Regulating Heavy Metals in Non-Contact Cooling Water: Defining Practical Limits

A power plant located on a tidal river in Connecticut experienced difficulties meeting revised permit limits on heavy metals in its non-contact cooling water. The high concentration of dissolved solids in the saltwater interfered with the analytical test methods, making it appear that the plant was violating its discharge limits. The study determined the typical analytical methods for measuring metals were inaccurate at the metal concentrations being regulated. Even a test that used offline chelation to minimize matrix interferences fared poorly. The study spiked synthetic seawater and cooling water with known metal concentrations to establish practical limits for copper, lead, nickel and zinc in saltwater. It determined that regulatory agencies need to further consider the practical limits of laboratory analyses when setting discharge limits.