In 2004, Big Elk Water Association, near Estes Park, Colo., earned the unenviable Environmental Working Group label of Colorado water system with the worst quality water. Despite multiprocess treatment, BEWA’s finished water had some of the highest concentrations of total trihalomethanes (TTHMs) and haloacetic acids (HAA5) in the state. BEWA delivers water to about 390 people in Big Elk Meadows, a mountain subdivision.
After surface water from a series of aerated lakes is treated by microfiltration (MF), ultraviolet (UV), and sodium hypochlorite for disinfection, as well as granular activated carbon for taste and odor, sodium hydroxide is added for corrosion control. However, quarterly disinfection by-product (DBP) tests showed TTHM and HAA5 levels over 250 μg/L (current limits are 80 and 60 mg/L, respectively). BEWA received a notice of violation from the Colorado Department of Public Health and Environment for failing to comply with the maximum contaminant levels (MCLs) set by the Stage 1 Disinfectants and Disinfection Byproducts Rule.
How did this happen? Several years of testing had shown that source water levels of dissolved organic carbon (DOC) were consistently in the 9 to 13 mg/L range. DBPs, particularly TTHMs and HAA5, form when DOC reacts with free chlorine during disinfection. Investigation upstream where raw water enters Big Elk Meadows property revealed high levels of DOC, which the MF/UV plant couldn’t effectively remove. The exact cause of the DOC couldn’t be determined, and an alternative water source wasn’t available.