August 21, 2016. The controversy over changing state advice to well owners near Duke Energy’s coal ash impoundments has exploded again over conflicting accounts — within the McCrory administration — of the basis for “do not drink” letters sent in 2015 and later withdrawn. Two earlier posts here and here provide background on groundwater and drinking water standards for vanadium and hexavalent chromium (the contaminant of greatest concern).
In 2015, the N.C. Department of Health and Human Services (DHHS) sent health advisory letters to the owners of wells with concentrations of hexavalent chromium (chromium 6 or Cr-6) above 0.07 ppb. The 0.07 ppb threshold represented the concentration of Cr-6 associated with an increased cancer risk of 1:1 million. In early 2016, the McCrory administration rescinded most of the letters and advised well owners that water meeting the federal drinking water standard for total chromium (100 ppb) should be considered safe to drink. The total chromium standard covers both chromium-3 and the more toxic chromium-6.
Within the last two weeks, the conflict between DHHS and the Department of Environmental Quality (DEQ) over the content of the health advisory letters again made headlines. This post describes the roles of DHHS and DEQ in groundwater contamination incidents; explains the criteria for developing groundwater standards; and makes a few observations on the implications of the conflict for future groundwater contamination incidents.
The role of DHHS in groundwater contamination incidents and development of groundwater standards. When contamination affects drinking water wells, DHHS toxicologists often advise on the potential health effects. If there is no existing drinking water or groundwater standard for the specific contaminant, the toxicologists use established protocols to assess the contaminant’s short-term and long-term health effects. Acute health effects include organ damage, skin rashes, respiratory problems and other short to intermediate term problems. Long-term health effects often focus on increased cancer risk. DHHS may also work with the Department of Environmental Quality (DEQ) to develop a health-based groundwater standard for a contaminant that has no existing numeric standard in state or federal rules. DHHS toxicologists advise rather than regulate. DEQ has responsibility for enforcement of state groundwater standards and oversight for groundwater cleanup.
Cancer risk as a factor in setting groundwater standards and assessing groundwater contamination. Both state and federal environmental agencies consider increased cancer risk as a factor in assessing groundwater contamination and setting goals for groundwater cleanup. North Carolina’s groundwater rules list a 1:1 million increased cancer risk as a primary criteria for setting groundwater quality standards. In 15A NCAC 2L.0202(d), the rules require a state groundwater standard to be based on the lesser of the
(1) Systemic threshold concentration calculated as follows: [Reference Dose (mg/kg/day) x 70 kg (adult body weight) x Relative Source Contribution (.10 for inorganics; .20 for organics)] / [2 liters/day (avg. water consumption)];
(2) Concentration which corresponds to an incremental lifetime cancer risk of 1×10-6;
(3) Taste threshold limit value;
(4) Odor threshold limit value;
(5) Maximum contaminant level[the federal drinking water standard]; or
(6) National secondary drinking water standard.
Based on recent public statements by DHHS scientists, DHHS and DEQ staff in the Division of Waste Management calculated increased cancer risk associated with Cr-6 exposure using a standard protocol. The two agencies concluded that 0.07 ppb represented the break-point for the 1:1 million increased cancer risk. The DEQ/DHHS calculation of increased cancer risk associated with > 0.07 ppb of Cr-6 then became the basis for “do not drink” letters sent to well owners in 2015.
Health advisories based on groundwater contamination. DHHS has long worked with DEQ staff to advise well owners on health risks associated with groundwater contamination. Both DHHS and DEQ report to the Governor, creating a strong incentive for the agencies to agree on assessment of public health risk. Environmental and public health experts may debate the appropriate standard for a contaminant, but public conflict between the two agencies is extremely unusual and may be unprecedented.
