Two overlapping sets of water quality parameters are important to MUS performance and so must be considered in designing MUS systems. Constituents regulated in drinking water (as described by the Safe Drinking Water Act [SDWA]) comprise a well-defined list with concentrations that must be met in drinking water supplies for either human health or aesthetic reasons. While the SDWA prescribes the list of both chemicals and microorganisms that have been the primary impetus for water quality goals, this list is not sufficient to evaluate the quality of the various waters (source water, native groundwater, stored water, etc.) for an MUS system. In order to establish a sustainable MUS system, constituents that lead to aquifer clogging or dissolution, or other reactions that improve or degrade water quality during MUS operations must also be evaluated. The constituent concentrations that are important for operations are not embodied in a regulatory list, but emerge from consideration of the reactions that can impact MUS performance and the particular type of MUS system (e.g., type of source water, recharge method, native groundwater characteristics, and aquifer geochemistry). Importantly, the microbial and chemical water quality can improve or degrade during any stage of MUS.

The list of contaminants developed under the SDWA includes the list of chemical and microbiological constituents that have established legal enforceable maximum contaminant levels (MCLs) and/or treatment technology requirements and MCLGs (maximum contaminant level goals). Total coliform bacteria are used from a regulatory monitoring perspective to judge drinking water microbiological safety. There is also emerging concern about “new” (previously unmonitored) chemicals and constituents that occur in water as a consequence of human activities and are not regulated (e.g., endocrine disrupting chemicals, pharmaceuticals, personal care products). For many of the chemicals in this classification, analytical techniques appropriate for environmental samples are relatively new and complex. The World Health Organization also has developed a list of constituents of interest in water for health goals that includes some compounds that are not regulated by the U.S. Environmental Protection Agency (EPA) including, for example, the cyanobacterial toxins that can be found in surface waters.

To fully appreciate the broad water quality characteristics found in MUS systems from the ambient groundwater to the source, stored, and recovered water, the physical, chemical, and microbiological water quality constituents need to be understood and measured. These are described briefly in the following sections, and extended descriptions are available in Appendix A.

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