Title
An Ordinance approving Change Order #1 to the On-Call contract with Wiedenmann Inc. for the installation of a leachate cut-off trench at the Resource Recovery Park, an increase of $26,337.51 for a revised contract price of $90,018.51. (PWC 11/27/18)
Body
Issue/Request:
An ordinance approving Change Order #1 to the On-Call contract with Wiedenmann Inc. for the installation of a leachate cut-off trench at the Resource Recovery Park, an increase of $26,337.51 for a revised contract price of $90,018.51.
Key Issues:
• The On-Call contract is based on set hourly personnel and equipment rates plus the cost of materials. The original contract modification was for an estimated price based on information known at that time.
• Lab testing of the Bentonite-Cement slurry using the local mix quoted by Wiedenmann, Inc. revealed that it would not perform in a way to prevent leachate migration. SCS Engineers worked with Geiger Ready-Mix to create a suitable mix. That mix was 55% higher in price.
• The contract realizes that the scope of each job may not be entirely known until work commences due to the involvement of buried infrastructure. The bottom of the trench was to be at bedrock, which was expected to be at 14 feet. The depth varied and was greater than 20’ at the center.
Proposed City Council Motion:
FIRST MOTION: I move for a second reading of an Ordinance approving Change Order #1 to the On-Call contract with Wiedenmann Inc. for the installation of a leachate cut-of trench at the Resource Recovery Park, an increase of $26,337.51 for a revised contract price of $90,018.51.
SECOND MOTION: I move for adoption of an Ordinance approving Change Order #1 to the On-Call contract with Wiedenmann Inc. for the installation of a leachate cut-of trench at the Resource Recovery Park, an increase of $26,337.51 for a revised contract price of $90,018.51.
Background:
SCS Engineers prepared a work plan to the satisfaction of the Missouri Department of Natural Resources (MDNR) to fix a leachate seep at the landfill. The agreed upon fix was to construct a cut-off trench, down to bedrock, partially filled with a bentonite/cement slurry to block subsurface seepage from reaching the ground surface of the embankment to the east. Subsurface exploration before the work would have either yielded very limited information or duplicate the work necessary to make the repairs. Based on these conditions and the immediate need to cutoff seepage thorough subsurface exploration was not conducted to pinpoint the limits of the seepage.
The trenching operation was observed by SCS Engineers, MDNR, and City staff. As underground conditions were revealed, engineering decisions were made during the excavation to adjust the amount and elevation that the bentonite/cement slurry would be placed. Due to the exploratory nature of this excavation and the presence of MDNR at the site, decisions were made on-site during construction. These decisions were made to meet MDNR requirements and to avoid duplicating the Contractor’s and thus incur even greater costs. It was imperative that the bentonite/cement form a homogenous impervious barrier. Additional bentonite/cement slurry was used due to the depth of the trench and location of groundwater seams observed during the repair process.
Impact/Analysis:
Once the bentonite/cement slurry pour was started, it needed to be completed to create the homogenous impervious barrier approved by MDNR to mitigate the violation.
Timeline:
Start: 9/17/2018
Finish: 9/24/2018
Other Information/Unique Characteristics:
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Presenter
David Lohe, Supervisory Engineer
Recommendation
Recommendation: Staff recommends approval of an Ordinance approving Change Order #1 to the On-Call contract with Wiedenmann Inc. for the installation of a leachate cut-off trench at the Resource Recovery Park, an increase of $26,337.51 for a revised contract price of $90,018.51.
Committee Recommendation
Committee Recommendation: The Public Works Committee voted unanimously 4-0 to recommend to City Council approval of an Ordinance approving Change Order #1 to the On-Call contract with Wiedenmann Inc. for the installation of a leachate cut-of trench at the Resource Recovery Park, an increase of $26,337.51 for a revised contract price of $90,018.51.