Diffuse pollution of groundwater
in urban areas
David Lerner, Nigel Tait and Brenda Chisala
Catchment Science Centre
University of Sheffield
With thanks to Mike
Rivett, Yuesuo Yang,
Mike Barrett and other
colleagues
…and thanks to our
funders, NERC,
EPSRC, EA
Outline
• The message:
– Multiple urban sources ≡ diffuse pollution
• Outline:
– Urban recharge
– Urban groundwater pollution
– Nitrate loads in Nottingham
– Organic sources and risks
– Summary
Urban pathways for
precipitation
Evapo- Precipitation
transpiration
Evaporation
Roofs
Surface runoff
Urban recharge
Storm sewers
Direct Sewer
Roof Infiltration
recharge leakage soakaways systems
Lerner, 2002, Hydrogeology Journal, 10, 143-152
Urban supply pathways
Consumptive
use
Imported
water supply
Urban recharge
Local
groundwater
Sewers
Mains Irrigation Septic
tanks
leakage excess
Lerner, 2002, Hydrogeology Journal, 10, 143-152
Sewer
leakage
Water supply and rainfall to
selected cities
Urban recharge
City
Rainfall
(mm/y)
Leakage
(%)
Nottingham
700
Water
supply
(mm/y)
600
Lima, Peru
(1979)
<10
1650
~50
Hong Kong
(1980)
2000
280+1250
<10
25 ↓
250
250
200
200
150
150
100
100
0
0
19
59
-9
5
8
-5
41
19
19
15
-4
4
18
82
-1
91
-8
50
0
50
1
50
18
Urban recharge
Recharge rate mm/yr
Urban recharge, Nottingham
Yang et al. 1999, Environmental Geology, 38, 183-198
Rural
Urban
Pptn
Mains
Sewers
Chlorinated solvents in urban
groundwater
Urban groundwater pollution
Chlorinated
hydrocarbon
%age of pumped
boreholes over 1 µg/l
Coventry Birmingham
Trichloroethene
72
74
Tetrachloroethene
40
40
Trichloroethane
52
22
Chloroform
43
17
Carbon Tetrachloride
31
2
Rivett et al. 1990, Journal of Hydrology, 113, 307-323
Burston et al. 1993, Journal of Hydrology, 149, 137-161
Urban groundwater pollution
Sewage in groundwater,
Meadows, Nottingham
Borehole
A- park
B - park
C - park
D - park
E - 1970s
F - 1970s
G - 1970s
H - 1970s
I - 1970s
J - 1970s
K - C19th
1
δ15N
?
9
9
9
9
9
9
9
?
?
9
Microbiological1
?
9
?
9
9
?
9
9
?
?
9
?
?
?
?
?
?
9
9
?
?
?
?
?
?
?
9
9
9
9
?
?
9
limonene
x
x
x
Sewage impact
9
x
9
x
x
x
9
x
?
999
9
999
999
999
999
999
9
9
9
Total coliforms, E. Coli, F. Streptococci
• Meadows, like all UK urban areas, is fully sewered
Barrett et al. 1999. Water Research. 33(14), 3083-3097
Road salt in groundwater
Location
Roads
Salt (103
(103 km) t in 86-87)
UK
Urban groundwater pollution
Germany
347
2000
40
627
Toronto
Salt applied
>100x103 t/year
Cl in groundwater near Toronto highways
2000 – 13000 mg/l
Cl in springs on Toronto lakefront
400 mg/l
Howard & Haynes, 1993 Geoscience Canada, 20, 1-8
Howard & Beck, 1993 JCH, 12, 245-268
N in Nottingham groundwater
Urban groundwater pollution
Location of
sampled
boreholes
NO3-N
NH4-N
Detects
%
Mean
mg/l
Detects
%
Mean
mg/l
Deep rural
100
12
75
0.35
Deep urban
100
13
27
0.3
Shallow urban
100
10
45
0.2
Nitrate loads in Nottingham
Nottingham case study
Sheffield
Nottingham
Meadows
Hydrogeological map of
Nottingham
80
70
Meadows
Nitrate loads in Nottingham
90
11
0
0
13
120
140
100
Multi-level
sampler
0
15
60
50
40
20
30
Groundwater level
River
Mercia Mudstone
Triassic Sandstone
L. Magnesian Lst.
Glacial drift
Alluvium
Nottingham
20
10
0
10
20 Km
Nitrate loads in Nottingham
Recharge rates from solutes
Cl:N:SO4
Cl:N:SO4
Cl:N:SO4
Rain
Water
Mains
Sewers
Cl:N:SO4
Nitrate loads in Nottingham
Process for estimating
recharge and loads
Conceptual
aquifer
model
Groundwater
flow model
START
Transport
models for
Cl, SO4, N
No
Yes Change flow
model?
