Doing your own perk test

Started by cbc58, March 03, 2018, 09:25:36 AM

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cbc58

Wonder if anyone has done their own perk test to get an idea of what a septic system might cost -- before hiring someone to do it officially.  In my neck of the woods they want $400 for a perk test and my understanding is that they dig holes, fill them with water and measure the amount that drains over a set length of time.   As you dig and see the color/soil makeup - you can also get a feel for the location of the high water table.  Watched a few vids on it and it looks fairly straight forward.  They don't require test pits here (backhoe required) -- like some other areas of the country.

Has anyone done this and how did your results match up to the official results?

NathanS

In my opinion one of the first things you should do on a piece of land you're looking at is do a perc test. NYS actually has a septic system handbook that the engineers use, and it tells you exactly what to do.

The government also has detailed survey maps that should give you a basic idea of the type of soil on the land you're looking at.

In NYS -
The most standard system requires 4 feet of free draining soil. A shallow bed requires at least 2 feet, but you will have to bring in, or move, dirt to get back to a total of 4 feet. Less than 2 feet of draining soil, and you're in the 'sand mound' raised bed territory that requires extra legal loops to jump through and would at least double - maybe quadruple - the overall cost of the system.

You dig down to the necessary depth, in our case we would hit impermeable hard pan at around 2 feet. Make sure the sides of the hole are crumbly so they will accept water. Stick a stake in with marks 2 inches apart, keep filling the hole with water to the top line, time it until it gets to the bottom line. Keep doing that until the drain time is equal to the prior test. That is your perc rate.

Based on that drainage rate there is a table that tells you how long and how many pipes you need.



cbc58

from what i have seen - you fill the hole with water until the immediate soil gets saturated - then once that is done - fill it full with water to a line and then time how long it takes to drain. 

NathanS

Yup that's it. Timing the level drop until it equalizes is how the engineer will do it.

Some people think waiting until late summer will change the test, but it shouldn't do much because you basically keep inundating the ground until it behaves like it is saturated.

The engineer we used just had a shovel. He said he will do tests  all winter too, just bust his way through the frozen ground until he hits the soft stuff.

The design guide I believe will also specify how high up the water should be filled. It is a lot like reading the building code, as long as you aren't doing something weird you probably don't even need the engineer.

GaryT

I had a perc test done before we bought our land in New Brunswick, Canada.  The province has a very specific hole that must be dug.  It has to go down 6ft at one end, have about 3 feet of ground showing at that level, then a step up to 3 feet down, and same amount of ground showing at that level. 
They don't fool around up there!  Just getting the hole dug cost $250!
Gary


hpinson

These are very easy to do yourself.

My question is - if you do it yourself - will your results be taken seriously by the septic permit givers?  I'd like to hear knowledge/ opinions on this.

NathanS

I bet some places would allow it, but overall no.

If there is something obviously wrong when you do the test yourself you can rule out the property before hiring an engineer or paying a lawyer to create a conditional offer on the land. Those two things alone could easily cost $1000.

jsahara24

Some towns allow local engineers/soil scientists to perform the soils/perc test, and some require their sewage enforcement officer to complete them or witness them.  I've never heard of a homedone perc test being accepted for permitting.  I definitely recommend doing a perc test on land you are looking to buy, I did on my last purchase. 

There are two things to consider, limiting zone (high water table or bedrock) and percolation rate (soil permeability).  The limiting zone is generally noted as bedrock (pretty obvious) or high water table (which is either observed water or evidence of mottling in the soils). I am sure this varies by state but you typically need ~2 feet for a sand mound and ~4 feet for a standard septic.  Ideally a 6' limiting zone would be good but you can work with less. 

Perc test is a ~6" hole to your desired bottom elevation.  Fill the bottom with stone and presoak it twice.  Then measure the drop until it stabilizes within 1/4".  It would be good if you had a 1"/hr but you can get away with less.  There are a lot of cool systems out there today that are suitable for questionable soils, but they get expensive quick and include more maintenance that most people are used too. 

