COUNTRY IN FOCUS
United Kingdom – An overview of groundwater

 

 

Our environment is the air we breathe, the water we drink and the ground we walk on. We must not turn our back to the environment, but looking after it to make it a better place, for us and our future generations.

 

In United Kingdom, groundwater forms the largest available store of fresh water – in fact there is far more groundwater than there is fresh surface water. This one provides one third of the drinking water and feeds to many of the rivers and wetlands.

 

1. Groundwater, how does it work?

 

Groundwater comes from rainfall that has filtered down through the ground and is stored in permeable rocks, known as aquifers. The amount of water aquifers receive (known as recharge) varies throughout the year and depends on the temperature and rainfall. Failure of winter rainfall over one or more years can lead to shortages in groundwater.

 

In Britain, the average annual recharge to the main aquifers is seven billion m3, and about 30 per cent of this is abstracted at a rate of nearly 7 million m3 per day. Most of this is abstracted in the south east of England as is shown on the Figure 1. It is worth noting that any water abstracted from the ground is water that will not reach rivers.

 

Figure 1: Public water supplied by groundwater in UK

Source: Environment Agency

 

As well, the amount of water taken (or abstracted) from an aquifer needs to be in balance with the rate of recharge and the amount of water that plants and animals in rivers and wetlands need to survive. Consequently, excessive pumping would risk that the wells no longer supply water—they can "go dry."

 

It has to be highlighted that the quality of groundwater in United Kingdom (UK) aquifers has deteriorated significantly over the last few decades. Primarily as a result of increased agricultural production since the 1940s, nitrogen concentrations affect many groundwater supplies. Sadly, the list of pollutants has also increased from the use of pesticides, or well accidental spills or leaks from tanks of petroleum products, phenols and chlorinated hydrocarbons. The more soluble and mobile of these pollutants can infiltrate to the water table resulting in plumes of slowly moving contaminated groundwater from many industrial sites.

 

This scenario suggests a need to increase users, policymakers and public authorities’ awareness of the necessary conservation of our sources.

 

2. To turn raw water into drinking water

 

Focusing on south east of England, the highest populated area in UK with relatively low annual rainfall comparing with the rest of the country. More than 1,000 litres of water a week on average to each of more than 9 million drinking water population.

 

The water comes from two types of sources: river and groundwater. Consequently, the quality of it can be different, so to turn raw water into safe and wholesome drinking water, the water treatment process it goes through is tailored to make sure the water supplied is the best-quality water possible.

 

A third of drinking water supplies come from groundwater, this one is pumped from aquifers up to the surface by boreholes. Being so thoroughly and slowly filtered through the rock, groundwater usually needs only minimum treatment after being pumped to the surface. Therefore, the treatment process for water abstracted from boreholes differs slightly from that for water abstracted from rivers and reservoirs.

 

As a result of water supplied to the users is a mix of different sources, the water treatment that is carried out is as described in Figure 2. Firstly is required to remove any large item by a screening process, passing the raw water through coarse screens. Subsequently, the water is pumped into large flocculation tanks to be clarified. This clarifying process adds a dose a chemical coagulant into the water, and acts to bind together fine suspended material such as silt and mud particles. The clarified water is sent to large filtration tanks to remove the rest of the particulate matter. The water moves through tanks containing activated carbon granules. These grains of pure carbon remove any remaining chemicals such as pesticides from the water.

 

The major public concern with drinking water contamination has been possible contribution to cancer risks from organic hazardous substances identified already into groundwater / surface water. They can’t be removed with the standard water treatments and should be used advanced oxidation processes such as ozone. Ozone dosing involves injecting ozone into the water to breakdown toxic pollutants including pesticides, organic chemicals and substances leaching from contaminated sites.

 

In the subsequent step, chlorine is added to the water before it enters a contact tank, where disinfection occurs. Nevertheless, the residual chlorine level is carefully monitored throughout the system, enough chlorine is left in the water to prevent bacterial growth in the distribution system.

 

Finally, drinking water is then pumped to a network of service reservoirs where it is stored to supply users demand. The water then travels through pipes to user’s taps.

 

Figure 2: Water treatment process

source: Thames water website

 

3. Who does look after the groundwater in United Kingdom?

 

The legal and technical framework on groundwater policy issues are provided by Department of Environment Food & Rural Affairs (DEFRA) and the Environment Agency in United Kingdom. Their work is based on the European Water Framework Directive (WFD).

 

Regarding groundwater, the Directive requires to prevent hazardous substances entering into groundwater. It also puts limits on some non-hazardous substances going into groundwater. So, the Environment Agency has a duty to manage the use of groundwater. They balance the need to supply users with the need to preserve the environment, protect it from pollution and over-abstraction, and where it is already polluted they restore it. The Environment Agency does this by:

  • promoting sustainable development
  • legislation and regulation
  • information and education
  • investigation and monitoring
  • research

 

The main legislation that protects groundwater are:

 

Other requirements of the 2006 Groundwater Directive have been transposed through the Water Framework Directive Regulations and through statutory Directions in 2006, 2009 and 2010 to the Agency under section 40 of the Environment Act.

 

The Environment Agency routinely monitors groundwater quality and level to help them understand the condition of groundwater, and ideally identify any problems before they become too difficult to deal with. There are 7,300 groundwater level monitoring sites. They also work with and advise others, such as development planners and industrial groups, to identify groundwater issues.

 

It is worth stressing that it takes a long time to restore groundwater. There are no quick fixes for groundwater, but preventing harm in the short term will protect the resource for years to come.

 

 

 

By Ruth García

PhD Chemical Engineer


Published on 2016-05-20 13:45:15

 
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