Geochemical investigations in view of the implementation of a monitoring system at a former base metal mining and ore processing site (Kirki, Thrace, Greece)
Mining sites are usually sources of metal pollution many years after closure. Specific geo-chemical phenomena such as acid drainage contribute to an increase of environmental impacts, especially if remediation measures were not taken at the time of mine closure (Bird et al., 2005). When a site is left exposed to the elements , pollution may arise from unmanaged waste piles, mine runoff water and tailings. The implementation of a reliable monitoring system is required to assess risks for the exposed resources (groundwater, cultivated areas, urban settlements or littoral), until the site is remediated. Monitoring data are essential to design remediation works. The monitoring network is designed using water, sediment or soil quality data along time at the critical points of the pollution transfer model. Traditionally, such points are selected from a large number of sampling points and laboratory analyses (baseline data). This is both expensive and lengthy. IGME followed an alternative route at Kirki, where mining and ore beneficiation for copper, zinc and lead ceased in 1995, and no remedia-tion was undertaken. A baseline monitoring program was implemented in 2005 with the support of the Euro-pean Union, incorporating field analysis campaigns to improve its efficiency (heavy metals in water by polarography, in solids by portable XRF and multiparametric probes). This allowed to identify quickly pollutant variation ranges, emission or attenuation points, and to design conceptual transfer models. Field techniques were particularly efficient to design an optimised monitoring network, by allowing an immediate feedback between results, investigations and sampling. They do not substitute to laboratory techniques, but optimise their use for a better representativity of phenomena. Examples of critical points include:-neutralisation fronts for acid mine drainage, and metal precipitation sites,-separation between rainfall recharge and contaminated aquifer in shallow wells,-migration distance of each contaminant in sediments within the catchment. The monitoring plan provides key data for remediation options, and for the design of a community alert system.