I managed (eventually) to get the following statement out of the EA. This
goes some way to clarifying the reason behind the water quality standard
value of 10ug/l that the Agency (in my experience) consistently applies in
considering water pollution risks associated with TPH impact. A key
statement is that the 10ug/l threshold remains current in the Private
Water Supplies Regulations 1991.
Hope this helps,
Dr Ian Williams
Ground Investigation Ltd
tel 01792 411013/07979 230046
The Agency, as for a long time, advised that UK drinking water standards
should be used for polluting substances, where they exist. The target
concentration is usually of an order of magnitude that is both protective
of health (the reason of the target), and of groundwater quality
(environmental). It is acknowledged that the 10ug/l hydrocarbon DWS was
removed from the 2000 Regs, but it does remain in Private Water Supplies
Regulations 1991, and so is still current in UK legislation. The change
is due to health considerations, rather than environmental considerations.
There have never been any statutory groundwater quality standards in the
UK. Relevant environmental standards used as a basis for setting target
concentrations at the receptor should be justified as appropriate to the
site specific circumstances.
The new WFD & Groundwater Daughter Directive reaffirms (with some changes)
previous requirements to 'prevent and limit' the introduction of
pollutants into groundwater. The new 'hazardous' substance category is
likely to equate to the old List I wrt prevention of entry. Petroleum
hydrocarbons remain classed as List I ,and therefore hazardous, and should
not be present in groundwater. Other substances will be a broader list
than the present List IIs. Transposition of the Directive is required by
Jan 09, the replacement groundwater regulations are expected from DEFRA
later this year.
The Agency is currently finalising new guidance on Total Petroleum
Hydrocarbons, including a review of the current appropriateness of the
10ug/l as a remedial target for environment purposes. It is possible to
simulate the fate and transport of different TPH fractions in groundwater,
but the difficulty arises at the end of the process when assessors need to
make a judgement of the environmental significance of the predicted
concentrations of individual (or combined) TPH fractions.This review will
be based on available science. Until is work is completed we continue to
advise the use of 10ug/l as a target concentration, unless a site specific
case can be made for a higher target concentration, considering the any
historic nature of the pollution, distance to & uses of groundwater
(targets), and the significance of the resource.
The standard for benzene remains at 1ug/l, and in many cases is the
limiting contaminant for remediation of fuel TPH pollution. For surface
waters, EQS values exist for Benzene, Toluene, Xylene and Naphthalene. For
many sensitive surface waters/ groundwater's compliance in the groundwater
adjacent to the river will be required.
I hope this will help clarify our position.
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