1 Field Studies and Groundwater Protection | Feb 2012
Virus Transport in
Groundwater – Field Studies and Groundwater
Protection
Jack Schijven
VIRUS ATTACHMENT AND INACTIVATION
FIELD STUDIES
QMRA
GROUNDWATER PROTECTION
GWPCalc: tool for calculating the size of groundwater protection zones
Field Studies and Groundwater Protection | Feb 2012
VIRUS ATTACHMENT AND INACTIVATION
2
Groundwater: Focus on viruses● Viruses may be transported with groundwater farther than bacteria
and protozoa
– Viruses are very small
– Viruses may attach little to sand grains
– Viruses may survive long
● Viruses may be very infectious
● Diseases outbreaks from contaminated groundwater sourcesreported in developing and developed countries
– Howard et al, WHO Groundwater Monograph, 2006, chapter 10
● Usually vulnerable geologic settings
– Fractured rock, cross connecting well bores, leaking well cases X presence of sources such as wastewater treatment facilities, septic tanks, animal manure
● Contamination may be overestimated: Mostly studies of high-risk wells
Field Studies and Groundwater Protection | Feb 2012
VIRUS ATTACHMENT AND INACTIVATION
3
Viruses
Polio Rota MS2 PRD1
● Human viruses: host= human cells
● Bacterial viruses: host = bacteria cells
● Bacteriophages MS2 and PRD1 aremodel viruses
– Harmless to humans
– Same shape and size(smallest microorganisms)
– Negative charge: Poor attachment to sand
– Survives well at low temperature
– Easy to enumerate
Attachment
Penetration
Host
DNA or RNA Virus
Protein synthesis
DNA-replication
Assembly
Lysis
Mature viruses
Protein coat
Field Studies and Groundwater Protection | Feb 2012
VIRUS ATTACHMENT AND INACTIVATION
4
Enumeration of viruses
● Enteroviruses
– Tissue culture (infectious virus particles)PCR (infectious+non-infectious virus particles)
● Bacteriophages
– Double Layer Agar Plate
– Tube
› 1 ml sample (bacteriophages)
› 1 ml host bacteria
› 2.5 ml growth mediumwith semi-solid agar
– Solid agar plate
– Count plaques
Field Studies and Groundwater Protection | Feb 2012
VIRUS ATTACHMENT AND INACTIVATION
5
Major removal processes
● Inactivation
● Attachment
--
- - -
lµ
Grain of sand
�
�
Attachment
Inactivation
Inactivation
Detachment
-
+----
-- +-
--
--
--
+
+-
---
-
-
-
--
-
--
-
--
---
-
--
--
-
---
- -
--
- --
--
-
--
-
- --
+
+
--
sµ
detk
attk
Field Studies and Groundwater Protection | Feb 2012
VIRUS ATTACHMENT AND INACTIVATION
6
Virus attachment
● Bacteriophages as model viruses
● Bacteriophages MS2 and PRD1 strongly negative => attach less than most viruses
● Poliovirus neutral
● Coxsackievirus B4 probably negative
● Sticking efficiency αmeasure for attachment and depends on surface properties of virus and sand
0.000001
0.00001
0.0001
0.001
0.01
0.1
1
10
0 24 48 72 96
Time [hours]
C/C0MS2PV1
0.00001
0.0001
0.001
0.01
0.1
1
10
0 24 48 72 96 120 144 168
Time [hours]
C/C0MS2CB4
Field Studies and Groundwater Protection | Feb 2012
VIRUS ATTACHMENT AND INACTIVATION
7
Colloid filtration theory
● Collision efficiency η: Probability of collision
– Physical conditions
– Diffusion, interception, sedimentation
● Sticking efficiency α: Probability of attachment
– Chemical conditions (DLVO)
● Viruses are small
– Diffusion / Brownian movement →collision efficiency η
– Surface charge → sticking efficiency α
– At lower pH, higher ionic strength →higher α
Field Studies and Groundwater Protection | Feb 2012
VIRUS ATTACHMENT AND INACTIVATION
8
Collision efficiency η0
● Collision: Interception, sedimentation, diffusion
● Viruses: Diffusion
0.05 0.10 0.50 1.00 5.00 10.00
0.010
0.100
0.050
0.020
0.200
0.030
0.015
0.150
0.070
Diameter microorganism,mm
h0
Viruses 20-200 nm
