Environment

Duke Energy says computer models don’t accurately represent the flow of groundwater contamination at Allen plant

The blue dots represent drinking water wells. The lines from those dots leading to the ash basins shows where the groundwater originated. Consultants for Duke Energy used nontoxic particles to trace the pathways from the wells to the basins, and the direction of the flow. (Map: HDR Consulting/UNC-Charlotte)

For more than two years, Duke Energy has consistently reassured residents living near its unlined coal ash basins that contaminated groundwater flowed away from their drinking water wells. Computer modeling, the utility said, conducted by “some of the most experienced environmental engineering firms in the nation” proved it.

However, new studies conducted last year by UNC-Charlotte and a Duke Energy consultant HDR Engineering show that at the Allen Steam Plant in Gaston County, contaminated groundwater deep beneath the coal ash basins actually could flow toward some of the 192 drinking water wells.

But Duke Energy and the consultants say the computer models don’t accurately reflect what’s really happening underground.

Patrick Hunter, a staff attorney with the SELC, said that the original flow studies failed to account for the pumping effect. In this part of the Piedmont, bedrock is less fractured, limiting the flow of water. However, when multiple private wells withdraw water from the bedrock layer, the pressure can create fissures and change the flow of groundwater.

These wells have not tested high for contaminants related to coal ash, although Duke is providing drinking water options to the residents for their “peace of mind.” But that doesn’t mean the wells aren’t pulling from contaminated water sources, Hunter said. For example, a well could withdraw some of its water from a highly contaminated plume of cobalt and another portion from an uncontaminated source. The mix of the two keeps the contaminant levels low.

“The potential for dilution is great,” Hunter said, “but I disagree with Duke that there is a lack of impact.”

Duke Energy spokeswoman Danielle Peoples said that the figure referenced in SELC’s news release “is a draft model using very conservative assumptions that do not reflect more real-world conditions. Because it looks more broadly than just the plant property, experts did not have all the data on neighbors’ wells they’d need to be an exact match with what we know on the ground.”

Bill Langley, a groundwater expert at UNC-Charlotte told the Charlotte Business Journal that the study is only a preliminary draft based on computer modeling. It examines a worst-case scenario of the pumping effect, which would siphon water from beneath the Allen site to the neighborhood. Actual testing at the site, he told CBJ, shows coal ash contaminants moving through groundwater toward Lake Wylie and away from the neighborhood. The modeling, Langley said, does not reflect the results of data collected onsite.

The NC Department of Environmental Quality had requested that Duke Energy redo some of its computer modeling about the groundwater flow from its unlined coal ash basins.

A November 2016 document from Duke Energy states that “This work has been the most comprehensive look at groundwater ever performed at our facilities.” With the exception of the Sutton plant in Wilmington, the “monitoring data demonstrate groundwater near ash basins is moving away from neighbors’ wells, which are generally upgradient. … Computer modeling also validates that flow directions are expected to continue moving away from neighbors’ wells in the future.”

The Southern Environmental Law Center subpoenaed UNC-Charlotte to obtain the documents, which are dated September 2016.

Maps by SELC show that water from beneath both the ash basin waste boundary and the compliance boundary drains toward at dozens of the residential wells. The two boundaries are important because Duke is legally required to keep contamination from breaching them.

Researchers used nontoxic particle tracers to learn about the groundwater pathways from the basins. They pinpointed four paths from the closest wells to the far western area of the active ash basin. Particles were found to originate in the western part of the basin; the same results were found in two pathways on the southern side.

Topographic maps show that the active and inactive coal ash basins range from 640 to 645 feet above sea level. Gradually, the elevation declines, to about 580 feet near the Catawba River. However, underground rock formations, whose fractures change over time, can also alter groundwater flow.

“Duke has said there are no impacts on the groundwater,” Hunter said. “This contradicts what they’re saying.”

Duke plans to close the basins through cap-in-place method. The ash would be placed in a lined landfill onsite. Many environmental advocates, including the SELC, and neighbors of the Allen plant, want Duke to excavate all of the ash from the site. Together, the active and inactive basins at the Allen Plant contain about 11 million tons of coal ash.

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