Environment

In groundwater wells near the Dan River plant, arsenic is a culprit

A map of sampling locations at the Dan River plant (Map: Duke Energy)

Policy Watch recently reviewed more than 20,000 pages of data and published a story about groundwater contamination in wells around four of Duke Energy’s coal ash ponds. We covered Marshall and Cliffside last Monday and Allen on Friday. Today, we look at the contamination at the Buck and Dan River plants. Later this week, we’ll publish results of the contamination at Sutton and Roxboro.

Levels of arsenic at as much as 15 times the state standards have been found in groundwater wells near the Dan River plant in Eden, according to data filed by Duke Energy. (See the tables below for detailed results.)

The groundwater standard is 10 parts per billion; the highest reading was 158 ppb. Fourteen percent of the samples taken from the wells tested above the state’s groundwater standard.

Duke Energy has monitored the groundwater at its plants, but these results were released as part of the EPA’s coal combustion residuals law. The wells in question are within the plant’s compliance boundary and are not used for drinking.

However, state and federal regulators require monitoring of groundwater because of its potential to travel underground and then enter drinking water supplies and surface water, such as lake and rivers.

Known to cause cancer, arsenic is commonly found in coal ash. It also used in other applications, such as pesticides on cotton plants.

Dan River is the most notorious of Duke Energy’s coal-fired plants. In February 2014, an impoundment breached, sending 39,000 tons  of contaminated wet coal ash into the waterway and 70 miles downstream.

The EPA fined Duke $68 million in criminal fines for violations of the Clean Water Act, and required the utility to pay another $34 million toward environmental projects and land conservation.

Although four years after the spill, tests have shown the surface water no longer has exceedances of arsenic — thanks to dilution — some contaminants may have settled into the riverbed. But it’s inadvisable to excavate the affected portions of the riverbed because it could release more contamination, including PCBs.

A map of groundwater well sampling locations at the Buck plant (Map: Duke Energy)

The primary contaminant at Buck plant near Salisbury is not arsenic, but cobalt. More than half the samples tested above the groundwater standard. A toxic metal, cobalt is widespread in groundwater near coal-fired power plants, but it’s also naturally occurrin. Further analysis will be required to determine the sources of the contamination. Federal health officials have determined that cobalt likely causes cancer.

Dan River    
20 wells, 172 samples
ContaminantMaximum contaminant level, groundwater and drinking waterRange of exceedances, lowest to highest (ppb)Number of exceedances% of samples that exceeded maximum contaminant levels
Antimony1 ppb2.1 – 2.621.1
Arsenic10 ppb11.1 – 1582514.5
Boron700 ppb718 – 8792112.2
Cadmium2 ppb2.3 – 2.621.1
Chromium10 ppb13 – 44.574
Cobalt1 ppb1.1 – 21.77644.1
Thallium0.2 ppb2.310.5
Buck    
28 wells252 samples
ContaminantMaximum contaminant level, groundwaterRange of exceedances, lowest to highest (ppb)Number of exceedances% of samples that exceeded maximum contaminant levels
Antimony1 ppb1.410.003
Boron700 ppb704 – 20805521.8
Chromium 10 ppb10.4 – 45.120.007
Cobalt1 ppb1.1 – 78.512951.1
Sulfate250 ppm45510.003

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