1. Remco van Ek remco.vanek@tno.nl Saltwater intrusion in the Netherlands in relation to the WFD Seminar on Ground- and surface water monitoring Smardzewice, 9-12 July 2007 - INFRA 24055 Deltares (in formation)

2. 2 Content 1.Introduction 2.Origin of saline groundwater 3.Impact analysis 4.Implications for WFD implementation 5.Conclusions

3. 3 1. Introduction According to WFD Annex II – GWB status Alterations to flow direction resulting from level changes may occur temporarily, or continuously in a spatially limited area …. but such reversals do not cause saltwater or other intrusion, and do not indicate a sustained and clearly identified anthropogenic induced trend in flow direction likely to result in such intrusions.

4. 4 1. Introduction WGC-2 Groundwater “Status compliance and trends” Types of intrusion

5. 5 1. Introduction WGC-2 Groundwater “Status compliance and trends” Groundwater good status is not met if Relevant TVs are exceeded and there is either a significant and sustained upward trend in one or more key parameters at relevant monitoring points or there is an existing significant impact on a point of abstraction as a consequence of an intrusion.

6. 6 1. Introduction Threshold values (Stuyfzand, 1993) Main classSubdividedmg Cl / l FreshOligohaline0-5 Oligohaline-fresh5-30 Fresh30-150 Fresh-brackish150-300 Brackish 300-1000 Brackish-salt1000-10.000 Salt 10.000-20.000 Hypersaline > 20.0000 Fresh - Brackish: 150 mg Cl / l Brackish – Salt: 1000 mg Cl / l

7. 7 1. Introduction WGC-2 Groundwater “Status compliance and trends” Identify areas with natural high saline concentrations Identify areas where there is risk of intrusion (pressure due to pumping) Identify monitoring points which exceed relevant GW-QS and TVs Integrate the data mentioned above Calculate trends in Electrical Conductivity (EC) and other relevant substances concentrations indicating an expansion of intrusion Is there a significant impact on any point of abstraction due to intrusion?

8. 8 2. Origin of saline groundwater NL has been part of the North sea in the past Development of brackish aquifers

9. 9 7100 AD Holocene

10. 10 Holocene 3150 AD

11. 11 2. Origin of saline groundwater Distribution of fresh water aquifers

12. 12 2. Origin of saline groundwater Distribution of fresh water aquifers Depth [m] relative to sea level < 100 100 - 200 200 - 300 300 - 400 400 - 500 ≥ 500 Areas with inversion (e.g. saltwater above fresh water) Source: REGIS (TNO)

13. 13 2. Origin of saline groundwater (Stuyfzand & Stuurman, 1994) Sea water or saline water pollution? 12 sources

14. 14 3. Impact analysis Mining of fresh groundwater in the Dune region

15. 15 3. Impact analysis Mining of fresh groundwater in the Dune region (Stuyfzand, 1994)

16. 16 3. Impact analysis Large scale intrusion in Polder areas

17. 17 3. Impact analysis Large scale intrusion in Polder areas (Oude Essink, 1996) Distance [m] Depth [m] Sea Dune area Haarlemmermeer polder 1902 Distance [m] Depth [m] Sea Dune area Haarlemmermeer polder 1854 Distance [m] Depth [m] Sea Dune area Haarlemmermeer polder 1957 Distance [m] Depth [m] Sea Dune area Haarlemmermeer polder 2006

18. 18 3. Impact analysis Saltwater wells (de Louw, 2006)

19. 19 3. Impact analysis Saltwater wells (Oude Essink, TNO)

20. 20 3. Impact analysis Impact on pumping stations: upconing of saltwater n > 200

21. 21 3. Impact analysis (n = 16) Impact on pumping stations: upconing of saltwater

22. 22 3. Impact analysis Sea level rise

23. 23 3. Impact analysis Sea level rise Affected zone (λ) equals  (kDc) For x=3λ, ΔΦ(x) = Φ 0 *e -3 = Φ 0 *0.05 So for x=3λ only 5% of Φ 0 remains Affected zone (λ) equals  (kDc) For x=3λ, ΔΦ(x) = Φ 0 *e -3 = Φ 0 *0.05 So for x=3λ only 5% of Φ 0 remains Noordzee/Nieuwe Waterweg North sea Low polder area Mazure equation

24. 24 3. Impact analysis Sea level rise Affected zone due to sea level rise and land subsidence in the Province Zuid-Holland Difference in hydraulic head (m) at -12.5 below sea level between 2000 and 2050 Source: TNO, Oude Essink, 2004

25. 25 3. Impact analysis Sea level rise: saltwater intrusion through rivers

26. 26 4. Implications for WFD implementation Large database (> 60.000 bore holes) but only 10% deeper than 70 m Based on these measurements a 3D model of salinity in groundwater was created A good estimate of the initial Cl-distribution is vital for modelling (TNO, 2004) 60764 chloride concentrations in NL Modelling

27. 27 Modelling NAGROM (MLAEM-VD) National scale Saltwater distribution (3D) is fixed MODFLOW (MOCDENS3D) Regional scale Saltwater distribution is not fixed Chloride distribution (Cl mg l -1 ) Salt load in kg/ha/yr during an extreme dry year 4. Implications for WFD implementation

28. 28 Monitoring: Distribution salt water in groundwater Depth [m] of Cl concentration 1000 mg/l 4. Implications for WFD implementation

29. 29 Horizontal intrusion Vertical intrusion Area vulnerable for upconing Main salt water border for WFD Area vulnerable for lateral Intrusion from the Peelhorst aquifer Depth [m] of Cl concentration 1000 mg/l 4. Implications for WFD implementation Monitoring: Distribution salt water in groundwater

30. 30 Monitoring: Locations Depth [m] of Cl concentration 1000 mg/l Outside DWPA (drinking water protection area) Inside DWPA (drinking water protection area) Filter in brackish zone Filter below salt border Salt ‘gard’ Filter in brackish zone Filter below salt border Salt ‘gard’ 4. Implications for WFD implementation

31. 31 Present monitoring locations for WFD Possible extension of monitoring locations Salt water intrusion in groundwater 4. Implications for WFD implementation Monitoring frequency - Regional (vertical) 1/6yr - Dunes1/2yr - Peel border1/2yr - Dunes with abs.1/yr - GW abs.1-2/yr

32. 32 5. Conclusions 1.Saltwater is abundantly present in the groundwaterbodies of NL (especially in the western and northern part). Mostly it is ‘old’ marine water. 2.Most important cause of saltwater intrusion is due to the deep polder areas. It is a slow process and considered to be irreversible (exemption). 3.Saltwater intrusion due to groundwater abstraction can occur on a small scale. It is considered as reversible. 4.Monitoring system is available and operational, but some modifications may be needed.