I did a lot of perc tests in my high school days.  I don't miss digging those holes in the rocky PA soils. 

cbc58

#8
I can't imagine the govt. allowing any DIY results to approve a system.  But it would interesting to see how DIY results match up to official results when getting approvals.

Tried a perk test yesterday on some land that I was told won't perk - to see for myself what the soils were like.  Dug a hole on slightly sloping land - 24" deep by 1' in diameter, and the first 7" or so was nice loamy soil (lots of pines on property), then it fairly quickly went into clay soil - with a compacted clay layer around 13".  Filled the hole with water - let it soak for 10 minutes - then filled it again and waited 30 minutes.  Water level dropped 4" over the half hour.  Spent a few more hours at the property digging other holes - most of which showed the clay layer closer to the surface.  Checked the perk hole when leaving and there was about a quarter inch more drop in water level.  So over course of 4 hours the water level dropped by 4.25" total.

I did not see any real color changes in the soil except where the loam turned to clay.  How would you determine the seasonal high water table in this situation?  Is it where the compacted clay layer starts or is it up where the water level in the hole is - 4.25" down - or somewhere in between?  The geological survey classification says that the typical SWT for the type of soil is 12"-16".  I am guessing this is a failed perk. 

   





jsahara24

Quote from: cbc58 on March 05, 2018, 08:01:21 AM
I can't imagine the govt. allowing any DIY results to approve a system.  But it would interesting to see how DIY results match up to official results when getting approvals.

Tried a perk test yesterday on some land that I was told won't perk - to see for myself what the soils were like.  Dug a hole on slightly sloping land - 24" deep by 1' in diameter, and the first 7" or so was nice loamy soil (lots of pines on property), then it fairly quickly went into clay soil - with a compacted clay layer around 13".  Filled the hole with water - let it soak for 10 minutes - then filled it again and waited 30 minutes.  Water level dropped 4" over the half hour.  Spent a few more hours at the property digging other holes - most of which showed the clay layer closer to the surface.  Checked the perk hole when leaving and there was about a quarter inch more drop in water level.  So over course of 4 hours the water level dropped by 4.25" total.

I did not see any real color changes in the soil except where the loam turned to clay.  How would you determine the seasonal high water table in this situation?  Is it where the compacted clay layer starts or is it up where the water level in the hole is - 4.25" down - or somewhere in between?  The geological survey classification says that the typical SWT for the type of soil is 12"-16".  I am guessing this is a failed perk. 

Google 'soil mottling pictures' to get an idea of what mottling (seasonal high water table) does to soils. 

Any chance you get through the clay layer if you dig down to ~5 feet?  Sometimes you can have a perched high water table due to a layer of clay and the soils beneath it are suitable.  But based on your description it doesn't sound good. 


cbc58

#10
yeah - just got off the phone with a soil scientist who knows the area and they said the seasonal high water table is probably perched 4"-5" above the hard clay line.  not worth further effort.

thanks for the info on the pics/mottling...

flyingvan

They let me dig the holes but not do the test.  It saved money, and there was a guy whose perc test had failed but when he measured the holes some of them were nowhere near the proper depth.  Like just about everything else, if you want it done right....
Find what you love and let it kill you.

cbc58

#12
QuoteAny chance you get through the clay layer if you dig down to ~5 feet?  Sometimes you can have a perched high water table due to a layer of clay and the soils beneath it are suitable.

I have a question regarding this and it would be good to know for future reference.  If the soils were good under a thick layer of clay (say the clay was 4' thick and then it went to suitable soils), how could you put in a system for that type of situation?  Would you excavate almost like a cellar hole - put in septic sand/ materials where the clay was, and then place drains around the perimeter of the system?  I have been told that the typical system here requires an approx. 4500 s.f. leach field - that is a big hole and probably can get pretty expensive...

Canvasman

Here in Wisconsin,no perc test. You dig a hole and look at the soils and their colors. If you hit clay at 4 feet down ( you need to have 3 feet of good soil under the tubes) and dig through clay to good soils. You can add rock to bring back up to depth, and install system.