Commissioned by the Metropolitan St. Louis Sewer District (MSD), construction of the concrete lining of this monumental underground tunnel of the Deer Creek storm drainage system was completed in August 2021. Penetron’s antimicrobial concrete admixture was specified to permanently protect the tunnel's concrete lining from microbially-induced corrosion (MIC).
The Deer Creek Tunnel is a key element of the Metropolitan St. Louis Sewer District’s (MSD) “Project Clear” initiative to eliminate sewer overflows during heavy storms due to the limits of older wastewater collection and treatment systems. The goal of the $82.8-million project is to reduce and eliminate years of discharges that have sent hundreds of millions of gallons of raw sewage into local waterways, including Deer Creek and the nearby Mississippi River.
Digging large stormwater tunnels out of the limestone rock that underlies the region’s geology is an important strategy for MSD to create a more resilient and higher-capacity stormwater & wastewater management system, much like the nearby Maline Creek Storage Facility, also a Penetron project. This half-mile long, 28-feet wide tunnel lies 175 feet below St. Louis’ riverfront. During a period of extreme precipitation, the tunnel fills up, then a pump station moves the stored contents to the Bissell Point Wastewater Treatment Plant before being discharged into the Mississippi River.
Mrs. Nancy Gets the Job Done
While the concrete lining of the 4.3-mile-long tunnel of the Deer Creek Sanitary Tunnel project has been completed, plenty of work remains before the tunnel is officially commissioned and begins operation in late 2022. The $150-million project features a 19-feet wide storm sewer drain that was dug 150 to 250 feet below ground by “Mrs. Nancy,” a tunnel boring machine.
“Once it’s operational next year, this cavernous storm drain will collect and temporarily hold wastewater during heavy rains until the local wastewater treatment facilities can handle the volume,” says Christopher Chen, Director of The Penetron Group. “The new tunnel will significantly reduce basement backups, rainwater flooding, and overflows into nearby Deer Creek, which has suffered from raw sewage overflows in past years.”
The concrete mix of the tunnel’s concrete lining was specified by Black & Veatch, a construction engineering firm. The final design was elaborate, containing many chemical admixtures to ensure pumpability, placeability, setting time, strength gain, and durability.
Looking for a MIC Solution
The project contractor needed a solution to prevent microbially-induced corrosion (MIC) in the concrete lining of the Deer Creek Tunnel. MIC is a process where micro-organisms found in sewer systems, such as thiobacillus bacteria, metabolize hydrogen sulfide gas (H2S) into biogenic sulfuric acid (H2SO4). Then, the biogenic sulfuric acid rapidly deteriorates concrete.
“Traditional approaches to protect concrete against MIC are PVC liners or epoxy coatings installed on the exposed concrete surface. These systems are very expensive, labor intensive and need to be maintained and replaced at the end of their service life," says Christopher Chen. “A better solution is simply adding Penetron’s antimicrobial admixture to the concrete during batching, which prevents MIC from taking place.”
Innovative Antimicrobial Mechanism
Penetron’s antimicrobial admixture uses an electro-physical mechanism to destroy the cell-walls of micro-organisms, in particular the thiobacillus family of bacteria, on contact. Because the admixture becomes part of the concrete matrix, it is a permanent solution. In addition, it is leach resistant and its effectiveness is not lessened by repeated contact with bacteria.
Penetron’s antimicrobial admixture was used to treat over 17,050 yds3 of concrete used to line the Deer Creek Tunnel.
“Penetron’s antimicrobial admixture was specified for the Deer Creek Tunnel project thanks to our close relationship with the concrete ready-mix suppliers and our technical support services provided throughout the project,” concludes Christopher Chen.