The Department of the Army, Army Corps of Engineers, Baltimore District has a requirement for design-bid-build construction at the Washington Aqueduct (WA) McMillan Water Treatment Plant to replace the entirety of the existing clearwell to provide structurally sound reservoir with improved water quality and reliable operation.

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• Construct a replacement for the existing NCW with an underground reinforced concrete, watertight tank (to prevent water seepage and infiltration). The project shall include the partial demolition of the existing NCW. The existing roof of the clearwell has strict loading requirements. The contractor shall adhere to these and establish a sequence that allows for the roof to be demolished safely prior to any interior demolition work.
• Utilize existing structural walls to establish a support of excavation (SOE) system to facilitate construction of the new walls. Proposed SOE system cannot use any tiebacks or penetrations through existing walls. The SOE system shall consist of struts, lateral bracings, supporting columns with micropile foundations, and connection elements between struts and existing concrete wall. Dewatering is expected to be required in order to reduce hydrostatic pressures on existing walls. A monitoring and contingency plan will be required to allow for measuring lateral and vertical movements along the existing walls. Careful sequencing of existing foundation mat slab and construction of the new foundation mat slab will be required to maintain structural stability of the existing walls.
• Reconstruct in kind two historic building structures which will sit in their original locations on the above-ground landscape which will rest upon the roof of the newly replaced NCW. Reconstruction will be carried out in accordance with the Secretary of Interior’s Standards for Reconstruction. The buildings will be clearly identified as contemporary re-creations through the incorporation of corner stones or other means. Their replacement shall meet District of Columbia State Historic Preservation Office (SHPO) requirements to match original building historical construction. A responsive bidder will be required to demonstrate qualifications and experience with historic preservation and reconstruction projects that follow these standards.
• Replace multiple valve actuators. This will require installing and field testing slide gates and actuators complete with frames, operating stems, stem guides, and all necessary accessories and appurtenances. Cast-Iron slide gates must be constructed and assembled in accordance with AWWA C560. Electric actuators must meet the requirements of AWWA C542.
• Construct cast in place concrete baffle walls inside the clearwell to assist with process mixing.
• Construct multiple access hatches and drainage chambers. Drainage chambers shall be protected during construction to prevent infiltration and damage to the overall system.
• Install and field test chemical dosing and sampling equipment.
• Install a roof underdrain system to control drainage on top of the NCW.