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477 Temperance Street | St. Paul, MN 55101 | (651) 286-8450 Building a legacy –your legacy. Equal Opportunity Employer | wsbeng.com Technical Memorandum To: Sue Polka, PE City Engineer/Public Works Director City of Arden Hills From: Greg Johnson, PE Ray Theiler, EIT WSB & Associates Date: June 2, 2017 Re: TCAAP Development –Water System Model Review City of Arden Hills, MN WSB Project No.3450-000 As requested by the City, WSB has updated and calibrated the existing WaterCAD water distribution system model that was originally developed by Wenck Associates (Wenck). The model was updated and calibrated to verify the accuracy of the current and proposed conditions for the City’s water system. The recommendations for ultimate system improvements from the 2016 Wenck technical memorandum were also reviewed. The water model was updated to be consistent with the existing system and demands. An analysis of the future system was completed to service the projected demands from the future TCAAP development site and determine the future improvements that are required for the future water system. ORIGINAL MODEL SUMMERY Wenck developed a WaterCAD model to evaluate the adequacy of the City’s water system network to serve the proposed TCAAP development. The Wenck model primarily included existing trunk and lateral watermains along with future water system improvements associated with the extension into the TCAAP development site. In addition to trunk and lateral watermains, the Wenck model also included tanks, reservoirs, pumps, controls, and junction nodes throughout the City. The pumps represented the existing and proposed booster stations that supply water for the North pressure zone. The Wenck model includes reservoirs at each of the City’s interconnections to model the water supplied from the City of Roseville. The controls in the model were set-up to turn the booster pumps on and off based on hydraulic grades at various locations. This is not a typical method for operating a multi-zone water distribution system like the Arden Hills system. The Wenck model estimated the existing average da y water demands for each junction node, from the years 2004 through 2011, using meter data supplied by the City of Roseville. For the future TCAAP development, the Wenck model incorporated the Metropolitan Council’s Sewer Availability Charge (SAC) units to estimate the average day water demands. A factor of three times the average day demand was used to develop the maximum day demand. The Wenck model was calibrated using system pressures collected during hydrant flow tests from 1990 since current hydrant flow testing data was not available at the same time. It is critical to use current hydrant flow data when calibrating a water distribution system model because the frictional coefficient factors for watermain usually change (decrease in value) as the mains age. During the hydrant flow tests