Health officials in North Dakota said they're investigating potential water quality issues related to a small spill of liquids associated with oil production.

About 40 barrels, or 1,680 gallons, of brine, a liquid associated with production in the state, spilled into a creek about seven miles west of Williston.

Energy companies inject brine, or salt water, to improve oil and gas production from shale deposits. The Environmental Protection Agency said brine may contain toxic metals and radioactive substances that can be "very damaging" to the environment and public health if released on the surface.

"The spill impacted a nearby creek and water quality impacts are being investigated," the North Dakota Department of Health said in a Tuesday statement.

The department said it was working with Golden Eagle Trucking, the responsible party, on a remediation plan. The trucking company, which transports water and brine in Montana and North Dakota, had no public statement on the release.

At least two brine releases were reported in January.

North Dakota lies at the heart of the shale boom in the United States. Oil production in December, the last full month for which data are available, was 1.2 million barrels per day, an all-time high for the state.