VOLATILE HALOCARBONS AS TRACERS OF PULP-MILL EFFLUENT PLUMES

This work describes the use of volatile halocarbons in a pulp mill eff luent, including chloroform, bromodichloromethane, and tri- and tetrac hloroethylene, as tracers for the distribution and movements of efflue nt currents in a receiving water bay (Jackfish Bay) on the northern sh ore of Lake Superior. The results indicate the simplicity and usefulne ss of the technique and the significantly improved resolution of efflu ent plume delineation over the customary use of conductance profiles. Concentration patterns of the effluent volatiles suggest counterclockw ise circulation of bay water that mixes with inflowing lake water at t he eastern reach of the outer bay. The distribution of volatile contam inants is governed by the thermal regime of the receiving waters. Duri ng the summer months, the effluent plume wedges between the thermoclin e and epilimnion, mixing into the surface waters as the distance from the input source increases. In the fall, the colder effluent plume sin ks into the hypolimnion and is confined by a bay/lake water-density gr adient. In the specific case at hand, the distribution patterns of chl oroform and a brominated analog, bromodichloromethane, also suggest th e release of chloroform from sediments in the bay.