MOST Americans take cheap and
plentiful supplies of pure drinking water for granted. Some even
consider it to be an inalienable right. However, clean water sources,
especially pristine underground aquifers, are being consumed at
an increasing rate, and contaminants and changing patterns in rain
and snowfall are threatening the adequacy of supplies.
Ensuring plentiful water supplies is becoming a critical issue
in California, which uses 10 percent of the nation’s freshwater.
State water managers are closing many contaminated or impaired
drinking wells; Sierra snowpacks have diminished in recent years;
and the state’s farmers, fishermen, environmentalists, and
city dwellers cannot always agree on the best uses for a limited
California is not alone with respect to these issues. They are
relevant throughout the western U.S. and are becoming more so in
other parts of the country. They also are critically important
in highly populated and developing nations such as China, India,
and Mexico as well as in many parts of Africa and the Middle East.
consider possible methods to address these challenges, a team of
Lawrence Livermore scientists is working on a three-year Water
Initiative that is managed by Livermore’s Energy and Environment
(E&E) Directorate. The initiative, now in its second year,
marshals Livermore’s expertise in chemistry, materials science,
environmental science, microbiology, and computer modeling. The
team’s goal is to develop innovative tools that water resource
managers can use to make informed decisions about the state’s
water-supply infrastructure, protection and purification efforts,
and flood control. In so doing, the scientists are helping to position
the Laboratory as a leader in the science and management of water
Three Projects Tap Lab Expertise
“We are creating tools and methods that will serve the water management
community,” says Robin Newmark, who leads the E&E Water and Environment
Program as well as the Water Initiative. When Newmark and her colleagues studied
the problems facing California water managers, they found three areas where Livermore’s
expertise could make the greatest contributions: providing better predictive
models, improving the scientific understanding of water contamination, and developing
more cost-effective technologies for purifying water.
The three resulting scientific projects that form the Water Initiative are funded
by Livermore’s Laboratory Directed Research and Development Program. Additional
institutional funding supports planning and outreach activities aimed at establishing
relationships with water managers at the local and state level.
The first project links climate and surface hydrology models run on Livermore’s
supercomputers to predict how climate variability can affect the supply of freshwater
in the coming decades. The second project studies ways to better understand and
manage nitrate, the leading contaminant of California groundwater. The third
project focuses on treating contaminated water with new, cost-effective membranes
The Department of Energy (DOE) might not seem a logical choice to be leading
a water effort, but energy and water are inextricably linked. “Energy security
depends on water security,” says Newmark. The production of energy is the
second largest consumer of freshwater in the nation, after agriculture. At the
same time, the processes involved in treating and distributing an abundant supply
of clean water depend on having low-cost energy readily available. Nationally,
about 4 percent of electricity is used to pump, process, and treat water.
The demands for both energy and water are expected to grow substantially in the
next 25 years. “As a result,” says Newmark, “a strong
federal role is needed to provide scientific research, technology development,
and analysis capabilities so the nation can achieve energy and water security
Water and energy are inextricably
linked. Energy production is the second largest consumer
of the nation’s freshwater, after agriculture. The
treatment, storage, and distribution of water are dependent
on readily available energy. The needs for both resources
are expected to grow substantially for the next 25 years.
Simulations Guide Decision Makers
California, the availability of sufficient freshwater to meet agricultural,
urban, fishing, recreational, and other needs depends on properly managing a
complex system of water storage and delivery. In making decisions, water managers
are guided by past observations of the natural hydrologic cycle, including such
factors as rainfall, the water content of snow, and river flow rates.
are useful only if the future behavior of California’s
hydrologic system is similar to its past behavior. Yet, such an assumption may
no longer be correct. If the natural hydrologic cycle continues to change significantly,
water management practices must adapt to the new patterns. These changes require
building new reservoirs, pipelines, aqueducts, flood-control projects, and treatment
plants and in many cases, operating existing facilities differently.
“There’s a compelling need for improved water management based on the best
models,” says Livermore physicist Philip Duffy, who leads the initiative’s
modeling project and is director of the University of California’s (UC’s)
Institute for Research on Climate Change and Its Societal Impacts. The goal of
the modeling effort is to project future changes in the hydrologic cycle in California
and determine how those changes will affect the availability of freshwater. Water
managers and policy makers would benefit if such projections were available for
assessing proposed changes in water management practices.
“We’re looking at how water supplies are likely to change during the next
several decades,” says Duffy. The team’s simulations of future water
supplies are done on Livermore’s massively parallel supercomputers. Fortunately,
California’s water system is well suited for modeling because most of its
supply comes from precipitation or groundwater within the state. Only 5 percent
is drawn from out of state (from the Colorado River).
