THE GLOBAL DISTRIBUTION OF
IODINE-129 AND ITS POTENTIAL
APPLICATION AS AN AGE TRACER
IN THE TUCSON BASIN
By: Claire Tritz
_______________
A Thesis Submitted to The Honors College
In Partial Fulfillment of the Bachelors Degree With Honors in
Environmental Hydrology
The University of Arizona
May 2016
Approved by:
_________________________________________
Dr. Jennifer McIntosh
Department of Hydrology and Water Resources
2
Abstract
Radiogenic tracers help determine groundwater recharge rates and flow paths. Decreasing
environmental tritium concentrations necessitate the use of a new radiogenic tracer. Iodine-129
(129I), a long-lived radioisotope generated by nuclear weapons and fuel reprocessing, offers a
potential alternative. This study compared the isotopic ratio of 129I to stable 127I with ages
previously calculated with tritium. A strong logarithmic correlation was found between the
tritium ages and the isotopic ratio. Values from Sabino Canyon and Marshall Gulch precipitation
and surface water were compared to global values from published research and in both cases
isotopic ratios in precipitation were higher than for surface water, which were higher than ocean
or groundwater. The Arizona samples show a seasonal variation in isotopic ratio between
summer monsoon and winter frontal precipitation, with values significantly higher in the
summer. Mixing model analysis performed on Marshall Gulch surface water and using deep
groundwater, precipitation, and soil water as end members, showed a shift in sulfate
concentration between these seasons that mimics the variation in isotopic ratio. However, the
difference in precipitation source between the summer monsoon and winter frontal precipitation
may be a factor in the variations.
3
Table of Contents
Introduction ……………………………………………………………………………………… 3
Literature Review ………………………………………………………………………………... 4
Tritium……………………………………………………………………………….……4
Iodine-129: Background…………………………………………………………………..4
Iodine-129 in the atmosphere and hydrosphere……………………………………….......5
Case study: Iodine-129 in the Orange County Aquifer System…………………………...7
Iodine-129 in the biosphere……………………………………………………………….7
Hydrology of the Tucson Basin…………………………………………………………...8
Additional research…………………………………………………………………….….9
Site Description……………………………………………………………………………………9
Methods…………………………………………………………………………………………..11
Results and Discussion..…………………………………………………………………………12
Conclusions………………..……………………………………………………………………..20
References………………………………………………………………………………………..20
Appendix 1……………………………………………………………………………………….22
Introduction
Radiogenic isotopes are one of the most common ways to date groundwater. Dating
groundwater is important for determining recharge rates and flow paths of groundwater, an
important source of water for many people. Since the era of above-ground nuclear testing,
tritium has been the standard isotope for dating recent groundwater. Tritium (3H), a radioactive
isotope of hydrogen, entered groundwater via thermonuclear testing. Since the United States
(U.S.) and the Soviet Union stopped above-ground nuclear weapons testing in 1963 very little
new anthropogenic tritium has entered the hydrosphere. The short half-life of tritium (12.43
years) means that concentrations in groundwater are now close to natural background levels. In
fact, by around 1990 most anthropogenic tritium had been washed from the atmosphere and
entered the two largest tritium reservoirs, the ocean and groundwater, where radioactive decay
reduces its concentration by approximately 5.5% per year. As such, there is a need to find a new
radiogenic isotope to use instead of tritium. Iodine-129 (129I) is a long-lived isotope that is
released not only by nuclear weapons, but by the reprocessing of nuclear fuel from power plants
as well. The goals of this study are twofold: determine the feasibility of using the isotopic ratio
of 129I to 127I as a means of dating groundwater in the Tucson Basin, and trace the path of 129I
from the atmosphere, to precipitation, and then to surface and groundwater.
4
Literature Review
Tritium
Tritium (3H), a radioactive isotope of hydrogen, entered groundwater in such large amounts from
thermonuclear testing that its concentration dwarfed that of naturally-produced tritium. Since the
United States (U.S.) and the Soviet Union stopped above-ground nuclear weapons testing in
1963 very little new anthropogenic tritium has entered the hydrosphere. The half-life of tritium
is only 12.43 years; consequently, the concentration of tritium in groundwater is slowly returning
to natural background levels (Clark and Fritz, 1997). In fact, by around 1990 most
anthropogenic tritium had been washed from the atmosphere and entered the two largest tritium
reservoirs, the ocean and groundwater, where radioactive decay reduces its concentration by
approximately 5.5% per year. The result of this continual radioactive decay and limited tritium
input means that the tritium concentrations of soil water in the vadose zone can no longer be
related to the tritium concentrations of modern rainfall. These concentrations only correlate
today in areas with low infiltration rates or thick vadose zones since in those areas the water was
recharged when tritium concentrations in precipitation were higher and haven’t yet been
completely flushed by newer, tritium-low rainfall (Clark and Fritz, 1997).
Iodine-129: Background
As a consequence of such significantly reduced tritium concentrations there is a need to find a
new method of dating recent groundwater, since soon those concentrations will be either below
detectable limits or back to natural background levels. One possible replacement tracer is the
only long-lived radioisotope of iodine, 129I. Although 129I is produced naturally, now almost all
129
I found in the environment is due to releases from both nuclear weapons testing and the
reprocessing of nuclear fuels from nuclear power plants. The continual release of 129I from
nuclear fuel reprocessing means that current concentrations of 129I are now at least two orders of
magnitude greater than natural background levels (Hou et al., 2009). Additionally, the half-life
of 129I is 15.7 million years, which means its concentrations in the hydrosphere won’t diminish as
fast as those of tritium (Hou et al., 2009).
While today the most common anthropogenic 129I comes from material released from nuclear
fuel reprocessing plants, previously moderate amounts came from weapons testing. Nuclear
weapons testing from 1945 to 1975 resulted in the release of approximately 57 kilograms (kg) of
129
I into the atmosphere. On the other hand, nuclear power plants produce around 7.3 milligrams
of 129I for every megawatt-day (MWd) of energy produced (Hou et al., 2009). For comparison,
in 2011 the world’s nuclear power plants generated around 104.9 million MWd of electricity,
which produced about 766 kg of 129I (World Nuclear Association, 2013). A large portion of this
129
I, however, is in storage and pending processing and therefore hasn’t been released into either
the atmosphere or the hydrosphere. Regarding the spent nuclear fuel that has been processed, the
two largest fuel reprocessing plants in the world, La Hague in France and Sellafield in the UK,
are responsible for releasing a total of 5200 kg of 129I into the oceans and 255 kg into the
atmosphere since they opened in 1976 and 1950, respectively. Other, smaller reprocessing
plants, such as the Marcoule in France, Hanford in the U.S., Tokai in Japan, and Karlsruhe in
Germany have released lower amounts of 129I. Nuclear accidents have also released measureable
quantities of 129I: for example, the Chernobyl accident released an estimated 1.3-6 kg of 129I
(Hou et al., 2009).
5
Natural 129I originates from two different processes: the spontaneous fission of uranium-238 and
the splitting of xenon in the atmosphere due to cosmic rays (Schwehr et al., 2004). In
comparison to anthropogenic releases, the total amount of natural 129I in the world before the
nuclear era was probably only around 80 kg in total (Moran et al., 1997).
Iodine-129 in the atmosphere and hydrosphere
Iodine-129 concentrations are commonly expressed in terms of the isotopic ratio, the ratio of 129I
to stable iodine, iodine-127, abbreviated as 129I/127I. The accepted representative isotopic ratio
for the hydrosphere as a whole for the pre-nuclear era is 1.15x10-12 (Osterc et al., 2011). In areas
closer to point sources of contamination, usually individual reprocessing plants, this ratio is
much higher. For example, the 129I/127I ratio of the Irish, North, and Nordic Seas, as well as for
the English Channel, has risen to between 10-8 and 10-5 due to releases from the Sellafield and La
Hague reprocessing plants. Areas within 50 kilometers of a reprocessing plant have seen the
isotopic ratio of ocean water rise to between 10-6 and 10-3 (Hou et al., 2009). For terrestrial
rather than oceanic samples, the isotopic ratio is between 10-9 and 10-7, rising to up to 10-4 near
reprocessing plants (Osterc et al., 2011).
However, the above ratios represent a global average and the amount of 129I in the atmosphere
and the ocean departs from these values depending on location. The highest isotopic ratios are
found at the mid-latitudes of the northern hemisphere, mostly because almost all current, and
previously operational, reprocessing plants are in the northern hemisphere. Transport of
anthropogenic 129I in the atmosphere (mainly the troposphere) has resulted in another, although
smaller, peak in the isotopic ratio around the mid-latitudes of the southern hemisphere, while
equatorial regions have a lower isotopic ratio (Snyder and Fehn, 2004). One estimate is that the
northern hemisphere’s atmosphere contains between 10 and 100 times more 129I than the
atmosphere over the southern hemisphere. Even more drastic is that the atmosphere over
Europe, because of the operation of La Hague and Sellafield, potentially contains 1000 times
more 129I than the North American atmosphere (Aldahan et al., 2009). Despite these differences
in the isotopic ratio, it is worth noting that all areas of the planet, including the Antarctic and the
Arctic have seen increases in the isotopic ratio due to human activities (Snyder et al., 2004).
Once 129I enters the atmosphere, it has to potential to enter the hydrosphere, often through
precipitation events. Atmospheric 129I dissolves into precipitation and then enters surface waters
via both wet and dry deposition (Snyder et al., 2004). The measured ratio of stable iodine, 127I,
between precipitation and the ocean is 1/50. Since 129I and 127I have similar chemical properties,
this should also be the ratio of 129I in precipitation to that in the oceans. As previously stated,
these ratios are global averages, so by definition the ratio of 129I in precipitation to the oceans
will be higher in some places and lower in others. As expected, then, places closer to discharge
from reprocessing plants will have higher measured 129I concentrations in the precipitation than
predicted using measured oceanic values (Aldahan et al., 2009). Previously, few studies have
been performed on the distribution of 129I in precipitation. However, the Fukushima Nuclear
Accident in March, 2011 created opportunities for the study of the transport of 129I. In the region
of Japan near the Fukushima Power Station, the natural background isotopic ratio is 10-12, which
is similar to the global average of 1.15 x 10-12 (Xu et al., 2013 and Osterc et al., 2011). After the
accident, this ratio in precipitation rose from 2 x 10-7 to 7 x 10-5 (Xu et al., 2013). An
anthropogenic tracer needs to have a clear input curve, which documents a local release of the
6
tracer into the atmosphere. The Fukushima disaster also provided an opportunity to see if 129I
can be traced from its source, to the atmosphere, then to precipitation. Precipitation
concentrations of 129I were measured for 2 years after the accident, and showed both a clear
increase and decrease, along with several concentration peaks that are attributed to extra
injections of iodine into the atmosphere.
