Working
Report
2009-06
Isotopic Composition of Atmospheric
Precipitation and Shallow Groundwater
in Olkiluoto: O-18, H-2 and H-3
Nina
Kortelainen
February
POSIVA
OY
Olkiluoto
FI-27160 EURAJOKI, FINLAND
Tel
+358-2-8372 31
Fax +358-2-8372 3709
2009
Working
Report
2009-06
Isotopic Composition of Atmospheric
Precipitation and Shallow Groundwater
in Olkiluoto: O-18, H-2 and H-3
Nina
Kortelainen
Geological Survey of Finland
February
2009
Base maps: ©National Land Survey, permission 41/MML/09
Working Reports contain information on work in progress
or pending completion.
The conclusions and viewpoints presented in the report
are those of author(s) and do not necessarily
coincide with those of Posiva.
ABSTRACT
Isotopic composition of oxygen and hydrogen in local precipitation is a key parameter
in modelling of local water circulation. This study was initiated in order to provide
systematic monthly records of the isotope content of atmospheric precipitation in the
Olkiluoto area and to establish the relation between local rainfall and shallow
groundwater. During January 2005 – June 2008 a total of 35 cumulative monthly
rainfall samples and 38 shallow groundwater samples were collected and their O-18, H2 (= D) and H-3 values were detected. Based on the three years' monitoring, the
weighted annual mean isotope values of the precipitation and the mean values for
groundwater are -12.15‰ and -11.31‰ for oxygen, -86.8‰ and -80.4‰ for hydrogen
and 10.2 and 9.9 TU for tritium, respectively. In general, the isotope signatures of
atmospheric precipitation and groundwater at Olkiluoto are close to unity and represent
the typical isotope values of this area in Finland. The coastal location of the study area
is reflected in the isotopic composition of oxygen and hydrogen in the precipitation. In
contrast to inland rainfall, the temporal correlation between the stable isotope ratios and
surface temperatures is poor and the seasonal isotopic variations are decreased. The
seasonal behaviour of tritium concentrations in Olkiluoto precipitation follows a typical
H-3 pattern observed in the northern hemisphere and, hence, not any significant input of
secondary tritium can be suggested during this monitoring period. The precipitation data
were used to establish the local meteoric water line (LMWL) for the Olkiluoto area. The
line is formulated as: D = 7.29 δO-18 + 2.01.
Keywords: atmospheric precipitation; ground water; isotopes; O-18; H-2; tritium;
Olkiluoto; Finland
SADANNAN JA POHJAVEDEN ISOTOOPPIKOOSTUMUS OLKILUODOSSA:
O-18, H-2 JA H-3
TIIVISTELMÄ
Sadannan hapen ja vedyn isotooppikoostumus on keskeinen lähtötieto tutkittaessa veden
alkuperää, viipymää, ja geokemiallisia reaktioita pohjavesimuodostumassa. Tämän
tutkimuksen tavoitteena oli luoda kuukausittaiseen seurantaan perustuva ajallisesti
kattava aineisto sadannan hapen ja vedyn isotooppisuhteista sekä tritiumin pitoisuuksista Olkiluodossa. Tutkimuksessa tarkasteltiin myös paikallisen sadannan isotooppikoostumuksen suhdetta muodostuvan pohjaveden vastaavaan. Seurantajakso alkoi
tammikuussa 2005 ja päättyi kesäkuussa 2008. Kuukausittaisia sadantanäytteitä
kerättiin 35 ja pohjavesinäytteitä 38 kappaletta. Näistä analysoitiin hapen ja vedyn
isotooppikoostumus, sekä tritiumpitoisuus. Olkiluodon sadannan ja pohjaveden kolmen
vuoden isotooppikeskiarvot hapelle ovat -12.15‰ ja -11.31‰, vedylle -86.8‰ ja 80.4‰ ja tritiumille 10.2 TU ja 9.9 TU. Sadeveden isotooppiarvo on painotettu
kuukausittaisilla sademäärillä. Sadannan ja pohjaveden isotooppikoostumukset ovat
melko lähellä toisiaan ja tyypillisiä tälle alueelle Suomessa. Itämeren läheisyys heijastuu Olkiluodon sadannan hapen ja vedyn isotooppisuhteisiin. Se mm. heikentää hapen ja
vedyn isotooppikoostumuksen ja lämpötilan välistä korrelaationa, sekä alentaa isotooppikoostumuksissa havaittavia vuodenaikaisvaihteluja. Tritiumissa havaittavat vuodenaikaistrendit ovat tyypillisiä pohjoisen pallonpuoliskon sadannalle, eikä seurannan aikana sadannassa havaittu selvää ydinvoimalaperäistä tritiumia. Olkiluodon alueelle luotiin
lokaali meteoristen vesien suora (LMWL), mikä perustuu seurannassa kerättyyn
sadannan isotooppidataan. Regressioanalyysillä johdettiin LMWL, joka saa muodon:
D = 7.29 δO-18 + 2.01. Pohjavesien hapen ja vedyn isotooppikoostumus osuus tarkasti
tälle suoralle. Lokaalia suoraa suositellaan käytettäväksi referenssisuorana Olkiluodon
pinnallisten vesien hapen ja vedyn isotooppisuhteita tarkasteltaessa.
Avainsanat: sadanta; pohjavesi; isotoopit; O-18; H-2; tritium; Olkiluoto; Suomi
1
TABLE OF CONTENTS
ABSTRACT
TIIVISTELMÄ
ISOTOPE NOTATIONS AND EXPRESSIONS ............................................................. 2
1
2
3
4
INTRODUCTION ................................................................................................. 3
1.1
Isotope hydrological background................................................................... 3
1.2
Aims of the study .......................................................................................... 4
MATERIALS AND METHODS ............................................................................... 5
2.1
Samples........................................................................................................ 5
2.2
Sampling procedures .................................................................................... 5
2.3
Isotope analysis ............................................................................................ 6
RESULTS AND DISCUSSION ............................................................................... 8
3.1
Precipitation .................................................................................................. 8
3.2
Local meteoric water line ............................................................................ 12
3.3
Groundwater ............................................................................................... 14
3.4
Comparison of precipitation and groundwater ............................................. 15
SUMMARY .......................................................................................................... 18
4.1. Recommendations for future studies ........................................................... 19
REFERENCES ........................................................................................................... 20
APPENDIX 1 .............................................................................................................. 22
APPENDIX 2 .............................................................................................................. 23
2
ISOTOPE NOTATIONS AND EXPRESSIONS
The isotopic composition of the stable nuclides of oxygen and hydrogen is measured as
isotope ratios. The isotope ratios are reported using the δ notation as a per mil (‰)
difference relative to the international VSMOW (Vienna Standard Mean Ocean Water)
standard for oxygen and hydrogen. The δ value is defined as
where R is the O-18/O-16 or D/H (D = H-2) ratio of the sample (sa) or standard (std)
and δ is δO-18 or δD.
