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Takai, Shizuka; Shimada, Taro; Takeda, Seiji; Koike, Katsuaki*
Journal of Contaminant Hydrology, 251, p.104097_1 - 104097_12, 2022/12
Times Cited Count：3 Percentile：46.08(Environmental Sciences)When assessing the risk from an underground environment that is contaminated by radioactive nuclides and hazardous chemicals and planning for remediation, the contaminant plume distribution and the associated uncertainty from measured data should be estimated accurately. While the release history of the contaminant plume may be unknown, the extent of the plume caused by a known source and the associated uncertainty can be calculated inversely from the concentration data using a geostatistical method that accounts for the temporal correlation of its release history and groundwater flow modeling. However, the preceding geostatistical approaches have three drawbacks: (1) no applications of the three-dimensional plume estimation in real situations, (2) no constraints for the estimation of the plume distribution, which can yield negative concentration and large uncertainties, and (3) few applications to actual cases with multiple contaminants. To address these problems, the non-negativity constraint using Gibbs sampling was incorporated into the geostatistical method with groundwater flow modeling for contaminant plume estimation. This method was then tested on groundwater contamination in the Gloucester landfill in Ontario, Canada. The method was applied to three water soluble organic contaminants: 1,4-dioxane, tetrahydrofuran, and diethyl ether. The effectiveness of the proposed method was verified by the general agreement of the calculated plume distributions of the three contaminants with concentration data from 66 points in 1982 (linear correlation coefficient of about 0.7). In particular, the reproduced large spill of organic contaminants of 1,4-dioxane in 1978 was more accurate than the result of preceding minimum relative entropy-based studies. The same peak also appeared in the tetrahydrofuran and diethyl ether distributions approximately within the range of the retardation factor derived from the fraction of organic carbon.
Takai, Shizuka; Shimada, Taro; Takeda, Seiji; Koike, Katsuaki*
Joho Chishitsu, 32(3), P. 95, 2021/09
We received best presentation award GEOINROUM-2021 for the presentation on "Estimation of contaminated materials concentration by a geostatistical method with groundwater flow". We submit the comments of impression for getting the Award to Geoinformatics.
Takai, Shizuka; Shimada, Taro; Takeda, Seiji; Koike, Katsuaki*
no journal, ,
For underground contamination by such as radioactive nuclides and chemicals, the contaminant plume distribution needs to be clarified accurately for effective remedy. However, once a pollutant reaches an aquifer, the transport will be affected by groundwater. In such case, only spatial interpolation of measurement data may be unable to reproduce the contaminant plume. In this study, we considered the estimation method integrated transport information into geostatistical analysis. To gain physically feasible solution, we also considered the non-negativity constraint by Gibbs-sampling. The applicability of the method was confirmed for both hypothetical model and actual contamination case (Gloucester landfill, Canada). As the hypothetical model, we assumed that 
H is leaked for 300 days with 2 peaks. The two peaks of plume could not be reproduced by spatial interpolation (Kriging with a Trend). However, the plume was reproduced well by the geostatistical method with the mean average error (MAE) of 2.8E-9. In the Gloucester landfill, the contamination by 1,4-dioxane in the aquifer (300 
300 40m) was evaluated using 69 points measured in 1982. By the geostatistical method considering groundwater flow and nonnegativity constraint, the large spill in 1978 could be reproduced well compared to previous research by other methods such as minimum relative entropy. The plume was also evaluated well with the MAE of 2.8E-2 mg/L; therefore, the applicability of the method was confirmed.
Takai, Shizuka; Shimada, Taro; Takeda, Seiji; Koike, Katsuaki*
no journal, ,
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.
