W912DR20B0020 Dalecarlia Clearwells Maintenance

The Washington Aqueduct provides potable water to approximately one million people in the District of Columbia and Northern Virginia. As part of the water treatment and supply system, the Washington Aqueduct maintains and operates the Dalecarlia and McMillan Water Treatment Plants (WTPs). At the Dalecarlia WTP, two Clearwells are used for final chemical treatment, disinfection, and storage of water before it is pumped to the distribution system. The 15 million gallon (MG) Clearwell is approximately 25 feet deep. It was constructed in the 1920s and rehabilitated in 2000. The 30 MG Clearwell was constructed in the 1950s and rehabilitated in the 2000s; its approximate depth ranges between 20’ and 50’. Both Clearwells are covered by about 2’ feet of soil and topped with grass cover.

The project consists of implementing upgrades and improvements to these Clearwells and their connecting conduits to include: upgrades to their drain lines to eliminate potential cross connections, rehabilitation and replacement of large sluice gates, installation of new flow meters and induction mixers, improvements to the Clearwell overflow structure, chemical analyzer drain pipe re-routing and soil drainage improvements Both Clearwells are critical in maintaining adequate supply and quantity of water, so outage periods are restricted. The timing of outages must be coordinated with lower seasonal demands and sequenced so that only one Clearwell is out of service at a time. Finally, mold remediation and HVAC upgrades will be required in a building adjacent to the 15 MG Clearwell.