California’s water system is dependent on storage of water in reservoirs
and in the snowpack. However, few new reservoirs are being built, and increasing
amounts of precipitation are falling as rain, not as snow.
“The only source that feeds reservoirs and rivers in the summer is melting snowpack,” says
Duffy. Measurements show that snowpack water levels are dropping as California’s
climate continues to warm. If that decrease continues, it could reduce late spring
and summer stream flows into reservoirs. And unless the state increases its reservoir
capacity, additional water supplies cannot be stored during the winter even if
river flow rates increase because of the changing precipitation pattern. Ironically,
to protect against flooding, water managers may need to lower water levels in
reservoirs, effectively reducing the total volume of water in storage. As a result,
less water would be available in summer to support agriculture, hydropower production,
fisheries, and recreation, thus compounding the state’s need for increased
Melting snowpack is the only water
source for California reservoirs and rivers in summer,
when water usage increases. For example, as the chart shows,
residents of California’s Livermore Valley (blue
line) use the most water during summer—the time of
lowest precipitation in the Sierra (red line), where much
of the valley’s water originates. (1 acre-foot equals
1,214 cubic meters of water.)
Linking More Detailed Models
how these changes will affect California’s water supply,
Duffy’s team is using a sequence of models, starting with global climate
models and ending with surface hydrology models. Each successive model increases
the simulation’s spatial resolution, which improves how closely the results
agree with observations. “High spatial resolution is even more important
for simulating the hydrologic cycle than it is for simulating climate,” says
A model with fine
resolution can more realistically represent the topographic features of an area
and, thus, its surface temperature, which determines whether
precipitation is rain or snow. The spatial pattern of precipitation within California
is strongly influenced by topographic variations such as coastal hills, inland
valleys, and the Sierra Nevada, so surface hydrology models must map topography
at a fine resolution to show accurate routes for surface runoff into rivers.
Duffy’s team generates the initial predictions of the sequence using a
global climate model run at a spatial resolution of about 75 kilometers. Although
this resolution is much finer than typical for global models, it does not provide
enough detail for the project. Data from the global climate models are then used
to drive two regional climate models, one with a grid size of 9 kilometers and
the other with a grid of 36 kilometers. Having results from two models helps
the team estimate uncertainties in the model predictions.
Next, the researchers
feed surface temperatures and precipitation data from the regional climate model
into a surface hydrology model run with a lumped-mode
grid—that is, each watershed is treated as one irregularly shaped grid
cell. This simulation is designed to predict snow depth, soil moisture, surface
runoff, and most importantly, selected stream and river flow rates. The spatial
resolution is fine enough to provide the detailed information needed by water
managers who oversee different watersheds.
The data generated
by the hydrologic model will also be useful for flood control.
Because California’s water system is used for both flood control and water
storage, water managers need accurate predictions of the maximum values for precipitation,
runoff, and river flows as well as the averages over time. That way, they can
make informed decisions about how much reservoir capacity is needed to absorb
surges in river flow and runoff.
A key component of
this project is making the research results useful to water managers and policy
makers. “Our approach is to predict exactly the same
quantities at the same observation points that water managers use to guide their
decisions,” says Duffy. “For example, when we simulate future climate
patterns, we’ll predict river flows at locations above major reservoirs.
With data from these important reference points, water managers can use the predictions
to understand how to operate the water system in an altered climate regime.”
simulations are being used to project future changes in California’s
hydrologic cycle and determine how these changes will affect
the availability of freshwater. Researchers use a sequence
of models, and each successive model increases the simulation’s
spatial resolution. The surface hydrology models are run with
a lumped-mode grid—that is, each watershed is treated
as one irregularly shaped grid cell.
of the project is to estimate the uncertainty in the predictions. “We’re
emphasizing the uncertainties both from a research perspective and in response
to discussions with water managers,” says Duffy. “They gave us a
clear message: ‘Tell us the uncertainties associated with your models.’ One
approach is to compare results from a range of accepted models.”
The project team
has compared the simulations of present and future climates in California provided
by 15 global climate models. These models predict surface
temperature, precipitation rate, solid moisture content, water-equivalent snow
depth, and other meteorological quantities. Because each model was developed
at a different research institution, each one treats climate physics slightly
differently. Thus, the models give a range of predictions for both the present
and future climates of the western U.S., which provides a measure of uncertainty.