After 129I enters precipitation, it then enters surface waters. In North America, the average
isotopic ratio for rainwater is 3.8x10-9, while for rivers that ratio varies between 0.1 - 3x10-9
(Schwehr et al., 2005). Using precipitation measurements from the U.S., 2.8x107 atoms/liter, as
representative of the entire northern hemisphere, it can be estimated that approximately 1.5 kg of
129
I are deposited each year, for the past 30 years of nuclear fuel reprocessing, via rainfall
(Moran et al., 1997). Since 129I is emitted to the atmosphere, its behavior is very dependent on
daily variations in emissions, as well as seasonal and yearly variations in air currents and weather
patterns. These changes could easily alter where 129I is deposited and in what amounts, and thus
drastically influence a given region’s input curve (Schwehr et al., 2004). Additionally, the length
of time that 129I remains free in the environment must be considered. Studies after the
Fukushima nuclear disaster suggest an ecological half-life of 19-63 days. In the atmosphere, 129I
can commonly be bound in I2 and CH3I, which are not as soluble in water. As such, 129I is
removed from the atmosphere at slower rates than other anthropogenic radiogenic isotopes,
included a short-lived iodine isotope, 131I (Xu et al., 2013).
The concentration of iodine in surface waters varies depending on the climate. Wetter climates,
with greater rainfall, are lower (3-20 ppm) when compared with the concentrations in drier,
desert climates. The concentration in the Rio Grande River near Las Cruces, New Mexico was
near 80 ppm during times of low flow, while the concentration dropped to 15 ppm during times
of higher flow. The variation caused by climate can be demonstrated by the fact that further
downstream along the Rio Grande, near Brownsville, Texas, the concentration was measured as
around 236 ppm due to high levels of evaporation and high water extraction for irrigation
(Moran et al., 1997). These concentrations are inversely proportional to the isotopic ratio,
meaning that as total iodine concentration in North American surface waters increase, that
addition is attributable mostly to “old, ‘dead’ iodine,” iodine-127, leached from surrounding soils
(Moran et al., 1997). As such, surface waters in drier climates will have lower 129I concentrations
when compared to wetter climates. Figure 1 below briefly illustrates the production and
pathways of 129I in the hydrosphere, biosphere, and atmosphere.
7
Figure 1: The lifecycle and sources of Iodine-129
Case study: Iodine-129 in the Orange County Aquifer System
One of the few studies of 129I in groundwater in the U.S., and possibly globally, was a study on
the behavior of 129I in the Orange County Aquifer System. According to the study, the average
isotopic ratio for the groundwater in the aquifer system is 27x10-11, with a 129I concentration of
4x107 atoms/L. In general, high 129I concentrations and a high isotopic ratio corresponded to
older groundwater. The reverse also generally held true, with younger groundwater having
lower 129I concentrations and isotopic ratio. This pattern was contrary to expectations, which
held that older groundwater should have lower 129I concentrations and a lower isotopic ratio,
since older groundwater would be more thoroughly mixed with pre-nuclear era waters lacking
anthropogenic 129I (Schwehr et al., 2004). Some of these abnormalities may be caused by high
evaporation and transpiration rates inherent to the desert environment, and exacerbated by high
irrigation rates. This phenomenon is also seen in many rivers sampled in the southwestern
U.S. In the Orange County Aquifer System, additional variation from expected isotopic ratios
could be due to the addition of sea spray to the atmosphere, and consequently to the
groundwater. Because almost all 129I added to water sources within the U.S. comes from nonmarine transport of reprocessed nuclear fuel from Europe, the addition of sea spray to the
atmosphere would decrease both the 127I concentration and the isotopic ratio since seawater also
has lower 129I concentrations than the atmosphere (Schwehr et al., 2004).
One of the major finds of the study of the Orange County Aquifer System is that stable iodine, as
well as 129I, behave “conservatively” in the subsurface (Schwehr et al., 2004). An example of
this is two wells whose ages are separated by twenty years, had a four-fold difference in the
isotopic ratio. The older well had the lower isotopic ratio, corresponding to the mid-1970s when
iodine releases were lower. The difference between this lower isotopic ratio and the isotopic
ratio of the well with the more recent water is the same as the difference between the mid-1970s
and the mid-1990s. This also suggests that 129I is transported in the same way as other common
radioactive isotopes, including tritium (Schwehr et al., 2004).
Iodine-129 in the biosphere
Iodine-129 collects not only in the hydrosphere, but in the biosphere as well. As a consequence,
the concentration of 129I and the isotopic ratio can both be measured in various plants and
8
animals. One of the most significant aspects of this is that some plants, including epiphytes like
algae, bromeliads, and orchids, collect and store 129I, thus providing a more long-term measure of
atmospheric 129I concentrations than precipitation measurements (Moran et al., 1997). A study in
Japan has demonstrated that leaves and pine needles serve as an iodine, including 129I, sink;
which can then be washed into the soil. The fact that atmospheric 129I can be transferred to pine
needles suggests that they can be used to accurately monitor 129I concentrations in precipitation.
Seaweed also serves as a 129I sink, containing a higher isotopic ratio than the corresponding
seawater. Seaweed’s isotopic ratio varies from between 10-9 and 10-7, while that of seawater is
closer to 10-9 (Muramatsu et al., 2004). The nuclear fuel reprocessing plant of Hanford, in the
Pacific Northwest of the US, releases 129I into the Columbia River estuary. A study of seaweed
from the Pacific Coast of the U.S. discovered that the isotopic ratio of the Columbia River
averaged to around 2x10-9. The isotopic ratios of the various seaweeds used in the study
correlated to distance from the Columbia River estuary, with seaweeds closer to the estuary, and
therefore Hanford, having higher isotopic ratios (Kilius et al., 1994). Iodine-129 stored in the
biosphere can be released into the atmosphere or hydrosphere. For example, in Japan, additional
peaks of high 129I concentration observed after the initial decline of Fukushima-derived 129I have
been attributed in part to releases from algae in the ocean and rice (Xu et al., 2013)
Hydrology of the Tucson Basin
The hydrogeology of the Tucson basin is very well known, as are the ages of its
groundwater. As such, it is a good place to test the utility of 129I as an environmental tracer. The
Tucson Basin aquifer is an unconfined aquifer that occupies most of the basin. The growth of
the Tucson metropolitan area has resulted in sufficient groundwater pumping to lower
groundwater levels between 30 and 60 meters (Eastoe et al., 2004). One of the major sources of
groundwater in the area is mountain front recharge, with small precipitation events infiltrating
closer to the front of the range. Most of the mountain front recharge most likely occurs during
the winter: studies in the Upper San Pedro River basin suggest that 65% of recharge occurs
during the winter and there is “a distinct seasonal isotopic signature of precipitation” that “allows
inference on recharge seasonality” (Ajami et al., 2012). The oldest water in the shallow regions
of the Tucson Basin comes from portions of the aquifer that run parallel to the Santa Cruz and
other normal faults, which cause upwelling. In addition, groundwater age increases with
increasing distance from major washes, since washes are one of the main areas where
groundwater recharge occurs. However, one anomaly present in the Tucson basin groundwater is
related to the mixing with modern precipitation, which appears to be slow and occurring over
several tritium half-lives (Eastoe et al., 2004). Therefore, rapid pumping of shallow groundwater
would result in introduction of deep groundwater that is not mixed with recent precipitation,
causing possible input differences between isotopic concentrations in precipitation and those of
deep groundwater. These differences, while suggested for tritium, could also potentially apply to
129
I as well.
The limited research on the distribution and behavior of 129I in the atmosphere means that
comparisons will be made to the behavior of tritium in the atmosphere and precipitation,
assuming the behavior of 129I to be similar. A majority of tritium in the atmosphere is present in
the troposphere and at higher latitudes in the northern hemisphere. Globally, and especially in
the northern hemisphere, tritium concentrations in precipitation have a marked seasonal
9
variation, with an increase in concentration in May through July due to the rise of tropopause at
high latitudes (Rozanski et al., 1991).
Additional research
For 129I to be a successful groundwater age tracer, it must satisfy several
characteristics. Currently, it does not. First, 129I needs to trace only one process (in this case,
anthropogenic input via nuclear fuel reprocessing) and it must be correlated to stable iodine
concentrations. In addition, 129I must exhibit conservative behavior within groundwater (Osterc
et al., 2011). This last qualification of 129I may be satisfied if the results from the Orange County
Aquifer System study can be verified (Schwehr et al., 2004).
Unfortunately, there still is a lack of data regarding 129I input curves for specific regions and/or
reservoirs, including the southwestern U.S. As such, 129I input curves, as well as correlations
between 129I and stable iodine, possibly in the form of the isotopic ratio, must be firmly
established for 129I to become a successful environmental tracer. Additional research is therefore
needed to determine the applicability of using 129I as a groundwater age tracer in the Tucson
basin. A reliable input curve needs to be developed, which would originate from the collection
and measurement of precipitation and surface water samples. Further research should also be
conducted to determine the applicability of using plants, such as desert mistletoe and lichens, to
create the 129I input curve. This would necessitate the collection and analysis of plant samples in
addition to precipitation samples in order to find any correlations and develop the mathematical
equations to describe those correlations. Also, samples should be taken from a wide geographic
and temporal range in order to determine if any aberrations exist for certain geological features
or periods of time. This would allow for the alteration and correction of the above possible
developed mathematical formulas.
