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• <br /> • Scope of Services <br /> Continued <br /> current GIS data. (As-built data is regularly updated in the City's GIS database, <br /> but not necessarily in the InfoSWMM model.) <br /> b. Repair/reconstruct model for 17th Street Interceptor from City GIS data. <br /> c. Incorporate/verify construction record drawing data for Sewer System"I", <br /> Sewer System"J",and Lift Station#4, and#8 force mains,as provided by the <br /> City. <br /> d. Obtain additional regulator structure data from the City and incorporate into the <br /> model. <br /> e. Determine if additional model elements are needed due to regulator structures. <br /> f. Model backwater effects in the downstream 17th Street Interceptor lift station,by <br /> assuming a constant flow rate (derived from modeling done previously (for <br /> Sewer j),provided by the City.The lift stations will be more accurately modeled <br /> in Phase 2 of this scope of services. <br /> g. Run the InfoSWMM hydrologic module with the full ten (10) year record of <br /> precipitation data the hydraulics module for current sewer conditions. <br /> h. Complete a flood frequency analysis at the flood-prone area(s) to identify peak <br /> storm water runoff rates for the statistical 1-year, 2-year, 5-year, 10-year, 50-year, <br /> and 100-year flood frequencies, plus the June 9, 2010 event. <br /> i. Select runoff hydrographs of the historical storms to match the peak runoff from <br /> the statistical flood frequencies, so these design storms will be used as input <br /> hydrographs to analyze and compare alternative sewer system scenarios using a <br /> common storm event.Based on the level of flooding during these design storms, - <br /> design storms with different flood frequencies may be substituted for these <br /> design storms. <br /> 3. Model Alternate Sewer System Scenarios <br /> Otak will model and analyze the combined sewer system north of the 17th Street <br /> Interceptor, using the design storm developed in Task 10.1. Otak will create a flooding <br /> characterization map for each scenario modeled,by color coding the flood frequencies <br /> along the sewer system at three different levels of concern.The three levels of concern <br /> are the frequencies when the sewer system (1) is just beginning to surcharge above the <br /> crown of the sewer pipes, (2) surcharges to a level that would flood basements, and (3) <br /> surcharges to a level that would flood the street intersections. The following sewer <br /> system scenarios will be analyzed: <br /> a. The current sewer system as it existed on June 9,2010 during the flooding. <br /> b. The current sewer system with the current hospital construction completed. <br /> c. Sewer system improvement with the Sewer L project completed as originally <br /> designed. <br /> d. Sewer system improvement with the Sewer L project and augmented with a high <br /> flow bypass pipe on Lombard Avenue, from 16th Street to 17th Street, to increase <br /> sewer capacity by removing a bottleneck at this location. <br /> City of Everett—North Everett Combined Sewer System Evaluation 5 <br /> otak <br /> IC:\project\31500\31520\Contract\Amendll_NAreaFlooding\31520 Everett Sewer Amendment 1 Scope082510.doc <br /> 7 <br />