
Subject :Imported soil and P values..
20130902 10:54:05



Daniella 

Fresh Boarder 

Joined: 20130902 10:47:24
Posts: 2
Location: 



Can anybody advise me on how to ascertain the p value for soil that is imported?
I recorded the time it took 0.5l to empty from the 150ml cubed hole for each 300 ml lift of soil.
How do I convert that figure to a p value to determine how big an area the polishing filter should be.
Is the time taken the p value? or is there some calculation to carry out? I can't seem to find the answer in the COP.
Cheers 
IP Logged






Subject :Re:Imported soil and P values..
20130902 20:22:22



Tim Clifford 

Fresh Boarder 

Joined: 20120417 21:26:42
Posts: 10
Location: 



Hi,
These comments are made in respect of a soil polishing filter.
As you have probably seen on page 32 and 96 the requirement is for 0.5l of water to empty from the from the 150ml cubed hole for each 300ml lift of soil between a time of 10min and 2hr. This is assuming the imported subsoil had a T value of between 3 and 30. (pg 43). Whenever I import subsoil off site I also conduct T/P tests on the virgin ground from where I am sourcing the material. Once I achieve the required 330 parameter I then import to the new site and then carry out the onsite test as you listed above.
In relation to sizing of the filter the loading rate is dependent on the percolation rate and in the case of an imported mound then the higher of the Pvalue of the insitu subsoil and of the imported material should be used to size the polishing filter. (pg 44)
This is my reading of the CoP. I hope this helps.
Tim 
IP Logged






Subject :Re:Imported soil and P values..
20130904 14:36:18



Daniella 

Fresh Boarder 

Joined: 20130902 10:47:24
Posts: 2
Location: 



Thanks Tim
I was trying to determine how you convert the time it takes the 0.5l to diasappear into a p value to enable me to work out the area needed for the filter.
I did some calculations and worked out that the height of the 0.5l of water in the 150m3 hole is approx 22mm. this would mean that the p value is the actual time it takes for the water to percolate through. ie the time it takes to drop 25mm (100mm/4).
Therefore if it took 24 minutes for the water to percolate then p = 24
So 24 x 0.125 x p.e. = area of filter (m2)
Am I on the right track?
The whole system is a treatment plant then through 2 x puraflo on top of a raised filter 
IP Logged






Subject :Re:Imported soil and P values..
20130904 20:04:06



Tim Clifford 

Fresh Boarder 

Joined: 20120417 21:26:42
Posts: 10
Location: 



Hi Daniella,
Your maths are correct however the time limits afforded to imported sub soil are between 10min and 2hrs (120min). I find this confusing myself as the upper limit for T testing is 90 (pg 16). Either this is a misprint or this test is not to be uses to determine the actual percolation rate of the subsoil and is only a general guide.
Now based on your WWTU calculations you are using the equation for tertiary systems (from the clarification in Feb 2011). This equation can only be used if:
* There is at least 0.3m of naturally occurring soil above the bedrock.
* The maximum high groundwater level is at least 0.3m below the natural ground surface.
If for example you were on a site and the T value was <3 then you are only required to pretreated to tertiary quality then the site will be hydraulically suitable to assimilate this hydraulic load. The only issue with this scenario is you may have to prove to the local authority that the underlying subsoil is hydraulically suitable.
You got me thinking though in relation to the 10min and 2hrs quandary so I'll shoot an email to a person who knows the answers to all these questions and get back to you.
thx
tim 
IP Logged






Subject :Re:Imported soil and P values..
20130905 09:34:53



Tim Clifford 

Fresh Boarder 

Joined: 20120417 21:26:42
Posts: 10
Location: 



Hi Daniella,
I contacted one of the trainers on the EPA course and a serious hydrologist guru in relation to the subsoil/p/t value and this was the response:
The subsoil should have been tested back in its own field natural environment... To make sure you weren't being sold a pup.. But the whole structure changes when it was excavated and transported and moved...
But really the pore structure would change with replacing but the actual component bits wouldn't... So, in reality the ribbons and threads should stay more or less intact as representative of its original state.
I hope this helps.
Tim 
IP Logged




