April 1, 2005

10 Min Read
Passing the Smell Test

Kim A. O'Connell

IT'S THE MESSAGE NO LANDFILL wants to receive. Recently, the Massachusetts Department of Environmental Protection, Boston, issued a notice of non-compliance to a construction and demolition (C&D) debris landfill for its failure to control odor. According to the notice, the decomposition of C&D debris was causing the release of odor-causing hydrogen sulfide (H2S) gas. Those who don't recognize the gas by name would know it by its smell — the unmistakable odor of rotten eggs.

Unless the C&D landfill figures out what to do about the odor, it may have to stop collecting construction debris altogether — a fate that is facing C&D recyclers and landfills all across the country.

In Ohio, for example, thousands of tons of C&D debris, leftover from the recycling process, have been rail-hauled to the Buckeye state from the Northeast, often at a substantial savings in tipping fees. Yet several landfills that accept the C&D waste are receiving numerous citizen complaints about H2S odor. If states respond to such complaints by banning C&D debris in landfills — where it is often applied as an alternative daily cover (ADC) — it could have widespread effects on the C&D recycling industry.

In New Hampshire, for example, complaints about sulfuric odor were so numerous that, in July 2004, the state banned the use of C&D fines as a daily cover. Concerned about the effects on the C&D recycling industry, the Construction Materials Recycling Association (CMRA), Eola, Ill., participated in a working group to develop a set of best management practices (BMPs) for the use of C&D fines in New Hampshire landfills. The BMPs may now serve as a national model .

“The BMPs allow us to continue to provide this product to the landfill industry,” says William Turley, executive director of CMRA. “C&D recyclers should keep trying to get better-value products for what they're bringing in. But there's always going to be a level of material that's leftover, so there needs to be an outlet for it.”

Paying the Fines

Without question, the C&D recycling market has gained steam in recent years. Depending on the region, C&D debris comprises an estimated 25 to 45 percent of North American waste, and up to 25 percent of that waste is recycled, according to CMRA. As debris is processed through a typical system of grinders and screeners, it leaves behind a significant portion of “fines,” those ¼-inch to 3-inch pieces that are byproducts of the recycling process. C&D fines typically are made up of sand, dirt, asphalt, gypsum, organics and other material.

C&D fines have been used as an ADC material at landfills since the 1980s. Using fines can have several positive benefits for landfills. Depending on the site conditions, fines can shed water, resist erosion, be easily spread and prevent fire if the organic content is low enough, among other benefits. But C&D fines also can contain a large portion of gypsum, the primary component in drywall, which can produce hydrogen sulfide gas.

Generally, H2S is produced in a landfill when sulfur-reducing bacteria consume and metabolize sulfate. Ideal conditions for the production of the gas include the presence of moisture, the absence of oxygen, and a certain percentage of organic material [See “Optimal Conditions for H2S Production” on page 102.] Although the most notable problem related to H2S is its rotten-egg odor, some reports also have attributed respiratory ailments and other health problems to a high exposure to the gas.

“This is not a new issue,” says Timothy Townsend, an associate professor at the University of Florida's Department of Environmental Engineering Sciences, Gainesville, Fla. “We've known for a number of years that drywall in a landfill can result in hydrogen sulfide formation. More recently, with the growth of the C&D debris recycling industry, there's been a continued need to find markets for the products of those operations [such as ADC]. In the Northeast, there have been landfills that have hydrogen sulfide odors that have been attributed to ADC use. It's caused some people to step back and say, ‘maybe this is not what we want.’”

With a team of researchers, Townsend is developing uniform testing protocols to determine the levels of gypsum in C&D debris, a first step in the creation of nationwide BMPs. “There is no good testing protocol to determine the amount of gypsum in the C&D debris,” Townsend says. “You might get extremely variable results from place to place. We're developing a standard operating procedure to get reliable estimates on the amount of gypsum that's in an alternative daily cover. We're hoping to ultimately answer the question of ‘how much matters’ in the development of hydrogen sulfide.”

Interim Steps

Although the University of Florida's research is ongoing, it did not preclude the C&D recycling industry from developing interim BMPs to deal with the hydrogen sulfide issue in New Hampshire. With leadership from the New Hampshire Department of Environmental Services in Concord, the work group was composed of C&D recyclers, landfill operators, academics and CMRA, represented by its New England chapter.

In New Hampshire, solid waste officials saw that C&D fines were not affording the benefits that they have in other locations. “It didn't shed water very well, and it didn't hold gas in very well,” says Mike Sills, chief engineer of the state's Waste Management Division. “We set up a pretty large work group and developed pilot programs at one of the C&D processing facilities to nail down which combinations of soil and coal ash would keep down the formation of this gas.”

