Question:
Does anyone have any suggestions on why concrete risers, distribution boxes and lids deteriorate? I’m guessing it’s due to detergents and similar products, but what are the ones homeowners should avoid? It’s stuff like this that makes me love plastic distribution boxes, risers and other components. Granted, homeowners should use environmentally friendly products, but in reality the group that does so is a pretty small segment. I’d like to come up with a list of “bad” products and “good” products.
Answers:
I think hydrogen sulfide gas combines with the moist atmosphere in the top of the tank and creates an acid that deteriorates the concrete. The baffle below the water line always seems to be in better shape than what is above the water line. We have seen some baffles crumble in as few as six years. I wonder if it’s a weak mix of concrete, or household products. Or does it have something to do with how well the system is vented?
I’ve found that most deterioration issues are associated with heavy garbage disposal usage, and when combined with bad ventilation you have a disaster waiting to happen. The rotting food creates hydrogen sulfide.
I’ve seen one-year-old septic tanks that are vented well (the neighbors can smell it) but are still deteriorating. We pump the tank and educate the homeowner about garbage disposals and a few other things, and the foul smell and deterioration stop.
I’ve also seen septic tanks five years and older that weren’t vented well, and the 6-inch-thick concrete lid fell apart after a couple of sledgehammer raps. The underside of the lid and the concrete above the water line is a chalky green/ white/yellowish crumbly mess. It’s typical to be able to rub away an inch of concrete with the swipe ofa glove.
However, I have yet to see a precast tank manufactured by one of our local precast companies cave in. I have seen a few plastic tanks buckled (not from H2S).
Hydrogen sulfide gas is responsible for the concrete deterioration. That is why the concrete below the water line is still OK. It is perfectly normal for standard concrete to break down like this. A lot depends on the quality of the concrete. All septic tanks and related components should be manufactured in sulfate-resistant cement to counteract this deterioration, but this is not always done, as this cement is much more expensive than normal cement. Even the cement quantity in the concrete could affect its useful life.
Use of a garbage disposal or any other means of getting excess food to the septic tank will raise the hydrogen sulfide levels. It also lowers the pH in the tank when the H2S and water mix.
I’m not sure about water softeners, either, as far as concrete deterioration goes, but there is strong evidence that water softeners raise the salinity of the effluent, causing the sludge in the tank to sit lighter and fluffier. This brings the sludge up into the agitation area of the tank sooner (maybe a year or two).
If I lived in a house with a septic system and a water softener, I would pump the tank more often to keep the sludge closer to the bottom.
I’ve found that in our business, an inexpensive vent installed in any tank will help abate the gas. It should be a vent with some sort of replaceable activated charcoal filter to control odors.
