1. Trend assessment Setting the scene
Benjamin Lopez, Laurence Gourcy
Brgm, French Geological Survey
Water, Environment & Ecotechnologies division
April 2015, 28th meeting of WG Groundwater
I will give you some words to introduce this session on Trend assessment

2. Trend assessment Introduction Goal of the activity Procedure
Regulatory issues
Goal of the activity
Procedure

3. Introduction Trends references in WFD/GWD WFD : GWD
Recitals 26 et 28 :« For groundwater, in addition to the requirements of good status, any significant and sustained upward trend in the concentration of any pollutant should be identified and reversed.”
Article 4.1.b (iii) - environmental objectives,
Article 17 2 (b) and article criteria for the identification of significant and sustained upward trends and for the definition of starting points for trend reversals
Annexe V: (groundwater monitoring network) (surveillance monitoring) (operational monitoring), (identification of trends in pollutants), (interpretation and presentation f groundwater chemical status) and 2.5 (presentation of grounwater status)
GWD
Recital 6 and 11
Article 1(b) (purpose), Article 2.3 (definition), Article 5 (Identification of significant and sustained upward trends and the definition of starting points for trend reversals), Article 6.1.b (Measures to prevent or limit inputs of pollutants into groundwater)
Annex IV « Identification and reversal of significant and sustained upward trends”
Where can you find Trends references in Directives?
The WFD and GWD also require that trends in pollutant concentrations are detected and that these trends are assessed to determine whether they are environmentally significant. Where significant upward trends exist they must be reversed through the application of programmes of measures to ensure that there are no future failures of environmental objectives.
The GWD starting point for trend reversal must be defined as a proportion of the threshold value or quality standard (75% by default).

4. Introduction Relevant guidance documents
Technical Report No. 1: Statistical aspects of the identification of groundwater pollution trends and aggregation of monitoring results – WG 2.8 Statistics (2001)
Guidance Document No. 18 : Guidance on groundwater status and trend assessment
Conceptual model and trend assessment
Concentrations below the limit of quantification and trend assessment
Reporting and trend assessment
Trend and trend reversal assessment

5. Introduction
What was reported in COMMISSION STAFF WORKING DOCUMENT European Overview Accompanying the document « Report from the Commission to the European Parliament and the Council on the Implementation of the Water Framework Directive (2000/60/EC) River Basin Management Plans ) »
68 River Basin Management Plans reported by 17 Member States reported that trend assessments have been performed
in 57 RBMPs the assessment methods have been described
=>mainly statistical methods were applied
The length of the considered time series varies considerably starting mainly from up to 2008
=> But due to WFD surveillance monitoring started in dec 2006, trend assessment was premature, a more complete picture is expected in 2015
Only very few RBMPs reported the application of additional plume trend assessment
=> No details reported, it is not clear whether such assessments were performed already or are to be performed.
Trend reversal methodology: 23 RBMPs of 6 Member States already reported information on the establishment of such a methodology whereas 42 RBMPs of 9 Member States stated that a methodology is not yet defined.
Due to the fact that in many groundwater bodies in Europe monitoring started in December 2006 under the WFD with the surveillance monitoring, performing trend assessment is currently premature. A more complete picture on trends is expected in 2015 with time series of WFD monitoring of seven years (in case of operational monitoring).
Additional trend assessments are required by the Article 5.5 GWD to assess the impact of existing plumes of pollution resulting from point sources and contaminated land and to verify that these plumes do not expand and do not present a risk for human health and the environment.
Trend reversal assessment usually needs the assessment of a trend first therefore longer time series will be necessary to complete them. Even in 2015 trend reversal assessments might not be carried out in every RBD.

6. Introduction
Guidance 18 : A significant and sustained upward trend is: “any statistically and environmentally significant increase of concentration of a pollutant, group of pollutants, or indicator of pollution in groundwater for which trend reversal is identified as being necessary in accordance with Article 5” (GWD Article 2(3));
A statistically significant trend is one that has been identified using a recognised statistical trend assessment technique.
An environmentally significant trend is one that is statistically significant and would lead to the failure of one or more of the WFD’s environmental objectives if not reversed. »
Challenges
Monitoring (locations, sampling frequencies)
Identifying trends
Statistically significant : statiscal tests
Environmentally significant
Concentrations below the LOQ or lack of data to apply statistical test
Assessment of long term trends due to natural condition (long time cyclical patterns)
Identifying trend reversal
Baseline level of concentration for naturally occuring substances
Distinguish natural variations/trends from anthropogenic ones …
Regarding the trend assessment
Design of monitoring program
guidance 18 : « A high proportion of measurements below the LOQ within a time series can pose a major bias in the assessment. In this situation, the trend test should not be performed if the influence of values below LOQ is considered to be too high. »

7. Goal of the activity
Information exchange on MS trend assessment and reversal methodologies
Sharing experience /best practice on the subject :
Statistic tests used
Tools that have been developped
Solutions found to tackle main challenges …
Main questions we would like to answer?
How is monitoring designed for trend identification?
How to assess trend for pesticides when most monitoring value are below limit of quantification
How to go from trend at monitoring site to trend at GWB scale?
How to distinguish natural variations
...
CIS work programme for WG Groundwater on trends = Information exchange on MS trend assessment and reversal methodologies
Main questions we would like to answer?
Comment la surveillance est adaptée pour les tendances?
Comment faire pour les pesticides quand la plupart des valeurs sont inférieures à la LQ
Comment passer à la masse d’eau quand peu de points ou nuages de points avec poids important (champ captant)... Reprendre le schéma FR
Veut-on parler des plumes?

8. Procedure
Presentations from voluntary MS (7 MS : AT, CZ, DK, FR, NL, RO, UK)
Presentations are in two parts :
General information on main elements of trend and trend reversal assessment
Focus with a higher level of details on specific issues (different one per MS relevant for the MS)
Methods used by the 7 voluntary MS are synthetised in a « trend assessment document »

9. Thank you

10. Introduction Reporting requirement:
Upward Trend – required for 2nd cycle
Upward Trend Pollutants and Upward Trend Other Relevant Pollutants - conditional
Trend reversal – required for 2nd cycle
Trend reversal Pollutants and Trend reversal Other Relevant Pollutants – conditionnal
Trend Assessment Performed – required
Trend Assessment methodology - conditional
Time Series - conditional
Statistical Elements - conditional
Additional Trend assessment - required
Starting Point Reversal and Percentage Starting Point - required
Trend Reversal Methodology - required
Guide rapportage :
How are the groundwater chemical status monitoring programmes designed in order to detect significant and sustained upward trends in pollutants? Indicate which aspects, and how, were they incorporated in the monitoring programme:
Trend assessment only carried out in groundwater bodies at risk of not meeting WFD objectives
Trend assessment on groundwater bodies not currently at risk in order to distinguish long term trends both as a result of changes in natural conditions and through anthropogenic activity
Trend assessment based on surveillance and operational monitoring data from individual monitoring sites
Statistical method for assessing trends at each monitoring point (statistical method adapted to initial conditions such as regression analysis for normal distributions and non-parametric tests for non-normal distributed time series)
Individual parameter concentrations (or values) below Limit of Quantification (LOQ) replaced by half of the value of the highest LOQ occurring in the time series being analysed;
How upward trends were identified in sufficient time to allow measures to be implemented;
Length of time series considered to be appropriate to detect significant trends
How baseline levels for substances which occur both naturally and from anthropogenic sources were considered
How was it ensured that upward trends can be distinguished from natural variation with an adequate level of confidence and precision;
What was considered to be an acceptable level of confidence in the trend assessment;