AWWA MTC53745

Customers of the Olivenhain Municipal Water District (District) receive all oftheir water from the Colorado River and from northern California. Both of thesesources are imported over distances of hundreds of miles before reaching theOlivenhain service area. In the event of an emergency interruption of theseimported supplies, the District currently has approximately seven average days oftreated water storage available. However, an extended interruption of theimported water system, such as could occur in a large earthquake, wouldjeopardize the health and safety of the District's customers and the economy ofthe San Diego region. To enhance the reliability of the District's water supply,and to further sustain the increasing demand for a rapidly growing population,the District is joining forces with the San Diego County Water Authority toproduce what has come to be known as the Olivenhain Water Storage Project.Together, they will construct a 24,000 acre-foot reservoir and 308-feet rollercompacted concrete (RCC) dam-- the tallest dam of its kind in the UnitedStates--resulting in a two month supply of emergency water storage for residentsin the District's service area and neighboring districts. This duration of supplyis designed to sustain the region's water supply following an earthquake-inducedfailure of the imported water system and until the system can be repaired. Aspart of this initiative, the District has designed and initiated the constructionof a 25 mgd (million gallons per day) immersed membrane water treatment plant(WTP). This plant, the largest drinking water ultrafiltration treatment plant inthe world, will utilize membrane treatment technology that provides more certainremoval of waterborne health threats while also benefiting the environmentthrough less chemical usage. The immersed (sometimes referred to as submerged)membrane water treatment process is to be supplied by Zenon Environmental,located in Ontario, Canada. The District decided upon an ultrafiltration membraneprocess for its water treatment plant in order to ensure high quality water thatmeets and exceeds regulatory standards. A detailed history of this project, itssignificance, and the steps the District has taken over the years to implementthis initiative are discussed in this paper. Environmental and other factors used inselecting the membrane treatment process as the preferred method of treatmentwill be enumerated. Pilot testing programs and membrane procurement proceduresused by the District and its consulting engineer, Boyle Engineering Corporation,will be highlighted, in addition to quantifying lessons learned relative to itsimplementation, actual construction cost information, and financial impactsresulting from the membrane procurement process. Water purveyors seeking toinvestigate the use of immersed membrane processes or improve their currentdrinking water treatment processes will find the Olivenhain Experience to beenlightening and informative. Includes 2 references, figures.