March 17, 2016. In 2015, the N.C. Division of Public Health (Department of Health and Human Services) sent letters advising the owners of 369 wells located near coal ash ponds not to drink their well water because of elevated levels of vanadium and chromium-6. Last week, the Division of Public Health sent letters to those same well owners to withdraw the “do not drink” advisory. Some questions and answers on the conflicting advice below.
What are vanadium and chromium-6 (Cr-6)? Both elements occur naturally in the environment and can be found in coal ash. Both may be concentrated in the air or in groundwater as a result of industrial activities. Inhalation of Cr-6 (or hexavalent chromium) has been associated with increased risk of lung cancer. In 2010, the U.S. Environmental Protection Agency began a new health study to determine whether ingestion of Cr-6 in drinking water increases other types of cancer risk. The Erin Brokovitch story of hexavalent chromium contamination in the town of Hinkley, California raised public awareness of Cr-6 as a public health issue. In Hinkley, Pacific Gas & Electric had used Cr-6 as an additive in cooling water for a natural gas compression station. The Cr-6 percolated into groundwater from unlined ponds used to store the cooling water, contaminating the town’s drinking water supply. (Levels of Cr-6 in Hinkley’s groundwater were exponentially higher than concentrations found in North Carolina wells.)
Are there drinking water standards for vanadium and Cr-6? There is no federal drinking water standard for vanadium. The U.S. Environmental Protection Agency has adopted a drinking water standard for total chromium of 100 parts per billion (ppb); the standard covers combined concentrations of chromium-3 (a nutritional element found in plant material) and chromium-6. Water systems required to meet federal Safe Drinking Water Act standards monitor total chromium levels, but not necessarily Cr-6. Nationally, only the State of California has adopted a specific drinking water standard for Cr-6. In 2014, after years of study prompted by the Hinkley contamination, California adopted a standard of 10 parts per billion for Cr-6 in drinking water — 1/10th the concentration allowed under the federal drinking water standard for total chromium.
How are N.C. groundwater standards different from federal drinking water standards? In part, the two sets of standards serve different purposes. Drinking water standards adopted by U.S. EPA under the Safe Drinking Water Act only apply to the treated water that public water systems provide to their customers. Under the law, “public water system” means any system providing water to 15 or more connections or to 25 or more people whether the system is operated by a local government or a for-profit water utility. Federal drinking water standards do not apply to privately owned water supply wells serving individual homes or businesses.
N.C.’s groundwater standards are used to identify unsafe levels of groundwater contamination; set goals for groundwater remediation; and advise well owners on use of water from affected wells. Most N.C. groundwater standards track the federal drinking water standard for the same contaminant, but in a few cases the state has adopted a more stringent groundwater standard or has adopted a groundwater standard for a contaminant that has no corresponding drinking water standard. Leading up to the well testing around coal ash ponds, N.C. had no groundwater standard for vanadium and no specific standard for Cr-6. although the state had a groundwater standard of 10 ppb for total chromium (more stringent that the 100 ppb drinking water standard for total chromium.)
How does N.C. set groundwater standards? The N.C. Environmental Management Commission has adopted state groundwater standards as rules. Since existing groundwater standards may not address every potential contaminant, the rules also create a process for developing a temporary standard — an Interim Maximum Allowable Concentration or “IMAC” — to address an unregulated contaminant. Epidemiologists in the N.C. Division of Public Health generally develop a recommended IMAC based on review of human health effects such as toxicity and increased cancer risk.
Why did the Division of Public Health send “do not drink” letters in 2015 based on vanadium and chromium-6? Since no state groundwater standard or federal drinking water standards existed for vanadium and Cr-6, DEQ asked the Division of Public Health to develop interim groundwater standards (the IMACs described above) to be used in assessing wells around the coal ash ponds. Division of Public Health calculated a standard of 0.07 ppb for Cr-6 and 0.3 ppb for vanadium. In each case, the deciding factor was the concentration associated with an incremental increase in cancer risk. The table below shows the IMAC standard compared to the federal Safe Drinking Water Act standard and the N.C. groundwater standard.
|Contaminant||Fed. Drinking Water Standard||N.C. Groundwater Standard||IMAC|
|Vandadium||No standard||No standard||0.3 ppb|
|C.hromium-6||None –Total Cr 100 ppb||None – Total Cr 10 ppb||0.07 ppb|
Why did Division of Public Health withdraw the “do not drink” letters? None of the well owners who received “do not drink” letters based solely on the vanadium and Cr-6 IMAC standards have well water that would violate Safe Drinking Water Act standards for a public water system. DEQ has reported that 70% of public water systems in the U.S. exceed the IMAC standards set by Division of Public Health, including several large public water systems in North Carolina. (The information, provided in a report to the legislature’s Environmental Review Commission, did not indicate how many of those systems exceeded the IMAC standard for vanadium versus Cr-6. You can find the entire DEQ presentation to the Commission here.)
The gap between the IMAC standards and Safe Drinking Water Act standards meant that well owners were being advised not to drink water that meets current drinking water standards and could lawfully be provided to customers of a public water system. As a practical matter, that also means the well owners may not have access to an alternative water supply of any better quality since the nearest public water system also may not meet the IMAC standards.
None of this means the analysis done by the Division of Public Health in developing the IMACs was wrong. Environmental and public health standards change with additional knowledge; the fact that the U.S. Environmental Protection has undertaken a new health study of Cr-6 in particular suggests some question about the adequacy of the federal drinking water standard based solely on total chromium. The standards adopted by EPA and the states also sometimes involve compromise between the most protective health-based standard and the practicalities (and cost) of meeting that standard.