Estimation of contaminated materials concentration by a geostatistical method with groundwater flow

Takai, Shizuka ; Shimada, Taro ; Takeda, Seiji ; Koike, Katsuaki*

For occurrence of underground contamination by such as radioactive nuclides and chemicals, the contaminant plume distribution needs to be clarified accurately for effective remedy. If the pollutant reaches an aquifer, the plume needs to be estimated considering groundwater effect, not only spatial interpolation of measurement data. However, the release history may possibly be unknown or uncertain. In this study, we considered the geostatistical estimation method with groundwater flow. For the hypothetical plume of H (2-dimension), in which the measurement error is small and hydrogeological structure is fully known, the unknown release history and contaminant plume was estimated well from a limited number of measurements. We also applied the method to the underground contamination by diphenylarsinic acid (organic arsenical compound) occurred in Kamisu, Ibaraki. The trend of measurement data, which the concentration is high around a well and below the source, agreed with that of estimated plume. The mean absolute error for 32 measurement data was 3.0 mg-As/L. The total release amount of As was estimated as 2.9 kg; however, the total amount calculated by the product of measured concentration and groundwater volume is 40.89 kg. To improve the estimation accuracy, the uncertainty of hydrogeological structure (boundary condition, sorption characteristics etc.) needs to be considered.