No
Calibrated
heads?
Yes
TOTAL
RECHARGE
Calibrated Yes
concentrations?
No
Deconvolute
RECHARGES
LOADS
Time and space division of 4
mass balance models
1900
1950
•
•
•
•
•
River Le
en
Nitrate loads in Nottingham
1850
Ri
nt
e
r
T
ver
2000
20 km N-S
16 km W-E
standard spacing 500m
1 layer
MODFLOW
&
MT3D
in Visual MODFLOW
N loads to Nottingham
groundwater
25
• 1990s urban
load
21 kg/ha/y
• Comparable
to intensive
arable load
• Where from?
Nitrate loads in Nottingham
N load kg/ha/yr
20
15
10
5
0
1850-
1882-
1915-
1941-
1958-
1881
1914
1940
1958
1995
Urban fertilisers
Location
Nitrate loads in Nottingham
Perth, Australia
USA
Loading
(kg N/ha/y)
100
1-55
Wakida & Lerner, 2005, Water Research, 29 3-16
Nitrate loads in Nottingham
Leaking sewers
Nitrate loads in Nottingham
Septic tank systems
Location
Merida, Mexico
New England
N load from septic tanks
(kg N/ha/y)
100
48
Wakida & Lerner, 2005, Water Research, 29 3-16
Nitrate loads in Nottingham
Housing and house building
Nitrate loads in Nottingham
Industrial use and spillage
Ammonium plume from
Rexco
2000
mg/l
1800
Farm
Borehole
T4
Field Well
Nitrate loads in Nottingham
1600
1400
100
Factory
T3
14
Former
Coking
Plant
Ponds
T2
Yard Well
Drain
Former Colliery
Pit Head
Spoil Heap
1200
1000
150
N
200
400
600
Lagoon
Large Lagoon
Monitoring
BH
Abstraction
BH
Groundwater
head
Ammonium
concentration
50
10
800 1000 1200 1400 1600 1800
1
Nitrate loads in Nottingham
Landfills
• NH4 in leachate
up to 1500 mg/l
• >10 000 closed
landfills in UK,
mostly unlined
• Loads up to
4000 kg N/ha/y
Total N load (kg/ha/yr)
Nitrate loads in Nottingham
N loads in Nottingham
25
20
15
Con. Land
House building
10
Soil N
Sewers
Mains
5
0
1850- 1882- 1915- 1941- 19581881 1914 1940 1958 1995
Recharge period
Wakida & Lerner, 2005, Water Research, 29 3-16
Organic sources and risks
• Density of sources
– National
– Nottingham
• Risks from urban sources
– Nottingham
Organic sources
• Loads
Chlorinated solvent industry
database Tait et al. 2004
Industry
Engineering
Electronics
Chemical
Metal
Textile
Sector
•
•
•
•
•
•
•
•
•
Transport
Mechanical
Machine Tools
Plant
Machinery
Precision
Aerospace
Defence
Electrical Eng.
Electronic
Eng.
•
•
•
•
•
Paints
Varnishes
Inks
Pesticides
Adhesives /
Sealants
• Rubber
• Finishing
• Pretreatment
• Dry Cleaning
Sites
Data Analysis
• 75,000 industries
50,000 • 60,000 manufacturing sites
• Postcodes give 100m
12,000 resolution1
• Bartholomew digital map
2
data
3,500
• Geoplan digital postcode
3
map
2,000
7,000
1University of Essex, 2University of Manchester,
3University of Greenwich
Density of chlorinated solvent
users
Density
scale:
sites/km2
• 75 000 current
sites
• London - 2,500
dry cleaning
outlets
Sheffield
Organic sources
Nottingham
London
Tait et al. 2004,
SOTTE 319, 77-98
Nottingham:
point or diffuse sources?
Potential TCE sources
• Potential TCE
sources in
Nottingham
Organic sources
– 1991
– Unconfined aquifer
• How dense a
pattern to become
diffuse pollution?
