At the May 9, 2016 City Council meeting, Council approved the Airport's Pond D Storm Drainage System project. This multiphase project will enhance the Airport's ability to collect and convey storm water from the airfield, particularly areas between the main taxiway and runway, into the new detention Pond D complex and then pipe that water into Alkali Creek.  One of the construction phases was to bore a tunnel through the sandstone Rimrocks to get the storm water pipe from the Airport down to Sun Valley Road where it would hook into an underground pipe that drains to Alkali Creek. Soil bore tests taken at the top and the bottom of the proposed route indicated layered sandstone rock with compressive strengths of 2,134 psi to 3,420 psi and silty sand. In two past boring projects, soil with similar compressive strength was bored without difficulty.  Based on the test bores and the previous success with boring projects, directional drilling was specified.  The contractor, COP Construction, has drilled pilot holes at three different locations with a 10,000 psi bit to try to establish a boring route.  Unfortunately, they have continually hit a very hard layer of rock that has resulted in the failure of the drilling bits. They then drilled a hole using a 28,000 psi bit, only to have that drilling bit fail.  It is estimated that the rock that is being hit exceeds 30,000 psi in compressive strength. Subsequently, the contractor has exhausted all directional drilling options to drill through this hard rock layer and will need to move to a different drilling method that is more expensive.

This change order will change the drilling method to a Mud Motor Drilling method that uses a series of hard rock drills and fluid flow to transmit power to rotate the drill heads. This method requires specialized hard rock boring equipment and a fluid reclaiming system.  This process is similar to what is used for deep bedrock drilling in oil exploration.

Airport staff and Morrison-Maierle have reviewed the proposed drilling methods and costs associated with this additional work and found them to be acceptable.
 

City Council may:

• Approve Change Order One for the Pond D Storm Drainage System; or
• Decline approval and significantly delay the completion of the project.

The total cost of this Change Order is $444,014.68. This project will have multiple funding sources.  It is estimated that $265,945 of the project will be funded with Airport Improvement Program (AIP) entitlement grant funds, $29,945 with a local share match, and the balance will be paid for with $148,521 of Passenger Facility Charge (PFC) funds. Local share and local capital portions are available in the Airport's capital and PFC  accounts.

Staff recommends that the City Council approve Change Order One with COP Construction Company for the amount of $444,014.68.