2.1 Sewage treatment plants and septic systems

Environment Canada calls municipal wastewater effluents “one of the largest threats to the quality of Canadian waters.” Canadians connected to sewer systems cannot count on their sewage receiving adequate treatment. In 1999, three percent of the connected population dishcarged their sewage, untreated, into the nearest lake, river, or ocean. Another 19 percent had access to only primary treatment.4

A conventional primary plant removes between only 40 and 60 percent of suspended solids and only half of the total coliforms and reduces biological oxygen demand (BOD) by only 25 to 40 percent.5  Industrial wastewaters often add heavy metals and organic contaminants to sewage treatment plant effluents. These toxic pollutants are more difficult to treat or remove than conventional sewage pollutants (such as total suspended solids, fecal coliforms, aberrant pH, oil, and grease) and excessive biological oxygen demand.6 Some sewer systems collect road and other runoff in the same pipes, adding other toxic pollutants such as fuel-derived substances, pesticides, and materials poured into street drains.

Sampling of sewage discharges can be tricky since most plants discharge far offshore through long outlet pipes. You may obtain permission to sample at the plant itself, but make sure that the managers allow you to sample the final effluent that goes into the effluent pipe.

Almost all municipalities in Ontario and other Canadian provinces have sewer overflows, which combine sanitary sewage and storm water. When the system becomes overloaded, the excess volume flows directly into the receiving waters (lakes, streams, and rivers). To identify where the combined sewer overflow outlets discharge, obtain sewage system maps from your municipality’s engineering department. Almost all Ontario municipalities have unsatisfactory and underdesigned sewage systems. Reports on Ontario’s more problematic systems are available at the Ministry of the Environment’s headquarters in Toronto. The studies and reports contain information about the systems’ specific problems and include maps.

As society looks towards less environmentally costly ways of dealing with sewage, constructed wetlands are being used to filter wastewater and runoff. Although these wetlands are generally boons to environmental protection and conservation, if they are improperly constructed or not properly maintained they can pose hazards to the surrounding environment. For example, some plants in constructed wetlands filter out certain metals, trapping and storing them in their roots. Should the plants become saturated by the pollutants, they may develop into sources of pollution, rather than the sink for metals they were designed to be.

Septic systems can also be problematic if not properly maintained. Material may leach into nearby surface waters or groundwaters.

Bacteria, viruses, and protozoans make water contaminated by sewage unfit for drinking, swimming, or raising shellfish. Nutrients from leaching septic systems, inadequately treated sewage, and untreated sewage may cause the proliferation of algae and the eutrophication of water bodies. Scientists have repeatedly found raw sewage to be toxic to aquatic life.

What to look for on-site

The most common signs of sewage discharge are discoloured water and “floatables,” such as condoms and tampon applicators. Look for effluent pipes or leaching from combined sewer overflow tanks, which are usually buried near watercourses and form large grass-covered mounds.

Contaminants to test for

Liquid discharges: You should have the laboratory measure ammonia, biological oxygen demand, chlorine, E. coli, nitrates, nitrites, oil and grease, pH, phosphorus, total coliforms, total nitrogen, and total suspended solids. Chlorinated aromatics (chlorophenols, dioxins, PCBs), detergents, heavy metals, low molecular weight halogenated and chlorinated hydrocarbons (carbon tetrachloride, chloroform, trihalomethane), and phthalate esters are also typically in sewage effluent.

Sediments may also be contaminated because suspended solids in effluents often adsorb toxins and rapidly settle to the bottom.

Acts and regulations that may apply

Fisheries Act

Canada Water Act

Ontario Water Resources Act

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