Risk analysis for urban
groundwater
Organic sources
Sources
Pathways
Receptor
BOS: the model components
Groundwater
flow model
Catchment zone
tool
Organic sources
Landuse analysis
Databases
Pollution risk model
Tait et al., 2004, Environmental Modelling and Software, 19, 1111-1124
The catchment zone model
• Stochastic MODPATH
• 1 particle per node
• Monte Carlo simulations
– E.g., recharge, permeability
Organic sources
• Frequency of arrival gives
probability of node in
capture zone
Landuse GIS
1991 landuse
Residential
Recreational
Institutional
Industry
Agricultural
Commercial
Waste
Transport
Water
Organic sources
N
W
E
S
0.9
0
0.9
1.8 Kilometers
Organic sources
Specific industry databases
New unconfined catchment
Raw predicted catchment
Probability contoured catchment
with industries
Organic sources
Confined
Unconfined
New borehole
Existing borehole
Industries
Organic sources
The pollution risk component
n
Cj = ∑
i =1
RAi S j exp( λu t u,i Rf , j )
Q exp( λs t s,i Rf , j )
• Monte Carlo analysis
Organic sources
Predicted concentrations
Validation
• Risk models are rarely validated
• Construct and believe
• Attempted validation against field data
– 2 wells
Organic sources
– 7 contaminants
14 (not
independent)
measurements
• Also national MTBE observations (not shown)
Validation
Parameter
Drinking
Water Std
Organic sources
(µg/l)
TCE
1,1,1 TCA
PCE
Benzene
Toluene
Ethylbenzene
Xylene
30
30
10
1
<10
<10
<10
Borehole 1
Borehole 2
Field
Model
Field
Model
(µg/l)
(µg/l)
(µg/l)
(µg/l)
140
230
100
220
4
9
5
13
260
360
320
400
bql
0.07
bql
0
bql
0.03
bql
0
bql
0.05
bql
0.1
bql
0.001
12
0.1
bql = below quantification limit
• 13/14 predictions within a factor of 2
Predicted PCE concentrations
50%ile log(CPCE), 2005
Borehole
Simulation
Location
Organic sources
Study
Area
Tait et al., submitted, Environmental Modelling and Software
Risks from leaking sewers
• Nottingham sewer network
• Stochastic distribution of leaks
– Related to sewer age
• Total leakage ≡ 10 mm/y
• Amended pollution risk model
Organic sources
– Bacterial sorption and die-off
Nottingham:
Potential MTBE load
Organic sources
Potential MTBE sources
• Summing sources
in Nottingham risk
analysis
• Load ~10 kg/ha/yr
• Probably too high
Chlorinated solvent load in
Birmingham aquifer
Aquifer
boundary
Organic sources
Load
(kg/ha/
yr)
0.4
~1
Bi
rm
ing
ha
m
Fa
ult
Borehole and
catchment
Unconfined
aquifer
Mass
%
recharge removed
pumped (kg/yr)1
1987
43
1811
1998
5
228
Year
Tame
Valley
Confined
aquifer
Industrial area
0
4 km
1
from Rivett et al. 2005 QJEGH 38, 337-250
Assume:
– Steady state
– Boreholes are pumping
representative concentrations of
TCE, PCE, etc
Reminder of the story
• Urban recharge
– plenty in cities
• Urban groundwater pollution
– N, organics, sewage, salt, etc
• Nitrate loads in Nottingham
– 21 kg/ha/yr from contaminated land, sewers, mains
• Organic sources and risks
Summary
– Many sources, significant risks
• The message:
– Multiple urban sources ≡ diffuse pollution
Summary
Selected Nottingham references
M.H. Barrett, K.M. Hiscock, S. Pedley, D.N. Lerner, J.H. Tellam and M.J. French, 1999.
Marker species for identifying urban groundwater recharge sources – a review and
case study in Nottingham UK. Water Research. 33(14), 3083-3097.
Y. Yang, D.N. Lerner, M.H. Barrett, and J.H. Tellam, 1999. Quantification of groundwater
recharge in the city of Nottingham, UK. Environmental Geology, 38(3), 183-198.
D.N. Lerner, 2002. Identifying and quantifying urban recharge: a review. Hydrogeology
Journal, 10(1), 143-152.
D.N. Lerner, 2003. Estimating urban loads of nitrogen to groundwater. Journal of the
Chartered Institution of Water and Environmental Management. 17(4), 239-244.
N. G. Tait, R. M. Davison, J. J. Whittaker, S.A. Leharne and D. N. Lerner, 2004. Borehole
Optimisation System (BOS) - A GIS based risk analysis tool for optimising the use of
urban groundwater. Environmental Modelling and Software, 19, 1111-1124.
F.T. Wakida & D.N. Lerner, 2005. Non-agricultural sources of groundwater nitrates: a
review and case study. Water Research, 39, 3-16.
F.T. Wakida & D.N. Lerner, 2006. Potential nitrate leaching to groundwater from house
building. Hydrological Processes, 20(9):2077-2081.
B.N. Chisala, N.G. Tait and D.N. Lerner,in press . Evaluating the risk of methyl tertiarybutyl ether (MTBE) to urban groundwater at city scale: Nottingham case study.
Journal of Contaminant Hydrology, December 2005.
N. G. Tait, R. M. Davison, S. A. Leharne and D. N. Lerner. Borehole Optimisation
System (BOS) - Assessing the Potential Value of Urban Groundwater in Nottingham.
Submitted, January 2006.
Also papers led by R Taylor, K Powell and S Trowsdale.