By Robert J. Stewart, Saskatchewan Environment and Resource Management, Regina
How sensitive are shallow aquifers to land uses that occur above them? Has the quality of groundwater in these aquifers been affected by farming practices?
These were the questions pondered by the Sustainable Water Management Committee in initiating a recent survey of shallow groundwater quality in rural Saskatchewan. The survey was conducted in Autumn of 1995 and was funded under the Canada-Saskatchewan Agriculture Green Plan Agreement.
The survey examined groundwater samples from 86 private water wells located within a 15,000 km2 area east of Rosetown and south of Saskatoon. Samples were analyzed for the possible presence of commonly-used pesticides, and for major ions and other physical properties. Water wells selected for sampling had to be of shallow construction in unconfined aquifers (aquifers exposed directly to the atmosphere through openings in the soil), were being used to obtain groundwater for domestic consumption, and were located within crop production areas.
Groundwater samples were collected from the distribution system before treatment at each residence. A rigid quality assurance and control program was maintained throughout the course of the survey to ensure the consistency and accuracy of sample collection and to ensure the reliability of sample quality analyses.
Six wells out of the 85 tested contained pesticides above the detection limit, however all were at concentrations below 1 ug/L (1 part in 1 billion). All six wells are located on farms which had previously used agricultural chemicals on adjacent land. The pesticides and number of wells in which they were found above detection limits are listed as follows in decreasing order:
The provincial water quality objective for municipal drinking water stipulates no detection of pesticides. However, concentrations of pesticides encountered in the survey are all well below Health and Welfare Canada's standards for long-term health exposure.
Concentrations of nitrate in groundwater were greater than the maximum provincial standard of 45 mg/L in 28 of 86 wells sampled. Twenty of the subject wells were located on farms that raise livestock.
Results of the groundwater quality survey show that shallow sources of rural drinking water can be affected by adjacent farming practices. Agricultural producers should be aware of the vulnerability of these aquifers.
The Sustainable Water Management Committee is considering a follow-up survey, which is intended to investigate the seasonal variance of pesticide occurrence and other similar surveys in different geographical areas of the province.
To contact the author, write to the Groundwater Quality Unit, Saskatchewan Environment and Resource Management, 3211 Albert Street, Regina, SK S4S 5W6
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