Estimation of groundwater flow rate using the decay of 222Rn in a well

A method of estimating groundwater flow rate using the decay of 222Rn in a well was investigated. Field application revealed that infiltrated water (i.e., precipitation, pond water and irrigation water) accelerated groundwater flow. In addition, the depth at which groundwater was influenced by surface water was determined. The velocity of groundwater in a test well was estimated to be of the order of 10-6 cm s-1, based on the ratio of 222Rn concentration in groundwater before and after it flowed into the well. This method is applicable for monitoring of groundwater flow rate where the velocity in a well is from 10-5 to 10-6 cm s-1.