A drilling mishap led to the release of an estimated 36,000 gallons of slurry, including a potentially cancer-causing ingredient, in Blanco County in late March, according to records obtained by the American-Statesman.

Kinder Morgan had previously said the amount of drilling fluid spilled as it was building a gas pipeline was under review.

But in an email sent last week alerting the Texas Railroad Commission about the incident, a Kinder Morgan official reported that between the evening of March 28 and the evening of March 30, when drilling was shut down, "an estimated 36,000 gallons were released underground into the bedrock formation."

That’s about the amount of liquid that could fit into the beds of roughly 70 full-size pickup trucks.

The incident, about 5 miles east of the city of Blanco, has apparently led to the muddying of the water for at least two well owners who reported chocolate-colored water coming out of their taps.

Kinder Morgan, which operates more than 25,000 miles of pipeline in Texas, has suspended work in the area on its underground Permian Highway Pipeline, which has been opposed by Hill Country residents over environmental concerns. The 42-inch, 430-mile-long natural gas pipeline is scheduled to cut through 17 counties, passing through environmentally sensitive areas along the way.

Company officials had said that only non-toxic material — clay and water — leaked below ground in the incident last weekend.

In the email to the Railroad Commission, which the Statesman obtained through an open records request, the company attached label information about the makeup of the clay portion of the lost drilling fluid.

According to the label, AMC Gel, used to lubricate a drilling hole and cool cutting material, rates as "low" for toxicity, "may cause cancer" and "causes damage to organs through prolonged or repeated use."

Company spokeswoman Katherine Hill said the drilling fluid is not classified as being harmful if ingested and poses no known risks to drinking water. She said the material is used to drill drinking water wells.

On Wednesday, the Wimberley Valley Watershed Association and the Trinity Edwards Springs Protection Association notified Kinder Morgan that they planned to file suit on behalf of landowners and their members for alleged violations of the federal safe drinking act.

The clay is "not a benign, inert material as Kinder Morgan is portraying in the public media," said the letter from attorney Jeffery Mundy.

Ron Fieseler, general manager of the Blanco-Pedernales Groundwater Conservation District, said water chemistry tests done last week on wells in the area "showed all wells to be within the expected ranges" for the water quality safety parameters measured, including iron, fluoride, sulfate, nitrate and phosphorus, as well as temperature and alkalinity.

Fieseler said he expected the sediment to settle out in time.

Teresa Albright, who lives with her husband about a mile from the drilling incident, said Wednesday that water from her well was still cloudy. She has connected a 2,500 gallon tank to her house to meet her water needs.