Proposed Abstract Title

Sewage in the Strait of Georgia: how big is the problem and what can we achieve by treatment?

Type of Presentation

Oral

Session Title

Contaminants of Emerging Concern: Intersection of Occurrence, Impacts, Research, and Policy

Location

2016SSEC

Description

The discharge of municipal wastewater from Vancouver and Victoria into the coastal ocean is controversial. The controversy stems in part from a lack of a common understanding of the scope of the problem and of what might be achieved by further treatment. We have determined the footprint of wastewater in the Strait of Georgia, using regional geochemical budgets and nearfield monitoring. We present the results of this work together with an analysis of the likely effects of secondary treatment. Wastewater contributes less than 1% of the nitrogen, organic carbon and oxygen demand in the Strait and is unlikely to cause eutrophication, harmful algal blooms or hypoxia in this region. Metals (Hg, Pb, Cd) are controlled by natural cycles, augmented by past mining and urbanization, with 0.3 - 5% of the flux contributed by wastewater. Wastewater contributes about 5-10% of PCBs but as much as 60% of PBDEs and is likely also important for pharmaceuticals and personal care products. The high organic flux affects benthic animals in the sediment immediately around the studied outfalls (Iona and Macaulay). Secondary treatment, slated for completion in Vancouver and Victoria over the next 15 years, will reduce fluxes of some contaminants, but will have negligible effect on regional budgets for organic carbon, nitrogen, oxygen, metals and PCBs. Removal of PBDEs from wastewater will affect regional budgets, depending on how the sludge is sequestered. Sludge disposal on land might result in increased cycling of PBDEs in streams and groundwater.

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Sewage in the Strait of Georgia: how big is the problem and what can we achieve by treatment?

2016SSEC

The discharge of municipal wastewater from Vancouver and Victoria into the coastal ocean is controversial. The controversy stems in part from a lack of a common understanding of the scope of the problem and of what might be achieved by further treatment. We have determined the footprint of wastewater in the Strait of Georgia, using regional geochemical budgets and nearfield monitoring. We present the results of this work together with an analysis of the likely effects of secondary treatment. Wastewater contributes less than 1% of the nitrogen, organic carbon and oxygen demand in the Strait and is unlikely to cause eutrophication, harmful algal blooms or hypoxia in this region. Metals (Hg, Pb, Cd) are controlled by natural cycles, augmented by past mining and urbanization, with 0.3 - 5% of the flux contributed by wastewater. Wastewater contributes about 5-10% of PCBs but as much as 60% of PBDEs and is likely also important for pharmaceuticals and personal care products. The high organic flux affects benthic animals in the sediment immediately around the studied outfalls (Iona and Macaulay). Secondary treatment, slated for completion in Vancouver and Victoria over the next 15 years, will reduce fluxes of some contaminants, but will have negligible effect on regional budgets for organic carbon, nitrogen, oxygen, metals and PCBs. Removal of PBDEs from wastewater will affect regional budgets, depending on how the sludge is sequestered. Sludge disposal on land might result in increased cycling of PBDEs in streams and groundwater.