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Liquid liabilities Robert Jackson and Elizabeth Ord discuss the implications of recent UK legislation on the protection of potable water supplies.

GROUNDWATER LEGISLATION

All key players in land, property and waste management now face onerous liabilities and the risk of prosecution, particularly with respect to groundwater contamination. They need to appreciate the threats to water quality; understand the impact of contamination on groundwater; understand the extensive liabilities and responsibilities on businesses with land and property holdings; and understand the liability for environmental damage leading to criminal charges and civil litigation.

In the UK, aquifer vulnerability to pollution is determined by the nature of the overlying soil cover, the presence and nature of drift deposits, the nature of rock strata and the thickness of the unsaturated layer. Together, these reflect the accessibility of the aquifer to recharge. Reliable estimation of recharge is pivotal in understanding the processes of groundwater pollution.

The most important British aquifers are the Permo-Triassic sandstones, the Cretaceous chalk and the Jurassic limestones. Groundwater is defined legally as 'all water which is below the surface of the ground in the saturation zone and in direct contact with the ground or subsoil', and represents about 35% of water distributed for potable supply in England and Wales.

A key question is the likelihood of accelerated climatic change and its effect on the UK. Balance of opinion suggests that lowland England may experience more frequent and extended warm dry periods in summer and autumn, with higher intensity rainfall episodes in winter. This may lead not only to different rates of groundwater recharge but also to changes in recharging mechanisms as a result of higher rainfall intensity, and in contaminant mobilisation/leaching as a result of dryer, more aerobic and higher temperature soils.

The requirement that all groundwater resources must be protected derives from the European Community Groundwater Directive (80/68/EEC) and generally leads to the installation of some engineered containment at the base of new landfill developments. The groundwater protection policy developed by the then National Rivers Authority states that the disposal of domestic, commercial and industrial wastes is only acceptable on major and minor aquifers with such containment.

Aquifers can be considered as layers of rock sufficiently porous to store water and permeable enough to allow water to flow through them in economic quantities. Major aquifers are defined in the groundwater protection policy as highly productive strata of regional importance which are often used for large potable abstractions. Minor aquifers are defined as formations of variable permeability which support locally important abstractions. Non aquifers have negligible permeability and support only very minor abstractions, if any.

Most groundwater originates as excess rainfall locally infiltrating the land surface and so surface activity threatens groundwater quality. Indeed, groundwater everywhere is vulnerable to surface-derived pollution and the only way it differs geographically is the time scale for effects to become manifest.

A particular problem in the UK is glacial till, which overlies bedrock over a significant part of upland and much of lowland Britain. A reasonably satisfactory rule of thumb is that till reduces the potential recharge to the underlying aquifer by 30%.

The recharge mechanism is very important and depends on the rock type. Recharge has two direct effects on dispersed pollutants. Greater recharge leads to more potential for dilution but also results in more efficient pollutant transport from the surface to the water table. Subsurface water flow and contaminant transport are complex processes. In particular, the degree of attenuation will vary significantly with type of contaminant and pollution process in any given situation.

The potential role of the soil zone in adsorbing or attenuating surface- derived pollutants is too often overlooked in groundwater studies. In this respect, soil is defined as the weathered zone into which plants will root and is the zone or layers formed from the interaction of climate, soil organisms, vegetation and geology. The role of the soil zone is also critical in the infiltration process and together, the soil's texture and grain size control its ability to retain or drain soil moisture.

The soil's structure and density influence the progress of permeating fluids and the presence of clay minerals and organic matter influence the soil leaching potential, ie its ability to transmit non-conservative pollutants. Interestingly, cation exchange assists in the degradation and attenuation of some pollutants within the soil zone. Soil usually contains millions of organisms per cubic metre, ranging in size from mammals and earthworms down to the microscopic. It can provide natural physical barriers to the vertical movement of water and pollutants, thus having a major influence on land use especially in conjunction with climate.

