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R G Cresswell - One of the best experts on this subject based on the ideXlab platform.
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Assessment of recharge to groundwater systems in the arid southwestern part of Northern Territory, Australia, using Chlorine-36
Hydrogeology Journal, 1999Co-Authors: R G Cresswell, John D.h. Wischusen, Gerry Jacobson, Keith FifieldAbstract:The sustainability of community water supplies drawn from shallow aquifers in the arid southwest of the Northern Territory has been evaluated using the radioactive isotope Chlorine-36 (36Cl). These aquifers include fractured sandstones of the Ngalia Basin, fractured metamorphic rocks and Cainozoic sands and gravels. 36Cl/Cl ratios for these shallow, regional groundwaters exhibit a bimodal distribution with peaks at 205 (±7) and 170 (±7)×10–15. The higher ratio probably represents modern (Holocene) recharge, diluted with windblown salts from local playa lakes, and occurs mostly around the margin of the basin. The lower ratio corresponds to a 36Cl "age", or mean residence time, of 80–100 ka, implying that the last major recharge occurred during the last interglacial interval (Oxygen Isotope Stage 5). These values are mainly observed in the interior of the Ngalia Basin. Lower values of the 36Cl/Cl ratio measured near playa lakes are affected by addition of chloride from remobilised salts. Finite carbon-14 (14C) data for the groundwaters are at variance with the 36Cl results, but a depth profile suggests low recharge, allowing diffusion of recent atmospheric carbon to the water table. The 36Cl results have important implications for groundwater management in this region, with substantial recharge only occurring during favourable, wet, interglacial climatic regimes; most community water supplies are dependent on these "old" waters.
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Fallout of Chlorine 36 to the Earth's surface in the southern hemisphere
Journal of Geophysical Research: Atmospheres, 1998Co-Authors: Melita Keywood, Allan R. Chivas, L.k. Fifield, R G CresswellAbstract:Chlorine 36 is a radioactive isotope produced in the atmosphere by the cosmic-ray spallation of 40Ar. It has many applications as an environmental tracer which require an understanding of 36Cl in modern deposition. Data are currently available only for high latitudes in the northern hemisphere and for Antarctica. In the present work, the first data for 36Cl in modern deposition for the southern hemisphere are presented. Excluding the tropical data, the latitude dependence of this fallout is found to follow the form predicted by Lal and Peters, and its magnitude is within 40% of their predictions. In tropical Australia, however, a substantial excess of 36Cl is observed in rainfall from sites that derived most of their precipitation from the summer monsoon. If the high-latitude northern hemisphere data are representative of the entire hemisphere, then the southern hemisphere fallout appears to be 2–3 times less than in the northern hemisphere. It is suggested that this may be due to enhanced stratosphere-troposphere exchange north of the equator promoted by the greater area of landmass, while the symmetric thermal structure of the southern atmosphere dampens this exchange.
