As stated in the previous City Council request for consideration of approval for engineering services related to this request, on May 4, 2019 the City’s WWTP had a section of buried 20” ductile iron pipe rupture. Subsequent to staff’s inspection of the pipe, it was determined that the interior of the pipe contained major corrosion characteristics that caused the pipes failure. Upon further investigation of additional sections of the pipe, it has been identified that these sections contained corrosion characteristics as well. The pipe was installed in 1988 and is used to transfer influent from aeration basin/tank number two (2) to the plants headwork’s for preliminary treatment of the material. Another 20” ductile iron pipe was installed for aeration basin/tank number one (1) as part of the 1988 project. None of the four aeration basins/tanks had shut off valves installed at their exterior sections where the basins/tanks connected to the two 20” pipes.
As described in Task Order No. 36 from Stroud Engineering Consultants, Inc. the following is the scope of work included in this phase of the project.
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The installation of a shut off valve directly on the outside of the aeration basin/tanks number three (3) and number four (4). Basin/tank number one (1) and number two (2) valves where installed during temporary repair work at the site.
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The installation of 20” ductile iron pipe from aeration basin/tank number one (1) and number two (2) to the plant headworks.
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Cap and fill with grout the existing abandoned 20” pipe.
It should be noted that all ductile iron pipe and fittings utilized in the construction have a interior protective coating to eliminate the possibility of pipe failure due to the interior metal corrosion process that occurred in the existing pipe. Finally, all of the pipe and fittings are to be bedded in a manner as to be visible and accessible to repair/repairs without the use of OSHA trench and confined space entry requirements.