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Use of Statistics . . . .
Is this forum now open up to consultants?  I often thought that it was a forum for LA/academics and enforcement officers to discuss professional issues?  I noted your comments that we should not be too harsh in our reply because your consultant read this board.
 
Ken
-----Original Message-----
From: Contaminated Land Management Discussion List [mailto:[log in to unmask]]On Behalf Of David Fountain
Sent: Friday, May 26, 2006 1:03 PM
To: [log in to unmask]
Subject: Re: Use of Statistics . . . .

"Unfortunately a number of the houses didn't get the clean cover in the gardens"
 
and
 
"Both the mean and the 95% UCL for all the samples exceeded the SSAC (by a factor of 4)"
 
So I was surprised when the re-test in the affected gardens resulted in "The developer has considered all the samples a single population and the stats indicate that the 95% UCLs are below the SSAC".  How convenient.
 
In this somewhat unusual case, I would consider each garden as a separate averaging area.  There's really no excuse for the capping not to have been laid in every garden, and given the salient facts above, you can happily state you have to reason to suspect a problem will be present in SOME of the re-tested areas.
 
Just remember - 88.2% of statistics are made up on the spot...

Dave Fountain
Contaminated Land Officer
East Staffordshire Borough Council
Tel: 01283 508848
Fax: 01283 508890

-----Original Message-----
From: Contaminated Land Management Discussion List [mailto:[log in to unmask]]On Behalf Of Stephen Moreby
Sent: 26 May 2006 12:51
To: [log in to unmask]
Subject: Use of Statistics . . . .


Just after a reality check on a 'use of statistics issue' . . .


Redevelopment of a slightly contaminated site for residential with gardens.

28 soil samples tested - only 6 had exceedances of the SSAC for the contaminant of concern, but some of these were quite high.

Both the mean and the 95% UCL for all the samples exceeded the SSAC (by a factor of 4), but no identification of hotspots was possible as the ground conditions were fairly uniform.

A clean-cover remediation was proposed.


Unfortunately a number of the houses didn't get the clean cover in the gardens - and then managed to get sold and occupied (don't ask how !)

This was identified during the validation process ( - which is a good example of why it's so important) and further testing undertaken

3 or 4 samples were taken from every garden not remediated
The developer has considered all the samples a single population and the stats indicate that the 95% UCLs are below the SSAC

However 6 of the gardens exceed the SSAC if you consider each garden to be an appropriate averaging area in its own right - some marginally, some more so


I know it's hard to comment on specific cases, so all I'm asking is for comments on the use of stats.

Is every individual garden now best considered a single appropriate averaging area ?
Or is it OK to consider the validation data for all the gardens not remediated together ?
Or should ALL the data be included (both the original SI and the validation data) ?

Or should I simply not worry about it and act on the clear breech of planning condition ?


I know the consultants involved read this board, so don't be too harsh - we all make mistakes.

I hope I've explained the issue well enough.
Thanks in advance.



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