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The groundwater source as a hygienic barrier

The groundwater source as a hygienic barrier. Dr. Sylvi Gaut, NGU. GroPro, September 2008. Present a method to evaluate to what extent drinking water sources in Norway can act as a hygienic barrier towards pathogenic microorganisms Focus on crystalline bedrock aquifers. www.zoologi.no.

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The groundwater source as a hygienic barrier

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  1. The groundwater source as a hygienic barrier Dr. Sylvi Gaut, NGU GroPro, September 2008

  2. Present a method to evaluate to what extent drinking water sources in Norway can act as a hygienic barrier towards pathogenic microorganisms Focus on crystalline bedrock aquifers

  3. www.zoologi.no Norwegian Drinking Water Regulations • Two separate hygienic barriers • the barrier shall remove, inactivate or kill the organisms • natural or manmade • normally one hygienic barrier is established in the drinking water source B. O. Hilmo, Asplan Viak Contaminant Ill: Based on figure from J. Czichos: "What's so funny about microbiology"

  4. Focus on preventing contamination • Low population density • Access to large areas with no domestic animals, farmland or industry • choose drinking water sources with good natural water quality

  5. The drinking water source as a hygienic barrier Questions? • to what extent is the drinking water source a hygienic barrier towards pathogenic microorganisms • which conditions must be met in order to have such a barrier Picture: Steinar Grønnesby, Trondheim kommune

  6. The drinking water source as a hygienic barrier • Project initiated by Norwegian Water to answer these questions • surface water as the main drinking water source • groundwater sources investigated by NGU • Method based on: • the Scottish method for risk assessment of Cryptosporidium • a model for evaluating the barrier efficiency required through water treatment for Norwegian waterworks [The drinking water source as a hygienic barrier]

  7. Criteria to evaluate the drinking water source as a hygienic barrier • Historical water quality (microbiological) • The source (well construction, location and recharge area) • Monitoring of the raw-water quality and contingency plans • The size of the waterwork

  8. The method • Criteria 1-3 are divided into subgroups • Scoring system is used to evaluate the barrier effect for each subgroup • 0 is no barrier • 10 is a full barrier

  9. Suggested score for factors related to the subgroup Well design Total score = (criterion 2.1 + criterion 2.2 + criterion 2.3)/3

  10. Criterion 1 - Historical water quality • Describes the microbiological quality through time • representative for the raw-water throughout the year • sample interval minimum once a month for 2 years • sampling directly from (or close to) production well • sample from each production well • Divided into two groups • E. coli • parasites (Cryptosporidium and Giardia) • Challange • E. coli is analysed, parasites are not

  11. Criterion 2 The groundwater source • What are the important factors influencing the microbiological water quality? • crystalline bedrock aquifers • Four groups • the superficial deposits • land use • well design • wellhead completion Picture: B. Frengstad, NGU

  12. Thickness of the superficial deposits • Should be ≥ 2.5 m thick • If not, water treatment or disinfection is necessary a) b)

  13. The groundwater source

  14. The groundwater source

  15. Well design – focused on well casing

  16. Leakage between well casing and bedrock Raising main Water Bottom of well casing

  17. Well design – focused on well casing

  18. Well design – focused on well casing

  19. The groundwater source

  20. Wellhead completion

  21. Criterion 3: Monitoring of the raw-water quality and contingency plans • Regular sampling intervals • once a month • Variations in certain physio-chemical parameters can indicate contamination • colour, turbidity and iron • for single wells • changes in concentrations both up and down

  22. Criterion 3: Monitoring of the raw-water and contingency plans

  23. Criterion 4: Size of the waterwork • Implemented as a risk parameter • Criterion 4 = 1/log10(number of persons supplied) • Illustrate that contamination is more serious for a large waterwork than for a small

  24. Estimation of total barrier effect • Total barrier effect = (C1*C2*C3*C4)/100 • Values ≥ 1: • the groundwater source can act as a hygienic barrier Lillehammer waterwork. A. Gaut, Sweco

  25. Estimation of total barrier effect • Values < 1: • actions must be taken to improve the protection of the groundwater source or • a barrier must be added through water treatment or disinfection • If improvements are effectuated, microbiological water quality must be monitored for a new two year period

  26. Conclusions • Four criteria is suggested to evaluate to what extent a groundwater source is sufficiently protected and thereby can act a hygienic barrier. • Historical water quality • The groundwater source • Monitoring and contingency plans • The size of the waterwork • The method is still under development. Subgroups and scores suggested for each criterion are preliminary.

  27. Thank you!

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