Combination of radon and stable isotope analysis as a tool for decision support concerning the remediation of NAPL-contaminated sites

The non-aqueous phase-liquid (NAPL)-contaminated aquifer at a major refinery site in Mexico was investigated. Owing to the depth of the contaminated aquifer section (NAPL source zone) of over 100 m below the surface, the actual aquifer material was not accessible for sampling. Information on the residual NAPL contamination of the aquifer could only be obtained indirectly by analysing groundwater samples from a few wells available at the site. To tackle the problem, an approach alternative to conventional groundwater analysis for dissolved NAPL was chosen. For evaluating the recent contamination and estimating its probable future development, the radioisotope radon-222 and the stable isotopes 13C, 34S and 18O were used as naturally occurring contamination tracers and process indicators. Radon was used as partitioning tracer for the approximate localization and semi-quantitative assessment of the NAPL source zone. The stable isotopes were used as indicators for naturally occurring biodegradation processes, which might potentially be implemented into future remediation schemes.     

Measurements of soil radon in south Russia for seismological application: Methodological aspects

As a first step in the monitoring of soil radon in search of harbingers of earthquakes, an investigation of suitable measurement techniques was conducted. As a result of these investigations, the following recommendations are made. Semiconductor and scintillation (ZnS) counters are the most suitable for Rn monitoring with chambers for natural drift of emanations to the detector. The method of compulsory selection of soil air is hardly effective. Soil aerosols might enter the drift chamber; these aerosols transfer many radioactive isotopes. The most suitable locations for placement of detectors of radon are cellars. Measurements should be continuous in character. The choice of a place for monitoring near mud volcanoes and faults should be determined by an Rn survey. In mud volcanoes, the best locations are areas with an average concentration of radon. For faults, identical tendencies of change in radon are maintained at some distance from the borders of the fault. For large faults, this distance is equal to half the width of the fault. For small faults, this distance increases by up to 3 times the fault width. All the recommendations were applied in the Northern Caucasus. Reliable results of the changes in soil radon were obtained during strong geophysical processes.     

Spatial and temporal variations of radon concentration in soil air

The spatial and temporal variability of the soil gas radon concentration in typical soils is studied. The results obtained will be further used to predict indoor radon levels. To this end, 50 measuring points along geologic sections with known physicogeological parameters of soils were chosen. The soil gas radon concentration was measured with SSNTDs (Type III-b) at a depth of 70 cm from June to October, 2000. The radon exposure time was 72–96 h. The average radon concentration in the soil pore air for an urban area was 11 kBqm⁻³ (1.7–24 kBqm⁻³). Small-scale spatial variations in the concentration were found to lie within a narrower range. The effect of meteorological conditions on the soil gas radon concentration was investigated by performing 8 series of measurements at 5 closely spaced points in September–October, 2000. A significant correlation was found between the soil radon concentration and atmospheric pressure (K=−0.86), ambient temperature (K=0.75), and soil temperature (K=0.75).     

The use of radon (Rn-222) and volatile organic compounds in monitoring soil gas to localize NAPL contamination at a gas station in Rio Claro,São Paulo State,Brazil

This study focuses on the presence of radon (²²²Rn) and volatile organic compounds (VOCs) in soil gases at a gas station located in the city of Rio Claro, São Paulo, Brazil, where a fossil fuel leak occurred. The spatial distribution results show a correlation between ²²²Rn and VOCs, consistent with the fact that radon gas has a greater chemical affinity with organic phases than with water. This finding demonstrates that the presence of a residual hydrocarbon phase in an aquifer can retain radon, leading to a reduced radon content in the soil gas. The data in this study confirm the results of previous investigations, in which the method used in this study provided a preliminary fingerprint of a contaminated area. Furthermore, the data analysis time is brief, and only simple equipment is required.     

Determination of radon concentration in soil gas by gamma-ray spectrometry of olive oil

Measurements of radon concentration in soil gas have been carried out using a bubbling system in which the soil gas is drawn through an active pumping to bubble a liquid absorber (olive oil) for the deposition of the soil gas in it. After the bubbling process, the absorber is then taken for gamma-ray measurements. Gamma-ray photopeaks from the ²¹⁴Pb and the ²¹⁴Bi radon progeny are considered for the detection of the ²²²Rn gas to study the concentration levels for radon soil gas. Results for some field measurements were obtained and compared with results obtained using AlphaGuard radon gas monitor. The technique provides a possible approach for the measurements of radon soil gas with gamma-ray spectrometry.     

