R2009-52 AUTHORIZING AMENDMENT TO AGREEMENT WITH HANSON PROFESSIONAL SERVICES, INC.

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. { , The Lake Decatur Dam is a Class 1 structure, as classified by the Illinois Department of Natural Resources. This classification indicates that failure of the dam would have a high probability of causing loss of life or substantial economic loss. As a condition of the Operating Permit, the City is required to undertake annual inspections. On January 20, 2009, the City Council authorized a design services agreement with Hanson Pmfessional Services (of Springfield, IL)to develop detailed design drawings and prepare construction documents for a rehabilitation project to address the recommendations contained in the annual inspection reports for the past five years. The original scope of work for this agreement identified four general groups of improvements that were needed: 1. Repairs to the training wall between gated outlet works and spillway 2. Repairs to north and south sections of the spillway 3. Repairs to south abutment and training walls 4. Repairs to the gated outlet structure. Current Design Status As part of the design work, Hanson performed a detailed inspection of the dam and the mechanical components of the structure that contml the release of water and provide Lake Managers with the ability to control the elevation of the water level of the Lake. Hanson's inspections determined some items of concern: 1. The mechanical systems that raise and lower the sluice gates on the north side of the dam are in need of rehabilitation to assure reliable operation. The gears are showing evidence of extreme wear and are functioning beyond their useful life. This added work is the primary focus of the current amendment request. 2. The Bascule Gates which run along the top of the dam are raised and lowered by the means of large hydraulic cylinders. The cylinders on the north Bascule Gate are showing signs of serious deterioration, corrosion, and damage. The cylinders need to be replaced. The north gate is only operated during extreme water events. The cylinders serving the south Bascule Gate are in better condition but still in need of extensive repair or replacement. These cylinders are functioning beyond their useful lives. This work requires further review and is proposed to be added in a future amendment to be brought to the City Council by early summer. 3. Preliminary soundings of the river downstream of the dam shows some extensive erosion of the stream bed that may affect several pipe systems the City has in place and possibly the dam itself. Further review is needed of the preliminary information provided by Hanson and may require a future amendment to perform a detailed survey of the tail water pool downstream of the dam and model the erosion effects of the dam spillways. In addition to the work identified in Item 1 above, some of the added work is related to the seal replacements for the Bascule Gates and Sluice Gates along with the removal of nonfunctioning heating units that were originally designed to keep ice offthe gates. The heating units have not been operational for many yeazs. Experience has shown that it is not necessary to keep ice offthe gates. Page � 2