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cosmogenic Chlorine 36 production in calcite by muons
Geochimica et Cosmochimica Acta, 1998Co-Authors: John O Stone, G L Allan, L.k. Fifield, J.m. Evans, R G CresswellAbstract:Abstract At depths below a few metres, 36Cl production in calcite is initiated almost entirely by cosmic ray muons. The principal reactions are (1) direct negative muon capture by Ca; 40Ca(μ−,α)36Cl, and (2) capture by 35Cl of secondary neutrons produced in muon capture and muon-induced photodisintegration reactions. We have determined rates for 36Cl and neutron production due to muon capture in calcite from a 20 m (5360 g cm−2) depth profile in limestone. The 36Cl yield from muon capture by Ca in pure calcite is 0.012 ± 0.002 atom per stopped negative muon. The surface production rate of 36Cl by muon capture on Ca in calcite is, therefore, 2.1 ± 0.4 atom g−1a−1 at sea level and high latitude, approximately 11% of the production rate by Ca spallation. If it is assumed that 34% of the negative muons are captured by the Ca atom in calcite, the α-yield from 40Ca following muon capture is 0.043 ± 0.008, somewhat lower than the result of a recent muon irradiation experiment (0.062 ± 0.020), but well within the extremes of existing theoretical predictions (0.0033–0.15). The average neutron yield following muon capture in pure calcite is 0.44 ± 0.15 secondary neutrons per stopped negative muon, in good agreement with existing theoretical predictions. Cosmogenic isotope production by muons must be taken into account when dating young geomorphic surfaces, especially those created by excavation of only a few metres of overlying rock. Attention to isotope production by muons is also crucial to determining surface erosion rates accurately. Due to the deep penetration of muons compared to cosmic ray hadrons, the accumulation of muon-produced 36Cl is less sensitive to erosion than that of spallogenic 36Cl. Although production by muons at the surface is only a small fraction of production by spallation, the fraction of muon-produced 36Cl in rapidly eroding limestone surfaces can approach 50%. In such cases, erosion rates estimated using conventional models which attribute production solely to spallation will be in error by up to 40%. The difference in sensitivity to erosion of spallogenic and muon-produced 36Cl suggests methods for dating deeply eroded surfaces, checking the assumption of steady-state when calculating erosion rates, and unravelling multi-stage exposure and erosion histories.
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Cosmogenic Chlorine-36 production in K-feldspar
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1997Co-Authors: J.m. Evans, John O Stone, L.k. Fifield, R G CresswellAbstract:The high production rate of in-situ cosmogenic 36Cl from potassium allows K-rich minerals to be dated with high sensitivity and precision. K-rich minerals, such as K-feldspar and biotite are commonly associated with quartz in which 26Al and 10Be are produced, allowing three cosmogenic nuclides, with half-lives ranging from 0.3 Ma to 1.5 Ma, to be measured in a single sample. To calibrate the production rate of 36Cl from potassium we have measured K-feldspar samples from ice-scoured bedrock from three separate sites, covering a range of altitudes, latitudes and exposure ages. The results from each site are internally consistent, with eight glacial pavements from the Sierra Nevada giving a production rate of 1290 ± 220 atom/(gK)/yr at 3000 m and 38°N, three Scottish glacial pavement samples giving 301 ± 27 atom/(gK)/yr at 520 m and 58°N, and two Antarctic bedrock samples giving 1310 ± 50 atom/(gK)/yr at 2000 m and 70°S. Normalising these production rates to sea level and high latitude, results from the Sierra Nevada and Scotland are found to be in good agreement with each other, but the production rate derived from the Antarctic samples is found to be approximately 35% higher. Repeat measurements and stepwise dissolution indicate that the high 36Cl concentration of the Antarctic samples is real and cannot be attributed to meteoric 36Cl. We must therefore conclude that either the 36Cl production rate differ on the 104 and 106 yr time scales, or that the current altitude scaling factor applied to the Antarctic results underestimates the true scaling factor for the Antarctic atmosphere. The production rates derived above are based principally on K-feldspars with low chloride contents. Samples with high chloride contents required corrections for 36Cl produced by neutron capture on 35Cl. The 36ClCl ratio of this component was measured directly in four samples from the Sierra Nevada after crushing the K-feldspar to release Cl-rich fluid from inclusions. The 36ClCl ratios measured appear to be in reasonable agreement with values predicted by recent calibrations of the production by neutron capture on 35Cl, but the final comparison awaits measurements of uranium, thorium and neutron absorber (B, Gd, Sm) concentrations in our samples.
