Accentuating the positive: lab tests seek to confirm and document the successful use of C&D fines in landfill applications.

Good news doesn't always get much attention, and for C&D recyclers, good news in New England has been somewhat hard to come by in recent years. At a time when market development for products made from recycled C&D debris is more important than ever, the industry has fallen under regulatory scrutiny that has hampered markets in many states.

Among the stories generating negative publicity for C&D recyclers is the issue of hydrogen sulfide gas (H2S), a foul-smelling gas that has been reported at certain landfills using fines from construction and demolition debris as alternative daily cover (ADC) or shaping and grading material. Its presence has generated nuisance complaints from neighbors, prompting some states, including New Hampshire and Rhode Island, to ban the material from use in landfill applications, slamming the door on one of the industry's major markets.

While cases of H2S gas generated by the use of C&D fines has been well documented by local media and regulatory agencies, a number of landfill facilities have used the same material with no such problems. This data is missing from the discussion of the H2S gas generation issue, according to Greg Wirsen of Green Seal Environmental, Sandwich, Mass. "In the past, there has really only been negative documentation if a landfill had a issue with hydrogen sulfide, even though this material has been used many times without any negative impacts," says Wirsen, who is also the New England director of the Construction Materials Recycling Association (CMRA).

The industry is counting on these undocumented success stories to keep ADC and fill material made from C&D fines a viable end market for mixed C&D recyclers. Representatives from industry associations, academia, private companies and government agencies have partnered to initiate a H2S demonstration project--testing the use of C&D fines at a full-scale landfill facility to demonstrate how generation of H2S can be controlled if used properly.

PUT TO THE TEST

According to Wirsen, initial testing has been conducted over the past couple years at the University of Florida, University of New Hampshire and LL&S Inc. of Salem, Mass. "The next step is to perform testing full scale to see how hydrogen sulfide gas can be controlled so that there are no offsite nuisance conditions," he says.

A number of stakeholders have joined this effort, including the University of New Hampshire; the CMRA; the EPA; the Massachusetts Department of Environmental Protection (DEP); and a number of private companies, including LL&S, New England Recycling (NER) of Taunton, Mass., and ERRCO (Environmental Resource Return Corp.) of Epping, N.H., among others.

Many questions remain unanswered about how the gas is generated. However, gypsum, commonly found in wallboard, seems to be a constant factor, says Wirsen. "There are other sources of sulfate, but it appears that gypsum products are the largest contributor," he says.

Even though sulfate content has been identified as a contributing factor to the generation of H2S gas, many other questions remain. How much sulfate is needed to generate the gas, the size of the landfill at which it is used, how long an incubation period is required and what effect mixtures with other materials might have are still all unknowns, according to Wirsen.

The project's organizers have set some specifications for the materials used in the testing. Fines used in the demonstration project will have limited sulfate content and will be between 1/2-inch minus to 1-inch minus in size. Organic content will also be less than 20 to 30 percent, depending on the screen size.

The fines will be used as shaping and grading material, and a location for the test has yet to be determined, but the site would have to conform to certain requirements. The demonstrators are looking for a site that is between 1 to 4 acres in size with a 100,000-cubic-yard capacity and a minimum thickness of 10 feet to create anaerobic conditions. The site must also have the ability to monitor the demonstration for at least four consecutive seasons.

Dr. Jenna Jambeck from the University of New Hampshire, who has performed laboratory scale experiments with C&D fines, will partner on the monitoring of the project. She has conducted studies on the utilization of recycled materials as H2S attenuation materials by mixing them in large columns simulating landfill conditions and monitoring the gas and leachate concentrations. The full-scale demonstration project will be monitored by Jambeck and her graduate students, tracking temperature, quantities and quality of gas generation and any leachate that is able to be collected.

The people and organizations behind the demonstration project hope its results will yield some much sought-after answers to the problem of H2S gas generation.

The general goal, Wirsen says, is to document how C&D fines can be used successfully in a landfill environment. Wirsen and the project's fellow organizers also hope the data yielded by the project will be able to be used to help set up guidelines for the safe use of C&D fines, including limitations for sulfate content, organic content and how to set soil-to-fines rations that will not require active gas collection and will prevent nuisance odors.

With the data in hand, the industry will be poised to define best management practices for the use of C&D fines, according to Wirsen. "There have not been any published documents about the successful use of C&D fines and/or residuals," he says. "This demonstration will provide quantitative data that can be used by the industry in the future."

The author is associate editor of Construction & Demolition Recycling and can be contacted [e-mail].