radon in groundwater - Mark- och vattenteknik - KTH

Kirlna Skeppström TRITA LWR.LIC 2032Detailed study on LjusteröThe results of the detailed study are presentedin Fig.7. The observed concentrationof 222 Rn in groundwater tended to increasewith increasing concentration of uranium(total U) and radium ( 226 Ra) in the solution.However, the correlations were weak, 0.16and 0.18 for 238 U and 226 Ra respectively. Thisobservation supports the concept that radonconcentration in groundwater principallycomes from its parent elements ( 238 U and226 Ra) deposited on the surfaces of fractures(Åkerblom and Lindgren, 1997). Regardingground measurements of equivalent uranium(eU) made directly on outcrops, it could beobserved that high radon concentrationscould occur in bedrock of low to moderateuranium content. It was also observed thatthe radon concentration in groundwater didnot increase with increasing content of uraniumin the bedrock. The same observationwas made for the analysis of 222 Rn ingroundwater and airborne uranium measurements.These observations could beexplained by the fact that the bedrock identifiedby visual inspection above the groundsurface might not be the same in the subsurfacewhere groundwater is extracted. Anotherplausible argument relates to the migrationof radionuclides (mainly 226 Ra and238 U) in groundwater flow. The bedrockmight originally contain low concentrationsof actinide but transportation of 238 U and226 Ra can contribute to increasing the radonconcentration in the groundwater. The localconditions are difficult to identify in reality.The activity ratio of 226 Ra/ 238 U in solutionvaried between 0 and 12, which clearly indicatesa state of disequilibrium in thegroundwater system.(a)(b)(c)Fig. 7: (a) Relationship between 222 Rn anduranium in groundwater; (b) Relationshipbetween 222 Rn and radium in groundwater;(c) Relationship between 222 Rn in groundwaterand measured uranium in bedrock outcrops.18