Proposed nutrient criteria for water supply lakes and reservoirs

Nutrient enrichment of lakes and reservoirs used for potable water supply (PWS) can cause adverse effects, ranging from operational problems to increases in health-related risks such as disinfection by-products (DBPs), cyanotoxins, and arsenic. New York state is developing numeric nutrient criteria (NNC) for the protection of PWS lakes and reservoirs by establishing relationships between total phosphorus (TP), algal biomass (chlorophyll a [Chila]), dissolved organic carbon (DOC), and trihalomethanes (THMs), and then establishing NNC that target existing regulatory endpoints for total THMs. This represents a much-needed bridge between the Safe Drinking Water Act (SDWA) and the Clean Water Act (CWA). Findings to date from the investigation of 21 systems indicate that a mean Chla threshold of 4-6 mu g/L would likely be protective of public health.