Investigation on Shallow Groundwater in a Small Basin Using Natural Radioisotopes.

Abstract

The authors conducted an investigation on shallow groundwater using natural radioisotopes as indicators in the small basin of the Hinuma River, Kasama City, Ibaraki Prefecture, Japan.3H concentrations in the groundwater showed that it originated from precipitation in the 1960's .Since 222Rn concentrations decreased as groundwater flowed downstream, they were influenced by infiltration of surface water. Especially, during the irrigation period, the decrease of 222Rn concentrations was remarkable in the lowland. From the distribution of 222Rn concentrations in surface water, the sections where groundwater seeped into a river were found, and a quantitative analysis of groundwater seepage in the two sections was conducted on the basis of 222Rn concentrations in groundwater and in surface water. The ratios of groundwater seepage to the flow at the upstream station for the two sections were about 5% and 10%, respectively.The water movement within the basin, i.e., the actual manner in which surface water infiltrated underground and groundwater seeped into a river, was clarified by analyzing the variations of natural radioisotope concentrations in water and the water balance of the basin.

Application of a Self-Organizing Map of Isotopic and Chemical Data for the Identification of Groundwater Recharge Sources in Nasunogahara Alluvial Fan, Japan

“…Using these characteristics, 222 Rn is often used as a target tracer to investigate the hydrological aspects of groundwater (e.g., estimation of infiltration from surface water to aquifers [34] and groundwater flow rate [35]), because far more 222 Rn is contained in groundwater than in surface water. The radioactivity of 222 Rn in samples was analyzed using a liquid scintillation counter (Packard, 2250 CA, CT, USA) after extraction with toluene within one week after collecting the water, and the concentrations of 222 Rn were calculated based on the count rate [36]. The stable isotopic compositions of the water were measured using a cavity ringdown spectrometer-based water isotope analyzer (Picarro, L2140-i, Santa Clara, CA, USA).…”

Integrated field- and model-based study of hydro-environmental aspects of a small, endangered wetland in eastern Hokkaido, Japan

“…For example, Hoehn and von Gunten (1989) and Hamada (2000) estimated groundwater flow rates from variations in 222 Rn concentrations in groundwater. Fukui (1985) and Hamada and Komae (1996) analyzed the arrival of surface water at the groundwater table. Hamada and Kishi (2003) developed a couple of models for analyzing the hydrological aspects of a small pond system, expressed as…”

“…The vials were then sent to the laboratory, and the radioactivity was counted for 50 min using a liquid scintillation counter (Packard 2250 CA). The same method as Hamada and Komae (1996) and Hamada (2000) was used to calculate 222 Rn concentrations based on the count rate. The detection limit was 0.03 Bq/L, and the measurement deviation was in the range of 6-17%.…”

“…Radon-222 ( 222 Rn) is a radioactive gas generated by the decay of radium-226 ( 226 Ra) in geological strata. Because 222 Rn dissolves in water and its concentration increases according to the radioactive growth curve, this isotope has been frequently used to analyze groundwater flow (Hoehn and von Gunten 1989;Fukui 1985;Hamada and Komae 1996;Hamada 2000). Hamada and Kishi (2003) proposed an analytical method using the radon mass balance and water balance equations to investigate the hydrological aspects of a small pond system.…”