1. Partner for progress Does arsenic, in groundwaters of the compound Rhine-Meuse delta, menace drinking water supply in the Netherlands? IAH -Meeting, Utrecht, 29 Nov 2006 Pieter J. Stuyfzand 1,2, Igor Mendizabal 1,2, & Peter van Rossum 1 1 2

2. 2 Active well fields and surface water intake points, for drinking water supply

3. 3 Water resource types in the Neths (for drinking water supply) and their characteristics 1,250 Mm3/y produced by 246 well fields + 16 surface water treatment plants

4. 4 38 Oostrum (A) 14 Tolkamer (B) 12 Dorst (B) 11 Macharen (A) 12 Zwijndrecht (U) 21 Loosdrecht (B) No trends 1989-2002

5. 5 Mean composition of raw water from well field types in the Neths, in 1989

6. 6 Plot of As versus resp. Fe and HCO 3 for all well fields (for drink. water supply) in Neths

7. 7 Plot of As versus resp. PO 4 and pH for all well fields (for drink. water supply) in Neths

8. 8 Plot of As versus resp. SO 4 and NO 3 for all well fields (for drink. water supply) in Neths

9. 9 Plot of As versus resp. As in sludge and depth, for all well fields (for drink. water supply) in Neths

10. 10 Concl.1: On a large scale (well fields), As does not pose problems to drinking water supply Concentrations in raw groundwater from well fields = 0.1 – 38 µg/L. Stable situation during past 16 years Enough Fe 2+ in groundwater (0.01-25 mg/L) to bind most As upon aeration and RSF. As DW = 0.05-7 µg/L Water treatment sludges  high As content (10- 3100 mg/kg d.w.)  hazardous waste. Ferric sludges used for making construction bricks No clear relations between As and {PO4, Fe, Mn, SO4, HCO3, DOC}. Max with pH 7-7.5, NO3 < 2. Low As in limestone aquifers and basin AR systems High(er) As in sandy (conf) aquifers and RBF systems

11. 11 Sites with detailed hydrogeo- chemical surveys, incl. As behaviour

12. 12 Site 1: Changes in TEs (incl As) in coastal dune groundwater along a flow path (Stuyfzand, 1991 )

13. 13 Site 2: Phreatic groundwater under agricul- tural stress, Vierlingsbeek (data C.v.Beek)

14. 14 Site 3: RBF flow path near Opperduit (1983 and 1994/5), with As isoconc lines 1.2 y 5 y 8 y 2.5 y

15. 15 Site 3: Detailed survey of TEs in Rhine RBF (site Opperduit) in 1983 Conc 0.45 um filtr sample

16. 16 Site 4: RBF-study in compound Rhine – Meuse estuary (Hollandsch Diep)

17. 17 Site 4: Distribution of watertypes (incl. distinction in age and recharge area) m MSL 100 m

18. 18 Site 4: Different interactions of RBF with recent sludge deposits in Hollandsch Diep (R-M estuary)

19. 19 Site 5: high As-belt south of Amsterdam (data P. van Rossum) Area south of Amsterdam PO4, NO3, SO4, DOC, SiO2 FeS2 FeOOH, FeS2 Fe(OH)3 CH4

20. 20 Site 6: Pretreated Rhine water along an AR flow path, dunes Zandvoort 1983

21. 21 Site 7: AR with Meuse River water, near The Hague (DZH); snapshot 2006

22. 22 Redox zoning on Langerak AR pilot, after 1.5 yr injection As in layer C (very reactive FeS 2 ) on Langerak site A B C Site 8: DWI

23. 23 Trace Elements from pyrite are largely immobilized in fresh Fe(OH) 3 - precipitates (Stuyfzand, 2001)  Fe 0.98 Co 0.003 Ni 0.01 Zn 0.01 S 2 As 0.005  + O 2 + NO 3 - + xH 4 SiO 4  Si x Fe(OH) 3 Co 0.0027 Ni 0.009 Zn 0.009 (HAsO 4 ) 0.004  +2SO 4 2- +0.001 (H 3 AsO 3 + Ni 2+ + Zn 2+ ) +  N 2 + 0.0003 Co 2+  High As-concentrations if: ΔSO 4 high ΔSO 4 high Δx or t small Δx or t small pH high pH high PO4 and H 4 SiO 4 high PO4 and H 4 SiO 4 high

24. 24  Does ripening of ferrihydrite to goethite mobilize As? Pumping wells often clog by mixing of Fe 2+ with O 2 /NO 3 -water

25. 25 Concl.2: on small scale (indiv wells) As may become nasty for drinking water supply As mobilization by: (Sub)recent disturbances of hydrol. system, like drawdown/rise of watertables, flow reversal, flow accelleration etc. (Sub)recent changes in quality infiltrating water, esp. rise of PO 4, SO 4, NO 3, HCO 3, DOC, F, temp, Reducing gases, esp.CH 4 (and H 2 S) Needed / to be studied: As behaviour in SIR and ASR systems An As risk assessment method

26. 26 Concl.3: As mobilizing processes and bias H 2 S + 4 HAsO 4 2- + 6H +  4 H 3 AsO 3 + SO 4 2- CH 4 + 4HAsO 4 2- + 8H +  4H 3 AsO 3 + CO 2 + 2H 2 O Positive As-bias: FeS 2 / Fe(OH) 3 particles dissolved by HNO 3 due to lack of (sufficient) filtration Negative As-bias: filtration in lab of oxidized sample with Fe 2+

27. 27 Changes in spatial distribution of groundwater types in Neths: land recl, drainage, river endikement, Q etc.

28. 28 Ni and Fe in phreatic groundwater under agricultural stress, Vierlingsbeek (data v.Beek)

29. 29 NO3 and SO4 in phreatic groundwater under agricultural stress, Vierlingsbeek (data v.Beek) High As

30. 30 Site 3: Mean composition Rhine River and 3 redox types of River Bank Filtrate from pumping wells

31. 31 Site 4: Interpreted age of Rhine bank filtrate in cross section, in 1997-1999 Water age [year] m MSL

32. 32 Mean composition of raw water from well field types in the Neths, in 1989

33. 33 Water resource types in the Neths (for drinking water supply) and their characteristics 1,250 Mm3/y produced by 246 well fields + 16 surface water treatment plants