Duckett Dam Intake Repair

 

Duckett Dam Intake Repair

 

Duckett Dam Intake Repair

 

Duckett Dam Intake Repair

 

Duckett Dam Intake Repair

 

Duckett Dam Intake Repair

 

Duckett Dam Intake Repair

 

Duckett Dam Intake Repair

 

Duckett Dam Intake Repair

 

Duckett Dam Intake Repair

 

Contract: $2,029,191

Design-Build Team Members
Owner: Washington Suburban Sanitary Commission
Engineer: Gannett Fleming, Inc.
Design-Builder: Johnston Construction Company

Key Accomplishments:

• JCC substituted an epoxy product to protect existing steel surfaces from corrosion. The product reduced the application time during critical underwater operations. This solved constructability issues and protected the existing steel surfaces better.
  
• JCC’s innovative rigging scheme eliminated the need for work from a barge with a large crane. We constructed a monorail and hoist to lower the trash racks, fine screens and 6,000 pound sluice gates into position up to 76’ below grade and 60’ below the water level. Materials were brought to the monorail on a job built rail mounted handling cart. This method saved the owner $1 million dollars in anticipated costs.
• Outage time was reduced by running two shifts, 24 hours a day, seven days a week, to install the fine screens and Penstock Sluice Gate.

JCC, under a public-bid fixed price contract, made repairs to the 50 year old intake structure of Duckett Dam in suburban DC. Work involved replacing the screens and screen guides, trash racks and four sluice gates. The intake is part of the T. Howard Duckett Reservoir (formerly called Rocky Gorge) supplying raw water for Montgomery and Prince Georges County residents. Two of the sluice gates and all of the trash racks had to be done by divers at up to 60’ below water. The screens and the Penstock Sluice Gate in the 78’ deep structure had to be replaced using a field installed scaffold tower during a full water plant shutdown.

Near the conclusion of the project, WSSC had us replace the siding and roofing panels on the structure. All work had to be accomplished while working from a barge with a boom lift. A work plan was developed in consultation with JLG to safely use the boom lift over water.

The pump stations include three 6’ by 8’ and one 6’ by 6’ Hydro Gate sluice gates. A LubeUSA automatic lubrication system was installed to grease the bearings on the torque guides, which were under water. New stainless steel trash racks and screens were fabricated by Northern Iron Works for the project. The trash racks had to be field modified to fit the existing structure as it was slightly out of plumb.

The trash racks and screens must be removed for cleaning frequently during the fall. Therefore, new multi-purpose lifting device was provided as part of the contract. This was designed to pick the screens and racks, lower them into place and release them under 70’ of water. It also latched onto the screens and racks under water for retrieval.

The project was started in October 2007 and was completed in May 2008. It included an extremely critical shutdown phase during the month of December, which required 24 hour, seven day per week work, up to 70’ below the water.