AWWA WQTC63997

Small water systems face challenges complying with existing regulations including the Stage 1 Disinfectants/Disinfection Byproducts Rule (D/DBPR) and will face increased challenges when the Stage 2 D/DBPR becomes effective. There will be additional challenges for surface water supplies that contain natural organic matter (NOM) with characteristics that produce DBPs exceeding the total trihalomethane (TTHM) or the five regulated haloacetic acid (HAA5) maximum contaminant levels (MCLs). In addition some source water characteristics and other treated water quality goals may interfere with DBP control strategies. This presentation describes the Calaveras County Water District (District) Jenny Lind Domestic Water System (JLDWS) experience with the Stage 1 D/DBP Rule. Specifically, the JLDWS exceeded the HAA5 running annual average (RAA) MCL of 60 µg/L during 2005. the raw water treated at the Jenny Lind Water Treatment Plant (JLWTP) has been more difficult to treat due to a relatively high manganese concentration in its source water, and a higher than normal TOC level during the past 4 years associated with a three-year drought followed by a higher than normal rainfall during the winter in 2004 and 2005. The JLWTP operators have used ozone, chlorine and potassium permanganate for pre-oxidation, and use polyaluminum chloride (PACl) or PACl blended with polymer for coagulation. The treatment process includes contact clarification and filtration in five modular treatment units. Chlorine is added to the filtered water between the water treatment units and two on-site clearwells. Distribution system strategies include seasonally reducing the volume in the storage tanks located throughout the JLDWS to reduce the maximum water age. The TTHM and HAA5 monitoring frequency was also increased from quarterly to monthly to reduce the risk that a single laboratory result could create a compliance problem. A bench scale evaluation of TTHM and HAA5 formation as a function of time conducted in October 2005 indicated that the water age should be less than 3 days to facilitate compliance with the HAA5 MCL. Potential process modifications included optimizing operation of the existing ozone system, evaluating use of chlorine dioxide for pre-oxidation, using granular activated carbon (GAC) filter media to remove the TOC fraction associated with UV254 absorbance and high SUVA values, and/or switching to chloramines as a final disinfectant. Includes 5 references, table, figures.