Benzene found in Parachute Creek
Benzene has been found in Parachute Creek for the first time since testing began in response to a natural gas liquids leak north of Parachute.
Williams and the state Department of Natural Resources said in news releases that the carcinogen was found Thursday at multiple locations, but in amounts below Environmental Protection Agency safe drinking water standards of 5 parts per billion.
Williams said an initial result came back Thursday showing a detection of 2.8 parts per billion. The state said another detection at the same location was 2.7 ppb. It said the detections were from lab samples taken Tuesday and Wednesday.
Williams said the initial detection was about 1,200 feet downstream from where a pressure gauge on a natural gas liquids line from its gas processing plant leaked thousands of gallons. The state said the point was about 1,800 feet downstream.
No benzene has been found upstream of the leak site.
In response to the detections, Williams did real-time sampling farther downstream Thursday and they showed benzene at 1.5 ppb 680 feet from the first detection point, and 1.1 ppb 1,900 feet from the first point.
Samples taken Thursday where Parachute diverts water for its irrigation supply showed no benzene. Williams said benzene floats on water, dissolves only slightly in it and evaporates quickly from the surface.
Williams is installing aeration, or air-sparging, technology to remove benzene near the initial detection point and 1,900 feet farther downstream. It also has added an additional boom below the initial detection point.
Parachute’s diversion site is 2.7 miles downstream of Williams’ gas plant.
High benzene levels have been found in groundwater on either side of the creek, but benzene hadn’t previously been detected in the creek despite frequent testing.
Authorities have said that’s because the groundwater below the creek apparently flows away from it. But the state said the situation appears to be different at the initial point of benzene detection in the creek, with groundwater flowing toward the stream.
That point is the farthest downgradient from the valve site where benzene has been detected in groundwater, and the groundwater detection there was 440 ppb on Monday, prompting surface water sampling nearby the next day, the state said.
Part of Williams’ response is building a 200-foot-long groundwater interception trench adjacent to the creek at that point, with an air-sparging barrier to remove benzene before it reaches the creek, the state said.
Williams said that it is continuing twice-daily sampling at Parachute’s diversion point.
“As a precautionary measure, the city of Parachute’s irrigation gate on Parachute Creek will remain closed until additional data is collected,” it said.
It said it immediately notified the Colorado Oil and Gas Conservation Commission about the benzene detection, along with Parachute and Garfield County officials, the Environmental Protection Agency and the Colorado Department of Public Health and Environment.