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1.
 The radon-222 (222Rn) activity in groundwater of the Apulian karstic aquifer in southern Italy is as great as 500 Becquerel per liter (Bq/L) locally. Normal radium-226 (226Ra) activity in the limestone and calcareous dolomites of the aquifer is not enough to explain such a high level. Laboratory investigations identified high 226Ra activity in the "terra rossa," the residuum occupying fissures and cavities in the bedrock, and also the relation between (1) 226Ra-bearing bedrock and "terra rossa" and (2) 222Rn in water. The "terra rossa" is the primary source of the radon in the groundwater. The experimental results show the need to characterize the "terra rossa" of Apulia on the basis of 226Ra activity and also to study the distribution and variations in 222Rn activity over time in the aquifer. Received, January 1996 · Revised, March 1997, September 1997, June 1998 · Accepted, July 1998  相似文献   

2.
The ground waters circulating in the Apulian mesozoic carbonate aquifer, of coastal type, show high concentrations of 222Rn everywhere. Considering their variation during the different phases of a hydrological year, such high concentration values can reach activity of 20 Bq/L, in the more internal zones of the aquifer. Moreover, it is often observed that, in correspondence of wells and springs nearest the coast, the concentrations of radioactive gas reach values greater than 400 Bq/L and vary considerably during the course of a day and with withdrawals. The research carried out over the last few years, has confirmed that 226Ra and 222Rn concentrations in the karst groundwater of Apulia, are mainly related to the occurrence of Terra Rossa inside the aquifer and the capacity of these paleosols to fix the salts of 226Ra coming from the dissolution of the calcareous and calcareous-dolomitic rocks. This paper shows the results of the analysis performed to define 222Rn increase in the brackish waters that come in contact with carbonate rocks and terra rossa. It also indicates the results of surveys performed in a coastal zone with well-known hydrogeological features. The controls performed during one hydrological year, have confirmed the relationships between the salt content of the ground waters and the enrichment of 222Rn and have highlighted that the manner of increase of this radioisotope is related to cases of ionic exchange and adsorption regulated by the dynamics of marine intrusion.  相似文献   

3.
A total of 1270 raw-water samples (before treatment) were collected from 15 principal and other major aquifer systems (PAs) used for drinking water in 45 states in all major physiographic provinces of the USA and analyzed for concentrations of the Ra isotopes 224Ra, 226Ra and 228Ra establishing the framework for evaluating Ra occurrence. The US Environmental Protection Agency Maximum Contaminant Level (MCL) of 0.185 Bq/L (5 pCi/L) for combined Ra (226Ra plus 228Ra) for drinking water was exceeded in 4.02% (39 of 971) of samples for which both 226Ra and 228Ra were determined, or in 3.15% (40 of 1266) of the samples in which at least one isotope concentration (226Ra or 228Ra) was determined. The maximum concentration of combined Ra was 0.755 Bq/L (20.4 pCi/L) in water from the North Atlantic Coastal Plain quartzose sand aquifer system. All the exceedences of the MCL for combined Ra occurred in water samples from the following 7 PAs (in order of decreasing relative frequency of occurrence): the Midcontinent and Ozark Plateau Cambro-Ordovician dolomites and sandstones, the North Atlantic Coastal Plain, the Floridan, the crystalline rocks (granitic, metamorphic) of New England, the Mesozoic basins of the Appalachian Piedmont, the Gulf Coastal Plain, and the glacial sands and gravels (highest concentrations in New England).  相似文献   