Radon emanation from soil samples

The soil or bedrock beneath a building is one of the sources of radon gas in the indoor air. The ²³⁸U content of samples of the soil or the bedrock can be measured by gamma ray spectrometry and is of interest because the uranium content in the soil is a precursor of the presence of the radon gas in the soil. The emanation of radon gas from different types of material can be estimated to some extent if the content of ²³⁸U of a sample is known and the ²²⁶Ra content is only minorly affected. The true emanation is, however, affected by various parameters. One of these parameters is the possibility or not for the gas to come out from the grains into the air in the space between the grains of the sample.

In this study we report the results from measurements of radon gas emanating from samples of soil frequent in the Lund region in Sweden and in the Barcelona region in Spain. As soils have different grain size it is important to know the type of soil. The ²³⁸U content of the soil is measured with gamma ray spectrometry. The radon measurements are made by Kodak plastic film in closed cans, filled with the soil according to a technique, developed for radon measurements in water samples.

The result shows, that the combination of grain size and uranium content is important for the emanation of the radon gas from the grains of the soil.     

Seasonal variation on radon emission from soil and water

Radon is being measured continuously in spring water and soil-gas at Badshahi Thaul Campus, Tehri Garhwal in Himalayan region by using radon Emanometer since December 2002. An effort was made to correlate the variance of radon concentrations in spring water and soil-gas with meteorological parameters at the same location. The main meteorological parameters that affect the radon emanation from host material is surrounding temperature, barometric pressure, wind velocity, rain fall and water level of the spring. The correlation coefficient between radon concentration in spring water and different atmospheric parameters was computed. The correlation coefficient between radon concentration in spring water and the maximum atmospheric temperature was 0.3, while it was 0.4 for minimum atmospheric temperature at the monitoring site. The correlation coefficient for radon concentration in spring water with minimum and maximum relative humidity was 0.4. Spring water radon concentration was found positively correlated (0.6) with water discharge rate of the spring. A weak correlation (0.09) was observed between the radon concentration in spring water and rain fall during the measurement period. As temperature of near surface soil increases, the radon emanation coefficient from the soil surface also increases. The possible effects due to global warming and other climatic changes on environment radiation level were also discussed in detail.      

Correlation between radon exhalation and radium content in granite samples used as construction material in Saudi Arabia

Measurements of radon exhalation for a total of 205 selected samples of construction materials used in Saudi Arabia were carried out using an active radon gas analyzer with an emanation container. It was found that granite samples were the main source of radon exhalation. The radon exhalation rates per unit area from these granite samples varied from below the minimum detection limit up to with an average of 1.5 . The radium contents of 27 granite samples were measured using an HPGe-based γ spectroscopy setup. The ²²⁶Ra content of the granites varied from below the minimum detection limit up to , with an average of . The linear correlation coefficient between exhaled radon and radium content was found to be 0.90.     

The effect of soil particle size on soil radon concentration

It has been suggested in the literature that the radon concentration in the soil gas is related to the particle size distribution of the soil. This paper examines this relation. Radon concentration was measured in the soil on the Carboniferous limestone south of Buxton in Derbyshire, England, using the can technique. At each site, a sample of soil was taken at the bottom of the hole in which the dosimeter was placed to determine the particle size distribution.

The correlations between the raw values of radon concentration, soil particle size fractions and elevation were weak. Nevertheless, the kriged maps of radon, silt, clay and elevation showed some spatial relation to one another. The kriged estimates showed stronger correlations among these properties, especially between radon and elevation.     

In situ measurements of radon levels in water and soil and exhalation rate in areas of Malwa belt of Punjab (India)

Radon concentration levels in water and soil gas from 36 locations pertaining to some areas of Malwa region of Punjab have been measured on an in situ basis using a continuous active radon detector (AlphaGuard, Model - PQ 2000 PRO, Genitron instruments, Germany). Exhalation rate measurements have also been carried out at these places, using a closed-circuit technique. The radon concentrations in soil and water varied from 1.9 to 16.4?kBq?m(-3) and 5.01 to 11.6?kBq?m(-3), respectively. The exhalation rate (E (Rn)) ranged between 7.48 and 35.88?mBq?m(-2)?s(-1) with an average value of 18.17?mBq?m(-2)?s(-1). Annual dose rates have been calculated for water radon concentrations. The minimum to maximum values of dose rates were found to be 13.42-31.08?μSv?y(-1). The recorded values of radon concentration in water are within the safe limit of 11?Bq?l(-1) recommended by the US Environment Protection Agency [National Research Council, Risk Assessment of Radon in Drinking Water (Academy Press, Washington, DC, USA, 1999)]. All measurements were made in similar climatic and environmental conditions to ensure minimal variations in meteorological parameters. An intermediate correlation coefficient (0.5) was observed between radon exhalation rates and soil gas values.     

