Motion to Finalize Scope of Proposed Work Fairview/Grand Sewer Project

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April 27, 2023 TO: Mayor Julie Moore Wolfe & Decatur City Council Members FROM: Scot Wrighton, City Manager RE: Motion to Finalize the Scope of the Proposed Fairview/Grand Sewer Project In October 2022 the City Council awarded a design engineering contract to AECOM for the proposed Fairview/Grand Sewer project. As a part of the project's early preliminary design, staff developed and examined several alternatives.The least costly and most practical alternatives were subsequently identified and labeled as Alternative 3 and Alternative 5a. Neighborhoods in the near west side of Decatur(either side of Route 48, lying north of US 36/Norfolk-Southern Railway line) are places where the city's sewer collection system suffers excessive infiltration and inflow of storm and ground water, and from storm pipes/inlets directly connected to combined sewers.The Fairview/Grand Sewer project separates storm and sanitary sewer flows(as the city has done in recent years in other parts of the city)to reduce and eliminate basement back-ups, reduce and eliminate combined sewer overflows, and to reduce total sewerage volumes discharged to the treatment facilities of the Decatur Sanitary District. Both Alternative 3 and Alternative 5a will separate storm and sanitary sewers north of the US 36/Norfolk-Southern Railway line.Alternative 3 keeps them separated by constructing a large storm sewer across Fairview Park that eventually discharges only storm water directly to Stevens Creek. In lieu of Alternative 3's storm sewer across Fairview Park,Alternative 5a would require the construction of a large storm water detention lagoon near Route 36 where rainwater would be stored until it could be discharged back into existing combined sewers in Fairview and then carried to the Sanitary District's facilities for treatment. Although the City Council approved the AECOM design engineering contract last October to keep the project moving,they also directed staff to consult with USEPA, TEPA,the city's water/sewer intergovernmental/grant consultant,the Sanitary District, and others, and to further refine the estimated project costs before deciding whether Alternative 3 or Alternative 5a should be adopted.At the time,the cost differential between the two options was close to $3 million dollars.Since October,the cost differential has shrunk to about$500,000(i.e., Alternate 3's estimated cost is about$500,000 more than Alternative 5a). The principal reasons for such a large reduction in the cost delta are two: 1) IDOT has allowed the city to use the Route 48 right-of-way to install the new storm sewer under the US 36/Norfolk-Southern Railway corridor,whereas the early estimates for Alternative 3 assumed the city would have to dig a new and expensive utility tunnel under the highway and railroad starting in the back parking lot of Fairview Plaza;and 2)the pumping, monitoring and treatment costs associated with permanently maintaining a large storm water detention basin east of the Green/Fairview intersection as part of Alternate 5a are substantial.