The radioactive isotope of hydrogen, tritium (H-3), has a half-life of 12.32 years (Lucas
& Unterweger 2000). Tritium concentrations are expressed as tritium units (TU), where
the H-3 activity of 1 TU denotes 0.118 Bq/kg of water in the SI system.
3
1
INTRODUCTION
The isotopic composition of oxygen and hydrogen in local atmospheric precipitation
forms primary background data in explaining the sources, retention times and
circulation of groundwater as well as the water-mineral interactions. It renders also
principal information for assessing the significance of the changing climate in
perspective of the Olkiluoto Repository. This study was initiated in order to provide
systematic monthly records of the isotope content of atmospheric precipitation in the
Olkiluoto area and to establish the relation between local rainfall and shallow
groundwater. Contact persons of this study at GTK and Posiva Oy were Nina
Kortelainen and Mia Ylä-Mella, respectively.
1.1 Isotope hydrological background
Most of the atmospheric water vapour is formed over the subtropical oceans (Craig &
Gordon 1965), from where the air masses are transported polewards with gradual
rainout. The rainout process preferentially removes the heavier isotopes of oxygen (O18) and hydrogen (D) from the air mass, leading to a gradual decrease in the δO-18 and
δD values in atmospheric vapour and precipitation as an air mass moves towards the
higher latitudes. This so called latitude effect is seen as a clear spatial isotope pattern in
the Finnish precipitation and recent groundwaters (Kortelainen 2007). In the mid and
high latitudes of the northern hemisphere the δO-18 and δD values of the precipitation
vary by season. The seasonal variations are related to temperature, which causes a great
depletion of O-18 and D in rainfall during the cold winter months. In Finland the
temperature effect increases when moving from the southern coast towards the north
and also to the inland (Kortelainen 2007). Tritium is produced in the atmosphere and
enters the hydrological circulation in atmospheric precipitation. Resolving the natural
behaviour of tritium in local precipitation is essential in order to evaluate the potential
inputs from secondary sources such as nuclear power plant.
Globally, a linear correlation was observed between the δO-18 and δD values detected
in fresh water samples and the global meteoric water line (GMWL) was established by
Craig in 1961. The GMWL is defined by the equation:
D = 8 δO-18 + 10‰ VSMOW
(1)
The global line is actually a mixture of numerous local meteoric water lines, as any
given locality will have a characteristic local meteoric water line (LMWL) with
somewhat different slope and intercept. A local line can reflect the origin of the water
vapour and subsequent modifications by secondary processes of re-evaporation and
mixing (Clark & Fritz 1997). The Finnish LMWL is based on the spatial isotope data of
precipitation, which yielded the following line
δD = 7.67 δO-18 + 5.79‰ (Kortelainen 2007)
(2)
It is recommended that any detailed hydrogeological study using δO-18 and D should
attempt to define as best as possible the LMWL.
4
The deuterium excess parameter has been used to characterize the meteoric conditions
prevailing in the initial moisture source (Merlivat & Jouzel 1979) and it is defined by
d (‰) = D - 8 O-18 (Dansgaard 1964)
(3)
The GMWL has a d-excess value of 10‰, which is the average value for global
precipitation and derived waters formed from the vapour that was evaporated in the
global average humidity of 85% over oceans (Merlivat & Jouzel 1979; Gonfiantini
1986). In addition, the d-excess is affected by secondary processes such as the
evaporation during rain events and/or recirculation of moisture from the continental
water bodies (Rozanski 1984; Froehlich et al. 2002). In practice, d-excess can be
thought of as an index of deviation from the GMWL. Evaporated surface waters, for
instance, are strongly displaced from the GMWL.
Groundwater is formed from local atmospheric precipitation. Due to evapotranspiration
and runoff, however, only a minor proportion of rainfall actually replenishes the
groundwater reservoirs. In temperate climates, as in Finland, the isotopic composition
of the local mean annual precipitation closely follows that of local groundwater
(Kortelainen 2007; Kortelainen & Karhu 2004). In groundwaters most of the seasonal
isotopic variations in rainfall are smoothed out during the infiltration process. The
weighted mean annual δO-18, δD and H-3 content in atmospheric precipitation are key
values as considered the groundwater recharge. They refer to the annual or perennial
isotope signal of the cumulative rainfall that reaches the earth’s surface at a particular
location.
1.2 Aims of the study
The primary objective of this study was to generate the basic isotopic tools to be used as
background values in hydrological studies in the Olkiluoto area. This comprises
defining of the long-term (three-year) weighted mean annual isotopic composition of
precipitation and the local meteoric water line (LMWL). Additionally, the isotope data
of precipitation was considered in respect to that of local groundwater as well as to
isotopic composition of precipitation on a national scale.
5
2
MATERIALS AND METHODS
2.1 Samples
Isotope monitoring of atmospheric precipitation and adjacent shallow groundwaters
began in the beginning of 2005. Cumulative rainfall was collected in one location on
monthly basis. Groundwater from shallow soil deposits was sampled in two locations
(PVP14, PVP4a) six times a year. Figure 1 illustrates the locations of the rainfall
collector, the groundwater observation wells and the Olkiluoto weather mast (OLWOM1). From January to May 2007 there was an unfortunate brake in water sampling,
and therefore the monitoring period of precipitation was extended to May 2008 and that
of groundwater to June 2008. During January 2005 – June 2008 a total of 35
precipitation samples and 38 groundwater samples were collected. In March 2005, the
rainfall sample was not received due to the very small amount of monthly precipitation.
2.2 Sampling procedures
The precipitation collection device was placed in an open undisturbed location (Fig. 1).
The sampling period for the monthly precipitation was from the beginning to the end of
the month. Rainwater was collected in a 2-litre Teflon® separatory funnel. To prevent
evaporation, a layer of paraffin oil was added to the funnel (IAEA/WMO 2006). The
collector was covered by aluminium foil. Snow was collected in a thick-walled plastic
cylinder sealed at one end. A plastic bag inside the cylinder was replaced after every
snow event. Paraffin oil was added to the plastic bag when thawing. Even though oil
was added, the plastic bag was replaced at least once a week. At the end of the month
the sub-samples were combined. The monthly precipitation in mm was calculated from
the total volume of the collected rainwater.
