A tank overflow at a natural gas well site in Argyle spilled about 840 gallons of liquid waste onto the property last month, Williams Production has reported.

About 20 barrels of wastewater spilled at the energy company’s drilling site at 209 N. Gibbons Road on July 29, company spokesman Kelly Swan said. Half of the spill was vacuumed and collected, while water remaining in the adjacent soil was contained and the dirt is being excavated, Swan said.

“Williams is working closely with authorities to remediate the part of the site affected by the spill and will subsequently perform tests to verify the effectiveness of the cleanup,” Swan said by e-mail in response to a Denton Record-Chronicle inquiry. “We are investigating the cause of the spill.”

The liquid byproduct of gas drilling is mostly salt water, or brine, but can also contain toxic metals and radioactive materials.

The property, located east of U.S. Highway 377 and north of FM407, includes a home and ranch owned by Lemoine Wright and is close to a flood plain, according to town records. Wright could not be reached for comment.

Williams officials quickly notified the Texas Railroad Commission and the Argyle fire marshal after a contractor alerted them to the spill, Swan said. He said he did not believe any water sources were polluted.

Ramona Nye, a spokeswoman for the railroad commission, which is charged with regulating the oil and gas industry, said the commission would conduct a follow-up inspection by the end of the month.

“If the cleanup is completed and no violations are noted on the lease during the Commission’s follow-up inspection, there will likely be no penalties issued,” Nye said in an e-mail.

LOWELL BROWN can be reached at 940-566-6882. His e-mail address is lmbrown@dentonrc.com.