Spatial variations of radon and helium concentrations in soil-gas across the Shan-Chiao fault, Northern Taiwan

Spatial variability of gases like radon and helium in soil-gas can be used for seismic surveillance and for finding fault system. The present study is aimed at determining a possible connection between eventual radon/helium anomalies and active fault. Radon and helium concentrations in subsurface soil-gas have been monitored along the Shan-Chiao fault, Northern Taiwan. Twenty transverse profile surveys have been conducted across the fault, where 235 and 125 samples were collected for helium and radon analyses, respectively. The data analysis clearly reveals anomalous values of both radon and helium along the fault. To find the fault system, where the migration of gases is governed by advection, it is essential to identify the anomalies in both radon and helium together. The consistency of this pattern confirms that radon and helium together can act as a powerful tool for the detection and mapping of active fault zones.     

The role of soil gas radon survey in exploring unknown subsurface faults at Afamia B dam,Syria

The purpose of this work is to determine a possible connection between anomalous radon values and some expected subsurface geological faults at Afamia B dam which is currently suffering a serious problem of large leakage through its bedrocks. A total of 82 soil gas radon sampling points were measured, using direct active method, over an area of 300 × 300 m which almost covers the entire surface of the reservoir basin. The results revealed a reasonable correlation between the geometric pattern of radon anomalies and the probable orientation of some underlying tectonic lineaments. Abnormal radon values, with peak signals of about 2–5 times higher than the background level, led to the detection of two probable fractured zones, denoted as F₁ and F₂. The data analysis suggests that the leakage of water from Afamia B dam almost runs vertically downwards along N60E trending fault zone F₂. Such a fault is very likely extending down within the Neogene formation to reach the permeable karstic carbonate rocks of Cretaceous at depth, forming large conduits through which the water of the reservoir is possibly drained off. This suggestion was in agreement with the general direction of the groundwater flow in the study area which indicates clearly that the supposed fractured zone F₂ may represent a catchment area for groundwater, and thereby it may constitute the most important structural element concerning the leakage problem of Afamia B reservoir.     

Experience from using plastic film in radon measurement

Plastic film is a useful detector of radon gas. The method of detection of the gas is used for several decades to measure radon concentrations both indoors and in soil. Experiences from radon measurements in Sweden indoors, in soil and in water using the plastic film Kodak LR 115-II are discussed in this report. Some examples are given from various projects. One example is taken from a large scale mapping of indoor radon levels in houses, where the building material is the main source of radon. In anotther example the measurements from a large scale soil radon mapping are discussed. The use of the plastic film for measurements of radon levels in water is also discussed. All the investigations are made in order to give the authorities concerned information of the radon situation and to study the connection between high indoor radon levels and various types of cancers.     

A method for estimating the convective radon transport velocity in soils

A method for estimating the convective radon transport velocity in soils is developed. The approach under review is based on measurements of the radon concentration in soil air. Mathematical models for describing the convective radon transport velocity are discussed. Data on the convective radon transport velocity in commonly encountered soil types are presented. The results obtained from a 2-month experiment aimed at investigating the effect of the atmospheric condition on the convective radon transport velocity are reported. The soil gas radon concentration at 30–70 cm depth was measured by means of passive track detectors (Type III-b SSNTDs) with 72–96 h exposure time.     

Measurements of radon concentration in soil gas by CR-39 detectors

A miniature diffusion chamber with a 25 × 4 × 0.5 mm CR-39 track etch detector (Pershore Moulding Ltd.), mounted on the 1.1 m long pole has been developed for radon gas measurements at 1 meter depth in the soil. For chemically etched CR-39 (7h, 70°C NaOH) and automatic track analysis the lowest detection limit of the chamber was found to be 0.5 MBq h m⁻³ and the useful exposure range from 2 to 20 MBq h m⁻³. The typical exposure time in the soil is between 2 to 14 days. The chamber was tested against the active AlphaGUARD PQ-2000 (Genitron Instruments GmbH) probe. The test yielded consistent results for soils with typical values of permeability and which are not miniature with water. The pilot measurements of radon gas in soil conducted with the miniature diffusion chambers around 48 buildings in Kraków and Silesia regions yielded an average radon concentration of 13 kBq m⁻³. The chambers are to be applied to measure radon concentration in soil before constructing new houses in order to avoid high radon risk areas.     

