Risks of buying vacant lot for new home construction with existing but unused septic system?

Question

My wife and I are considering purchasing a vacant lot for a new home construction. One of the main advertised selling points of the lot is that it has an unused septic system (tank, distribution box, and leach field) that was installed for a planned prior construction that fell through (for financial reasons, we're told). We've obtained copies of the inspection from the installation and learned that the system is nearly ten years old.

Our builder and others we've spoken with think the land is a good value and that the existing system could save us a good chunk of money, but we're trying to better understand what risks are involved. What could go wrong with a septic system that's been sitting in the ground for nearly a decade without ever being used? How bad could the worst case be?

Finally, is there anything that could be reasonably done to inspect what's already been installed? Everyone we've talked to so far has suggested that looking up the inspection of the installation should be sufficient, and that they couldn't do much more since the system is in the ground. That's a little unsatisfying to us considering how long the system has been sitting there. Are we being paranoid, or have we just not talked to the right people yet?

Answer 1

Yes, you're being paranoid.

If it was installed correctly, there really isn't much of anything that will go wrong with it from sitting - most septic problems are from using the system and not maintaining it, leading to material that should have been pumped out getting into the drain field and clogging it. If it's not used, that won't happen. The materials do not degrade in the ground. (Orangburg pipe does degrade, but a system built circa 2004 is a good 30+ years removed from the end of Orangeburg - nasty, hateful stuff - basically tar-paper pipes.)

If you keep hunting you can probably find someone who will take your money to run an inspection camera into the pipes. If you like, you could dig up (or open the access manhole, if your area was moving into modern ideas 10 years ago and did not allow the access to be buried below-ground) the septic tank access - but DO NOT stick your head into even an unused septic tank - they can still collect/generate poisonous gases and should aways be treated as if they were, in fact going to kill you if you did that - use a flashlight & mirror on a stick, or hire a pro. If the system is accurately mapped, the distribution box could also be dug down to for a look. If it passed inspection 10 years ago, there's not likely to be much of anything to see in either place, though the tank at least should be looked into (Title V inspection may, in fact, be required before sale, even though it's unused as yet) just to make sure it hasn't shifted or something, and to be sure you know where the access is if it's not above-ground access (consider adding a riser and manhole cover if you have to dig to find the access.)

Don't be surprised if you find it full of water - rainwater seeps in and won't flow out until the liquid inside reaches the outlet level. 10 years allows for quite a bit of rain to fall.

If it was not installed with a particulate filter on the outlet, you might want to have one retrofitted before starting to use it. It may have been - 10 years ago those were starting to become standard in many locales.

Answer 2

The usual disclaimer: I'm not an engineer, lawyer, contractor, or septic installer... this advice is worth what you paid for it :)

As Ecnerwal says, I'd guess the system itself should be fine. If you have doubts, septic pumping companies often offer a pump out (necessary for inspection) and inspection for a cost perhaps in the $300 to $400 range (highly dependent on your area). Assuming you are spending large sums for this lot, that's money potentially well spent as the seller is undoubtedly marking up the lot for the system and you could use any material defects to bargain hard. I'm talking about the tank here. I do think the leach field can be damaged by vegetation. You don't want to see a bunch of trees growing in it.

The fine points of the risk, IMHO, are related to engineering and permitting. I'd ask the following questions at your building department:

1. Was the system permitted?
2. If it was, for what size house? Most counties will require a certain size tank and leach field for a certain number of bedrooms or bathrooms.
3. Does the originally permitted size still meet code? In many areas, septic permitting was very loose even 10 years ago but this is an area that has more regulation now.

Basically, I'd make sure that the building department is going to be ok with you using the old system for the general size of house you plan.

Next, the question of engineering. Not all locations work well with leach fields. I'd ask the following questions:

1. What kind of system do your neighbors have? Leach field, raised bed, pump-out tanks, what. Perhaps the original system was not engineered for the site conditions.
2. Try to find out what the water table is. If the neighbors have wells or basements, they may be able to tell you.
3. Is there a percolation test with the city/county/etc for when the septic was installed? No perc test is not usually a good sign. You could have one performed with a backhoe but you'll need permission from the seller and that will cost you a bit.
4. Is there any chance that your lot is seasonally wet (even if not wetlands), has a seasonally high water table, is in a riparian area or in a floodplain? These conditions would all make a standard system more challenging. For example, a system on a flat lot between a house and a lake may have high water.

These questions are important because a raised bed system can be a lot more than a standard system and usually requires engineering design work.

Another risk for a new system is rocky ground or steep slopes.

If it was perc'd, permitted, and engineered, and the local building code hasn't changed, then you might be in business. If it wasn't perc'd, permitted, engineered, etc I would be leary of paying anywhere near the 'retail' cost of such a system. You might as well get familiar with the local building department anyways since you will presumably be dealing with them a lot if you buy the lot.

In final, if it were me, I would do the due diligence required to determine the cost of installing a new system. I wouldn't want to find out the reason the project was abandoned was because the standard system won't work and the required engineered solution exceeds the value of the lot.

Good luck!