Protozoa5-10 µm
Bacteria1-3 µm
Field Studies and Groundwater Protection | Feb 2012
VIRUS ATTACHMENT AND INACTIVATION
9
Virus attachment
● Attachment rate coefficient
● Collision efficiency
● Peclet number
● Diffusion coefficient
● Happel’s porosity dependent parameter
with
vd
nk
catt αη)1(
2
3 −=
3/23/14 −= Pes NAη
BMcPe DnvdN /=
)3/()273( µπ pBBM dTKD +=
)2332/()1(2 655 γγγγ −+−−=sA3/1)1( n−=γ
Field Studies and Groundwater Protection | Feb 2012
VIRUS ATTACHMENT AND INACTIVATION
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CFT: Literature and spreadsheet
● Yao KM, Habibian MT, O'Melia CR, Water and waste water filtration: concepts and applications, EST, 1971, 5, 1105-1112
● Tufenkji N, Elimelech M. Correlation Equation for Predicting Single-Collector Efficiency in Physicochemical Filtration in Saturated Porous Media, EST, 2004, 38, 529-536
● www.yale.edu/env/elimelech/publication-pdf/TECorrelationEqn.xls
● http://biocolloid.mcgill.ca/publications.html
( ) αη10ln
1
2
3
10ln
1log
010
L
d
n
v
Lk
C
C
catt
−−=−=
Field Studies and Groundwater Protection | Feb 2012
VIRUS ATTACHMENT AND INACTIVATION
11
DLVO: Derjaguin-Landau-Verwey-Overbeek theory● Double Layer force (electrostatic)
– Attractive or repulsive surface charge– Depends on pH and ionic strength (IS)
● Lifshitz-Van der Waals attractive force● Born repulsive force
– Overlap of electron clouds at <1 nm● Extended DLVO: + Hydrophobic interaction● Virus mantle
– Positively and negatively charged groups, like NH2
+, COO-
● Isoelectric point (Ip)– pH at which net charge is zero– pH<Ip => positively charged virus– pH>Ip => negatively charged virus
● Ip (MS2) 3.9 Ip (PRD1) 3-4
Field Studies and Groundwater Protection | Feb 2012
VIRUS ATTACHMENT AND INACTIVATION
12
DLVO energy profile
● Energy barrier Φmax
– Repulsion
● Primary minimum Φmin1
– Irreversible attachment
● Secundary minimum Φmin2
– Reversible attachment
● Effect of pH and IS on attachment of PRD1 to sand
– pH increase: more repulsive
– IS increase: less repulsive
● Equations: e.g. Hahn and O’Melia, EST, 2004, 38, 210-220
-10 -9 -8 -7 -6
-5
0
5
Log10 Separation distance @mD
Dimensionless
energy
FêHkB TL
PRD1-Quartz
ÿÿÿ Electrostatic interaction
ÿÿÿ London-van de Waals attraction
ÿÿÿ Born repulsion
—DLVO-profile
Fmax 6.94212 zPRD1 -17.5572 mV
Fmin1 -4.39547 zQuartz -42.1402 mV
Fmin2 -0.772816
Field Studies and Groundwater Protection | Feb 2012
VIRUS ATTACHMENT AND INACTIVATION
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Virus inactivation
● Depends on
– Virus
– Temperature
– pH
– Other environmental conditions
● Literature data virus inactivation in groundwater
– Schijven JF and Hassanizadeh SM, CREST, 2000, 31, 49-127
– Pedley S, Yates M, Schijven JF, West J, Howard G, Barrett M, Pathogens: Health relevance, transport and attenuation. In: Protecting groundwater for Health, eds: Schmoll O, Howard G, Chilton J, Chorus I, WHO, 2006, chapter 3
● Inactivation rate coefficient µlat 5-12 °C
– 0.023 (0.01 – 0.1) /day = 0.01 (0.0043 – 0.043) log10
/day
[ ] ttC
CtExpCC ll
tlt µµµ
3.2
1
10ln
1log
0100 −=−=⇒−=
Field Studies and Groundwater Protection | Feb 2012
VIRUS ATTACHMENT AND INACTIVATION
14
Long term inactivation study
● Objective
– Determine change of ratio of infectious to defective virus particles over time
● Experimental design
– Three enteroviruses PV1, PV2, CB4
– BGM cell culture: Infectious virus particles, Poisson-distributed plaque counts
– RT-PCR: Most Probable Number estimates
– Artificial Ground Water (AGW) + Artificial Surface Water (ASW)
– 4 °C and 22 °C– T= 0 – a year
● Biphasic inactivation ( )[ ]ttt effeCC 21 10
λλ −− −+=
