R2021-114 Resolution Authorizing a Professional Engineering Services Agreement with AECOM Technical Services, Inc. to Provide Preliminary Design Services for the Oakland and Grand Area Sewer Separation Study, City Project 2021-01

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ACOExhibit A-4 AECOM 312 938 0300 tel 303 East Wacker Drive 312 373 6800 fax Suite 1400 Chicago,IL 60601 www.aecom.com TASK 4: ALTERNATIVES ANALYSIS The previous three tasks will be used as the basis for developing and analyzing the following five (5) proposed alternatives for the proposed separate sewer system: Alternative 1 —Connect to existing drainage system in IDOT right-of-way (existing 60-inch diameter storm sewer in N. Fairview Avenue—Illinois Route 48) Alternative 2— Discharge directly to Stevens Creek(proposed parallel sewer to the existing 60-inch diameter storm sewer) Alternative 3—Connect to the existing drainage system (96-inch diameter sewer)just east of the Fairview Park Tennis Center Alternative 4—Connect to the existing drainage system both in IDOT right-of-way (N. Fairview Avenue— Illinois Route 48) and just east of the Fairview Park Tennis Center Alternative 5—Other(to be determined during the study) • Alternatives 2 through 4, and possibly 5, include total sewer separation. However, Alternative 1 is assumed to include only partial sewer separation, since the existing 60-inch diameter storm sewer may not have sufficient capacity to drain all of Basins 5/6. In this case, the existing Basin 5/6 hydraulic and hydrologic model may need to be updated to estimate th 1/1 reduction benefit, number of basement backups reduce , etc. to Basin 5/6 (see Task 7 allowance). • The existing combined sewer system will be converted to a separate sanitary system and that a new drainage system will be used to convey stormwater out of Basins 5/6 • Alternatives 2 and 3 will require the proposed storm sewer to cross the existing Norfolk Southern (NS) railroad tracks The alternatives analysis will also include the following: 1. Description, schematic layout, and engineer's opinion of probable construction cost 2. Obtaining utility records and performing a general utility evaluation to identify large diameter (20-inch diameter and greater) utility crossings. If required, potholing and field investigation will be performed using an allowance from Task 8. 3. Evaluation of NSRR permitting requirements. 4. Inspection of proposed connection points. Manholes at proposed connection points will be opened to confirm approximate existing sewer invert elevations to assist in confirming alternative feasibility. 5. Rerouting of known commercial/industrial/institutional private storm sewer connections to the proposed drainage system. 6. Identification of disconnections and rerouting of existing catch basins, inlets, and storm manholes to the proposed drainage system. 7. Recommend system rehabilitation based on the condition assessment of existing combined sewers. 8. Perform hydraulic analysis to determine if existing combined sewers are appropriately sized for conversion to sanitary sewers, and if low velocities/deposition of solids may be a concern. 9. Perform sizing of the proposed new storm sewers to meet the appropriate City design standards by utilizing a hydrologic and hydraulic model. 10. The alternatives analysis will not include green infrastructure (GI) or storage, since these items were already evaluated in AECOM's 2017 SCSAA, but the report (see Task 5) will summarize and refer to previously performed evaluation for GI and storage. 11. Confirming existing utility elevations during design will be critical to avoid conflicts during construction. While most of this work will take place during the next phase of the project, conflicts may impact the feasibility and cost of the proposed alternatives. Therefore, if necessary, AECOM will recommend critical existing utility locations for potholing and evaluate the results. The potholing will be performed by the City of Decatur through an 4