Historical impact of urbanization on water quality, a diachronic study in Paris and surrounding areas. – HUNIWERS

With the HUNIWERS project, we propose to apply an innovative approach to the city of Paris and its conurbation that includes: i) present day water analyses (quality, quantity, modelisation) of perched aquifers and diffuse infiltrations; ii) secondary carbonate deposits (urban speleothems) of underground systems iii) the study of archives of soil occupation and urbanization in order to build maps occupation.

The main objectives of HUNIWERS are organized in 5 tasks: : 1) Hydrological cycle modelling in 2 contrasted Parisian watersheds: water budget and comparison between land use, outflow and climatic data (measurement and historical archives) 2) Characterize the current groundwater physico-chemistry; 3) Obtaining time series of the geochemical evolution of past water geochemistry using speleothems in different sites; 4) Determine the sources and mechanisms of pollutant transfer today and in the past; 5) explore the possibilities for the re-use of sub-surface waters from Oligocene strata, as alternative water supply.

Results (partial, before the end of the project)
-A thematic seminar on «Valuing spring water in urban environments« was held on 23 May 2023 in Paris. It brought together various stakeholders from the Ile-de-France region (research institutes, local authorities, the Water Agency, ARS, etc.) to discuss the perceptions and uses of spring water, as well as the constraints and levers with regard to this use.
-Scientific articles are currently being written to present the main results obtained.

Several prospects have already been highlighted:
Putting the work carried out on present-day water into perspective with that on climate change and the prospects for the evolution of the urban water cycle (new project to be set up).
-applying the methodologies developed to other sites, particularly as regards the geochemical study of aqueduct concretions and urban underground passages.

Several publications are currently being written.
Articles already published below
-Pons-Branchu E. Caffy I et al.,. Radiocarbon dating of urban secondary carbonate deposit: site effect and implication for chronology: Case study of Paris and Versailles Palace fountains. Radiocarbon, 2022, 64 (6), pp.1323-1332. ?10.1017/RDC.2022.78?. ?hal-03918048
-Fernandez M., Dumont E., et al.. Amélioration de l’information spatiale concernant des infrastructures hydrauliques historiques de la Ville de Paris. 18ème congrès international de spéléologie 2022, Union internationale de spéléologie, Jul 2022, Le Bourget Du Lac, France. ?halshs-04085440?

The aim of the HUNIWERS project is dual: i) to use urban speleothems and “classical” archives to determine and compare the past and current quality and availability of groundwaters (water table but also infiltrating diffuse water) in the Paris conurbation in order to identify the sources and spread of pollutants; ii) evaluate the state/quality of the perched aquifers, evaluate the efficiency of environmental policies (impacts on pollutant sources) and evaluate, in relation with public authorities and stakeholders, the possible use of these waters as alternative water supply.
The impact of urban development on water resources is a major issue. It is particularly acute for near surface urban groundwater. In Paris, these groundwater, once providing drinking water, are now disused. Understanding their present and past chemical status would be extremely useful to assess past public remediation policies and to open discussion for their use as non-conventional water resource. Determining urbanization/industrialization impacts on water quality is hampered by two majors scientific locks: i) knowing the initial (pre-urbanization) state; ii) identifying key elements and natural archives suitable to reconstruct pollution sources and levels through time.
Over the past 5 years, we have developed a pioneer approach to reconstruct the past evolution of groundwater quality in urban environments. By coupling the analysis of “urban speleothems” (calcareous crusts) formed in a historical underground aqueduct with today’s water analysis, we obtained a 300 years record of selected chemical pollutant (lead, sulfur, rare earth elements) in a small watershed of NE Paris and identified today’s pollution sources but also back in the 18th century.
With the HUNIWERS project, we propose to apply and extend this dual and innovative approach to the city of Paris and its conurbation in order to (1) reconstruct the origin and the quality of past groundwater by using urban speleothems in different undergrounds and (2) compare past and current quality and availability of groundwater table and infiltrating diffuse water.
The HUNIWERS consortium involves 41 staffs from 7 main partners: LSCE, CRPG, ISTO, EDYTEM, GEOPS (cutting edge laboratories involved in environmental research) but also Cerema (a governmental scientific and technical resource center with a strong regional integration) and HT2S/CNAM (relation between science-technology and society).
The main objectives of HUNIWERS are organized in 5 tasks: : 1) Hydrological cycle modelling in 2 contrasted Parisian watersheds: water budget and comparison between land use, outflow and climatic data (measurement and historical archives) 2) Characterize the current groundwater physico-chemistry; 3) Obtaining time series of the geochemical evolution of past water geochemistry using speleothems in different sites; 4) Determine the sources and mechanisms of pollutant transfer today and in the past; 5) explore the possibilities for the re-use of sub-surface waters from Oligocene strata, as alternative water supply.


HUNIWERS combines a highly innovative approach (we are the only group to use urban speleothems worldwide) with a relatively low risk, because we have already used the methodology on smaller - and now completed - investigations
HUNIWERS’ outputs include fundamental aspects such as the legacy of human activities in the urban environment and the perspective to assess the impact of urban and industrial development and public remediation policies. HUNIWERS will also intend to develop operational tools for water management such as:
- heavy metal and organic pollution mapping to determine the most sensitive groundwaters;
- assessment on whether subsurface groundwaters are suitable for “non-conventional” uses;
- geochemical tools for establishing, the presence of leakages from the networks.

Extending the HUNIWERS methodology to other European cities will pave the way for a participation to the H2020 call.