Page 4: Guidelines for Canadian Drinking Water Quality: Guideline Technical Document – Toluene, Ethylbenzene and the Xylenes
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, toluene, ethylbenzene and xylenes are 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 toluene, ethylbenzene and xylenes, which are usually detected in groundwater in the vicinity of sites where there have been spills or other potential contamination with these compounds.
The drinking water guidelines are based on lifetime exposure (70 years) to toluene, ethylbenzene and xylenes 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 toluene, ethylbenzene and xylenes are present, especially if the land use history is unknown. Quarterly monitoring for toluene, ethylbenzene and xylenes should be conducted for groundwater sources that are or may have been impacted by hydrocarbon spills or other potential contamination with these compounds. Monitoring of the distribution system is recommended when contamination has occurred in soil where there are plastic pipes.
Authorities may consider reduced monitoring when it has been demonstrated that a previously contaminated site has been successfully remediated. In the event that monitoring data show elevated levels of toluene, ethylbenzene and xylenes, it is suggested that a plan be developed and implemented to address these situations.
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