LPRV Aquifer Management: Water Quality Impacts

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.

It is for these reasons that city water managers contracted with consulting engineers to draw up plans for special wells to capture the moving TCE, remove it from the water, and return clean water to the aquifer (this approach has been successfully adopted by the City of Chubbuck for one of its most contaminated wells). This plan has the advantages of curtailing the spread of TCE, protecting downstream wells from future contamination, and pumping part of the cleaned water into the water distribution system to meet current and future demand.

However, the city decided not to proceed with this costlier solution, and instead directed water managers to install Well #44 in an uncontaminated portion of the aquifer (directly across the river from the TCE plume). Though it is impossible to predict with current information, but there is a good possibility that Well #44's pumping may eventually smear the TCE plume across the width of the aquifer. If nothing is done to stop the spread of TCE, it could be only a matter of time before the entire southern aquifer is contaminated.

Although some argue that by cleaning up the TCE at its source (the old landfill), the TCE plume problem will disappear and make it unnecessary to protect downstream wells, it is known that even if the TCE source can be 100% contained at the landfill, it will be decades (perhaps many) before TCE that has already leaked out of the landfill will be flushed out of the system by natural through-flow. A report on the TCE problem* identified that more than 100 gallons of liquid TCE have already passed through the aquifer, suggesting that much more remains at the source to continue contaminating the aquifer in future. If pools of liquid TCE exist somewhere in the aquifer, it could take centuries for natural flushing to clear the aquifer of this contaminant. This is a very safe prediction, based on examples of TCE contamination in many other aquifers.

The TCE problem, and its costly solutions, typify the logic behind the adage that "it is always cheaper to prevent ground water pollution than to clean it up after it has occurred."

* TCE Report is in MS Word format.