Tuesday, June 16, 2020

MWRD: Sidestream Elevated Pool Aeration (SEPA) Stations

The Cal-Sag Channel was widened in 1911-22 to 60' to reverse the flow of the various Calumet Rivers in Southeast Chicago. It was widened again in the 1960s to improve navigation. Since it was dug across swamps, the water tended to stagnate.
MWRD posted
[An aerial view of SEPA #3. 3D Satellite]

Stagnate water looses its dissolved oxygen content and then the wrong things grow in the channel. After extensive research, the MWRD built five SEPA stations along the calumet system to add oxygen to the water.

In terms of the wrong things growing, not only do the fish die, blue-green algae, which is toxic, can thrive in stagnant water. In 2014 I visited Morris, IL, as part of a trip to check out the Illinois & Michigan Canal. The good news is that the canal is watered in that town. They have a lot of signs and displays that celebrate the town's canal heritage such as the Canalport Park. The bad news is that the water was stagnant and growing a lot algae.

20140627 0114
[View of the canal just West of the IL-47 bridge over the canal and river. (Satellite)]

By the time I got to the railroad bridge that has been converted to a trail bridge, there was a solid mat of algae on the canal.

When I went on the bridge, I could not help but notice that the canal STUNK. This photo taken from the bridge shows that mold was growing on the algae.

I learned just last week that this scum is probably blue-green algae and that it is toxic! It can kill dogs even if they just swim in the water. Given all of the money the sanitary district spends maintaining and operating Wastewater Treatment Plants to keep bacteria and stuff out of our waterways, they certainly don't want to be growing toxic algae in them. So they pump water to the top of a cascade of little, turbulent waterfalls to emulate the aeration action of rapids in a river.

SEPA #1, 3D Satellite

MWRD-geohub, 260 mgd (million gallons per day)

They need to turn on the pumps! It has become part of the problem rather than part of the solution.
3D Satellite

SEPA #2, 3D Satellite

MWRD-geohub, 56 mgd
[This is the only one I have gone by so far, and it was closed to the public. It had a closed gate across the entrance.]

SEPA #3, 3D Satellite

MWRD-geohub, 310 mgd

SEPA #4, 3D Satellite

MWRD-geohub, 310 mgd


SEPA #5, Satellite

This one is documented as not accessible to the public.
MWRD-geohub, 372 mgd

[SEPA #5, Satellite]


The five stations located along the Calumet-Sag Channel and the Calumet River pump up to 1.3 billion gallons of water per day and add up to 25 tons of oxygen to the waterways each day. At the stations, up to half of the river's flow is pumped up as high as 17 feet to an elevated, shallow pool, from which the water then cascades over a number of drops back into the waterway. The waterfalls aerate the river water and enhance the aquatic environment by improving and protecting fish populations and eliminating odors. The SEPA stations are thus not only attracting spectators to the park areas, but also creating new schools of fish, and as a result, new birds of prey and other natural habitat are arriving.

How it works
When the upstream water meets the station, it passes through coarse bar screens inclined on 20-degree angles before drifting into the pumping process. All stations rely on large spiral screw pumps, except for the SEPA 1, which uses vertical propeller pumps. The screw pumps, several feet in diameter, spiral the water up a 30-degree incline, elevating the water as high as 17 feet. All stations, except for the smaller SEPA 2, will pump water at least 400 cubic feet per second (CFS) with SEPA 5 pumping as high as 576 CFS. The aeration during the pumping process is so strong that it in fact generates more oxygen than the waterfalls. The circular screw pumps upward rotation turns the water into something more resembling white water ascending from a rapid. Each of the screw pumps at SEPA stations 3,4 and 5 can pump more than 50,000 gallons of water per minute, while the smaller SEPA 2 will pump 19,300 gallons per minute. There are four at SEPA stations 3 and 4, while SEPA 5 has five pumps. The water then passes through a lengthy discharge channel before cascading down a series of waterfalls and returning to the waterway. During the winter, MWRD workers maintain the stations by inspecting gears, rotating pumps, replacing seals and changing oil to ensure that the pumps are ready to go come April and that the water can flow.
Archimedean Screw Pump
So sometimes the oldest solution is still the best solution. The screw pump creates a lot of surface area between air and water. And it evidently splashes the water around a lot. Normally engineers try to minimize turbulence in a pump. But in this application, they want turbulence because that helps mix air (oxygen) into the water.

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