Innovative approaches to evaluate geochemical risk related to sulphide-bearing Abandoned Mine Lands
Creators: name: SERVIDA, DIEGO
Publisher: name: Universit� degli Studi di Milano
Year: 2009

description: Abandoned Mine Lands (AML) are often perceived to have significant environmental impacts, particularly on superficial and ground waters, from water contaminated with acid and elevated metals flowing from eroding waste dumps and from underground workings. These conditions would require risk assessment and remediation in case of necessity.
However AML have heritage and historical value because of their age and the significance of their structures and the processes used. This value could be destroyed by remediation done following the environmental law in force.
Take into account the particular features of AML (terrains characterised by natural high metal and metalloid concentrations) and environmental law problems (the inability of agencies to cite or allocate clear ownership for the problems at the sites), rise the need to develop an approach that allows the right and complete geo-environmental characterisation of AML and that supports the management and/or the remediation of AML.
The main problems related to AML comprise:
? the identification and characterisation of mine dumps;
? the assessment of the geochemical hazard;
? the persistence in time of the chemical processes which occur at the site.
Mine dumps are the waste products of exploitation, composed mainly of rocks with metal concentration too low to be economic but rather high to be a source of environmental pollution.
A preliminary low-cost identification of mine dumps could be done by means of digital elaboration of topographic maps. This operation allows to identify and to evaluate the morphology and dimension of mine dumps having bibliographic data and CAD software (Servida et al., 2009).
Mine dumps characterisation could be completed and refined by Electrical Resistivity Ground Imaging (ERGI) investigations (Mele et al., 2007) that enable to reduce direct investigation number and, consequently, to reduce costs and acquisition time. Moreover ERGI investigations supply 3D information concerning a more extended area.
Geochemical hazard related to sulphide-bearing AML could not be evaluated taking into account only the metal and metalloid concentrations of terrains, since it is high by nature. It is suggested to evaluate geochemical hazard starting from the combination of high metal and metalloid concentrations and of the acid production or neutralising potential of terrains by AMIRA procedure (IWRI &amp; EGI, 2002). Hazard evaluation was performed by geostatistical analyses, resulting from 1) the interpolation of the terrain chemical features on the whole area, 2) the overlapping of previous results and 3) the adding of the topographic setting. This approach allows to identify the areas where the presence of metal and metalloids is really hazardous. It also supports the choice of areas that need any treatment.
Since AMD processes have a key-role in environmental damages from mining pollution, it is important to know their persistence in time. No studies about this topic have already done. In a preliminary step, the persistence of AMD processes could be calculated starting from common data as yearly rainfall, mining waters pH and acid production or neutralising potential of terrains. The following step is to consider the results of kinetic tests.
These approaches have been developed on three pilot sites with different geo-environmental setting:
? Rio Marina mining district (Elba Island, LI), characterised by hematite + pyrite ore association, exploited for iron from Etruscan age till 1981;
? Libiola mine (GE), characterised by chalcopyrite + pyrite ore association, exploited for copper from 1864 till 1962;
The application of the proposed methodologies and techniques allows a better geo-environmental characterisation of AML.
Moreover we think that the proposed approach for the assessment of geochemical risk related to AML could contribute to reduce the areas that need remediation. Consequently will be possible to reduce costs of remediation and impact of remediation on AML.