A U.S. Geological Survey investigation has uncovered evidence that a natural gas wastewater disposal site in West Virginia is contaminating a nearby creek.

The results, published in two recent studies, show that water and sediment samples collected downstream of the gas waste site had higher salt levels, radioactive compounds and chemicals that disrupt hormones, compared to upstream samples.

Although the exact source of the surface water contamination was not identified, this research clearly shows “unconventional oil and gas wastewater disposal can impact the environment,” USGS scientist Denise Akob said to InsideClimate News. Akob was one of the authors of both articles.

These papers raise new concerns about the environmental risks associated with sites where operators inject unconventional oil and gas wastewater hundreds to thousands of feet underground for disposal. This widespread practice has increasingly come under fire from activists, politicians and officials for being poorly regulated—and linked with earthquakes in states such as Arkansas, Kansas and Oklahoma.

A coalition of environmental groups last week sued the Environmental Protection Agency for failing to adequately regulate the disposal of this waste, citing risks of earthquake and water contamination. This comes after the U.S. Government Accountability Office published a report in February charging the EPA with failing to collect enough information to determine whether injected oil and gas waste is contaminating underground sources of drinking water.

According to Akob, the USGS studies are the first to link surface water contamination to one of the approximately 36,000 Class 2 injection wells in the U.S. where operators dispose of wastewater from oil and gas operations. Other parts of the waste handling process, however, have already been linked to water problems. Last month, Duke University researchers detailed the lingering impacts on water quality around the site of four wastewater spills in North Dakota.

The West Virginia research “demonstrates that even at injection sites you can have contamination of surface waters,” said Desirée Plata, a researcher at the Yale School of Engineering and Applied Science. “One of the questions that arises from the studies is whether or not the surface contamination is derived from the injection well itself” or some other source at the waste facility, added Plata, who was not involved in either study.

Akob, along with her nine colleagues from the USGS, Duke University and the University of Missouri, got rare access to take water and sediments around a commercial wastewater disposal site just south of Fayetteville, W. Va. The waste site is located along Wolf Creek, a small waterway that empties into the New River about six miles downstream. New River is a source of water for drinking and recreation.

Researchers collected more than 20 water samples, mostly between June and September 2014, from five sites along Wolf Creek—upstream, at the facility and directly downstream—and from a nearby waterway. Researchers also collected sediment samples from the Wolf Creek sites.

Researchers found elevated salt levels in the samples taken near and directly downstream of the facility, compared to those collected upstream and from the non-Wolf Creek site. Scientists also observed higher levels of certain metals such as strontium, barium and lithium in the downstream water; but these levels were not high enough to pose a major impact on aquatic life.

Akob and others also found higher levels of radium, a radioactive compound, in sediment samples downstream of the facility compared to those collected elsewhere.

“The study shows clear, though modest, changes in water quality downstream of the injection well,” said Robert Jackson, a Stanford University scientist not involved in either study.

Plata said, “I think all of these [sources of contamination] are controllable, but we have to look for them and right now it’s not normal to do this kind of analytical sweep at an injection well.”

Akob and her colleagues also looked at the microbial communities in Wolf Creek. “Microorganisms are important because they are the base of the food chain,” Akob said. The researchers found less microbial diversity downstream of the waste facility, which “indicates that there’s some kind of change in the ecological functioning at the site,” Akob said.

The microbial review and the other geochemical analyses were published Monday in the journal Environmental Science & Technology.

Scientists ran additional tests to look for so-called endocrine disruptors, or chemicals that impact hormones. Some of these chemicals are known to change the sex in certain types of fish, for example. Their results, published this week in the journal Science of the Total Environment, show several such chemicals at elevated levels in the samples collected directly downstream of the waste site.

InsideClimate News asked regulators at the West Virginia Department of Environmental Protection to comment on the studies and whether officials plan to investigate the water contamination claims. DEP spokeswoman Kelley Gillenwater wrote in an email: “At this point, we are aware of the research and are looking into it.”