Perhaps the most well-known example of ground water contamination in the lower Portneuf Valley is the trichloroethylene (TCE) plume in the southern valley and in the vicinity of the old County landfill. A similar chlorinated solvent, perchloroethylene (PCE), is the cause of Chubbuck's water quality problems. Both originate from disposal on the land surface, and find their way to the water table where they are then carried by the movement of ground water.
Due to the rapid rate of ground water flow in the southern valley aquifer (up to 50 feet per day), the TCE plume at one time was advancing and affecting water quality in downstream wells at the rate of a mile per year. Several wells have been closed because their concentrations of TCE exceed safe limits; some remain closed, others have reopened. The plume still extends the length of the southern valley, but remediation is underway.