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H:\ARDH\M20121694\2_Preliminary\C_Reports\Design Alternatives Memo\ARDH LS 10 Memo 10-08-20.docx MEMORANDUM Date: October 8, 2020 To: Todd A. Blomstrom, City Engineer/Public Works Director From: Seth A. Peterson, PE Subject: Lift Station 10 Arden Hills, Minnesota Project No.: M20.121694 Introduction Lift Station 10 is a wastewater pumping station in the City of Arden Hills, located at 3804 North Cleveland Ave, on the east side of the street and just south of the County Road E2 West and Cleveland North intersection. The current duplex submersible pump wet well/valve vault station was constructed in 1989. In the wet well side of the station are two Hydromatic submersible pumps with 3-horsepower motors, designed to pump 100 gallons per minute each. Flow exits the station through a 4-inch PVC force main which runs for approximately 976 feet before discharging into a trunk sewer manhole at the corner of County Road E2 West and New Brighton Road. Lift Station 10 is over 30 years old and is in need of rehabilitation. One of the main concerns with the current configuration is flooding of the upstream manholes that occurs due to the operating elevations in the existing station. The invert of the gravity pipe which enters the wet well sits 1.12 feet above the structure invert. This does not allow enough depth f or the pumps to be adequately submerged per the manufacturer’s recommendations while also having an operating depth shallow enough to prevent wastewater from backing up the influent gravity pipe and into the first few upstream manholes during normal operat ion. One of the main goals of this project is to eliminate or at least minimize this backup. Based on the City’s comments and additional information about the station provided to Bolton & Menk, three main options for the project are considered: rehabilitation of the existing lift station, replacement of the existing submersible station with one of a similar type, or replacement of the existing station with a small prefabricated grinder station and new small - diameter force main.