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Several factors change the behaviour of mineral liners, like freeze-thaw cycles, erosion and different chemical actions. This report deals with the requirements set by the Finnish National Road Administration to both mineral and geosynthetic liners used to protect aquifers at road slopes against pollutants released during accidents. The short term requi­rements connected to accidents, asking for a 12 hours retention period, are superposed by demands for groundwater pro­tection against migration of r.oad salt. Weak points in common construction practice influencing hydraulic performance of slope protection structures are relatively low degrees of compaction and erosion channels, which occured often in connec-tion with rockfill structures; and problems of quality assurance measures. Material parameters for clayey and silty soil liners to achieve acceptable permeability v t1es are given in the report. In most demanding cases and to ensure long-term performance geosynthetic clay liners, geomembranes or bituminized geotextiles are recommended for use in combination with a mineral liner. Testing procedures and test results for the assessment of suitability are presented for such geosynthetic products.