More planning of construction dewatering schemes will be needed under the UK's new abstraction licence regime, says Martin Preene.
Abstraction of groundwater for dewatering and groundwater control in the UK is about to be regulated much more closely than in the past. In England and Wales this has been on the cards since the Water Act 2003 passed into law, removing historic exemption from licensing enjoyed by dewatering of excavations for construction and quarrying.
Based on the latest information from the Environment Agency (EA), the exemption will cease to apply from October, when secondary regulations will come into force. In Scotland, the controlled activities regulations are also planned for 2006 and may require additional permissions for dewatering.
In England and Wales, the upshot is that all groundwater abstractions over 20m 3/day, including those for dewatering, will require an abstraction licence. There will be three types:
A temporary licence, for any groundwater abstraction of less than 28 days duration.
A transfer licence, for groundwater abstraction from excavations, discharged to surface watercourse, or recharged back to the aquifer, provided the water is not put to any intervening use.
A full licence, required for any groundwater abstraction where the water is used for any purpose.
Most dewatering projects, apart from very short ones, will require transfer licences. This applies to new abstractions as well as those for existing excavations.This should not affect the way dewatering is carried out, but it may affect planning.
This is based on two premises.
The first is the EA's most recent consultation document, published in September: Review of the water abstraction charges scheme. Second consultation document. This outlines a transitional period of up to five years following the loss of exemption.
During that time the EA is likely to target sites with significant potential to affect the groundwater environment, most importantly, long duration of dewatering, large drawdown of groundwater levels, nearby sensitive groundwater features such as wetlands and existing plumes of groundwater contamination.
Second, dewatering abstractions are not unregulated at present.
The Water Resources Act 1991 requires that the EA be notified in advance of any dewatering works, and if environmental impacts are of concern, the agency can issue a conservation notice requiring additional monitoring or mitigation measures.
Any dewatering works where the EA imposes conditions and restrictions under the new transfer licence system would most likely have been subject to similar restrictions under a conservation notice.
This mechanism has been used to require contractors to recharge dewatering water back into the aquifer to avoid depleting groundwater resources.
Differences are likely to come when planning dewatering, with a hydrogeological impact assessment (HIA) possibly needed to support a transfer licence application.
For the vast majority of dewatering projects, where the potential for impact on the groundwater environment is low, the HIA may simply be a tick-box exercise.
But on a small number of projects considerable work may be required to develop the HIA, perhaps including field monitoring to establish background conditions and numerical modelling of groundwater flow.
Overall, the message for those carrying out dewatering from 2006 is positive, in that environmental mitigation measures required are unlikely to be more onerous than at present.
However, more time will be needed in planning of all dewatering works - for licence applications to be processed by the EA, and on a smaller number of projects, for the work involved in producing a detailed HIA to demonstrate dewatering can be implemented without unacceptable impacts.
Martin Preene is Golder Associates UK groundwater manager.