Roadmap for Determining Natural Background Levels of Trace Metals in Groundwater

Denitza D Voutchkova,Klaus Hinsby,Jörg Schullehner,Vibeke Ernstsen,Birgitte Hansen,Lærke Thorling

doi:10.3390/w13091267

Denitza D Voutchkova, Klaus Hinsby + Show 4 more

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https://doi.org/10.3390/w13091267

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Abstract

Determining natural background levels (NBLs) is a fundamental step in assessing the chemical status of groundwater bodies in the EU, as stipulated by the Water Framework and Groundwater Directives. The major challenges in deriving NBLs for trace metals are understanding the interaction of natural and anthropogenic processes and identifying the boundary between pristine and polluted groundwater. Thus, the purpose of this paper is to present a roadmap guiding the process of method selection for setting meaningful NBLs of trace metals in groundwater. To develop the roadmap, we compared and critically assessed how three methods for excluding polluted sampling points affect the NBLs for As, Cd, Cr, Cu, Ni, and Zn in Danish aquifers. These methods exclude sampling points based on (1) the primary use of the well (or sampling purpose), (2) the dominating anthropogenic pressure in the vicinity of the well, or (3) a combination of pollution indicators (NO3, pesticides, organic micropollutants). Except for Ni, the NBLs derived from the three methods did not differ significantly, indicating that the data pre-selection based on the primary use of the wells is an important step in assuring the removal of anthropogenically influenced points. However, this pre-selection could limit the data representativity with respect to the different groundwater types. The roadmap (a step-by-step guideline) can be used at the national scale in countries with varying data availability.

Highlights

Trace metals are ubiquitous in groundwater in concentrations that are determined primarily by natural processes, but in addition, they may be affected by anthropogenic factors
The remediation measures aim at reducing the groundwater concentrations below a specific threshold value (TV) for the pollutant, defined by the member states based on the estimated natural background levels (NBLs) for the pollutant according to EU legislation and guidance [1,2,3]
To thetoneed for harharmonization in the member states for the purposes of assessing monization in the NBL derivation by EU member states for the purposes of assessing the the chemical status of groundwater bodies stipulated by the WFD and GWD. It provides a chemical status of groundwater bodies stipulated by the WFD and GWD

Summary

Introduction

Trace metals are ubiquitous in groundwater in concentrations that are determined primarily by natural processes, but in addition, they may be affected by anthropogenic factors. Significant exceedances of the natural backgrounds are a question of anthropogenic pollution or other human activities changing the natural geochemistry that may eventually require the development of action plans and remediation measures. The assessment of natural background levels (NBLs) for trace metals is a prerequisite to determine whether observed concentrations are affected by human activities. Remediation measures need to be introduced to protect the legitimate groundwater uses and groundwater-dependent terrestrial and associated aquatic ecosystems. Derivation of NBLs and TVs for Assessment of Groundwater Chemical Status in EU

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