A statistically based trigger mechanism for evaluation of groundwater quality in landfill monitoring wells

Abstract

According to the Ontario Ministry of Environment and Energy (OMEE) requirement, the owner/operator of a municipal landfill site should develop a detailed contingency plan to deal with unexpected and unacceptable deterioration of groundwater quality at compliance locations. In order to implement such a contingency, a comprehensive trigger mechanism including trigger limits for leachate related parameters, should be in place. The straightforward application of the Reasonable Use Policy Objectives (RUPO) or the Ontario Drinking Water Objectives (ODWO) for defining trigger concentrations can provide a false alarm of unacceptable groundwater contamination at the site boundary due to landfilling operations. In fact, on some occasions, elevated (above the RUPO and ODWO) concentrations at compliance locations could be caused by the variability in groundwater quality rather than the natural man-made activity. In order to avoid this false alarm for contingency implementation, it is proposed to establish trigger limits based on tolerance limits calculated for the independent and normally distributed background data. For trigger parameters with tolerance limits below the RUPO, trigger concentrations should be set at the RUPO. For trigger parameters with tolerance limits above the RUPO but below the ODWO, trigger concentrations should be established at the ODWO, and finally, for parameters with tolerance limits above the ODWO, trigger concentrations should be established above the upper tolerance limits calculated. An example of such an approach is given for a landfill site in central Ontario. © 1994 Taylor & Francis Group, LLC.