Basics of Evaluating Mound Systems for Real Estate Transactions

Basics of Evaluating Mound Systems for Real Estate Transactions

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When evaluating any onsite system, always start by collecting any records of the system (plan, soil test, etc.) from the local regulating agency. This aids in making your report more accurate. Include whatever documents you find with your final report to your customer.

There are those who will run water into the system as a step in the system evaluation, but I caution not to do so. The most important reason is there is already a court precedent saying that the act of running water into the system caused the failure. The regulatory agency that required water be run into the system lost in court. So don’t go against a court precedent. The second reason is there isn’t any uniformity nor rationale for how much water to run in a system. It won’t be emulating 24 hour usage in any way, as most systems are designed based on max use in 24 hours.

Start at the tanks. If the covers are exposed, are they locked? Any exposed covers should be locked to prevent unauthorized access (i.e. protect curious children from falling in). What is the condition of the cover and risers?

Septic tank  

As with all onsite evaluations, note the level in the septic tank prior to pumping. DO NOT allow anyone to pump the tank prior to you observing the level in the septic tank. You want to make certain you know if the level is normal (bottom of outlet pipe,) high or low prior to pumping.  

A mound system should also have a pump or dose tank or chamber after the septic tank or septic chamber. If you have a high level, is the level also high in the next chamber or tank? Or maybe there is a blockage between the two. Low level is an indication that the system could have recently been pumped, or the tank might not be watertight such as a crack.

If the tank has a normal level, are there any signs that the system had a high level at some previous time, such as toilet paper on top of the baffle or on top of an effluent filter? A tank that has maintained normal levels will be very dark on the walls below the normal level line and quite clean above the normal level line. Are there signs above the normal level line that water has been above normal at some time in the past?

After noting the level in the tank, next have the tank pumped. What is the condition of the tank, the baffle, the effluent filter? Do not ever enter a tank for an evaluation as it is a dangerous confined space. A thorough evaluation will include use of a mirror on a long pole and a powerful spotlight to observe inside the tank. If the tank is shallow enough I always turn on the flash on my cellphone camera, reach my arm in and take lots of pictures I can look at closer on my desktop. 

Pictures are important and make excellent support for your final report. I’ve had pictures of a severe crack in a tank. The owner called a different pumper who said there wasn’t a crack. When I sent the picture to all involved the other pumper admitted never looking in the tank. I cannot recommend pictures enough. My current phone is three years old and has over 25,000 pictures on it.

If there is more than one septic tank or a two chamber tank, repeat the above for each tank or chamber.

Pump or dose tank  

Follow all of the above for the pump tank but remember, the pump tank has a different ‘normal’ level. Pump tanks in most cases will have two float switches hanging inside, one for the pump on/off and one for the alarm. Level should be below or at the lowest float switch. There are differing thoughts on this but pump this tank dry also. If you don’t there is no way you will accurately be depicting the actual condition of the tank. 

If you can safely trip both floats without entering the tank using a long-handled tool, confirm each float performs its function: one turns on the pump and one activates an alarm. Is there a filter in the pump tank? Your report should make note of any filters and that they and the tanks themselves require regular maintenance. Are the electrical connections made outside the tank in a watertight box?  

Make sure all manholes are securely replaced and locked for safety. This is so vitally important that I highly recommend either having a line right on your field notes that manhole covers were securely replaced and locked and/or take an ‘after’ picture of every evaluation you do showing the manhole covers were properly and securely replaced before you left the site.

The mound  

If possible, have somebody else trip the pump float before the tank is pumped dry while you are standing at the mound. Watch for signs of any effluent surfacing at grade or flowing to the surface of the ground from the mound. This would be considered a failed system if that occurs. 

Whether or not you see water gushing out of the mound while the pump is running, walk the entire length of the mound. Walk on top and walk the long sides. Failure of a mound occurs when a clog or biomat is mature enough to restrict water flow to such a point that water flows out of the mound to the ground surface. You will typically see failure of a mound about halfway up the (long) sides typically (but not always) along the downslope side. I’ve seen effluent coming out of the top and ends of mounds as well. If water is coming out of a mound to grade or to ground surface, the system should be considered failed unless it can be proven that the water you are seeing is due to a broken pipe or fitting. In that case it is still in failing condition until the broken pipe or fitting is repaired and it can be shown that water no longer comes out of the mound when the pump is on.   

There should be observation pipes on the mound. Note whether there is water observed in them or if they are dry. Water in observation pipes is not in itself failure. Water in observation pipes is merely an indication that a biomat has matured to the point that it is slowing the water’s rate of infiltration into the mound. If the mound has flushout valves, the system evaluation is a good time to flush the laterals before the pump tank is pumped out.

Make certain your report is accurate and thorough. Never skew your report based on whether your customer is a buyer or seller. No matter who your customer is, the report should be a thorough, honest depiction of what was observed.

About the author Todd Stair is vice president of Herr Construction, Inc., with 34 years’ experience designing, installing, repairing, replacing and evaluating septic and mound systems in southeast Wisconsin. He is the author of The Book on Septics and Mounds and a former president of the Wisconsin Onsite Water Recycling Association.


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