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3) The single set of catch basins reduces inlet capacity at Morton Ave. When increased to 2 catch basins on either side of the road, a more substantial reduction in peak water surface elevation is observed. The reduced depths narrow the spread of water in the street and brings the design closer to compliance with typical gutter spread standards. 4) Option 2 is recommended for the maximum benefit at the Morton Avenue low point. The increase in pipe size across Main St to the connection with the 18" pipe provides additional flood reduction benefit above the 10-year rainfall event. Furthermore, the added inlets will help protect the adjacent properties from flooding during high intensity, short duration rainfall events. 5) A surge pond in Bailey Point Nature Preserve is needed with option 2 to allow back flow of water out of the storm sewer system for temporary retention to reduce the flow rate and the amount of sediment at the discharge point to the Mississippi River. VI. Opinion of Probable Cost Estimated project costs were developed for the 2 options including improvements along Main Street and Morton Avenue. Costs for peak flow mitigation are also included in these options. The Baily Point Nature Preserve storm pond option is estimated at a cost of $39,000. The perforated pipe option was estimated to cost approximately $66,000. Given these costs, we have included the cost of this downstream ponding rate control in Option 2 below. We have also included one SAFL Baffle in options 2 and 3 to improve sediment reduction prior to the discharge point. Table 4 is a summary of estimated project costs. A full breakdown of costs is included in Appendix A. Table 4: Summary of Opinions of Probable Cost. Opinion of Probable Cost Summary Option 1 - Do Nothing $0 Meets 10-year Design, No flood improvement Option 2 $245,000 Addresses flooding issue and discharge rate Option 3 $524,700 Eliminates property damage risk, still minor flooding VII. Funding & Assessments Funding for the project could come from a combination of special assessments and the city storm water utility fund. It has been determined that the full cost of Option 2 could be paid through the Storm Water Utility fund without the use of special assessments. However, the City could elect to follow the special assessment procedure regarding any direct additions to the system should they choose. Special assessments could be levied in accordance with the City Special Assessment Policy which states the proposed improvements can be assessed to the Service District based on gross area and a weighting factor based on zoning type. The improvements needed to resolve the flooding at the low point on Morton Avenue would be distributed over all of the drainage area flowing to the low point sub -catchment area. The improvements at the system discharge point at Bailey Point would be distributed to the full sub - catchment area contributing water to the discharge point. Prepared by: Bolton & Menk, Inc. Opinion of Probable Cost Morton Avenue Drainage Study I OR11.127809 Page 7