R99-73 AUTHORIZING THE EXECUTION OF AN AGREEMENT

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Proiect Obiective and General Scope of Work I. Proiect Obiective The City of Decatur water supply experiences periodic elevated nitrate levels above the 10 mg/I primary drinking water standard. The major source of the nitrate contamination is runot�' from a mainly agricultural watershed into Lake Decatur, the source water supply for the City. The City is under a Letter of Commitment (LOC) with the Illinois Environmental Protection Agency to be in compliance with the drinking water standard by April 15, 2001. As a solution to the nitrate problem, the City is considering using a low-nitrate natural source of water for blending. However, this source of water may not prove to be viable for blending pending the results of further studies. Therefore, the City may have to install nitrate treatment in the South Water Treatment Plant in the form of ion exchange (IX) or reverse osmosis (RO) as a method of compliance with the 10 mg/1 drinking water standard, and the City wants to determine the various associated costs and advantages/disadvantages to the two treatment methods. Ezisting reports available for use in this study are: Water Resources/Storage/Production Study, Haria Engineering, August 1996 ' Feasibility Study of Lake Decatur Watershed 1�Ianagement Alternatives I for Nitrates, Environmental Planning and Economics, Inc., July 1997 '� Addendum No. 1 to the Feasibility Study, Black& Veatch and Environmental Planning and Economics, Inc. June 1998, Revised August and September 1998 City of Decatur Reverse Osmosis Treatment Facility, Strand Associates Inc.Brian Hackman, November 1998 Safe Drinking Water Act Compliance Study, Black& Veatch, January 1999 The following are assumptions that will be used for the study: ■ A total treated flow rate of 24 mgd (million gallons daily) from the water treatment plant. • A mazimum of 12 mg/1 (first assumption) and 16 mg/1 (second assumption) of nitrate in the source (lake)water. • A maximum of 9 mg/1 nitrate after treatment in finished (drinking) water. • Use of the IX for blending during times of nitrates > 9.5 mg/1 for a period of 90 days. • Use of RO for blending both during times of high nitrates and during at least 6 months of the year for TOC, THM-HAA, and taste and ador(T & O) control.