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Cosmogenic Chlorine-36 from calcium spallation
Geochimica et Cosmochimica Acta, 1996Co-Authors: John O Stone, G L Allan, L.k. Fifield, R G CresswellAbstract:Calcium is a major target element for cosmogenic 36Cl production. Consequently 36Cl rapidly reaches detectable levels in minerals such as calcite and calcium feldspar exposed at the Earth's surface. Spallation of calcium isotopes typically accounts for 80–90% of 36Cl production in these minerals, with subsidiary contributions from negative muon capture by 40Ca and thermal neutron capture by 35Cl. To provide a basis for surface exposure dating, we have calibrated cosmogenic 36Cl production in calcium feldspar from the 17,300 year old Tabernacle Hill basalt. At an altitude of 1445 m and an effective geomagnetic latitude of 40.9 ° the calcium spallation rate is 152 ± 11 atoms (g Ca)−1 a−1. The corresponding rate at sea level and high latitude is estimated at 48.8 ± 3.4 atoms (g Ca)−1 a−1. The muon capture rate used to derive these values is 8.8 ± 2.2 atoms (g Ca)−1 a−1 at the Tabernacle Hill site, scaled from a value of 4.8 ± 1.2 atoms (g Ca)−1 a−1 at sea level and high latitude. The calcium spallation rate determined in this study is in excellent agreement with previous whole-rock calibration measurements at Tabernacle Hill, when these are recalculated with respect to the absolute timescale. The calibration of 36C1 production from calcium underpins development of an exposure dating technique for calcite. Due to its high calcium content, the 36Cl production rate in calcite is higher than in any other common rock-forming mineral. Measurement of 36Cl in calcite, with an accelerator mass spectrometric detection limit of ~5 × 103 atoms per gram, allows dating of limestone surfaces exposed for periods ranging from ~102–106 years. Alternatively, erosion rates from less than 1 to greater than 1000 μm per year can be determined in the case of eroding karst surfaces. Though the 36Cl production rate is lower in calcium feldspar than in calcite, measurements on this mineral will provide a useful means of dating young basalt lavas.
Marek Zreda - One of the best experts on this subject based on the ideXlab platform.
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Chlorine-36 in groundwater of the United States: empirical data
Hydrogeology Journal, 2003Co-Authors: Stanley N. Davis, L. De Wayne Cecil, Stephen Moysey, Marek ZredaAbstract:Natural production of the radionuclide Chlorine-36 (36Cl) has provided a valuable tracer for groundwater studies. The nuclear industry, especially the testing of thermonuclear weapons, has also produced large amounts of 36Cl that can be detected in many samples of groundwater. In order to be most useful in hydrologic studies, the natural production prior to 1952 should be distinguished from more recent artificial sources. The object of this study was to reconstruct the probable preanthropogenic levels of 36Cl in groundwater in the United States. Although significant local variations exist, they are superimposed on a broad regional pattern of 36Cl/Cl ratios in the United States. Owing to the influence of atmospherically transported ocean salt, natural ratios of 36Cl/total Cl are lowest near the coast and increase to a maximum in the central Rocky Mountains of the United States.
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Chlorine-36, bromide, and the origin of spring water
Chemical Geology, 2001Co-Authors: Stanley N. Davis, Marek Zreda, L. De Wayne Cecil, Stephen MoyseyAbstract:Natural ratios of Chlorine-36 (36Cl) to stable Chlorine (i.e., 36Cl/Cl×10−15) vary in shallow groundwater of the United States from about 50 in coastal areas to about 1400 in the northern Rocky Mountains. Ratios lower than these indicate the presence of chloride (Cl−) that has been isolated from the atmosphere for hundreds of thousands of years, if not longer. Higher ratios, which can exceed 5000, usually originate from fallout from testing thermonuclear devices in the western Pacific in the 1950s. Natural mass ratios of chloride to bromide (Cl−/Br−) in precipitation vary in the United States from about 250 in coastal areas to about 50 in the north-central states. Lower ratios may suggest contamination from human sources. Higher ratios, which may exceed 2000, commonly reflect the dissolution of halite. Seawater has a Cl−/Br− ratio of 290. Both 36Cl and Cl−/Br− ratios have been measured in 21 samples of spring water collected from springs in 10 different states. Brackish water from Saratoga Springs area in New York has low values for both 36Cl and Cl−/Br− ratios. This indicates that a large component of the water has a very deep origin. Brackish water from Alexander Springs in Florida has a low 36Cl ratio but a high Cl−/Br− ratio similar to seawater. This suggests the addition of ancient seawater that may be trapped in the aquifer. Big Spring in Iowa discharges water with a very high Cl−/Br− ratio but a moderate 36Cl ratio. The high ratio of Cl−/Br− may be produced by dissolution of road salt or agricultural chemicals. Of the 21 springs sampled, only 10 appeared to have potable water not significantly affected by human activity. Chlorine-36 from testing of nuclear devices is still being flushed out of four of the spring systems that were sampled. Thus, more than 45 years have passed since 36Cl was introduced into the aquifers feeding the springs and the systems, as yet, have not been purged.