Site Description
This study focuses on regions within the Tucson basin and surrounding mountain ranges. The
Tucson basin is located in South-Central Arizona, within the basin and range province. The
Tucson basin is semi-arid, with an annual precipitation of approximately 12 inches. Tucson and
the surrounding metropolitan areas occupy most of the region, and are the largest drain on the
region’s water resources, namely groundwater. Groundwater samples were collected from
within the Tucson metropolitan area from wells operated by Tucson Water. North of Tucson lie
the Santa Catalina Mountains, which rise to approximately 9000 feet above sea level.
Precipitation and surface water samples were collected from the Santa Catalina Mountain
Critical Zone Observatory site at Marshall Gulch (elevation, 8000 feet). Marshall Gulch receives
about 35 inches of precipitation annually and supports perennial surface water. Precipitation and
surface water samples were also collected from Sabino Canyon, a perennial flowing drainage on
the southern side of the Catalina Mountains. Figure 2 shows an Arizona road map with the
Tucson basin highlighted in the green box. The area within the green box is expanded in Figure
3, which also has the collection sites labelled.
10
Figure 2: Arizona road map showing the location of the study area, the Tucson basin
Figure 3: The Tucson basin, with collection sites labelled
The hydrogeology of the Tucson basin is also an important consideration for this study. As is
common in arid and semi-arid basins, most recharge occurs as mountain front recharge, meaning
that groundwater is replenished by runoff from the mountains, infiltrating as it drains towards the
basin floor. The basin is composed of alluvial and lacustrine sediments overlying a gneiss
basement, which also composes the Santa Catalina Mountains. Groundwater in the Tucson basin
is found almost exclusively in one unconfined aquifer, which has suffered declining levels (up to
200 feet). Most production wells in the basin draw from depths of around 800 feet or less.
11
Tucson, along with much of the southwestern United States, has two distinct precipitation
seasons. Summer precipitation, from the North American Monsoon, draws moisture from the
Baja California region of the Pacific Ocean. Winter frontal precipitation draws moisture from
off the coast of California. Differences in storm formation (summer convective storms versus
winter frontal events) also draw moisture from have different origins.
Methods
Sample Collection
Surface Water Surface water samples were collected using standard USGS techniques at two
different field sites: Sabino Dam and Marshall Gulch. See USGS (2006) for more details.
Samples for iodine analysis were collected in 1-liter deionized (DI) water-washed HDPE bottles
which were rinsed three times with sample water before being filled and capped underwater.
Separate samples for cation and anion analysis were collected for some Sabino Canyon samples.
Cation samples were collected in acid-washed 30 mL HDPE bottles while anion samples were
collected in DI-washed bottles, both with a 0.45 μm syringe filter to eliminate particulates.
Groundwater A total of 15 groundwater samples were collected from various wells in the
Tucson basin, including production wells owned by Tucson Water and a University of Arizona
test well. Since gas exchange is not an issue in this type of analysis, samples were collected in 1L DI washed HDPE bottles, rinsed three times with water that had been running for ten minutes.
Cation and anion splits were collected for some Tucson Water wells, with the same sample
technique as for the surface water samples.
Precipitation Precipitation samples were collected from locations in Tucson and at Marshall
Gulch. Samples were collected in 1-L DI washed HDPE bottles, filled from funnel rain gauges
and from multiple storm events until a volume of approximately 1 liter had been obtained.
All iodine splits were stored at room temperature, and ion splits were stored in a sample
refrigerator prior to analysis.
Sample Analysis
All samples were delivered to the Accelerator Mass Spectrometry Laboratory at The University
of Arizona for iodine analysis: see Biddulph et al., 2000 for details on the process. Results were
delivered in the form of the isotopic ratio (129I/127I). Common cation and anion concentrations
were measured via iron chromatography (IC) at The University of Arizona’s Department of
Hydrology and Water Resources (Biddulph et al., 2000).
12
Analysis of the results involved the comparison of the groundwater isotopic ratio (129I/127I) to
tritium concentrations preciously measured by Carslon et al. (2011). Isotopic ratios were also
compared to other measured global ratios, mostly in the North and Baltic Seas, and to studies
that analyzed the fate of radionuclides released by the Fukushima-Dai Nuclear Disaster.
Additional analysis involved using the cation and anion data collected for this study, as well as
data collected by others (McIntosh, 2015), to create a mixing model to determine the source and
therefore potential age of water in Sabino Canyon. The mixing model compares potential source
waters (Marshall Gulch surface water, deep groundwater, and precipitation) to the composition
of Sabino Canyon. With this information, the path of 129I can be traced and its behavior and
transport better quantified. Since data suggested a seasonal influence on the isotopic ratio, the
analysis also explored this behavior in tritium and to relate that to 129I. This involved tracing the
sources of atmospheric moisture in the Tucson Basin, the formation of precipitation events, and
the global transport of 129I and tritium from their sources. One aspect of this was the creation of
a typical two-tracer, three-end-member mixing model of Marshall Gulch surface water. The
tracers used were sodium and sulfate, which are widely accepted conservative tracers, and the
end members used are precipitation, soil water, and deep groundwater. No long term ion studies
have been performed on the different hydrologic components of Sabino Canyon (namely
baseflow and soil water), so a similar mixing model could not be made for that field site. Data
from the CZO field site in Marshall Gulch was used for the years 2011 and 2012 (which is the
most recent year for which CZO data has been made public). Deep groundwater is not measured
at Marshall Gulch, so an estimate of those values was determined by selecting the stream flows
that had the highest sodium concentrations. Since sodium enters surface water via weathering in
the subsurface, and not from precipitation, flows with extremely high sodium concentrations
were assumed to comprise of deep groundwater. Along with the soil water and precipitation
data, these were then further split into summer and winter values, with summer being defined as
the period from June through September.
Results and Discussion
In total, 11 groundwater samples, 8 surface water samples, and 7 precipitation samples were
analyzed for the iodine isotopic ratio. Table 1 summarizes all values for all samples. Figure 4
graphically displays this data. Notable is the increased variability in the precipitation samples as
compared to the surface water and groundwater samples.
13
Table 1: Isotopic Ratio for All Collected Samples
Sample ID
A036A
A037A
A055A
B010
A005
A009
Z002A
Z005A
ADWR 55-618690
ADWR 55-618690 #2
ADWR 55-618690 #3
Sabino Canyon #1
Sabino Canyon #2
Sabino Canyon 9/24/2009
Marshall Gulch 8/23/2013
Marshall Gulch 8/23/2013
Marshall Gulch 8/21/2014
Sabino Canyon 3/3/2015
Marshall Gulch 5/17/2015
Tucson 3/1/2014
Tucson 8/1/2013
Marshall Gulch 2/1/2013
Marshall Gulch 1/16/2014
Marshall Gulch 5/1/2015
Tucson 8/12/2014
Marshall Gulch 5/17/2015
129I/127I
(x10-12)
103 ± 103
4.7 ± 2.7
97 ± 31
44 ± 32
< 23
109 ± 39
7.8 ± 4.0
31 ± 31
110 ± 50
60 ± 60
170 ± 60
679 ± 92
1150 ± 96
234 ± 31
350 ± 60
320 ± 110
190 ± 130
637 ± 27
485 ± 26
650 ± 200
235 ± 80
1010 ± 120
1120 ± 380
100 ± 100
566 ± 73
3260 ± 110
3H/3He
or CFC age (in years from
2009) from Carlson et al. (2011)
17
12
21
34
31
17
56
Bad age calculation
Figure 4: Isotopic Ratio for All Samples
Table 2 numerically summarizes some of the trends visually displayed in Figure 4, including the
average and standard deviation of different subsets: including type, location, and season.
Samples collected in Marshall Gulch had slightly higher isotopic ratios than samples collected at
lower elevations. More significant is the larger difference in isotopic ratio between samples
collected in the summer monsoon season versus the winter frontal precipitation season. Summer
14
monsoon samples had lower isotopic ratios with less variability. Lastly, surface water samples
regardless of season and location had lower and less variable isotopic ratios than precipitation
samples.
Table 2: Mean and Standard Deviation of Sample Categories
Marshall Gulch
Tucson/Sabino
Summer Monsoon
Winter Frontal
Surface Water
Precipitation
Mean
Standard Deviation
Mean
Standard Deviation
962.2
1117.0
904.8
940.0
Mean
Standard Deviation
Mean
Standard Deviation
361.7
173.8
852.1
980.5
Mean
Standard Deviation
Mean
Standard Deviation
407.4
180.5
1117.7
1109.9
While the original purpose of this study was to look at the applicability of using 129I as a
replacement to tritium to date groundwater, it expanded to include an attempt to categorize 129I in
the Tucson basin hydrologic cycle. The data, while sparse as yet, suggested a number of
interesting trends. Figures 5 and 6 show precipitation and surface water samples, respectively,
with the data color coded by precipitation season, where gray represents winter frontal
precipitation (October through May) and red represents the summer monsoon season (June
through September).
Figure 5: Precipitation Samples' Isotopic Ratios
Figure 6: Surface Water Samples' Isotopic Ratios
A number of trends and patterns are worth noting here: first, the isotopic ratio from the
precipitation samples are much more variable than the surface water samples. Additionally, the
average isotopic ratio of precipitation (1117.7 x 10-12), regardless of season, was higher than for
surface water (407.4 x 10-12). Possible explanations for the high variability in precipitation ratios
15
is that the moisture is coming from a large number of different sources, and have gone through a
number of atmospheric and hydrologic processes that differentiate between heavier and lighter
isotopes. A more definite explanation for the lack of variability in the surface water samples is
that, as shown in the Marshall Gulch mixing model (Figure 7), streamflows are composed of a
mix of waters, from new precipitation, to slightly older soil water, to older still deep
groundwater. Since stream water is composed of a mix of waters, including older groundwater
that has a lower isotopic ratio than precipitation, its isotopic ratio is lower than that of
precipitation. This mixing is also the reason for the lower variability, since flows are not solely
dependent on highly variable precipitation.
Results of the mixing model analysis performed on Marshall Gulch are shown in Figure 7. The
deep groundwater end member was calculated from a subset of 10 Marshall Gulch stream flow
values that had the highest sodium concentrations (Table 3). Appendix 1 includes the data points
used as precipitation, stream flow, and soil water end members.