Aquifer porosity can comprise different types ranging from microfissures which allow rapid egress of storm water, to microfissures which promote storage and transport and large fractures and dilated bedding planes which offer egress to percolating water. However, within rock strata, the presence of well defined preferential flow paths is highly relevant in assessing aquifer vulnerability to faecally contaminated discharges containing bacteria, viruses and even protozoa such as cryptosporidium and to industrial solvent and hydrocarbon fuel spillages. Such paths are also of major importance in relation to the transport of pesticides to aquifers, providing routes for deep penetration of any pesticide compounds leached from the soil.

The wide ranging scope of the regulations is likely to impact on the majority of concerns which make, use, distribute, store or dispose of chemicals.

The most affected sectors will be those which indirectly discharge chemicals, such as chlorinated solvents and hydrocarbons in metal manufacture and dry-cleaning, and those with underground tanks. The petrochemical industry is likely to be hit quite hard. Petrol stations pose a risk to groundwater and the cost of pollution prevention measures to petrol retailers could be high. Five years ago, Shell revealed that one third of its petrol stations in the UK had leaked and other retailers most certainly have similar problems.

Major liabilities also exist with regard to acid mine drainage which is a major source of pollution worldwide. This pollution arises from the bacterially catalysed oxidation of pyrite which is widely disseminated in Coal Measures through one of the most prolific acid producing reactions in nature. Mining is the main cause of the large scale circulation of water and oxygen through pyritiferous strata and while operators of active mines often treat pumped water to minimise environmental impact, abandoned mines usually discharge in an uncontrolled manner. This leads to widespread acid mine drainage pollution problems. In England and Wales alone there are some 200km of waters affected by abandoned coal mines with pollution spreading to hitherto unaffected river reaches.

Similarly, those activities which directly discharge listed substances to groundwater through discharge consents or integrated pollution control (IPC) authorisations will still be regulated by those regimes and will not be subjected to the Groundwater Regulations. Some sites, whose operations are partly covered by IPC authorisations, will probably need a separate authorisation under the groundwater rules for non-IPC activities. The two permits will have to be harmonised to ensure consistency.

Controversially, all activities for which a waste management licence is required are excluded. This is because the 1994 Waste Licensing Regulations (SI1994 No 1056) already apply the directive's requirements. Regulation 15 imposed a duty on the EA to review all existing landfill licences and modify or revoke them to give effect to the directive. However, not all sites with waste management licences are subject to Regulation 15 assessment. Regulation 15 applies only to waste disposal sites that have the potential to generate leachate. Other licensable operations, like metal recycling sites, transfer stations and civic amenity sites are not covered. To exacerbate this oversight, Regulation 15 has encouraged very few reviews in any event and widely different approaches to its implementation may be found across the country. If this attitude continues, then some of the most polluting sites may escape control.

This lackadaisical tendency towards landfills is not mirrored in other areas of groundwater pollution control however. The EA has successfully prosecuted its first groundwater cases over the last few years, resulting in high fines and bad publicity for the errant companies.

A recent case concerned ICI at Runcorn, which breached an IPC authorisation condition under section 6(1) of the Environmental Protection Act 1990 and caused chloroform to enter groundwater contrary to section 85(1) of the Water Resources Act 1991. It was fined £300,000.

Another case involved British Energy's Dungeness nuclear power station where oil leaked from a pipeline into a drinking water aquifer contrary to section 85(1). The company was fined £70,000. Hence, although the agencies' resources are limited and many polluters escape conviction, public perception is encouraging these bodies to take a harder line and to implement the 'polluter pays' principle wherever possible.

Those who ignore groundwater protection legislation do so at their peril.

Robert Jackson is head of civil and environmental engineering and Parkman professor of water and environmental engineering at John Moores University, Liverpool. Elizabeth Ord is a solicitor specialising in safety, health and environmental litigation and is principal of EC Ord & Co.

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