Groundwater natural background levels assessment The French approach A. BLUM, L. CHERY (BRGM, French Geological Survey) H. LEGRAND (MEDD, French Ministry for the Environment)

Water Division European Groundwater Conference 2006 – Vienna

Context and main objectives

> Definition : •

Reference state of groundwater quality (without any human influence) …

•

…resulting of natural processes:

•

Concentrations can naturally be very high (even more than drinking water standards)

– Water – rock interactions (sandstones, limestones….) – Processes (leakage, redox conditions, salinity, soil…) – Residence time (a few weeks to several thousand years)

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Context and main objectives

> Initial needs •

1999 : National Monitoring Network of groundwater quality à how to distinguish natural from anthropogenic elements ? à how to identify the geochemical background of an aquifer?

•

2000 : Water Framework Directive – Further characterisation (article 5 – annexe II.2.2) :” characterisation of the chemical composition of the groundwater […] Member States may use typologies for groundwater characterisation when establishing natural background levels” – Future Groundwater Daughter Directive : except for Nitrates and Pesticides, Member States will have to identify thresholds values for the definition of “good chemical status”

European Groundwater Conference 2006 – Vienna

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Context and main objectives

> The project (1999 – 2005) • •

Water Agencies + French Ministry for the Environment Main outlines: 1) State of the art on geochemical baseline of French aquifers : major elements, trace elements, natural processes 2) Methodology 3) Application on 4 different case studies

Crystalline basement

Alluvial

Volcanism

Jurassic limestones European Groundwater Conference 2006 – Vienna

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State of the art – Major elements

> Review of the literature • •

Review of natural background levels (NBL) in French aquifers Expected levels of each type of aquifer

> Statistical analysis • •

To define the typical composition of each type of aquifer Based on the data available in the French national groundwater database (ADES)

www.ades.eaufrance.fr

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State of the art – Major elements

> •

A selection of the data has been necessary Selected data

– NO36

State of the art – Major elements

> Typology based on four levels of criteria • • • •

Lithology (sandstones, sands, limestones, chalk, crystalline, basalts) Nitrates concentration Distance to the seaside (> ou < 100 km) Confined/unconfined Chloride concentrations in rainfalls

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State of the art – Major elements Statistical results Unconfined limestones, NO3 < 10mg/L, distance from the coast > 100 km

Location of sampling sites

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Schoeller and Piper diagram of the median values

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State of the art – Trace elements

> Statistical analysis • •

Useful but… … not absolutely representative : – deterioration of the borehole, point source pollution,…) – Analytical performance are often not sufficient to have data of “good quality” (limits of quantification too high)

> Literature review • •

Exhaustive (mostly in France but not only) Main goal : identify the most favourable geological context of each element

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State of the art – Trace elements

+++ very common, a part or the whole aquifer ++ relatively common European Groundwater Conference 2006 – Vienna

absence

+ very occasional - absence or very rare > 10

Proposed methodology

> A step by step approach… …that can easily be applied by water managers

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Proposed methodology

> 3 levels of application •

“predictive application”: to know the geochemical background of lowly documented area

•

“subtractive application”: to get back to the natural geochemical background of an anthropised aquifer

•

“prospective application”: to give recommendations or guidelines for a better calibration of the measurement networks according to their purpose.

European Groundwater Conference 2006 – Vienna

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Proposed methodology

> Results reported in one single book Chery, 2006. Qualité naturelle des eaux souterraines : méthodologie de caractérisation des états de référence des aquifères français. Collection Technique. Ed. BRGM.

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Proposed methodology

Lithology NO3 concentration Confined / unconfined

Distance to the coast

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Conclusions and further steps

> Support to French policy makers • •

Definition of the groundwater bodies “good chemical status” Mapping of the high natural background levels zones regarding trace elements

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Conclusions and further steps

> BRIDGE •

Sharing “European” experiences to build a common methodology to derive the “threshold values” required by the Groundwater Daughter Directive

> Challenges for the coming years • •

Apply the methodology on each groundwater body Improve the knowledge on natural geochemical background levels of trace elements – Improving the monitoring networks pertinence – Leading local studies

European Groundwater Conference 2006 – Vienna

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