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16 <br />Subtask 211- Extreme Event Modeling. The purpose of this task is to complete a modeling <br />analysis of "extreme event" impacts on Sewer "M" design. The following subtasks are included: <br />211.1. Project Management - same as in current agreement. <br />211.2. Meetings - One 1-hour phone meeting to discuss results. <br />211.3. Model Recent Rainfall Events. <br />a. Apply 6/9/2010, 8/29/2013, 9/5-6/2013 rainfall events to the Sewer <br />Phase 1 and Phase 2 alternatives. <br />b. Compare results to design event. <br />c. Note which event is worst. <br />d. Note if CSO is predicted for any of the events. <br />e. Assumes 6 simulations. <br />211.4. Mitigate Impacts <br />a. If additional basement flooding occurs, attempt to mitigate with additional <br />system improvements (for the worst -case scenario of the three storms). <br />b. Otherwise, summarize the additional street flooding from stormwater. <br />c. Assumes 2 simulations. <br />211.5. Test Grand Avenue Trunk for Surcharging <br />a. Test to see if the existing Grand Avenue trunk surcharges under Phase 1 <br />conditions with: <br />1. The single 36-inch, stormwater HDD installed. <br />2. The low -flow connection between the stormwater and combined systems <br />closed. <br />b. Assumes 1 simulation. <br />211.6. CSO Compliance with Once -Per -Year Requirement <br />a. Apply 69-storm series, adding the recent 8/29/2013, 9/5-6/2013 rainfall <br />events. <br />b. Run simulation of Single HDD Alternative with Sewer "M" Phases 1 & 2 <br />completed. <br />c. Identify predicted CSO events. <br />211.7. Summarize Findings - in brief memorandum, using a table or bullet -point format. <br />211.8. QAIQC <br />Deliverables: <br />1. Brief memorandum summarizing findings of model runs and conclusions, using a table or <br />bullet -point format. <br />Subtask 212 - Refinement of Alternatives for Single HDD vs. Utility Bridge <br />212.1. Project Management - same as in current agreement. <br />212.2. Meetings <br />Version 3 15 <br />4/29/14 <br />137 <br />