Soil radon levels measured with SSNTD's and the soil radium content

The source of the radon gas ²²²Rn in the ground air is the soil and the bedrock underneath. The potential radon level in the ground is given by the content of ²²⁶Ra in the ground. The presence of ²²⁶Ra is in turn dependent on the amount of ²³⁸U in the ground, and these two isotopes are not always found to be in equilibrium in a sample of soil or bedrock. Especially if the soil is washed out, the radium content may be reduced. When the soil is the relevant source of the radon gas, it is interesting to look for a possible relation between the radon level and the radium content of the soil.

In this paper we report on measurements of soil radon level carried out with SSNTDs at several European sites. Soil samples were collected at these sites and analysed with gamma spectrometry to determine their radium content. A comparison of the different degree of disequilibrium of radon, defined as the ratio between the actual and the secular equilibrium-with-radium soil radon concentration, found at the different sites and depths is presented. The influence on the result of soil type and climate is briefly discussed.     

Measurements of radon concentration levels in thermal waters in the region of Konya,Turkey

²²²Rn (radon) is one of the most important sources of natural radiation to which people are exposed. It is an alpha-emitting noble gas and it can be found in various concentrations in soil, air and in different kinds of water. In this study, we present the results of radon concentration measurements in thermal waters taken from the sources in the region of Konya located in the central part of Turkey. The radon activity concentrations in 10 thermal water samples were measured by using the AlphaGUARD PQ 2000PRO radon gas analyser in spring and summer of the year 2012. We found that radon activity concentrations range from 0.60±0.11 to 70.34±3.55 kBq m^?3 and from 0.67±0.03 to 36.53±4.68 kBq m^?3 in spring and summer, respectively. We also calculated effective doses per treatment in the spas for the spring and summer seasons. It was found that the minimum and maximum effective doses per treatment are in the range of 0.09–10.13 nSv in spring and in the range of 0.1–5.26 nSv in summer.     

In situ measurements of radon levels in water and soil and exhalation rate in areas of Malwa belt of Punjab (India)

Radon concentration levels in water and soil gas from 36 locations pertaining to some areas of Malwa region of Punjab have been measured on an in situ basis using a continuous active radon detector (AlphaGuard, Model – PQ 2000 PRO, Genitron instruments, Germany). Exhalation rate measurements have also been carried out at these places, using a closed-circuit technique. The radon concentrations in soil and water varied from 1.9 to 16.4 kBq m^?3 and 5.01 to 11.6 kBq m^?3, respectively. The exhalation rate (E _Rn) ranged between 7.48 and 35.88 mBq m^?2 s^?1 with an average value of 18.17 mBq m^?2 s^?1. Annual dose rates have been calculated for water radon concentrations. The minimum to maximum values of dose rates were found to be 13.42–31.08 μSv y^?1. The recorded values of radon concentration in water are within the safe limit of 11 Bq l^?1 recommended by the US Environment Protection Agency [National Research Council, Risk Assessment of Radon in Drinking Water (Academy Press, Washington, DC, USA, 1999)]. All measurements were made in similar climatic and environmental conditions to ensure minimal variations in meteorological parameters. An intermediate correlation coefficient (0.5) was observed between radon exhalation rates and soil gas values.     

Indoor radon measurements in dwellings of four Saudi Arabian cities

An indoor radon survey of a total of 269 dwellings, with one dosimeter per house, distributed in four Saudi Arabian cities was carried out. The objective of this survey was to carry out indoor radon measurements of two cities in the Eastern Province, Khafji and Hafr Al-Batin and to compare this with two cities in the Western Province, Al-Madina and Taif. The survey provides additional information about indoor radon concentrations in Saudi Arabia. The results of the survey in these cities showed that the overall minimum, maximum and average radon concentration were 7,137 and 30 Bqm⁻³, respectively. The lowest average radon concentration (20 Bqm⁻³) was found in Hafr Al-Batin, while the highest average concentration was found in Khafji (40 Bqm⁻³).     

Field Measurements of Radon Exhalation and Ra-226 Content in Soil using the Can-Technique

CR-39 and LR-115 plastic nuclear track detectors in the can-technique have been employed in the field measurements of radon exhalation, Ra-226 and U-238 content in dry-soil air at numerous regions in Sudan (the Blue and White Nile and Mogran regions). Measurements gave an average radon exhalation from the soil to the atmosphere and Ra-226 content of (23.4 ± 2.60) kBq · m^?2 and (123 ± 13.65) Bq · kg^?1 respectively. A polyethylene permeable membrane cover was used to eliminate the contribution of thoron activity inside the can. Assuming a radioactive equilibrium between the U-series, the average U-238 content in the soil was found to be (9.92 ± 1.01) ppm. This survey may be used for uranium prospection in soil.