Observation wells were sampled using a frequency-controlled electric submersible
pump. Prior to sampling the wells were pumped for 20 minutes or more in order to
replace the water volume in the well several times.
Posiva Oy was responsible for collecting and sampling the monthly precipitation and
groundwater and delivering the samples for analyses to GTK.
6
Figure 1. Locations of the precipitation and groundwater monitoring sites in Olkiluoto
(Base map: © National Land Survey, permission 41/MYY/08). Layout Jani Helin,
Posiva Oy.
2.3 Isotope analyses
Unfiltered water samples for isotope analyses of O-18 and D were poured into 50 ml
and H-3 into 50–500 ml HDPE bottles. Samples were stored in dark and cold. In every
step of sample handling, care was taken to prevent secondary evaporation.
For the analysis of  O-18 the water samples were equilibrated with CO2 gas and the
isotopic composition of CO2 was analysed (Epstein & Mayeda 1953). The isotopic
composition of hydrogen was analysed after reduction of water to H2 gas using zinc
metal (Coleman et al. 1982). The zinc reagent was prepared from pure metal by adding
Na as an impurity (Karhu 1997). Isotopic ratios of the produced CO2 and H2 were
measured by a Finnigan MAT 251 gas source mass spectrometer at GTK. O-18 and D
values are given normalized to values of -55.5‰ and -428‰, respectively, for SLAP
(Standard Light Antarctic Precipitation) relative to VSMOW (Coplen 1994). The
repeatability of analyses was ≤ 0.1‰ for oxygen and ≤ 1.0‰ for hydrogen in water.
During the first year of the study, i.e. 2005, the tritium content of water samples was
analyzed in STUK - Radiation and Nuclear Safety Authority, Finland. From the
beginning of 2006, subcontracting of the H-3 analyses was moved to CIO, the
University of Groningen, the Netherlands. The reason to this rearrangement was the low
concentration of H-3 observed in the water samples. Tritium was determined from
enriched samples by liquid scintillation counting (LSD). The detection limit and the
7
analytical uncertainty reported by STUK were 1 Bq/kg (8.5 TU) and 7-10%,
respectively. For the CIO analyses the detection limit was 2 TU and the analytical error
generally ± 0.2.
Table 1. Weighted three-year monthly and annual mean δD, δO-18, d-excess and H-3 in
Olkiluoto precipitation.
Month
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Mean£
min
max
max-min
$)
Prec sum
mm
61.5
24.2
19.2
43.2
34.3
33.1
52.0
83.7
66.3
85.1
85.2
72.6
660.4
19.2
85.2
66.0
$
(36.0)
(27.6)
(27.3)
(27.8)
(38.3)
(53.3)
(56.0)
(62.8)
(52.1)
(61.3)
(40.2)
(42.5)
Temp
°C
-1.0
-2.8
-3.3
4.2
9.1
14.1
17.6
17.6
13.0
8.1
3.1
1.5
6.8
-3.3
17.6
20.9
$
(-2.7)
(-4.3)
(-1.6)
(3.8)
(8.6)
(13.5)
(17.2)
(16.5)
(11.8)
(6.8)
(1.5)
(-1.3)
#
d -excess Months
δD
δO-18
‰ vs. VSMOW
‰
n
-93.4
-12.93
10.1
3
-100.7
-13.88
10.3
3
-97.4
-13.97
14.3
2
-91.5
-12.83
11.1
3
-77.6
-10.93
9.8
3
-79.1
-10.76
7.0
3
-76.4
-10.51
7.7
3
-89.4
-12.42
10.0
3
-72.4
-10.58
12.2
3
-90.4
-12.65
10.8
3
-96.0
-13.53
12.3
3
-81.2
-11.31
9.3
3
-86.8
-100.7
-72.4
28.2
-12.15
-13.97
-10.51
3.45
10.4
7.0
14.3
7.4
35
&
H-3 Months
TU
n
10
3
9.4
3
9.6
1
10.1
3
11.8
2
14.1
3
11.8
3
15.1
3
10.1
3
8.1
2
7.8
2
7.3
2
10.2
7.3
15.1
7.8
Mean monthly temperature and precipitation at Olkiluoto station WOM1 in 1993-2006 (Ikonen 2007)
Number of months available in weighting the δD and δO-18 data
&)
Number of months available in weighting the H-3 data
£)
Mean annual total
#)
30
8
3
RESULTS AND DISCUSSION
The isotopic composition of stable oxygen and hydrogen was analysed in 35
precipitation samples and 38 (19 + 19) groundwater samples. 30 precipitation and 35
groundwater samples were studied in respect of their tritium content. The δO-18, D
and H-3 values of monthly precipitation and groundwater and the amount of
precipitation, recorded in the precipitation monitoring, are presented in Appendices 1
and 2. The table of Appendix 1 shows also the respective monthly mean meteorological
data including the amount of precipitation, temperature and humidity measured in the
Olkiluoto weather station (OL-WOM1). Long-term weighted monthly and annual
isotope records with the number of weighting months, minima, maxima and their
difference (max-min) are summarized in Table 1. Averages of monthly temperatures
and the amount of precipitation are also included (Table 1). For comparison, the longterm (1993-2006) mean monthly temperatures and precipitation sums at the OL-WOM1
station are also presented (Ikonen 2007).
Based on the three-year monitoring of precipitation the weighted annual mean δO-18 is
-12.15‰, D -86.8‰ and the H-3 content 10.2 TU. The mean δO-18, D and H-3
values for the groundwater monitored in this study are -11.31‰, -80.4‰ and 9.9 TU,
respectively. The dataset comprising the isotope ratios of oxygen and hydrogen in
precipitation and groundwater has a good coverage concerning the whole three-year
monitoring period. However, the tritium dataset has gaps concerning certain months,
which may cause some distortion especially for the precipitation data. The gaps are
caused by reasons like too high detection limits of the laboratory (STUK) and missing
or too small monthly samples.