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Ages of Prehistoric Earthquakes Revealed by Cosmogenic Chlorine-36 in a Bedrock Fault Scarp at Hebgen Lake
Science (New York N.Y.), 1998Co-Authors: Marek Zreda, Jay Stratton NollerAbstract:Cosmogenic Chlorine-36 reveals dates of the multiple prehistoric earthquakes that have produced a scarp on the Hebgen Lake fault. Apparent Chlorine-36 ages are stratigraphically correct, follow a predicted theoretical pattern, and produce geologically reasonable model ages of 24, 20, 7.0, 2.6, 1.7, and 0.4 thousand years ago. This result demonstrates the feasibility of using cosmogenic Chlorine-36 to extract paleoearthquake records from bedrock fault scarps.
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Chlorine-36 and the initial value problem
Hydrogeology Journal, 1998Co-Authors: Stanley N. Davis, Marek Zreda, De Wayne Cecil, Pankaj SharmaAbstract:Chlorine-36 is a radionuclide with a half-life of 3.01×105a. Most 36Cl in the hydrosphere originates from cosmic radiation interacting with atmospheric gases. Large amounts were also produced by testing thermonuclear devices during 1952–58. Because the monovalent anion, chloride, is the most common form of Chlorine found in the hydrosphere and because it is extremely mobile in aqueous systems, analyses of both total Cl– as well as 36Cl have been important in numerous hydrologic studies. In almost all applications of 36Cl, a knowledge of the initial, or pre-anthropogenic, levels of 36Cl is useful, as well as essential in some cases. Standard approaches to the determination of initial values have been to: (a) calculate the theoretical cosmogenic production and fallout, which varies according to latitude; (b) measure 36Cl in present-day precipitation and assume that anthropogenic components can be neglected; (c) assume that shallow groundwater retains a record of the initial concentration; (d) extract 36Cl from vertical depth profiles in desert soils; (e) recover 36Cl from cores of glacial ice; and (f) calculate subsurface production of 36Cl for water that has been isolated from the atmosphere for more than one million years. The initial value from soil profiles and ice cores is taken as the value that occurs directly below the depth of the easily defined bomb peak. All six methods have serious weaknesses. Complicating factors include 36Cl concentrations not related to cosmogenic sources, changes in cosmogenic production with time, mixed sources of chloride in groundwater, melting and refreezing of water in glaciers, and seasonal groundwater recharge that does not contain average year-long concentrations of 36Cl.
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Cosmogenic Chlorine-36 production rates in terrestrial rocks
Earth and Planetary Science Letters, 1991Co-Authors: Marek Zreda, Fred M. Phillips, David Elmore, Pankaj Sharma, Peter W. Kubik, Ronald I. DornAbstract:Abstract Chlorine-36 is produced in rocks exposed to cosmic rays at the earth surface through thermal neutron activation of 35Cl, spallation of 39K and 40Ca, and slow negative moun capture by 40Ca. We have measured the 36Cl content of 14C-dated glacial boulders from the White Mountains in eastern California and in a 14C-dated basalt flow from Utah. Effective, time-intergrated production parameters were calculated by simultaneous solution of the 36Cl production equations. The production rates due to spallation are 4160 ± 310 and 3050 ± 210 atoms 36Cl yr−1 mol−139K and 40Ca, respectively. The thermal neutron capture rate was calculated to be (3.07 ± 0.24) × 105 neutrons (kg of rock)−1 yr−1. The reported values are normalized to sea level and high geomagnetic latitudes. Production of 36Cl at different altitudes and latitudes can be estimated by appropriate scaling of the sea level rates. Chlorine-36 dating was performed on carbonate ejecta from Meteor Crater, Arizona, and late Pleistocene morainal boulders from the Sierra Nevada, California. Calculated 36Cl ages are in good agreement with previously reported ages obtained using independent methods.
