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Arsenic Threat to Dutch Drinking Water Supply

Investigation on the presence of arsenic in the groundwater of the Rhine-Meuse delta in the Netherlands and its potential impact on drinking water. Analysis of arsenic levels in well fields and surface water treatment plants reveals stable conditions but hazardous waste issues in water treatment sludges. Detailed surveys show varying arsenic concentrations in different aquifers. Recommendations include studying arsenic mobilization factors and implementing risk assessments.

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Arsenic Threat to Dutch Drinking Water Supply

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

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

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

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

  6. Plot of As versus resp. Fe and HCO3 for all well fields (for drink. water supply) in Neths

  7. Plot of As versus resp. PO4 and pH for all well fields (for drink. water supply) in Neths

  8. Plot of As versus resp. SO4 and NO3 for all well fields (for drink. water supply) in Neths

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

  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 Fe2+ in groundwater (0.01-25 mg/L) to bind most As upon aeration and RSF. AsDW = 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. Sites with detailed hydrogeo-chemical surveys, incl. As behaviour

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

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

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

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

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

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

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

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

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

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

  22. Redox zoning on Langerak AR pilot, after 1.5 yr injection Site 8: DWI As in layer C (very reactive FeS2) on Langerak site A B C

  23. Trace Elements from pyrite are largely immobilized in fresh Fe(OH)3- precipitates (Stuyfzand, 2001) • High As-concentrations if: • ΔSO4 high • Δx or t small • pH high • PO4 and H4SiO4 high • Fe0.98Co0.003Ni0.01Zn0.01S2As0.005 • + O2 + NO3- + xH4SiO4 • SixFe(OH)3Co0.0027Ni0.009Zn0.009(HAsO4)0.004 • +2SO4 2- +0.001 (H3AsO3 + Ni2+ + Zn2+) + • N2 + 0.0003 Co2+

  24.  Does ripening of ferrihydrite to goethite mobilize As? Pumping wells often clog by mixing of Fe2+ with O2/NO3-water

  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 PO4, SO4, NO3, HCO3, DOC, F, temp, • Reducing gases, esp.CH4 (and H2S) Needed / to be studied: • As behaviour in SIR and ASR systems • An As risk assessment method

  26. Concl.3: As mobilizing processes and bias H2S + 4 HAsO42- + 6H+ 4 H3AsO3 + SO42- CH4 + 4HAsO42- + 8H+  4H3AsO3 + CO2 + 2H2O Positive As-bias: FeS2 / Fe(OH)3 particles dissolved by HNO3 due to lack of (sufficient) filtration Negative As-bias: filtration in lab of oxidized sample with Fe2+

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

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

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

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

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

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

  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

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