June 1, 2020
Staff Accomplishment

As the Conceptual Site Model Changes

Remediation approaches may need to adapt based on new data

Pump-and-treat equipment

Pump-and-Treat Operations at the Hanford 200 Area.


PNNL is located just adjacent to the Hanford Site. Some people think the Laboratory is part of Hanford. While that’s not the case, PNNL does support Hanford cleanup in significant ways. Environmental engineer Mike Truex is one of PNNL’s key players in applying science to the cleanup of contaminated groundwater below the Hanford Site. He works with U.S. Department of Energy (DOE) and Hanford officials to determine approaches for cleanup and then interfaces with the teams executing the work.

Early in the cleanup process, a conceptual site model is developed, but sometimes necessary  data isn’t available. Truex recently presented to staff from remediation agencies across the country, via an Environmental Protection Agency Clean-up Information (CLU-IN) virtual meeting, about how conceptual site models must change over time as new data is acquired.

Teaming with colleagues from Hanford and the U.S. Environmental Protection Agency (EPA), Truex described this evolution with the cleanup of the toxic chemical, carbon tetrachloride, at the Hanford Site. Truex explained that the pump-and-treat process used to clear carbon tetrachloride from the groundwater in Hanford’s 200 Area began in 2012. The full extent of the contamination was unknown at the time. It turns out there is more carbon tetrachloride than originally anticipated. The pump-and-treat process—pumping contaminated water out of the ground, removing the carbon tetrachloride with air strippers, and then injecting cleaned water back into the ground—is working. The team has removed about 15,000 kilograms to date. But it’s taking longer than models predicted.

“Analyzing data collected during remediation can provide useful information to determine if modifications or adaptations to the plan are needed,” said Truex.

This adaptive management approach to refining the conceptual model and remediation implementation is one that the DOE and contractor team has embraced. One of Truex’s co-presenters from the EPA explained it’s an approach that her agency now supports as well because adaptive management allows remediation teams to optimize the original plan.  

For instance, the pump-and-treat process must remove other co-contaminants in the groundwater at the same time, which has affected the amount of carbon tetrachloride that can be processed. Learning from data collected during the initial remediation period, adaptation of the original remediation approach is now being implemented in coordination with DOE and EPA. The optimized approach will increase the amount of carbon tetrachloride that can be removed over time. This adaptation is being tested as a potential approach to better reach the remediation objectives for the contaminated groundwater. 

Watch Truex’s presentation, “Using Remedy Implementation Information to Guide Remedy Optimization,” and find the webinar slides on the CLU-IN website