Groundwater can either be very young, representing recent recharge to the subsurface, or it can exist as very old water that has been interacting with the rock and sediments that host it. For example, a shallow flow system would constitute recharge in a small upland area followed by discharge to an immediately adjacent low-lying area. The distance of groundwater travel may be on the order of ‘s of metres. In contrast, groundwater flow in deeper regional flow systems can travel several ‘s to 1,’s of kilometres. A classic example of a deep regional flow system in Alberta is the general flow of groundwater from the recharge area in the western part of the province near the Rocky Mountain cordilleran and foothills region eastward across the plains areas towards the province of Saskatchewan see chart – right. The time that it can take for recharged groundwater to travel this distance is in the order of several million years. Work conducted by groundwater scientists and hydrogeologists in the province of Alberta has begun to establish the age of some of the waters collected from the various water-bearing formations beneath the province Lemay , Lemay and Konhauser , WorleyParsons Although more work is needed to understand the full range of groundwater ages, initial results indicate that some of the water beneath our landscape has been there for a very long time. Table 4 provides a very cursory review of some of the ages of groundwater measured in samples collected from near-surface bedrock and confined aquifers. These ages have been obtained using radiogenic isotopes of carbon and chloride, each with a half-life of 5, and , years, respectively.
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Bentley is a recognized expert in the fields of groundwater chemistry, environmental and chemical tracers for groundwater and soil gas, the fate of organic contaminants in the subsurface, treatment of water for recalcitrant contaminants, and quantitative evaluation of landfill gas production. Bentley pioneered the use of chlorine as an environmental tracer to date young and very old groundwater and has used various environmental tracers including stable isotopes to identify sources of groundwater contamination.
He developed a number of groundwater tracers and applied them to hydrogeologic problems in groundwater contamination and geothermal problems. He directed Hydro Geo Chem, Inc. Bentley founded Hydro Geo Chem, Inc.
Scientists expected chlorine from the nuclear bomb tests to have also rebounded. However, the Vostok ice showed very high levels of chlorine, with the using the isotope to date ancient ice and uncover Earth’s past climate, Robinson on South Napa Earthquake linked to summer groundwater.
Chlorine 36 dating of very old groundwater. 1 The Great Artesian Basin, Australia.
Researchers at the University of Delaware used chlorine isotopes as chemical tracers to determine the age and origin of groundwater in the Eastern Desert of Egypt. The paper, recently published in the Earth and Planetary Science Letters journal, said that in order to measure the age and origin of the groundwater. Twenty-nine samples were collected from different wells during several field expeditions in Egypt. The researchers used the long-lived radioactive isotope chlorine to estimate the age of the groundwater.
This isotope forms in the atmosphere and travels to earth and has a half-life of , years. Mahmoud Sherif, doctoral candidate at the University of Delaware and the main author of the paper, told Daily News Egypt that the study focused on using chlorine isotopes to identify sources of chloride, and to estimate the relative age of groundwater from the Nubian aquifer and the shallow alluvial aquifers, in addition to the fractured basement aquifers in the Eastern Desert of Egypt.
FOR OLD GROUNDWATER DATING formation ( to × -1), can be explained either by i) mixing with “old” chlorine in equilibrium Most Oxfordian groundwaters seem to follow a mixing trend on a 36Cl/Cl ratio vs chlorine plot.
Chlorine 36 dating of very old groundwater: 2. Milk River Aquifer, Alberta, Canada
Groundwater dating is an important step in understanding how much groundwater will be available over the long term, especially important at a time when drought is diminishing above-ground fresh water resources in the U. The process involves using isotopes in groundwater to calculate just how long the water has been in the subsurface, comparable to how archeologists use carbon dating with fossils.
So knowing the age of aquifers would give you an idea of how long it took and how valuable that resource is. Using what he calls first-of-its-kind equipment in his lab, Lu is able to determine the age of such old groundwater by quantifying the concentration of krypton isotopes in a given groundwater sample. As that water seeps underground, so does a small amount of krypton
) as well as 36Cl in water having very low concen- Very old chloride mixing with younger water. ing old groundwater beyond the range of 14C dating.
Chlorine has 9 isotopes with mass numbers ranging from 32 to Only three of these isotopes occur naturally: stable 35 Cl The ratio of 36 Cl to stable Cl in the environment is about x 10 : 1 Bentley et. In the subsurface environment, 36 Cl is generated primarily as a result of neutron capture by 35 Cl or muon-capture by 40 Ca Fabryka- Martin, The half-life of this hydrophilic nonreactive isotope makes it suitable for dating in the range of 60, to 1 million years. Additionally, large amounts of 36 Cl were produced by irradiation of seawater during atmospheric detonations of nuclear weapons between and The residence time of 36 Cl in the atmosphere is about 1 week.