4.
High concentrations of 222Rn have been found throughout the waters of the coastal carbonate-rock Mesozoic aquifer located in the region of Apulia in southern Italy. Studies undertaken have determined that such concentrations are due to the radioisotopic features of terra rossa, a type of paleosol that is generated as a residual byproduct of carbonate dissolution and is found to be widespread throughout the aquifers fissures and karst cavities.These special types of soil feature a rather high clay content (80–95%) and, although variable, their specific 226Ra activity (70–147 Bq/kg) is nonetheless considerably greater than that of limestone (~50 Bq/kg). In fact, there are substantial differences in 222Rn concentrations found in waters that come into contact with this type of rock and paleosol.The partial dissolution of some carbonate rock samples in the laboratory confirmed that the 226Ra released by the dissolved rock primarily accumulates in the residual soil deposits, especially in ones containing finer granules. This has also been the result of experiments conducted on 15 terra rossa samples collected from the region, which indicates that there is a close correlation between the specific 226Ra activity and the clay content of such paleosols, which varies with the stage of weathering.It has been found that the 222Rn concentrations in the regions waters, depend on the specific terra rossa 226Ra activity rather than on the quantity of terra rossa.Field checks have confirmed the possibility of using 226Ra and 222Rn as natural tracers in order to define hydrogeological problems in special environments such as karst. They can be used to distinguish the different water bearing zones in the carbonate-rock aquifer; analyze the influence of tides on coastal springs; determine the flow direction in the proximity of a well; recognize, recharge and the progressive decline of the groundwater level; derive indications of underground flow paths; and the occurrence of fissures and karstic cavities in the carbonate-rock aquifer.
Michele SpizzicoEmail: Phone: +39-080-5963676Fax: +39-080-5963675
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5.
In arid regions of western China, water resources come from mountain watersheds and disappear in the desert plain. The exchange of surface water and groundwater takes place two or three times in a basin. It is essential to analyze the interaction of groundwater with surface water to use water resources effectively and predict the change in the water environment. The conventional method of analysis, however, measures only the flow of a stream and cannot determine groundwater seepage accurately. As the concentration of Radon-222 (222Rn) in groundwater is much higher than in surface water, the use of 222Rn was examined as an indicator for the analysis of the interaction between surface water and groundwater. Measurement of the 222Rn concentration in surface water was conducted to detect groundwater seepage into a stream in the middle Heihe Basin of northwestern China. Furthermore, the simultaneous groundwater flow into and out of a stream from the aquifers was quantified by solving the 222Rn mass balance equation, in which the losses of gas exchange and radioactive decay of 222Rn are considered. Meanwhile, river runoff was gauged to determine the exchange rates between surface water and groundwater. The result shows that 222Rn isotope can be used as a good environmental tracer with high sensitivity for the interaction between surface water and groundwater, especially in the fractured aquifer system, karst aquifer system and discharge basins.  相似文献   

6.
The study reports the age evolution of groundwater as it flows from the recharge area through a regional alluvial aquifer system in North Gujarat-Cambay region in western India. Radiocarbon (14C), 4He and 4He / 222Rn dating methods have been employed. Sediments from a drill core in the Cambay Basin were also analysed for uranium (U) and thorium (Th) concentrations and the measured values have been used to estimate the 4He and 222Rn production rate for groundwater age calculations. Additionally, factors controlling the distribution of 222Rn, 4He and temperature anomalies in groundwater, vis-à-vis their relation to the tectonic framework and lithology of the study area, have also been examined.The multi-isotope study indicated a reasonable correspondence in groundwater age estimates by the three methods employed. The groundwater 14C ages increased, progressively, in the groundwater flow direction: from the foothills of Aravalli Mountains in the east, and reached a value of ∼35 ka towards the region of lowest elevation, linking Little Rann of Kachchh (LRK)-Nalsarovar (NS)-Gulf of Khambhat (GK) in the western part of the study area. In this region, groundwater ages obtained for free flowing thermal wells and springs employing 4He and 4He / 222Rn systematics are in the order of million years. Such anomalous ages are possibly due to enhanced mobilisation and migration of ‘excess helium’ from hydrothermal circulation vents along deep-seated faults. Excluding such anomalous cases and considering all uncertainties, presently estimated 4He and 4He / 222Rn groundwater ages are in reasonable agreement with 14C age estimates in the Cambay Basin for helium release factor (ΛHe) value of 0.4 ± 0.3. The 4He method also indicated west-southwards progression of groundwater ages up to ∼100 ka beyond the Cambay Basin.Large ‘excess helium’ concentrations are also seen to be generally associated with anomalous groundwater temperatures (> 35 °C) and found to overlie some of the basement faults in the study area, particularly along the east and the west flanks of the Cambay Basin. Groundwater 222Rn activities in most of the study area are 800 ± 400 dpm/l. But, a thermal spring at Tuwa on the east flank of the Cambay Basin, having granitic basement at shallow depth, recorded the highest 222Rn activity (∼63,000 dpm/l).  相似文献   

