State regulators clarify reports on arsenic test results near coal ash spill

The N.C. Department of Environment and Natural Resources clarified today the differences between its reporting on arsenic levels in the Dan River on Thursday and Friday.

The agency originally reported Thursday that arsenic levels for all sampling locations were within state standards. However, DENR should have noted on Thursday that testing of water samples collected downstream of the Dan River spill found total arsenic levels in two samples collected Monday did exceed state standards for human health, which is 10 micrograms per liter. The state agency did note in a Friday news release that arsenic levels had exceeded that same standard.

Arsenic levels appear to be decreasing at downstream collection points, the state reports.

“We made an honest mistake while interpreting the results,” said Tom Reeder, director of the Division of Water Resources. “The bottom line remains that we are concerned for the long-term health of the Dan River and are working with our state and federal partners and the utility to begin the cleanup. We will continue to test the water in the river as we assess the spill's impacts and determine the most appropriate ways to clean up the river. We are in this for the long haul.”

When reviewing surface water quality data, the state uses the North Carolina state surface water quality standards per state rules. For the Dan River at and below the spill site in North Carolina, two separate standards have been adopted and are enforced — one standard for aquatic life of 50 micrograms per liter, and one for human health of 10 micrograms per liter.

In DENR’s release of test results on Thursday, the agency was relying on surface water quality standards for aquatic life when reporting results. The arsenic concentrations collected on Feb. 3 below the spill site were 40 micrograms per liter at the site closest to the spill (Draper Landing) and 13 micrograms at the Virginia state line. On Feb. 4, the concentrations had decreased to 6.3 micrograms per liter at the Draper Landing site, and 10 micrograms per liter at the Virginia state line. The data review indicated that while control of the spill had not yet been accomplished, levels of contaminants in the surface water were decreasing, reducing the risk to human health and aquatic life within the water column. 

The aquatic life standards for arsenic (50 micrograms per liter) were developed per EPA standards based on toxicity testing of fish and other organisms that live in the waters. The human health standards (10 micrograms per liter) were adopted to protect humans from exposures other than drinking, such as skin contact and fish consumption, also using EPA guidance. Both the aquatic life and human health standards are water concentrations not to be exceeded over time.

Arsenic has a low accumulation rate in fish tissue, which means that increased arsenic levels in fish tissue in the Dan River below the spill would not be seen in the near future, and any impacts to human skin would require extended direct contact. DENR is recommending that the public avoid prolonged direct contact with the Dan River in the area of the spill until further notice. 

Downstream water authorities are still reporting that water is safe to drink, and that they are able to treat water at their intakes using normal water treatment processes.