Initial results from
this project have led to endorsements by federal, state, and local agencies for
a center to address long-term water-supply predictions
for California. Such a center would provide projections of regional climate hydrology
to water managers, much as the Program for Climate Model Diagnosis and Intercomparison,
established at Livermore in 1989, develops methods to validate and compare global
climate models. The proposed center would include participants from the major
research groups working to improve the science of predicting future water-supply
patterns and problems.
validate the accuracy of a computer model, scientists compare
the model’s results with observations. In this example
comparison, the Livermore team used (a) the observed mean annual
precipitation in the western U.S. from 1971 to 2000 and (b)
results from a regional climate model of annual precipitation
for that same period. The model’s resolution is 9 kilometers.
The Threat of Nitrate Contamination
of the most important tasks for California water managers is to
protect the purity of groundwater,
which supplies about half of the state’s drinking
water. However, since 1988, about one-third of the state wells that supply public
drinking water have been abandoned, destroyed, or inactivated, frequently because
they have been contaminated with nitrate from fertilized farmland, dairies, feedlots,
and septic tanks.
Nitrate, a nitrogen–oxygen compound, is a significant source of nitrogen,
an essential nutrient. However, high levels of nitrate in drinking water can
cause serious illness and sometimes death. Nitrate poses a special risk for infants.
It can diminish the oxygen-carrying capacity of an infant’s blood (called
blue baby syndrome), which can lead to death. High nitrate levels can also harm
the ecosystems of lakes, streams, and the coastal ocean.
Ten percent of active
California public supply wells have nitrate contamination exceeding the drinking
water standard of 45 parts per million, and another 20 percent
contain nitrate levels that are significantly above background levels. In agricultural
counties, up to 80 percent of groundwater tapped for drinking water is affected
or polluted by nitrate. Alternatives such as drilling a new well or treating
contaminated water to remove nitrate are costly.
With a better understanding
of how nitrate levels in these wells will evolve over time, water managers can
decide which approach to use. In addition, their
efforts to protect drinking water will be improved if they have more accurate
information on how land-use and farming practices affect nitrate levels in groundwater.
The second project
of the Water Initiative, which is led by Livermore chemist Brad Esser, is designed
to address the nitrate contamination problem. Esser’s
team is studying the natural processes that control groundwater nitrate movement
and degradation. In this effort, the researchers are applying new diagnostic
tools and computer models and drawing on Livermore expertise in isotope hydrology,
groundwater modeling, and molecular biology. They are studying the problem at
the laboratory, farm, and water-basin scales.
(a) About 10 percent of active California
public water-supply wells have nitrate contamination exceeding
the drinking water standard of 45 parts per million.
In agricultural areas, such as Stanislaus County, up to
80 percent of groundwater is affected or polluted by nitrate.
(b) The map shows the extent of nitrate contamination
throughout the state.
Solubility, Stability Are a Problem
of its mobility, nitrate readily contaminates groundwater. Nitrate
is mobile because it is soluble
and stable in oxygen-rich water and does not bind
readily to soils. In oxygen-deficient waters, certain bacteria convert nitrate
to molecular nitrogen—a harmless component of the atmosphere—in a
process called denitrification. Esser and his colleagues are studying microbial
denitrification under laboratory and field conditions, so they can determine
a groundwater basin’s capacity to assimilate nitrate and understand how
nitrate distributions will evolve over time.
“We are developing better tools to detect and understand denitrification,” says
Esser. For example, one test is designed to determine whether bacteria capable
of denitrification are present and if they are removing groundwater nitrates.
The test detects a gene in the bacteria that indicates the presence of enzymes
responsible for the process. In addition, Livermore scientists have developed
a mass-spectrometry method to quantify the amount of nitrogen that has dissolved
in groundwater as a result of denitrification. The two tests allow researchers
to study what factors control the rate of denitrification in groundwater.
Water managers also
need to know the source or sources of nitrate contamination. For example, if
the source is septic discharge, then converting septic tanks
to sewer lines will be more effective than implementing a farm fertilizer management
program. Esser notes that many water contaminants, such as trichloroethylene,
are found in high-concentration plumes with easily identified sources. Groundwater
nitrate contamination, however, is often low-level and pervasive, reflecting
multiple sources such as septic systems or synthetic fertilizer or manure used
on crops, so identifying nitrate sources is more difficult.
To understand groundwater
flow paths and trace contaminants such as nitrate back to their source, the Livermore
team is combining an isotopic technique to determine
groundwater age (see S&TR, November 1997, Isotope
Tracers Help Manage Water
flow models that take advantage of the Laboratory’s supercomputing capability
(see S&TR, June 2001, Environmental
Research in California and Beyond).
