Administration - Jon Haukaas, Public Works Director
Title
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Approve a Contract Amendment with TKDA for Professional Engineering Services for the Lift Station 13 Force Main Project, Project No. 21-30
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Executive Summary
Staff requests Council approval to amend the contract with TKDA for professional engineering services to expand the scope of the Lift Station 13 Force Main Project, Project Number 21-30.
Background
The City Council approved a contract with TKDA on February 1, 2021 with Motion 21-29 to investigate preliminary design, prepare a report and plans and specifications for Lift Station 13 and its associated force main on the means, methods and details of:
• How to best rehabilitate the existing 4,500 linear feet of in-place 20” diameter force main which runs from Lift Station 13, located just south of 99th Court on Naples Street to the intersection of the I35W Service Road and 93rd Avenue.
• Installing a second, redundant force main along the above route.
• Modifications to Lift Station 13 and the downstream receiving manhole at 93rd Avenue needed for operating the new redundant force main in conjunction with the rehabilitated force main.
• How to best operate and utilize the two force main lines upon completion of the construction and rehabilitation project.
At the initial scoping meeting between TKDA and City staff, the original project scope was expected to be a rehabilitation of the existing force main and installation of a new redundant force main by utilizing trenchless methods. During the preliminary design process and preparation of the report, a second meeting with TKDA and City staff was held to discuss TKDA’s initial findings. At the meeting it was determined that the project goals and results could be significantly improved by revisiting key assumptions in the original project scope regarding rehabbing the existing force main and installing a new redundant force main via trenchless methods. The findings were as follows:
• Installing a new force main via trenchless methods would likely not be feasible after TKDA talked with trenchless pipe contractors about the preliminary design. The large 20” diameter of the force main, shallow depth, high water table and soil conditions meant that conventional trenchless methods, such as directional drilling, were likely to have issues that would make trenchless methods likely to suffer failures such as sinkholes and blowout of the drilling fluid. The trenchless contractors recommended that the force main be installed by conventional open cut methods.
• Installing the new redundant force main by open cut methods makes it viable to install two new force mains in the same trench excavation. This makes rehabbing the existing force main, with its attendant concerns about structural integrity and being able to successfully clean and rehab it without issues, a less attractive option. It was decided that for a reasonable cost increase, abandoning the existing force main in place and installing a new dual force main system by open cut methods would provide the City a better product with less potential for future problems. In addition, the dual force main would now be within the Naples Street road corridor and there would no longer be a portion of the existing force main running under the Park and Ride parking lot.
• Changing the plan to have a dual force main from the north side of 95th Avenue to 93rd Avenue into a single gravity sanitary sewer would eliminate the need to have dual force mains cross under 95th Avenue. A gravity sanitary sewer under 95th Avenue would also benefit the City by eliminating any potential for a future catastrophic force main failure under a major county highway.
In addition, it was determined that Lift Station 13 should be upgraded fully to match the new City standard lift station design. This added a new control building, a rehab of the lift station wet well and addition of an influent grinder pump to the project scope.
The above changes to the project scope will result in a better overall product for the City and eliminate some key concerns that were discovered in the initial pre design phase with constructability and overall reliability of the system. These changes do come with additional construction costs. The estimated construction costs of the original scope of rehabbing the existing force main and installing a second redundant force main was approximately $1,800,000. The preliminary estimate for the new project scope is approximately $4,700,000.
With this new scope change in the project, there is the need for significantly more engineering design time to prepare plans and specifications and TKDA has requested an amendment to the original contract. Staff has reviewed the requested amendment in detail and is in agreement that the costs are reasonable and justified.
City Council is asked to approve a contract amendment in the amount of $160,000.00 to cover the expanded scope of work.
Strategic Plan Relationship
This project aligns with the City’s strategic plan goal of well-maintained infrastructure by providing high quality sanitary sewer infrastructure.
Board/Commission Review
Not required.
Financial Impact
With approval of this amendment, the budget for this phase is as follows:
Initial contract $110,100.00
Approved Contingency $ 11,010.00
Contract Amendment $160,000.00
$281,110.00
The funding source for these improvements will be the Sanitary Sewer Utility Enterprise fund and sufficient funding is available.
Public Outreach/Input
None required.
Staff Recommendation
By motion, approve the amendment the contract with TKDA for additional services in the total not to exceed amount of $160,000.00, bringing the total approved project budget to $281,110.00, and authorize the City Manager to sign the amendment to the contract.
Attachment List
Project Map
Amendment to the Contract