Table 3: Streamflows with Maximum Sodium Concentrations for Estimating Deep Groundwater End Member
Date
10/9/2009
12/4/2009
1/18/2010
7/24/2010
11/29/2010
9/8/2011
11/21/2011
3/13/2012
7/9/2012
11/19/2012
Na (mg/L)
47.229
32.749
26.511
27.911
7.667
8.513
8.085
7.514
7.200
8.504
SO4 (mg/L)
1.830
6.502
6.833
4.160
5.859
4.352
4.763
5.269
3.341
4.968
Figure 7 shows the visual results of the mixing model on Marshall Gulch. The streamflows from
the summer monsoon season have lower sulfate concentrations than streamflows from the winter
frontal precipitation season. It is worth noting that sulfate concentrations mimic the isotopic ratio
trends, with higher values in the winter. This suggests that the variation in 129I and sulfate have
the same root cause. Further studies are needed to determine the exact reasons for this difference
in isotopic ratio, and would include performing a full mixing model on Sabino Canyon. At this
point there was not enough long-term ion data for Sabino Canyon to perform a sodium-sulfate,
three end-member mixing mode, as was done for Marshall Gulch. However, knowing if the
same processes are at work in Sabino Canyon as Marshall Gulch is essential for accurately
tracing the path of 129I in the hydrologic cycle.
16
129
0I⁄
127 :
0I
485 × 10−12
Soil Water
129
0I⁄
127 : 190 ×
0I
10−12
Deep
Groundwater
Precipitation
Figure 7: Marshall Gulch Mixing Model, with One Standard Deviation Error Bars on End Members. Callouts Refer to Iodine-129
Samples taken at the Same Time as Marshall Gulch Streamflow Samples
Moisture source may be a reason behind the isotopic variability of precipitation and a possible
driver behind the seasonal differences. Figures 8 and 9 show the different sources of moisture
that form precipitation in the Tucson Basin. Summer monsoon moisture generally comes from
the Baja California area, and to a lesser extent the Gulf of Mexico, while winter frontal moisture
comes from the Pacific Ocean. Winter precipitation isotopic ratios were generally higher than
the summer monsoon ratios (Table 2, Figures 5 and 6). Figure 10 shows the main production
centers of 129I, most of which are located in the Northern Hemisphere. The Pacific Ocean
receives more inputs of 129I than more southern oceans, which may in turn translate to higher
isotopic ratios in precipitation derived from that moisture (Figure 10).
17
Figure 5: North American Monsoon Moisture Sources, http://www.wrh.noaa.gov/twc/monsoon/monsoon_NA.pdf
Figure 6: Winter Frontal Storm Track Frequency, Plots a, c, and d cover the winter frontal precipitation season while plot b covers
the summer monsoon season. http://www.cpc.ncep.noaa.gov/products/precip/CWlink/stormtracks/strack_NH.shtml
18
Figure 7: Major Global Centers of Iodine-129 Production
The isotopic ratios for groundwater were compared to ages previously determined by tritium.
Apart from one outlier well, well A037A, there’s a strong logarithmic correlation between the
groundwater age and the isotopic ratio (Figure 11). The exact reason for the difference between
A037A’s isotopic ratio and the trend seen by the other wells is unknown, although possibilities
include that the well draws from a different layer than the others, or pulls in older water from
different layers. Regardless, the otherwise strong correlation suggests the isotopic ratio can be
used in lieu of tritium to determine groundwater ages, at least for the Tucson Basin. Additional
studies need to expand this analysis to other basins, to see if similar trends are found. Most
likely individual basins and/or aquifer systems will have a unique function that relates iodine
isotopic ratio to groundwater age.
Figure 11: Groundwater Sample Isotopic Ratio versus Tritium Ages
19
An important characteristic of an age tracer is that it can be used globally, and not just in a
particular area (like the Tucson basin). Therefore, the isotopic ratios obtained for the Tucson
Basin were compared to isotopic ratios averaged from nine published global studies. Figure 12
below shows these results. The Tucson Basin isotopic ratios (shown by the points) are lower than
the globally-averaged values: reasons for this include the fact that Tucson is located far away
from the main centers of production, and that Tucson is not coastal. Many of the global studies
focused on areas that have been heavily impacted by releases, such as the Baltic Sea and offshore
Japan. Coastal areas also have higher isotopic ratios than inland areas, since the oceans release
129
I, and plants (like seaweeds) collect and release higher amounts of 129I than other organisms.
Globally, the precipitation ratios were higher and more variable than the surface water ratios,
which in turn with higher and more variable than oceanic ratios, which is the same trend seen in
the Tucson basin between precipitation, surface water, and groundwater. Here, groundwater and
the oceans were compared since there are few studies that have looked at iodine in groundwater,
and groundwater and the oceans are the two largest global sinks of 129I.
3-9
Global
AZ Precipitation
AZ Surface Water
Figure 8: Comparison Between Globally Averaged and Tucson Basin Isotopic Ratios
AZ Groundwater
20
Conclusions
In summary, 129I offers a potential alternative to tritium as an age tracer for anthropogenic
groundwater. The path of 129I through the hydrosphere is not yet fully understood, and further
studies are needed to explore the seasonal variation in isotopic ratio in precipitation and surface
water. These studies also need to be expanded to basins other than the Tucson Basin, to ensure
that 129I can function as a tracer globally.
References
Ajami, , H., T. Meixner, F. Dominguez, J. Hogan, T. Maddock, 2012. Seasonalizing mountain
system recharge in semi-arid basins - climate change impacts. Ground Water, 50(4): 585-597.
Aldahan, A., S. Persson, G. Possnert, X. L. Hou, 2009. Distribution of 127I and 129I in
precipitation at high European latitudes. Geophysical Research Letters, 36(11).
Biddulph, D., J. W. Beck, G. S. Burr, D. J. Donahue, A. L. Hatheway, A. J. T. Jull, 2000.
Measurement of the radioisotope 129I at the NSF-Arizona AMS laboratory. Nuclear Instruments
and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms: 20,
693-698.
Carlson, M. A., K. A. Lohse, J. C. McIntosh, J. McLain, 2011. Impacts of urbanization on water
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Clark, I. and P. Fritz, 1997. Dating Groundwater with Tritium, In Environmental Isotopes in
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Eastoe, C., A. Gu, A. Long, 2004. The origins, ages, and flow paths of groundwater in Tucson
Basin: Results of a study of multiple isotope systems. Groundwater Recharge in a Desert
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Hou, X., V. Hansen, A. Aldahan, , G. Possnert, , O. Lind, , G. Lujaniene, , 2009. A review on
speciation of iodine-129 in the environmental and biological samples. Analytica Chimica Acta,
632: 181-196.
Kilius, L., J. Rucklidge, C. Soto, 1994. The dispersal of I from the Columbia River estuary.
Nuclear Instruments and Methods in Physics Research B, 92: 393-397.
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McIntosh, J., 2015. Personal communication regarding CZO and Field Hydrology datasets.
Moran, J. E., S. Oktay, P. Santschi, D. Schink, 1997. Surface 129Iodine/127Iodine ratios: Marine
vs. terrestrial. AIP Conference Proceedings, 392.
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Muramatsu, Y., S. Yoshida, U. Fehn, S. Amachi, Y. Ohmomo, 2004. Studies with natural and
anthropogenic iodine isotopes: iodine distribution and cycling in the global environment. Journal
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Osterc, A. and V. Stibilj, 2011. The potential of I-129 as an environmental tracer, pp. 367-390. In
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Schwehr, K. A., P. H. Santschi, J. E. Moran, D. Elmore, 2004. Near-conservative behavior of
129Iodine in the Orange County Aquifer System, California, In Lawrence Livermore National
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Schwehr, K. A., P. H. Santschi, D. Elmore, 2005. The dissolved organic iodine species of the
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127
Snyder, G. and U. Fehn, 2004. Global distribution of I in rivers and lakes: implications for
iodine cycling in surface reservoirs. Nuclear Instruments and Methods in Physics Research B,
223-224: 579-586.
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USGS, 2006. Chapter A4: Collection of Water Samples. National Field Manual for the
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World Nuclear Association, 2013. Nuclear Power in the World Today. Web. 1 December 2013.
Xu, S., S. Freeman, X. Hou, A. Watanabe, K. Yamaguchi, L. Zhang, 2013. Iodine Isotopes in
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129
Appendix 1
Tables 4, 5, and 6 detail the Marshall Gulch
data used as end members in the mixing
model.