De Roda Husman et al. AEM, 2009, 75(4):1050-1057
Field Studies and Groundwater Protection | Feb 2012
VIRUS ATTACHMENT AND INACTIVATION
15
Inactivation curves
AGW ASW
● Bleu: RT-PCR; Green: BGM cell culture
● Ratio RT-PCR/BGM cell culture increases over time
Field Studies and Groundwater Protection | Feb 2012
VIRUS ATTACHMENT AND INACTIVATION
16
Conclusions● Ratio RT-PCR/BGM cell culture
– Time dependent (increases with time)
– Virus type dependent
– Conditions (temperature, water) dependent
● Inactivation CB4 first order; PV1 and PV2 biphasic
● Inactivation rate coefficient of 0.01 log10/day at ≈10°C from literature data not too conservative
Inactivation rate coefficient, log10/day
Water °C PV1 PV2 CB4AGW 4 0.0031 0.0031 0.0035
22 0.011 0.022 0.03ASW 4 0.0023 0.0013 0.0043
22 0.012 0.0069 0.022
De Roda Husman et al. AEM, 2009, 75(4):1050-1057
Field Studies and Groundwater Protection | Feb 2012
VIRUS ATTACHMENT AND INACTIVATION
17
One site kinetic model
● Virus transport processes through saturated porous media
– Advection / dispersion / attachment / detachment / inactivation
● Governing equations
SkCCkx
Cv
x
Cv
t
C BlattL θ
ρµα det2
2
+−−∂∂−
∂∂=
∂∂
SSkCkt
S Bs
Batt
B
θρµ
θρ
θρ −−=
∂∂
det
Field Studies and Groundwater Protection | Feb 2012
VIRUS ATTACHMENT AND INACTIVATION
18
One kinetic site model: breakthrough curves
0.0001
0.001
0.01
0.1
1
0 5 10 15 20 25
t(h)
C/C0
katt=0.1; kdet=0.001; mul=0; mus=0
katt=0.2; kdet=0.001; mul=0; mus=0
katt=0.1; kdet=0.004; mul=0; mus=0
katt=0.1; kdet=0.001; mul=0.1; mus=0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0 5 10 15 20 25
t(h)
C/C0
Log scale to show tail
(katt
+µl)C
=> Cmax
kdet
S =>level of tail
µsS =>
slope of tail
Field Studies and Groundwater Protection | Feb 2012
VIRUS ATTACHMENT AND INACTIVATION
19
Two site kinetic model
● Governing equations
22det11det212
2
SkSkCCkCkx
Cv
x
Cv
t
C BBlattattL θ
ρθρµα ++−−−
∂∂−
∂∂=
∂∂
1111det11 SSkCkt
S Bs
Batt
B
θρµ
θρ
θρ −−=
∂∂
2222det22 SSkCkt
S Bs
Batt
B
θρµ
θρ
θρ −−=
∂∂
Breakthrough curve of PRD1 2-site kinetic model
0.001
0.01
0.1
1
0 1 2 3 4 5 6 7
Days
C/C0
Field Studies and Groundwater Protection | Feb 2012
VIRUS ATTACHMENT AND INACTIVATION
20
Modeling breakthrough curves: one and two kinetic sites
– v and αL
from NaCl tracer
– µlfrom inactivation experiment
– CXTFIT: 1 kinetic site model
– HYDRUS-1D: 2 kinetic site model
– µs
≈ slope of tail
0.000001
0.0001
0.01
1
0 24 48 72 96 120 144 168 192
Time [hours]
C/C0
b
c
a
Rate coefficients(day-1)
Aone site
Bone site
Ctwo sites
katt1 4.8 2.6 2.0
kdet1 6.7 0.065 0.065
katt2 3.36
kdet2 13.7
µs1=µs2 5.8 0.43 0.43
Goodness of fit 98% 92% 98%
22det11det212
2
SkSkCCkCkx
Cv
x
Cv
t
C BBlattattL θ
ρθρµα ++−−−
∂∂−
∂∂=
∂∂
1111det11 SSkCkt
S Bs
Batt
B
θρµ
θρ
θρ −−=
∂∂
2222det22 SSkCkt
S Bs
Batt
B
θρµ
θρ
θρ −−=
∂∂
Field Studies and Groundwater Protection | Feb 2012
FIELD STUDIES
21
Field study dune recharge Castricum
Field Studies and Groundwater Protection | Feb 2012
FIELD STUDIES
22
Field study dune recharge Castricum
Field Studies and Groundwater Protection | Feb 2012
FIELD STUDIES
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Field study dune recharge Castricum
Field Studies and Groundwater Protection | Feb 2012
FIELD STUDIES
24
Salt tracer
● NaCl
● 7 days pulse
● Pore water velocity (1.5 m/day)
● Dispersivity
800
1800
2800
3800
0 5 10 15 20 25 30 35 40Day
EC
(µS
/cm
)
CompartmentPCO3 (3.8 m)PCO5 (10 m)PCO7 (30 m)
800
1800
2800
3800
0 5 10 15 20 25 30 35 40
EC
(µS
/cm
)
CompartmentPCO2 (2.4 m)PCO4 (6.0 m)PCO6 (17 m)
Field Studies and Groundwater Protection | Feb 2012
FIELD STUDIES
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Breakthrough curves
