Of all environmental sample types — groundwater, wastewater, soil — leachate is the most complicated to sample and analyze, because it contains many constituents that landfill operators must be aware of and understand.
Meanwhile, emerging contaminants, mainly per- and polyfluoralkyl substances (PFAS), are adding new challenges because they are in thousands of products, even those that workers wear or use in the field. Therefore these compounds are driving new, stricter protocols in leachate sampling techniques. However, most advancements, whether around PFAS or other compounds, such as dioxins/furans, have involved analytical techniques — for instance, the ability to separate compounds to study them individually.
“We have to manage whatever goes in the trash, and even by educating the community about proper waste disposal, some items end up in the landfill that shouldn’t, including potentially harmful substances,” says Stephanie Bolyard, research and scholarships program manager at the Environmental Research and Education Foundation. “So we have to deal with the inevitable, which is treating leachate. And treating leachate first means identifying and understanding its contents, which could be hormones, endocrine disrupters among emerging contaminants of concern.
“Now that landfill operators are sampling for compounds in products used in everyday life, including some that could be used in the field, we need to be sensitive to not introduce what may come from sources other than landfills to avoid false positives,” Bolyard says.
Another issue requiring consideration is that because some compounds can now be detected at extremely low levels, operators will find a complex mixture of them in leachate. PFAS are getting the most attention for this reason. Twenty-four ounces of Scotchgard can contaminate the entire Chesapeake Bay at 20 parts per trillion, which is the advised or regulated drinking water limit for PFAS constituents in some states, says Ivan Cooper, principal at Civil & Environmental Consultants.
“It’s easy to get small amounts in samples that will skew results,” Cooper says. “But as sampling techniques get more refined, they will help us avoid cross-contamination even at these very low levels.”
Still, PFAS are requiring additional time and money due to prep protocols for sampling and careful selection of equipment.
Many states are adopting sample collection guidelines specifically to look for PFAS, such as the use of designated sampling ports/valves or designated pipes for direct collections. Some are specifying not to use glass sample containers because PFAS can sorb to them. As an alternative, they recommend polypropylene or high-density polyethylene. Some states instruct or recommend that landfill operators ensure the use of PFAS-free drilling fluids or alternative techniques like sonic drilling. The direction has also been to recommend the use of labs with an understanding of potential PFAS contamination sources and PFAS analytical issues.
With leachate sampling in general, it’s important to get representative samples that are not just a snapshot in time but that identify liquid stream characteristics over 24 hours, because leachate concentrations could change over time. In fact, they may change considerably in a couple of hours because of differences in where the liquid is coming from during different times of day, says Kevin Torrens, vice president and national landfill liquids practice leader at Brown and Caldwell, which is based in Walnut Creek, Calif.
But concentrations average out over a day, so it’s advisable to do composite samples that are collected over that time frame using an automated sampler.
“We recommend getting composite samples when possible,” says Torrens. “You need multiple data sets. You want a minimum of three samples.”
Most advancements revolve around analytical techniques following collection, such as those involving the identification of more compounds.
These techniques are important, especially with new contaminants on the radar. But they are also important tools because chemical, physical, and biological transformations can occur within the waste mass that makes analysis complex.
“For instance, we may know how to detect for acetaminophen, but how do we detect for the transformation of this and other compounds?” says Bolyard. “And how do we determine where and why the transformation occurred? And what might have occurred before it entered the leachate versus once it’s in the leachate?
“If we understand what happened to that compound in the landfill, we can say it gets transformed into ‘Compound X’,” she says. “If we know this is happening, we can detect for that compound and maybe estimate what was originally in the landfill.”
Bolyard adds that knowing the byproducts from a transformation helps one better understand what comes into the landfill before it’s exposed to complicated processes. And understanding what’s coming in initially helps one plan how to manage it.
Some analytical advances have involved separation techniques such as chromatography, which enables detection of specific compounds and concentrations in samples that contain multiple compounds.
Scientists put samples through columns that they develop based on materials’ chemical properties. Compounds emerge from instruments at different times and, based on timing, scientists can identify and analyze each one.
Similarly, through a technique called solid phase extraction, certain substances stick to the column and others don’t. This enables the substances that do stick to be separated and analyzed.
While some of these techniques have yet to be fine-tuned, they are helping to avert interference or false positives due to the presence of multiple reagents.
Landfill owners typically must do broad analyses for a large suite of compounds, and they tend to miss some key parameters that are not routinely analyzed but are important for managing leachate. Torrens recommends periodically checking for these parameters.
“For instance, chemical oxygen demand and dissolved metals are not often analyzed for, but are important parameters to understand,” Torrens says. “It’s a little more cost, but these tests can provide important information to know how to treat leachate.”
Bolyard echoes that it’s wise to with labs due to the complex and often changing nature of landfill leachate.
“We find that as we understand emerging compounds of concern, you have to go to a professional test lab or academic institution to analyze for them, because some techniques are so new and are still being developed,” Bolyard says. “We need to be able to trust the results, and certified labs and academic institutions are equipped to do this.”