Mohawk Valley Water Authority (MVWA) in New York State is a supplier of potable water. With source water from the Adirondack Mountains, MVWA works to improve on nature and provide superior water quality by meeting or exceeding drinking water standards.
Like many other surface water sources, MVWA’s water supply is rich with natural organic matter (NOM). Unfortunately, growing research has demonstrated that NOM in water, combined with chlorine, leads to the formation of potentially harmful disinfection byproducts (DBPs), such as Trihalomethanes (THMs). New regulations, such as the U.S. Environmental Protection Agency’s Stage 2 Disinfection By-Products Rule, have been implemented to protect the public from these potential cancer-causing substances and improve drinking water quality.
For several years, MVWA has been examining potential treatment strategies to meet the upcoming regulatory requirements. Its comprehensive research project indicated that it was very important to monitor for DBP precursor levels in the raw and filtered water continuously in real time. This tool would enable the authority to monitor the effectiveness of the treatment processes in removing NOM and thereby reducing the potential of DBP formation. MVWA’s parameter of choice: UV254.
Unlike TOC testing, UV254 organic testing has been recognized as the best detector of reactive NOM. This is significant because reactive NOM more readily combines with chlorine to form DBPs.
MVWA determined that the Real UVT online monitor  by Real Tech, Inc.  was a reliable, easy-to-use and affordable continuous real-time UV254 monitor. The initial cost of the instrument is approximately 80% less than the initial cost of an online TOC analyzer and equivalent to the maintenance cost of using a TOC analyzer for one year.
MVWA purchased the online monitor and Real Tech’s portable Real UVT field meter for its UV254 grab sample needs. The organic testing instrumentation provides the authority with affordable DBP precursor monitoring solutions for raw water and treated water needs, as well as for expanded monitoring in its distribution system.
MVWA’s first online monitor was installed at the treatment plant to continuously monitor the plant’s raw water organic content. This single monitor was then programmed to also monitor the filtered water UV254 levels. Using these two UV254 readings, MVWA can assess the effectiveness of the treatment process in removing natural organic matter. MVWA was able to go one step further by synchronizing its raw water UV254 results to correspond to the filtered water result. This results in a true real-time measure of NOM reduction, which can aid in coagulation optimization and potential cost savings.
By setting its targeted finished water UV254 goal to 0.03 to 0.035 UVA, MVWA is able to ensure that its corresponding TOC levels are less than 2 mg/L. Since MVWA experiences higher reactive organic levels and therefore forms higher THMs during the summer months, it has been piloting the use of granular activated carbon (GAC) to enhance the removal of these DBP precursors during this period of time. UV254 testing is aiding MVWA with this study to help determine the effectiveness of the GAC filtration in removing the reactive NOM and ensuring that they fall below DBP maximum contamination levels (MCLs) during the summer months.
Additionally, to monitor the quality of their distribution system water, MVWA has installed the online monitors at two key distribution system real-time monitoring stations. The UV254 results from these monitors are linked directly to an auto-dialer that provides instant notification of any detection of organics that fall outside of baseline values. This provides MVWA with the added benefit of providing real-time security monitoring for accidental or intentional organic contamination of the drinking water supply.