7.
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8.
Dissolved Rn was determined in 192 samples collected from cold shallow volcanic and sedimentary aquifers, deep thermal aquifers and from waters associated with bubbling gases in the western sector of the Sabatini Volcanic District and the Tolfa Mountains (central Italy). Shallow aquifers hosted in the Quaternary volcanic complexes show values ranging from 1.0 to 352 Bq/L (median value 55 and inter-quartile distance 62 Bq/L), while waters circulating within the permeable horizons of the sandy-to-clayey sediments of the Tolfa flysch have values from 1.0 to 44 Bq/L (median value 6.9 and inter-quartile distance 8.1 Bq/L). Thermal waters are hosted in the Mesozoic carbonate formations and move towards the surface along faults. Here, dissolved Rn values range from 0 to 37 Bq/L (median value 3.0 and inter-quartile distance 9.5 Bq/L). Waters associated with bubbling gases show dissolved Rn contents ranging from 2.0 to 48 Bq/L (median value 6.2 and inter-quartile distance 23 Bq/L). Those results suggest that lithology is the main factor affecting the Rn contents in shallow aquifers, due to the high levels of Rn progenitors U and Ra in the volcanic rocks relative to sedimentary units. The influence of other factors such as the presence of a fracture network, seasonal flow variations, type of discharge (from well or spring) was also investigated. Radon contents of thermal waters result from mixing with shallow waters (from both volcanic and sedimentary rock aquifers) and decrease of Rn solubility with temperature, while for bubbling pools the effects of strong degassing were also considered.In terms of health hazard from direct ingestion of Rn-rich waters, 20.8% of those circulating within the volcanic aquifer show values higher than the recommended value of 100 Bq/L, while none of those circulating within the sedimentary aquifers exceed the threshold value. Geostatistical techniques were used for the elaboration of contour maps by using variogram models and kriging estimation aimed at defining the areas where a potential health hazard due to the direct ingestion of Rn-rich waters and to inhalation of air following degassing of Rn from waters may be expected.  相似文献   

9.
To investigate the possible variations of Rn concentration in crystalline rocks as a function of flow conditions, a field study was carried out of a fractured aquifer in granite. The method is based on the in situ measurement of Rn in groundwater, aquifer tests for the determination of hydraulic characteristics of the aquifer and laboratory measurement of Rn exhalation rate from rocks. A simple crack model that simulates the Rn concentration in waters circulating in a fracture intersecting a borehole was also tested. The Rn concentrations in groundwaters from boreholes of the study site ranged from 192 to 1597 Bq L−1. The Rn exhalation rates of selected samples of granite and micaschist were determined from laboratory experiments. The results yielded fluxes varying from 0.5 to 1.3 mBq m−2 s−1 in granite and from 0.5 to 0.9 mBq m−2 s−1 in micaschists. Pumping tests were performed in the studied boreholes to estimate the transmissivity and calculate the equivalent hydraulic aperture of the fractures. Transmissivities ranged from 10−5 to 10−3 m2 s−1. Using the cubic law, hydraulic equivalent fracture apertures were calculated to be in the range of 0.5–2.3 mm.  相似文献   