● Bacteriophages
– MS2
– PRD1
– 7 days seeding
MS2
1.E-03
1.E-02
1.E-01
1.E+00
1.E+01
1.E+02
1.E+03
1.E+04
1.E+05
1.E+06
1.E+07
1.E+08
1.E+09
0 25 50 75 100 125
C (
pfp/
l)
CompartmentPCO2 (2.4 m)PCO3 (3.8 m)PCO4 (6.4 m)PCO5 (10 m)PCO6 (17 m)PCO7 (30 m)
PRD1
1.E-03
1.E-02
1.E-01
1.E+00
1.E+01
1.E+02
1.E+03
1.E+04
1.E+05
1.E+06
1.E+07
1.E+08
0 25 50 75 100 125
C (
pfp/
l)
CompartmentPCO2 (2.4 m)PCO3 (3.8 m)PCO4 (6.4 m)PCO5 (10 m)PCO6 (17 m)PCO7 (30 m)
Field Studies and Groundwater Protection | Feb 2012
FIELD STUDIES
26
Inactivation
● Mild conditions
– near neutral pH
– low temperature
●→ First order rate decrease
MS2
0.01
0.1
1
10
0 10 20 30 40
Day
C/C
0
Obs in peptone/saline at lab
Linear fit: 0.0008 log10/day .Obs in compartment water atlabLinear fit: 0.019 log10/day
Obs in well water at lab
Linear fit: 0.028 log10/day
Obs in well water at field
Linear fit: 0.013 log10/day
PRD1
0.01
0.1
1
10
0 10 20 30 40
Day
C/C
0
Obs in peptone/saline at lab
Linear fit: 0.0026 log10/day .Obs in compartment water atlabLinear fit: 0.0032 log10/day
Obs in well water at lab
Linear fit: 0.0041 log10/day
Obs in well water at field
Linear fit: 0.050 log10/day
Field Studies and Groundwater Protection | Feb 2012
FIELD STUDIES
27
Modeling breakthrough curvesMS2 - Well PCO2 at 2.4 m
0.1
10
1000
100000
10000000
0 20 40 60 80 100 120 140
Day
C (viruses/l)
ObservationOne-site modelTwo-site model
Rate coefficients(day-1)
one site two sites
katt1 4.1 4.2
kdet1 0.00087 0.00079
katt2 0.47
kdet2 0.54
µs1=µs2 0.085 0.085
Goodness of fit 75% 79%
Rate coefficients (day-1)
one site two sites
katt1 3.2 3.2
kdet1 0.0016 0.0022
katt2 0.17
kdet2 0.24
µs1=µs2 0.092 0.092
Goodness of fit 77% 80%
MS2 - Well PCO3 at 3.8 m
0.1
10
1000
100000
10000000
0 20 40 60 80 100 120 140
Day
C (viruses/l)
ObservationsOne-site modelTwo-site model
Field Studies and Groundwater Protection | Feb 2012
FIELD STUDIES
28
Deep well injection study
● Redox-zones: Attachment to iron oxyhydroxides in O2-zone
71477 R 03
- 250
m-Field LevelPP.1
3
2
1
5
55
4 4 44
3
33
22 22
1 111
IP.2WP.1
3898 0
WP.3
8
[distance to IP.2;m] [distance to IP.2;m]
WP.2
12
WP.4
22
- 260
- 270
- 280
- 290
- 300
- 310
- 320
- 330
- 340
4 4
4
4 44
2 2
2
2 22
66
6 6 66
8
88
888
10
1010
101012
12
12
12
12
10
12
5
4
3
2
1
(1)
5
6
33
ntemperature sensorscreensfine sand
coarse sand
clay, loam
71477 R 03
- 250
m-Field LevelPP.1
3
2
1
5
55
4 4 44
3
33
22 22
1 111
IP.2WP.1
3898 0
WP.3
8
[distance to IP.2;m] [distance to IP.2;m]
WP.2
12
WP.4
22
- 260
71477 R 03
- 250
m-Field LevelPP.1
3
2
1
5
55
4 4 44
3
33
22 22
1 111
IP.2WP.1
3898 0
WP.3
8
[distance to IP.2;m] [distance to IP.2;m]
WP.2
12
WP.4
22
- 260
- 270
- 280
- 290
- 300
- 310
- 320
- 330
- 340
- 270
- 280
- 290
- 300
- 310
- 320
- 330
- 340
4 4
4
4 44
2 2
2
2 22
66
6 6 66
8
88
888
10
1010
101012
12
12
12
12
10
12
5
4
3
2
1
(1)
4 4
4
4 44
2 2
2
2 22
66
6 6 66
8
88
888
10
1010
101012
12
12
12
12
10
12
5
4
3
2
1
(1)
5
6
33
5
6
33
ntemperature sensorscreensfine sand
coarse sand
clay, loam
Field Studies and Groundwater Protection | Feb 2012
FIELD STUDIES
29
Soil passage effectively removes viruses
● 8 log10 removal (non-linear with distance)
– After 25 days (30 m) dune passage
– After 40 days (38 m) deep well injection
-10
-8
-6
-4
-2
0
0 10 20 30 40
Travel time [days]
RemovalLog10(C/C0)
MS2 - dune rechargePRD1 - dune rechargeMS2 - deep well injectionPRD1 - deep well injection
Field Studies and Groundwater Protection | Feb 2012
FIELD STUDIES
30
Removal processes during soil passage
● Effective virus removal if sites for attachment are present (mostly iron hydroxides; sticking efficiency α∼10-3)
● Virus populationheterogeneity?
