Study Shows Treated Leachate Still Contains Contaminants

A recent study conducted by the U.S. Geological Survey (USGS) shows that treating liquid waste from landfills does not remove all contaminants.

“Landfills are the final depository for much of the solid waste we generate across the U.S. While it is known that such landfill waste can contain a wide variety of contaminants, little research to date has been conducted regarding contaminants of emerging concern (CECs) in landfill leachate that has undergone treatment or storage processes,” says Dana Kolpin, research hydrologist at USGS.

In this national-scale study, scientists provided an assessment of CECs in final leachate disposed offsite at landfills across the U.S. to gain a greater understanding of this potential contaminant source to the environment or to pathways that ultimately lead to the environment.

“The importance of moving our landfill research from examining fresh leachate to final leachate is that final leachate provides a much better understanding of chemical concentrations being disposed offsite to input pathways that lead to the environment,” says Kolpin. “Such input pathways include discharge to streams, seepage into groundwater, diversion to wastewater treatment plants, and even onsite spraying or irrigation.”

The chemicals detected included a wide range of compounds including pharmaceuticals, industrial chemicals, household chemicals, steroid hormones, and plant or animal sterols.

“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 Kolpin.

The most frequently detected 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.

A total of 22 final leachate samples were analyzed for this study and were comprised of a mix of 16 public and six private landfills to properly capture the range operating conditions that exist for the landfills present within the U.S. The landfills were selected to provide a range of hydrogeologic setting, climate, size, and leachate treatment and disposal practices. The landfills sampled originated from 12 states across the U.S.

“Our experience has shown that many landfill operators are reluctant to participate in this type of research if the specific landfill name and locations are provided,” says Kolpin. “As such locational information has no bearing on the interpretations of study results; we made the decision to keep all landfill locations anonymous for this study to maximize the sampling options during the site selection process.”

This study was not designed to determine the overall effectiveness of the various types of storage and treatment practices that are implemented at landfills across the U.S.

“However, a comparison of paired final leachate samples from 10 landfills from this study to fresh leachate from the same 10 landfills from in a previously published study indicated that levels of CECs were significantly less in final leachate compared to those observed in fresh leachate samples. Nevertheless, final leachate still contained a complex mixture of CECs at concentrations that may be potential cause for concern if released to the environment,” says Kolpin.

This research is part of continuing USGS efforts to quantify the contribution of contaminants in leachate released from landfills to various pathways that ultimately lead to the environment.

“Use of landfills as a means of waste disposal will likely increase as the global population continues to increase. Despite advancements in recycling, source reduction, and composting, the amount of municipal solid waste discarded in U.S. landfills increased from 150 million tons in 1985 to 165 million tons in 2010. The study is intended to inform landfill managers, stakeholders, and regulators about chemicals present in landfill leachate disposed offsite to various pathways,” says Kolpin.