What's That Smell?

[Author's Note: The practices described herein may not be applicable in every situation. They are simply the experience of one landfill operator who learned these lessons firsthand.]

A GOOGLE SEARCH of the phrase “landfill odor” yields more than 700,000 results. Unfortunately, a quick survey reveals that such smells continue to trouble the solid waste industry.

Odor problems at landfills steadily are becoming more newsworthy, and the issue is the most critical one facing landfill operators today. The nuisance is difficult for operators to manage, and makes their relationship with the public a vulnerable one, as unpleasant smells are an easy concern for landfill foes to rally around.

The reality is clear: Every landfill that handles putrescible waste will produce distasteful smells. In the past, this nuisance was accepted by most affected parties as something that could not be controlled, and most people simply learned to live with the fact that “it smelled bad around the landfill.”

However, the expectation of what is an acceptable level of odor has changed, and the inability or unwillingness to control stenches has resulted in a collective black eye for the industry. High-profile odor emergencies invariably elicit significant reactions from landfill operators, resulting in dramatic improvement — but usually only after the public relations damage is done. Landfill operators obviously know how to address the problems — they just need to tackle them aggressively and before they become an issue with the public.

A serious investment of time and money is required to insure a successful odor control program, and several practices must be diligently followed in order to stay ahead of the curve.

Odor Sources

Obvious sources of odors are incoming waste, workface activities, landfill gas, condensate systems, and leachate collection and handling systems. All other site areas and activities should be evaluated as well. Every landfill should have a trained landfill gas technician to monitor and manage odor issues. Gas extraction systems require constant maintenance to insure that odor-causing leaks are promptly repaired. A landfill may produce minimal odors during daylight hours and have significant ones at night — long after workers have gone home. Only by diligent monitoring will these situations be identified.

Workface Management

An active workface will produce undesirable aromas throughout the course of a day that often need to be addressed before the daily cover is applied. Deodorants and odor neutralizers are effective and can be used in a variety of ways on an active workface. Fixed line sprayers, portable sprayers and equipment-mounted devices all will deploy these chemicals directly onto the active working area and into the air surrounding the workface.

In addition, certain wastes, such as domestic and industrial sludge, can be immediately buried rather than commingled with other waste to quickly reduce the potential for unpleasant smells. Particular care should be taken during landfilling to insure that stormwater infiltration is minimized. Excess moisture in the landfill will significantly increase the potential for gas odors.

Lift configuration, stormwater diversion and leachate recirculation all need to be carefully evaluated for odor potential. Odor mitigation should be incorporated into design and operating plans.

Covering the Bases

A good daily cover program is critical to controlling of powerful stenches. If possible, soil or soil-like material should be used for daily cover. This provides an effective seal against the odors generated by new waste. Many alternative daily cover options also are available and can provide an effective barrier.

Intermediate cover is required on areas that will be undisturbed for an extended period of time but have yet to be filled to final elevation. In these areas, a 12-inch layer of soil is used to cover the waste, and a vegetative zone is established. Vegetation on the intermediate and final covered portions of sites is important for more than just aesthetic reasons. Particular attention needs to be paid to the areas for erosion rills and gullies.

Leachate breakouts and erosion gullies are significant odor sources, and stressed vegetation is a good indicator of landfill gas migration. Fortunately, these areas are easily repaired. If odor control is the priority, then active gas extraction and final cover should be installed as soon after final waste placement as possible. This contradicts the earlier industry standard of postponing capping as long as possible to allow for maximum settlement and airspace conservation.

Active Gas Extraction

Traditionally, deodorants and odor neutralizers have been the first (and last) line of defense for most landfill operators. While these products are effective for workface odors, as described above, effective control of the smells from landfill gas must occur before the odors ever reach the surface.

Active gas extraction is the only effective means of controlling landfill gas odors. For many years, the industry standard for extraction has been vertically drilled wells spaced out by 200-foot centers. That practice is effective when employed along with an aggressive closure plan. If a landfill is filled to capacity and properly capped, vertical gas extraction wells will perform as intended and odor control will be achieved.

However, today's larger landfills may remain open for many years before final elevations are reached. In these cases, closure is not possible, and large acreages remain open, or under intermediate cover, with no means of active gas collection. This condition produces the perfect environment for significant landfill gas odors.

The Modern Landfill in York County, Pa., has employed an effective solution to this problem in recent years: the horizontal gas collection trench. The process allows active gas collection to take place long before final landfill elevations are reached.

Upon completion of a typical trash lift, a series of parallel trenches are excavated into the newly placed waste. Trenches are typically 4 to 5 feet wide and 3 to 4 feet deep. Trenches can be several hundred feet in length and are installed approximately 200 feet apart.

A perforated corrugated metal pipe (CMP) is placed within the trench, and the trench is backfilled with porous stone and then covered with refuse. Trenches are terminated at 50 feet from the side slope and finished off with a conventional wellhead to allow for tie-in to the landfill gas extraction system. Using this approach, a layered series of gas collection zones are created in the uncapped portion of the landfill, thereby capturing landfill gas before it migrates to the surface and creates the potential for off-site odors. Horizontal collection trenches are inexpensive, easily installed and very effective. Modern Landfill has realized dramatic reductions in gas odors using this method.

The Public and Regulators

Too often, a landfill manager's first interaction with the public comes when residents are upset with the site. The old saying “make friends before you need them” is most applicable when it comes to odor control. A good rapport with key neighbors will help a site manager truly understand how the odor control systems are working.

If a landfill manager has good relationships with his or her neighbors, many odor concerns can be addressed quickly. A 24-hour odor hot line can add significantly to a manager's understanding of how the landfill truly affects the surrounding residents. It also provides an opportunity for valuable feedback from the community on other issues.

In many cases, landfill operators do not think that they have an odor problem unless government regulators think they have one. As mentioned above, operators can no longer allow outside forces to tell them if and when they have an issue. Site managers need to be dealing with odor issues long before anyone forces them to. In many cases, the regulators are only responding to complaints — after the opportunity to proactively correct the issue has passed.

The bottom line in odor control is that landfills are expected to have no off-site odors, and the solid waste industry must do a better job of minimizing and mitigating this nuisance. Today, a landfill's future is directly impacted by its ability to control odor. The industry has a history of safely and efficiently responding to society's waste disposal challenges. The sector needs to accept the challenge presented by landfill odors, realize such smells can be controlled and continue to seek innovative ways to make odor complaints a thing of the past.

Tim O'Donnell is the general manager of Republic Services' Modern Landfill in York County, Pa.