Pankaj Sharma - One of the best experts on this subject based on the ideXlab platform.
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Chlorine-36 and the initial value problem
Hydrogeology Journal, 1998Co-Authors: Stanley N. Davis, Marek Zreda, De Wayne Cecil, Pankaj SharmaAbstract:Chlorine-36 is a radionuclide with a half-life of 3.01×105a. Most 36Cl in the hydrosphere originates from cosmic radiation interacting with atmospheric gases. Large amounts were also produced by testing thermonuclear devices during 1952–58. Because the monovalent anion, chloride, is the most common form of Chlorine found in the hydrosphere and because it is extremely mobile in aqueous systems, analyses of both total Cl– as well as 36Cl have been important in numerous hydrologic studies. In almost all applications of 36Cl, a knowledge of the initial, or pre-anthropogenic, levels of 36Cl is useful, as well as essential in some cases. Standard approaches to the determination of initial values have been to: (a) calculate the theoretical cosmogenic production and fallout, which varies according to latitude; (b) measure 36Cl in present-day precipitation and assume that anthropogenic components can be neglected; (c) assume that shallow groundwater retains a record of the initial concentration; (d) extract 36Cl from vertical depth profiles in desert soils; (e) recover 36Cl from cores of glacial ice; and (f) calculate subsurface production of 36Cl for water that has been isolated from the atmosphere for more than one million years. The initial value from soil profiles and ice cores is taken as the value that occurs directly below the depth of the easily defined bomb peak. All six methods have serious weaknesses. Complicating factors include 36Cl concentrations not related to cosmogenic sources, changes in cosmogenic production with time, mixed sources of chloride in groundwater, melting and refreezing of water in glaciers, and seasonal groundwater recharge that does not contain average year-long concentrations of 36Cl.
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Chlorine-36 in fossil rat urine: An archive of cosmogenic nuclide deposition during the past 40,000 years
Science (New York N.Y.), 1997Co-Authors: Mitchell A. Plummer, Fred M. Phillips, June Fabryka-martin, H. J. Turin, Peter E. Wigand, Pankaj SharmaAbstract:Knowledge of the production history of cosmogenic nuclides, which is needed for geological and archaeological dating, has been uncertain. Measurements of Chlorine-36/Chlorine (36Cl/Cl) ratios in fossil packrat middens from Nevada that are radiocarbon-dated between about 38 thousand years ago (ka) and the present showed that 36Cl/Cl ratios were higher by a factor of about 2 before ∼11 ka. This raises the possibility that cosmogenic production rates just before the close of the Pleistocene were up to 50% higher than is suggested by carbon-14 calibration data. The discrepancy could be explained by addition of low–carbon-14 carbon dioxide to the atmosphere during that period, which would have depressed atmospheric radiocarbon activity. Alternatively, climatic effects on 36Cl deposition may have enhanced the 36Cl/Cl ratios.
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maximum ages of the coa valley portugal engravings measured with Chlorine 36
Antiquity, 1997Co-Authors: Fred M. Phillips, David Elmore, Montgomery Flinsch, Pankaj SharmaAbstract:Panel faces in teh Coa valley, Portugal, were available for engraving during the Upper Palaeolithic, according to 36Cl exposure ages of 16,000 to 136,000 years.