10.
222Rn was used to assess river–groundwater interactions within Castel di Sangro alluvial aquifer (Italy). The effectiveness of results obtained through this indicator was verified by also analyzing δ18O, major ions and temperature in both surface and groundwater, and carrying out piezometric head monitoring and discharge measurements. Hydrogeological investigations suggested that the river infiltrates into the aquifer in the south-eastern aquifer portion, while groundwater discharges into the river in the north-eastern portion. The latter phenomenon is supported by 222Rn data. Nevertheless, flow-through conditions cause the modelled discharge along this river reach, estimated by 222Rn data in a degassing-corrected two-component mixing model, to be greater than the measured discharge. Concerning river infiltration into the aquifer, δ18O, major ions and temperature data show that the river contribution is negligible in terms of aquifer recharge. Thus, the observed increase in 222Rn concentration in that portion of the aquifer is due to the enrichment process caused by infiltration of rainwater (222Rn free) which flows from the local divide area. Hence, in the study site, the use of only 222Rn to predict river–groundwater interactions causes some estimation inaccuracies and it must be coupled with other hydrochemical and hydrogeological parameters to gain a thorough understanding of such interactions.  相似文献   

11.
In this study, natural (222Rn) and fluorescent (uranin) tracers were used to investigate the interactions between surface and subsurface waters in a small hydrographical basin located in the southeast region of Brazil. Levels of 222Rn were measured in 117 water samples with the use of an alpha solid-state detector. After the identification of the probable discharge sections along the stream, a measurement of the natural flows, upstream and downstream of these sections, was done with the use of a fluorimeter and fluorescent tracers. Also, scanning was done to verify a correlation between the natural gamma radiation and the 222Rn in the areas where its activity was higher. The results showed some sections where the 222Rn activity is more significant and contributed to the growth of the flows along the stream. It was possible to confirm a correlation between the discharge sections and the natural gamma radiation, what can be used as a preliminary approach to finding these sections in scenarios similar to the one studied here.  相似文献   

12.
River water infiltration into an unconfined porous aquifer (∼73% gravels, ∼12% sands, ∼15% silts and clays) in the Petrignano d’Assisi plain, central Italy, was traced combining isotopic techniques (222Rn) with hydrochemical and hydrogeologic techniques in order to characterize the system under study. The 222Rn gave information about the river water residence times within the aquifer and hydrochemical data, in a two-component mixing model, which allowed estimating the extent of mixing between surface waters and groundwater in wells at increasing distances from the river. The mixing measured in the well closer to the riverbank indicated a higher contribution of river water (up to 99%) during the groundwater recession phase and a moderate contribution (up to 64%) during the recharge phase. A model describing 222Rn concentrations in groundwater as the result of both parent/daughter nuclide equilibrium and mixing process (222Rn mixing/saturation model) was used to describe observed Rn concentrations and mixing index trends with the aim of evaluating water mean infiltration velocities along the transect. The stream bank infiltration velocities obtained by the model ranged from 1 m day−1 during groundwater recharge periods, when river water infiltration is lower, to 39 m day−1 during recession phases, when river water infiltration is larger.  相似文献   

