Agenda - Council Work Session - 08/09/2010

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CITY COUNCIL WORK SESSION Topic Report: Water Treatment Plant By: Brian E. Olson, Director of Public Works /Principal City Engineer Background: Comprehensive Water Supply Study ~_~a I.. %' The number of residents of the City served by municipal water and sewer services is increasing yearly. Water supply capacity must be added as users are added. The City has a Comprehensive Water System Study that was completed in 2004 which identifies the capacity increases needed as the population grows. The City has worked with the Department of Natural Resources (DNR) to identify potential sources of water. The DNR and Metropolitan Council have defined the aquifers (underground water sources) that can be used in the 7 County Metropolitan Area. The DNR said it would permit 3 additional wells prior to the completion of the Comprehensive Water System Study. These wells were included in the Study as sources; however additional capacity will be needed. All of the three wells has been constructed and are online. The DNR indicated additional sources such as the surface water should be investigated. The Study includes an alternative for a surface water treatment plant. Water Supply and Treatment Evaluation The River Bank Water Supply Collection System Pilot Study was approved in November of 2005 and resulted in an agreement from the Anoka County Parks Department to allow us to utilize the Mississippi West Regional Park for our analysis of the Mississippi River for water supply purposes. As you may recall the idea at the time was that the proposed water supply facility will draw water indirectly from the river using a riverbank infiltration system. This will require constructing a series of wells, horizontal collectors or infiltration galleries on the riverbank. Pumping water from these devices will lower the local water table under the river and water will flow from the river into the aquifer. Our investigations indicated that there is not enough capacity in the test wells that we constructed indicating that there must be a confining layer between the river bank and the river and that we are only drawing on ground water. A solution to this is to pulling water directly from the surface water supply or the river, however, this required us to use the pilot plant for a longer time (approximately 8-9 months instead of 3-4 months) During this study there was consideration and testing for three willing suppliers (GE, Siemens-Memcor, and Ionics) After 30 days of testing, Ionics requested to discontinue testing and did not request further consideration for the proposed Water treatment facility. GE and Siemens-Memcor piloted ultrafiltration membranes. Both performed well during the length of the pilot program and exhibited similar backwashing characteristics which will lead to similar operation and maintenance costs. The conclusions of the study were: