Factors Effecting the Determination of Radon in Groundwater

Introduction and Background: In 1991 the U.S. Environmental Protection Agency (EPA) issued a “proposed” analytical method for radon in water (EPA Method 913.0). This method involves injecting a measured amount of sample beneath a liquid-scintillation (LS) cocktail, and then measuring the amount of radon that diffuses into the cocktail (based on the radioactive emissions). The Radiochemistry Unit of the Wisconsin State Laboratory of Hygiene (SLH) was one of a select group of laboratories that participated in a collaborative study of the method, and thus was able to gain experience with this method early on. While using this method to test Wisconsin groundwater samples, the Radiochemistry Unit thought that the chemical characteristics of the water may affect the measured radon concentration through an interaction with the sewer-disposable cocktail recommended by the EPA.

The purpose of this study was to determine the effect of several factors, especially the effect of the chemical composition of the water sample, on the analysis of radon in water by EPA Method 913.0. Various types of water samples (with different chemical compositions) were spiked with known concentrations of radon. These samples were analyzed using EPA method 913.0 and the recovery of the radon determined. Variations from expected recoveries were evaluated with respect to the chemical composition of the water. An attempt was made to identify which factors affected the results and how the method could be modified to overcome these effects.