R2011-57 AUTHORIZING AMENDMENT TO AGREEMENT WITH HANSON PROFESSIONAL SERVICES, INC.

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i . APPENDIX B A Summary of the Major Construction History of Lake Decatur Dam The City owns and operates the Lake Decatur Dam located on the Sangamon River just west of Business Route U.S. 51. Built in 1922, the dam provides an impoundment for the City's source of drinking water. In 1955 bascule gates were added to the concrete spillway to increase the lake level from elevation 610 to 614.5. The following table summarizes the history of major construction projects for the Lake Decatur Dam: Year Activity 1922 Original Construction 1950's Fish ladder removed 1954-55 Flashboards removed and bascule gate installed Sluice gate replacement and trash racks installed 1955-1996 Sluice gates reconditioned 1955-1996 Resurfaced downstream face of spillway access platform 1995 Overlay laced on downstream face of spillway 1996 Shotcrete applied to left and right abutment walls 1998 North bascule gate hydraulic cylinders refurbished (Cylinders 1 thru 4) 2000 South bascule gate hydraulic cylinders refurbished (Cylinders 5 thru 8) 2000 Approximately 30 concrete panels on upstream slope of right embankment replaced 2000 Pile cap and all concrete panels along the downstream right riverbank training wall replaced. 2001 New joints saw cut into spillway overlay to match original dam joints 2001 Spalling along upstream face of outlet works and downstream face of spillway patched 2001 New riprap placed downstream of stilling basin and along the left river bank 2004 New sluice gate lift mechanism at the lower tail water dam 2005 S allin along upstream face of outlet works structure patched A major rehabilitation project began that included: replacement of the 8 hydraulic 2010 cylinders operating the 2 bascule gates; repairs to the bascule gates; rehabilitation of the sluice gate machinery; and concrete patches using preplaced aggregate. A test patch is to be placed on the downstream side of the dam. Page 15