3.1
Precipitation
Notable seasonal variations are recorded in the isotopic composition of atmospheric
precipitation in Olkiluoto area. Figure 2 presents the time series of δO-18, D and H-3
in the cumulative monthly rainfall. However, considering the isotope signal of the
amount weighted rainfall in a longer time period, the variation is considerably
decreased. Figure 3 illustrates the isotope characteristics of the Olkiluoto precipitation
based on the weighted data of Table 1. When comparing the monthly values, ranging
from -16.7‰ to -6.26‰ in oxygen and from -119.5‰ to -43.6‰ in hydrogen (Fig. 2),
the difference between the highest and lowest amount weighted values decreases to
3.5‰ in oxygen and to 28‰ in hydrogen (Table 1; Fig 3). This is low, as even in the
Espoo coastal station the respective variation for oxygen is 5.5‰ and that for hydrogen
41‰. The highest δ values are generally measured during spring and summer whereas
the lowest values are recorded in autumn and winter precipitation (Fig. 3). The weighted
annual mean δO-18 value of -12.15‰ and D value of -86.8‰ are typical for
precipitation in this area (Kortelainen & Karhu 2004).
9
Figure 2. Time series of δO-18, δD and H-3 values in the monthly precipitation of
Olkiluoto.
The seasonal pattern in tritium roughly follows those ones recognized in stable water
isotopes (Figs. 2 and 3). The maximum monthly tritium contents of up to 16.9 TU were
measured in late spring and summer and the lowest values of down to 6.8 TU during
autumn and winter. This seasonal behaviour of tritium concentrations in Olkiluoto
precipitation follows a typical H-3 pattern observed in the northern hemisphere (Faure
& Mensing 2005) and gives no reason to suggest any significant input of tritium from
the nuclear power plant during this monitoring period. The weighted annual mean H-3
content of 10.4 TU corresponds to the values reported from recent precipitation on
northern latitudes (Meijer et al. 1995; Pitkänen et al. 1996, 1999; Gat et al. 2001).
Rough temperature dependence is recognized in the isotopic composition of
precipitation (Fig. 3). Figure 4 demonstrates the temporal correlation between the
10
Figure 3. Monthly weighted mean δO-18, δD and H-3 values of precipitation, the mean
amount of precipitation and mean monthly temperature and humidity in Olkiluoto. The
diagrams are based on Table 1.
11
monthly temperatures and δ values, which is, however, fairly poor. This is somewhat
different compared to data from other Finnish precipitation stations in Espoo, Kuopio
and Rovaniemi, which show a better correlation (Kortelainen 2007). In Olkiluoto, the
difference between the lowest and highest mean monthly temperatures is about 21 °C
(Table 1), which is low in contrast to the Finnish inland stations having a respective
value of 27 °C (Kortelainen 2007). This reflects the proximity of the sea and its
attenuation effect to local mean temperatures. In coastal stations the seasonal variations
in the isotopic composition of precipitation are generally much less pronounced
compared to continental areas (Rozanski et al. 1993; Kortelainen 2007). Besides the
lower variations in the local surface temperatures, the Baltic Sea as an additional vapour
source may have significant impact on the isotopic composition of rainfall in the
Olkiluoto area (Alalammi 1987).
The d-excess value describes the initial source of water vapour and the secondary
processes affecting the local atmospheric moisture in the study area. The d-excess of
Olkiluoto precipitation strongly varies by month and year (Appendix 1). The maximum
range recorded in d-excess values was from 6.5 to 21.5‰. The weighted isotope data
gives a better picture of the seasonal variations recognized in the d-excess of Olkiluoto
rainfall (Fig. 3). The minimum values are reached in Jun/July when the d-excess values
clearly plot below the global average of 10‰. Most of the d-excess values surrounding
the mid-summer months vary between 9–12‰. The annual mean d-excess in Olkiluoto
precipitation, calculated from the weighted isotope data, is 10.4‰, which agrees with
the global value as well as the d-excess values reported from other Finnish precipitation
stations (Kortelainen 2007). The similar results in Finland suggest a uniform source of
moist air masses derived through the North Atlantic Ocean by the westerlies throughout
the year. Overall, the d-excess pattern with the winter highs and the summer lows is
expected for precipitation recorded in the northern hemisphere (Froehlich et al. 2002).
12
Figure 4. Covariation of the monthly δO-18 (red) and δD (blue) values in precipitation
and the monthly mean surface temperature. The equations of the lines are given in the
graph.
3.2 Local meteoric water line
The isotopic composition of oxygen and hydrogen in monthly precipitation samples was
used as initial data to determine the local meteoric water line (LMWL) for the Olkiluoto
area. Ordinary linear regression analysis was conducted on 35 precipitation samples and
the results and regression parameters are listed in Table 2. The regression for all
precipitation data yielded the slope (a) of 7.29 and the y-intercept (b) of 2.01. The result
is very close to the regression model defined for the precipitation in the Espoo station
where the slope and the intercept were 7.56 and 4.71, respectively (Kortelainen 2007).
The regression model gives a good fit to the Olkiluoto data as the squared multiple
correlation coefficient (R2) of 0.97 approaches 1 (perfect fit) and the high significance
of the slope (p-value of 0.000) are recorded. In Table 2 the standard error (SE) and the
95% confidence intervals for the defined slope and y-intercept are also given.
The meteoric water line specific to a certain location is controlled by local climatic
factors including the oceanic moisture source and secondary processes affecting the
isotopic composition of water vapour such as evaporation and re-circulation of moisture
from large water bodies (Clark & Fritz 1997). These factors together define the
particular LMWL. The LMWL established for the Olkiluoto area is defined as:
D = 7.29 δO-18 + 2.01‰
(4)
13
In Figure 5, the spread of δO-18 and D values in monthly precipitation is presented
against the developed LMWL. 95% confidence limits (dashed lines) of the data are
illustrated with the LMWL. The GMWL (Equation 1) is also shown for comparison.
The local line is recommended to be used whenever any isotopic data of oxygen and
hydrogen from Olkiluoto waters is reviewed.
Table 2. Linear regression results for precipitation samples of Olkiluoto.
Linear regression parameters for δD = a δO-18 + b
Regression
model
Unstandardized Std. Error 95% Confidence Interval
Lower bound Upper bound
Significance
Correlation
p-value
coefficient, R2
0.972
Coefficients
SE
Slope, a
7.29
0.214
6.854
7.726
0.000
Y-intercept, b
2.012
2.625
-3.328
7.352
0.449
Figure 5. Monthly δO-18 and δD values of precipitation. The local meteoric water line
(LMWL) defined by the rainfall data is illustrated with thick blue line. 95% confidence
limits (blue dashed lines) of the data are illustrated with the LMWL. The GMWL (gray
dotted line) is also shown for comparison.
