Communication Dans Un Congrès Année : 2013

Assessing groundwater contamination by an industrial mega-site through a multi-isotope (S, S(SO4), N, O(NO3), B, H, O(H2O)) approach

Résumé

Industrial mega-sites are characterised by the multiplicity and the generally complex succession of industrial activities. Consequently, the history of contamination, not always well documented, induces a succession or superposition of contaminant sources and contamination pathways. Assessment of the contamination of the different reservoirs (soil, surface water, groundwater, biota) at a given moment and the related risks for their present and future use as well as the conception of remediation strategies requires indications on both the origin and the timeline of contamination processes in order to foresee their release and propagation in the receptor milieus. Isotope fingerprinting and groundwater dating increase our ability of disentangling the chronology of multiple contaminations; the large choice of isotopic tools offers the possibility of selecting specific direct or indirect tracers of most inorganic or organic contaminants. Here we present results from an industrial area in Northern France, a former coal mining area, where the first coking plant was installed in 1897. Over the following century, a large diversity of coal-based chemical industries developed on this site, including the treatment of coke oven gas, ammonia and PVC production. Coking activities ceased in 1986, the present day production concerns ammonia water, fertilisers and PVC. Over time, several decantation basins were constructed and two settling zones representing potential contamination pathways for groundwater in the Upper Cretaceous chalk aquifer, partly overlain by Tertiary to Pleistocene sediments and modern alluvial deposits. Main contaminants are cyanides, arsenic, nitrate, ammonium and sulphate, found mainly in groundwater but also, to a lesser extent, in surface waters downstream of the site To complete a comprehensive chemical monitoring programme, a multi-isotope and groundwater dating study was conducted combining delta15N and delta18O of nitrate, delta34S and delta18O of sulphate, stable isotopes of the water molecule and delta11B of dissolved boron with CFCs and SF6 as indicators of groundwater residence times. For part of the contaminated groundwaters, mean CFC-derived residence times exceed 30 years so that the contamination can be qualified as historical. A rough anticorrelation of SF6 with total cyanide and arsenic points to the same conclusion. Arsenic concentrations are not clearly correlated with any major compound or isotope tracer. Nitrate contents are related to ammonium and fertiliser production [1] and are partly limited by denitrification processes induced by the release of organic compounds by the industrial processes. delta34S values of sulphate around 0 ‰ vs. CDT are compatible with hydrolysis and oxidation of sulphur produced by coal combustion [2], delta18O of sulphate indicates variable contribution of atmospheric oxygen and water depending on the reaction mechanism (hydrolysis-oxidation, or oxidation-hydrolysis, [3]). Boron concentrations and isotope signatures of most groundwaters in the vicinity of the industrial site and immediately downstream do not significantly differ from upstream baseline values. Boron appears rather as a tracer of groundwater-surface water mixing processes than as co-tracer of the industrial contaminations. Stable isotopes of the water molecule show clear signs of evaporation for the highly contaminated groundwater below the site and directly downstream which indicate a strong impact of decantation basins as vector of contamination.

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Dates et versions

hal-00819755 , version 1 (02-05-2013)

Identifiants

  • HAL Id : hal-00819755 , version 1

Citer

Hélène Pauwels, Wolfram Kloppmann, Valérie Wypych. Assessing groundwater contamination by an industrial mega-site through a multi-isotope (S, S(SO4), N, O(NO3), B, H, O(H2O)) approach. 10th Applied Isotope Geochemistry Conference, AIG-10, Sep 2013, Budapest, Hungary. ⟨hal-00819755⟩

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