Thus, as an event marker of s water in soil and ground water, 36 Cl is also useful for dating waters less than 50 years BP. The attractiveness of chlorine in hydrologic studies is that it is highly soluble, exists in nature as a conservative non-sorbing anion, does not participate in redox reactions, and has some quickly identifiable sources e.
The abundance of 36 Cl is usually reported as the atomic ratio of 36 Cl to total chloride in the sample. The ratio is always quite small in natural waters, typical values ranging from 10 to 10 Over geologic time an equilibrium will be established between the subsurface in-situ production of 36 Cl and its decay similar to the secular equilibrium of U isotopes.
Determining Timescales for Groundwater Flow and Solute Transport
Most of the water used by people in Egypt comes from the Nile River, which originates from precipitation over mountainous areas in the Ethiopian highlands. In areas far from the Nile River Valley, however, where water is scarce and the population is growing, groundwater is the only available freshwater resource. Knowing how much water is available in the groundwater aquifers and how fast it is being replenished is vital for providing the population with water for drinking and irrigation.
Determining the age of water sources helps in those calculations. A new study from the University of Delaware looked at chlorine isotopes as chemical tracers to determine the age and origin of groundwaters from the Eastern Desert of Egypt. The work resulted in a paper recently published in the Earth and Planetary Science Letters journal.
Article “Chlorine 36 dating of very old groundwater. 1 The Great 非常に古い地下水の塩素36を用いた年代測定 I オーストラリアの大さん井盆地. Publisher site.
Case studies were conducted on ground water salinity sources. Chloride and bromide ratios in atmospheric precipitation, water influenced by halite dissolution, shallow ground water, domestic sewage and summer runoff from urban streets may be used in potable water research. In natural ground water systems, both chlorine and bromine occur primarily as monovalent anions, chloride and bromide. Although dissolution or precipitation of halite, biological activity in the root zone, anion sorption, and exchange can affect chloride thromide ratios in some settings, movement of the ions in potable ground water is most often conservative.
Atmospheric precipitation will generally have mass ratios between 50 and ; shallow ground water, between and ; domestic sewage, between and ; water affected by dissolution of balite, between and 10,; and summer runoff from urban streets, between 10 and These, and other distinctive elemental ratios, are useful in the reconstruction of the origin and movement of ground water, as illustrated by case studies investigating sources of salinity in ground water from Alberta, Kansas, and Arizona, and infiltration rates and pathways at Yucca Mountain, Nevada.
The purpose of this study is to focus attention on the numerous ways in which bromide [Br. The study of [Br. In addition, a growing number of hydrogeologists have used [Br. Bromide has also been used extensively as an artificially introduced tracer for the movement of subsurface water Tennyson and Settergren ; Leap ; Bowman ; Davis et al.
Accelerator mass spectrometry group
Environmental Tracers in Subsurface Hydrology pp Cite as. One of the principal uses of environmental tracers is for determining the ages of soil waters and groundwaters. Information on soil water and groundwater age enables timescales for a range of subsurface processes to be determined. The use of environmental tracers to determine water ages allows groundwater recharge rates and flow velocities to be determined independently, and commonly more accurately, than with traditional hydraulic methods where hydraulic properties of aquifers are poorly known or spatially variable.
and quantified mixtures of young and old groundwater by combining. Chemical Geology the basin and near-zero in most wells deeper than ~– m. Groundwater with chlorine and carbon dating techniques. J. Hydrol. .
A groundwater dating for very old porewater using 36 Cl and 4 He was applied to the Koetoi and Wakkanai formations distributed in the northernmost part in Japan. He concentration in porewater ranged from 1. However, the possibility of mixing of young water was indicated because He concentration was lower than that calculated by multiplication of in situ He production and time after the uplift.
The porewater in the Koetoi Formation and the shallow part of the Wakkanai Formation were found to be affected by young surface water. Geological disposal is one of the most promising methods for high-level radioactive wastes HLW. In geological disposal, the transportation of radionuclides by groundwater is one of the most important phenomena for safety assessment of the HLW disposal groundwater scenario. Some geological formations with low hydraulic conductivity are considered potential host rock for radioactive waste disposal [ 1 — 3 ] because these formation will be able to isolate the radionuclides for a long time.
The migration of water and radionuclides needs to be understood in the safety assessment of radioactive waste disposal.