(gate clicking) - Good.

(door clanking) (lift whirring) - Here we go.

(door clanking) So this is the pump room.

We're about 320 feet underground.

This is where 28 and a half miles of deep tunnel come to an end.

Everything gets pumped out here and either sent to Jones Island or the Oak Creek plant in South Shore.

(drill whirring) 28 and a half miles long, it's about 300 feet underground for the most part and 17 to 32 feet in diameter.

So it's massive and it holds about 521 million gallons.

And that's the whole point of this tunnel system is to help reduce the risk of sewer overflows.

And our highest priority during a storm is to keep wastewater out of people's basements.

1994 was the first full year of operation.

Ever since then, we have captured and cleaned 98.4% of every drop of water that's gotten into the regional sewer system.

(doors clicking) This is the harbor siphon.

There are two pipes that come in, one from this direction and one from the north, that go under the river and then this siphon system brings it up to the plant just to help lift it to a level where all the water could flow by gravity through the rest of the plant.

(soft upbeat music) So there are four stages.

The first being screening, where big towels and other stuff that gets either flushed or gets into a storm drain, that gets taken out, so it doesn't damage any equipment that we have or infrastructure.

This is the second stage of treatment.

So the solids sink to the bottom, oils and greases float to the top.

We take all the solids and put them in a pipeline that goes down to the Old Creek plant, and that goes into the anaerobic digester, and that's where it produces the gases to help us produce the energy we need to mostly run that plant.

And then it goes to where the real workhorses of a wastewater treatment are, it's called secondary treatment, where the bugs live, and the bugs eat organic material out of the wastewater.

Right here what you're seeing are the filter presses.

We take the bugs out, a certain portion each day, but this is how it comes in.

It comes in, this is a special filter fabric that lets water drain out.

But then the water is also squeezed out at this other end, before it drops down and onto a conveyor belt.

(conveyor whirring) And then they go to the dryer.

They're in the dryer until they hit a certain temperature that helps guarantee there's no pathogens left, potentially.

And from there we bag it, sell nine different products.

(latch clicking) And then from there it goes to a disinfection, where we add a chlorine byproduct.

Then we have to add another product to take the chlorine byproduct out, before we discharge the water to the lake.

(soft music) This system has really paid huge dividends for Lake Michigan, which is also our drinking water and for public health.

It's been a great, great investment.

There are a lot of cities around the country that would love to have the infrastructure that we have here in the Milwaukee area.

(soft music)