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The cost of barrier pipe installation and MDPE

Between 2006 and early this year, our firm was approached by a number of developers, house builders and contractors faced with water supply companies insisting on barrier pipe to mitigate the effects of what they perceived to be contaminated ground.

In my previous Talking Point column (GE July 2006) I said the thresholds prescribed by the Water Regulations Advisory Service seemed to be unusually onerous and that protective barrier pipe could be overspecified in situations where it may not be needed, resulting in substantial and unnecessary extra cost.

This proved to be the case and our company has faced a number of difficult situations, including one where the additional cost of the barrier pipe was over £750,000.

There have been other cases on smaller developments where standard medium density polyethylene (MDPE) pipe had already been installed, only for the water supply company to subsequently specify barrier pipe. We have been able to successfully defend the use of MDPE pipe in several cases.

As far as Soil Consultants is aware, the position appears to have changed rapidly and the additional cost of barrier pipe has reduced significantly.

This means there will be many cases, particularly on small housing developments, where cost has reduced so much that it may not be economic to carry out additional ground investigation to prove that barrier pipe is unnecessary. There may be cases where the best option is to install barrier pipe as standard.

Nevertheless, there are still likely to be larger projects where additional sampling and contamination testing within an ongoing ground investigation may be economic. This will provide useful data to enable MDPE pipe use to be defended when the water supply company could potentially specify barrier pipe.

Alan Watson
Senior geotechnical engineer, Soil Consultants

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