There are 17 landfills operating in Massachusetts that accept typical household and business trash and construction and demolition (C&D) debris (although most C&D first goes to a C&D recycling processor).  Another six landfills accept primarily ash from municipal waste combustors and incidental quantities of municipal solid waste. Landfills are not allowed to accept hazardous waste and banned recyclable materials.  Landfills must be located, constructed, operated, and monitored in accordance with state and federal environmental requirements, and also must receive local Board of Health approval of their location. 

Landfills are built in phases or cells.  In Massachusetts, new landfill cells must have double-liners to prevent water that leaches through the waste from contaminating groundwater.  Landfills must collect leachate (rainwater that percolates through the waste) , and must implement specific operating practices that protect public health (such as compacting and covering waste frequently with soil to help reduce odor and control litter, insects, and rodents).  Landfills also have on-site environmental monitoring systems that provide early warning of groundwater contamination and dangerous levels of landfill gas.  Before a landfill (or a new cell) can be built, the owner must have a MassDEP-approved plan to cap the landfill when it is full and to ensure its long-term care, which often includes new uses (e.g., sports fields).  These requirements are established in MassDEP's regulations governing solid waste management facilities.

Many Massachusetts landfills collect methane gas (which results from the decomposition of waste) and convert the gas into energy.  Plans for collecting gas and for flaring it or generating electricity must be approved by MassDEP under the Air Quality Regulations (310 CMR 7.00) before the system can be built.  Facility owners must submit periodic reports to MassDEP about the operation of these systems and air emissions.

MassDEP reviews environmental monitoring reports that are submitted periodically by active landfills and by landfills that have been closed under a MassDEP permit.  When a facility reports a problem, MassDEP follows up to ensure that it is resolved.  The Department inspects active landfills on a regular basis, to ensure that they are complying with their permit requirements. Inspections also cover compliance with waste bans. The Department uses "Notices of Noncompliance" and escalating enforcement actions (which can include fines and penalties) to ensure that the facilities correct violations of Department regulations.

Between October 1, 2007, and September 30, 2008, MassDEP conducted 358 inspections of the operating landfills.  These inspections led to the issuance of seven Notices of Noncompliance and eleven Orders to correct specific violations.

In-state capacity for waste disposal at landfills is expected to decline significantly over the next decade as currently active landfill cells are filled and closed.  By 2018, nine of the 17 active MSW landfills are expected to close, reducing annual statewide landfill waste disposal capacity to 1.1 million tons, a million tons less than capacity today. 

There are seven municipal waste combustors (MWCs) operating in Massachusetts, which together burn just over three million tons of municipal solid waste (MSW) each year.  Also known as "waste-to-energy" plants, MWCs burn trash at a very high temperature (approximately 2,500 degrees Fahrenheit) and generate electricity or steam power.  The combustion process reduces the trash about 90 percent by volume and 75 percent by weight, and residual ash is buried in landfills.  MWCs also recover metals for recycling from their process. 

As the result of new air quality regulations that MassDEP adopted in 1998, emissions control systems at the five largest Massachusetts MWCs (those handling more than 250 tons of waste per day) were substantially renovated and updated by 2000, and the facilities established "mercury separation plans" for collecting and recycling mercury products before they are burned.  These programs help to ensure that the facilities meet stringent limits on their emissions of mercury into the air. Air pollution control equipment at the two smaller MWCs was renovated in the early 2000s; these facilities are not required to implement mercury separation plans.

MWCs must be operated in accordance with state and federal solid waste and air regulations that ensure that they handle wastes properly at the facility and that their air emissions remain below levels and concentrations that could pose significant risks to public health or the environment.  All facilities are required to monitor key air pollutants continuously, and to test other pollutants (primarily "air toxics" such as dioxin and mercury) coming out of their smoke stacks every nine months.  The facilities must report the results of these monitoring efforts semi-annually and annually, identify instances in which air quality standards were exceeded, and describe how they corrected problems.  Annual and semi-annual emission monitoring reports submitted by the five largest MWCs are are available for review on the MassDEP web site.

Six of the seven Massachusetts MWCs produce electricity for the New England electric power grid (One MWC produces steam, which is used by nearby businesses).  As of November 1, 2008, these six facilities together can produce up to 222.88 megawatts of electricity per hour (based on their total winter seasonal claimed capacity), or 1.55 percent of the total winter seasonal claimed capacity of electrical generating plants located in Massachusetts.

Since 1990, the Commonwealth has imposed a moratorium on the construction of new capacity for incinerating waste.  The moratorium was originally established to avoid overbuilding in-state disposal capacity with facilities that must receive large amounts of trash for decades.  In the "Beyond 2000" Solid Waste Master Plan, the moratorium was also continued, to prevent increased mercury emissions from these facilities. 

MassDEP inspects all of the MWCs annually to review solid waste handling; the facilities' air pollution control equipment is inspected every three years.  In fiscal year 2008, these inspections resulted in two Notices of Noncompliance.  In addition, Department staff reviews the reports that the facilities submit describing their air emissions, and may observe the periodic tests of emissions from the facilities' smoke stacks.

Both Nantucket and Marlboro operate MSW co-composting facilities.  Co-composting involves mixing MSW (after recyclables are removed) with sewage sludge in a composting vessel.  Air and water are added to the vessel to optimize biological decomposition (or "digestion") while the material is held in the vessel for several days.  After the material has decomposed, a screening process is used to separate organic materials for further processing as compost (i.e., several weeks of compost curing) from materials not suitable for compost, which are disposed in a landfill.  This process can reduce the amount of solid waste disposed by up to 80 percent.

MassDEP oversees the co-composting facilities as it does other solid waste management facilities, by conducting periodic inspections and (if needed) taking enforcement action when problems are not corrected in a timely way.