Bolton on Landfill Management: Converting Cubic Yards to Tons
Some landfills charge by the ton. Others charge by the cubic yard. A few use both weight and volume, depending on the load or vehicle type.
Sometimes landfills charge by the cubic yard because they don't have a scale. Sometimes it's simply tradition held over from when they didn't have a scale. And sometimes it seems that its only purpose is to keep the customers or the competition guessing.
If you find you're stuck in the middle, wondering how to connect the dots between weight and volume, read on. We'll take a look at how to convert between inbound yards and tons.
Charging by Volume
In general, when landfills charge by volume, it is expressed in cubic yards ...say, $12 per cubic yard. Most landfills that charge by volume have at least two rates--one for compacted waste, the other for loose waste.
On average, a cubic yard of loose waste (i.e., a self-haul load) will weigh between 250 and 350 pounds. In my experience, 325-350 pounds per cubic yard (pcy) is typical and provides a good planning figure.
However, a cubic yard of compacted waste (i.e., in a packer truck) can weigh, on average, 400-800 pcy. Again, for most landfills, 500-600 pcy is typical.
Demolition and construction debris can be much heavier. Typically it's a good idea to differentiate between building construction debris (i.e., lumber, insulation, sheetrock, etc.) and things like asphalt, concrete, and other heavy construction materials.
Conducting a Weight Study
Keep in mind that these figures will vary from one landfill to another and may even vary seasonally. The most reliable means of determining what your conversion factors are is to do a weight study...assuming you have a scale on-site. Here's how to conduct one.
Periodically measure certain loads. Then weigh them. Select loads randomly or use some other means of getting a true representative sample of vehicles. Sort the results by type of vehicle (i.e., self-haul, front-loader, rear-loader, roll-off, etc.) or type of waste. Different types of vehicles will vary and you'll want an average density for each one. For example, front-loaders and rear-loaders are both packer trucks. However, the density will often vary from one type of truck to another. Also, in many areas, front-loaders handle lots of motel and restaurant waste and therefore may achieve greater density.
If your landfill's climate varies through the year, you may want to do a study during each season—one in the winter and one in the summer. When you're finished, you could set up a table showing the average density for various vehicles and factor for converting from cubic yards to tons. Here's an example.
Using a simple table like this, the gate attendant could easily convert every load from yards to tons. For example, consider a contractor's dump truck that comes in with 8 cubic yards of building construction debris. The gate attendant would then multiply 8 (cubic yards) by 0.37 (the conversion factor) for an estimated weight of 2.96 tons.
It's All About Airspace
Remember, all landfills have one thing in common. They're all selling airspace. And while their method of charging may vary, for every landfill the gate fee really boils down to: "How much is a cubic yard of landfill airspace worth?"
By developing an accurate means of converting volume to weight, landfills can make sure that their rates are competitive and affirm that they're not giving away airspace.
About the author: Neal Bolton, a registered engineer, author of "The Handbook of Landfill Operations," and principal of Blue Ridge Services, provides operational consulting for landfills in the U.S. and abroad. He can be reached at firstname.lastname@example.org.