Diffuse pollution

Diffuse pollution can leach from the land surface into groundwater from non-point sources such as crop spraying.

Groundwater is vulnerable to pollutants that leach from the land surface.

Diffuse pollution comes from non-point source, widespread activities within the current and past agricultural and urban environments.

There is also a contribution from atmospheric deposition.

Rural sources of diffuse pollution

Rural diffuse pollution arises from land use activities spread across large areas, such as:

fertiliser and pesticide applications used in the cultivation of land to grow crops
livestock grazing and associated manure and slurry storage and disposal
sewage sludge disposal
forestry operations

Dispersed housing may also be a source. The pollutants of concern have included the nutrients nitrogen (typically in the form of nitrate) and phosphorus, pesticides, biodegradable substances, ammonia and micro-organisms, such as faecal coliforms.

Urban sources of diffuse pollution

In urban areas, both industrial and municipal activities generate pollutants.

Urbanisation changes the natural pattern of recharge to groundwater with run-off from built areas and impervious surfaces, such as roads and car parks, and input from mains water, leaking sewers and pluvial drains.

Infiltration may carry a mix of polluting substances, such as toxic metals, pesticides, oils and hydrocarbons, sediments and oxygen-depleting substances.

Emerging contaminants

Recently advancing analytical techniques have identified a range of widespread emerging contaminants in groundwater, including pesticide breakdown products, pharmaceuticals, food additives, industrial compounds and caffeine and nicotine.