14
3.3 Groundwater
The seasonal variations in the isotopic composition of oxygen and hydrogen in shallow
groundwater of the Olkiluoto area are barely detectable. Three-year mean δO-18, D
and H-3 values with 2 standard deviations (2σ in brackets) for groundwater in the
monitoring well PVP14 were -11.28(0.14)‰, -80.0(2.3)‰ and 9.8(3.1) TU,
respectively. The corresponding values for the well PVP4a were -11.34(0.15)‰ for
oxygen, -80.8(2.3)‰ for hydrogen and 10.0(1.0) TU for tritium. The combined threeyear averages of δO-18, D and H-3 for the shallow groundwaters are -11.31(0.16)‰
(n=38), -80.4(2.4)‰ (n=38) and 9.9(2.2) TU (n=35), respectively. The mean isotopic
composition of oxygen and hydrogen in groundwater plots directly on the Olkiluoto
LMWL as illustrated in the δO-18 – D –diagram of Figure 6. For comparison, another
mean isotopic composition for none-evaporated waters was also calculated using the
isotope dataset analysed from the Olkiluoto waters during 2005–2008 (a study ordered
by TVO). Here, the water samples showing the common d-excess values of 9–11‰ for
groundwaters in southern Finland were included (Kortelainen & Karhu 2004;
Kortelainen 2007). The obtained δO-18 and D values and the standard deviations (2σ)
are -11.42(0.94)‰ (n=176) and -81.6(7.4)‰ (n=176), respectively (Fig. 6). This agrees
with the isotopic composition of groundwater observed in this study. The isotope ratios
determined in Olkiluoto are typical for the groundwaters of this area in Finland
(Kortelainen & Karhu 2004).
Figure 6. Comparison of monthly δO-18 and δD values of precipitation to the weighted
three-year monthly and annual δ values. The mean δO-18 and δD values in
groundwater monitored in this study (yellow) and those analysed for TVO (light blue)
are also presented. The data are shown with reference to Olkiluoto LMWL.
15
3.4 Comparison of groundwater and mean precipitation
Groundwater is formed from the local atmospheric precipitation. The attenuation of the
strong seasonal isotopic variations seen in monthly precipitation is the most distinctive
feature in the formation of groundwater. A significant proportion of the total variations
is smoothed out when considering the weighted isotope values of monthly rainfall as
illustrated in Figure 6. In temperate climates the isotopic composition of groundwater is
generally close to that of the mean annual precipitation in a particular location (e.g.
Rozanski 1984, 1985; Darling 2004; Kortelainen & Karhu 2004; Kortelainen 2007). A
comparison between the isotopic records of precipitation and groundwater in Olkiluoto
is presented in Table 3. Here, the groundwater is slightly more enriched in O-18
(0.84‰) and D (6.4‰) in comparison to the respective values of precipitation, which
clearly appears in the δO-18 – D graph of Figure 6. This suggests a possible seasonal
bias in recharge of Olkiluoto groundwater. A closer look to the three-year weighted
monthly δ values in Figure 7 reveals that the isotopic composition of groundwater is
slightly shifted towards that of the precipitation received during the months of May–Jul,
Sep and Dec. The three-year precipitation monitoring period is, however, fairly short,
and the difference has to be examined with caution as it may as well reflect short-term
changes in groundwater recharge. The H-3 content of precipitation is practically the
same as that of groundwater.
Table 3. Comparison of the weighted mean annual δD, δO-18 and H-3 values of
precipitation with the isotopic composition of local groundwaters. Standard deviations
(2σ) of the rainfall data are derived from the monthly records.
Water type
δD (‰ vs. VSMOW)
Mean Stdev, 2σ n
δO-18 (‰ vs. VSMOW)
Mean Stdev, 2σ n
H-3 (TU)
Mean Stdev, 2σ
n
Precipitation
-86.8
32.2
35
-12.15
4.36
35
10.2
5.8
30
Groundwater (this study)
-80.4
2.4
38
-11.31
0.16
38
9.9
2.2
35
Groundwater (TVO)
-81.6
7.4
176
-11.42
0.94
176
-
-
-
16
Figure 7. The weighted three-year monthly δO-18 and δD values of precipitation.
Monthly data is compared to the mean δO-18 and δD values in groundwater and the
weighted mean annual δ values of precipitation. The data are shown with reference to
Olkiluoto LMWL.
The seasonal variations recorded in isotopic composition of atmospheric precipitation
are generally attenuated when a “critical depth” of a certain aquifer is attained (Clark &
Fritz 1997). This means that the isotopic variation in groundwater is less than the 2σ
error of the isotopic analyses of oxygen, which in this case is 0.2‰. In Olkiluoto
shallow groundwaters monitored in this study, the groundwater table varies
approximately between 1–5 m, and the definition of the critical depth is filled because
the variation observed in the δO-18 values of groundwater is as low as 0.16‰ (Table 3).
In spite of this, especially the highest and the lowest seasonal isotope signals
determined in precipitation are distinguishable in groundwater, however, as delayed.
The phenomenon is illustrated in Figure 8, and it suggests that groundwater is
cumulated from atmospheric precipitation throughout the year.
17
Figure 8. Comparison of the monthly H-3 content (above) and the δO-18 values (below)
of precipitation and shallow groundwater. The long-term mean H-3 and δO-18 values
of groundwater are illustrated with black dashed line and arrow. The variation of the
δO-18 in precipitation is also illustrated as smoothed trend curve, as three-month
moving average (gray dotted curve). The variation of δO-18 in groundwater is shown in
the vertical axel on the right hand side. It should be paid attention that the scale of the
δO-18 groundwater axel is only one twelfth out of that of precipitation.
18
4
SUMMARY
The coastal location of the study area is reflected in the isotopic composition of oxygen
and hydrogen in the precipitation at Olkiluoto. The proximity of the Baltic Sea
attenuates local surface temperatures and plays a role as a secondary vapour source.
This is characterized by fairly poor temporal correlation between the monthly δ values
and surface temperatures and the low seasonal isotopic variation in the long-term
weighted monthly isotope ratios of oxygen and hydrogen. The highest δO-18, D and
H-3 values are generally measured during warm periods and low ones during cold
seasons. This seasonal behaviour of tritium concentrations in Olkiluoto precipitation
follows a typical H-3 pattern observed in the northern hemisphere and, hence, gives no
reason to suggest any significant input of tritium from the nuclear power plant during
this monitoring period.
