The Safe Drinking Water Act (SDWA), as amended in 1996, requires EPA to make regulatory determinations every five years on at least five unregulated contaminants. A regulatory determination is a decision about whether or not to begin the process to propose and promulgate a national primary drinking water regulation for an unregulated contaminant. These unregulated contaminants are chosen from the Contaminant Candidate List (CCL), which SDWA requires the agency to publish every five years. The CCL is a list of contaminants which are not subject to any proposed or promulgated national primary drinking water regulation (NPDWR), are known or anticipated to occur in public water systems, and may require regulation under SDWA. Through an October 20, 2014 Federal Register notice, EPA announced, and is requesting comments on its preliminary regulatory determination for five unregulated contaminants. The five contaminants include:
EPA’s preliminary determination is to regulate one contaminant (strontium) and to not regulate the other four. For EPA to make a determination to regulate a contaminant, SDWA requires the Administrator to determine that:
If EPA determines that these three statutory criteria are met and makes a final determination to regulate a contaminant, the agency has 24 months to publish a proposed Maximum Contaminant Level Goal (MCLG) and NPDWR. After the proposal, the agency has 18 months to publish and promulgate a final MCLG and NPDWR. The MCLG is the “maximum level of a contaminant in drinking water at which no known or anticipated adverse effect on the health of persons would occur, and which allows an adequate margin of safety.” MCLGs are non-enforceable health goals. The NPDWR, on the other hand, is a legally enforceable standard that applies to public water systems. It sets a legal limit, called a maximum contaminant level (MCL) or specifies a certain treatment technique for public water systems. The MCL is the highest level of a contaminant that is allowed in drinking water and is set as close to the MCLG as feasible using the best available treatment technology and taking cost into consideration.
Strontium is a naturally occurring element found in air, rocks, soil, dust, coal, oil, and surface and groundwater. Strontium has 16 known isotopes. Strontium compounds are used in making ceramics and glass products, pyrotechnics, paint pigments, fluorescent lights, and medicines. Other isotopes are radioactive and can be found in nuclear reactors, and are used in industry and medicine. Strontium mineral mining ceased in the United States in 1959. The U.S. imports both strontium minerals for refining and refined strontium containing compounds. Historically, the most important commercial use of strontium has been in the faceplate of cathode-ray tube televisions to block x-ray emissions. As flat panel TV technology has become widespread in the U.S. in the last decade, demand for strontium for this application has fallen. Strontium is considered to have moderate or moderate-to-low mobility in soils. The primary target of strontium exposure is the bone. The chemical similarity of strontium to calcium allows it to exchange imperfectly for calcium in a variety of biological processes; the most important of this is the substitution of calcium in bone, affecting skeletal development.
EPA used a non-cancer drinking water-based health reference level (HRL) for strontium of 1.5 mg/l as part of this regulatory determination. Currently EPA uses a lifetime health advisory level of 4 mg/l and a one-day health advisory level of 25 mg/l. Naturally occurring strontium in ground water is not radioactive. According to the FR Notice, 99 percent of public water systems tested had detectable concentrations of strontium, with 14 percent of systems detecting strontium at more than 0.750 mg/l and 7 percent of systems detecting strontium at levels above the agency’s HRL. In Ohio, strontium is present in each of the major aquifer types — sand and gravel, sandstone, and carbonate — with median values of 0.37, 0.38, and 14.7 mg/l, respectively (Ohio EPA’s “Major Aquifers in Ohio and Associated Water Quality”). Based on this information, it is very possible that an MCL, if promulgated, could be lower than naturally occurring levels of strontium for at least Ohio’s carbonate bedrock aquifer. This would not be the first time a primary MCL is lower than naturally occurring concentrations. Arsenic is a good example.
Of the four other contaminants for which EPA has preliminarily determined that regulation is not needed, one is an industrial chemical (1,3-dinitrobenzene) and three are pesticides (dimethoate, terbufos, terbufos sulfone). Even if EPA makes a final determination to regulate strontium, a drinking water limit is likely years away, as EPA has failed to meet regulatory deadlines for existing drinking water contaminants.
George H. Colvin is a hydrogeologist with over 30 years of consulting experience. Much of his experience has focused on RCRA Corrective Action, RCRA closure, and groundwater investigation, monitoring, and cleanup. He holds a BS in Geology from Ohio University and MS in geology and hydrology from Vanderbilt University. He is a Certified Professional Geologist with the American Institute of Professional Geologists, a registered geologist in Kentucky, Pennsylvania, and Tennessee, and a Certified Hazardous Materials Manager.