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JBartels May 20, 2020 09:26 AM
Dear Sir, Madam,

For an EU wide project we are checking the presence of Hexachlorocyclohexane (HCH) in ground and surface waters. For this we are using the WISE WFD database (, specifically the information on groundwater bodies. In this dataset quantities of HCH are not recorded.
Is it possible to obtain this information?
If that is not the case, is there another way to assess how much HCH is present?

Furthermore, could you give us information on how it is determined that HCH is present in a certain groundwater body?
We have found in a different dataset (Waterbase Water Quality,[…]/waterbase-water-quality-2) that HCH is recorded in instances where there are no measurements above the detection limit (or Limit of Quantification (LOQ)). How can we assure that this is not the case in this dataset?
Replies (2)
EEA May 20, 2020 11:35 AM
Dear JBartels,

Thank you for contacting the European Environment Agency (EEA).

Your enquiry has been forwarded to our relevant experts. We will get back to you as soon as possible.

Thank you for your patience.
With kind regards,
EEA Enquiry Services
EEA May 25, 2020 10:15 AM
Dear JBartels,
For the WFD data, please find information on the reporting available at , which sets out what reporters were required to do, explaining groundwater measurements etc. There is also the groundwater directive 2006 As amended by[…]/?uri=CELEX%3A32014L0080
Under WFD reporting, Member States report status according to quality thresholds. They do not report concentrations, so that information is not available under WFD.

More information: - via the exports tab, the technical specification for the dataset sets out that:

Countries are required to report the LoQ
“5. Values below the limit of quantification in disaggregated data
If, for a specific sample value, the measured concentration is below the limit of quantification, then report the limit of quantification value in the "Observed Value" field and report 'True' (or '1') in the boolean "Observed value below LOQ" field.
6. Values below the limit of quantification in annually aggregated data
When preparing annually aggregated data, sample concentrations below the limits of quantification must be treated in accordance to the QA/QC Directive (Commission directive 2009/90/EC of 31 July 2009 laying down, pursuant to Directive 2000/60/EC of the European Parliament and of the Council, technical specifications for chemical analysis and monitoring of water status): - If a sample concentration value is below the limit of quantification, then, for the mean value calculation only, it must be replaced with a value equivalent to HALF THE LIMIT OF QUANTIFICATION value;
If the calculated annual mean value of the measurements results is below the limit of quantification value, then report the limit of quantification value in the "resultMeanValue" field and set 'True' (or '1') in the boolean "resultQualityMeanBelowLOQ" field. Use the same rule when reporting minimum, maximum and median values. If the samples in the aggregation had different limits of quantification, then the highest of the different LOQ values must be used in these cases.”
When the observation does not exceed LoQ it is set to the value of the LoQ and therefore the rounded figure. The LoQ field would not have had the < character, so that is not the issue.
Analytically, it is not correct to convert a <LoQ (or LoD) value to zero. The LoQ value is the lowest concentration that can be measured with confidence. Chemical analysis may have detected the substance being present, but was insufficiently sensitive to quantify how much was there.
Commonly, people use “half LoQ” as an estimation of the concentration, though that can create other issues.
We hope you will find this information useful.
With kind regards,
EEA Enquiry Services