Ask the Carpenter: Hunting down cause of mysterious septic smell
Rob Robillard explains how to spot problems in your septic system.
Q. We certainly could use some advice. We get a septic odor whenever we use the washing machine, which is in the basement. We have had the septic system checked, and it is fine. We have had a few visits from a plumber, who concedes that odors can be challenging problems to solve. He plugged the septic outlet to look for leaks in the system but found and patched only a few tiny ones. Still the odor continues. We like our house, but this smell is disgusting.
D.P.
A. Is the odor coming from your washing machine? Some can develop a musty, sour stench and require cleaning. If it’s not coming from the washing machine, then the odor can be tricky to track down. I reached out to my friend Steve McGonagle, a consultant with Septic Genie.
Usually, McGonagle said, if there are no leaks in the pipes, odors in the basement indicate either:
■ The septic system has very high effluent (wastewater) levels, causing a backup into the waste pipe from the house, OR
■ There is a blockage in the pipe that is causing organic material to remain inside it.
If all of the waste lines are adequately vented, someone should check the vent pipes from the roof to make sure there are no blockages reducing the air flow up and out. A partial blockage would trap septic gases in the vent pipes.
Because this problem cropped up suddenly, I strongly recommend you open the septic tank to see how high the water level is.
If the water level is normal, have someone flush a toilet a couple of times, and watch to see whether the water freely enters the septic tank. If the water flow is low, this could indicate a buildup of organic waste and slime in the line somewhere. If this is the case, the line needs to jetted.
If the water level is high and covers the inlet pipe, that could be the reason for the sudden odor. If waste and water are trapped in the waste pipe (inlet pipe to the septic tank), septic gases will build up. Over time, the level of water and waste in the pipe will creep up toward the lowest fixture, like a washing machine in the basement, for instance. When large volumes of water (a laundry load’s worth, for example) disturb the trapped water and waste, the gases escape into the basement.
Taking showers and flushing toilets upstairs will also release gases.
High water in your septic tank is one of the classic signs that the drain field is failing. When new wastewater enters the septic tank from the house, the same amount is supposed to be pushed through the outlet pipe and into the drain field. If the drain field is already full of water, the septic tank fills up and wastewater is pushed back up the inlet pipe toward the house.
Drain field failure is almost always (more than 95 percent of the time) due to “biomat’’ — a slime released by intestinal bacteria that is carried out into the drain field along with bits of solid waste. Biomat builds up over the years and clogs the soil around the drain field.
Many septic contractors will recommend digging up and removing the pipes and surrounding soil, then having a new field installed. This doesn’t solve the biomat problem; it just buys you time until it happens again. Replacing a drain field is also very expensive, ranging from $10,000 to $50,000.
If the root cause is biomat, the best way to remove it and prevent it from reoccurring is to install a system that eliminates the solid waste when it first enters the tank, so the intestinal bacteria will die and never end up in the drain field in the first place. Once the system is working properly, you may want to have the wastewater lines from the house to the septic tank hosed out to remove any trapped waste.
Rob Robillard is a general contractor, carpenter, editor of AConcordCarpenter.com, and principal of a carpentry and renovation business. Send your questions to [email protected] or tweet them to @robertrobillard. Subscribe to our free real estate newsletter at pages.email.bostonglobe.com/AddressSignUp.
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