This study generated the basic isotopic tools to be used as background information for
further hydrological studies in the Olkiluoto area. This comprises the long-term (threeyear) weighted mean annual isotopic composition of precipitation and the local meteoric
water line (LMWL). Based on the three years' monitoring of precipitation the weighted
annual mean δO-18 value is -12.15‰ and D value is -86.8‰. The respective annual
reference value for the tritium content is 10.4 TU. For developing the LMWL, an
ordinary linear regression analysis was completed for all precipitation samples. This
yielded a specific slope and y-intercept for the Olkiluoto precipitation data and the
LMWL for the Olkiluoto area could be formulated as (Equation 4):
D = 7.29 δO-18 + 2.01‰
The local meteoric water line is recommended to be used as a reference line whenever
any isotopic data of oxygen and hydrogen from Olkiluoto waters is examined.
The mean isotopic composition determined in Olkiluoto shallow groundwater gives the
δO-18, D and H-3 values of -11.31‰, -80.4‰ and 9.9 TU, respectively. The isotope
ratio of oxygen and hydrogen in groundwater plots directly on the Olkiluoto local
meteoric water line. Reviewing the weighted annual δ values in precipitation and
groundwater reveals that during this monitoring period the groundwater is slightly more
enriched in O-18 (0.84‰) and D (6.4‰) compared to the respective values in
precipitation. This suggests a possible seasonal bias in recharge of Olkiluoto
groundwater, however, short-term effects in groundwater recharge are also possible.
The H-3 content of rainfall closely agrees with that of groundwater. In general, the
isotope signatures of atmospheric precipitation and groundwater at Olkiluoto are close
to unity and represent typical values reported for the waters of this area in Finland.
The seasonal variations in the isotopic composition of oxygen and hydrogen in shallow
groundwater of the Olkiluoto area are barely detectable. In spite of this, especially the
highest and the lowest seasonal isotope signals determined in precipitation are
distinguishable in groundwater, which suggests that groundwater recharge is taking
place throughout the year.
19
4.1. Recommendations for future studies
Isotopic composition of oxygen and hydrogen in local precipitation is a key parameter
in modelling of local water circulation. It is also the first factor recording possible
changes in global production of atmospheric moisture powered by climatic regimes.
Therefore, permanent or further extended isotope monitoring of precipitation is highly
recommended in such a detailed hydrological research program, which is presently run
by Posiva Oy in the Olkiluoto area.
It seems that the influence of the Baltic Sea is notable regarding the isotope signature of
precipitation at Olkiluoto. In order to make reliable evaluations concerning the input of
secondary moisture sources into the primary Atlantic moisture arriving to the Finnish
coast, more hydrological and meteorological background data and a longer period of
isotope monitoring of local rainfall are needed.
20
REFERENCES
Alalammi, P. (ed.) 1987. Atlas of Finland, Folio 131, Climate. Helsinki: National Board
of Survey and Geographical Society of Finland. 31 p.
Clark, I. & Fritz, P. 1997. Environmental Isotopes in Hydrogeology. Boca Raton, FL:
Lewis Publishers. 328 p.
Coleman, M. L., Shepherd, T. J., Durham, J. J., Rouse, J. E. & Moore, G. R. 1982.
Reduction of water with zinc for hydrogen isotope analysis. Analytical Chemistry 54
(6), 993–995.
Coplen, T. B. 1994. Reporting of stable hydrogen, carbon and oxygen isotopic
abundances. Pure & Applied Chemistry 66, 273–276.
Craig, H. 1961. Isotopic variations in meteoric water. Science 133, 1702.
Craig, H. & Gordon, L. I. 1965. Deuterium and oxygen-18 variation in the ocean and
the marine atmosphere. In: Tongiorgi (ed.) Stable Isotopes in Oceanographic Studies
and Paleotemperatures. Pisa, Italy, 9–130.
Dansgaard, W. 1964. Stable isotopes in precipitation. Tellus 16, 436–468.
Darling, W. G. 2004. Hydrological factors in the interpretation of stable isotopic proxy
data present and past: a European perspective. Quartenary Science Reviews 23, 743–
770.
Epstein, S. & Mayeda, T. 1953. Variation of 18O content of waters from natural sources.
Geochimica et Cosmochimica Acta 4, 213–224.
Faure, G. & Mensing, T. M. 2005. Isotopes: principles and applications, 3rd ed. U.S.A.:
John Wiley & Sons. 897 p.
Froehlich, K., Gibson, J. J. & Aggarwal, P. 2002. Deuterium excess in precipitation and
its climatological significance. In: Study of environmental change using isotope
techniques. Vienna: International Atomic Energy Agency, C&S Papers Series 13/P, 54–
65.
Gat, J. R., Mook, W. G. & Meijer, A. J. 2001. Environmental isotopes in the
hydrological cycle. Principles and applications. In: Mook, W. G. (ed.) IHP-V, Technical
Documents in Hydrology, No. 39, Vol. II: Atmospheric water. Paris: UNESCO. 113 p.
Gonfiantini, R. 1986. Environmental isotopes in lake studies. In: Fritz, P. & Fontes, J.
Ch. (eds.) Handbook of Environmental Isotope Geochemistry, The Terrestrial
Environment, B, Vol. 2. Amsterdam: Elsevier, 113–168.
IAEA/WMO 2006. Global Network of Isotopes in Precipitation. Technical procedure
for sampling. Accessible at http://isohis.iaea.org/userupdate%5Csampling.pdf.
21
Ikonen, A.T.K. 2007. Meteorological data and update of climate statistics of Olkiluoto
2005-2006. Posiva Oy, Working Report 2007-86, 72 p.
Karhu, J. A. 1997. Catalytical reduction of water to hydrogen for isotopic analysis using
zinc containing traces of sodium. Analytical Chemistry 69, 4728–4730.
Kortelainen, Nina 2007. Isotopic fingerprints in surficial waters: stable isotope methods
applied in hydrogeological studies. Espoo, Geological Survey of Finland 41, 55 p.
Kortelainen, N. M. & Karhu, J. A. 2004. Regional and seasonal trends in the oxygen
and hydrogen isotope ratios of Finnish groundwaters: a key for mean annual
precipitation. Journal of Hydrology 285, 143–157.
Lucas, L. L. & Unterweger, M. P. 2000. Comprehensive review and critical evaluation
of the half-life of tritium. Journal of Research of the National Institute of Standards and
Technology 105, 541–549.
