Use of hydrochemistry and isotopes in a mixing-cell model to quantify the relative contribution of multiple-source contaminants to seepage from a fractured chalk aquitard

Environmental isotopes and dissolved pollutants were used to identify sources of contaminants that recharge a fractured chalk aquitard. A compartmental mixing cell approach was applied to quantify the relative contribution of pollutants to the local groundwater and to the seepage into an ephermeral stream. Results identified leakage of highly concentrated industrial effluent from a domestic sewer at some of the factories and from sections along the main sewer. The relative contribution of each source was assessed as a percentage of the total discharge. Results indicate that natural uncontaminated groundwater accounts for only 56% of the total discharge. The rest is directly from leaking sewers and already contaminated groundwater from factories in the upper basin. Results show that due to limited storage capacity, even a relatively small leak that reached the multilayer fracture system intersecting the low-permeability chalk formation, raised the local water table and increased the hydraulic gradient which further enhanced groundwater flux along preferential flow paths.