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DRAFT 8 -17 -07 <br />44x84x10 feet deep with a dividing wall. The tanks will be partially above ground <br />and insulated or soil could be mounded around the tanks to cover them. <br />Examples of a modular style gravity filters include the plants in the City of Forest <br />Lake. <br />We chose not to recommend the gravity open style filters, because of the shallow <br />ground water table and the construction costs associated with a treatment plant of <br />this type. <br />B. PRESSURE FILTERS <br />Pressure filters function in the same fashion as gravity filters except that the filters <br />are constructed from horizontal, cylindrical pressure vessels. Pressure filters from <br />most manufacturers use the same chemicals and media described above for <br />gravity filters, and the remainder of that section applies except that intermediate <br />pumping is not required. The well pump can provide the pressure required to pump <br />the water through the filter and into the ground storage reservoir. <br />Some manufacturers (e.g. Filtronics) utilize a proprietary media that can be <br />operated at a higher hydraulic loading. The advantage of this is that the filters and <br />building can be smaller. The actual filter rate is determined through pilot testing, <br />but is typically 10 gpm/ft. These plants also require shorter backwash times, <br />thereby reducing the volume of backwash water generated, and correspondingly, <br />results in a smaller backwash reclaim tank. Several cities in the vicinity utilize <br />Filtronics plants including Coon Rapids, Moundsview, Blaine, and Anoka. <br />Water Treatment Plant Study 14 13843.000 <br />