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

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

www.zoologi.no Contaminant

Ill: Based on figure from J. Czichos: "What's so funny about microbiology"

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

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

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]

Criteria to evaluate the drinking water source as a hygienic barrier

1. Historical water quality (microbiological)

2. The source (well construction, location and recharge area)

3. Monitoring of the raw-water quality and contingency plans

4. The size of the waterwork

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

Suggested score for factors related to the subgroup Well design

Criterion Score

2.1 Sealing between well casing and bedrock.

Sealing between well casing and bedrock and/or no visible leakage of water into the well.

10

Sealing or lack of water leakage between bottom of well casing and bedrock are not demonstrated, but the super-ficial deposits are fine grained and more than 5 m thick.

5

Leakage between bottom of well casing and bedrock is suspected or observed.

0

2.2Length of well casing.

The well casing is drilled ≥ 2 m into solid bedrock. 5The well casing is drilled < 2 m into solid bedrock. 0The well casing is ≥ 5.5 m long. 5The well casing is < 5.5 m long. 0

2.3Well casing above ground level (a.g.l.).

Top of well casing is ≥ 40 cm a.g.l. Cap is tight. 10Top of well casing is 20-40 cm a.g.l. Cap is tight 5Top of well casing is < 20 cm a.g.l. 0Top of well casing has no cap or the cap is not tight. -5

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

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

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

Thickness of the superficial deposits

• Should be ≥ 2.5 m thick• If not, water treatment or disinfection is

necessary

a) b)

The groundwater source

Main groups

Subgroups

Superficial deposits

Is the thickness more or less than 2.5 m?

Land use.

Farmland (incl. grazing animals), septic tanks, sewage infiltration systems, sewers. Is the distance from the well more or less than 100 m?

Rivers/streams flowing on bare rock. Is the distance from the well more or less than 100 m?Wildlife including birds.Protection zones.

Well design. Well casing.

Wellhead completion.

Well-house or concrete well-protection (manhole).Fencing.Well location and drainage.

The groundwater source

Main groups

Subgroups

Superficial deposits

Is the thickness more or less than 2.5 m?

Land use.

Farmland (incl. grazing animals), septic tanks, sewage infiltration systems, sewers. Is the distance from the well more or less than 100 m?

Rivers/streams flowing on bare rock. Is the distance from the well more or less than 100 m?Wildlife including birds.Protection zones.

Well design. Well casing.

Wellhead completion.

Well-house or concrete well-protection (manhole).Fencing.Well location and drainage.

Well design – focused on well casing

Criterion Score

2.1 Sealing between well casing and bedrock.

Sealing between well casing and bedrock at the bottom of the well casing and/or no visible leakage of water into the well.

10

Sealing or lack of water leakage between bottom of well casing and bedrock are not demonstrated, but the super-ficial deposits are fine grained and more than 5 m thick.

5

Leakage between bottom of well casing and bedrock is suspected or observed.

0

2.2Length of well casing.

The well casing is drilled ≥ 2 m into solid bedrock. 5

The well casing is drilled < 2 m into solid bedrock. 0

The well casing is ≥ 6 m long. 5

The well casing is < 6 m long. 0

2.3Well casing above ground level (a.g.l.).

Top of well casing is ≥ 40 cm a.g.l. Cap is tight. 10

Top of well casing is 20-40 cm a.g.l. Cap is tight 5

Top of well casing is < 20 cm a.g.l. 0

Top of well casing has no cap or the cap is not tight. -5

Leakage between well casing and bedrock

Bottom of well casing

Water

Raising main

Well design – focused on well casing

Criterion Score

2.1 Sealing between well casing and bedrock.

Sealing between well casing and bedrock at the bottom of the well casing and/or no visible leakage of water into the well.

10

Sealing or lack of water leakage between bottom of well casing and bedrock are not demonstrated, but the super-ficial deposits are fine grained and more than 5 m thick.

5

Leakage between bottom of well casing and bedrock is suspected or observed.

0

2.2Length of well casing.

The well casing is drilled ≥ 2 m into solid bedrock. 5

The well casing is drilled < 2 m into solid bedrock. 0

The well casing is ≥ 6 m long. 5

The well casing is < 6 m long. 0

2.3Well casing above ground level (a.g.l.).

Top of well casing is ≥ 40 cm a.g.l. Cap is tight. 10

Top of well casing is 20-40 cm a.g.l. Cap is tight 5

Top of well casing is < 20 cm a.g.l. 0

Top of well casing has no cap or the cap is not tight. -5

Well design – focused on well casing

Criterion Score

2.1 Sealing between well casing and bedrock.

Sealing between well casing and bedrock at the bottom of the well casing and/or no visible leakage of water into the well.

10

Sealing or lack of water leakage between bottom of well casing and bedrock are not demonstrated, but the super-ficial deposits are fine grained and more than 5 m thick.

5

Leakage between bottom of well casing and bedrock is suspected or observed.

0

2.2Length of well casing.

The well casing is drilled ≥ 2 m into solid bedrock. 5

The well casing is drilled < 2 m into solid bedrock. 0

The well casing is ≥ 6 m long. 5

The well casing is < 6 m long. 0

2.3Well casing above ground level (a.g.l.).

Top of well casing is ≥ 40 cm a.g.l. Cap is tight. 10

Top of well casing is 20-40 cm a.g.l. Cap is tight 5

Top of well casing is < 20 cm a.g.l. 0

Top of well casing has no cap or the cap is not tight. -5

The groundwater source

Main groups

Subgroups

Superficial deposits

Is the thickness more or less than 2.5 m?

Land use.

Farmland (incl. grazing animals), septic tanks, sewage infiltration systems, sewers. Is the distance from the well more or less than 100 m?

Rivers/streams flowing on bare rock. Is the distance from the well more or less than 100 m?Wildlife including birds.Protection zones.

Well design. Well casing.

Wellhead completion.

Well-house or concrete well-protection (manhole).Fencing.Well location and drainage.

Wellhead completion

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

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

Criterion (group)

3.1 Measurement of physio-chemical parameters.

For example turbidity and colour.Are the measurement done automatically or manually? Is there an alarm?

3.2 Measurements of microbiological parameters.

E.coli and parasites.Sampling interval.

3.3 Inspections.

Well site and recharge area.

3.4 Contingency plans.

Disinfection/increased disinfection.Use of reserve water source.Closure of well or waterwork.

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

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

Estimation of total barrier effect

• Values < 1:– actions must be taken to improve the protection of

the groundwater sourceor– 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

Conclusions

• Four criteria is suggested to evaluate to what extent a groundwater source is sufficiently protected and thereby can act a hygienic barrier.

1) Historical water quality2) The groundwater source3) Monitoring and contingency plans4) The size of the waterwork

• The method is still under development. Subgroups and scores suggested for each criterion are preliminary.

Thank you!Thank you!