Crossover Cable Replacement at Lock and Dam 2 in Hastings, MN

Scope of work

Dam Feeder Cable Replacement

1. general

1.1 Project description

The work consists of replacing segments of circuits Dam Feeder No.1 and Dam Feeder No. 2 and the removal of unused cables located in the crossover system at Lock and Dam No. 2 in Hastings, MN. The cable segments requiring replacement start at manhole 1 and end at manhole 2 as shown in Figure 1-1 (see SOW Attachments). Dewatering the crossover system is required to access the cables. Additionally, the contractor will identify conductors currently in use and provide documentation showing the cable routing through the crossover system. All electrical work must comply with the latest edition on NFPA-70, National Electrical Code.

1.1.1 Crossover System

All cables required for the electrical systems located on the river wall, the dam, or the hydropower plant, are routed underneath the lock via the crossover system. Access to the crossover system is obtained from either manhole 1 or manhole 2 via a vertical shaft starting at the manhole floor. The manhole 1 shaft is 12'x 2'-6" with a depth of 28'. The manhole 2 shaft is 10'x 2'-6" with depth 32'. Both shafts have four sets of embedded ladder rungs that are used to traverse the shaft. The use of fall protection equipment is required when accessing the crossover system and the entire system is considered a confined space.

On both sides of the lock, a 4'-6"x 6'-6" tunnel connects the bottom of the shafts to the crossover duct bank. Two, 9" cable trays are mounted on both sides of each tunnel and are used to route cables from the vertical shafts to the crossover duct bank. Additionally, two 13.2 kV cables, protected by flexible conduit, are routed underneath the cable trays on the upstream wall of each tunnel. The crossover duct bank is shown in Figure 1-3 (see SOW Attachment) and consist of 49, 3" fiber conduits, with porcelain end bells.

1.1.2 Dam Feeder Cables

The dam feeder circuits provide primary and emergency power to the dam. Each circuit consists of two sets of parallel cables (DFXA&DFXB). An attempt was made to replace both circuits in 2015. However, challenges with dewatering the crossover system resulted in the new cables being spliced to the exiting cables routed through the crossover system. The splices are located at the bottom of manholes 1 & 2, near the entrance to the vertical shafts. The routing of the cables in manhole 2 is shown in Figure 1-2 (see SOW Attachment). From the splices in manhole 2, the cables continue vertical to the ceiling of manhole 2. The cables then run down the inside of the downstream wall where the cables exit the manhole through 4" holes located at the manhole floor.

The contractor must remove and replace all four cables (DF1A, DF1B, DF2A, and DF2B) from the splice in manhole 1 to the splice in manhole 2. The splices for the new cables must be made near the ceiling of each manhole to reduce the likelihood of them being submerged in water. The existing cables exiting manhole 2 must be rerouted to run up the cable tray installed on the exterior manhole 2. The abandoned communication cable shown in Figure 1-2 (see SOW Attachment) should also be rerouted with the dam feeders, but it does not require reconnecting.

During construction, one of the dam feeder circuits must always remain serviceable to allow for continued operation of the dam. 14 days prior to the commencement of work, the contractor should coordinate with the Contracting Officer to determine which circuit should be replaced first. Following the replacement of the first circuit, the contractor must obtain written approval from the Contracting Officer that the dam electrical equipment has been transferred to the first circuit, and that work can commence on replacing the second circuit. Power will be deenergized during work hours (10 hrs. /day) but one dam feeder must remain serviceable during non-work hours in order to operate the dam. Coordination with the COR is required when river flows are expected to reach 40,000 CFS (cubic feet/second). Work cannot be performed when high-water river flow conditions exceed 40,000 CFS.

It is the contractor's responsibility to establish an electrically safe work condition, per NFPA-70E, prior to the removal of any cable. The contractor must coordinate the application of lockout devices with the Contracting Officer. If circuits other than dam feeders 1&2 are required to be deenergized to perform any of the work outlined in the scope of work, the contractor must notify the Contracting Officer of the need to deenergize additional circuits. The notification should include the name of the circuits that are required to be deenergized and the estimated time duration of the outage. Following notification, the Contracting Officer will coordinate the application of lockout devices with the contractor.

1.1.3 Cable Removal and Organization

There are approximately 30 abandoned Type SOW of various lengths, located within the crossover system. In addition to the abandoned Type SOW cables, there are approximately 5 spare Type AC cables. The spare and abandoned cables are intermixed with the live cables that are required for lock operations. The total number of cables located within the crossover system has far exceeded the capacity of the 4 cables trays located in the crossover tunnel. As a result, numerous cables are laid on the tunnel floor as shown in Figure1-3 (see SOW Attachment).

The contractor must identify cables located within the crossover system, remove all abandoned Type SOW cables, and relocate any live cables on the floor to the cable trays. Pull cords should be placed in each conduit that has a SOW cable being removed. The spare Type AC cables can remain. The contractor must verify that all live cables have cable tags, and the contractor must replace any cable tags that are missing. Lastly, the contractor will document the cable routing throughout the crossover system.

1.1.4 Cable Routing Documentation

The contractor must document the cable routing in the crossover system. The routing must be documented from the prospective of a person in the land wall crossover looking towards the lock. The documentation must indicate what cable is in each conduit of the duct bank and in each cable tray. The documentation must be submitted to the Government in a .PDF format.

1.1.5 Disposal of Material

The contractor is responsible for the disposal of all cable and material removed under this contract.

1.1.6 Crossover Dewatering

The contractor is responsible for dewatering the crossover system. This includes providing all the equipment necessary to dewater the crossover. The equipment should be either gas powered, or the contractor must make temporary power arrangements with the utility. The contractor must submit a dewatering plan for review 14 days prior to the commencement of work.

1.2 PRE-bid visit

Potential bidders are encouraged to visit the site prior to placing bids to ensure that they understand the existing site conditions and the potential challenges associated with completing contract work.

A site visit for potential offerors is scheduled for May 5, 2025, at 10:30 am. Site visit will be coordinated through Karl Just at karl.p.just@usace.army.mil or 651-290-5768.

1.3 Construction Schedule

The contractor shall provide a work schedule in writing no longer than 14 days after receiving the notice to procced. Point of contact for questions is the Contracting Officer Representative (COR) (Available at Award). Work hours are Monday through Friday 07:00 - 17:00.

1.4 Safety

Submit an Accident Prevention Plan (APP) and be in conformance with the Corps of Engineers Safety and Health Requirements Manual EM 385-1-1 (latest edition) and will be the sole responsibility of the contractor. The manual is available at the Corps of Engineers web site: http://www.usace.army.mil/publications/eng-manuals/

1.5 Drawings

Select as-built drawings and a site plan are included in Appendix A for reference.

1.6 Submittals

Submittals must be approved prior to the installation of any material.