13.
The Aral Sea has been shrinking since 1963 due to extensive irrigation and the corresponding decline in the river water inflow. Understanding of the current hydrological situation demands an improved understanding of the surface water/groundwater dynamics in the region. 222Rn and 226Ra measurements can be used to trace groundwater discharge into surface waters. Data of these radiometric parameters were not previously available for the study region. We determined 222Rn activities after liquid phase extraction using Liquid Scintillation Counting (LSC) with peak-length discrimination and analyzed 226Ra concentrations in different water compartments of the Amu Darya Delta (surface waters, unconfined groundwater, artesian water, and water profiles from the closed Large Aral Sea (western basin).The water samples comprise a salinity range between 1 and 263 g/l. The seasonal dynamics of solid/water interaction under an arid climate regime force the hydrochemical evolution of the unconfined groundwater in the Amu Darya Delta to high-salinity Na(Mg)Cl(SO4) water types. The dissolved radium concentrations in the waters were mostly very low due to mineral over-saturation, extensive co-precipitation of radium and adsorption of radium on coexisting solid substrates.The analysis of very low 226Ra concentrations (<10 ppq) at remote study sites is a challenge. We used the water samples to test and improve different analytical methods. In particular, we modified a procedure developed for the α-spectrometric determination of 226Ra after solid phase extraction of radium using 3M Empore™ High Performance Extraction Disks (Purkl, 2002) for the analysis of the radionuclide using an ICP sector field mass spectrometer. The 226Ra concentration of 17 unconfined groundwater samples ranged between 0.2 and 5 ppq, and that of 28 artesian waters between <0.2 and 13 ppq. The ICP-MS results conformed satisfactorily to analytical results based on γ-measurements of the 222Rn ingrowth after purging and trapping on super-cooled charcoal. The 226Ra concentrations were positively correlated with the salinity and the dissolved NaCl concentrations. The occurrence of unusually high 226Ra activities is explained by radium release from adsorption sites with increasing salinity. The inferred spatial variability of 222Rn in the Aral Sea and of 222Rn and 226Ra in the groundwater of the Amu Darya Delta is discussed in the context of our own previous hydrochemical studies in the study sites. Relatively low 222Rn activities in the unconfined GW (1–9.5 Bq/l) indicate the alluvial sediments hosting the GW to be a low-238U(226Ra) substrate. Positive correlations between U and 226Ra, and U and 222Rn are likely related to locally deposited Fe(Mn)OOH precipitates. The 222Rn activity of the GW, however, distinctly exceeds the 222Rn concentration in the Aral Sea (10 mBq/l), in principle, making 222Rn a sensitive tracer for the inflow of GW. The high water volume of the Large Aral Sea and wind induced mixing of its water body, however, hamper the detection of local groundwater inflow.  相似文献   

14.
In the Gran Sasso fissured carbonate aquifer (central Italy), a long-term (2001–2007) spatio-temporal hydrochemical and 222Rn tracing survey was performed with the goal to investigate groundwater flow and water–rock interaction. Analyses of the physico-chemical parameters, and comparisons of multichemical and characteristic ratios in space and time, and subsequent statistical analyses, permitted a characterisation of the hydrogeology. At the regional scale, groundwater flows from recharge areas to the springs located at the aquifer boundaries, with a gradual increase of mineralisation and temperature along its flowpaths. However, the parameters of each group of springs may significantly deviate from the regional trend owing to fast flows and to the geological setting of the discharge spring areas, as corroborated by statistical data. Along regional flowpaths, the effects of seasonal recharge and lowering of the water table clearly cause changes in ion concentrations over time. This conceptual model was validated by an analysis of the 222Rn content in groundwater. 222Rn content, for which temporal variability depends on seasonal fluctuations of the water table, local lithology and the fracture network at the spring discharge areas, was considered as a tracer of the final stages of groundwater flowpaths.  相似文献   

15.
This study was conducted primarily to measure and map radon activity concentration in soil gas and to understand the effect of geology and lithology and meteorology on radon concentration. Portable radon meter has been used for the measurement of soil gas radon at 30 different locations around Uro and Korn area in eastern Nuba Mountain South Kordofan State. The results indicate that the activity concentrations of 222Rn in soil gas fall within the range of 20–1,359 Bq/m3 with geometric mean of 102.80 Bq/cm3. The obtained data show that samples around Uro have anomaly of 222Rn concentrations than the sample around Korn. The reason could be attributed to differences in the geological structure, lithology and climate parameters. GIS predicative map has shown that the elevated levels of radon concentration were measured in North study area. Upon comparing the results with global data, it was found that the obtained values are far below the reported range of India, Slovenia, Portugal and Syria. However, the range of 222Rn concentrations in the soil observed in this study is significantly high relative to similar data reported from Libya. The regression analysis has shown that no correlation was noted between radon concentrations, climatic parameters and trace element.  相似文献   

