastructure Strategy. The strategy outlines the county's need for green infrastructure and establishes a vision for its implementation. It emphasizes how housing, employment, infrastructure development, and land management may be used to accomplish this. The goals consist of:

  • Establishing a framework of values and objectives in order to satisfy the interconnected demands of industry, the natural world, the historic environment, and the communities.

  • Include the advantages of green infrastructure and the services the environment offers in order to promote Worcestershire's economy's successful expansion as well as the community's health and well-being

  • To influence future planning and management of green infrastructure, it is necessary to synthesize existing evidence to identify needs and opportunities

  • Drive the creation, delivery, and long-term upkeep of high-quality green infrastructure throughout the county