Advances in Water Treatment and Enviromental Management

18 WATER TREATMENTTable 1: Comparison of regulations in US and in Europe.Some examples of differencies in MCLquality determination by nitrates, seen as nationwide problem. On a local scale, however,things may work out differently. Some sources, such as these generated by household effluentscan reach quite large proportions compared with farming activities. However, remedial solutionscan be found to alleviate this kind of pollution.The situation when it comes to agricultural pollution is quite another matter. Its maincharacteristic is its wide diffusion making the struggle to protect the quality of water highlycomplex.A dozen or so sounding were carried out on the entire depth of the ground between the topsoil and the phreatic layer in different regions by the Geological and Mining Research Bureauin France (BRGM) (1). Their results bring interesting elements:On all cultivated land a stock of nitrates has been detected migrating towards the aquifers,and this without any noticeable attenuation of its concentration at increasing depths. Theseresults show that the possibilities of natural denitrification are limited. Just few cases ofdenitrification have been identified normaly in the chalk aquifer in northern France.The nitrate concentrations in intersticial waters are rarely under 45 mg/1 and the projectcarried out in Brittany under market gardening sites shows that the water contained in thenon-saturated zone can reach a nitrate content in the region of 170 mg/1 with an average of130 mg/1.In intensely cultivated areas, the total quantities of nitrogen involved per annum are in theregion of 200 to 250 kg per hectare (Nitrogen of the soil plus extra input from fertilizers). Itcan be assumed that the annual range of residual nitrates likely to be leached into the subsoilis between 30 and 45 kg of nitrogen per hectare (15 % of the stock in soil). This leakageproduce concentrations in the aquifers of dose on 50 to 60 mg/1 of NO - 3 .This indicates that in order to maintain the quality of the groundwater, the farming practiceshould be able to reduce the leakage of nitrogen under 15 % of the total stock of nitrogencontained in the soil. This is a difficult challenge.The origin of the increase in nitrate concentration doses not appear to be solely due to anincrease in the doses of nitrous fertilizers, but just as much to the changes in crop rotationand above all a great increase in cropped areas. The draft Directive of the Council of the