Fish Kill in Choptank River

Wastewater from Unsewered Properties

There are almost half a million septic tanks in the country. These are the individual sewage treatment systems attached to one-off houses in rural areas, not joined up to a ‘mains’ sewerage system. Also known as On-site Domestic Waste Water Treatment Systems (DWWTS), these can threaten public health and the environment when they fail to operate correctly.

Effluent emanating from a septic tank contains human excrement as well as household chemicals and detergents, among other things. When it is not absorbed by the soil surrounding the septic tank, it can form stagnant pools on the ground surface; humans are increasingly likely to come in contact with it, being thereby exposed to pathogens, e.g. faecal coliforms. According to the EPA, there are approximately 1 million E. coli bacteria in one litre of effluent from a septic tank. The typical volume of effluent from a single house is 180 litres per person per day. On a national scale, this equates to a liquid discharge of 210,000 m3 per day or 46 million gallons (equivalent to 84 Olympic swimming pools).

In addition to posing an immediate health risk to the system owners and their neighbours, poorly constructed and maintained septic tanks are a significant source of environmental diffuse pollution, running into rivers and streams and leading to the eutrophication of surface waters, degradation of the aquatic environment and loss of fish and other species.  It can also contaminate groundwater, especially when constructed over porous rock, which allows effluent to permeate down into deeper groundwaters. These same groundwaters may then be used as a source of drinking water for private wells and group water schemes. In rural areas, 86% of water abstracted for public and private drinking water supply is from groundwater. Pollution of such groundwater supplies can lead to public health hazards, such as gastro-intestinal infections resulting from faecal contamination, and ‘Blue Baby Syndrome’, which is caused by excessive nitrate levels.