Meijer, H. A. J., van der Plicht, J., Gislefoss, J. S. & Nydal, R. 1995. Comparing longterm atmospheric 14C and 3H records near Groningen, The Netherlands with Fruholmen,
Norway and Izaña, Canary Islands 14C stations. Radiocarbon 37 (1), 39–50.
Merlivat, L. & Jouzel, J. 1979. Global climatic interpretation of the deuterium-oxygen
18 relationship for precipitation. Journal of Geophysical Research 84 (C8), 5029–5033.
Pitkänen, P., Snellman, M. and Vuorinen, U. 1996. On the origin and chemical
evolution of groundwater at the Olkiluoto site. Posiva Oy, Helsinki, Report POSIVA
1996-04, 41 p.
Pitkänen, P., Luukkonen, A., Ruotsalainen, P., Leino-Forsman, H. and Vuorinen, U.
1999. Geochemical modelling of groundwater evolution and residence time at the
Olkiluoto site. Posiva Oy, Helsinki, Report POSIVA 1998-10, 184 p.
Rozanski, K. 1985. Deuterium and oxygen-18 in European groundwaters – links to
atmospheric circulation in the past. Chemical Geology 52, 349–363.
Rozanski, K. 1984. Temporal and spatial variations of deuterium and oxygen-18 in
European precipitation and groundwaters. ZFI-Mitteilungen 85 (2), 341–353.
Rozanski, K., Araguás-Araguás, L. & Gonfiantini, R. 1993. Isotopic patterns in modern
global precipitation. In: Climate change in continental isotopic records. American
Geophysical Union, Geophysical monograph 78, 1–3
APPENDIX 1. Monthly isotopic data of precipitation
SI-LabID
Sample code
Sampling
δD
δO-18
‰ vs. VSMOW
d-
month
date
excess
Jan-05
Feb-05
Mar-05
Apr-05
May-05
Jun-05
Jul-05
Aug-05
Sep-05
Oct-05
Nov-05
Dec-05
Jan-06
Feb-06
Mar-06
Apr-06
May-06
Jun-06
Jul-06
Aug-06
Sep-06
Oct-06
Nov-06
Dec-06
07/02/2005
03/03/2005
03/05/2005
01/06/2005
30/06/2005
29/07/2005
31/08/2005
30/09/2005
01/11/2005
05/12/2005
27/12/2005
03/02/2006
03/03/2006
03/04/2006
03/05/2006
01/06/2006
30/06/2006
31/07/2006
31/08/2006
29/09/2006
31/10/2006
30/11/2006
02/01/2007
-86.2
-97.4
n.d. $
-74.5
-43.6
-84.8
-86.7
-81.8
-53.7
-99.8
-89.1
-93.5
-97.4
-119.5
-91.3
-100
-86.7
-67.9
-48.1
-94.7
-96.5
-90.3
-96
-78.9
-12.40
-13.32
n.d.
-10.78
-6.26
-11.43
-11.84
-11.46
-8.04
-14.05
-12.63
-13.35
-13.13
-16.65
-14.1
-13.93
-12.09
-9.23
-6.86
-12.91
-13.37
-12.52
-13.28
-11.01
13.0
9.2
n.d.
11.7
6.5
6.6
8.0
9.9
10.6
12.6
11.9
13.3
7.6
13.7
21.5
11.4
10.0
5.9
6.8
8.6
10.5
9.9
10.2
9.2
Jun-07
Jul-07
Aug-07
Sep-07
Oct-07
Nov-07
Dec-07
Jan-08
Feb-08
Mar-08
Apr-08
May-08
29/06/2007
30/07/2007
28/08/2007
01/10/2007
01/11/2007
30/11/2007
02/01/2008
01/02/2008
06/03/2008
01/04/2008
05/05/2008
03/06/2008
-78.2
-69.5
-100.5
-67.8
-85.9
-106.6
-81.2
-98.6
-97.8
-99.5
-85.6
-76.9
-10.85
-9.63
-13.91
-10.25
-12.14
-15.18
-11.18
-13.35
-13.51
-13.92
-11.95
-11.57
8.6
7.5
10.8
14.2
11.2
14.8
8.2
8.2
10.3
11.9
10.0
15.7
H-3 &
H-3
Bq/kg (1σ)%
1.6
1.1
n.d.
1.5
1.8
1.7
1.0
2.0
1.3
<1.0
<1.0
<1.0
¤
7
7
n.d.
7
9
9
8
9
10
¤)
Analytical uncertainty; &) H-3 analysed in STUK; #) meteorological data provided by Posiva; £) inaccurate measurement;
$)
n.d. = no data; !) <__ = the result below detection limit.
TU
13.3
9.2
n.d.
13.1
15.0
14.3
8.5
16.9
11.3
<8.5
<8.5
<8.5
8.6
7.7
n.d.
8.4
11.0
12.8
11.9
14.8
10.4
8.4
6.8
6.8
14.9
15.3
12.1
9.3
7.8
8.8
8.3
7.6
9.9
9.6
11.7
n.d.
Prec #
Prec
+/- TU
mm
mm
Temp # Humidity #
°C
%
0.25
0.25
n.d.
0.25
0.2
0.2
0.35
0.2
0.2
0.2
0.2
0.2
75.8
24.5
3.7 £
22.6
19.8
50.8
74.8
138.3
52.2
43.7
112.9
22.3
21.7
10.0
9.8
71.0
74.8
23.7
9.9
35.3
57.8
122.7
69.8
121.6
66.2
29.4
3.6
19.2
30.3
59.8
68.6
155
50.6
52.8
94.9
21.2
17.4
8.6
18.8
57.5
67.4
22.3
9.8
31.6
70.6
131.9
67.6
94.8
-0.5
-3.6
-4.5
3.9
8.7
13.3
17.7
16.4
13
8.1
4.3
-2.3
-3
-5.9
-5.7
3.7
9.2
14.4
18.4
19
14.4
8.1
3.3
4.5
90.6
84.5
73.8
74.9
74.6
75
77.8
80
80.3
85.7
92.8
87.9
88
87.7
81.3
75.5
73.1
72.3
66.7
72.3
83.8
87.7
90.9
88.1
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
n.d.