● Little removal if attachment sites are absent(e.g. when oxygen deficient aquifer) → conservative value for attachment to be used in calculation of protection zones (sticking efficiency α∼10-5)
-10
-8
-6
-4
-2
0
0 10 20 30 40
Travel time [days]
Virus removalLog10(C/C0)
MS2 - dune rechargePRD1 - dune rechargeMS2 - deep well injectionPRD1 - deep well injection
Field Studies and Groundwater Protection | Feb 2012
QMRA
31
Dutch Drinking Water Act 2001
● No pathogens in drinking water in concentrations that adversely affect public health ≠ zero => risk
● Quantitative Microbiological Risk Assessment (QMRA)
– WHO Drinking Water Guidelines (eds 3+4): Health based target
– The Netherlands: Max infection risk = 10-4 per person per year
– Drinking water concentration ≈ 1 pathogen in 1 000 000 liter
● QMRA required for drinking waterfrom surface water and vulnerable groundwater
● Index pathogens
– Enteroviruses, Campylobacter, Cryptosporidium, Giardia
Field Studies and Groundwater Protection | Feb 2012
QMRA
32
Environmental Inspectorate Guideline 5318 (2006)● How to do QMRA
● QMRA from surface water to drinking water
– Quality of source water (index pathogens)
– Treatment efficiency (indicator organisms)
● QMRA from vulnerable groundwater to drinking water
– Is protection zone of 60 days an adequate barrier (natural treatment)?
● Unconfined sandy aquifers and karst aquifers are vulnerable
– No protective confining (clay) layers
– Karst: fast flow paths
Index pathogens Indicator organismsEnteroviruses 20-200 nm Bacteriophages 20-60 nmCampylobacter 1-2 µm E.coli 1-2 µmCryptosporidium 5-6 µm Spores of sulphiteGiardia 8-10 µm reducing clostridia (SSRC) 1 µm
Field Studies and Groundwater Protection | Feb 2012
QMRA
33
QMRA from surface water to drinking water● Csw = Pathogen concentration in source water [N/liter]
● R = Recovery = fraction of detected pathogens [-]
● Z = Fraction of microorganisms passing treatment [-]
● Cdw = Pathogen concentration in drinking water [N/liter]
● V = Consumption of unboiled drinking water [liter]
● Pm = Infectivity of pathogen [-]
● Pinf = Infection risk [per person per day or year]
● Pinf,day = Csw x 1/R x Z x V x Pm
● Pinf,year = 365.25 x Pinf,day or
● Drinking water companies: point estimates (average values)
● RIVM: Monte Carlo simulations (variability)
( )∏=
−−=365
1inf,inf, 11
idayyear i
PP
Field Studies and Groundwater Protection | Feb 2012
QMRA
34
QMRA from groundwater to drinking water
● Guideline 5318
– Unconfined sandy and karst aquifers are considered vulnerable therefore QMRA required
● Protection zone:
– No sources of contamination allowed within that zone
● Source concentration, Cs
● Setback distance rs and travel time T determine size of protection zone, which is the soil barrier
● Z = fraction of pathogensable to pass the soil barrier
Pinf = Cs x 1/R x Z x V x Pm ≤ 10-4
Field Studies and Groundwater Protection | Feb 2012
GROUNDWATER PROTECTION
35
History of 60-days protection zone
● Knorr, Das Gas- und Wasserfach 1937, 80: 330-334
– Survival of bacteria in a bottle of water
– No bacteria detected after 60 days
● 60-days protection zone
– After 50-60 days no danger to public health
● Austria, Denmark, Germany, Ghana,Indonesia,The Netherlands, UK
● But viruses (and other pathogens)may survive longer
● Is 60-days enough protectionfor a maximum infection risk of 10-4 p-1y-1?
