Evaluation of the Sufficiency of the Federal Regulatory Framework When Applied to Reuse
The overarching question in relationship to potable water reuse is whether the CWA and the SDWA offer sufficient protection for water supplies that are derived from sources that include significant municipal wastewater effluent. As described in Chapter 2, there are many communities in the United States where municipal wastewater treatment plant discharges make significant contributions to the drinking water source. In some cases wastewater discharges are a principal source; thus, it can be argued that the SDWA has already been given this assignment. The SDWA and the CWA are the federal laws in place to protect the public from contaminants of wastewater origin. The SDWA alone applies to groundwater resources where septic systems or other sources of pollution contribute to the overall groundwater replenishment. Potable reuse projects may also be required to meet local or state regulations, above the requirements of the SDWA (state reuse regulations are discussed later in the chapter). However, de facto reuse scenarios are not subject to additional regulations.
As outlined earlier, the SDWA does provide limits (MCLs) for many chemical and biological contaminants, and a great deal of research, careful thought, and public dialogue underlies each of these limits. For contaminants regulated through MCLs, it is logical that the same limits would apply regardless of the source of the water. Where potable reuse is concerned, unregulated organic contaminants are an issue of special interest. The question remains as to the adequacy of existing drinking water regulations to protect public health where unregulated trace organic contaminants are concerned. In the following section, the committee examines the adequacy of CCL datasets for evaluating contaminants relevant to water reuse, the challenge of unknown contaminants, and the concern of greater microbial risks when raw water supplies contain significant amounts of municipal wastewater effluent.
Adequacy of CCL Data for Prioritizing Chemicals Relevant to Water Reuse
The CCL process (Box 10-3) is the primary mechanism for considering trace organic contaminants for regulation under the SDWA. Therefore, the committee first evaluated whether the CCL process adequately targeted contaminants for water reuse applications. From a review of the history of the CCL (see Box 10-3), it is evident that the process used to gather data for the CCL is evolving to become increasingly comprehensive in character. This becomes particularly clear in the third CCL (CCL3). Nevertheless, expanding the water quality monitoring datasets that inform the CCL process, particularly targeting contaminants encountered in municipal effluents, could improve the effectiveness of the CCL for reuse applications.
The CCL3 universe encompasses a wide array of potential water contaminants, both chemical and microbial. To generate the CCL3 universe, EPA relies primarily on databases that are electronically accessible at no charge. Although some databases include data on contaminants in municipal effluents, much of the data published in peer-reviewed literature is not included. The UCMR program under SDWA monitors unregulated contaminants in drinking water, but this program does not directly target contaminants in water reuse systems or municipal wastewater. At present, the data on unregulated contaminants in wastewater discharges primarily originate from research efforts conducted by utilities and academic research funded by water industry research foundations. The program would benefit from an effort to include these data in the CCL as well. Also, a federal monitoring program for unregulated contaminants directed toward wastewater effluents, mirroring the UCMR program for drinking water, would be highly beneficial in characterizing the occurrence of emerging contaminants in reuse (and de facto reuse) applications.
The Challenge of Unknown Contaminants
Although the SDWA provides protection to public health from priority chemicals and microbial contaminants, unknown chemical compounds (i.e., those that have not yet been identified through chemical analysis or whose occurrence has not been characterized) represent a primary concern in potable reuse projects that is not currently addressed by the SDWA. This concern also applies to conventional supplies to the extent that they are influenced by wastewater sources or exposed to independent sources of contamination. The current paradigm for discrete chemical monitoring of a pre-identified suite of contaminants will not be capable of addressing the large number of potential but currently