This paper summarizes the results of a water quality master plan that was completed for Erie City Water Authority's (ECWA) Chestnut Street and Sommerheim water treatment plants. Specific issues that were addressed included disinfection, liquid stream processes, and residual disposal alternatives. Specifically, this paper discusses the disinfection alternatives, including ultraviolet (UV) light, that were considered for each treatment plant and the final alternatives that were selected for each plant to comply with the Pennsylvania Department of Environmental Protection (PADEP) disinfection design requirements. Both plants currently produce high quality water and meet all of the major drinking water regulations (i.e. D/DBP's, ICR, IESWTR, etc.); however, due to the limited clear well volumes with little or no baffling, both plants cannot meet the PADEP disinfection design requirements. Currently PADEP requires that new or modified water treatment plants be designed to achieve 3-log inactivation of Giardia through the treatment plant with at least 1-log inactivation of Giardia occurring after filtration. Both treatment plants are currently "grandfathered" under this regulation, which means they are not required to meet the disinfection requirements outlined above. However, due to the age of both treatment plants, ECWA is planning on upgrading their liquid as well as solids stream processes. With these modifications, the plant will no longer be grandfathered under the regulations; therefore, they will need to consider disinfection alternatives which will allow them to comply with the PADEP standards as well as the anticipated inactivation requirements for Cryptosporidium in the LT2ESWTR which may also be adopted by PADEP. Based on the process and site conditions, it was determined that UV light followed by chlorine is the best option to meet the LTESWTR and the PADEP disinfection requirements. Includes tables, figures.
