R2003-88 AUTHORIZING THE EXECUTION OF CONSULTING SERVICES AGREEMENT

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� Task 3: Confirm Basic Desi�n Parameters for Off-Stream Reservoir and Dred�posal Site MWH will confirm basic design parameters needed for the computation of volume and area requirements far ' off-stream storage reservoir and dredge disposal facilities. Specific activities to be completed as part of this task will include: Sub-task 3.1 —MWH will review the scope of the proposed dredging program with City staff. Consideration will be given to the proposed near-term dredging program and the potential for maintenance dredging at some time in the future. Results from this review will be used to determine project active reservoir storage volume for a 50-year planning period. Sub-task 3.2 — Based on the results of Task 3.1, MWH will project probable reservoir yield from Lake Decatur for drought conditions with an annual probability of occurrence of 4%,2% and 1%. Sub-task 3.3—MWH will review recent projections of water withdrawal requirements for Lake Decatur with the City and assist in the selection of requirements to be used in evaluating off-stream storage requirements. MWH will perform a comparison of the selected water withdrawal requirements and projections of reliable reservoir yield developed under Sub-task 3.2. Results from the comparison will be used to confirm the design volume required for an off-stream storage reservoir intended to supplement existing supplies during drought conditions with an annual probability of occurrence of 4%, 2% and 1%. Sub-task 3.4 — MWH will perform a preliminary analysis of excavation/embankment options to deternune the approximate land area required for the off-stream storage reservoir options being considered. MWH will document the results of this analysis and analyses completed under Sub-tasks 3.1, 3.2 and 3.3 in a technical memorandum. A draft of the technical memorandum will be prepared for review with the City. Following receipt of comments, MWH will revise the memorandum to serve as a chapter in the final feasibility study report. Sub-task 3.5 — Results of previous investigations of sedimentation and dredging options for Lake Decatur are documented in the Illinois State Water Survey Contract Report 2002-09 Sedimentation Survey of Lake Decatur's Big and Sand Creek Basins, Macon County, Illinois (Bogner, 2002). MWH will review this document, as well as supplemental information provided by the City related to past and proposed dredging activities, to define the likely settling and environmental characteristics of the dredge material that will require disposal in the proposed disposal facility. These characteristics will be used together with the City's estimates of dredge disposal volumes as the basis for preliminary sizing of the proposed, new dredge disposal site. Depending on the completeness of available data, MWH may recommend that the City consider supplemental material sampling and testing. MWH will document the results of this analysis in a technical memorandum for review by the City. Following receipt of comments, MWH will revise the memorandum to serve as a chapter in the final feasibility study report. Task 4: Sitin��Analysis for Dred e�D�isposal and Off-Stream Stora�e Facilities Based on consideration of technical factors, consideration of anticipated regulatory and permitting requirements, and input from City staff and the Water Resources Advisory Committee regarding non- technical issues, MWH will develop three options for siting of a new dredge disposal facility and a new off- stream storage reservoir. Options may include adjacent siting of both facilities or separate siting of the dredge disposal and off-stream storage reservoir facilities. Key elements of the siting analysis will include the following sub-tasks. 12 Consulting Services(CPFF)(Rev. 1-14-2003)