1. WGGW Bratislava – 26 October 2016
Trend Assessment in the National Groundwater Quality Monitoring Network in the Slovak Republic
Robert Chriastel
Slovak Hydrometeorological Institute Bratislava

2. Monitoring of Groundwater Quality in the Slovak Republic
The main objectives
Identification of significant pollution of GW within GW bodies,
Identification of significant trends in concentrations of chemical compounds in GW caused by anthropogenic activities,
Identification of significant trends in concentrations of chemical compounds in GW caused by natural process,
Information source for decision making process in the field of water management,
Fulfillments of other requirements of EU directives (characterization of GWB, monitoring of protected areas etc.).

3. Monitoring of Groundwater Quality in the Slovak Republic
Monitoring programme
Groundwater quality monitoring and assessment is performed since 1982 (till 2006 focused mainly on the important water management aquifers) Monitoring programme was redesigned in accordance with WFD requirements in 2007.
Monitoring network:
Consists of 545 sampling sites:
- 132 in surveillance monitoring,
- 413 in operational monitoring
Sampling frequency: from 1 to 4 times per year
- 1/year – Pre-Quaternary rocks (except karstic areas),
- 2/year – Quaternary sediments,
- 4/year – Karst (limestones and dolomites)

4. Monitoring of Groundwater Quality in the Slovak Republic
Measured parameters:
Measurement in situ: Depth of object, Temperature of air/water, Level of water before/during sampling, Strength of sampling pump, pH – value, Standardised conductivity, Oxygen content/saturation, Acid neutralisation capacity, Base neutralization capacity, Colour, Odour, Sediment content.
Chemical analysis:
Basic group of parameters – measured in every sampling site
Supplementary group of parameters – measured based on identified pressures.

5. Monitoring of Groundwater Quality in the Slovak Republic
Basic group of parameters:
Basic physico-chemical substances: Natrium, Potassium, Calcium, Magnesium, Manganese, Iron, Ammonia ions, Nitrates, Nitrites, Chlorides, Sulphates, Phosphates, Silicates, Carbonates, Hydrogencarbonates, COD-Mn, forms of CO2, O2, pH-value
Trace elements: arsenic, aluminium, cadmium, copper, lead, mercury, zinc, chromium, nickel
Common Organic Compounds: TOC, nonpolar extractable substances (UV, IR), steam distillable phenols, humic substances
Supplementary group of parameters:
Basic physico-chemical substances: Hydrogen sulfides, total cyanides
Common Organic Compounds: surfactants
Specific Organic Compounds: Pesticides, ΣPCB, Aromatic hydrocarbons, Chlorinated phenols, Chlorinated dissolvents, Polyaromatic hydrocarbons

6. Monitoring network
Layer of Quaternary GWB
Layer of Pre-Quaternary GWB

7. Criteria for identification of significant and sustained upward trends:
Statistically significant upward trend is detected and mean concentration of 2 last yearly mean concentrations ≥ 0,75 limit value (GW quality standard, threshold value).
Statistically significant upward trend is detected and predicted concentration for 2021 ≥ limit value.
Calculation of predicted concentration:
Sen's estimate – data do not follows normal distribution
Linear regression – data follows normal distribution

8. TREND ASSESSMENT
Trend assessment is conducted only for those groundwater bodies, where at least one monitoring point showed occurrence of significant sustainable upward trend  required trend assessment at sampling site level.
Time frame:
Minimum requirement for data sets:
Minimum length of time series: 6 years;
End of time series in 2012 or 2013;
Maximum gap in time series: 1 year;
Percentage of non-detects: LOQ < 50%.
Treatment of LOQ values:
Measurements bellow limit of quantification (LOQ) replaced by Max LOQ in each time series fulfilling minimum requirements (determinand/monitoring point);
Measured values < Max LOQ replaced by Max LOQ .

9. ANOVA - if data set follows normal distribution;
TREND ASSESSMENT
Data aggregation
On the sampling site level: calculation of mean concentration recorded within 1 year in individual monitoring point (parameter/monitoring point/year).
On the GWB level: calculation of mean of annual mean concentrations of all monitoring sites located within the GWB.
Detection of upward statistically significant trends
ANOVA - if data set follows normal distribution;
Mann-Kendall test - if data set do not follows normal distribution;
Goodness-of-fit tests (Lilliefors test, Kolmogorov-Smirnov test);
All tests are performed on 95% confidence level

10. TREND ASSESSMENT
Percentage of statistically significant trends identified by individual tests
Number of st. significant trends: 468

11. Výsledky hodnotenie trendov Trend assessment in groundwater: NH4

12. Trend assessment in groundwater: NO3

13. Trend assessment in groundwater: TOC

14. Trend assessment in groundwater: Cl

15. Trend assessment in groundwater SO4

16. TREND ASSESSMENT Preliminary trend assessment in GWB SK1000100P
Average concentration of Cl- in sampling site (Záhorská Ves) is 6.3 times higher than the average concentration calculated for other sampling sites  significant influence on the overall trend assessment.
Repeated assessments:
Original dataset excluding results from sampling site , data aggregation – mean of yearly means;
Original dataset – all data, data aggregation – median of yearly means.
Result – no st. significant trend  preliminary classification of trend rejected
Preliminary trend assessment in GWB SK P
Average concentration of SO4 in sampling site (Záhorská Ves) is 6.1 times higher than the average concentration calculated for other sampling sites  significant influence on the overall trend assessment.
Repeated assessments:
Original dataset excluding results from sampling site , data aggregation – mean of yearly means;
Original dataset – all data, data aggregation – median of yearly means.
Result – no st. significant trend  preliminary classification of trend rejected

17. TREND ASSESSMENT Preliminary trend assessment in GWB SK1000600P
Average concentration of Cl- in sampling site (Bíňa) is 5.4 times higher than the average concentration calculated for other sampling sites  significant influence on the overall trend assessment.
Repeated assessments:
Original dataset excluding results from sampling site 56090, data aggregation – mean of yearly means;
Original dataset – all data, data aggregation – median of yearly means.
Result – no st. significant trend  preliminary classification of trend rejected
Preliminary trend assessment in GWB SK P
Trend reversal assessment (two-section linear regression model)  no trend reversal found
Classification of significant and sustained upward trend was accepted

18. Thank you for your attention