For more than 20 years, onsite professionals have popped the lids on precast tanks, sometimes to find eroded outlet baffles, a flaky white substance engulfing exposed concrete aggregate, and deteriorating and collapsing walls. Now experts are working to find out why this deterioration affects only a few tanks, and when it does attack, why it doesn’t follow a consistent pattern. Hydrosulphuric acid, a byproduct of the Thiobacillus bacteria in septic tanks, is clearly the culprit, though until recently no one asked if specific circumstances were accelerating deterioration. The Wisconsin Onsite Water Recycling Association held a panel discussion on concrete deterioration
