Stormwater entering wastewater system causes 6.9-million gallon sewer spill

Heavy rainfalls during the week of March 2 flooded the DeKalb County sewer system with an extraordinary amount of stormwater causing a 6.9-million-gallon spill on Meadow Creek Path.  In February, a 9.2-million-gallon spill occurred at this site that also was due to stormwater intrusion into the wastewater system.

Stormwater intrusion occurs when rainwater enters the wastewater system from a structural defect, such as broken or damaged sewer lines, root intrusion and aging infrastructure. Identifying the location of the stormwater intrusion can be challenging because the actual source of stormwater intrusion could be located miles away from the actual spill site.

DeKalb’s wastewater system is comprised of 2,600 miles of pipes—farther than the distance from Atlanta to Los Angeles. Additionally, the system has 70,000 manholes. During last week’s continued rainfalls and resulting stormwater intrusion, 16 of these 70,000 manholes spilled.

DeKalb CEO Michael Thurmond has established identifying the source or sources of stormwater intrusion that caused the spills along Meadow Creek Path as a top priority. The county is using the following detection methods:

• Helicopter flyovers
• Drones flight investigations
• Ultrasonic tracking
• Sonar testing
• Visual observations while walking miles of sewer pipes during storms
• Flow monitoring
• Smoke testing

Prior to rain events, DeKalb crews are engaged in proactively monitoring the system, securing resources, and preparing mobile response units.  After all sewer spills, DeKalb crews work to mitigate health concerns and protect the environment by:

• Placing signs in the immediate area to notify the public of the spill.
• Assessing and determining a cleanup response plan.
• Removing any debris around the site.
• Disinfecting the spill area.
• Re-inspecting the site before removing signs to determine if additional cleanup steps are needed, such as soil removal.

• Monitoring the waterways for water quality.

DeKalb County is in the third year of its 10-year plan to fix its wastewater system. Since 2017, the county has spent more than $301 million in capital improvements that include wastewater treatment plant upgrades, sewer pipe rehabilitation and upsizing, manhole repairs and replacement, and lift station renovations.

Some of these capital improvements are designed to reduce stormwater intrusion and other decades-old infrastructure defects.