Ian,

The1991 PWS Regs have been quoted by the EA for a while now (ever since
the Water Supply (Water Quality) Regs were replaced 2000), however the
PWS Regs are only current in England and Wales and were replaced in
Scotland in 2005.  The new Scotish Regs don't have a hydrocarbon
threshold, just benzene and PAHs, and it would be interesting to know
what SEPA now uses.

I've tried on a number of occasions to use speciated TPH thresholds
derived using the published toxicological data for hydrocarbon ranges
(the same as those used to derive the GAC values) and a daily ingestion
rate of 2liters, but the EA always insist on the 10ug/l threshold.

The new England and Wales PWS Regs are due to be issued later this year
and it will be interesting to see what happens then.  

Dan

-----Original Message-----
From: Contaminated Land Management Discussion List
[mailto:[log in to unmask]] On Behalf Of Ian
Williams
Sent: 04 April 2008 10:11
To: [log in to unmask]
Subject: Re: Water Quality Standards

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.