Sanitary sewers account for the majority of sewers in the region. Municipal street sewers flow directly into the largest of all sanitary sewer pipes, GVRD trunk sewers. Trunk sewer pipes can reach diameters of over 3.5 metres. To reach a treatment plant, wastewater must flow through these sewers for up to 35 km. Along the way, pump stations raise the wastewater over high points of land so it can continue to flow downhill by gravity.
Storm sewers carry stormwater to the nearest stream, river, lake or ocean.
Wet Weather Influence Because the wastewater collection system is aging, leaks and cracks have developed in pipes where groundwater can seep in. Seeping groundwater raises the volume of wastewater in sewers. Diluted and untreated sewage may spill into storm drains and creeks, or may back up through private sewers into basements. The GVRD estimates that more than half of groundwater seepage comes from holes in pipes on private property. Other sources of excess water are leaky manhole covers and improper sewer connections.