The Challenge Many municipal and private water treatment plants need to condition their incoming raw water with the removal of suspended solids materials. This task is typically performed through chemical conditioning with the addition of an approved precipitating / flocculating chemical in preparation for gravity settling of these solids. [...]
In early 2016 a private firm contracted BUC to provide consultation for a planned decommission of a fossil fuel power generation plant. BUC assisted with project planning, construction methodology and system condition assessments to ensure a successful project. In May of 2016 all eight coal fueled units were taken offline after 26 years of operation and the water infrastructure decommissioning started. BUC was contracted to perform dewatering services and permanent sealing of five separate intake fore bays and tunnels, as well as, five separate discharge tunnels. Following the pre-construction investigations, BUC mobilized a team of divers from the BUC Midwest Division, Michigan office and custom built pumps to dewater and seal the system bays and tunnels. A significant amount of debris removal was required prior to dewatering the systems. BUC utilized a series of owned and operated dredge pumps and pipelines to perform diver assisted dredging services. Approximately 1,000 cubic yards of material was pumped over 2,300 feet to the site approved disposal area. Once debris removal was completed, system isolation commenced to include gate sealing, gate cover installation, stop log installation, discharge pipe isolation, and plug installations. Custom built inflatable tunnel plugs were provided to be installed prior to dewatering the eight foot diameter discharge tunnels. Once dewatering started, continuous dives were completed to seal additional piping within the 900LF tunnels. Following dewatering, custom forms were erected and a flowable fill was pumped to permanently seal the intake bays, tunnels and discharge tunnel systems. Each of the unit systems were unique and presented a different challenge. Collaboration and excellent communication from all parties of the decommissioning team resulted in a successful project with zero safety incidents.
Bern Underwater Contractors (BUC) achieved a significant nuclear power decommissioning milestone for Sellafield Ltd by safely completing a nuclear diving project in its oldest legacy pond, the Pile Fuel Storage Pond (PFSP), located in Cumbria, England. Through the development of specialized processes, equipment, and trials, BUCsupported Sellafield’s cleanup goals while maximizing safety and reducing long-term risk during this nuclear power decommissioning mission. The pile fuel storage pond is the oldest pool on the Sellafield site. The facility was constructed between the late 1980s and early 1990s as a storage and cooling facility for irradiated fuel and isotopes from the two Windscale reactors and was in full operation until 1999. Through the mid-1990s, the pond facility, one of six onsite, was then used for storage of intermediate-level waste and fuel from the UK nuclear program. Today, Sellafield is challenged with cleaning up the legacy of the site’s early operations, including the Pile Fuel Storage Pond, one of Europe’s most hazardous nuclear facilities. BUC and its UK subsidiary’s nuclear divers complement Sellafield’s vision and legacy ponds cleanup mission.
On July 14, 2011, divers from Bern Underwater Contractors (BUC) performed an underwater video and ultrasonic thickness inspection of a water intake barge located on in West London. The ultrasonic inspection of the hull revealed plate thickness ranging between 0.360 and 0.380 of an inch. These measurements were consistent with as-built drawings indicating the hull was constructed from 3/8-inch steel plate. During the inspection, a pattern emerged showing reduced wall thickness (0.005 to 0.010) on the starboard side. Upon inspection of the inner hull, approximately two inches of standing water was found on the starboard side. The port side was found to be dry. The hull coating was found to be about 90 to 95 percent intact, although rust nodules were found over the entire submerged surface of the hull near the bow. Upon removal of several of the rust nodules, pitting was found. Pit depths ranged between 1/16 to 1/8 of an inch. A majority of the rust nodules appeared to be concentrated along the weld seams. Several inches of water were found in the bilge. It was believed that at least some of the leakage was caused by pinhole perforations of the hull at pitting corrosion sites. The barge is permanently moored and cannot be dry-docked. It was decided that underwater coating repair of the pitted area would be attempted in hopes that it would not only arrest corrosion but plug any pin hole leaks. The divers cleaned the surface with a 3,500 psi pressure washer. This was followed by a mechanical surface prep to SP 11 using a 3M Clean N Strip to remove any remaining corrosion and roughen the coating around the pit. Bio-Dur 561 was applied at 40 to 50 mils. Approximately 500 repairs were made, ranging in size from 1/2 inch to three feet in diameter. TFT epoxies are distributed by Progressive Epoxy Polymers, Inc. The work was performed in a one knot current. Water temperature was 50 degrees F, with visibility at approximately two feet. After the coating was fully cured, the main compartment was sealed and pressure tested to five psi. No pressure loss was detected over 30 minutes. Subsequent inspections indicate there has been no additional leakage.
