Review of groundwater contamination hazard rating systems for old landfills.

A large number of old uncontrolled landfills exist in developing countries. These are potentially harmful to the environment, especially with respect to groundwater contamination, and therefore, are in need of appropriate control and remedial measures. However, due to resource constraints, such measures are to be undertaken in a phased manner. An appropriate landfill hazard rating system that can evaluate relative groundwater contamination hazard of different sites is a useful tool for site ranking in order to set priorities. This paper reviews 18 existing hazard rating systems that follow the index function approach. Nine systems that are best representative of the existing systems, have been applied to six hazardous waste landfills as well as six municipal solid waste landfills. When used for ranking hazardous waste landfills, some systems such as HRS-1990, ERPHRS, WARM and RSS respond well whereas others like DRASTIC, NCS, NPC system and JENV system show a clustering effect. However, these rating systems do not perform well when applied to old municipal solid waste landfills. Even the HRS-1990, which is observed to be the most sensitive among all rating systems, exhibits some shortcomings. Improvements have been suggested in the waste quantity factor values of HRS-1990 to make it suitable for old municipal solid waste landfills. The improved system is observed to provide superior results in comparison with the existing systems, making it appropriate for use as a tool for ranking of old landfills in need of remediation and control measures.