Five Arkansas residents who sued two oil companies claiming wastewater disposal wells from fracking caused earthquakes that damaged their homes settled with the companies for an undisclosed sum on Wednesday, according to U.S. court documents and the plaintiffs’ lawyers.

Several similar suits against the two companies, Chesapeake Energy’s operating subsidiary and BHP Billiton , remain active in federal court in eastern Arkansas, though those may also be settled, the lawyers said.

The residents claimed a swarm of earthquakes that hit central Arkansas in 2010 and 2011 was triggered by the injection of wastewater into deep wells, damaging their homes.

The wastewater is produced by natural gas drilling using hydraulic fracturing, or fracking, which deploys a highly pressurized mix of water and chemicals to break apart shale rock to release oil and natural gas.

Seismologists at the U.S. Geological Survey say fracking can cause tiny “micro earthquakes” that are rarely felt on the surface, but that disposing millions of gallons of wastewater flowback underground can cause slightly larger quakes in rare cases.

Scientists found disposal wells in Greenbrier, Arkansas, likely touched off more than 1,000 quakes in 2010 and 2011, prompting the group of homeowners to sue. They were seeking unspecified compensation to cover their repairs.

Corey McGaha of law firm Emerson Poynter, which represents the plaintiffs, confirmed that the parties had settled one lawsuit and that it was being dropped. He said the terms of the agreement were confidential.

Jarl Strong, a spokesman for defendant BHP Billiton, declined to comment, as did Chesapeake spokesman Jim Gipson.

The lawsuits are among the first in the United States that sought to link earthquakes to wastewater wells, and the first attempt to win compensation from drilling companies for quake damage.

Plaintiffs’ lawyers in Arkansas said they still were planning to file lawsuits on behalf of 20 other residents in state court.

The earthquake cases are being closely watched by the industry because they are seen as providing environmentalists and citizens’ groups with a possible new legal avenue to oppose fracking.

Since 2009, some 40 civil lawsuits related to the fracking process have been filed in eight states, claiming harm ranging from groundwater contamination to air pollution to excessive noise. So far none has gone to trial and about half have been dismissed or settled.

Suits are often settled with court orders to not discuss monetary awards or details of the case.