Field Studies and Groundwater Protection | Feb 2012
GROUNDWATER PROTECTION
36
Protection zones that comply with 10-4 infection risk
● Shallow, unconfined sandy aquifers
● Viruses leaking from a sewage pipe
● Horizontal transport to the pumping well
● Literature data distributions of parameters (Monte Carlo simulation)
● Removal processes
– Little attachment (field data at anoxic conditions), α=10-5
– Extensive literature data on virus inactivation, µ=0.01 log10/day
● Dilution in groundwater
– Pumping rate QW at well
Field Studies and Groundwater Protection | Feb 2012
GROUNDWATER PROTECTION
37
Steady state model
Removal = Attachment + Inactivation + Dilution
CA
is virus concentration at well
C0
is virus concentration in wastewater
α is sticking efficiency (attachment parameter) = 10-5
µlis the inactivation rate coefficient = 0.01 log
10/day
k1
en k2
physical constants
q is leakage rate of sewage pipe
Q is abstraction rate of groundwater
R is radial distance source<=>well
● QMRA: pinf
= C0
x Z x V x pm≤ 10-4
+
+−==
Q
qRkRkZ
C
Cl
A10
22
3/5110
010 log
2
1
5
3
3.2
1loglog µα
Field Studies and Groundwater Protection | Feb 2012
GROUNDWATER PROTECTION
38
MonteCarloSimulations
VIRUS PROPERTIES AQUIFER PROPERTIES RISK ASSESSMENT
Sewage: 100 Enteroviruses/L Aquifer thickness Consumption 0.27 L/day
Leakage rate q=1m3/day Grain size Rotavirus infectivity
Inactivation 0.01 log10/day Porosity Protection zone 200-400m
Sticking efficiency αααα=10-5 Temperature Protection zone 1-2 years
Field Studies and Groundwater Protection | Feb 2012
GROUNDWATER PROTECTION
39
Sensitivity analysis
● Size of protection zone most sensitive to inactivation and attachment
0.0829550.4
0.31091050.1
2.48592800.01
Inactivation µl
(day-1)
0.3294710-3
0.621513210-4
1.760323110-5
Attachment α
T95(year)T95(day)R95 (m)Parameter value
Parameter
Field Studies and Groundwater Protection | Feb 2012
GROUNDWATER PROTECTION
40
Conclusions
● Shallow unconfined sandy aquifers (20-35 m deep)
– Travel time of 1 to 2 years (206 - 418 m setback distance)
– Infection risk below 10-4 per person per year with 95% certainty
● Most sensitive model parameters for size of protection zone
– Attachment and inactivation
● A smaller protection zone
– Demonstrate aquifer properties that lead to more virus removal
– Location specific investigation
● Only horizontal transport considered
– If vertical transport is significant thenprotection zone may be overestimated
Field Studies and Groundwater Protection | Feb 2012
GROUNDWATER PROTECTION
41
Vulnerability● Environmental Inspectorate Guideline 5318 (2006)
– All unconfined sandy aquifers and karst aquifers are vulnerable
– QMRA of drinking water from vulnerable groundwater
● Groundwater companies
– Deeper unconfined aquifers should be less vulnerable
● Vulnerability
– Ability of viruses to be transported with the groundwater
– Less attenuation of virus in a more vulnerable aquifer
– Attenuation depends on properties of viruses and aquifer
● Size of protection zone:
– Maximum risk level (health based target) [risk]
– Virus source concentration [source]
– Attenuation of virus concentration [vulnerability]
Field Studies and Groundwater Protection | Feb 2012
GROUNDWATER PROTECTION
42
Properties of viruses
● Significant threat to public health
– Very infectious
– Commonly gastroenteritis, but also more severe illness
● Can be very persistent
– survive well = inactivate slow; µ=0.01 log10/day
● Usually little attachment to sand grains
– Many viruses are negatively charged; α=10-5
● Very small
– 20-200 nm
– Negligible straining
● λ= virus removal rate coefficient(inactivation + attachment)
Field Studies and Groundwater Protection | Feb 2012
GROUNDWATER PROTECTION
43
Properties of unconfined sandy aquifers● No confining layers
● High permeability
● In the Netherlands often shallow
● Properties relevant to virus attachment and inactivation = λ– porosity, grain size, iron hydroxides, temperature, pH, ionic
strength, ion composition, organic content, etc.
