Mitigation of radon in drinking water of Finnish drilled wells ― Present state and Cost-benefit analysis

摘要

The annual collective dose from natural radioactivity of ingested drinking water in Finland is estimated at 260 manSv. The users of drilled wells receive about half of the collective dose, although their proportion of the population is only about 5%. Radon causes approximately 70% of the ingestion dose. Apart from ingested water, consumers are exposed to radon and its decay products when radon is released into indoor air in situations like showering and washing cloths and dishes. The lung cancer risk from inhaled decay products of radon depends strongly on the smoking prevalence in the exposed population. To combine the both exposure paths, ingestion and breathing, it is more feasible to calculate the number of cancer deaths rather than doses. In addition to the number of annual cases, the cost per averted cancer case is influenced by the total costs of the chosen removal method, frequency distribution of radon concentration in the wells and the action level applied. When the action level for radon in drinking water in a private well is exceeded, STUK recommends joining the municipal water system or a water co-operative as a primary alternative. These options assure both the quality of drinking water and a proper wastewater disposal. However, neither of these alternatives is commonly available in sparsely populated areas. Another viable choice is to dig a well into the soil. If none of these alternatives is possible, two methods can be used for removing radon from drinking water: aeration and activated carbon filtration. If the filtration method is used without adequate shielding, an additional dose may incur due to external gamma radiation emitted by the short-lived decay products of radon that are retained in the carbon. STUK recommends that an activated carbon filter unit not be installed inside a dwelling, but be placed in a separate building or in the subsurface service space beside the drilled well.