For this project,
the team is working with colleagues from the UC Cooperative Extension and UC
Davis in a study of a dairy farm in California’s Central
Valley. The scientists are installing multilevel monitoring wells to determine
groundwater flow paths and to understand nitrate transport and denitrification.
The team is also
working with the Santa Clara Valley Water District to characterize nitrate transport
in the Llagas basin, a primary source of the groundwater needed
to meet future demands in southern Santa Clara County. The basin has pervasive
nitrate contamination in shallow aquifers but little contamination in deep aquifers.
“Deep wells in the basin do not contain nitrate either because denitrification
is occurring or because the deep water is old and uncontaminated,” says
Esser. “We’d like to determine which process is at work here. We
also want to identify the source of nitrate in the basin’s shallow wells.”
For this project,
the Livermore scientists are using geochemical models to identify input of nitrate
from synthetic fertilizer and developing analytical methods
to distinguish septic discharge from manure as sources of groundwater nitrate.
So far, they are finding that shallow wells contain young water, whereas the
deeper water is older and oxygen deficient. However, they have found no evidence
of denitrification under current conditions, indicating that nitrate contamination
has not yet penetrated deeper parts of the basin.
The researchers are
incorporating these data into a highly resolved three-dimensional (3D) model
of Llagas basin groundwater flow and transport. The flow field is
based on a 3D geostatistical model of sediment distribution that is derived from
drilling logs of more than 300 wells. Results from these simulations will be
used to develop groundwater resources in the basin and protect the basin from
future nitrate contamination.
Livermore researchers are installing
a network of multilevel monitoring wells near a dairy farm
in California’s Central Valley so they
can study the groundwater flow paths, nitrate transport, and denitrification.
The arrow shows the direction of groundwater from an irrigation canal
toward the monitoring wells. Manure used on crops is one possible
source of nitrate found in groundwater.
Creating “New” Water
wells closed by nitrate contamination could be reopened if a cost-effective
found. One significant cost of the water treatment technologies
developed in the 1960s and 1970s is their high energy use. For example, one-half
the overall cost of seawater desalination using reverse osmosis is the cost of
energy. Another treatment technology, electrodialysis, is more energy efficient
at removing salt from less saline, or brackish, waters. However, even electrodialysis
is not a cost-effective treatment method for the growing volumes of marginally
impaired waters—those that contain small concentrations of one or more
contaminants but are otherwise adequate for domestic use. A better approach would
be selective technologies designed to extract only a few problem species, which
would reduce both the volume of the waste stream and the overall energy cost
The third project
of the Water Initiative is focused on providing a cost-effective option for treating
these marginally impaired waters. If successful, the new
technology would undoubtedly help increase water supplies everywhere. In this
project, lead investigators geochemist Bill Bourcier and engineer Kevin O’Brien
are creating energy-efficient membranes to replace the solid polymer membranes
used in electrodialysis. This approach taps Livermore’s capabilities in
computational chemistry and nanomaterials synthesis. Says Bourcier, “We
want to use it to treat brackish water in a way that sharply lowers operating
is characterizing the Llagas groundwater basin, which is managed
by the Santa Clara Valley Water District. As shown in data
from wells at one location (Gilman), the basin has pervasive
nitrate (NO3) contamination in shallow aquifers but little
contamination in deep aquifers, where oxygen (O2) is absent.
(* = less than 1 milligram per liter.)
Livermore researchers are evaluating
a modified electrodialysis setup to lower the energy costs
for this process by 50 percent. If the goal is met, electrodialysis
would become a much more important technology in treating
electrodialysis, transport of either positively charged ions (cations)
or negatively charged ions
(anions) through copolymer membranes is driven by a voltage
applied by a pair of flat electrodes. The ions are driven toward the electrode
with the opposite charge. Water flows between alternate cation-permeable and
anion-permeable copolymer membrane sheets sandwiched between the electrodes and
separated by spacers. As water flows between the membranes, salt is removed from
one compartment and concentrated in adjacent compartments, with up to a hundred
or more membrane pairs per stack. A manifold separates the exiting fluid into
a relatively salt-free permeate product and a salt-enriched brine for disposal.
The current electrodialysis
technology is inefficient because it forces all dissolved ions, including those
that are considered benign or healthy, through the solid
membranes. The Livermore team is replacing these membranes with “smart” membranes
of polycarbonate—the material used to make compact disks—which are
then coated with a thin layer of gold. These
smart membranes can be designed to selectively remove only one contaminant of
interest by specifying the pore size, voltage, and electric field to attract
the target contaminant. For nitrate cleanup, a small fraction of a volt will
be applied to each membrane, and the overall electric field will measure 1 to
2 volts per membrane pair.
