CRITICAL PARAMETERS CONTROLLING POLLUTANT MIGRATION FROM WASTE-DISPOSAL SITES - FIELD INVESTIGATIONS AND INFLUENCE ON AQUIFER POLLUTION

This paper considers processes which are of relevance to contaminant r elease from four types of waste disposal sites in Switzerland: disposa l sites for municipal solid waste, for solidified filter ashes, for lo w- to intermediate-level radioactive waste (SMA), and for high-level r adioactive waste (HAA). A comparison of contaminant release times and expected lifetimes of engineered barriers underlines the importance of the geological barrier for long-term disposal site safety. With respe ct to the geosphere, current regulations concerning non-radioactive wa ste disposal in Switzerland (TVA) relate only to bulk (effective) hydr aulic properties. Although bulk properties may influence the stability of engineered barriers, they are inadequate for the evaluation of the disposal site's long-term impact because contaminant migration in the geosphere is controlled primarily by heterogeneity and preferential p athways. Field methods are described which allow such heterogeneities to be detected and characterized, and are illustrated by data which su ggest that practically all geological barriers considered in Switzerla nd include preferential pathways (fractures, faults, coarse-grained la yers). A sensitivity analysis using a numerical transport code and par ameters from a field investigation for a potential landfill site in No rthern Switzerland shows that neglecting the existence of preferential pathways may lead to severe errors when estimating contaminant breakt hrough times and peak concentration levels.