Testing of GW-quality data from subsequent surveillance monitoring for a significant increase Proposal developed by Umweltbundesamt and quo data (subcontractor) for the Federal Ministry for Agriculture, Forestry, Environment and Water Management (Austria)

Background information (1) Trend assessment - Proposal of WG 2.8 Minimum length of time series for the detection of an upward trend Annual data: Length >= 8 years and >= 8 values Half-yearly data: Length >= 5 years and >=10 values Quarterly data: Length >= 5 years and >=15 values this is practical for operational monitoring in case of surveillance monitoring: 42 years would be needed

Background information (2) WFD, Art. 4: ... to prevent the deterioration of the status of all bodies of groundwater ... in case of surveillance monitoring: criteria for deriving activities at an earlier stage than 42 years would be needed

Proposal (1) Testing of GW-quality data from subsequent surveillance monitoring activities for a significant increase at the GW-body level Starting point: There is random variability in the annual mean (not larger than 30%, say) Conclusion: Trends <30% cannot be assessed by subsequent surveillance monitoring!

Proposal (2) Idea: No action is required if it can be proven statistically that the actual increase is below 30 %. It may be concluded that there is random variability only - no action required if it cannot be proven statistically - action is required application of precautionary principle: burden of proof is with the monitoring manager Formal test hypotheses: according to null hypothesis it is assumed that the actual increase is at least 30%; i.e. that there is a systematic trend the null hypothesis will be rejected only if the increase is significantly below 30 % (or below another appropriate limit)

Proposal (3) Proposed methods Analysis of site-wise level differences in case of temporal correlation within the sites, the hypotheses may be tested using the relative site-wise level differences Comparison of the spatial mean The hypotheses can be tested with the test statistic AM1/AM0, where AM1 and AM0 denote the spatial mean in the sampling periods t=0 and t=1, respectively.

Proposal (4) Both methods consider number of sampling sites and variability within the GW-body actual increase > 30% decision for action (with both methods) actual increase 0 - 30% decision depends on number of sampling sites and variability within the GW-body e.g. for poor network > 10 % decision for action might be possible (depends on parameters) for good network > 20 % decision for action might be possible (depends on parameters)

Proposal (5) Proposed procedure: test of subsequent surveillance monitoring data in case that the increase is not significantly below the set limits => action is required - operational monitoring to be introduced the proposed test does not replace a trend assessment

Current state Currently both methods are tested with Austrian data and data from CIS WG 2.8 for various GW-body and parameters results and formal description of methods can be provided before the next EAF-GW it seems that for some parameters e.g. pesticides due to high variability 40 or 50 % seem to be adequate