Table 4: Precipitation Used As End Member
Date
3/28/2011
4/19/2011
7/7/2011
7/11/2011
7/14/2011
7/21/2011
7/25/2011
8/4/2011
8/8/2011
8/15/2011
8/22/2011
8/25/2011
9/5/2011
9/8/2011
9/12/2011
9/15/2011
9/26/2011
9/30/2011
10/4/2011
10/7/2011
11/14/2011
3/28/2011
4/11/2011
7/7/2011
7/11/2011
7/14/2011
7/21/2011
7/25/2011
8/4/2011
8/8/2011
8/15/2011
8/22/2011
8/25/2011
9/5/2011
9/8/2011
9/12/2011
9/15/2011
9/26/2011
9/30/2011
10/4/2011
10/7/2011
3/28/2011
4/18/2011
7/7/2011
7/11/2011
SO4 (mg/L)
3.798749
1.977155
2.043412
0.871907
1.068758
0.929522
0.606878
0.684658
0.864225
0.604958
0.533899
1.473984
1.662193
0.873828
0.901675
0.041291
1.434614
1.054355
1.03803
4.53238
2.423671
5.123894
2.743434
4.371058
1.424051
1.530639
0.980415
0.721148
0.942005
1.064917
0.73075
0.530058
1.241603
1.91954
1.209915
0.773962
0.376418
1.401005
1.487427
1.206074
3.935105
1.700603
2.001161
1.225279
1.100447
Date
3/28/2011
4/19/2011
7/7/2011
7/11/2011
7/14/2011
7/21/2011
7/25/2011
8/4/2011
8/8/2011
8/15/2011
8/22/2011
8/25/2011
9/5/2011
9/8/2011
9/12/2011
9/15/2011
9/26/2011
9/30/2011
10/4/2011
10/7/2011
11/28/2011
3/28/2011
4/11/2011
7/7/2011
7/11/2011
7/14/2011
7/21/2011
7/25/2011
8/4/2011
8/8/2011
8/15/2011
8/22/2011
8/25/2011
9/5/2011
9/8/2011
9/12/2011
9/15/2011
9/26/2011
9/30/2011
10/4/2011
10/7/2011
1/4/2012
3/28/2011
4/18/2011
7/7/2011
Na (mg/L)
3.168
0.627
0.314
0.274
0.363
0.23
0.286
0.073
0.236
0.125
0.002
0.333
0.108
0.071
0.028
0.002
0.29
0.061
0.002
2.169
0.246
3.365
1.134
3.405
1.487
1.178
0.634
0.794
0.259
0.251
0.182
0.026
0.13
0.181
0.266
0.033
0.002
0.341
0.552
0.062
1.716
0.877
1.185
0.593
0.35
Table 5: Soil Water Chemistry Used As End Member
Date
1/18/2011
1/18/2011
1/18/2011
1/18/2011
1/18/2011
1/18/2011
1/18/2011
1/18/2011
1/18/2011
1/18/2011
1/24/2011
1/24/2011
1/24/2011
1/24/2011
1/24/2011
1/24/2011
1/24/2011
1/24/2011
1/24/2011
SO4 (mg/L)
42.15786
5.148861
7.743456
12.39491
5.671237
2.767441
13.52608
6.368378
18.71239
7.972956
36.5548
6.724631
6.49033
11.23204
3.164984
8.264872
4.143479
25.13454
5.805672
Date
1/18/2011
1/18/2011
1/18/2011
1/18/2011
1/18/2011
1/18/2011
1/18/2011
1/18/2011
1/18/2011
1/18/2011
1/18/2011
1/24/2011
1/24/2011
1/24/2011
1/24/2011
1/24/2011
1/24/2011
1/24/2011
1/24/2011
Na (mg/L)
6.193
6.759
4.522
8.857
34.181
39.307
2.769
5.526
4.835
21.574
12.589
6.015
5.933
4.487
8.93
29.889
3.102
4.843
4.564
7/14/2011
7/21/2011
7/25/2011
8/4/2011
8/8/2011
8/15/2011
8/18/2011
8/22/2011
8/25/2011
9/5/2011
9/8/2011
9/12/2011
9/15/2011
9/26/2011
9/30/2011
10/4/2011
10/7/2011
11/14/2011
2/20/2012
2/27/2012
3/30/2012
4/16/2012
4/16/2012
4/16/2012
7/6/2012
7/6/2012
7/6/2012
7/9/2012
7/9/2012
7/9/2012
7/16/2012
7/16/2012
7/16/2012
7/24/2012
7/24/2012
7/24/2012
7/30/2012
7/30/2012
7/30/2012
8/16/2012
8/16/2012
8/16/2012
8/20/2012
8/20/2012
8/20/2012
8/23/2012
8/23/2012
8/23/2012
9/7/2012
9/7/2012
9/7/2012
11/13/2012
11/13/2012
11/13/2012
12/26/2012
1/31/2011
1/31/2011
1/31/2011
1/31/2011
1/31/2011
1/31/2011
1/31/2011
1/31/2011
1/31/2011
2/7/2011
2/7/2011
2/7/2011
2/7/2011
2/7/2011
2/7/2011
2/7/2011
2/7/2011
2/21/2011
2/21/2011
2/21/2011
2/21/2011
2/21/2011
2/21/2011
0.791246
0.73075
0.564627
0.65105
0.917039
0.680817
0.782604
0.484926
1.22912
1.698682
1.347231
0.790286
0.354332
1.349151
1.220478
1.187829
3.600938
0.821014
1.676597
1.412528
1.224319
1.225279
1.034189
0.84406
0.040331
0.040331
0.040331
0.040331
0.040331
0.040331
0.040331
0.040331
1.11197
0.040331
0.040331
0.040331
0.982336
0.040331
0.040331
1.653551
1.406766
1.411568
0.040331
0.040331
0.040331
0.040331
0.040331
0.040331
1.30402
0.040331
0.040331
1.680438
0.040331
0.987137
0.040331
6.45288
7.176909
8.60192
3.827557
3.413689
6.934926
3.88037
26.21771
5.45518
7.090486
8.233184
3.552925
7.601339
4.473805
30.43608
6.83698
4.249106
6.859066
33.49736
4.157883
3.208195
7.275814
3.692161
7/11/2011
7/14/2011
7/21/2011
7/25/2011
8/4/2011
8/8/2011
8/15/2011
8/18/2011
8/22/2011
8/25/2011
9/5/2011
9/8/2011
9/12/2011
9/15/2011
9/26/2011
9/30/2011
10/4/2011
10/7/2011
2/27/2012
3/30/2012
7/6/2012
7/6/2012
7/6/2012
7/9/2012
7/9/2012
7/9/2012
7/16/2012
7/16/2012
7/16/2012
7/24/2012
7/24/2012
7/24/2012
7/30/2012
7/30/2012
8/16/2012
8/16/2012
8/16/2012
8/20/2012
8/20/2012
8/20/2012
8/23/2012
8/23/2012
8/23/2012
9/7/2012
9/7/2012
9/7/2012
11/13/2012
11/13/2012
11/13/2012
12/26/2012
1/24/2011
1/24/2011
1/31/2011
1/31/2011
1/31/2011
1/31/2011
1/31/2011
1/31/2011
1/31/2011
1/31/2011
1/31/2011
1/31/2011
2/7/2011
2/7/2011
2/7/2011
2/7/2011
2/7/2011
2/7/2011
2/7/2011
2/7/2011
2/21/2011
2/21/2011
2/21/2011
0.511
0.115
0.176
0.097
0.075
0.24
0.216
0.001
0.002
0.126
0.782
0.068
0.106
0.002
0.1
0.065
0.002
1.391
0.73119
0.71465
0.63023
0.23669
0.50601
0.157
0.16
0.189
0.006
0.011
0.044
0.01
0.008
0.004
0.004
0.011
0.154
0.261
0.149
0.074
0.158
0.093
0.087
0.164
0.06
0.298
0.231
0.275
0.454
0.909
0.386
0.89284
24.887
15.619
5.397
5.016
8.433
29.485
37.35
3.173
4.351
4.632
24.195
15.219
4.699
28.696
3.242
4.326
4.106
25.35
16.255
41.346
6.449
27.399
37.928
23
2/21/2011
2/7/2011
2/28/2011
2/28/2011
2/28/2011
2/28/2011
2/28/2011
2/14/2011
2/14/2011
2/14/2011
2/14/2011
2/14/2011
2/14/2011
2/14/2011
12/6/2010
2/21/2011
3/7/2011
3/7/2011
3/7/2011
3/7/2011
3/7/2011
3/7/2011
3/7/2011
3/15/2011
3/15/2011
3/15/2011
3/15/2011
3/15/2011
3/15/2011
3/15/2011
3/15/2011
3/15/2011
3/21/2011
3/21/2011
3/21/2011
3/21/2011
3/21/2011
3/21/2011
3/21/2011
3/21/2011
3/21/2011
3/21/2011
3/28/2011
3/28/2011
3/28/2011
4/11/2011
4/11/2011
4/11/2011
4/11/2011
4/18/2011
4/18/2011
4/18/2011
4/25/2011
4/25/2011
4/25/2011
4/25/2011
4/25/2011
4/25/2011
5/5/2011
5/5/2011
5/12/2011
5/17/2011
7/7/2011
7/21/2011
7/21/2011
7/21/2011
8/15/2011
8/18/2011
8/22/2011
8/22/2011
8/22/2011
8/22/2011
8/25/2011
8/25/2011
8/29/2011
9/1/2011
9/12/2011
9/12/2011
9/12/2011
9/12/2011
9/12/2011
9/15/2011
7.748257
5.978517
7.684881
7.820276
4.314403
3.010384
4.392184
6.880191
8.930325
8.29464
4.903997
4.99234
5.319785
36.33202
16.61233
8.926484
9.71773
8.707547
8.02673
8.765162
2.053015
5.122934
3.660473
7.706967
5.545444
6.537382
6.22242
5.999642
4.024408
2.959491
4.60728
3.411768
22.14048
8.201495
6.037092
7.536042
5.390844
6.583474
4.145399
4.358575
4.290397
3.089124
5.450379
7.314224
6.460562
7.442898
21.22345
6.511455
5.720209
22.9807
6.305962
4.612081
6.479767
5.309222
2.632045
8.001763
6.405828
7.422733
8.302322
6.054376
9.998123
10.55219
12.5111
7.139459
