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EPA poised to mitigate threat to Des Moines drinking water [1]

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Date: 2023-06-20

DES MOINES – Federal regulators might pump contaminated water from the ground near Des Moines Water Works to keep it away from the metro area’s water supply.

The U.S. Environmental Protection Agency said Tuesday it will give priority cleanup status to the groundwater near the water utility, which lies just southwest of downtown Des Moines.

A solvent plume that has been tracked for nearly two decades is moving toward the utility’s water intake near the Raccoon River at a rate of about 30 meters per year.

The plume is made of trichloroethylene and other compounds that result from its degradation.

The chemical is most commonly used to remove grease from metal or to make other chemicals, such as refrigerant, according to the U.S. Centers for Disease Control and Prevention. Long-term exposure can cause a variety of health ailments in humans, including cancers.

Des Moines Water Works provides treated drinking water for more than a half million people in central Iowa. Its testing has discovered the chemicals in the water intake near the river, but no trichloroethylene has been detected in its finished drinking water.

Chemicals associated with its degradation have been detected in the finished water that is pumped to residents, but their concentration is about 2% of what is allowable under federal health requirements.

The heart of the plume where contamination is worst isn’t expected to reach DMWW’s water intake for more than 10 years, and the solvent’s concentration in the groundwater has been diminishing since 2012, so the true threat to the metro’s drinking water is difficult to quantify.

“I would define it as a potential threat,” said Ted Corrigan, DMWW’s chief executive. “From our perspective, it’s there, it appears to be moving, and we want them to come in and remediate it so there is no potential threat.”

An elusive source

At least three sites in an industrial area south of Water Works have been the suspected source of the plume, according to Iowa Department of Natural Resources documents.

Those suspicions arose from groundwater monitoring at more than a dozen sampling wells that have been drilled since 2004.

In recent years, state regulators have focused on 2201 Bell Ave., a site the DNR refers to as “the former Stone Container property.” It is owned by Mid-America Development Company of West Des Moines.

“Mid-America Group has repeatedly asserted that it is not responsible for any release that has been identified in the (contaminated area),” an attorney for the company wrote to the DNR in 2018. “The industrial nature of the area, together with the monitoring results reported by Mid-America, has established that the release occurred off of the 2201 Bell Avenue site.”

Citing an impasse with Mid-America, the DNR asked the EPA in 2020 to name the area a Superfund Site that would help expedite the remediation of the contaminated groundwater.

In a 2022 memo that gave an overview of its findings, the EPA said further sampling from existing wells and new wells would be needed to determine a source, along with more complicated analyses of the samples from the wells.

“The existing groundwater quality data is insufficient to pinpoint the exact release location(s) and timing of the release(s) with accuracy,” the memo said.

The plan for remediation

The overall remediation process will take years, but in the meantime, the EPA does plan to increase monitoring of the site.

Monitoring wells are already collecting data, but more could be on the way, according to Lauren Murphy, the site’s remedial project manager for the EPA.

“We should be getting out there in the next few months and maybe do some additional assessments to determine exactly where we want to put those wells,“ Murphy said.

The EPA plans to propose the site to the National Priorities List in September, the next step in cleaning up the contaminants. Sites on that list are eligible for long-term remediation that is funded through the Superfund program. The EPA estimates the site might be on the list as soon as spring 2024.

After placement on the list, the EPA will develop a remedial investigation.

“A big part of that is determining and developing our conceptual site model so we know exactly what we’re dealing with,” Murphy said. “The second part of that is our feasibility study, where we look into different types of remedies to see which remedy is best suited for the site.”

One potential solution is to pump the water and treat it, then place the water elsewhere. The pump-and-treat system was done at a similar site in Atlantic, in southwest Iowa, and the treated water was pumped into the municipal water supply. One option in Des Moines would be to pump the treated groundwater into the Raccoon River, after confirmation that the water is uncontaminated.

It’s unclear when the remediation might be complete.

Estimates say it will take seven years for the plume to reach Water Works’ infiltration gallery, but as far as Des Moines residents should be concerned, Murphy does not believe the contamination is severe enough to raise levels above the safety threshold.

“We’ve been doing calculations, and based on those calculations … it doesn’t appear that we would ever reach a maximum contaminant level at the infiltration gallery.”

That gallery is Water Works’ intake near the Raccoon River, and it is an important source of high-quality water for the utility, Corrigan said. If no remediation is done – and if the plume is more problematic than predicted – it will be costly to treat the incoming water to remove the chemicals.

“The process we use here right now would not be particularly effective,” Corrigan said. “We would have to evaluate the various options — and there are several — of which would be enormously expensive at the scale we’re talking about.”

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