Hennepin County

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PROJECT QUESTION: Concerning MCES Diversion System

Question:
It is our understanding that bid item 28-inch HDPE PIPE SEWER with Note #52 is to represent the necessary LF of MCES-FM Diversion piping system regardless of number of pipes used to meet flow and/or redundancy requirements. It is our understanding from spec section 18 - MCES Special Provisions sub-section 01569 that to meet flow requirements we must use either single 24-inch ID minimum or dual 16-inch ID minimum piping (not including redundancy), and to meet pressure requirements the piping must be 200 psi rated which requires DR 9 or 11 HDPE piping depending upon polyethylene characteristics. Per discussions with suppliers 28-inch HDPE DR 11 piping only has a 22.6-inch ID while 28-inch HDPE DR 15.5 (or larger DR #) is required to meet the 24-inch ID minimum requirement. Please clarify if 28-inch HDPE piping will be permitted as a single diversion pipe, or whether we will be required to increase up to a 30-inch HDPE DR 11 pipe in order to meet both the flow and pressure requirements of spec section 01569?

Response:
The Sewage Diversion System design is the requirement of the Contractor and the system must meet the requirements for both pipe minimum ID (single 24-inch or dual 16-inch) and required 200 psi pressure rating. The Contractor must determine what size of nominal HDPE and necessary DR are required to meet both the pipe minimum ID and the pressure rating requirements. The 28-inch nominal size call-out within the bid item and associated note #52 may be disregarded and Contractors shall size their planned diversion piping according to the specification requirements.