Diffuse Pollution:

Groundwater Pathways

Steve Buss

Summary

• Groundwater in catchment management• Groundwater in a rural catchment

– Predicting future concentrations– Mitigation & cost effectiveness

• Groundwater in an urban catchment

Why groundwater (water supply)?

Surface water

Ground-water

Public water supply, England OK

Other - closureOther - blending & treatmentPesticides - closurePesticides - treatmentPesticides - blendingNitrate - closureNitrate - treatmentNitrate - blending

Groundwater supply issues (by volume)

1975

-80

1980

-85

1985

-90

1990

-95

1995

-200

0

2000

-05

2005

-10

Why groundwater (regulation)?

Results of Water Framework Directive assessment of groundwater bodies at risk of failing to achieve good status in 2015 as a result of nitrate contamination across England and Wales

0% 20% 40% 60% 80% 100%

RiversLakes

EstuariesCoastal waters

Percentage of surface water bodies at risk of not achieving WFD

objectives: diffuse pollution

Groundwater catchments

!<!<

!<

Water!<

Nitrogen N(t) Time & Attenuation Prediction

Colour scale = 10-80 mg/lColour scale =1 – 0.05 %

%age of source yield contributed by the model cell Colour scale = 1 – 0.05 %

Groundwater catchments

!<!<!<

!<

Water!<

Nitrogen N(t) Time & Attenuation Prediction

Colour scale = 10-80 mg/lColour scale =1 – 0.05 %

mg/l of NO3 in water leaving the soil zoneColour scale = 10 – 80 mg/l

Groundwater catchments

!<!<!<

Dilution Delay

!<

Water!<

Nitrogen N(t) Time & Attenuation Prediction

Colour scale = 10-80 mg/lColour scale =1 – 0.05 %

Groundwater catchments

!<!<!<

Dilution Delay

!<

Water!<

Nitrogen N(t) Time & Attenuation Prediction

Colour scale = 10-80 mg/lColour scale =1 – 0.05 %

Opportunities for mitigation

Yellow = fertiliser applications to arable land

Nottinghamshire sources:% contribution to groundwater N loading

White = areas relevant forchange in arable land use

Cost effectivenessCOUNTERFACTUAL 64 mg/l

TARGET 50 mg/lReduction required 21.9 %Su

mmary 

statistics

Peak 

concentration vs. 

target

Engineering vs. 

catchm

ent 

managem

ent 

costs £0

£20,000,000

Min ML Max

0255075

Min ML Max

MEASURES:

Light touch scenario1. Cover crops before spring cereals 2. Reduce dietary intake of N and P3. Early harvesting and establishment of crops in autumn4. Use a fertiliser recommendation system 5. Integrate fertiliser and manure nutrient supply6. Avoid spreading manufactured fertiliser at high risk times

COUNTERFACTUAL 64 mg/lTARGET 50 mg/l

Reduction required 21.9 %Summary 

statistics

Peak 

concentration vs. 

target

Engineering vs. 

catchm

ent 

managem

ent 

costs £0

£20,000,000

Min ML Max

0255075

Min ML Max

Land use change scenario…plus…7. Convert 50% of arable land to low input extensive grazing

Timing

!<

Unsaturated zone thickness (5 to 65 m)

!<

Groundwater flow path length(0 to 9500 m)

!<

Travel time(3 to 60 years)

Timing

10 years

Groundwater catchments (2)

!< Colour scale = 10 – 0.05 %!<!<

Colour scale = 10 – 80 mg/l

Sewage treatment works, with population served

#

#

#

#

#

#

#

#

#

#

#!<

8777

2215

3763

32870

10990

24677

25352

20117

103043

Source apportionment

Treatedsewageeffluent

UrbanSurfacewater(other)

Groundwater (agriculture)

Urban groundwater

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Urban groundwater

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Conclusions• Groundwater is (mostly):

– Underground and slow-moving– Unconstrained by catchment boundaries– Vital for drinking water supply, for aquatic

ecosystems, for dilution of sewage effluent in the summer, for industry, for amenity…

• Challenging to predict and monitor effectiveness of measures but these can be constrained with simple tools