“With current electrodialysis design, every ion is pushed through a solid plastic
membrane that has high electrical resistivity and no selectivity,” Bourcier
says. “The smart membrane is designed to have low resistivity to ion transport
and, therefore, high energy efficiency—up to 50 percent greater than standard
Livermore’s modified electrodialysis
technology replaces the solid polystyrene membranes with “smart” membranes
of gold-coated polycarbonate. By specifying the pore size,
voltage, and electric field that will best attract and
isolate a target contaminant, researchers can design each
membrane to selectively remove only one contaminant of
This image shows a smart membrane
with pores drilled to 10 nanometers in diameter—the
size needed for nitrate ions to pass through.
Pores Drilled in Smart Membranes
membranes have pores drilled to an optimal size for selective removal
of the ions of interest.
If the system is optimized for nitrate ions, for example,
those ions will preferentially pass through the pores, while others remain with
the stream of water. The nitrates can then be collected in the waste stream.
The pores are created
with an etching process using Livermore’s
technology. For nitrate treatment, the membrane pores are about 10 nanometers
in diameter. Current polycarbonate
membrane samples contain about 1 billion holes per square centimeter.
Membranes are being
designed using quantum mechanical modeling, which simulates the ions of interest
in electrolyte solutions in varying concentrations. The
modeling work, which is done on supercomputers and led by physicist Bill Wilson,
uses a numerical method for calculating the electrostatic field in the vicinity
of the charged membrane pore surfaces. The modeling takes into account an ion’s
unique 3D geometry and electronic charge distribution. Its motion through the
membrane is determined by potentials applied to the membrane elements. The modeling
results determine the pore size and the optimum voltage to be applied to the
membrane. “Water purification research has always been an empirical field,” says
Bourcier. “We’re modeling the membranes before they are manufactured
to avoid a lot of trial and error.”
The project team
also wants to research contaminants besides nitrate. Many community wells do
not meet the new lower limits for arsenic, but treating them with reverse
osmosis would cost millions of dollars. Electrodialysis with smart membranes
could be a viable alternative. Other contaminants of interest include perchlorate,
a by-product of rocket fuel that is found in Santa Clara County groundwater,
and selenium, a natural element found in Central Valley groundwater and elsewhere.
Within a year, the
researchers plan to test a prototype unit in the field, and they are evaluating
potential demonstration sites. Bourcier believes that the
technology will be capable of purifying a metric ton of water for 20 cents in
energy costs, half of current costs. In addition, large-scale smart membrane
manufacturing would cost less than a dollar per square meter.
The team is confident
the pores also could be used to trap minor contaminants, such as perchlorate
molecules, which typically are present in parts-per-billion
concentrations. For those applications, the voltage applied to the membranes
would be turned up to electrochemically destroy the perchlorate molecules and,
thus, eliminate any waste stream.
In a similar manner,
a membrane could be designed to selectively remove viruses and then deactivate
them. Bourcier foresees specialized membranes for the military,
such as a unit mounted on a Humvee to purify brackish water for troops in the
field, or membranes designed to remove chemical and biological warfare agents
from water. The technology could also be used to purify the wastewater from the
production of oil, gas, and coal and to recover metals in industrial wastewater
and in silicon chip manufacturing. “There are many tricks we can try,” says
Bourcier. “If we’re successful, we’ll see much greater use
Quantum mechanical modeling is being
used to design the smart membranes. (a) A simulation of
a smart membrane pore shows the strong electric field gradients
near the pore surface, where blue is the lowest voltage
and red is the highest. The electrostatic forces will induce
a nitrate molecule to pass through the pore where the molecule
can be collected in a waste stream. (b) The same gradient
is shown from the top, looking down on the pore. (c) This
model shows the charge distribution of a nitrate ion, where
the white area denotes an area of negative charge.
California Again Leads the Nation
says she is seeing results from early progress of the Water Initiative.
For example, Livermore
researchers have received letters of endorsement from
many water districts and agencies. “Successful development of these tools
and methods may revolutionize the options water managers have to address the
challenges facing them.”
Although the immediate
focus is California, the Livermore tools and methods can be applied anywhere
in the nation. The state, Newmark says, is akin to “a
canary in a coal mine” because looking at California’s water picture
is like looking at America’s water future.
Key Words: denitrification, electrodialysis, global climate change,
hydrologic cycle, Laboratory Directed Research and Development,
nitrate contamination, water purification.
For further information contact Robin Newmark
(925) 423-3644 (email@example.com).
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