April 18, 2016. An earlier post discussed the confusion over “do not drink” advisories issued — and later withdrawn — for a number of wells near coal ash sites. There continues to be confusion among legislators, state agencies and the public about the correct response to high levels of hexavalent chromium (Cr-6) and vanadium in drinking water wells near coal ash impoundments. This post attempts to clarify some misconceptions and offers a proposal.
First, a clarification about individual contaminant standards. Some legislators understood presentations by the Department of Environmental Quality (DEQ) and the Department of Health and Human Services (DHHS) to mean that there are multiple, inconsistent standards for a contaminant. In fact, the state uses one standard for each contaminant to determine health risk and require groundwater remediation. But as the earlier post explained, the standard may come from Safe Drinking Water Act standards or state groundwater rules. Drinking water standards address a narrow set of contaminants likely to be found in public water systems; groundwater standards cover a broader range of extremely hazardous substances that may become a health threat because of a specific pollution incident.
State groundwater rules list health-based concentration limits for many hazardous substances, but also recognize that a pollution incident may involve a contaminant that does not yet have a groundwater standard. For those contaminants, the rules set the default standard at “non-detect” — any detectable concentration of the contaminant would be a violation. But the rules also create a process for setting an interim groundwater standard that would allow concentrations above detection levels based on an evaluation of health risk. DHHS used that process to develop the interim standards for vanadium and hexavalent chromium (CR-6) that led to “do not drink” advisories for a number of wells near coal ash facilities.
Gaps in the changing state response. DEQ and DHHS offered a two-part explanation for withdrawal of the “do not drink” letters. The two points and some additional context for each:
- Levels of vanadium and Cr-6 in the wells do not violate state or federal drinking water rules. Since there is no drinking water standard for either vanadium or Cr-6, this is true as far as it goes. But the lack of a drinking water standard does not imply safety. State and federal agencies have never relied solely on drinking water standards to make decisions about mitigation of health risks at contaminated sites because drinking water standards do not cover many extremely hazardous substances. That is why the process for asking DHHS to set interim state groundwater standards exists. The question should be whether concentrations of vanadium and Cr-6 in the wells represent a significant additional health risk that can be minimized by either providing an alternative water source or remediating the groundwater.
- A number of large N.C. public water systems also do not meet the DHHS interim standards for vanadium and Cr-6. The implication has been that the well water is as safe as water supplied to customers of public water systems. In recent weeks, media and public interest organizations have looked more closely at the levels of vanadium and Cr-6 in public water systems as compared to the wells near coal ash facilities. Although some N.C. water systems exceed the DHHS interim standards for vanadium or hexavalent chromium, most water systems appear to meet the DHHS standards. A WRAL news story includes a chart showing both maximum and average concentrations of Cr-6 in public water systems across the state here. DHHS set the interim standard for Cr-6 at 0.07 parts per billion, representing a 1:1 million cancer risk over a lifetime. WRAL’s analysis found that only about one-third of N.C.’s public water systems have average concentrations of Cr-6 exceeding 0.07 ppb. More importantly, those public water systems come much closer to meeting the DHHS standard than a number of the tested wells. The public water systems with the highest average concentrations of Cr-6 had concentrations less than half that of some wells tested near Buck Steam Station.
A proposal: Issuance of health advisories and steps to provide alternative water supply to well owners should be based on comparative health risk.
The discussion of health advisories issued to well owners around coal ash sites has become focused on whether public water systems meet the DHHS recommended standards for vanadium and Cr-6. That is the wrong question. Many (most) North Carolina water systems meet the DHHS standards; those that do not still provide water that is safer than water in a number of the tested wells. Environmental remediation programs exist in part to reduce health risks created by a pollution incident. To the extent well owners will be exposed to greater health risk as a result of groundwater contamination, the additional risk should be eliminated or minimized to the extent possible. The question is not whether all public water systems meet the DHHS standards. The question is whether groundwater pollution has exposed these well owners to greater health risk — and one way to answer that question is to compare contaminant levels in the well water to the nearest public water system. If the public water system provides water with lower contaminant concentrations that translate into lower additional cancer risk and less risk of acute toxicity, the well owner should be provided with advice on the higher risk of drinking the well water. And any person responsible for the contamination should be required to provide an alternative water source.