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Modern Chlorine-36 deposition in southern Maryland, U.S.A.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1994Co-Authors: L.j. Hainsworth, Pankaj Sharma, A.c. Mignerey, George R. Helz, Peter W. KubikAbstract:Abstract Monthly wet precipitation samples were collected at the Elms Environmental Education Center in St. Mary's County in southern Maryland from February 1991 to January 1993 and analyzed for 36 Cl. The analyses indicate that 36 Cl wet deposition undergoes seasonal variations, reaching a maximum in March/April. This pattern is well established for other stratospheric tracers such as Pu, 7,10 Be and ozone, and reflects seasonal variations in stratospheric-tropospheric mixing. The mean wet deposition 36 Cl flux was 3.86 ± 0.54 (× 10 −3 ) atoms/cm 2 s. Bulk precipitation samples were also collected at the site during the sampling period, and these data are compared to the wet-only data. The mean bulk deposition flux was 5.85 ± 0.78 (× 10 −3 ) atoms/cm 2 s. Dry deposition accounts for approximately 25% of the total 36 Cl deposition. Data from this study are compared with groundwater 36 Cl data from the Aquia Aquifer in southern Maryland, and it is concluded that modern deposition does not account for the relatively high 36 Cl concentrations found in the Aquia.
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Chlorine-36 Releases from the Savanniah River Site Nuclear Fuel Reprocessing Facilities
Ground Water, 1992Co-Authors: T. M. Beasley, D. Eimore, P. W. Kubik, Pankaj SharmaAbstract:Determinations of 36CI (T½= 301,000 a) in waters on and near the U.S. Department of Energy's Savannah River Site (SRS) in South Carolina reveal that nuclear fuel reprocessing activities there have released measurable amounts of this radionuclide to the environment. The natural atmospheric flux of 36CI at the latitude of SRS is 20-25 atoms m-2 sec-1. Atmospheric releases of 36CI from SRS, within the site boundaries, have increased this flux by a factor of at least 10 to 20. Approximately 3×109 Becquerels (Bq) [84 millicuries (mCi)] of site-derived 36 CI have been deposited within 200 km of the plant boundaries. By comparison, fallout of 36CI from nuclear weapons testing in the 1950s deposited twice this amount of activity in the same area. Surface-water 36CI concentrations in on-site streams represent about 0.01 percent of the Environmental Protection Agency (EPA) drinking-water standard and therefore pose no health concern. At SRS and similar facilities, this additional source of 36CI should prove useful for validating ground-water and atmospheric transport models.
Donald S. Sweetkind - One of the best experts on this subject based on the ideXlab platform.
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Chlorine-36 data at Yucca Mountain: statistical tests of conceptual models for unsaturated-zone flow.
Journal of Contaminant Hydrology, 2003Co-Authors: Katherine Campbell, June Fabryka-martin, Andrew V. Wolfsberg, Donald S. SweetkindAbstract:Abstract An extensive set of Chlorine-36 ( 36 Cl) data has been collected in the Exploratory Studies Facility (ESF), an 8-km-long tunnel at Yucca Mountain, Nevada, for the purpose of developing and testing conceptual models of flow and transport in the unsaturated zone (UZ) at this site. At several locations, the measured values of 36 Cl/Cl ratios for salts leached from rock samples are high enough to provide strong evidence that at least a small component of bomb-pulse 36 Cl, fallout from atmospheric testing of nuclear devices in the 1950s and 1960s, was measured, implying that some fraction of the water traveled from the ground surface through 200–300 m of unsaturated rock to the level of the ESF during the last 50 years. These data are analyzed here using a formal statistical approach based on log-linear models to evaluate alternative conceptual models for the distribution of such fast flow paths. The most significant determinant of the presence of bomb-pulse 36 Cl in a sample from the welded Topopah Spring unit (TSw) is the structural setting from which the sample was collected. Our analysis generally supports the conceptual model that a fault that cuts through the nonwelded Paintbrush tuff unit (PTn) that overlies the TSw is required in order for bomb-pulse 36 Cl to be transmitted to the sample depth in less than 50 years. Away from PTn-cutting faults, the ages of water samples at the ESF appear to be a strong function of the thickness of the nonwelded tuff between the ground surface and the ESF, due to slow matrix flow in that unit.
