Agenda - Council - 06/26/2012 - Laserfiche WebLink

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A direct raw water intake structure would be constructed on the bank of the Mississippi River as shown in Appendix C. Raw water would be pumped to the water treatment facility site. Grit, sand and organics in the raw water would be removed in the surface water detention basin. Further settling of solids will be accomplished utilizing clarifiers prior to the membrane filter. Membrane filters consist of microfiltration (0.1 microns) and ultrafiltration (< 0.1 microns) filters. These filters can be either pressure driven or vacuum driven. Currently, the typical membrane filter contains hollow fibers and the filtration takes place from the outer surface of the fiber to the hollow inner core. Feed liquid passes through the porous wall of the fibers while the solids in the feed stream are retained on the outside fiber wall. The difference in pressure between the outside and the inside of the fibers is known as the transmembrane pressure (TMP). The TMP is the pressure that drives the liquid through the porous walls of the membrane, filtering the liquid in the process. Feed and filtrate pressures are measured by pressure transmitters and the TMP is calculated. As particles build up on the membrane surface during filtration, an increase in TMP is required to maintain a constant flow rate. To restore performance, these particles must be removed periodically by backwashing. Backwashing typically consists of air scouring, chemical scouring and liquid backwashing. Backwash is sent to a backwash tank and eventually pumped to the head of the facility for treatment. Waste solids from the backwash system are routed for disposal to the sanitary sewer. High service pumping from a cleanwell/reservoir tank sends finished water to the distribution system. Existing groundwater sources will be routed to the treatment facility. These sources will be utilized as a backup supply in the case of a disruption in the surface water supply system. 3. Ground Water Source Treatment Treatment of groundwater for iron, manganese and other contaminants is typically accomplished utilizing granular media filtration. Granular media filtration is effective in removing arsenic, radionuclides, iron and manganese. Arsenic and City of Ramsey, Minnesota — R13.104504 Page 4-4 Comprehensive Water System Study Prepared by Bolton & Menk, Inc.