Assessing anthropogenic pressures on groundwater using stable OH isotopes: perspectives and issues
Résumé
Large developments of isotope hydrogeology were done and well-established techniques mainly applying stable
isotopes of the water molecule (hydrogen and oxygen) are now used largely to trace water provenance but also
recharge processes. New methods allow the use of non-traditional isotopes (metals, compound specific stable iso-
tope analysis CSIA. . . ) to trace anthropogenic pressures in surface- and groundwater. Groundwater contamination
in large industrial sites may come from several origins such as leakage from tanks during the production process
of chemical products, liquid storage tanks, solid end product or past accumulated product in soil which is released
over the time. The understanding of the origin and the further evolution of the chemical contamination in ground-
water in an industrial site issued from past or current industrial activities is essential for the industrial companies
regarding their environmental policies. The objective of this study was to use with an innovative way the stable
isotopes of the water molecule as a low cost tool to trace pollutant plumes in groundwater and help to a better
management of contaminated industrial sites.
We present data on stable isotopes O and H in an European region where electrochemistry plants occur. For
confidentiality purposes, the sites remain anonymous. Present day industrial activities have a direct impact on the
groundwater over the site and migration of the contaminant(s) plume out of the site is supposed.
We first characterize the natural groundwater background through the O-H characterization of surface water, lakes,
thermal waters and regional shallow aquifers. High and low altitude recharge can be demonstrated in the area.
Secondly, we used the stable isotope of the water molecule to trace over the site the impact of the Cl-rich liquor
manufacturing process. Large deuterium enrichment was evidenced in the groundwater and the high values can
be related to a direct contamination of the groundwater through leakage of Cl-rich liquor with a
D values up to
400
h
̇
After technical operations to improve sealing of the liquid storage tanks, no evidence of
D enrichment can
be shown in present day groundwater. All values are along the global meteoric water line even for wells previously
H-enriched, reflecting the absence of new leakage from tanks or during the manufacturing process over the site.
Therefore our study shows that the stable isotopes of the water molecule can also be successfully used in an
innovative way to trace pollutant plumes in groundwater