Environmental Performance

Environmental performance starts with operating the trash burning furnaces efficiently and finishes with the monitoring of the emissions as they go up the plant's stack, or chimney.

Wheelabrator North Andover monitors its environmental performance two ways. First, the facility monitors key emissions and operational parameters 24 hours a day, 7 days a week to assure clean burning, proper operation of air pollution control devices and maintenance of emission limits below permitted levels. This is achieved by the use of continuous emission monitoring systems (CEMS).

A second means of monitoring environmental performance is by "Stack Testing", also referred to as stationary source sampling or emission testing. This requires professional stack testers to set up sophisticated emissions sampling equipment to carefully withdraw samples of stack gas in a manner that captures or "traps" the emissions of interest. These samples are then sent to a laboratory for analyses. The amount of pollutants captured are so low that only very specialized analytical laboratories are capable of accurately measuring them!

CEMS Description

Wheelabrator North Andover continuously monitors levels of emissions so low that it was technically impossible to do so twenty-five years ago! How low is low? We continuously monitor levels of emissions so low that it would be the equivalent of finding one or two clear marbles in a jar of one million blue marbles!

We extract or sample emissions from each of our trash burning furnaces around the clock to measure the levels of carbon monoxide (CO), carbon dioxide (CO2), nitrogen oxides (NOx) and sulfur dioxide (SO2 ). We also measure for oxygen (O2) too!

Emissions are monitored or measured by specially designed analyzers using sophisticated analytical technology. It has taken decades to refine and improve this analytical technology to continuously and accurately monitor emissions from power plants such as ours. It's still tough to do!

Our plant utilizes the CEMS to operate the plant efficiently and to report our level of emissions to regulatory agencies.

Carbon monoxide helps verify the overall efficiency of the combustion. Low levels of carbon monoxide readings = efficient combustion = thorough destruction of the trash.

The levels of nitrogen oxides (NOx) that we measure help us control the feed of urea to the combustor. Likewise, levels of sulfur dioxide (SO2 ) that we measure help us determine the amount of lime slurry we feed to our scrubbers. If the NOx emissions begin to rise above normal, our CEMS detect this and we automatically feed more urea. If the SO2 levels become elevated, we automatically feed more lime to the scrubbers.

Finally, we also monitor Opacity, or visible emissions. Opacity is a measure of how much soot or smoke may be contained in stack emissions. The more smoke that is contained in the emissions, the higher the level of opacity. The opacities of the emissions from each boiler are measured by continuous opacity monitors located after all of the air pollution control equipment. Opacity readings are typically less than 3% and that is as low as the opacity monitors can accurately measure. Typically the human eye can not detect or see smoke that is less than 5% opacity; that's why you don't see smoke coming out of our chimney. What is often seen emitting from our chimney is water vapor, or condensation. Typical stack gases from a modern trash-to-energy plant are 20% water! And just like your breath is visible during the winter, our emissions will often look "white" from all the water condensing in the air! Smoke is gray or black. You won't see smoke from a modern trash-to-energy plant.

To assure proper operation of the Continuous Emission Monitors, we conduct daily calibrations of all analyzers and a rigorous maintenance schedule. The United States Environmental Protection Agency (USEPA) and the Massachusetts Department of Environmental Protection (MADEP) require that the analyzers be removed from service to calibrate every day. We also believe that it is better to take an analyzer out of service for a couple of hours to replace parts before they break than to wait for a catastrophic failure. It's sort of like changing the oil and oil filter on your car every 3000 to 6000 miles instead of waiting for your engine to break due to dirty oil. Despite our best efforts, the equipment can malfunction and break. We always report any malfunction or failure to the regulatory agencies. Every three months, we conduct specialized tests to assure the accuracy of the equipment. All of this together assures quality emission monitoring around-the-clock, 365 days a year.

All emissions data from the CEMS are sent to a computer that calculates averages that can be reported to the regulatory agencies. These averages are also compared to our permit limits. All this information is stored and reviewed continuously by plant operators to assure proper operation of the facility. Why now we even send our emission results our to the public every single day! Keep on reading to better understand all the monitoring and testing we do! Better yet, call us for a tour of our facility. We'll show you the equipment up close.

Emission Testing (Stack Testing)

Practically no industry in the world has tested their air emissions more than the trash-to-energy industry. Over the past 30 years, the USEPA and scientists have developed sophisticated testing methods to measure emissions that can't be measured by Continuous Emission Monitoring Systems. These testing methods require highly trained technicians to withdraw or sample emissions from our chimney with delicate equipment specifically designed for the job.

These testing methods are so sophisticated that they can detect the equivalent of one blue marble in a jar of one billion to one trillion clear marbles!!!

How small is that? If you put inch clear marbles side-by-side around the world, you would have slightly more than 6 billion marbles (about 6,336,000,000 give or take a few). We often measure the equivalent of one blue marble in that chain of marbles around the world! Now that's small!

Did you know


There are 16 ounces in a pound.
There are 27 grams in an ounce.
There are 27,000 milligrams in an ounce.
There are 27,000,000 micrograms in an ounce.
There are 27,000,000,000 nanograms in an ounce.
There are 27,000,000,000,000 picograms in an ounce.

Many test parameters, like dioxin and furans for example, are measured by stack testers down to the picograms!

We frequently test for emissions like mercury, dioxin, hydrochloric acid and other metals such as lead and cadmium. Trained technicians under the supervision of engineers, scientists and environmental officials conduct these tests. The results of these emission tests are compared to permit limits. You can find the results of these tests further on in this web site. Please feel free to call us if you have any questions about emission testing or the emission testing results.

Wheelabrator North Andover
285 Holt Rd.
North Andover, Massachusetts, U.S. 01845
Tel: 978.688.9011

Copyright © Wheelabrator North Andover