AWWA ACE94206

The East Bay Municipal Utility District's (EBMUD) Walnut Creek and Lafayette in-line filtration plants treat high quality Mokelumne River water from the Sierra Nevadas. In-line filtration, in comparison to direct filtration, does not include a flocculation step and is considered by the California SWTR to be an alternative treatment technology. Facilities using alternative treatment technologies must demonstrate to the state that they are able to meet the 2-log and 1-log removal requirements for Giardia cysts and viruses, respectively. The California SWTR states that this can be done by demonstrating that the facilities can be operated to reliably produce water meeting the performance requirements for filtration and disinfection, as demonstrated by the latest 12 months of operating data. The SWTR filtration and disinfection performance requirements were met by both facilities during 1992 and Giardia and virus removal credits of 2-log and 1-log, respectively, were received. EBMUD desired to determine if the two facilities could obtain additional Giardia-cyst removal credits through particle count demonstration studies. Two years previous, particle count demonstration studies were performed at the Orinda filter plant, a third EBMUD in-line filtration plant treating the same water source. These studies determined that the Orinda plant could achieve a 2.7-log removal of particles in the Giardia-cyst range size.