Remco van Ekremco.vanek@tno.nl

Saltwater intrusion in the Netherlands in relation to the WFD

Seminar on Ground- and surface water monitoring Smardzewice, 9-12 July 2007 - INFRA 24055

Deltares (in formation)

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Content

1. Introduction

2. Origin of saline groundwater

3. Impact analysis

4. Implications for WFD implementation

5. Conclusions

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1. Introduction

According to WFD Annex II – GWB status

Alterations to flow direction resulting from level changes may occur temporarily, or continuously in a spatially limited area ….

but such reversals do not cause saltwater or other intrusion, and do not indicate a sustained and clearly identified anthropogenic induced trend in flow direction likely to result in such intrusions.

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1. Introduction

WGC-2 Groundwater “Status compliance and trends”

Types of intrusion

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1. Introduction

WGC-2 Groundwater “Status compliance and trends”

Groundwater good status is not met if

•Relevant TVs are exceeded and there is either a significant and sustained upward trend in one or more key parameters at relevant monitoring points

•or there is an existing significant impact on a point of abstraction as a consequence of an intrusion.

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1. Introduction

Threshold values (Stuyfzand, 1993)

Main class Subdivided mg Cl / l

Fresh Oligohaline 0-5

Oligohaline-fresh 5-30

Fresh 30-150

Fresh-brackish 150-300

Brackish Brackish 300-1000

Brackish-salt 1000-10.000

Salt Salt 10.000-20.000

Hypersaline Hypersaline > 20.0000

Fresh - Brackish: 150 mg Cl / l

Brackish – Salt: 1000 mg Cl / l

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1. Introduction

WGC-2 Groundwater “Status compliance and trends”

• Identify areas with natural high saline concentrations

• Identify areas where there is risk of intrusion (pressure due to pumping)

• Identify monitoring points which exceed relevant GW-QS and TVs

• Integrate the data mentioned above

• Calculate trends in Electrical Conductivity (EC) and other relevant substances concentrations indicating an expansion of intrusion

• Is there a significant impact on any point of abstraction due to intrusion?

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2. Origin of saline groundwater

NL has been part of the North sea in the pastDevelopment of brackish aquifers

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7100 ADHolocene

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Holocene3150 AD

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2. Origin of saline groundwaterDistribution of fresh water aquifers

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2. Origin of saline groundwaterDistribution of fresh water aquifers

Depth [m] relative to sea level< 100100 - 200200 - 300300 - 400400 - 500≥ 500Areas with inversion(e.g. saltwater above fresh water)

Source: REGIS (TNO)

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2. Origin of saline groundwater

(Stuyfzand & Stuurman, 1994)

Sea water or saline water pollution?

12 sources

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3. Impact analysis

Mining of fresh groundwater in the Dune region

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3. Impact analysis

Mining of fresh groundwater in the Dune region

(Stuyfzand, 1994)

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3. Impact analysis

Large scale intrusion in Polder areas

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3. Impact analysis

Large scale intrusion in Polder areas (Oude Essink, 1996)

Distance [m]

Dep

th [

m]

SeaDunearea

Haarlemmermeerpolder

1902

Distance [m]

Dep

th [

m]

SeaDunearea

Haarlemmermeerpolder

1854

Distance [m]

Dep

th [

m]

SeaDunearea

Haarlemmermeerpolder

1957

Distance [m]

Dep

th [

m]

SeaDunearea

Haarlemmermeerpolder

2006

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3. Impact analysis

Saltwater wells (de Louw, 2006)

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3. Impact analysis

Saltwater wells (Oude Essink, TNO)

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3. Impact analysis

Impact on pumping stations: upconing of saltwater

n > 200

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3. Impact analysis

(n = 16)

Impact on pumping stations: upconing of saltwater

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3. Impact analysis

Sea level rise

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3. Impact analysis

Sea level rise

Affected zone (λ) equals (kDc)

• For x=3λ, ΔΦ(x) = Φ0*e-3 = Φ0*0.05

• So for x=3λ only 5% of Φ0 remains

Affected zone (λ) equals (kDc)

• For x=3λ, ΔΦ(x) = Φ0*e-3 = Φ0*0.05

• So for x=3λ only 5% of Φ0 remains

x/0e

(x) x/0e

(x)

kDc

Noordzee/Nieuwe Waterweg North sea

Low polder area

Mazure equation

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3. Impact analysis

Sea level riseAffected zone due to sea level rise and land subsidence in the Province Zuid-Holland

Difference in hydraulic head (m) at -12.5 below sea levelbetween 2000 and 2050

Source: TNO, Oude Essink, 2004

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3. Impact analysis

Sea level rise: saltwater intrusion through rivers

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4. Implications for WFD implementation

• Large database (> 60.000 bore holes) but only 10% deeper than 70 m

Based on these measurements a 3D model of salinity in groundwater was created

A good estimate of theinitial Cl-distributionis vital for modelling

(TNO, 2004)

60764 chloride concentrations in NL

Modelling

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Modelling

NAGROM (MLAEM-VD)• National scale • Saltwater distribution (3D) is fixed

MODFLOW (MOCDENS3D)• Regional scale• Saltwater distribution is not fixed

Chloride distribution (Cl mg l-1) Salt load in kg/ha/yr during an extreme dry year

4. Implications for WFD implementation

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Monitoring: Distribution salt water in groundwaterDepth [m] of Cl concentration 1000 mg/l

4. Implications for WFD implementation

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Horizontal intrusion

Vertical intrusion

Area vulnerable for upconing

Main salt water border for WFD

Area vulnerable for lateralIntrusion from the Peelhorst aquifer

Depth [m] of Cl concentration 1000 mg/l

4. Implications for WFD implementation

Monitoring: Distribution salt water in groundwater

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Monitoring: LocationsDepth [m] of Cl concentration 1000 mg/l

Outside DWPA (drinking water protection area)

Inside DWPA (drinking water protection area)

Filter in brackish zoneFilter below salt borderSalt ‘gard’

Filter in brackish zoneFilter below salt borderSalt ‘gard’

4. Implications for WFD implementation

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Present monitoring locations for WFD

Possible extension of monitoring locations

Salt water intrusion in groundwater

4. Implications for WFD implementation

Monitoring frequency

- Regional (vertical) 1/6yr- Dunes 1/2yr- Peel border 1/2yr- Dunes with abs. 1/yr- GW abs. 1-2/yr

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5. Conclusions

1. Saltwater is abundantly present in the groundwaterbodies of NL (especially in the western and northern part). Mostly it is ‘old’ marine water.

2. Most important cause of saltwater intrusion is due to the deep polder areas. It is a slow process and considered to be irreversible (exemption).

3. Saltwater intrusion due to groundwater abstraction can occur on a small scale. It is considered as reversible.

4. Monitoring system is available and operational, but some modifications may be needed.