Overview
As a subcontractor, Ballard performed underwater construction work during the demolition effort of the seventy-five-year-old, 1,330-foot-long cantilevered bridge that transported Interstate 5 (I-5) traffic through Lakehead, CA. In addition to their aid in the demolition clean-up, Ballard also assisted in the removal of Unexploded Ordnance (UXO) from a failed demolition attempt.

Scope of Work
Demolition of the bridge took place in two phases, identifying explosives and then removal. After the first attempt failed due to damp explosives, Ballard was tasked with the recovery of these UXOs. The unexploded ordnance consists of RDX Linear Shape Charges (LSCs), ranging in size from seven to thirty inches in length at 600, 900, 1,200, and 2,000 grains per linear foot. In addition to the LSCs, Ballard commercial divers removed the prima cord “pigtails,” non-electric booster caps, and detonators. The first attempt collapsed four out of the five spans into the Sacramento River, with the remaining five spans successfully collapsing a couple of days later.

Challenges and Solutions
Ballard was tasked with locating and removing demolished bridge pieces from the Sacramento River Arm in Shasta Lake.  This was accomplished through the utilization of a diamond wire saw cutter. With limited visibility underwater, a constant line of communication between the surface crew and the divers was essential to ensure everyone’s safety. Due to this low level of visibility, Ballard employed underwater metal detectors to locate the UXOs that may have not been visible because of the sediment.

Results
Ballard divers recovered and loaded bridge debris into recovery bags that were hoisted onto the deck of a barge for disposal. The UXOs were disposed of in a similar way; however, the bags containing the explosives were placed in a magazine for temporary containment.

With the demolition of the aging bridge and construction of the new Antlers Bridge complete, this I-5 corridor is left cleaner and safer due to Ballard’s involvement.