16.
Several recent studies have suggested that submarine groundwater discharge (SGD) occurs in the Venice lagoon with discharge rates on the same order or larger than the surface runoff, as demonstrated previously in several other coastal zones around the world. Here, the first set of 222Rn data, along with new 226Ra data are reported, in order to investigate the occurrence and magnitude of SGD specifically in the southern basin of the lagoon. The independent connection with the Adriatic Sea (at the Chioggia inlet), in addition to the relative isolation of the water body from the main lagoon, make this area an interesting case study. There is probably only minimal fresh groundwater flux to the lagoon because the surrounding aquifer is subsiding and mainly has a lower hydraulic head than seawater.The data show that the Ra and Rn activities are in slight excess in the lagoon compared to the open sea, with values on the same order as those observed in the northern and central basins. Taking into account the water exchange rate between the lagoon and adjacent seawater provided by previous hydrodynamic numerical modelling, it is shown that this excess cannot be supported at steady state by only riverine input and by diffusive release from the sediment interstitial water. High activities observed in groundwater samples collected from 16 piezometers tapping into the shallow aquifer over the coastal lowland substantiate that the excess radioactivity in the lagoon may indeed be due to the advection of groundwater directly into the lagoon bottom water through the sediment interface. However, the data show that the groundwater composition is extremely heterogeneous, with high Ra activities concentrated within a narrow coastal strip where the contact between fresh and saline water takes place, while Rn strongly decreases when approaching the lagoon shore across the 20 km coastal plain. Assuming that the average groundwater activities measured in the coastal strip are representative of the SGD composition, a SGD flux of 7.7 ± 3.5 × 105 and 2.5 ± 2 × 106 m3/d is calculated using a 226Ra and 222Rn budget, respectively, (i.e. about 1-3 times the surface runoff), substantially lower than in previous studies. The influence of all assumptions on SGD estimates (groundwater heterogeneity, diffusive sediment flux, one-box versus multi-boxes model calculations) is discussed, and a sensitivity analysis of the influence of imperfect exchange and mixing at the lagoon outlets that affects the lagoon composition is provided. Finally, the results confirm that the SGD flux, calculated with these assumptions, is largely (∼80%) composed of saline lagoon water circulating through the sediment under the lagoon margin, and that the fresh water discharge associated with SGD is at most a minor term in the lagoon hydrologic balance.  相似文献   

17.
Depth-discrete tracing of residual dense non-aqueous phase liquid (DNAPL) sources in the subsurface is of great importance in making decisions related to contaminated groundwater remediation. Temporal variations in the natural tracer 222Rn and contaminant concentrations in groundwater contaminated with multiple chlorinated contaminants, such as trichloroethene, carbon tetrachloride, and chloroform, were examined to trace residual multiple DNAPL contaminants at an industrial complex in Wonju, Korea. The 222Rn activities and multiple DNAPL concentrations in the groundwater fluctuated irregularly according to the groundwater recharge. The natural tracer 222Rn in groundwater present in the soil layer, originating from the underlying crystalline biotite granite, had a wide range from 29,000 to 179,000 Bq/m3, and total concentrations of chlorinated solvents ranged from 0.06 to 17.77 mg/l, indicating the ambiguous results of 222Rn for tracing the residual DNAPL sources. In this paper, a method is presented to locate zones with a high probability of containing depth-discrete residual multiple DNAPL sources using 222Rn and considering relative contaminant concentrations. The results demonstrate that the combination of the 222Rn activities as a natural tracer and the relative contaminant concentrations is able to be used as a useful tool for tracing residual DNAPLs.  相似文献   

