Page 4: Guidelines for Canadian Drinking Water Quality: Guideline Technical Document – Tetrachloroethylene
3.0 Application of the guideline
Note: Specific guidance related to the implementation of drinking water guidelines should be obtained from the appropriate drinking water authority in the affected jurisdiction.
Generally, tetrachloroethylene is not a concern for the majority of Canadians who rely on surface water as their source of drinking water, because it volatilizes easily. However, the anaerobic conditions of groundwater increases biodegradation time of tetrachloroethylene, which is usually detected in groundwater in the vicinity of sites where there have been spills or other potential contamination with this compound.
The drinking water guideline is based on lifetime exposure (70 years) to tetrachloroethylene in drinking water. For drinking water supplies that occasionally experience short-term exceedances above the guideline values, it is suggested that a plan be developed and implemented to address these situations. For more significant, long-term exceedances that cannot be addressed through treatment, it is suggested that alternative sources of water for drinking, showering, and bathing be considered.
3.1 monitoring
Groundwater sources should be characterized to determine if tetrachloroethylene is present, especially if the land use history is unknown. Quarterly monitoring for tetrachloroethylene should be conducted for groundwater sources that are or may have been impacted by spills or other potential contamination with this compound. Authorities may consider reduced monitoring when it has been demonstrated that a previously contaminated site has been successfully remediated.
Although components and coatings for distribution system pipes are now required to meet standards that limit the leaching of contaminants, distribution pipes installed prior to the 1983 may leach tetrachloroethylene if a vinyl-toluene lining was used to rehabilitate the inside of asbestos-cement pipes. Since this type of pipe lining was discontinued in 1983, it is generally not expected that tetrachloroethylene will be found in the distribution system. Quarterly monitoring for tetrachloroethylene should be undertaken in the areas of the distribution system where old asbestos-cement pipes with vinyl-toluene lining are located, specifically at locations with the maximum residence time (e.g., dead ends). Utilities that have baseline data indicating that tetrachloroethylene is not present within the distribution system may conduct less frequent monitoring. Jurisdictions may consider reduced sampling if an appropriate flushing protocol is in place.
In the event that monitoring data show elevated levels of tetrachloroethylene, it is suggested that a plan be developed and implemented to address these situations.
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