SUMMARY:
    Landfills are the final destination of a high percentage of waste in Spain and in other countries. Environmental concern has played an important role in developing a very restrictive legislation.
    Rules over wastes, landfills, integrated pollution prevention and control, environmental impact assessment and environmental liability have forced the elimination of waste by means of landfills in a safe way (sanitary  and environmental).
    However, after a exhaustive revision of the lay, it has been observed a legal lack referring leachate dams. Although leachate are very contaminating liquids (rich in organic compounds and heavy metals), there are no specific laws for these type of dams.
    As a supporting to UNE 150008 EX law of environmental risk, an alternative method has been applied; it main objective is to minimize the environmental risk of leachate dams and to avoid the environmental impact produced by the break of dams. This alternative method is based on an environmental risk index; this index values the risk of the dams over the existing environmental elements in the bed slope. It is necessary to know: geometric characteristics, contaminating properties of leachate and characteristics as well as environmental factors of environment recipient.
    According to these parameters, an specific risk index may be calculated for each dam. If the environmental risk index surpasses an established value, it will imply a high environmental risk dam due to lack of geotechnical stability or due to environmental factors sensitive to this type of pollution or due to both factors. To justify that this method is valid, the equation obtained is applied the real cases.