| Hexavalent chromium [Cr(VI)] has received significant attention as a drinking water contaminant in recent years---particularly in California where the Department of Health Services currently limits total chromium ([Cr(VI)] + trivalent chromium [Cr(III)]) in drinking water to 50 mug/L. The federal USEPA drinking water chromium standard is 100 mug/L. Media attention surrounding the movie Erin Brockovich sparked and raised public awareness to the possible health hazards of chromium in drinking water and public concern remains high, despite the uncertainties about the health effects associated with Cr(VI).; The primary objective of this dissertation research has been to investigate hexavalent chromium as a future regulated drinking water contaminant, at concentrations significantly lower than the current total chromium standards (i.e. < 5 mug/L). Information has been developed about the national occurrence of Cr(VI) in drinking water sources, the effectiveness of various Cr(VI) treatment technologies, and the costs associated with those treatment technologies. In addition, the Safe Drinking Water Act (SDWA) regulatory development process has been described and a cumulative risk approach to assessing drinking water regulations is discussed, including a case study using national occurrence information. Limitations to the evaluation and analysis of the SDWA are broached and assessed to understand the implications of a future hexavalent chromium-specific drinking water regulation.; This dissertation research has identified several unique conclusions. The national occurrence research determined Cr(VI) occurs predominantly in groundwaters, rarely in surface waters. Total chromium, however, occurs equally in both surface and groundwaters. Treatment research found that disposable iron-based adsorptive media, developed for arsenic treatment and hypothesized to be effective for chromium treatment, were ineffective. The MIEX RTM process, traditionally used for natural organic matter removal, was evaluated for the first time for inorganics removal and determined to be effective. The costs of technologies deemed effective through pilot testing for Cr(VI) treatment to low levels were estimated and found to vary most due to residuals disposal needs. The SDWA assessment revealed that substantial obstacles remain for the use of new regulatory concepts such as cumulative risk and cumulative cost. However, the assessment provides a new look at potential future regulatory development processes. |
