Determination of groundwater attenuation distances for municipal landfill sites in ontario

Abstract

Establishing an attenuation zone is widely used in Ontario to protect groundwater users on property adjacent to the landfill. The main purpose of such an establishment is to provide compliance with the Ministry of Environment and Energy Reasonable Use Policy Objectives (RUPO) at the downgradient attenuation zone boundary. Evaluation of an attenuation zone includes the following: identification of the aquifer to be protected; selection of the list of critical parameters; and the attenuation distance calculations. To select the list of critical contaminants it is recommended to calculate the pollution index (PI), or the ratio between the leachate and RUP concentrations for parameters with established Ontario Drinking Water Objectives. Parameters with the highest values of PI are considered as critical ones and used in attenuation distance calculations. Such calculations are based on the hydrochemistry results at two or more downgradient wells. In particular, a concentration gradient for each critical parameter, or specific attenuation is calculated and used for an attenuation zone estimate. Practical realization of this approach requires an extensive knowledge of both leachate and background hydrochemistry at the site under study. An example of an attenuation distance calculation is given for a municipal landfill site in southeastern Ontario. © 1995 Taylor & Francis Group, LLC.