Benzene near site drops
Williams is reporting sharp reductions in groundwater benzene levels at a natural gas liquids leak site near Parachute Creek, although areas with high concentrations remain.
Meanwhile, the company also has prepared a state-ordered contingency action plan should benzene reappear in the creek because of circumstances such as flooding.
Williams continues to work on the cleanup of the leak, which it believes happened about a year ago, from Dec. 20, 2012, to Jan. 3 of last year. It occurred in a valve pressure gauge on a pipeline leaving the company’s nearby gas processing plant. The company initially thought the leak was small, but in March discovered considerable soil and groundwater contamination.
Williams eventually estimated that about 10,000 gallons of hydrocarbons entered soil and groundwater. It believes it has recovered about 8,555 gallons to date.
Air sparge and soil vapor extraction systems “have been very successful” in reducing dissolved benzene in groundwater, with key monitoring points seeing reductions of 90 percent to 100 percent, the company says at its leak website, http://www.answersforparachute.com.
According to a recent update Williams provided to the Colorado Department of Public Health and Environment, some monitoring wells that once had benzene at levels of up to 2,400 parts per billion now are reading at less than 1 ppb. The safe drinking water standard for benzene is 5 ppb.
But readings at some sites remain much higher, including one site with a reading of 68,000 parts per billion. Williams spokesman Tom Droege said Friday that monitoring point “is located directly within the central area where the release occurred and liquid hydrocarbons are present, which significantly impacts the groundwater sample there.”
Williams is working to eliminate those hydrocarbons through means including pumping up groundwater, cleaning it and returning it to the aquifer.
Contaminated groundwater reached the creek in small amounts during part of last year, through early August. Williams’ new contingency plan is designed to prepare for scenarios such as a flood causing groundwater levels to rise enough for benzene again to reach the creek.
That potential has been a concern for Bob Arrington, who lives in nearby Battlement Mesa and believes that a flood in the creek on Aug. 23 may have shown the need for such a plan. That flood damaged booms in the creek and other equipment, although no sheens or other indications of contamination on the booms or in the creek were seen in daily inspections afterward.
“I think it was an eye-opener for them,” said Arrington, who said it’s possible diluted amounts of benzene still reached the creek.
None was detected in the creek in Aug. 26 testing.
Howard Orona, whose home draws water from a shallow well near the creek, said the flood left him more concerned that other oil and gas infrastructure up the Parachute Creek Valley might be damaged and leak. But he also was impressed by Williams’ response, and said it had people on the scene pretty quickly.