24.7
71.2
77.6
88.9
88.9
72.8
74.0
86.9
38.2
28.6
36.1
8.2
26.6
109
53.7
68.7
77
69.7
62.5
76.6
37.8
34.5
36.4
8.6
14.6
16.6
17.4
11.6
8.2
1.6
2.4
0.4
1
0.3
5.1
9.3
68.9
82.5
78.7
80.5
85.2
88.2
93
87
89.1
79.6
80.9
70.6
22
W-3065
OLKISA0501
W-3135
OLKISA0502
W-3165
OLKISA0504
W-3277
OLKISA0505
W-3278
OLKISA0506
W-3279
OLKISA0507
W-3280
OLKISA0508
W-3382
OLKISA0509
W-3383
OLKISA0510
W-3436
OLKISA0511
W-3437
OLKISA0512
W-3482
OLKISA0601
W-3483
OLKISA0602
W-3577
OLKISA0603
W-3578
OLKISA0604.2
W-3622
OLKISA0605
W-3623
OLKISA0606
W-3682
OLKISA0607
W-3683
OLKISA0608
W-3754
OLKISA0609
W-3755
OLKISA0610
W-3766
OLKISA0611
W-3795
OLKISA0612
Missing Jan-May 2007
W-3966
OLKISA0706
W-3968
OLKISA0707
W-3985
OLKISA0708
W-4014
OLKISA0709
W-4107
OLKISA0710
W-4119
OLKISA0711.1
W-4147
OLKISA0712
W-4148
OLKISA0801
W-4252
OLKISA0802
W-4253
OLKISA0803
W-4254
OLKISA0804
W-4255
OLKISA0805
Collecting
APPENDIX 2. Isotopic data of groundwater.
SI-LabID
Sample code
Site
Month
Sampling
date
#)
δO-18
‰ vs. VSMOW
dexcess
Jan-05
Jan-05
Mar-05
Mar-05
Apr-05
Apr-05
Jun-05
Jun-05
Aug-05
Aug-05
Nov-05
Nov-05
Jan-06
Jan-06
Apr-06
Apr-06
Jun-06
Jun-06
Aug-06
Aug-06
Oct-06
Oct-06
Nov-06
Nov-06
31/01/2005
31/01/2005
24/03/2005
08/03/2005
19/04/2005
19/04/2005
27/06/2005
27/06/2005
31/08/2005
31/08/2005
02/11/2005
02/11/2005
13/01/2006
14/01/2006
27/04/2006
26/04/2006
20/06/2006
20/06/2006
29/08/2006
29/08/2006
25/10/2006
25/10/2006
15/11/2006
15/11/2006
-81.2
-78.1
-82.1
-80.3
-81.6
-80.2
-82.1
-82.4
-81.7
-79.9
-82.7
-82.3
-81.2
-80.0
-81.4
-81.7
-80.6
-79.9
-79.3
-79.2
-79.4
-79.4
-77.9
-80.3
-11.33
-11.26
-11.30
-11.28
-11.25
-11.23
-11.27
-11.27
-11.48
-11.28
-11.34
-11.32
-11.25
-11.21
-11.50
-11.40
-11.36
-11.42
-11.36
-11.21
-11.34
-11.26
-11.34
-11.35
9.4
12.0
8.3
9.9
8.4
9.6
8.1
7.8
10.1
10.3
8.0
8.3
8.8
9.7
10.6
9.5
10.3
11.5
11.6
10.5
11.3
10.7
12.8
10.5
Jun-07
Jun-07
Aug-07
Aug-07
Oct-07
Oct-07
Nov-07
Nov-07
Feb-08
Feb-08
Apr-08
Apr-08
Jun-08
Jun-08
14/06/2007
14/06/2007
10/08/2007
10/08/2007
03/10/2007
03/10/2007
22/11/2007
22/11/2007
22/02/2008
22/02/2008
16/04/2008
17/04/2008
25/06/2008
25/06/2008
-81.3
-80.6
-79.5
-79.2
-81.2
-79.2
-80.4
-79.0
-80.4
-78.8
-80.6
-79.7
-80.3
-80.0
-11.37
-11.24
-11.41
-11.39
-11.44
-11.27
-11.26
-11.16
-11.29
-11.21
-11.35
-11.30
-11.25
-11.21
9.7
9.3
11.8
11.9
10.3
11.0
9.7
10.3
9.9
10.9
10.2
10.7
9.7
9.7
H-3 analysed in STUK; ¤) analytical uncertainty; !) <__ = the result below detection limit.
H-3 #
Bq/kg
1.3
1.7
1.3
1.0
1.1
1.1
1.2
1.2
1.1
1.5
1.2
<1.0 !
<1.0
<1.0
H-3
(1σ)%¤
7
7
7
7
7
7
10
10
10
9
10
TU
+/- TU
10.9
14.4
11.2
8.6
9.1
9.2
9.8
10.1
9.7
13.0
10.5
<8.5
<8.5
<8.5
10.0
9.8
9.7
9.6
10.1
9.6
10.4
9.6
9.9
8.6
0.25
0.25
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
9.9
9.8
9.7
9.0
10.1
8.9
9.9
9.3
9.9
9.5
9.8
9.1
9.4
9.4
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
23
W-3063
OLKI0501
PVP4a
W-3064
OLKI0502
PVP14
W-3133
OLKI0503
PVP4a
W-3134
OLKI0504
PVP14
W-3163
OLKI0505
PVP4a
W-3164
OLKI0506
PVP14
W-3273
OLKI0507
PVP4a
W-3274
OLKI0508
PVP14
W-3275
OLKI0509
PVP4a
W-3276
OLKI0510
PVP14
W-3380
OLKI0511
PVP4a
W-3381
OLKI0512
PVP14
W-3434
OLKI0601
PVP4a
W-3435
OLKI0602
PVP14
W-3579
OLKI0603
PVP4a
W-3580
OLKI0604
PVP14
W-3620
OLKI0605
PVP4a
W-3621
OLKI0606
PVP14
W-3680
OLKI0607
PVP4a
W-3681
OLKI0608
PVP14
W-3752
OLKI0609
PVP4a
W-3753
OLKI0610
PVP14
W-3767
OLKI0611
PVP4a
W-3768
OLKI0612
PVP14
Break in sampling during Jan-May 2007
W-3961
OLKI0701
PVP4a
W-3962
OLKI0702
PVP14
W-3982
OLKI0703
PVP4A
W-3983
OLKI0704
PVP14
W-4015
OLKI0705
PVP4a
W-4016
OLKI0706
PVP14
W-4108
OLKI0707
PVP4a
W-4109
OLKI0708
PVP14
W-4149
OLKI0801
PVP4a
W-4150
OLKI0802
PVP14
W-4257
OLKI0803
PVP4a
W-4258
OLKI0804
PVP14
W-4259
OLKI0805
PVP4a
W-4260
OLKI0806
PVP14
δD