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==Background==
 
==Background==
The increase of nitrate in groundwater was first identified as a local issue for the Chalk of the Eastbourne area in the 1970s (Greene and Walker, 1970<ref name="Greene 1970">  GREENE, L A, and WALKER, P. 1970. Nitrate pollution of Chalk waters. ''Water Treatment and Examination'', Vol.&nbsp;19, 169–182.</ref>). Awareness of the extent of high and rising nitrate in groundwater gradually increased, and it became clear that concentrations in public supply sources often exceeded the WHO values used at the time (Foster and Young, 1980<ref name="Foster 1980"></ref>). By the late 1970s the importance of storage of nitrate in unsaturated zone porewater was becoming recognised (Foster and Crease, 1974<ref name="Foster 1974">FOSTER, S S D, and CREASE, R I. 1974. Nitrate pollution of chalk ground water in east Yorkshire&nbsp;—&nbsp;a hydrogeological appraisal. ''Journal of the Institute of Water Engineers'', Vol.&nbsp;28, 178–194.</ref>; Foster and Young, 1980<ref name="Foster 1980">FOSTER, S S D, and YOUNG, C P. 1980. Groundwater contamination due to agricultural land-use practices in the United Kingdom. 262–282 in Aquifer Contamination & Protection''. ''Studies and Reports in Hydrogeology Series, 30. (UNESCO-IHP.)</ref>; Oakes et al., 1981<ref name="Oakes 1981">OAKES, D B, YOUNG, C P, and FOSTER, S S D. 1981. The effects of farming practices on groundwater quality in the United Kingdom. ''Science of the Total Environment'', Vol.&nbsp;21, 17–30.</ref>; Young et al., 1976b<ref name="Young 1976b">YOUNG, C P, OAKES, D B, and WILKINSON, W B. 1976b. Prediction of future nitrate concentrations in groundwater. ''Ground Water'', Vol.&nbsp;14, 426–438.</ref>). Pioneering work in understanding nitrate leaching to groundwater was carried out by drilling cored boreholes through the Chalk unsaturated zone to obtain profiles of porewater nitrate concentration as a function of depth (Foster et al., 1982<ref name="Foster 1982">FOSTER, S S D, CRIPPS, A C, and SMITH-CARINGTON, A K. 1982. Nitrate leaching to groundwater. ''Journal of Hydrology'', Vol.&nbsp;46, 343–364.</ref>; Young et al., 1976b<ref name="Young 1976b"></ref>) . At sites with good cropping records a relationship between historical land use and porewater nitrate concentration could be determined. This showed that retention in the unsaturated zone can retard the migration of nitrate for years or decades.
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The increase of nitrate in groundwater was first identified as a local issue for the Chalk of the Eastbourne area in the 1970s (Greene and Walker, 1970<ref name="Greene 1970">  GREENE, L A, and WALKER, P. 1970. Nitrate pollution of Chalk waters. ''Water Treatment and Examination'', Vol.&nbsp;19, 169–182.</ref>). Awareness of the extent of high and rising nitrate in groundwater gradually increased, and it became clear that concentrations in public supply sources often exceeded the WHO values used at the time (Foster and Young, 1980<ref name="Foster 1980"></ref>). By the late 1970s the importance of storage of nitrate in unsaturated zone porewater was becoming recognised (Foster and Crease, 1974<ref name="Foster 1974">FOSTER, S S D, and CREASE, R I. 1974. Nitrate pollution of chalk ground water in east Yorkshire&nbsp;—&nbsp;a hydrogeological appraisal. ''Journal of the Institute of Water Engineers'', Vol.&nbsp;28, 178–194.</ref>; Foster and Young, 1980<ref name="Foster 1980">FOSTER, S S D, and YOUNG, C P. 1980. Groundwater contamination due to agricultural land-use practices in the United Kingdom. 262–282 in Aquifer Contamination & Protection''. ''Studies and Reports in Hydrogeology Series, 30. (UNESCO-IHP.)</ref>; Oakes et al., 1981<ref name="Oakes 1981">OAKES, D B, YOUNG, C P, and FOSTER, S S D. 1981. The effects of farming practices on groundwater quality in the United Kingdom. ''Science of the Total Environment'', Vol.&nbsp;21, 17–30.</ref>; Young et al., 1976b<ref name="Young 1976b">
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YOUNG, C P, OAKES, D B, and WILKINSON, W B. 1976b. Prediction of future nitrate concentrations in groundwater. ''Ground Water'', Vol.&nbsp;14, 426–438.</ref>). Pioneering work in understanding nitrate leaching to groundwater was carried out by drilling cored boreholes through the Chalk unsaturated zone to obtain profiles of porewater nitrate concentration as a function of depth (Foster et al., 1982<ref name="Foster 1982">FOSTER, S S D, CRIPPS, A C, and SMITH-CARINGTON, A K. 1982. Nitrate leaching to groundwater. ''Journal of Hydrology'', Vol.&nbsp;46, 343–364.</ref>; Young et al., 1976b<ref name="Young 1976b"></ref>) . At sites with good cropping records a relationship between historical land use and porewater nitrate concentration could be determined. This showed that retention in the unsaturated zone can retard the migration of nitrate for years or decades.
 
