Maline Structure, St. Louis, MO
The Maline Drop Shaft located near the Chain of Rocks Bridge is just like concrete sewer structures everywhere. They corrode when hydrogen sulfide gas is present. Moderately-high temperatures, long retention times, high biological oxygen demand (BOD) levels, and turbulence contribute to elevated levels of hydrogen sulfide gas which, in turn, provide the food for acid-producing bacteria.
The technical name for this process is Microbiologically Induced Corrosion (MIC). This 40-year old concrete structure was severely deteriorated from MIC. The upper portion of the walls were mushy with more than two inches of the original wall missing; in the lower half of this 50-feet-deep structure, more than five inches of the walls had corroded away.
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