Starting-up equipment and moving millions of gallons of water at 3 a.m. has become the norm on the Tunnel Dewatering Pump Station and Enhanced Clarification Facility (TDPS/ECF) project as the team has worked toward, and now successfully completed, the system operational demonstration. This was the final full-system acceptance test before the tunnel bulkheads are removed from the influent tunnels, allowing combined sewer overflows (CSOs) during storms to be sent to the facility.
The facility is designed to treat 225 million gallons of incoming CSO from tunnels underneath Washington, D.C. Water enters through a 23-foot diameter tunnel and is stored in a shaft before being pumped by 83-mgd pumps to the ECF.
For the operational demonstration, influent was pumped from the existing plant to the ECF for treatment. The fine screens removed all solids larger than 6 millimeters from the influent and sent the material to storage containers for removal. The influent was then injected with ferric chloride and caustic soda to aid in settling and neutralize the pH before entering the grit vortexes. The influent then entered the three ACTIFLO High Rate Clarification trains, which are the largest in the world, and include coagulation, flocculation and settling tanks. The removal rates that were achieved far exceed the contract required performance guarantee.
Now that this test is complete, contractors upstream of the system can remove their bulkheads that are currently blocking flow from entering the facility. While that is taking place, our team will continue to make minor adjustments to the system, pump at limited capacity to keep the tunnel dry, and prepare for our next phase of testing scheduled to begin in early March. This next phase of testing will prove the facilities’ ability to handle the large combined sewer overflows the plant was designed to treat.