Laserfiche WebLink
ti O�.Df C9 <br /> — G <br /> V 7e <br /> '/[LINO�Y <br /> May 27, 1998 <br /> PUBLIC WORKS MEMORANDUM <br /> NO. 98 - 35 <br /> MEMORANDiJM TO: Honorable Mayor and City Council <br /> FROM: James L. Williams, Jr., City Manager �� <br /> Bruce A. McNabb, P.E., Director of Public Wor� <br /> John A. Smith, Water Production Manager <br /> Stephen P. Swanson, P.E., City Engineer� <br /> SUBJECT: NWTP Filter Media Replacement Engineering <br /> City Project 9816 <br /> The filter media at the City's North Water Treatment Plant (NWTP) must be replaced in the <br /> near future. The filter media consists of layers of anthracite and different sized gravel and sand, <br /> and is about 44 inches thick in the filters at the NWTP. These materials filter out the remaining <br /> silt from the water after it has gone through the primary and secondary treatment basins. This <br /> work must be done to keep the plant in compliance with Illinois Environmental Protection Agency <br /> (IEPA)turbidity standards and avoid having to put the plant out of service. <br /> The replacement of the filter media was identified as a need by Black& Veatch in the Phase I <br /> Report for the North Water Treatment Plant Expansion or Replacement Study completed in <br /> August, 1997. It was recommended by Black & Veatch that media in four of the eight filters be <br /> replaced as soon as practicable. This would enable the plant to remain in service while new filters <br /> are being built and to maintain compliance with IEPA turbidity standards. This work cannot be <br /> delayed until a final decision is made regarding a possible transfer of the NWTP to <br /> Archer-Daniels-Midland Company. ' <br /> The media was last replaced in 1987 (approximately ten years after the plant first started <br /> operating) at a cost of about $149,000. The media has been displaced and partially lost over the <br /> last ten plus years causing the media depth to be at less-than-specified levels. This occurs through <br /> the standard backwash cleaning operation of filters which is done approximately once every 64 <br /> hours, or about 140 times per year. In addition, the filter media has become encrusted with <br />