The split between DHHS and DEQ over advice to well owners. According to DHHS scientists, the 0.07 ppb standard for CR-6 based on increased cancer risk reflected the consensus of DHHS public health experts and staff in DEQ’s Division of Waste Management. DEQ leaders, however, encouraged DHHS to advise well owners that water exceeding the 0.07 standard should still be considered safe to drink as long as Cr-6 levels did not exceed the federal drinking water standard of 100 ppb. DEQ publicly raised concerns about the DHHS health advisories in a January 2016 presentation to a legislative committee. The presentation compared the 0.07 ppb standard to the federal drinking water standard and to standards adopted by other states. Within a month after the legislative presentation, DEQ and DHHS sent new letters advising well owners that well water with Cr-6 levels below 100 ppb should be considered safe to drink because the water meets federal drinking water standards. Recent statements by state toxicologist Ken Rudo and state epidemiologist Megan Davies (who has resigned over the issue) make it clear that DHHS public health experts did not believe the existing state and federal standards for total chromium sufficiently protected human health and objected to the revised letters. The 100 ppb standard for total chromium represents an increased cancer risk orders of magnitude higher than the 0.07 ppb standard — 1:700 increased risk of cancer versus 1:1 million increased risk.
♦ The state’s groundwater standard remains 10 ppb for total chromium and the Coal Ash Management Act of 2014 directs DEQ to use state groundwater standards in assessing drinking water wells around coal ash impoundments. DEQ has not proposed a specific state groundwater standard for Cr-6 based on the DEQ/DHHS cancer risk calculation. As a result, the 0.07 ppb standard remains a health advisory rather than an enforceable groundwater standard. The federal drinking water standard of 100 ppb does not apply to either groundwater assessment or evaluation of well safety near coal ash impoundments.
♦ According to Secretary Donald van der Vaart, DEQ does not question the DHHS calculation of increased cancer risk associated with Cr-6. Given the gap between the total chromium standard of 10 ppb and the 0.07 ppb threshold for a 1:1 million increased cancer risk associated with chromium-6, the total chromium standard does not meet a basic criteria for a N.C. groundwater standards — which requires a groundwater standard to be based on the 1:1 million increased cancer risk — and should be reviewed.
♦ State and federal agencies routinely use the 1:1 million increased cancer risk as a criteria for developing health-based standards for permitting and to set environmental remediation goals. Both state and federal programs also recognize that there may be a need to move off the 1:1million cancer risk criteria in individual cases because it is not technically or economically feasible to meet the standard. In those instances, the agency can adjust a groundwater cleanup goal (for example) to reflect the limits of available technology.
Going forward. As a practical matter, the difference between the DHHS health-based standard and the state groundwater standard has no direct enforcement consequences for Duke Energy. For the time being, the applicable state groundwater standard continues to be the total chromium standard of 10 ppb. Under 2016 amendments to Coal Ash Management Act, Duke Energy must provide a permanent alternative water supply to all well owners within 1/2 miles of a coal ash pond which makes both the cancer risk threshold and the state groundwater standard irrelevant to decisions about alternative water supply.
Assuming no change in the state groundwater standard, the 10 ppb total chromium standard will also drive development and approval of groundwater remediation plans for areas surrounding the coal ash impoundments.
The cancer risk threshold for Cr-6 does raise questions about the adequacy of the state’s total chromium standard. The DHHS calculation of cancer risk suggests the existing total chromium does not meet one of the basic criteria for state groundwater standards — protection against a 1:1 million increase in cancer risk.
The public conflict between DEQ and DHHS raises two other questions —
Should state environmental and public health agencies inform citizens of the health risk associated with contamination that meets existing regulatory standards? DHHS public health officials felt an obligation to inform well owners of the higher cancer risk potentially associated with elevated levels of CR-6; DEQ took the position that the warnings were unnecessarily alarming if the well water met federal drinking water standards.
The other question is more technical and would inevitably come up in any reevaluation of the groundwater standard for chromium: Is there any economic or technical reason not to use the more stringent 0.07 ppb standard as the basis for assessing risk of human exposure to Cr-6 in groundwater and setting groundwater remediation goals? The choice of a standard has implications beyond the immediate controversy over coal ash impoundments and so far there has not been a practical critique of the 0.07 ppb threshold based on technology or cost. The reason behind DEQ’s objection to the DHHS 0.07 ppb threshold as a basis for health advisories still isn’t entirely clear since it appears most public water systems in the state meet the DHHS health-based standard. Those that don’t meet the 0.07 ppb standard come much closer than a number of the wells DEQ argued should be considered safe because the water meets the federal drinking water standard of 100 ppb.