6.309803
5.090285
19.78307
8.359937
6.823537
3.478986
4.998101
3.985998
7.226842
7.847163
10.15272
9.966435
8.893836
6.000602
5.171907
7.517797
3.277333
3.443457
2/21/2011
2/21/2011
2/21/2011
2/21/2011
2/7/2011
2/28/2011
2/28/2011
2/28/2011
2/28/2011
2/28/2011
2/14/2011
2/14/2011
2/14/2011
2/14/2011
2/14/2011
2/14/2011
2/14/2011
12/6/2010
2/21/2011
3/7/2011
3/7/2011
3/7/2011
3/7/2011
3/7/2011
3/7/2011
3/7/2011
3/7/2011
3/15/2011
3/15/2011
3/15/2011
3/15/2011
3/15/2011
3/15/2011
3/15/2011
3/15/2011
3/15/2011
3/21/2011
3/21/2011
3/21/2011
8/29/2011
3/21/2011
3/21/2011
3/21/2011
3/21/2011
3/21/2011
3/21/2011
3/21/2011
3/21/2011
3/28/2011
3/28/2011
3/28/2011
4/11/2011
4/11/2011
4/11/2011
4/11/2011
4/11/2011
4/11/2011
4/11/2011
4/18/2011
4/18/2011
4/18/2011
4/18/2011
4/25/2011
4/25/2011
4/25/2011
4/25/2011
4/25/2011
4/25/2011
4/25/2011
5/5/2011
5/5/2011
5/5/2011
5/5/2011
5/5/2011
5/12/2011
5/17/2011
7/7/2011
7/21/2011
7/21/2011
7/21/2011
8/15/2011
8/18/2011
3.227
4.167
4.678
14.966
5.419
5.083
33.189
41.718
3.087
6.338
7.226
5.497
29.204
46.047
4.293
5.708
29.101
6.422
30.244
7.654
5.433
9.33
34.49
34.335
4.073
4.658
5.509
7.525
5.308
34.293
52.309
29.323
50.124
4.519
5.379
6.411
7.037
9.728
6.784
10.137
10.203
38.596
51.782
30.554
49.675
5.176
5.604
8.516
5.621
32.805
27.438
4.67
7.873
5.336
4.406
6.262
38.287
3.195
5.535
7.806
4.575
37.827
3.363
4.703
4.132
5.755
4.587
8.106
34.65
8.728
4.41
5.302
37.32
3.969
6.271
4.799
23.428
22.715
4.442
30.138
8.773
7.486
9/15/2011
9/19/2011
9/19/2011
9/19/2011
9/19/2011
9/19/2011
9/22/2011
9/26/2011
9/30/2011
9/19/2011
10/7/2011
10/7/2011
10/10/2011
11/14/2011
11/14/2011
11/14/2011
11/14/2011
11/14/2011
11/21/2011
11/21/2011
11/21/2011
11/21/2011
11/21/2011
11/21/2011
11/21/2011
11/28/2011
11/28/2011
11/28/2011
11/28/2011
1/9/2012
1/9/2012
1/9/2012
1/9/2012
1/9/2012
1/9/2012
1/9/2012
1/17/2012
1/17/2012
1/17/2012
1/17/2012
1/17/2012
1/17/2012
1/17/2012
1/17/2012
1/17/2012
1/17/2012
1/17/2012
1/23/2012
1/23/2012
1/23/2012
1/23/2012
1/23/2012
1/23/2012
1/23/2012
1/23/2012
1/23/2012
1/23/2012
1/30/2012
1/30/2012
1/30/2012
1/30/2012
1/30/2012
1/30/2012
1/30/2012
1/30/2012
1/30/2012
2/6/2012
2/6/2012
2/6/2012
2/6/2012
2/6/2012
2/6/2012
2/6/2012
2/6/2012
2/6/2012
2/6/2012
2/6/2012
2/6/2012
2/6/2012
2/13/2012
2/13/2012
2/13/2012
4.399866
4.987539
5.494551
4.309602
6.602679
4.743635
7.189392
8.022889
7.282536
2.923001
9.391245
10.21226
7.922063
9.041714
3.965833
7.571571
3.22548
8.896716
8.207257
4.834859
6.83506
6.79953
11.84756
26.41264
9.052277
5.894015
7.444818
8.388744
9.673559
2.177847
3.615341
3.192831
6.613242
3.936065
10.71255
5.242005
5.780705
4.902076
5.111411
6.95029
8.697945
26.54035
11.41161
2.121192
3.490509
1.915699
3.392563
1.516235
3.831398
4.324006
1.49703
11.1533
18.44256
9.205917
5.676038
6.591156
4.0705
1.830237
4.152121
3.012304
1.433653
13.64419
20.64922
5.538722
6.192652
3.164024
1.753417
4.14924
2.72615
1.502791
12.98162
6.18401
18.00373
5.323626
0.040331
2.059736
5.49071
3.189951
3.286936
1.368356
4.391223
3.11025
8/22/2011
8/22/2011
8/22/2011
8/22/2011
8/22/2011
8/22/2011
8/22/2011
8/25/2011
8/25/2011
8/25/2011
8/29/2011
9/1/2011
9/8/2011
9/12/2011
9/12/2011
9/12/2011
9/12/2011
9/12/2011
9/12/2011
9/15/2011
9/15/2011
9/15/2011
9/19/2011
9/19/2011
9/19/2011
9/19/2011
9/19/2011
9/19/2011
9/22/2011
9/22/2011
9/26/2011
9/26/2011
9/30/2011
9/30/2011
9/19/2011
10/4/2011
10/7/2011
10/7/2011
10/7/2011
10/10/2011
10/10/2011
10/17/2011
10/31/2011
11/14/2011
11/14/2011
11/14/2011
11/14/2011
11/14/2011
11/14/2011
11/21/2011
11/21/2011
11/21/2011
11/21/2011
11/21/2011
11/21/2011
11/21/2011
11/21/2011
11/28/2011
11/28/2011
11/28/2011
11/28/2011
12/12/2011
12/12/2011
12/20/2011
12/20/2011
12/20/2011
12/20/2011
12/28/2011
12/28/2011
12/28/2011
12/28/2011
12/28/2011
12/28/2011
12/28/2011
12/28/2011
1/4/2012
1/4/2012
1/4/2012
1/4/2012
1/4/2012
1/4/2012
1/4/2012
6.264
10.148
19.504
33.537
8.511
26.64
5.065
6.951
9.107
6.437
9.482
7.609
10.909
7.694
5.61
21.004
10.471
7.341
16.892
17.558
22.127
8.919
7.509
23.59
33.341
8.928
6.229
5.892
8.874
6.1
6.093
9.108
8.932
6.194
9.714
8.925
5.251
6.71
9.7
9.772
5.774
10.13
11.104
25.224
4.234
8.658
11.12
21.363
5.403
24.225
24.39
6.326
3.968
33.485
33.606
6.79
9.825
7.528
10.18
6.252
27.423
5.427
8.057
3.311
8.599
4.753
9.98
29.974
26.541
36.12
8.407
8.408
3.958
4.08
2.988
8.042
2.771
3.684
4.327
8.005
30.563
24.475
24
2/13/2012
2/13/2012
2/13/2012
2/13/2012
2/13/2012
2/13/2012
2/13/2012
2/13/2012
2/13/2012
2/20/2012
2/20/2012
2/20/2012
2/20/2012
2/20/2012
2/20/2012
2/20/2012
2/20/2012
2/20/2012
2/20/2012
2/20/2012
2/20/2012
2/27/2012
2/27/2012
2/27/2012
2/27/2012
2/27/2012
2/27/2012
2/27/2012
2/27/2012
2/27/2012
2/27/2012
2/27/2012
3/5/2012
3/5/2012
3/5/2012
3/5/2012
3/5/2012
3/5/2012
3/5/2012
3/5/2012
3/5/2012
3/5/2012
3/5/2012
3/5/2012
3/13/2012
3/13/2012
3/13/2012
3/13/2012
3/13/2012
3/13/2012
3/13/2012
3/13/2012
3/13/2012
3/13/2012
3/13/2012
3/13/2012
3/13/2012
3/19/2012
3/19/2012
3/19/2012
3/19/2012
3/19/2012
3/19/2012
3/23/2012
3/23/2012
3/23/2012
3/23/2012
3/23/2012
3/23/2012
3/23/2012
3/23/2012
3/23/2012
3/23/2012
3/23/2012
3/23/2012
3/23/2012
3/26/2012
3/26/2012
3/26/2012
3/26/2012
3/26/2012
3/26/2012
0.040331
12.89808
6.844662
18.16505
10.23434
5.714448
1.968513
2.358374
5.346672
1.539281
4.590955
3.123693
1.324185
12.01465
7.320946
17.94419
11.10625
5.594417
2.544663
6.122554
2.640688
1.446137
5.541603
3.99464
1.839839
15.40817
9.29426
21.7487
6.467284
2.696382
7.548525
2.406387
2.003082
4.986578
4.729231
1.875368
16.91864
10.86715
21.15527
9.386444
6.576752
3.291737
9.566011
3.040152
2.959491
4.035931
5.073961
1.665074
11.04288
10.16521
18.17369
9.304823
5.085484
84.59514
3.085283
7.699285
18.43104
2.849062
3.635507
10.17769
85.96926
6.992541
3.048794
1.220478
2.816413
4.668736
1.704444
1.80527
11.26469
9.856006
16.86199
8.936087
4.192452
79.02089
3.427132
2.65125
1.145578
2.753997
5.343791
1.324185
11.233
9.917462
1/4/2012
1/4/2012
1/9/2012
1/9/2012
1/9/2012
1/9/2012
1/9/2012
1/9/2012
1/9/2012
1/9/2012
1/9/2012
1/5/2012
1/5/2012
1/17/2012
1/17/2012
1/17/2012
1/17/2012
1/17/2012
1/17/2012
1/17/2012
1/17/2012
1/17/2012
1/17/2012
1/17/2012
1/17/2012
1/23/2012
1/23/2012
1/23/2012
1/23/2012
1/23/2012
1/23/2012
1/23/2012
1/23/2012
1/23/2012
1/23/2012
1/23/2012
1/30/2012
1/30/2012
1/30/2012
1/30/2012
1/30/2012
1/30/2012
1/30/2012
1/30/2012
1/30/2012
1/30/2012