BUC performed an inspection on the raw water intake structures of a power generation facility. Findings revealed that 75% of the structure cap and support members underneath the cap had collapsed over the winter. While final repair drawings were being developed BUC performed emergent repairs starting with the removal of damaged areas. Six underwater welders certified to AWS D3.6 and D1.1 were required for the project along with two certified level II underwater welding QC personnel. BUC’s welding and QC programs were reviewed, accepted and used by the customer. The intake structure was made fully operational.
In the summer of 2014, Bern Underwater Contractors (BUC) was contracted to perform turnkey mooring cell repairs for a large fossil fuel plant. A team of topside and underwater welder fabricators repaired 12 mooring cells that were 16’ in diameter. The repairs ranged from small patch work to installing new rolled plating around the entire mooring cell from top to bottom. After welding was completed, the cells were filled with stone to complete the repair. BUC utilized a spud barge with an 80 ton crane and other vessel platforms to support this project. This enabled multiple crews working at separate cell locations to increase productivity. All welders were certified to the AWS D3.6 & D1.1 standards and completed this project safely under OSHA and the Association of Diving Contractors regulations.
Forty years of harsh marine environmental impact required the rehabilitation of the bridge pier steel casings. Previous marine infrastructure repairs such as fiberglass jackets filled with no shrink grout or a combination of steel jackets with grout and reinforcing steel did not stand the test of time, in some cases less than five years. Awarded a contract to rehabilitate this and three other owner-operated bridges, Bern Underwater Contractors commercial services offered an innovative approach; Carbon Fiber Reinforced Polymer (CFRP). Thomas Bernhagen, BUC's CEO and Independent Contractor, stated, “These bridges were perfect candidates for our CFRP solution, both below the water’s surface and above. The high strength and corrosion-resistant product adds minimal weight to the existing structure”
Following the initial sedimentation of solids, the pre-treated water is then typically sent to mixed media sand/gravel filters for a final polishing step prior to disinfection (i.e., chlorine addition) then pumped to reservoirs/storage tanks for consumer distribution. The sand/gravel media filters at the Town of Braintree, MA Water Treatment Plant were fouling with solids much more frequently than normal requiring higher backwash cycles due to carryover of sludge from their Alum Sedimentation Pond No. 2. The Braintree Water Treatment plant manager investigated several methods of removing Alum sludge from the basins and found large cost variables among pumping, dewatering and disposal methods. Braintree Townships’ consultant reviewed mechanical (i.e., belt filter press, plate & frame filter press) and concluded for their application that Geotube® engineered geotextile bags for dewatering and disposal of sludge on a bone-dry-weight basis was most cost-effective.
In September 2018, Bern Underwater Contractors (BUC) was contracted by a hydroelectric utility to conduct repairs to a dam’s stilling basin. Previous inspections had identified areas of spalling and exposed concrete reinforcement. Additionally, a section of baffle blocks had become dislodged and swept downstream during a high-water event. Dam Stilling Basin Repair To access the areas needing repair, several challenges had to be overcome. Seven barge sections were assembled to create a work platform, which carried a tracked crane. In order to dewater the large work area, a temporary bulk-bag cofferdam reinforced with 28 pallets of sandbags was constructed. BUC assembled extensive scaffolding for safe access. A 6” dry-prime pump kept water clear of the area enclosed by the cofferdam.
During a routine ROV inspection performed by BUC, it was discovered that a head gate seal plate had fallen off. Upon further inspection, it was discovered that the attachment hardware had corroded to the point of failure on the other intake slots as well. This was most likely due to dissimilar metals being used for the seal plates and attachment hardware, causing an anodic effect on the hardware. In 2011, Bern Underwater Contractors developed a plan to utilize a custom-built ROV as well as divers to replace the seal plates and hardware. The water depth was between 200’ and 215’ for the duration of the project. This work was performed during winter pool to minimize the working depth. Winter lake levels are typically elevation 1640 while the summer pool levels are approximately elevation 1705. The ROV was built with the ability to drill out the old hardware and reattach the existing seal plates with new hardware. A few of the seal plates were replaced with new ones. When a new seal plate was needed, the ROV would be brought to the surface with a custom-built gantry crane attached to the front of the work barge, and the new guide would be placed in the ROV’s grip claw. The ROV would then be lowered back into place where it would hold the new seal plate in place while drilling, counter sinking, and threading the new hardware holes. The new hardware would be installed by the ROV utilizing a magazine-fed drill head. This was all accomplished without the ROV returning to the surface. The ROV utilized a turret-style head, which could use up to five tools without retuning to the surface for retool or calibration. All of these processes were controlled from the surface utilizing eight cameras with several joystick-style controllers.