18.
Submarine groundwater discharge (SGD) is herein recognized as a significant pathway of material transport from land to the coastal SW Atlantic Ocean and thus, it can be a relevant factor affecting the marine biogeochemical cycles in the region. This paper focuses on the initial measurements of 226Ra, 228Ra and 222Rn made in Patagonia’s coastal zone of Chubut and Santa Cruz provinces (42°S–48°S, Argentina). 226Ra activity ranged from 2.9 to 73.5 dpm 100 L?1, and 228Ra activity ranged from 11.9 to 311.0 dpm 100 L?1 in groundwater wells. The radium activities found in Patagonia’s marine coastal regions and adjacent shelf indicate significant enrichment throughout the coastal waters. Groundwater samples presented the largest 222Rn activity and ranged from 2.66 to 1083 dpm L?1. Conversely, in the coastal marine environment, the 222Rn activity ranged from 1.03 to 6.23 dpm L?1. The Patagonian coastal aquifer showed a larger enrichment in 228Ra than in 226Ra, which is a typical feature for sites where SGD is dominant, probably playing a significant role in the biogeochemistry of these coastal waters.  相似文献   

19.
Radiometric measurements were carried out for the beach sands from East Rosetta estuary to determine the activity concentrations of 238 U, 226 Ra, 232 Th, and 40 K, using a Hyper Pure Germanium spectrometer, to estimate the dose rates and radiation hazard indices. The average specific activities are 778.20 Bq/kg for 238 U; 646.89 Bq/kg for 226 Ra; 621.92 and 627.85 Bq/kg for the 222 Rn daughters 214 Pb and 214 Bi respectively. The average specific activity of 232 Th is 1510.25 Bq/kg, while the calculated specific activity for 40 K has an average of 8.41 Bq/kg. The average specific activity of 235 U is 38.61 Bq/kg. The average absorbed dose rate is 1211.36 nGy/h, 20 times higher than the estimated average global primordial radiation of 60 nGy/h and 6 times higher than that of the world range (10-200 nGy/h). The radium equivalent (Ra eq ) values are from 6 to 9 times the recommended value. The internal and external hazard indices (H int , H ex ) indicate that their values are from 6 to 11 times the permissible values of these indices. These higher values may be due to the presence of economic heavy minerals containing radionuclides as zircon and monazite as well as some trace minerals, thorite and uranothorite. The mineralogical study indicates the beach sands contain heavy minerals, zircon, monazite, rutile, ilmenite, leucoxene, magnetite and garnet. The average abundance of zircon is 0.175 wt% ranging from 0.125 wt% to 0.239 wt%, while it is 0.004wt% ranging from 0.001 wt% to 0.007 wt% for monazite. The average abundance is 0.087 wt% for rutile; 2.029 wt% for ilmenite; 1.084 wt% for magnetite; 0.384 wt% for leucoxene and 0.295 wt% for garnet.  相似文献   

20.
Groundwater surveys were performed by detailed(around 300 sites) grid-analysis of water temperature, pH, redox potential, electrical conductivity, 222Rn, alkalinity and by calculating the pCO2, throughout the Ciampino and Marino towns in the Alban Hills quiescent volcano (Central Italy). Following several episodes of dangerous CO2 exhalation from soils during the last 20 years and earlier ashistorically recorded, the work aimed at assessing the Natural Gas Hazard (NGH) including the indoor-Rn hazard. The NGH was defined as the probability of an area to become a site of poisonous peri-volcanic gas exhalations from soils to the lower atmosphere (comprising buildings). CO2 was found to be a ``carrier' for the other poisonous minor and in trace components (HsS, CH4, 222Rn, etc.). This assessment was performed by extrapolating in the aquifer CO2 and 222Rn conditions, and discriminating sectors where future CO2 flux in soils as well as indoor-Rn measurements have to be noted. A preliminary indoor-Rn survey was performed at about 200 sites. The highest values were found in the highest pCO2 and high 222Rn values in groundwater. This indicates convection and enhanced permeability in certain sectors of the main aquifer, i.e., along the bordering faults and inside the gas-trap of the Ciampino Horst., where ``continuous gas-phase micro-macro seepage mechanism' is invoked to explain the high peri-volcanic gases flux.  相似文献   

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