● Properties relevant to virus advection, dispersion, dilution
– m = anisotropy factor
– Q = Pumping rate of abstraction well
– H= thickness of aquifer
– zt=top of well screen
– zb=bottom of well screen
Field Studies and Groundwater Protection | Feb 2012
GROUNDWATER PROTECTION
44
Model development● Vulnerability parameters
– Virus+aquifer properties
● Dimensionless model
– Model parameters are dimensionless
– Lower number of model parameters
● Numerical calculations (FlexPDE)
– Calculate rs* = dimensionless setback distance
to achieve a required virus removal
● Empirical formula
– Fit a formula to values of rs* as a function of the vulnerability
parameters
● rs* = dimensionless setback distance = vulnerability index
– Different combinations of the vulnerability parameters leading to the same virus attenuation have the same rs
*
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-2 -1 0 1 2 3
-3
-2
-1
0
1
l*
r*
Field Studies and Groundwater Protection | Feb 2012
GROUNDWATER PROTECTION
45
● Steady state
– Constant pumping rate and constant leakage rate of virus from sewer
● Horizontal radial and vertical transport
● Dimensionless model
– The model domain was scaled=divided by H, the aquifer thickness
● Dimensional virus removal rate coefficient
– Inactivation + attachment: λ*= λ n π H3/Q
Model domainrs
*= rs /H
H/H=1
Q
*Contamination
source
Well screen
C*=10-8
Vulnerability index
Setback distance
Field Studies and Groundwater Protection | Feb 2012
GROUNDWATER PROTECTION
46
Radial water flow under steady state conditions● Governing equation
– where, t [T] is the time, h [L]is the hydraulic head, kr[LT-1] is the
hydraulic conductivity in the r-direction and kz[LT-1] is the
hydraulic conductivity in the z-direction
● Dimensionless flow equation
– Division of governing equation by krand scaling to H [L] which is
the total thickness of all aquifer layers
02
2
=∂∂
∂∂+
∂∂
r
hr
rr
k
z
hk r
z
011
*
**
**2*
*2
=
∂∂
∂∂+
∂∂
r
hr
rrz
h
m
Field Studies and Groundwater Protection | Feb 2012
GROUNDWATER PROTECTION
47
Virus transport
● Governing equation
– where, vrand v
zare the vertical and radial pore water velocities
– λ [T-1] is the virus removal rate coefficient, which entails both attachment and inactivation.
– Drr
≈αrvrand D
zz≈α
zvz[L2T-1] are the dispersion coefficients in r and
z directions.
● Dimensionless virus transport equation
Cr
CrD
rrz
CD
r
Cv
z
Cv rrzzrz λ−=
∂∂
∂∂−
∂∂−
∂∂+
∂∂ 1
2
2
***
***
**
*2*
*2**
*
**
*
** 1
1.0 Cr
Crv
rrz
Cv
r
Cv
z
Cv rrrrrz λαα −=
∂∂
∂∂−
∂∂−
∂∂+
∂∂
Field Studies and Groundwater Protection | Feb 2012
GROUNDWATER PROTECTION
48
Dimensionlessparameters
Parameter Description
sss lrA ** 2= Leakage area
2
*
H
AA w
w π=
Cross sectional area of the screen of the abstraction well
** 005.0 sr
r rH
== αα Dispersivity in the r -direction.
** 1.0 rz
z Hααα ==
Dispersivity in the z -direction
RC
CC =*
Virus concentration with RC [L-3] the concentration at the abstraction well at R [L] from the source of contamination.
*sC Virus concentration at the contamination source
H
hh =*
Aquifer thickness
∑== irr trQ
H
Q
Hkk
ππ 2*
Horizontal hydraulic conductivity, where itr [m2 day-1] is the transmissivity of i-th aquifer layer.
Q
Hn 3* πλλ =
Dimensionless removal rate coefficient,
z
r
k
km =
Anisotropy ratio
Q
qQ =*
Dilution, where 1=q m3 day-1 (Schijven et al., 2006).
