222Rn In Groundwater Research Articles

Radon variation in groundwaters in the Campi Flegrei Caldera (southern Italy) during and after the 1982?1984 bradyseismic crisis

Groundwater Rn concentration has been monitored at several sites in the Campi Flegrei Caldera since the time of the last episode of bradyseismic activity. The results concerning the period 1983–88 indicate that the Rn concentration is spatially variable due to the different chemico-physical characteristics of the waters or structural features. Rn concentration is generally influenced by the long-term changes of meteorological factors. Rainfalls appear to affect the Rn content of the most superficial aquifers. Several short-term spike-like Rn anomalies have been detected both during and after the period of the bradyseismic crisis. They do not show correlation with temporal changes of the pH and/or temperature of waters. A systematic correlation between Rn anomalies and episodic strong rainfall events is also absent. Furthermore, a clear relationship between Rn spikes and both uplift velocity changes and seismic activity has not been found. The overall evidence makes it very difficult to understand the temporal changes of groundwater Rn concentration that have occurred during and after the 1982–84 bradyseismic crisis. Nevertheless, a clear causal relationship between Rn concentration and the dynamics of the bradyseism is observed in some monitored sites. Its appearance may have been favoured by the low Rn concentration in the groundwaters during periods of quiescent activity.

Location of groundwater seepage points into a river by measurement of 222Rn concentration in water using activated charcoal passive collectors

A new method to measure 222Rn concentration in water is described. This method is an application of the activated charcoal passive collector method, which is sometimes used for measurement of 222Rn concentration in air. The model and the equation which express the quantity of 222Rn adsorbed in activated charcoal in the collector were constructed, inspected experimentally, and proved to work well enough for the measurement of relative concentration of 222Rn in water. We used this method to measure the 222Rn concentration in water at ∼ 20 points in an actual river. Based on the fact that the concentration of 222Rn in ground water is generally much higher than that of surface water, we found several possible groundwater seepage points along the river. For the absolute measurement of 222Rn concentration in water by this method, it would also be necessary to investigate the effect of temperature on the quantity of 222Rn collected in a collector.

Radon measurements of groundwater in Mexico

Radon measurement has important applications in hydrogeological studies (Fukui, 1985). Specifically, radon measurement is used to determine the fluctuations of the piezometric levels in groundwater and, in some cases, the path of the water, which is one of the key parameters to evaluate hydrogeological resources. Water from springs and deep wells in the Basin of Mexico and the valley of San Luis Potosí were sampled, measured and analyzed (Cortes and Jaimes, 1990). In this work a method for measuring 222Rn in groundwater by using a passive detector is presented and the results are compared with a similar experiment performed at the same time, using the dynamical method. The aim of the work is to develop a method for detecting, evaluating and measuring the 222Rn in groundwater by using SSNTD technology (Espinosa et al, 1981; Varhegyi et al, 1988).

Radiogenic elements in Finnish soils and groundwaters

In Finland, U and Rn concentrations in groundwaters are highest in the south of the country in bedrock composed of granites or migmatites with abundant granite or pegmatite veins. The areal distribution patterns of U and Rn in groundwater from bedrock are consistent with U and Th anomalies in the fine fraction of till and with the external gamma dose rate measured on the ground surface. The U and Rn concentrations in groundwater from bedrock are only moderately correlated; hence the elevated U contents do not imply abundant Rn contents. Both elements are practically independent of other dissolved components. The exception is the moderate correlation between U and HCO 3 suggesting the occurrence of U-rich carbonates as fracture-coating minerals. In a few areas with U and Rn anomalies, the exceptionally high Rn concentrations in ambient house air pose a considerable health risk, particularly in detached houses founded on pervious sand and gravel deposits. Regardless of the potential health risk no radiological recommendations for U and Rn concentrations in potable water have been officially set in Finland.

Helium 4 and radon 222 concentrations in groundwater and soil gas as indicators of zones of fracture concentration in unexposed rock

The presence of zones of fracture concentration in unexposed rock may be partially assessed by measuring the concentrations of 4He and 222Rn in groundwater and soil gas. Helium 4 in groundwater and soil gas and 222Rn in groundwater were measured in the vicinity of two intersecting lineaments in Lehigh County, Pennsylvania. The lineaments are thought to mark deep fracture systems which provide conduits for the migration of 4He and 222Rn. High groundwater 4He concentrations revealed the presence of the two lineaments. Low groundwater 222Rn activities are found near the lineaments and qualitatively support a numerical model which relates low 222Rn activity to high fracture transmissivity. Radon 222 activity correlates most strongly with the presence of H2S in groundwater, implying that geochemical controls or groundwater circulation patterns strongly influence radon concentration. Soil gas concentrations of 4He barely exceeded background levels and did not reliably indicate the lineament zones. The data show that groundwater 4He concentrations may be used to identify fracture zones in unexposed bedrock.

State of disequilibrium between 238U, 234U, 226Ra and 222Rn in groundwater from bedrock

Approximately one thousand drilled wells were investigated for their natural radioactivity. The determinations of 238U, 234U, 226Ra and 222Rn from 310 samples showed a high state of radioactive disequilibrium between the members of the uranium series present in water. The 238U 226Ra activity ratio usually fell in the range 1–20 and the 238U 222Rn activity ratio in the range 1–20 × 10 −4, the highest activity ratios being from samples with an elevated uranium content. The 234U 238U activity ratio varied between 0.76 and 4.67, the most frequent values showing a 60% excess of 234U in the samples. Most of the 234U 238U activity ratios near unity were found in samples with a high uranium content. Several drilled wells with anomalously high uranium contents were found in southern Finland. The average 226Ra and 222Rn contents of these wells were not exceptionally high, which suggests high mobility of uranium in groundwater from the areas involved.

Inert gases in groundwater from the Bunter Sandstone of England as indicators of age and palaeoclimatic trends

A study of the radiogenic and atmospherically derived inert gases in groundwaters from the Bunter Sandstone aquifer of Nottinghamshire, England, is described. The radiogenic gases, 222Rn and 4He, are derived by decay of the radioelements contained in the aquifer. The relationship between radioelement content of the rock and groundwater 222Rn and 4He contents is discussed. An increase in the dissolved 4He content with groundwater age is demonstrated and correlated with 14C ages. Excess 4He ages calculated from average physical properties and radioelement contents of the aquifer rock are greater than the corrected 14C ages and possible explanations for this are discussed. The dissolved Ar and Kr contents of the groundwaters indicate their temperature of air equilibration in the unsaturated zone at recharge. The recharge temperatures for groundwaters of age greater than 2·10 4 yr. are 5–7°C lower than those for waters recharged in the last 10 4 yr. This is shown to be consistent with the palaeoclimatic record for England during the late Pleistocene.