priority organic pollutants regulated under U.S. drinking water standards as well as additional compounds of concern. The organic analytes evaluated by San Diego included 62 volatile organic compounds; 68 semivolatile organic compounds, including trihalomethanes, benzene, N nitrosamines, chlorinated aromatics, phenols, and polynuclear aromatic hydrocarbons; pesticides and polychlorinated biphenyls (PCBs); chlorinated dibenzodioxins/dibenzofurans; and low molecular weight aldehydes (Western Consortium for Public Health, 1997). Concentrations of all regulated contaminants were below U.S. and state drinking water standards. Similar evaluations of organic chemicals, with similar results, were conducted at Tampa (CH₂M Hill, 1993) and Denver (Lauer et al., 1991).

The Denver reuse project conducted an organic challenge study in which 15 different organic compounds were dosed at approximately 100 times the normal levels found in the reuse plant influent (Lauer et al., 1991). Table 2-3 shows the initial doses and removal rates of these compounds for four different treatment processes. Five of the compounds were removed completely (i.e., to below detectable limits) by lime treatment, and eight of the remaining ten were removed completely by the granular activated-carbon filters. The reverse-osmosis membranes allowed 1.1 mg/liter of chloroform to pass through; this chloroform was subsequently removed by air stripping. The study showed that even