Cleaning complete on Lock 11, Tree Removal Begins for Long-Term Rehabilitation of Sewer Line

April 23, 2026
Excavation site outside the I-495 Beltway showing section of the PI
  • Crews completed cleaning on Lock 11 of the C & O Canal as prescribed by the National Park Service, with soil removal also nearing completion within the lock area.
  • Work continues to remove soil down to the canal’s clay liner between locks 11 and 12, with work expected to begin on the last section downstream to Lock 10 this weekend.
  • Tree removal is underway, after DC Water received the permits to move forward as part of the site preparations for the long-term accelerated rehabilitation of more than 2700 linear feet of the Potomac Interceptor sewer line that had been previously planned.
  • Once tree removal is complete, work will begin to construction a bypass chamber, to divert wastewater around sections of the pipe while they are being rehabilitated.
  • Crews also examined the pipe section recently excavated along Clara Barton Parkway outside the I-495 Beltway. The location is one of three sites, which will be used to access the interceptor for the rehabilitation that will reinforce and strengthen the pipe to like new condition.

Water Quality Sampling

Daily water quality testing continues to show E. coli levels within the typical range for recreation, with normal historical fluctuations attributed to rain, heat, stormwater runoff, and other known environmental factors. See the District Department of Energy and Environment webpage for more details.

Ongoing sampling is precautionary and intended to address community concerns, ensuring the highest standards of public health and safety.

For the Potomac River, historical water quality data shows E. coli levels may vary from a range as low as 10 MPN/100mL to as much as 5,000 MPN/100mL on a given day.

Results April 13 – present below: (past results can be found here)

graphic of water quality results

You can find more information about the environmental rehabilitation, get the latest news and information, and results of all the water quality testing on our Potomac Interceptor Response page

 

Latest News

Photo of manhole entrance withe completed geopolymer

Second of four high-priority repair projects is now complete

DC Water has completed the second of four critical repair projects on the Potomac Interceptor Sewer Line. Crews finished strengthening a 490-foot section of the pipe at Broad Run in Loudoun County today.

Image of Clara Barton Parkway showing lane closure

Beginning this week and continuing through the end of September, DC Water will temporarily close one lane overnight on Clara Barton Parkway at the Maryland-D.C. border. The closures are necessary to allow crews to safely begin geopolymer work, a concrete-like material, applied inside the sewer line as part of emergency repairs to a section of the Potomac Interceptor.

Last gantry at the bottom of the shaft where crews connect it

Final Gantry Completes Mobile Support Train Behind Mary Stretching More Than 700 Feet

DC Water’s tunnel boring machine Mary may be the muscle behind the Potomac River Tunnel Project, but the gantries that trail behind her form the heart, brains, and guts of the operation. Now crews have lowered and connected the final gantry section, giving Mary the tools and equipment she needs to continue tunneling north.

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Last gantry at the bottom of the shaft where crews connect it
Now Fully Assembled, It’s Full Speed Ahead for the tunnel boring machine Mary and the Potomac River Tunnel

Final Gantry Completes Mobile Support Train Behind Mary Stretching More Than 700 Feet

DC Water’s tunnel boring machine Mary may be the muscle behind the Potomac River Tunnel Project, but the gantries that trail behind her form the heart, brains, and guts of the operation. Now crews have lowered and connected the final gantry section, giving Mary the tools and equipment she needs to continue tunneling north.

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