Environmental Pollution by Mining Activities - A Case Study în the Criș Alb Valley Western Carpathians

Introduction

Metal Mining is an essential human activity to provide rough materials for our society. Although the ore extraction itself directly affects a relatively limited area of terrestrial land, its impacts on the environment, as well as on public health, may be found at greater distances from the source and for a long time period. Mining activities also influence strongly the economic wealth of the area and act on its social life. Both the environmental and socio-economic impacts of mining are well documented in numerous areas worldwide, nowadays

In terms of water contamination stemming from metal mining, acid mine drainage (AMD) represents the key impact in areas exhibiting sulfide-bearing ore deposits. AMD is pre-dominantly caused by the abiotic and microbial mediated oxidation of pyrite associated with ores extracted. Water draining from mine working, such as adits, open pits, tailings impoundments, tailings and mine waste deposits, may turn acidic, if the acid neutralizing capacity in the water or in the solid deposits is not sufficient. AMD is characterised by low pH-values, high concentrations of dissolved heavy metals, non-metals and sulfate. Large waste dumps and tailings containing a surplus of pyrite tend to produce AMD within a period of hundreds of years, depending on specific environmental factors, such as the mineralogy and hydrology in the deposit and the climatological condition. In principle, it is possible to estimate the AMD production potential by stoichiometric calculations of a given waste ore dump by taking the pyrite oxidation as acid producer and the weathering reactions of carbonates and silicates as acid neutralizer. In the literature, several such acid- base accounting methods exist, but there are all approximations since the contributions of silicate weathering reactions are difficult to determine.

Natural waters heavily charged with AMD exhibit toxic concentrations of heavy metals, which will impair the aquatic live and groundwater fed by rivers.

Recently, the European Union has set environmental quality standards (EQS) for dissolved concentrations of cadmium, lead and nickel in surface waters Those of chromium, copper, and zinc remain in discussion. Waters draining mines also carry suspended solids, undissolved minerals and precipitates of iron and aluminium, to which dissolved metals will sorb when unpolluted tributaries gradually neutralize the acidic river water. Surface runoffs from bare impoundments and waste dumps also contribute to the load of suspended matter. All these particles containing harmful metals are transported downstream and may accumulate in the river channel or disperse to floodplains depending on the flow regime.

In these fluvial deposits metals can be stored for tens or hundreds of years, a real long-term environmental problem Tailings failure, when suddenly huge amounts of fine-grained materials are sliding downwards from unconsolidated dams, may represent a high risk for settlements and people living nearby. These slurries will also affect river channels and floodplains.

In Romania, a country with a long tradition of mining, investigations on mining impacts just have evolved recently. West-European research groups in collaboration with Romanian institutes have undertaken studies concerning water pollution caused by ore extraction activities.

The objective of the present study was to investigate and evaluate the water pollution in the mining impacted upper Criş Alb catchment and to assess its effect to the entire Romanian Criş Alb basin.