How To Look At A House
McGarry and Madsen's home inspection blog for buyers of
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Why would a house have a septic mound system?
Sunday, January 16, 2022
A long, grass-covered mound of soil that is several feet high near the home usually means there is a mound septic system. The mound is constructed of layers of sand and gravel with the perforated drainfield pipes running through it. A mound system is used when the ground is not suitable for a regular septic tank and drainfield, and there are a couple of possible reasons why:
1) The water table is high under the property, with not enough soil depth to absorb and filter the wastewater from the drainfield before it reaches the groundwater below and contaminates nearby wells. An example would be low land near a swamp.
2) The soil is too dense and resistant to allowing the wastewater to gradually move through it. Or the soil is too porous and allows the wastewater to move too quickly for good filtration.
The rate that water moves through the soil is called “percolation” and is determined by a “perc test” at the site. An alternative like the mound system has to be used when a home fails the perc test.
Should you buy a house with a mound septic system?
A standard septic tank and drainfield operates entirely by gravity and is low-maintenace. But a mound system, on the other hand, requires a dosing chamber and pump to lift the wastewater up to the mound. Plus, a mound system will accept less abuse—like chemicals, grease, or excessive effluent flow—than a regular system. So there will likely be more maintenance, and the system will be more expensive to replace when the time comes. But, if you like the house and don’t find the mound offensive, it should be fine.
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And here’s some of our other articles about septic systems:
Mound system graphic - EPA
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