Thursday, November 17, 2011

Why is Flat Branch Creek Green?


Flat Branch Creek dyed green.  Photo courtesy of Benjamin Zach with Missourian

It's NOT anti-freeze.  The City uses dye testing to investigate sanitary sewers.  

So why is green dye in our creek?  

One of the biggest problems with our sanitary sewer system is too much stormwater finds it's way in.  This is a problem because the sanitary sewer system and wastewater treatment plant are not designed to handle stormwater - they are separate systems.  (See  Separate vs. Combined)  When too much stormwater gets into the sanitary sewer system, it can cause the lids of manholes to come off and stormwater mixed with raw sewage can flow onto the ground and into our creeks.  This is a health hazard. 

The City of Columbia has developed an extensive I&I Program.  I&I= Inflow and Infiltration.  The purpose of the I&I Program is to investigate how stormwater is entering the sanitary sewer system and prevent it from happening.  Some of the investigation methods include camera inspection of sewer pipes, visual inspection, smoke testing and dye testing.

Smoke testing fills the sanitary sewer line with a harmless, non-toxic smoke (think theater productions) and looks for places where the smoke comes out.  The smoke should come out of the vent stack for houses.  Smoke should not come out of the ground, downspouts and gutters, or storm drainage structures.  When it does, we do further investigations.

The next step when smoke comes out of storm drainage structures is dye flood testing.  We attempt to flood the storm drainage structure in question with water,  and then dye the water with a non-toxic coloring.  We do a camera inspection of the sanitary sewer line to see where the dyed water is getting into the sanitary system.  From this information we can determine what kind of fix the sanitary sewer system needs. 


Technician dying water going into a storm inlet.


Dyed water coming out of a storm inlet
 Once the camera inspection is complete, the dyed water in the storm system is released and goes downstream.  All of our current dye flood testing is taking place in the Flat Branch watershed.  So the Flat Branch may be bright green for a few days.  This will eventually make it's way to Hinkson Creek and Perche Creek, but will become diluted along the way.

By investigating stormwater leaks into the sanitary sewer system, we can prioritize improvements.  Improvements to our sanitary sewer system will reduce the occurrence of wastewater in our streams.

So next time you see a little of bit of green in the stream, it might be anti-freeze - report it!  But if it is a lot, the City is dye testing to figure out how to make our streams cleaner!

Photos from the Missourian