Stanley N. Davis - One of the best experts on this subject based on the ideXlab platform.
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Chlorine-36 in groundwater of the United States: empirical data
Hydrogeology Journal, 2003Co-Authors: Stanley N. Davis, L. De Wayne Cecil, Stephen Moysey, Marek ZredaAbstract:Natural production of the radionuclide Chlorine-36 (36Cl) has provided a valuable tracer for groundwater studies. The nuclear industry, especially the testing of thermonuclear weapons, has also produced large amounts of 36Cl that can be detected in many samples of groundwater. In order to be most useful in hydrologic studies, the natural production prior to 1952 should be distinguished from more recent artificial sources. The object of this study was to reconstruct the probable preanthropogenic levels of 36Cl in groundwater in the United States. Although significant local variations exist, they are superimposed on a broad regional pattern of 36Cl/Cl ratios in the United States. Owing to the influence of atmospherically transported ocean salt, natural ratios of 36Cl/total Cl are lowest near the coast and increase to a maximum in the central Rocky Mountains of the United States.
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Chlorine-36, bromide, and the origin of spring water
Chemical Geology, 2001Co-Authors: Stanley N. Davis, Marek Zreda, L. De Wayne Cecil, Stephen MoyseyAbstract:Natural ratios of Chlorine-36 (36Cl) to stable Chlorine (i.e., 36Cl/Cl×10−15) vary in shallow groundwater of the United States from about 50 in coastal areas to about 1400 in the northern Rocky Mountains. Ratios lower than these indicate the presence of chloride (Cl−) that has been isolated from the atmosphere for hundreds of thousands of years, if not longer. Higher ratios, which can exceed 5000, usually originate from fallout from testing thermonuclear devices in the western Pacific in the 1950s. Natural mass ratios of chloride to bromide (Cl−/Br−) in precipitation vary in the United States from about 250 in coastal areas to about 50 in the north-central states. Lower ratios may suggest contamination from human sources. Higher ratios, which may exceed 2000, commonly reflect the dissolution of halite. Seawater has a Cl−/Br− ratio of 290. Both 36Cl and Cl−/Br− ratios have been measured in 21 samples of spring water collected from springs in 10 different states. Brackish water from Saratoga Springs area in New York has low values for both 36Cl and Cl−/Br− ratios. This indicates that a large component of the water has a very deep origin. Brackish water from Alexander Springs in Florida has a low 36Cl ratio but a high Cl−/Br− ratio similar to seawater. This suggests the addition of ancient seawater that may be trapped in the aquifer. Big Spring in Iowa discharges water with a very high Cl−/Br− ratio but a moderate 36Cl ratio. The high ratio of Cl−/Br− may be produced by dissolution of road salt or agricultural chemicals. Of the 21 springs sampled, only 10 appeared to have potable water not significantly affected by human activity. Chlorine-36 from testing of nuclear devices is still being flushed out of four of the spring systems that were sampled. Thus, more than 45 years have passed since 36Cl was introduced into the aquifers feeding the springs and the systems, as yet, have not been purged.
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Chlorine 36 in ground water containing low chloride concentrations
Ground Water, 2000Co-Authors: Stanley N. Davis, Stephen Moysey, Laura E. Wolfsberg, June Fabrykamartin, Robert Shaver, Calvin E Alexander, Noel C. KrotheAbstract:Analyses of ground water from wells and springs in the United States indicate a broad regional trend in preanthropogenic (36Cl/total Cl) ×1015 ratios in potable water. Coastal areas influenced by marine chloride have ratios less than 100. These ratios increase inland and reach a maximum of about 1400 in the central and northern Rocky Mountains. However, the magnitude of these regional variations is greatly exceeded at a local level if water samples are considered regardless of age or origin. Most local departures from regional trends can be attributed to mixing of ground water recharge with either 36Cl from nuclear fusion tests to produce higher ratios or mixing with sources of old chloride such as from evaporite minerals to produce lower ratios. A useful interpretation of 36Cl data is difficult unless the origin of the chloride is understood. The interpretation is an unusually difficult problem for water having low chloride concentrations. The assumption that low concentrations originate primarily from wet and dry atmospheric deposition can be questioned even for some dilute waters with less than 2.0 mg/L chloride. Chloride/bromide ratios in ground water can help decipher the origin of the chloride. The presence of nonatmospheric chloride can be identified in part by its association with chloride/bromide mass ratios greater than about 200 in coastal areas and 100 in inland areas. Accurate chloride and bromide analyses are recommended for virtually all studies of 36Cl in natural waters, and particularly those with low concentrations of chloride.
