Last week, Water & Wastes Digest's editorial staff was invited to descend into Milwaukee’s Deep Tunnel, one of the largest storm water systems in the world.
The Milwaukee Metropolitan Sewerage District’s (MMSD) massive 500-million-gal “pipe” is one of few similar systems in the world.
During heavy rains, the tunnel fills with overflow storm water and sewage. Eventually, wastewater is pumped out and cleaned at the treatment facility; however, floating debris accumulates in the tunnel over the years.
Veolia Water crew cleaned out the tunnel for the first time in its 18-year history as part of its O&M contract with MMSD. This was a very involved process requiring strict safety protocols. The Veolia crew operated in semi-darkness for hours at a time, piloting a custom-built craft designed to convey the debris through the water and into baskets that are then hoisted aboveground by a huge crane.
The editorial staff had a once-a-decade opportunity to get a first-hand glimpse of the Deep Tunnel. We took a number of photos as we were lowered down the 300-ft access shaft. Visit our Facebook page  to view photos from this exciting experience.