Benzene not present in creek tests

Benzene hasn’t been detected in recent tests on Parachute Creek, where Williams also has begun operating a system that will be used to remove hydrocarbons from groundwater and return the water to the aquifer.

That system will be used to target continuing high levels of groundwater contamination some eight months after natural gas liquids are believed to have leaked from a pressure gauge on a valve of a pipeline leaving Williams’ gas processing plant northwest of Parachute. An estimated 10,000 gallons seeped into the ground.

On July 15, benzene at a sampling site on the creek spiked to 9.2 parts per billion, the highest since testing began following discovery of the leak. Williams expected possible spikes during remediation efforts.

According to a Colorado Department of Public Health and Environment update Friday, benzene readings at that test point in the creek have dropped off since mid-July, and the carcinogen hasn’t been detected in three tests between Aug. 8-15.

The creek isn’t a drinking water source, and is held to a state standard of no more than 5,300 ppb of benzene to protect aquatic life. The drinking water standard is 5 ppb.

The CDPHE update said three new air sparge systems have been added to use air injection into groundwater to try to keep benzene from migrating farther down-gradient. A second new air sparge system to treat groundwater benzene closer to the leak source “is in operation and effectively reducing benzene concentrations in groundwater,” according to the update.

But a number of groundwater testing sites still have shown benzene levels in the thousands of parts per billion as of this summer. One site sampled July 18 showed benzene at 35,000 ppp, and toluene, another toxic substance, at 17,000 ppb. Another site had benzene at 11,000 ppb on the same date.

CDPHE spokeswoman Kate Lemon the 35,000-ppb reading is immediately down-gradient from the spill site, where a 38,000-ppb reading was taken in April. No remediation efforts have yet occurred there, with the focus for now being further down-gradient, in an effort to prevent further expansion of the spill plume.

Still, many wells with high benzene levels in April have since seen those levels reduced on average by half despite no active treatment yet occurring near them, probably due to dilution by fresh groundwater, Lemon said.

Williams plans to use its new treatment system to remove up to 26 million gallons of groundwater, clean it and let it percolate back into groundwater. So far, it has only tried out the system on all the previously removed and stored groundwater on the site. All 225,000 gallons it treated was cleaned to state regulatory standards and returned to the aquifer.

Recovery wells to be used for removing and treating groundwater are expected to be operational by late August.

In July, Williams also undertook and completed a project to ship all 1,700-plus tons of contaminated soil related to the leak to an industrial landfill in Utah.


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