A key motivator for the group was cutting through the many assumptions that were being made about H2S. “Very early on, a lot of people were saying that this happens and that happens with the leaching of sulfur, and there was a lot of theory being thrown around,” says Mike Guilfoy, the department's supervisor of solid waste permitting and compliance. “We decided that we should have a short-term goal, and come up with some kind of interim BMPs that we could do immediately — even if they weren't the final answer. Let's come up with something quickly and get something on the table that we can all agree on.”

To develop the BMPs, CMRA worked with its member-companies LL&S, Salem, N.H., and ERRCO Recycling, Epping, N.H., to develop fines formulations that could be used in landfills without any significant production of H2S. Landfill conditions were simulated in 30-cubic-yard rolloffs, in which various combinations of fines were tested to see if odors developed. As part of the study, the group determined that, in New Hampshire, typical fines were up to 2 inches in size and contained up to 35 percent organic materials. [See “Suggested Characteristics of C&D Debris for Landfill Use” on page 102.]

The working group developed five standard operating procedures when using C&D fines as ADC or for grading and shaping:

  1. gypsum removal prior to processing or transfer;

  2. disposal of bulk gypsum in one area;

  3. mixing the ADC with soil;

  4. mixing the ADC with ash (coal or wood ash); and

  5. educating recyclers and landfill operators about the sulfur cycle in landfills.

Removing gypsum from C&D fines is the optimal way to reduce the likelihood of H2S production. The interim BMPs suggest that gypsum that is removed from C&D loads prior to processing or transfer, or source-separated at the site of demolition, should be disposed of at the landfill in a way that minimizes the generation of H2S. This could mean disposal in a single confined area of a cell and sealed with a soil cap or equivalent, which would help to limit the amount of H2S that is emitted out of the landfill or the amount of moisture coming in.

“In the real world, it's impossible to remove all the gypsum, because when you get this debris, it's often all ground up,” says Terry Bauer, chief operating officer of Green Seal Environmental, Sandwich, Mass., and CMRA's New England representative in the BMP working group. “You're always going to get the potential for H2S to be generated. What we can do to combat this is change the characteristics of the material. There have to be certain conditions for H2S to be produced, so the question was, how do you change the characteristics so that this bacteria won't grow? One way was using a bacterial additive or mixing in ash to change the pH.”

The interim BMPs recommend that the sulfate concentration in fines be determined and its gas and water infiltration sealing abilities verified, so that the material can be used alone as an ADC without excessive H2S generation. Until this concentration is achieved, however, mixing fines with soil at a 50:50 ratio or coal ash can control hydrogen sulfide generation. In addition to mixing the fines with another material, the BMPs also require mitigation of rainwater infiltration and the release of landfill gas.

Building Blocks

Probably the most important BMP, according to the New Hampshire working group, is educating recyclers, transfer station operators and landfill operators about the sulfur cycle in landfills. “When these groups of people are aware of the mechanisms that result in the production of H2S, the dangers of exposure and how to effectively restrict the production of H2S, then smart choices can be made on a daily basis that will result in a safer environment,” the group reports.

Already, at least two New Hampshire landfills have adopted the interim BMPs successfully. “The interim BMPs are rather general in nature and rely on a good-faith effort by the industry, the processors and the landfill operators to implement them correctly,” Guilfoy says. “We find that that's working. The processors don't want to be blamed for [odors], and neither do the landfill owners.”

CMRA and its partners also are working with other states and industry groups to develop nationwide standards for the use of C&D fines in landfills. Turley also urges the solid waste industry to look beyond C&D material. For example, the disposal of sludge in landfills might also be a significant cause of hydrogen sulfide generation, he says. Also, the University of Florida expects to confirm its standard gypsum testing proposal this spring.

As a result of such efforts, C&D recyclers and landfill operators may once again enjoy a mutually beneficial relationship without anyone raising a stink about hydrogen sulfide. “This is a vital outlet for the material C&D recyclers produce,” Bauer says. “There needs to be some beneficial use for this material, or else these facilities are not worth operating. The BMPs have widespread application across the country.”

Kim A. O'Connell is a Waste Age contributing editor based in Arlington, Va.

Optimal Conditions for H2S Production




Between 4 and 9 (optimum)


Between 30° C and 38° C (optimum)

Absence of Air

Anaerobic (no oxygen)

Food Source

Sulfate ions


Moist or wet

Carbon Source

Wood, paper, glue, etc.

Suggested Characteristics of C&D Debris for Landfill Use


Recommended Standard Range

Particle Size

Up to 2"

Organic Content

Up to 35%

Sulfate Content

Up to 60,000 mg/Kg

Suggested Procedures for Using C&D Debris as Daily Cover

• Gypsum removal prior to processing or transfer

• Disposal of bulk gypsum in one area

• Mixing the ADC with soil

• Mixing the ADC with ash (coal or wood ash)

• Education regarding the sulfur cycle in landfills

Source: New Hampshire Department of Environmental Services

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