By Althea Lincoln, Prairie Farm Rehabilitation Administration, Calgary
As part of its rural development mandate, PFRA assists rural residents in obtaining reliable supplies of groundwater for domestic, agricultural and industrial use.
Securing an adequate supply of good quality water is often a constraint in the development and growth of value-added businesses in rural communities. This is particularly apparent in low rainfall, drought prone areas on the Prairies.
Over the years, PFRA has successfully used traditional groundwater exploration methods to meet client needs. In an attempt to build on this success, for the past two years PFRA has been experimenting with geophysical techniques such as ground penetrating radar (GPR) and electromagnetic methods to assist in groundwater exploration.
This technology is most effectively employed where there is insufficient subsurface data and surface expressions of underlying features are poor. While geophysics is used to assist in targeting drilling locations, test hole drilling is always required to confirm potential well yields and water quality.
Typically, a groundwater exploration program starts with a detailed review of all available geological groundwater data. Potential aquifer sources are identified and decisions made on possible field exploration options. If judged to be desirable, a geophysical survey may be conducted to assist in identifying potential aquifers. A number of small diameter test holes are then drilled and flow tested. If sufficient yields and suitable water quality are obtained, a production well and pump may be installed.
One geophysical technique being evaluated by PFRA is ground penetrating radar, or GPR. It is a shallow depth investigation tool that can provide results to approxi mately 25 metres depth in fine grained material, with penetration depth increasing in coarse grained sediments.
The radar component is a high frequency electromagnetic pulse which is transmitted into the ground. Receivers then detect the radar signals reflected back to the surface of the ground.
Electrical properties of sediments are primarily controlled by their composition. The manner in which an electromagnetic pulse responds to sediments reflects their electrical and thus physical properties. Advanced computer technology, developed by the petroleum industry, is used to process and interpret the data.
With the assistance of geophysical consultants, PFRA has applied GPR technology to confirm or assist in locating groundwater sources in several areas in Alberta. Examples of potential aquifers which have been investigated with the support of GPR are the Calgary Buried Valley near Empress and a shallow buried channel located near the Village of Jenner. These communities are both in drought prone areas of southeastern Alberta. Evaluation of GPR as an exploration tool is continuing. A study is being conducted by the University of Calgary to assess geophysical results obtained from PFRA projects using GPR, electromagnetic and seismic methods. In addition, several water sourcing projects applying geophysical techniques are in progress in Alberta.
To contact the author, write to PFRA, Agriculture and Agri-Food Canada, 832 - 220 Fourth Avenue S.E., Calgary, AB
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