The groundwater source as a hygienic barrier
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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

Dr. Sylvi Gaut, NGU

GroPro, September 2008


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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


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www.zoologi.no sources in Norway can act as a hygienic barrier towards pathogenic microorganisms

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"


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Focus on preventing contamination sources in Norway can act as a hygienic barrier towards pathogenic microorganisms

  • Low population density

  • Access to large areas with no domestic animals, farmland or industry

  • choose drinking water sources with good natural water quality


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The drinking water source as a hygienic barrier sources in Norway can act as a hygienic barrier towards pathogenic microorganisms

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


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The drinking water source as a hygienic barrier sources in Norway can act as a hygienic barrier towards pathogenic microorganisms

  • 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]


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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


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The method barrier

  • 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


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Suggested score for factors related to the subgroup Well design

Total score = (criterion 2.1 + criterion 2.2 + criterion 2.3)/3


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Criterion 1 - Historical water quality design

  • 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


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Criterion 2 designThe 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


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Thickness of the superficial deposits design

  • Should be ≥ 2.5 m thick

  • If not, water treatment or disinfection is necessary

a)

b)





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Leakage between well casing and bedrock design

Raising main

Water

Bottom of

well casing






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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



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Criterion 4: Size of the waterwork plans

  • 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


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Estimation of total barrier effect plans

  • Total barrier effect = (C1*C2*C3*C4)/100

  • Values ≥ 1:

    • the groundwater source can act as a hygienic barrier

Lillehammer waterwork. A. Gaut, Sweco


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Estimation of total barrier effect plans

  • 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


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Conclusions plans

  • 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.


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Thank you! plans


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