Case study: Cleaning contaminated groundwater at former missile site

The four air strippers can treat up to 15,000 litres per minute of contaminated groundwater.
The four air strippers can treat up to 15,000 litres per minute of contaminated groundwater.
The four air strippers can treat up to 15,000 litres per minute of contaminated groundwater.

The US Army Corps of Engineers (USACE) Omaha District has funded the design and construction of a new groundwater treatment plant in Cheyenne, Wyoming, to treat groundwater from the city’s Borie well field.

This important groundwater supply was reportedly contaminated in the late 1960s with trichloroethylene (TCE) from the former F.E. Warren Atlas Missile Site 4. It was located several kilometres southwest and up-gradient of the current Borie water well field.

The new facility was designed, constructed and placed into long-term automatic operations by McMillen, LLC. Matt Moughamian, McMillen’s project manager says: “For the given application, the most logical and cost-effective groundwater treatment choice was low profile air strippers. Air stripping is a simple, reliable, and proven technology for the removal of TCE from water supplies. Furthermore, the air stripping technology was able to be implemented into the city’s existing well field hydraulic profile at a location where water re-pumping was not required.”

Current TCE concentration in the Borie well field source can range anywhere between 1 ppb – 25 ppb. In early 2010, the USACE contracted with McMillen to start the final design and construction of the new treatment facility to ensure that levels could be reduced to less than 2.0 ppb.

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Four six-level tray E-Z Tray Air Strippers from QED, each with a treatment capacity of 3,800 lpm, were used in McMillen’s design to ensure that the TCE treatment goal of less than 2 ppb could be reached without pretreatment.

In Cheyenne’s case, the E-Z Trays do not require off-gas treatment or sequestering agents, making the treatment process fairly simple. The turbulent mixing that occurs in the units creates a high air to water ratio and large mass transfer surface area. This resulted in highly efficient contaminant removal.

“Water goes straight from the Cheyenne wells into the E-Z Trays. The air strippers have been in constant operation since July 2011, with no need to clean the trays because of buildup or fouling,” Moughamian says.

QED’s Online Performance Modeler was used to evaluate Cheyenne’s treatment requirements and determine the best E-Z Tray models for the project. According to Moughamian, the units chosen for the Cheyenne treatment facility have more than enough capacity to handle the city water’s contamination load, “and there have been no issues so far.”

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