As City Council may recall, on May 4, 2019 the City’s WWTP had a section of buried 20” ductile iron pipe rupture resulting in a significant sewer spill. Subsequent to staff’s inspection of the pipe, it was determined that the interior of the pipe contained major corrosion characteristics that caused the pipe failure. Upon further investigation of additional sections of pipe, it was identified that these sections contain corrosion characteristics as well. The pipe was installed in 1988 and is used to transfer effluent from aeration basin/tank #1 to the plant’s headworks for preliminary treatment of the effluent. The project scope of work for phase 1 included subsurface utility engineering (SUE), to determine the location of existing utility lines, electric power cables, and potential utility facilities that were not identified in the plant’s as-built drawings. The installation of a shut off valve directly on the outside of the aeration tank and installation of temporary piping to get aeration basin/tank No. 2 back on line. Once the plant was operating at full capacity, work started on replacement pipe runs from aeration basins/tanks No. 1 and No. 2 and the installation of valves. Once completed, all of the original pipes were either removed or left in place, capped and filled with grout to avoid soil collapse below the newly installed replacement pipes. Finally, existing pipes connected to aeration basin/tanks No. 3 and No. 4 and the Schreiber tank were visually inspected and ultrasonically field tested to determine what type of work if any, might be needed such as pipe lining and/or pipe replacement. Subsequent to the Water Reclamation Facility Gravity Main Condition Assessment completed in April of 2020 by Reiss Engineering, it was recommended that the remaining pipes on the east side of the plant should be monitored annually utilizing the ultrasonic field testing process or lined with cured in place pipe (CIPP). Staff elected to proceed with the recommendation to City Council to proceed with the CIPP for aeration basin/tanks No. 3 and No. 4 and monitor the Schreiber tank pipe.
Subsequent to the completion of pipe and valve work on the east side of the plant, consultants familiar with the plant’s design layout and operational process where directed by staff to begin performing a pipe condition assessment analysis for all pipes installed on the west side of the plant due to the age of the pipes as well as the corrosive environment the pipes are subject to. A task order was present and approved for this phase by City Council on May 19, 2020 and the notice to proceed was issued to the engineer the following day.
On October 18, 2021 the 2020 WWTP Process Piping Condition Assessment – Phase II final report was submitted to the City. The recommendations section of the report page IV are as follows:
Based on the information above and obtained in this study, the tested segments of the force main and gravity piping that have less than 100% remaining wall thickness are Item 2 (UTT-4) at 79%, Item 3 (UTT-5) at 72%, Item 4 (UTT-8) at 74%, Item 6 (UTT-13) at 77%, Item 7 (UTT-16) at 35% and Item 8 (UTT-18) at 92%. The following sequence of pipe replacement is recommended based on the results of this condition assessment.
FY-2022 – Item 7 (UTT-16 at 35%), It is recommended that the City proceeds with the replacement of the 24” DIP effluent piping (approximately 60-feet) from the Oxidation Ditch No. 2 to the 48” MLSS piping (see location map above and Appendix C). Due to the MLSS continual flows, a single linestop just to the east of the wye from the 48-inch MLSS shall be installed by the Rangeline Group (Contact: Michael Mainelli at Mike@rangeline.com). Once installed, this will allow to isolate the 24-inch effluent pipe so the City’s As-Needed-Misc-Pipeline-Contractor can cut, remove and replace the pipe. The City’s As-Needed-Misc-Pipeline-Contractor shall also install a 24-inch gate valve just past the linestop location, this will facilitate the removal of the linestop and allow the 24-inch effluent line to be closed down in the future. It is also recommended that prior to returning the Oxidation Ditch No. 2 back into service, the City shall inspect the 24-inch horizontal and vertical flange effluent pipe inside the Oxidation Ditch No. 2 for possible leaks and defects.
Long Term – Continued monitoring of Item 2 (UTT-4) South 30” RAW Influent, Item 3 (UTT-5) 10” FM, Item 4 (UTT-8) 10” FM, Item 6 (UTT-13) 54” MLSS and Item 8 (UTT-18) 36” MLSS. The remaining wall thickness are 79%, 72%, 74%, 77% and 92% respectively. It is recommended that the City continues to monitor these five force main and gravity pipes, every two to three years with the UTT testing methodology. If the remaining wall thickness of the piping falls below 50%, or using a more conservative approach at 60%, then it is recommended to rehabilitate or replace the piping. The City should implement a policy between the Public Works Department and the WWTF staff to assure that the two to three year time frame is adhered to.
APPENDIX C
As a result, staff started the design phase of the report’s recommendations to replace aeration ditch pipe No. 2 and install valves on aeration ditch pipe No. 1 and No. 2.
On April 22, 2022 six (6) sealed bids were opened and announced by the City Clerk. The base bids ranged from $278,850 to $459,291.44 and $364,800 to $573,861.44 when bid alternate No. 1 is added to the amount. Subsequent to the engineer’s review of the bids submitted it's been determined that KRI is in fact the lowest bidder. Please see the attached Engineer of Record recommendation letter. In addition, staff has worked with KRI on several utility projects. All of which, were completed on time and either at or under the project budget.
The main elements in the proposed scope of work for this project include:
1. 60 linear feet of 24” diameter water main pipe.
2. The installation of two 24” line stops.
3. The installation of two 24” inch valves.
4. The installation of 24” fittings, boxes, and pipe joint restraints.
5. Survey Work
Bid alternate No. 1 work includes the installation of a line stop and 24” valve on pipe No. 1.