Although small in size, Unit 5 is an important and reliable resource for Manitoba Hydro. It is operated as part of Manitoba Hydro's integrated system. Other non-hydroelectric resources include two natural gas-fired steam turbines at Selkirk G.S. and two gas turbines at Brandon G.S., and the St. Leon wind farm.
The main components of Unit 5 are the steam generator, used to burn coal and heat water to produce steam, and the steam turbine, used to convert steam energy into electricity. The electricity enters Manitoba Hydro's grid through a transmission sub-station used for regulating voltages.
Operation of Unit 5 affects the environment through the withdrawal of water from the Assiniboine River, the discharge of treated wastewater to the river, and emissions to the atmosphere.
During operation of Unit 5, water is withdrawn from the Assiniboine River for several plant processes, primarily sluicing coal ash to the ash lagoon. Construction of a cooling tower in the mid-1990s greatly reduced the volume of water withdrawn from the Assiniboine River. Given the small proportion of flow that is withdrawn and the presence of a screen on the water intake, water withdrawal by the station does not significantly affect aquatic life in the river.
The station discharges wastewater from several sources to the Assiniboine River. The largest volume is water used to sluice ash from the combustion of coal to the ash lagoon, where the ash settles and the decant water is discharged to a ditch that flows into the river. Analysis of the wastewater discharged from the lagoon supports the conclusion that the wastewater does not have a significant negative effect on aquatic life or other uses of the river water (e.g., recreation).
The sources of air emissions include: the Unit 5 exhaust gas stack; the cooling tower; dust from coal handling operations and ash storage; and, the combined emissions from Unit 5 and Units 6 and 7 gas combustion turbines.
The air emissions from coal combustion in Unit 5 primarily consist of common contaminants such as oxides of nitrogen (NOx), carbon monoxide (CO), sulphur dioxide (SO2) and particulate matter (SPM, PM10 and PM2.5). There are also trace organic and inorganic substances released. The combustion of coal also results in greenhouse gas (GHG) emissions. Emissions of water vapour from the cooling tower include dissolved solids.
Generally, the results of the dispersion modelling analysis for air contaminants from Unit 5 operations are well below the Manitoba Maximum Acceptable Level air quality objectives or guidelines. The exceptions are a hypothetical exceedance of the nitrogen dioxide (NO2) objective (1 hour per year) and a potential exceedance of the suspended particulate matter (SPM) objective due to high background concentrations.
Manitoba Hydro is committed to voluntarily reducing its net average corporate GHG emission to 6% below 1990 levels over the 1991 to 2007 period. Annual mercury emissions from Unit 5 are also voluntarily limited. In the future, as mandatory regulations for GHG and mercury emissions are implemented, Unit 5 emissions will be managed to ensure compliance.
Water vapour emissions from the cooling tower have a minimal impact on fogging and icing in adjacent areas. The same is true for dissolved solids emissions from the cooling tower.
The results of the noise assessment indicate that sound level contributions from the Brandon G.S. do not influence the noise environment at the nearest residential locations in the vicinity of the station. Sound levels are predicted to be below those stipulated in the Environment Act Licence for the facility and the daytime and nighttime limits as defined by generally accepted noise guidelines.
Assessments concluded that there are no significant adverse impacts to wildlife, vegetation and groundwater from the operation of Unit 5 at the Brandon G.S. The results of the Manitoba Hydro's ongoing groundwater monitoring program implemented in 1993 indicate that groundwater quality has not been affected. Although higher levels of trace elements in some of the monitoring wells were recorded, adverse effects due to groundwater seepage to the river are not expected.
The results of the human health and ecological risk analysis determined that there will continue to be no measurable effects to human health or the environment from the operation of Unit 5.