1/30/2012
2/6/2012
2/6/2012
2/6/2012
2/6/2012
2/6/2012
2/6/2012
2/6/2012
2/6/2012
2/6/2012
2/6/2012
2/6/2012
2/6/2012
2/6/2012
2/13/2012
2/13/2012
2/13/2012
2/13/2012
2/13/2012
2/13/2012
2/13/2012
2/13/2012
2/13/2012
2/13/2012
2/13/2012
2/13/2012
2/13/2012
2/20/2012
2/20/2012
2/20/2012
2/20/2012
2/20/2012
2/20/2012
2/20/2012
2/20/2012
2/20/2012
31.692
22.032
3.28914
3.86203
3.61693
8.92287
4.72514
8.7715
20.00464
23.57279
38.03474
35.94888
36.65584
4.85149
39.47574
15.64713
18.86159
7.64764
6.88981
5.58327
19.58772
3.16298
3.76819
3.32878
20.86669
2.8788
3.58996
6.47765
2.62493
17.78102
4.98124
7.66286
5.01382
7.9014
17.35572
15.06327
3.252
3.492
5.852
2.712
19.532
4.952
4.432
7.952
20.312
18.432
15.572
3.58173
4.75959
6.69608
3.40896
22.46341
11.65408
6.167
5.68657
8.84703
19.3483
17.43458
17.79185
38.68319
2.38319
3.61655
5.43252
1.90819
15.8174
9.89316
4.53941
10.32956
5.36057
7.76349
15.53835
12.537
14.89624
2.42207
3.24858
5.65168
2.1083
15.88886
9.95668
4.57898
9.43207
3.97447
3/26/2012
3/26/2012
3/26/2012
3/26/2012
3/26/2012
3/26/2012
3/26/2012
3/26/2012
3/30/2012
3/30/2012
3/30/2012
3/30/2012
3/30/2012
3/30/2012
3/30/2012
3/30/2012
3/30/2012
3/30/2012
3/30/2012
3/30/2012
3/30/2012
4/2/2012
4/2/2012
4/2/2012
4/2/2012
4/2/2012
4/2/2012
4/2/2012
4/2/2012
4/2/2012
4/2/2012
4/9/2012
4/9/2012
4/9/2012
4/9/2012
4/9/2012
4/9/2012
4/9/2012
4/9/2012
4/9/2012
4/9/2012
4/9/2012
4/16/2012
4/16/2012
4/16/2012
4/16/2012
4/16/2012
4/16/2012
4/16/2012
4/16/2012
4/16/2012
4/16/2012
4/16/2012
4/16/2012
4/23/2012
4/23/2012
4/23/2012
4/23/2012
4/23/2012
4/23/2012
4/23/2012
4/23/2012
4/30/2012
4/30/2012
4/30/2012
4/30/2012
5/7/2012
5/7/2012
5/7/2012
5/7/2012
5/14/2012
5/14/2012
5/21/2012
7/16/2012
7/24/2012
7/24/2012
7/24/2012
7/24/2012
7/24/2012
7/26/2012
7/26/2012
7/26/2012
14.83874
8.029611
3.60958
63.65977
2.339169
6.313644
2.678137
2.124073
1.590174
2.834658
5.33707
0.9977
10.35342
9.434456
13.77767
7.665676
3.415609
55.50437
2.222019
5.204555
2.80201
2.290196
2.823135
13.54049
9.935707
9.675479
3.615341
50.29213
2.504332
4.770522
2.960451
3.808352
3.361835
5.518557
1.867686
11.03711
14.0667
8.378181
4.055136
50.19995
3.356074
5.127735
3.221639
3.855404
5.312103
2.510094
13.08053
10.90748
14.30676
8.985059
4.641849
50.21147
4.06954
5.539682
4.26255
4.478606
2.902836
15.56085
14.45176
4.869428
50.03095
7.187471
19.99433
5.353394
51.58079
6.541223
5.918021
23.96208
5.927623
55.92208
6.380861
61.87755
6.570031
7.18267
3.545243
8.015207
4.371058
31.60279
5.878651
3.640308
6.64397
4.906878
2/20/2012
2/20/2012
2/20/2012
2/20/2012
3/13/2012
3/13/2012
3/13/2012
3/13/2012
3/13/2012
3/13/2012
3/13/2012
3/13/2012
3/13/2012
3/13/2012
3/13/2012
3/13/2012
3/13/2012
3/19/2012
3/19/2012
3/19/2012
3/19/2012
3/19/2012
3/19/2012
3/23/2012
3/23/2012
3/23/2012
3/23/2012
3/23/2012
3/23/2012
3/23/2012
3/23/2012
3/23/2012
3/23/2012
3/23/2012
3/23/2012
3/23/2012
3/23/2012
3/26/2012
3/26/2012
3/26/2012
3/26/2012
3/26/2012
3/26/2012
3/26/2012
3/26/2012
3/26/2012
3/26/2012
3/26/2012
3/26/2012
3/26/2012
3/26/2012
3/30/2012
3/30/2012
3/30/2012
3/30/2012
3/30/2012
3/30/2012
3/30/2012
3/30/2012
3/30/2012
3/30/2012
3/30/2012
3/30/2012
3/30/2012
4/2/2012
4/2/2012
4/2/2012
4/2/2012
4/2/2012
4/2/2012
4/2/2012
4/2/2012
4/2/2012
4/2/2012
4/9/2012
4/9/2012
4/9/2012
4/9/2012
4/9/2012
4/9/2012
4/9/2012
4/9/2012
7.80421
16.0135
14.75216
14.21728
2.46824
3.51798
6.10001
2.21975
12.99234
11.74553
4.44516
9.17757
3.67211
7.99192
12.64353
11.66517
12.72475
3.60439
10.25201
4.35364
8.12288
11.98331
12.90965
1.7048
2.83132
5.24197
1.67913
17.44194
9.82375
3.89457
7.18992
3.02172
6.98166
16.90366
12.46433
14.90311
38.11692
1.86442
3.03872
5.68655
2.81581
17.70876
9.65213
3.50927
8.20991
3.0257
6.71918
15.60226
12.15034
12.19117
30.89684
2.41197
4.27174
6.60178
1.98204
16.41723
11.8407
4.34219
10.52424
3.79519
6.69399
14.42708
14.60952
14.36843
2.68868
4.29885
4.31783
16.08535
11.24239
3.62143
5.97464
14.49482
15.00376
5.21905
2.50227
5.28762
5.86983
2.46739
18.42826
3.66959
8.37325
3.3474
25
7/26/2012
7/26/2012
8/20/2012
8/30/2012
9/7/2012
9/7/2012
9/7/2012
9/7/2012
9/7/2012
9/7/2012
9/10/2012
9/10/2012
9/10/2012
9/10/2012
9/10/2012
9/13/2012
9/13/2012
9/17/2012
38.48106
4.780125
3.500111
46.63358
3.002702
3.289817
3.578852
44.18686
135.9455
3.862126
6.034211
4.076261
44.35683
23.60583
4.351853
5.193992
5.191112
6.406788
4/9/2012
4/9/2012
4/9/2012
4/16/2012
4/16/2012
4/16/2012
4/16/2012
4/16/2012
4/16/2012
4/16/2012
4/16/2012
4/16/2012
4/16/2012
4/16/2012
4/16/2012
4/23/2012
4/23/2012
4/23/2012
4/23/2012
4/23/2012
4/23/2012
4/23/2012
4/23/2012
4/30/2012
4/30/2012
4/30/2012
4/30/2012
5/7/2012
5/7/2012
5/7/2012
5/7/2012
5/14/2012
5/14/2012
5/21/2012
5/21/2012
7/16/2012
7/24/2012
7/24/2012
7/24/2012
7/24/2012
5.15638
15.89521
14.97779
2.37142
3.4112
5.60817
2.11461
21.78882
11.58645
3.7748
7.82963
3.86342
5.41228
16.22421
14.89865
3.1504
5.1792
2.525
21.9364
4.6513
4.3004
6.4737
16.7251
23.0219
4.5589
6.5618
19.7216
4.8913
25.5032
4.6416
6.6872
4.7299
8.4059
6.2349
10.42525
5.026
0.95
2.25
1.958
4.186
Table 6: Marshall Gulch Streamflows Used As End Member
Date
2/2/2009
2/9/2009
2/16/2009
2/23/2009
3/2/2009
3/9/2009
3/16/2009
3/23/2009
3/30/2009
4/6/2009
4/13/2009
4/20/2009
4/27/2009
5/4/2009
5/11/2009
5/18/2009
5/26/2009
6/1/2009
6/8/2009
6/15/2009
6/22/2009
6/29/2009
7/4/2009
7/14/2009
7/19/2009
7/24/2009
8/13/2009
8/23/2009
8/28/2009
9/7/2009
9/12/2009
9/17/2009
9/22/2009
9/27/2009
10/2/2009
10/9/2009
SO4 (mg/L)
0.568
0.557
2.347
1.991
2.719
2.739
2.987
2.877
1.489
39.205
8.137
3.008
37.498
8.967
8.280
2.474
2.359
2.623
2.666
2.664
2.673
7.845
4.706
5.043
0.358
3.500
8.329
7.071
1.780
4.939
5.335
5.700
5.800
6.179
1.959
1.830
Date
2/2/2009
2/9/2009
2/16/2009
2/23/2009
3/2/2009
3/9/2009
3/16/2009
3/23/2009
3/30/2009
4/6/2009
4/13/2009
4/20/2009
4/27/2009
5/4/2009
5/11/2009
5/18/2009
5/26/2009
6/1/2009
6/8/2009
6/15/2009
6/22/2009
6/29/2009
7/4/2009
7/9/2009
7/14/2009
7/19/2009
7/24/2009
7/29/2009
8/13/2009
8/23/2009
8/28/2009
9/7/2009
9/12/2009
9/17/2009
9/22/2009
9/27/2009
Na (mg/L)
4.623
4.550
4.028
3.810
2.683
4.155
3.660
3.069
4.309
6.010
4.626
5.204
5.592
6.009
6.046
6.163
6.163
6.230
6.494
6.613
6.835
7.011
6.300
6.144
6.771
6.648
6.819
7.084
7.640
7.751
7.219
7.106
7.055
7.443
7.686
7.577
10/16/2009
10/30/2009
11/6/2009
11/13/2009
11/28/2009
12/4/2009
12/11/2009
1/4/2010
1/18/2010
2/1/2010
5/11/2010
