www.mymanatee.org
Manatee County Government Administrative Center Commission Chambers, First Floor 9:00 a.m. - June 17, 2014
REVISED June 17, 2014 - Regular Meeting
Agenda Item #87


Subject
Lake Manatee Phase 1A Dam Repair Status Report

Briefings
None

Contact and/or Presenter Information
Mark Simpson, Water Division Manager - ext.5258

Action Requested
This is a project status report only. No Board action is requested.

Enabling/Regulating Authority
N/A

Background Discussion

On February 14, 2014, a press conference was held in the Board Chambers at which preliminary results were shared from a supplemental investigation by Carollo Engineers, Manatee County Utilities Engineer of Record, and their subconsultant AMEC Environment & Infrastructure which showed a need for priority repairs to the Lake Manatee Dam. Additional testing defined the scope and design for the needed priority repairs, Phase 1, to be the re-establishment of the dam cutoff wall along 3300 feet of the dam using two technologies, Trench cutting Remixing Deep (TRD) and Jet Grouting (JG) methodologies. Hayward Baker, Inc. of Tampa, Florida was selected to perform the work and Notice to Proceed was issued on April 2, 2014.

The highest priority portion of the Phase 1 repair, Phase 1A, includes the cutoff wall beneath the approach spillway and 300 feet south and 350 feet north of the spillway. The contract called for completion of Phase 1A by June 14th to allow the primary spillway to be utilized to pass elevated flows due to the onset of the rainy season. Phase 1B improvements, the remaining 2250 feet of cutoff wall, are to be completed by October 31st. Phase II improvements were not included in this contract and will require remediation of identified voids beneath the downstream spillway structures, unconsolidated soils next to the downstream training walls, and a pressure relieving drainage system for that area.

Funding for the project at this time comes from Utility System Reserves. Long-term financing for the project will be considered as part of the upcoming budget process.

Monthly status reports have been provided to the Board relaying the progress on individual project tasks. Mobilization and the significant preparatory sitework required for the dam crest proceeded in an orderly and rapid pace and was a credit to the organizational abilities of Hayward Baker, Inc., and their subcontractor (Woodruff & Sons). (The current status of the cutoff wall will be presented to the Board.)

(The jet grout portion of the cutoff wall was initiated north of the spillway with the TRD starting south of the spillway. Greater than expected hard subterranean layers were encountered with the TRD south of the spillway and hope for productivity was not achieved. However, 380 feet of TRD cutoff wall south of the spillway has been completed and the TRD operation has moved to the north side of the spillway. All of the planned jet grout columns on the north side of the spillway have been completed. Installation of the JG columns south of the spillway is underway and the JG columns beneath the approach slab are also on schedule to be complete by June 14th.

An unknown sheet pile wall along the dam crest in the footprint of the proposed TRD wall extending 180 feet north of the spillway was discovered on May 22nd. Re-engineering the cutoff wall in this area was required. Additional sitework preparation resulted in additional time and cost, such that the total 350 feet TRD north of the spillway may not be accomplished by June 14. The consulting engineer is evaluating whether operation of the spillway has to be delayed.)



County Attorney Review
Not Reviewed (No apparent legal issues)

Explanation of Other


Reviewing Attorney
N/A

Instructions to Board Records
N/A

Cost and Funds Source Account Number and Name
401 099 002 599000 Utilities Operating Fund - Reserves

Amount and Frequency of Recurring Costs
14,091,190.00. Non-recurring