Baffle and tank deterioration is always a hot topic and one where unfortunately there are not absolute answers in terms of repair and replacement. Recently I discussed a picture I received of a misguided attempt at baffle repair. This led to the following comment from Bob Boersema:

“Prior to repairing any concrete baffle, it is important to check out the structural integrity of the tank lid. If the baffle has deteriorated, chances are the top of the tank has also been damaged as it is exposed to the same gases. We often see people spending money repairing baffles only to find their tank partially or completely filled with soils due to a partial or complete collapse of the lid.”

The question I was responding to was about how to repair a baffle. I agree completely with Bob that if the baffle has deteriorated in a concrete tank the lid and the rest of the tank should be evaluated for structural integrity. There are other reasons to repair and replace baffles other than deterioration so it depends on the reason for the repair or replacement. For example, if it is a system upgrade to allow installation of an effluent filter there may not be the same need to evaluate the tank although it is good policy to look at it every time there is a service call.

In addition, I think spending some time trying to figure out the cause of the deterioration is also in order. If the tank is still sound and deterioration is slight, fixing the cause of the problem will save the homeowner from replacing that tank in a few years. While there is currently a lot of discussion in the industry right now about causes of premature deterioration in concrete tanks and a lot of speculation with few definitive answers, one major problem can be evaluated and that is to make sure the tank is being properly vented back through the house plumbing stack.

There are two things to check and to remedy if you find they are the problem. Is the inlet pipe cocked at an angle coming into the tank? This indicates that the sewer pipe from the house has a bend or kink in it due to improper installation. This dip or bend will cause plugging problems in the sewer pipe but it will also inhibit gas exchange back through the plumbing allowing the accumulation of hydrogen sulfide at the low point of the tank which is the outlet. Fixing the sewer pipe and making sure there is space between the pipe entering the tank and the baffle wall can go a long way to solving problems.

Second, to allow gas exchange there needs to be a gap between the bottom of the tank lid and the baffles to allow free gas exchange between parts of the tank and back through the plumbing. If this gap is not there, gases will collect again at the lowest points resulting in deterioration at those points.

If these two issues are corrected a number of the deterioration problems seen can be corrected. As I indicated, research into other problems including well-water quality and soil related deterioration continues. I am sure as results are reported we will add to the list of the things to look for when evaluating baffles and tanks.

About the Author
​Jim Anderson is connected with the University of Minnesota onsite wastewater treatment education program, is an emeritus professor in the university’s Department of Soil Water and Climate, and education coordinator for the National Association of Wastewater Technicians. Send him questions about septic system maintenance and operation by email to kim.peterson@colepublishing.com.