6/1/2010
6/7/2010
6/14/2010
6/21/2010
6/30/2010
7/5/2010
7/12/2010
7/19/2010
7/24/2010
7/29/2010
8/3/2010
8/8/2010
8/13/2010
8/18/2010
8/22/2010
8/28/2010
9/2/2010
9/8/2010
9/12/2010
9/18/2010
9/22/2010
9/28/2010
10/2/2010
10/8/2010
10/13/2010
11/29/2010
12/20/2010
1.928
1.879
4.269
3.820
6.602
6.502
6.088
6.539
6.833
5.869
8.514
8.247
7.981
7.597
9.853
7.238
7.709
5.936
6.051
4.160
3.872
4.848
3.693
5.555
4.364
5.947
6.504
6.572
32.436
7.178
7.091
6.599
5.472
5.747
4.451
5.011
5.859
6.260
7/24/2012
7/26/2012
7/26/2012
7/26/2012
7/26/2012
7/26/2012
8/20/2012
8/23/2012
8/23/2012
8/23/2012
8/23/2012
8/23/2012
8/23/2012
8/27/2012
8/27/2012
8/27/2012
8/30/2012
8/30/2012
8/30/2012
8/30/2012
9/7/2012
9/7/2012
9/7/2012
9/7/2012
9/7/2012
9/7/2012
9/7/2012
9/10/2012
9/10/2012
9/10/2012
9/10/2012
9/10/2012
9/13/2012
9/13/2012
9/13/2012
9/17/2012
12/26/2012
12/26/2012
12/26/2012
12/26/2012
7.1
3.641
5.843
7.66
7.532
17.496
13.775
8.907
15.14
30.835
4.758
7.945
10.746
4.498
8.75
18.069
8.67298
25.57608
4.41555
7.68346
3.78436
6.59682
10.21369
8.70347
26.39826
24.6456
15.6166
6.356
10.668
9.082
8.648
15.281
7.643
5.501
6.645
8.103
7.31
9.49
4.42
6.55
10/2/2009
10/9/2009
10/16/2009
10/30/2009
11/6/2009
11/13/2009
11/28/2009
12/4/2009
12/11/2009
1/4/2010
1/18/2010
2/1/2010
2/8/2010
2/15/2010
2/22/2010
3/1/2010
3/17/2010
3/23/2010
3/29/2010
4/6/2010
4/12/2010
4/21/2010
4/26/2010
5/1/2010
5/11/2010
5/17/2010
6/1/2010
6/7/2010
6/14/2010
6/21/2010
6/30/2010
7/5/2010
7/12/2010
7/19/2010
7/24/2010
7/29/2010
8/3/2010
8/8/2010
6.703
47.229
40.661
43.316
9.418
9.440
27.253
32.749
25.155
23.949
26.511
3.539
3.484
3.235
3.315
3.008
2.642
2.837
2.957
2.916
3.028
3.130
3.601
3.685
3.260
3.685
7.381
4.114
4.843
17.635
16.263
7.253
12.905
17.480
27.911
18.036
4.041
3.503
26
1/18/2011
1/24/2011
1/31/2011
2/7/2011
1/10/2011
2/28/2011
2/14/2011
2/21/2011
3/7/2011
3/7/2011
3/15/2011
3/21/2011
3/28/2011
4/11/2011
4/18/2011
4/25/2011
5/5/2011
5/12/2011
5/17/2011
5/23/2011
5/31/2011
7/7/2011
7/21/2011
7/25/2011
7/28/2011
8/8/2011
8/15/2011
8/18/2011
8/22/2011
8/25/2011
9/8/2011
9/12/2011
9/15/2011
9/19/2011
9/22/2011
9/26/2011
9/30/2011
10/4/2011
10/7/2011
10/10/2011
10/17/2011
10/31/2011
11/21/2011
11/8/2011
11/14/2011
12/5/2011
11/28/2011
12/12/2011
12/20/2011
1/9/2012
1/23/2012
1/30/2012
2/6/2012
2/13/2012
2/20/2012
2/27/2012
3/5/2012
3/13/2012
3/19/2012
3/23/2012
3/26/2012
3/30/2012
4/2/2012
4/9/2012
4/16/2012
4/23/2012
4/30/2012
5/7/2012
5/14/2012
7/9/2012
7/16/2012
7/24/2012
7/24/2012
7/24/2012
7/24/2012
7/24/2012
7/24/2012
7/24/2012
7/24/2012
7/24/2012
7/24/2012
7/24/2012
4.464
6.199
6.027
6.651
5.010
6.848
7.049
6.818
6.334
4.916
6.895
7.380
3.875
4.310
5.695
5.513
4.703
4.866
3.734
4.819
5.190
10.883
5.262
5.213
5.328
4.157
3.200
3.819
4.172
4.352
4.200
3.309
3.396
4.078
4.394
4.602
4.030
4.090
4.252
4.589
0.005
4.763
4.459
4.650
3.907
4.343
4.771
4.107
4.702
5.522
5.689
5.217
5.447
5.376
6.166
6.174
5.269
5.765
6.369
4.195
6.249
6.657
6.713
6.114
5.740
5.796
5.597
5.462
3.341
8.670
4.497
3.852
3.780
3.877
3.805
3.877
3.816
3.802
3.813
3.869
3.948
3.883
8/13/2010
8/18/2010
8/22/2010
8/28/2010
9/2/2010
9/8/2010
9/12/2010
9/18/2010
9/22/2010
9/28/2010
10/2/2010
10/8/2010
10/13/2010
11/29/2010
12/20/2010
1/18/2011
1/24/2011
1/31/2011
2/7/2011
1/10/2011
2/28/2011
2/14/2011
2/21/2011
3/7/2011
3/7/2011
3/15/2011
3/21/2011
4/4/2011
3/28/2011
4/11/2011
4/18/2011
4/25/2011
5/5/2011
5/12/2011
5/17/2011
5/23/2011
5/31/2011
7/7/2011
7/21/2011
7/25/2011
7/28/2011
8/8/2011
8/15/2011
8/18/2011
8/22/2011
8/25/2011
9/8/2011
9/12/2011
9/15/2011
9/19/2011
9/22/2011
9/26/2011
9/30/2011
10/4/2011
10/7/2011
10/10/2011
10/17/2011
10/31/2011
11/21/2011
11/8/2011
11/14/2011
12/5/2011
11/28/2011
12/12/2011
12/20/2011
12/28/2011
1/4/2012
1/9/2012
1/30/2012
2/6/2012
2/13/2012
2/20/2012
2/27/2012
3/5/2012
3/13/2012
3/19/2012
3/23/2012
3/26/2012
3/30/2012
4/2/2012
4/9/2012
4/16/2012
4.357
4.023
4.438
4.880
6.335
6.104
5.782
6.222
6.385
5.543
6.171
6.204
6.917
7.667
7.569
4.179
4.860
5.522
6.808
6.314
6.796
6.679
6.405
6.231
6.142
6.515
6.596
6.961
6.251
5.675
6.111
6.207
6.328
6.875
6.544
6.633
7.357
7.983
7.778
7.736
8.102
7.774
6.310
7.803
6.910
8.513
9.330
6.657
5.895
6.645
6.840
7.031
6.722
7.036
7.692
7.424
8.094
8.085
9.136
6.240
7.029
5.980
6.169
5.910
4.389
3.933
3.905
4.413
4.472
5.474
4.568
5.566
5.234
7.514
7.792
4.759
4.062
4.372
4.560
4.700
4.333
6.004
7/24/2012
7/24/2012
7/24/2012
7/24/2012
7/24/2012
7/24/2012
7/24/2012
7/24/2012
7/24/2012
7/24/2012
7/24/2012
7/24/2012
7/24/2012
7/24/2012
7/24/2012
7/25/2012
7/25/2012
7/25/2012
7/25/2012
7/26/2012
7/30/2012
8/16/2012
8/17/2012
8/17/2012
8/17/2012
8/17/2012
8/17/2012
8/19/2012
8/19/2012
8/19/2012
8/19/2012
8/19/2012
8/19/2012
8/19/2012
8/20/2012
8/20/2012
8/20/2012
8/20/2012
8/20/2012
8/23/2012
8/27/2012
8/30/2012
9/7/2012
9/10/2012
9/13/2012
9/17/2012
11/13/2012
11/19/2012
11/26/2012
12/3/2012
12/10/2012
12/17/2012
12/26/2012
3.867
3.853
3.945
4.256
3.874
4.021
4.179
3.768
3.829
3.888
4.011
3.847
3.851
3.900
3.951
3.989
3.905
3.856
3.946
4.536
4.429
4.999
4.451
4.689
4.553
4.606
4.560
2.239
2.308
2.379
2.261
2.500
2.497
2.766
3.652
3.143
3.210
3.322
3.151
2.806
3.781
4.238
2.589
3.177
3.349
4.245
4.968
4.853
4.963
4.924
4.868
3.883
2.567
4/23/2012
4/30/2012
5/7/2012
5/14/2012
7/9/2012
7/16/2012
7/24/2012
7/24/2012
7/24/2012
7/24/2012
7/24/2012
7/24/2012
7/24/2012
7/24/2012
7/24/2012
7/24/2012
7/24/2012
7/24/2012
7/24/2012
7/24/2012
7/24/2012
7/24/2012
7/24/2012
7/24/2012
7/24/2012
7/24/2012
7/24/2012
7/24/2012
7/24/2012
7/24/2012
7/24/2012
7/24/2012
7/25/2012
7/25/2012
7/25/2012
7/25/2012
7/26/2012
7/30/2012
8/16/2012
8/17/2012
8/17/2012
8/17/2012
8/17/2012
8/17/2012
8/19/2012
8/19/2012
8/19/2012
8/19/2012
8/19/2012
8/19/2012
8/19/2012
8/20/2012
8/20/2012
8/20/2012
8/20/2012
8/20/2012
8/23/2012
8/27/2012
8/30/2012
9/7/2012
9/10/2012
9/13/2012
9/17/2012
11/13/2012
11/19/2012
11/26/2012
12/3/2012
12/10/2012
12/17/2012
12/26/2012
6.205
6.601
7.365
7.200
8.463
6.653
7.388
7.396
7.320
7.413
7.389
2.008
1.829
1.784
1.976
2.204
3.152
2.537
1.938
2.134
2.032
2.141
2.379
1.918
2.078
2.514
2.152
2.318
1.830
1.903
2.439
2.318
2.173
3.115
2.031
7.363
7.798
8.227
8.053
8.240
8.450
8.328
8.502
8.512
5.942
6.132
6.169
6.229
6.381
6.484
7.045
7.308
7.569
7.812
8.065
7.679
6.216
7.676
8.267
6.179
7.426
7.285
7.844
8.504
8.764
8.430
7.908
8.260
6.760
5.960