Several decades ago, the town dump was a nasty place where drums of chemicals, oil cans, rusting metal, food debris and pesticides were haphazardly tossed into crude pits.
Lacking physical separation from surrounding grounds, the dumps let stews of contaminants leach into groundwater, at times ruining local drinking supplies.
Environmental regulations have drastically improved since the 1980s, spurring the creation of regional landfills designed to keep pollution on site. But the improvements also left behind innumerable shuttered dumps, like the Schuyler Falls Sanitary Landfill in upstate New York, due west of Lake Champlain.
The unlined, 30-acre Schuyler Falls dump took in town and industrial waste for nearly two decades, ending in 1996. As water percolated through the site, organic contaminants in the pollution stew known as leachate moved into surrounding areas, prompting a costly monitoring regime involving 22 wells, each hosting tests for dozens of waste signatures.
Far from an exception, Schuyler Falls is a classic example of what happens when motley chemicals escape closed dumps.
"You can imagine all the different chemicals that are present in these landfill leachates," said Paula Mouser, an environmental engineer at the University of Maine. "Because the leachate is so variable, we never really know what to monitor for in the groundwater."
This uncertainty means that closed dumps will test up to four dozen parameters on a regular, often quarterly basis. And despite their range, these tests -- which, for example, search for organic nutrients or sample temperature and salt conductivity -- often fail to detect the leading edge, or fringe, of groundwater contamination. Once the plume is detected, it is already well on its way.
"These are shallow systems that are in good communication with rivers and rainfall infiltration and saturated soil systems," Mouser said. "They are potentially harmful to the environment and human health, through connection with surface waters and groundwater wells."
Mouser, a young professor who worked as a landfill engineer in Logan, Utah, before pursuing her doctorate, is convinced there is a quicker way to detect the fringe, one less dependent on uncertain chemical sampling.
If we really want to know when groundwater is shifting, she said, we should ask the natives. We should ask the bugs.
Far from a dead, sedimentary place, the underground strata of rock are home to thriving communities of microbial life.
Far beneath the soil, these bugs colonize sediment particles, rock faces and detritus. Indeed, there is so much diversity in rock aquifers that scientists speak of their "microbial ecology."
These bacteria lead far from static lives.
Scientists have demonstrated that the bugs shift in response to harsh contaminants. And, according to new research led by Mouser, it appears these microbial communities respond to leaking groundwater waste -- the fringe -- well before it can be detected by direct, human measures.
Using the well-defined contamination at Schuyler Falls, Mouser and her colleagues sampled microbes extracted from the many wells ringing the dump. These samples were identified through one strand of their cellular RNA, allowing the researchers to develop "fingerprints" for each location. (A similar technology was used to typify the bacteria chewing through spilled oil in the Gulf of Mexico.)
Through complex statistical analysis, Mouser and her colleagues found that changes in these fingerprints revealed the waste's fringe well before more conventional monitors, a finding the team detailed recently in Water Resources Research. Indeed, in some wells, the bugs provided "more resolute information than the hydrogeochemistry," Mouser said.
Though more research is needed, the plummeting cost of genetic sequencing -- which has spurred a new field of large-scale microbial analysis, called metagenomics -- could and should see microbial fingerprinting become a low-cost supplement to traditional well monitoring, Mouser said.
"The idea is if we can detect the fringe earlier, we will have to spend less time and money [cleaning] the source," she said.
These microbial fingerprints are unlikely to play the prominent role seen in surface waste water, which is routinely tested for fecal bacteria, Mouser cautioned. The bugs remain an indirect measure, and direct gauges will still be needed. But the microbes can help optimize sampling at the many unlined dumps spread across the country, lowering the long-term costs of landfill monitoring.
"This microbial information is a really novel piece of the picture," Mouser said.
Most municipalities do not have the ability to conduct metagenomic analyses, of course, but U.S. EPA is well-acquainted with the techniques, and it is not infeasible that they could filter down to local landfill managers.
Before then, though, Mouser wants to expand understanding of her potential tool. She wants to establish whether these sampled bugs migrate with the waste plume, or whether they thrive in its presence. And she is looking at how these fingerprints can be classified for monitoring purposes, work that should appear soon.
Mouser also worries that while these microbes could prove useful, the human fingerprint is already being felt in these systems, through oil drilling and hydraulic fracturing for natural gas. These are realms the scientific community did not even expect to exist until a quarter of a century ago. Yet, in some places, they are vanishing just as well as more visible, diverse areas like the rainforest.
"We're destroying some of this microbial ecology," she said, "before we even know what's there."
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