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TALKING POINT

NEWS - Water companies must be aware of the limitations of guidance when specifying supply pipes through potentially contaminated land, says Alan Watson.

In view of the water shortages in southeast England and the need for the water companies to repair leaking pipes, I am concerned about the guidance of the Water Regulations Advisory Scheme (WRAS) on water supply pipes in contaminated land.

Some of the contaminant 'threshold' concentrations for soils, stipulated in the WRAS guidance document 9-04-03 (October 2002), seem unusually low.

I understand they are based on an earlier Foundation for Water Research document FR0448 (1994), which appears to use some values from the Interdepartmental Committee for the Redevelopment of Contaminated Land (ICRCL) guidance, withdrawn in 2002.

Even so, there is nothing to indicate, for instance, a toluene extractable matter (TEM) threshold as low as 50mg/kg. This prescribed value is in fact below the detection limit for routine testing techniques.

I was involved in a scheme for a large water supply pipe in the south of England. After a ground investigation, the water supply company was concerned about potential contamination on the basis of TEM concentrations of about 550mg/kg - because the WRAS threshold is only 50mg/kg.

While there is some risk of deterioration of plastic pipes in contact with hydrocarbon contamination, it is unreasonable to impose special measures on the basis of slightly elevated TEM concentrations alone.

Indeed, this was the conclusion after a more extensive investigation showed concentrations of TPHs (total petroleum hydrocarbons), PAHs (polycyclic aromatic hydrocarbons), Phenols, VOCs (volatile organic compounds) and SVOCs (semivolatile organic compounds) below the thresholds, except for a handful of samples.

There are also issues to address with regard to the other prescribed thresholds, particularly in the case of arsenic and selenium, for which the latest Defra/Environment Agency Soil Guideline Values for residential use are 20mg/kg and 35mg/kg respectively.

These are based on the allowance for a six-year-old girl ingesting soil from a private garden, which may be a more onerous scenario than the case of a potential contaminant pathway through water supply pipework. The WRAS thresholds for these determinands are 10mg/kg and 3mg/kg, respectively, which now seem quite low.

With regard to these and other toxic contaminants, which are potentially harmful to human health but not necessarily corrosive or organic, the WRAS guidance does not appear to have been based on a fully researched assessment of their potential to permeate particular pipe materials, or to what extent leaking joints can allow contaminants into the water supply.

There must be a review of relevant research since 2002 so that human health risks can be properly assessed.

Other site-specific factors such as soil permeability and contaminant mobility, or whether permanent drainage is to be installed in conjunction with the supply pipe, also need considering.

Given that water companies appear to be referring specifically to the 2002 WRAS guidance, I foresee problems with the over-specification of supply pipe materials. A number of questions need to be addressed:

What has been the outcome of the research funded by the water industry, to which the WRAS guidance refers, and was due to be reported in 2004?

Has WRAS received other similar enquiries from concerned companies?

Is WRAS able to issue a formal relaxation of the TEM threshold?

Does WRAS have plans to review its 2002 guidance in light of the latest Defra/EA derived Soil Guideline Values, or has there been more research into permeation of pipework by toxic contaminants?

Water companies should be made aware of the limitations of the 2002 guidance and WRAS should act quickly before excessive unnecessary expenditure is incurred.

Alan Watson is a chartered environmentalist and is a senior engineer at Soil Consultants.

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