Water held underground in the soil or in pores and crevices in rock is known as groundwater. The Ontario Geological Survey has an important groundwater mapping program that is designed to provide geoscience information on the location and character of subsurface water-bearing layers, called groundwater aquifers. The program has several components:

  • three-dimensional (3D) aquifer mapping studies
  • ambient groundwater geochemical survey
  • geology map and data compilations using geographic information system (GIS) applications
  • thematic groundwater investigations with partner agencies

Ontario Geological Survey

Through the groundwater mapping program, the Ontario Geological Survey collects, interprets and disseminates geologic information pertaining to groundwater resources. This is done by:

  • completing regional stratigraphic studies to define the extent of aquifers in the subsurface: water quantity
  • collecting groundwater samples from overburden and bedrock aquifers to establish the geochemical signature of the water: water quality
  • working with other agencies to complete thematic geological studies to address a local groundwater related concern or need


Groundwater mapping is a key to determining the future availability of this life-sustaining resource. Mapping determines the geologic conditions, both in bedrock and the overlying surficial sediments, that control where groundwater is found and how much is available for extraction. Testing samples of the water indicates its suitability for consumption and determines any human-induced impacts.

Knowledge of the quality and quantity of groundwater allows for its long-term sustainable extraction and use. Pumping of groundwater for personal, agricultural and industrial use can proceed at a rate that allows the resource to be maintained over time.

Mapping also provides an understanding of the vulnerability of groundwater resources to contamination from surface sources of pollution or waste. This information can be incorporated into planning decisions to guide development and preserve current and future sources of groundwater.