Assessment of the chlorine demand and disinfection byproduct formation potential of surface waters via satellite remote sensing

The ability of satellites to assess surface water quality indicators such as colored dissolved organic matter (CDOM) suggests that remote sensing could be a useful tool for evaluating water treatability metrics in considering potential drinking water supplies. To explore this possibility, 24 surface water samples were collected throughout Minnesota, USA with wide ranging values of CDOM (a₄₄₀; 0.41–27.9 m^-1), dissolved organic carbon (DOC; 5.5–47.6 mg/L) and specific ultraviolet absorbance at 254 nm (SUVA₂₅₄; 1.3–5.1 L/mg-M). Laboratory experiments were performed to quantify chlorine demand and the formation of two classes of halogenated disinfection byproducts (DBPs), trihalomethanes (THMs) and haloacetic acids (HAAs), using the uniform formation conditions (UFC) test. Chlorine demand and THM_UFC were linearly correlated with CDOM (R² = 0.97 and 0.91, respectively), indicating that CDOM is a useful predictor of these parameters. On the other hand, data comparing di- and tri-HAA_UFC with CDOM were better fit by a logarithmic relationship (R² = 0.73 and 0.87, respectively), while mono-HAA_UFC was linearly correlated with CDOM (R² = 0.46) but only for low-to moderately-colored waters (a₄₄₀ ≤ 11 m⁻¹). The correlations relating chlorine demand and DBP_UFC values with CDOM were coupled with satellite CDOM assessments to estimate chlorine demand and DBP_UFC values for all surface waters larger than 0.05 km² in the state of Minnesota, USA. The resulting maps suggest that only 21.8% of Minnesota lakes would meet both the THM and HAA maximum contaminant levels, but only when pre-disinfection treatment removes 75% of DBP precursors. There are limitations to determining CDOM using satellites for high color surface waters (a₄₄₀ > 11 m⁻¹), however, leading to underpredicted values for CDOM, chlorine demand, and DBP_UFC. Overall, the results demonstrate the potential benefits of satellite remote sensing for assessing potential drinking water sources and water treatability metrics.