How Organics Diversion Extends Landfill Life

Diverting food scraps and yard trimmings to composting extends a landfill’s life by the airspace those tons would have used: tons diverted, divided by the site’s in-place density, gives cubic yards saved each year, and that saving divided into remaining capacity gives the years gained. The gain is real but usually modest for a single program, so the stronger reasons to divert are often methane, state mandates and the value of the airspace itself. This guide shows how to run the numbers with your own survey data.

Key takeaways

Food is the largest single material in landfilled municipal solid waste. EPA puts it at about 24% of what US landfills received in 2018, with yard trimmings at about 7.2%.
Airspace saved per year equals net tons diverted divided by your landfill’s in-place density (also called the airspace utilization factor), measured from your own topographic surveys.
Subtract the residuals a compost facility sends back to the landfill (contaminants, oversize, rejects) before you claim a saving.
Years of life gained are small for one program on a large landfill and larger on a small or nearly full one. Run low, expected and high cases.
Methane is often the bigger benefit. EPA estimates that landfilled food waste is the source of about 58% of fugitive methane from municipal landfills.
A compost pad on the landfill property keeps the diverted tons, the scale house and the operators on the same site.

What is in the waste going into a landfill

Start with composition, because it sets the ceiling on what diversion can do. EPA’s national overview of materials and waste reports that about 146.1 million tons of municipal solid waste were landfilled in the United States in 2018, and that food was the largest component at about 24%. EPA’s yard trimmings data shows landfills received about 10.5 million tons of yard trimmings that year, about 7.2% of all municipal waste landfilled. Paper and cardboard add more organic material on top of that.

California’s numbers point the same way. CalRecycle says organics such as food scraps, yard trimmings, paper and cardboard make up half of what Californians send to landfills, and it summarizes SB 1383’s 2025 target as 75% less organic waste sent to landfills. Our list of key SB 1383 requirements and the guide to organics diversion laws by state cover the mandates.

National averages are a starting point only. Your own waste characterization study, or your state’s published composition data, tells you how many tons of food and yard material actually reach your working face. California jurisdictions can use the statewide waste characterization data and tools CalRecycle publishes for local planners; CalRecycle notes that its online tools reflect a 2014 study and give estimates, so check the study year before you rely on them.

The airspace formula

Landfill engineers track how quickly the site consumes permitted volume. The ratio between tons placed and cubic yards consumed is the in-place density (some sites call it the airspace utilization factor, or AUF). It already includes compaction, daily cover and early settlement, which is why it is the right number to use here rather than a textbook density for loose food scraps.

The calculation has four lines:

Net tons diverted per year = tons sent to composting minus residuals returned to the landfill.
Airspace saved per year (cubic yards) = net tons diverted x 2,000 pounds per ton / in-place density in pounds per cubic yard.
Remaining life without diversion (years) = remaining permitted airspace / current annual airspace use.
Remaining life with diversion (years) = remaining permitted airspace / (current annual airspace use minus airspace saved per year).

The difference between lines 3 and 4 is the life gained. If tonnage is growing, repeat the calculation year by year in a spreadsheet instead of using a single annual figure.

Inputs you need

Input	Where it comes from	Why it matters
Remaining permitted airspace	Latest topographic survey and permitted final grades	The capacity you are stretching
Current annual airspace use	Survey to survey volume change	Your burn rate today
In-place density	Scale tons divided by surveyed volume over the same period	Converts tons to cubic yards
Organics tonnage available	Waste characterization, collection program data	What can be diverted
Capture rate	Program design and comparable programs	How much of the available tonnage actually arrives
Residuals rate	Pilot data or a processor’s records	Tons that come back as trash
Tonnage growth	Population and program ramp-up	Changes the answer over time

A worked example with assumed inputs

Every figure below is an assumption chosen to show the method. None is a typical value. Replace each with your own data.

Remaining permitted airspace: 6,000,000 cubic yards (assumed)
Current airspace use: 400,000 cubic yards per year (assumed)
In-place density: 1,400 pounds per cubic yard (assumed)
Organics sent to composting: 20,000 tons per year (assumed)
Residuals returned to the landfill: 10% of incoming tons (assumed)

Net tons diverted = 20,000 minus 2,000 = 18,000 tons per year.
Airspace saved = 18,000 x 2,000 / 1,400 = about 25,700 cubic yards per year.
Life without diversion = 6,000,000 / 400,000 = 15.0 years.
Life with diversion = 6,000,000 / (400,000 minus 25,700) = 6,000,000 / 374,300 = about 16.0 years.

In this example the program buys about one year of landfill life. Double the diverted tons and the gain roughly doubles. Halve the remaining airspace and the gain is about half a year, but it arrives sooner, when the cost of siting and permitting the next disposal capacity is closest.