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Chlorine‐36 in Ground Water Containing Low Chloride Concentrations
Ground Water, 2000Co-Authors: Stanley N. Davis, Stephen Moysey, June Fabryka-martin, Laura E. Wolfsberg, Robert B. Shaver, E. Calvin Alexander, Noel C. KrotheAbstract:Analyses of ground water from wells and springs in the United States indicate a broad regional trend in preanthropogenic (36Cl/total Cl) ×1015 ratios in potable water. Coastal areas influenced by marine chloride have ratios less than 100. These ratios increase inland and reach a maximum of about 1400 in the central and northern Rocky Mountains. However, the magnitude of these regional variations is greatly exceeded at a local level if water samples are considered regardless of age or origin. Most local departures from regional trends can be attributed to mixing of ground water recharge with either 36Cl from nuclear fusion tests to produce higher ratios or mixing with sources of old chloride such as from evaporite minerals to produce lower ratios. A useful interpretation of 36Cl data is difficult unless the origin of the chloride is understood. The interpretation is an unusually difficult problem for water having low chloride concentrations. The assumption that low concentrations originate primarily from wet and dry atmospheric deposition can be questioned even for some dilute waters with less than 2.0 mg/L chloride. Chloride/bromide ratios in ground water can help decipher the origin of the chloride. The presence of nonatmospheric chloride can be identified in part by its association with chloride/bromide mass ratios greater than about 200 in coastal areas and 100 in inland areas. Accurate chloride and bromide analyses are recommended for virtually all studies of 36Cl in natural waters, and particularly those with low concentrations of chloride.
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Chlorine-36 in Water, Snow, and Mid-Latitude Glacial Ice of North America: Meteoric and Weapons-Tests Production in the Vicinity of the Idaho National Engineering and Environmental Laboratory, Idaho
1999Co-Authors: L. Dewayne, Jaromy R Green, Stanley N. Davis, P. Sharma S. Vogt, Shaun K. Frape, G. L. CottrellAbstract:Measurements of Chlorine-36 (36Cl) were made for 64 water, snow, and glacial-ice and -runoff samples to determine the meteoric and weapons-tests-produced concentrations and fluxes of this radionuclide at mid-latitudes in North America. The results will facilitate the use of 36Cl as a hydrogeologic tracer at the Idaho National Engineering and Environmental Laboratory (INEEL). This information was used to estimate meteoric and weapons-tests contributions of this nuclide to environmental inventories at and near the INEEL. The data presented in this report suggest a meteoric source 36Cl for environmental samples collected in southeastern Idaho and western Wyoming if the concentration is less than 1 x 10 7 atoms/L. Additionally, concentrations in water, snow, or glacial ice between 1 x 10 7 and 1 x 10 8 atoms/L may be indicative of a weapons-tests component from peak 36Cl production in the late 1950s. Chlorine-36 concentrations between 1 x 10 8 and 1 x 10 9 atoms/L may be representative of re-suspension of weapons-tests fallout airborne disposal of 36Cl from the INTEC, or evapotranspiration. It was concluded from the water, snow, and glacial data presented here that concentrations of 36Cl measured in environmental samples at the INEEL larger than 1 x 10 9 atoms/L can be attributed to waste-disposal practices.