Similar concerns about nitrate in water were raised across Europe and the Nitrates Directive (91/676/EEC) was ratified which sets out a series of requirements on Member States to assess and control the potential for pollution of waters with nitrogenous compounds generated from agricultural sources. In England, the Environment Agency has been asked to advise Defra on  this matter and propose areas subject to pollution or at risk of pollution for designation as nitrate vulnerable zones (NVZs) in compliance with the relevant regulations.
 
Similar concerns about nitrate in water were raised across Europe and the Nitrates Directive (91/676/EEC) was ratified which sets out a series of requirements on Member States to assess and control the potential for pollution of waters with nitrogenous compounds generated from agricultural sources. In England, the Environment Agency has been asked to advise Defra on  this matter and propose areas subject to pollution or at risk of pollution for designation as nitrate vulnerable zones (NVZs) in compliance with the relevant regulations.
  
For groundwater NVZs the Environment Agency have developed and published a numerical risk model which uses a range of risk factors including both nitrate concentration data and nitrate-loading data to assess the risk of nitrate pollution. The loading data are based on the NEAP-N algorithms developed by ADAS (Lord and Anthony, 2000<ref name="Lord 2000">LORD, E I, and ANTHONY, S. 2000. MAGPIE: A modelling framework for evaluating nitrate losses at national and catchment scales.''Soil Use and Management'', Vol.&nbsp;16, 167–174.</ref>). The risk model considers both current and predicted future concentrations as well as current loadings.
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For groundwater NVZs the Environment Agency have developed and published a numerical risk model which uses a range of risk factors including both nitrate concentration data and nitrate- loading data to assess the risk of nitrate pollution. The loading data are based on the NEAP-N algorithms developed by ADAS (Lord and Anthony, 2000<ref name="Lord 2000">LORD, E I, and ANTHONY, S. 2000. MAGPIE: A modelling framework for evaluating nitrate losses at national and catchment scales.''Soil Use and Management'', Vol.&nbsp;16, 167–174.</ref>). The risk model considers both current and predicted future concentrations as well as current loadings.
 
 
 
However, this approach has a number of disadvantages including a lack of a specific term for the time of travel to the water table and emergence of pollutant both into groundwater and to groundwater discharge points that support surface water features. Instead, these issues are considered at the conceptual level in workshops with local EA hydrogeologists.
 
However, this approach has a number of disadvantages including a lack of a specific term for the time of travel to the water table and emergence of pollutant both into groundwater and to groundwater discharge points that support surface water features. Instead, these issues are considered at the conceptual level in workshops with local EA hydrogeologists.
  

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