Groundwater problems in the karstic aquifers of the Dobrich region, northeastern Bulgaria

In the Dobrich region, with an area of a little over 4000 km(2), two import ant aquifer systems can be differentiated, which we have named the Upper an d Deep Aquifers. The hydrodynamic and hydrogeochemical characteristics of t hese two aquifers are different. Agricultural activities, livestock units, and urban waste waters and solid wastes constitute the principal sources of contamination of the Upper Aquifer. Furthermore, signs of marine intrusion in some coastal zones have been detected. The Deep Aquifer is found to be affected by hydrogeochemical processes related to hydrocarbons that generat e elevated concentrations of H2S and NO2 (which may exceed 10 mg 1(-1)). Th is aquifer has numerous deep overflowing boreholes that lack appropriate ca pping, with the consequent loss of resource, draining in the order of 4 m(3 )s(-1) of thermal and sulphurous waters.