Traces of World War I in groundwater: perchlorate contamination of the chalk aquifer in NE France
2019
Perchlorate is an environmental contaminant of growing concern due to its potential human health effects
and widespread occurrence in surface water and groundwater. It is considered potentially toxic even at low
concentrations (> 4 ppb) as an endocrine disruptor, especially for fetuses and infants. Analyzes have highlighted
presence of perchlorate in drinking water of Champagne-Ardenne (NE France) with two suspected
sources: a military source related to the WWI (World War I) and an agricultural one related to past use of
Chilean nitrates.
In order to define the origin and fate of perchlorate in groundwater, a study area of 500 km2 has been selected
east of Reims, where drinking water catchments of the chalk aquifer are concerned with perchlorate contamination.
Chalk groundwater flow and geochemistry are monitored for 2 years from June 2017 to June 2019 at 35
sampling points including boreholes, springs and rivers (mainly form chalk aquifer drainage). Water samples
are collected monthly to determine the major and trace elements contents, stable water isotopes, perchlorate
and organic pyrotechnic molecules. Perchlorate were detected at almost all sampling points (32 of 35) with a
maximum value of 63 ppb and an average value of 11 ppb. High levels of perchlorate (> 4 ppb) were detected
mainly downstream of the Monronvilliers military camp, where quantities of ammunitions were used, stored
and destroyed during and after the WWI. Statistical analysis shows no significant correlation between perchlorate
and other major ions. The isotopic signature of perchlorate was analyzed and showed a synthetic origin,
proving for the first time the military source of contamination in this area. In addition, groundwater dating
using CFCs and SF6 indicated an average residence time of < 30 years, implying that perchlorate contamination
is related to sources that may still subsist in the subsoil after the WWI (e.g. unexploded ammunitions)
rather than military activities during the conflict. Perchlorate concentrations are relatively stable with time
for most points except for decreases observed in September 2017 and 2018. Stable isotopic analysis of water
and monitored groundwater table showed that the chalk aquifer is recharged by precipitation mainly during
the winter season. Therefore, the decrease of perchlorate levels could possibly be explained by the very few
recharge and low groundwater table in September, as less perchlorate is dissolved and transferred into the
aquifer. This research provides insights on a combined use of hydraulic, geochemical and isotopic approaches
to study the origin and transfer of contamination in chalk groundwater. The chalk aquifer properties and the
long-term influence of the WWI on groundwater quality in NE France are better clarified, with the aim to
provide appropriate recommendations in terms of water management.
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