H
rr =* ,
H
zz =*
Radial and vertical coordinate
rr vQ
Hnv
2* π= , zz v
Q
Hnv
2* π=
Radial and vertical pore water velocity
H
zz b
b −= 1* , H
zz t
t −= 1* Bottom and top of the well screen
Varie
d in n
um
eric
al sim
ula
tio
ns
Field Studies and Groundwater Protection | Feb 2012
GROUNDWATER PROTECTION
49
Numerical simulations (FlexPDE)● Dutch groundwater database
– Dimensionless parameter values of 35 unconfined aquifers
– λ=0.03 day-1 (α =10-5, µl=0.01 log10/day)
● 212 cases simulated
● Set vulnerability index rs* to get required removal (such that C* at well =1)
● No effect of kr*
● Fit rs* to vulnerability parameters
Mean Min Max Values for numerical simulationλ* removal rate coefficient 45 0.79 645 0.01, 0.1, 1, 10, 100, 1000Q* dilution factor 0.00012 0.000037 0.0019 0.0001, 0.001kr* horizontal hydraulic conductivity 500 4.4 6900 10, 100, 1000m anisotropy factor 1.6 1 3.5 1, 2, 5, 10zt* top of well screen 0.72 0.31 1 1, 0.85, 0.75, 0.5
zt*-zb* length of well screen 0.43 0.042 0.82 025, 0.5H (m) aquifer depth 116 23 334 -Cs* virus source concentration 104…108
Dimensionless parameter
Field Studies and Groundwater Protection | Feb 2012
GROUNDWATER PROTECTION
50
First fitting step: If zt*=1 (horizontal transport)
● Numerical simulations =>Linear relation lnrs
* and lnλ*
● Steady state solution,neglecting dispersion
● Fit data to
● R2=99.9%
● a1 = 0.557
● a2 = 0.467
● Empirical formula
*
[ ] **** ln2
1lnlnln
2
1ln λ−+= QCr ss
[ ] *2
**1
* lnlnlnlnln λaQCar ss ++=
( )[ ] 467.0*557.0*** ln−= λQCr ss
*
**2*
λQC
r ss =
Field Studies and Groundwater Protection | Feb 2012
GROUNDWATER PROTECTION
51
Second fitting step: If zt*<1, vertical transport significant
● Strong decreaseof lnrs
* for large lnλ*
(vertical transport dominates)
● Add (1-zt*) x (terms of
vulnerability parameters with coefficients)
*
Field Studies and Groundwater Protection | Feb 2012
GROUNDWATER PROTECTION
52
Empirical formula
● R2=97.9%
( ) ( ) [ ]
−−=
−−−− ***64.117.119.2*383.0*227.0*467.0*557.0*** 99.2529.01207.0ln*
btt
z
sss zzExpzmQCExpQCr tλλ
Field Studies and Groundwater Protection | Feb 2012
GROUNDWATER PROTECTION
53
Conclusions
● Empirical formula developed to calculate vulnerability index (dimensionless setback distance) and setback distance of an unconfined sandy aquifer to protect against virus contamination
● Deeper unconfined aquifers with deep well screen are less vulnerable and even more is anisotropy factor m>1
● A higher pumping rate Q increases dilution and flow rate, the net effect is increased vulnerability
● Integral part of Quantitative Microbial Risk Assessment
● Next steps:
– Incorporate in Inspectorate Guideline 5318
– Compare calculated with actual setback distances
Field Studies and Groundwater Protection | Feb 2012
GWPCalc
54
GWPCalc
● Computable Document File, Mathematica version 8 (Wolfram Inc, Champaign, Illinois)
● Runs in Mathematica and the free CDF Player (add-on or internet browser)
Empirical formula from
numerical calculations,
including vertical
transport
(Schijven et al., 2010)
Virus source
(leaking sewer or
septic tank at
groundwater table)
or any other
contaminant
Well
screenAquifer
thickness H
Setback
distance rs
Required removal:
Source 100 vir/L=>
8 log10
removal=>
Groundwater 10-6 vir/L=>
Infection risk <10-4 pppy
Vulnerability
rs*=r
s/H
Field Studies and Groundwater Protection | Feb 2012
GWPCalc
55
Example 0
● Unconfined / shallow / well screen high● Most sensitive aquifer thickness, pumping rate
and removal rate coefficient
Field Studies and Groundwater Protection | Feb 2012
GWPCalc
56
Example 1
● Unconfined / less shallow / well screen high● Most sensitive aquifer thickness, pumping rate
and removal rate coefficient
Field Studies and Groundwater Protection | Feb 2012
GWPCalc
57
Example 2
● Unconfined / less shallow / well screen deep● Also sensitive to changes in anisotropy
Field Studies and Groundwater Protection | Feb 2012
GWPCalc
58
Example 3
● Confined / less shallow / well screen deep
Field Studies and Groundwater Protection | Feb 2012
GWPCalc
59
Example 4
● Well screen crosses a confining layer● Virus transport in upper aquifer● Dilution with water from lower, clean aquifer
Field Studies and Groundwater Protection | Feb 2012
GWPCalc
60
Conclusions● GWPCalc is a tool with a quick-
and-easy to use formula to identify vulnerable sandy aquifers and situations that require attention
● GWPCalc be used to identify sources of contamination
● One removal rate coefficient: GWPCalc can be used for any contaminant
GWPCalc
61 Field Studies and Groundwater Protection | Feb 2012
QUESTIONS?
● GWPCalc is for free