Conceptual modelling of the sewage and wastewater plume from Scott Base incorporating current and tidal data, seawater stratification and microbiological, physical and chemical indicators associated with the plume
Before the installation of the Scott Base sewage treatment plant, untreated sewage and wastewater was discharged directlyin front of Scott Base since its occupation in 1957. The distribution of sewage and wastewater discharge from Scott Base in the marine environment off Pram Point was investigated in the 1998/99 field season to gain a comprehensive picture of where to expect impacts (if any) on ... the local marine environment due to the Scott Base sewage and wastewater discharge and to assess the effects of tidal and current activity on the dispersion and dilution of sewage and wastewater contaminants released from Scott Base. The development of a conceptual model of the dispersion and fate of sewage and wastewater components from Scott Base was the expected outcome of this study. Past monitoring work has included measuring the effects of the outfall on marine benthic foraminifer communities, quantifying and characterising sewage and wastewater outputs, weekly (since 1995) sampling of the drinking water intake for faecal coliform bacteria and yearly (since 1995) monitoring of effluent component loading in the marine receiving water. The current and tidal patterns in the vicinity of Scott Base outfall during ice cover conditions was determined by deploying two current meters recording current direction and velocity at three depths (1m, 6.5m and 33m) for one minute every five minutes and installing a minidata pressure sensor down the reverse osmosis intake hole to determine water level every 15 minutes for tidal data. The degree of seawater stratification in the vicinity of the outfall was determined by measuring the conductivity, temperture, pH and dissolved oxygen profiles at the top (1m beneath ice/water interface), middle and bottom at each site. To determine the distribution of the Scott Base sewage plume, water samples were taken from a predetermined grid in front of the outfall. Water samples were analysed for faecal coliform bacteria, biochemical oxygen demand, total nitrogen and phosphorus, total organic carbon, copper and zinc. Soil samples were recovered from land between the outfall and the coast for analysis of trace metal content. Submarine sampling revealed no sediment samples as the benthos was found to be steep and rocky with what appeared to be sponges dominating the benthic community. A conceptual model was compiled on the basis of measured velocity vector and tidal cycle data, receiving water stratification and microbiological, physical and chemical indicators associated with the outfall plume. The data, along with estimates of diffusion coefficients, bacterial inactiviation rates and contaminant fate, can then potentially be used in the future to develop a full numerical dispersion model to predict contaminant concentrations at a given location through time.