Advice needed re Perc tests - is it an issue if they were undertaken at a depth greater than 1m?

[gb199]

Hi everyone.  Would appreciate some advice.  I had some perc tests done to judge how large a soak away I required.  These were done at a depth of 1.8m at the drainage companies suggestion.

 

After completion of the tests I messaged some other drainage companies to get quotes for remedial work, and one stated that perc tests should not be deeper than 1m.  Is this correct?  What's the potential impact of going deeper than 1m?

[ProDave]

What are the issues with the test results?  Draining too quick or too slow?

 

Why were they done so deep?

 

Why not re do at correct 1M depth?

[Gus Potter]

1 hour ago, gb199 said:

Hi everyone.  Would appreciate some advice.  I had some perc tests done to judge how large a soak away I required.  These were done at a depth of 1.8m at the drainage companies suggestion.

 

After completion of the tests I messaged some other drainage companies to get quotes for remedial work, and one stated that perc tests should not be deeper than 1m.  Is this correct?  What's the potential impact of going deeper than 1m?

Interesting question. The one metre depth may actually be to do with health and safety in terms of accessing an excavation without support. 

 

If your house is on a slope, on a hillock then we don't want the water just running out further down, especially if it is from a septic tank for example. Sometimes it works to sit a soakaway deeper, for example there is a gravel layer a bit deeper down that can accept a bit of extra water. There is a trade off in that the excavation is deeper thus more cost.. but in a good gravel layer the soak away can be less extensive. 

 

What you mention 1.8m depth seems more like an "Engineered" solution which can be elegant and offer best value for money while still performing.

[Mr Punter]

I think you need to get in touch with the people who did the tests and ask why they decided on 1.8m.

[Gus Potter]

12 minutes ago, ProDave said:

What are the issues with the test results?  Draining too quick or too slow?

 

Why were they done so deep?

 

Why not re do at correct 1M depth?

Good questions. A soak away draining too quickly can be more easily mitigated than one that drains too slow, the too slow causes problems.  Often you just need to understand the ground composition, then adapt the design a bit. 

[Nickfromwales]

Was it sloping, so needed to be below ground <1m at the boundary? 
 

Odd that no detail exists from their fees proposal at least?

[gb199]

Thanks for all your responses so far.  To answer a couple of questions, I believe the reason for going deeper was to do with checking the integrity of the existing septic tank.  The perc results were poor, and the holes actually gained water during the test.  The garden itself is tiered, with the house sitting lower than where the tests were conducted by about 1 ft

 

The solution proposed was to install a treatment plant, which will pump any liquid after treatment to a soak away on a higher bit of ground.  I was happy with this solution, but after the feedback from other drainage companies im not sure whether this solution is based on an inaccurate test in the first place!

[ProDave]

So this was a test to replace the existing soakaway for an existing septic tank?

 

The advice to replace it with a treatment plant is good, and it sounds like it needs a pumped solution due to the sloping ground and possibly high water table (or just saturated ground from the poor existing soakaway)

[gb199]

1 hour ago, ProDave said:

So this was a test to replace the existing soakaway for an existing septic tank?

 

The advice to replace it with a treatment plant is good, and it sounds like it needs a pumped solution due to the sloping ground and possibly high water table (or just saturated ground from the poor existing soakaway)

Thanks.  Yes it will have a pump.  

 

Thanks everyone for all the input.  Much appreciated!  Sounds like I don't need to worry about the depth of the tests, so will go forward with the quote.