Where the estimate goes wrong

Using a loose density. Food scraps in a collection truck weigh very differently from waste compacted in a cell. Use the in-place density from your surveys.
Forgetting residuals. Contamination in curbside organics comes back as trash. A cleaner program saves more airspace.
Counting gross, not net, tons. Material that would have been diverted anyway (backyard composting, existing green waste programs) is not new airspace.
Ignoring ramp-up. Food scrap programs reach full capture over several years. The guide to forecasting organics tonnage shows how to build that curve.
Double counting alternative daily cover. In California, CalRecycle explains that green material used as alternative daily cover has counted as disposal for per capita disposal measurement since January 1, 2020. If your green waste currently goes to cover, check how the cover material will be replaced before you credit the airspace.

Why airspace is worth more than the years suggest

A single extra year can look small in a staff report. Three points make it larger:

Airspace is the landfill’s inventory. For a public owner it is a finite asset that took years to permit. Each cubic yard used on compostable material is a cubic yard not available for waste that has no other outlet.
Replacement capacity is slow. A new cell, a vertical expansion or a new site involves design, permitting and public process. Extra years give the owner time to plan.
The value per cubic yard is site specific. The cost comparison guide shows how to put a value on airspace using your own disposal cost structure, without borrowing someone else’s numbers.

The methane benefit

Food waste breaks down fast in a landfill. EPA’s research on quantifying methane from landfilled food waste says that, because of its quick decay rate, food waste produces more landfill methane than any other landfilled material, that an estimated 58% of fugitive methane from municipal landfills comes from landfilled food waste, and that food can generate methane before gas collection systems are in place. EPA’s Landfill Methane Outreach Program reports that municipal landfills were the third-largest source of human-related methane in the United States in 2022, about 14.4% of the total, and that methane is at least 28 times more effective than carbon dioxide at trapping heat over 100 years.

For a landfill owner this means diversion affects gas generation as well as volume. The guide to landfill methane rules and organics explains how federal and state rules treat that gas, and why diversion supports, but does not replace, a gas collection and control system. To compare greenhouse gas outcomes for different management options, EPA’s Waste Reduction Model (WARM) compares landfilling, composting, anaerobic digestion and other pathways.

Composting on the landfill property

The diverted tons have to go somewhere, and for many municipal owners the nearest place is the landfill itself. Haulers already know the route, and the scale house, equipment and staff are in place. The composting at landfills guide covers siting on native ground, closed cells and inactive decks.

Two landfill sites in Sustainable Generation’s (SG) project profiles show the pattern. SG’s profile of the City of San Diego’s Miramar Greenery describes composting food and yard waste on top of a landfill: the city was composting green waste in turned windrows and adopted an SG MOBILE® System with GORE® Cover after a pilot, when food waste and curbside contamination entered the stream. At the Otay Landfill in San Diego County, SG’s profile says the system had to be modular and portable because it would sit on an active landfill. The Otay facility was announced by Republic Services as California’s first fully solar-powered compost facility, and SG’s SG SOLAR® Power page names landfill tops as an intended use.

Covered aerated static pile composting suits a landfill site because the piles do not need turning and the cover sheds rain. SG’s Cómo funciona page describes a 4 to 8 week treatment time versus 8 to 12 months for open windrow, which keeps the pad small, and SG describes SG MOBILE as installed in days to weeks, depending on the site. SG’s municipal solid waste page is its own summary for municipal buyers.

Data checklist for an airspace estimate

[ ] Two most recent topographic surveys and scale tonnage for the same period
[ ] Remaining permitted airspace to final grades
[ ] Waste characterization or state composition data for your service area
[ ] Current green waste and food scrap tonnage, and where it goes now (including alternative daily cover)
[ ] Planned collection program, with roll-out dates by route or sector
[ ] Expected capture and contamination rates, with the source of each
[ ] Residuals rate from a pilot or a comparable processor
[ ] Low, expected and high cases, presented side by side

FAQ

How much landfill airspace does one ton of diverted food waste save?

It depends on your landfill’s in-place density, not on the food. Divide 2,000 pounds by your in-place density in pounds per cubic yard. At an assumed 1,400 pounds per cubic yard, one net ton saves about 1.4 cubic yards. Measure your own density from surveys and scale data, and subtract residuals that come back from the compost facility before you apply it.

Will a food scrap program add many years to our landfill?

It depends on the ratio between the diverted tons and your landfill’s annual airspace use, so run the numbers rather than relying on a rule of thumb. In the assumed example above, 18,000 net tons a year buys about one year over a 15 year remaining life. The gain grows when the landfill is small, nearly full, or when diversion covers both food and yard material across the whole service area. The methane, compliance and mandate reasons are often stronger than the years alone.

Does diverting yard waste save as much airspace as diverting food waste?

Per net ton, the airspace saved is set by the landfill’s in-place density, so a ton is a ton. In practice, yard trimmings are often already diverted, so the new tonnage available is smaller. Food waste is the larger untapped stream in most service areas, and EPA identifies it as the main source of landfill methane.

Should the compost facility be on the landfill or somewhere else?

On the landfill property is often the simplest choice because roads, the scale house, staff and buffers exist, but closed cells settle and gas systems need protection. A separate site may suit a long haul from the service area. The composting at landfills guide walks through the siting questions.

Next step

Run the four-line calculation with your own survey data, then read the composting at landfills guide to see where a pad could go. For the process itself, see how covered aerated static pile composting works.

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