Two different models have been used to investigate how chemicals present in wastewater from a kraft mill are transported and spread in an aquatic environment. The models, FEQUM (Fugacity EQUilibrium Model) and EXAMS, are presented, their characteristics explained and a comparison of the models is made. In FEQUM the concept of fugacity is considered as the driving force behind chemical transport. The EXAMS dispersion model uses water and sediment flow as the basis for calculating the dispersion of chemicals. FEQUM encompasses the whole environment, water, air, soil, sediments, suspended matter in water and biota, whereas EXAMS includes the aquatic domain only.
Both models have been applied to the Norrsundet area. Norrsundet is a heavily polluted bay on the east coast of Sweden. The pollution is mainly due to a kraft mill located in the area. The models were calibrated using data on chloroform in wastewater and seawater, and then tested on four other pollutants present in the wastewater. Both models give satisfactory results for the compounds investigated, tetrachlorocatechol constituting the only exception. Correlation coefficients between calculated and measured concentrations vary from 0.86 to 0.97. The poor results obtained for tetrachlorocatechol are probably due to the especially high affinity of this compound for suspended particles.
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