A Response to the USGS Landfill Leachate Study

A recently reported study conducted by the U.S. Geological Survey (USGS) based in Iowa City, Iowa, found that treating liquid waste from landfills does not remove all contaminants. But now some solid waste industry experts are stepping forward to critique some of the methodology in the report.

The study found that leachate samples contained high levels of contaminants. “Study results documented that final leachate samples contained 101 of the 190 chemicals analyzed for the study, with at least one chemical present in every final leachate sample collected at levels ranging from as low as 2 nanograms per liter to as high as 17,200,000 nanograms per liter,” says Dana Kolpin, research hydrologist at USGS.

The most frequently detected contaminants of emerging concern (CECs) were lidocaine (local anesthetic, found in 91 percent of samples), cotinine (nicotine breakdown product, 86 percent), carisoprodol (muscle relaxant, 82 percent), bisphenol A (component for plastics and thermal paper, 77 percent), and carbamazepine (anticonvulsant, 77 percent), according to the study.

But Jeremy O'Brien, P.E., BCEE, director of applied research for SWANA, sat down with Waste360 to discuss these findings and how the industry is handling landfill leachate contaminants.

Waste 360: The USGS study reports that final leachate samples contained 101 of the 190 chemicals analyzed for the study, with at least one chemical present in every final leachate sample collected at levels ranging from as low as 2 nanograms per liter to as high as 17,200,000 nanograms per liter. How significant is that amount?

Jeremy O’Brien: To begin with, regulatory thresholds for most chemicals in liquid discharges—leachate, wastewater, storm water, etc.—are typically measured in milligrams per liter or micrograms per liter. An mg is one thousandth of a gram—a gram, for example, is the weight of about a small raisin—while a microgram is one millionth of a gram. A nanogram is one billionth of a gram, an extremely small unit of measure, which is only detectable because of advances in analytical technology. Therefore, from a simple concentration standpoint, the detected values for many of these chemicals are outside of the range where they would be considered significant.

Significance for any chemical entering the environment is based on its toxicity as measured by health and environmental impacts. The thresholds for toxicity vary by chemical and not every chemical has been thoroughly studied to date. So it is difficult to make general statements regarding all of the detected chemicals, but where toxicity data are available, the detected levels are below what would currently be considered significant from an environmental standpoint.

Also, the study involved the analysis of samples from leachate "that has undergone treatment or storage processes." Most landfills store collected leachate on site to moderate leachate flows off-site and, in some cases, to partially treat leachate. However, the leachate is then generally discharged to a publicly-owned wastewater treatment plant for further treatment. To determine potential environmental impacts, samples should be taken from leachate that has been fully treated—discharged from a wastewater treatment plant or on-site leachate treatment plant.

Waste360: The most frequently detected CECs were lidocaine, cotinine, carisoprodol, bisphenol A and carbamazepine, according to the study. Should people be concerned or is this fairly normal?

Jeremy O’Brien: The presence of these chemicals in landfill leachate is not surprising. Just like municipal wastewater, anything that people place in their trash or dump down their drains will end in the landfill or at the wastewater treatment plant, respectively. The chemicals noted above are present in products that people use in their homes and then discard, such as cigarettes, over the counter and prescription drugs, and household products made of paper and plastic. In fact, every natural and man-made product we use in our homes and businesses has chemicals like these present in them, so it would be expected that those chemicals would be detected in the waste materials left after the product is discarded. In addition, the significance of the concentrations being reported can only be assessed if the concentrations are tied to specific pollutants.

Waste360: The study is intended to inform landfill managers, stakeholders and regulators about chemicals present in landfill leachate disposed offsite to various pathways. What will they do with this information?

Jeremy O’Brien: The study could be used as an impetus to evaluate the potential environmental toxicity of these chemicals at the low concentrations that are being detected. And then where a real threat is determined, standards could be established to prevent environmental exposure to the chemicals above certain threshold levels. This is probably best conducted by environmental regulatory agencies, which can complete the studies and establish the necessary regulations, with appropriate stakeholder involvement. At this point in the process, it would not be appropriate or effective for the landfill managers or other stakeholders to start to take actions simply based on the presence of these chemicals at the low detected concentrations. 

Waste360: Is there anything the industry can do to eliminate these contaminants? 

Jeremy O’Brien: There are things that can be done but only when a real environmental threat is determined to be present for these chemicals at the detected levels. Again, these chemicals are present in everyday life. As noted, they come from the use of products containing these chemicals by people in their homes and businesses; that is, they are already being exposed to them, potentially at higher concentrations than what is present in leachate. Therefore, their presence alone, at these very low concentrations, should not be a trigger for action to control or limit the presence of these chemicals.

However, after appropriate study and sound scientific conclusions, regulations could be enacted that would include limitations on the use of these chemicals in the products in the first place, restrictions on their disposal into municipal refuse (or wastewater), and/or specific requirements for how landfill leachate should be handled if the specific chemicals are found above the threshold levels established. The regulations would need to be coupled with awareness programs so consumers will better understand the potential issues and are informed about how the chemicals (or products containing those chemicals) should be handled.

For example, many community solid waste management systems have household hazardous waste management programs. These programs are intended to keep certain known hazardous substances out of the refuse that is sent to landfills, transfer stations, recycling facilities, and waste to energy plants. However, the programs are only as effective as the awareness and participation level of citizens. If they continue to place these hazardous materials in the trash, dump them down the drain, or into the storm drain, then they will continue to show up in leachate, wastewater, and storm water. The same issue will have to be faced if there is a decision to regulate these CECs in the same manner.      

Waste360: What is the industry currently doing to manage contaminants in leachate?

Jeremy O’Brien: It is important to note that landfill leachate is already managed in an environmentally sound manner under the direction and oversight of regulatory agencies. It is not being used for drinking or potable water purposes or being directly discharged to streams, lakes, or oceans without treatment. In most cases, it is collected and sent along with other wastewater to municipal or industrial wastewater pretreatment facilities for treatment. In other cases, it is recirculated back into the landfill, evaporated in leachate ponds at the landfill, and/or used as dust control at the landfill; that is, it does not leave the landfill.

In the small number of cases where there is direct discharge of leachate into the storm drainage system or into bodies of water, the leachate is treated first on-site by an industrial wastewater pretreatment system and discharged under regulatory permit with specific limitation. A final note is that these same CECs, at similar and sometimes higher concentrations, are found in wastewater sent to publically-owned treatment works as well as in storm or surface water discharges. They are not unique to landfill leachate.