Environmental Engineering Reference
In-Depth Information
Environmental Impacts of the A6 Highway
in La Silva Stream in the Region of Bierzo.
(Leon). Spain
Lucas Vadillo, Virginia Rodriguez, Esther Alberruche, Osvaldo Aduvire,
Margarita Lacal, Victorio Monteserin, and Ines Iribarren
Introduction
La Silva valley is affected by old coal mine spoil dumps and several mine adits with
neutral drainages. When mining was in activity, the adits generated acid mine
drainages (AMD). The natural attenuation availability of La Silva neutralized them
and the stream supported a brown trout ( Salmo trutta ) population. The A6 highway
construction has changed the physiognomy and the characteristics of 2 km of La
Silva headwaters. Due to the blasting of the rock mass (Luarca slates), high acidity
levels are being produced. ARD is generated when pyrite (FeS 2 ) contained in the
slates is exposed to air and water in oxidizing and non-alkaline conditions. The
reactions involved in this processes are well described [1, 2] . ARD causes the deg-
radation of the water quality and impacts the aquatic biota [3-5] . A case of ARD
generation has occurred in Pennsylvania due to the construction of the highway I99
[6] . Due to the high concentrations of dissolved metals in the stream (mineral
acidity), mainly Fe, Al and Mn, the alkalinity of the tributaries is insufficient to
attenuate the acidity. The pH in the stream reaches 7 after 8 km. The contamination
spreads to 15 km downstream, where the river-bed is covered by iron and alumi-
num precipitates and colloids giving reddish, ochre-yellowish and whitish colors.
Only a few benthic species can withstand this conditions and the presence of
ichthyofauna is unviable. The purposes of this survey are: to determine hydrogeo-
chemical characteristics and spatio-temporal evolution of the ARD draining to
La Silva; to analyze the dilution and precipitation mechanisms of some metals
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