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Takai, Shizuka; Shimada, Taro; Takeda, Seiji; Koike, Katsuaki*
Mathematical Geosciences, 56(2), p.333 - 360, 2024/02
Times Cited Count：0 Percentile：0.01(Geosciences, Multidisciplinary)To enable proper remediation of accidental groundwater contamination, the contaminant plume evolution needs to be accurately estimated. In the estimation, uncertainties in both the contaminant source and hydrogeological structure should be considered, especially the temporal release history and hydraulic transmissivity. Although the release history can be estimated using geostatistical approaches, previous studies use the deterministic hydraulic property field. Geostatistical approaches can also effectively estimate an unknown heterogeneous transmissivity field via the joint data use, such as a combination of hydraulic head and tracer data. However, tracer tests implemented over a contaminated area necessarily disturb the in situ condition of the contamination. Conversely, measurements of the transient concentration data over an area are possible and can preserve the conditions. Accordingly, this study develops a geostatistical method for the joint clarification of contaminant plume and transmissivity distributions using both head and contaminant concentration data. The applicability and effectiveness of the proposed method are demonstrated through two numerical experiments assuming a two-dimensional heterogenous confined aquifer. The use of contaminant concentration data is key to accurate estimation of the transmissivity. The accuracy of the proposed method using both head and concentration data was verified achieving a high linear correlation coefficient of 0.97 between the true and estimated concentrations for both experiments, which was 0.67 or more than the results using only the head data. Furthermore, the uncertainty of the contaminant plume evolution was successfully evaluated by considering the uncertainties of both the initial plume and the transmissivity distributions, based on their conditional realizations.
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*
no journal, ,
For underground contamination typically caused by radioactive nuclides and hazardous chemicals, the contaminant plume distribution should be accurately clarified for risk assessment and proper environmental remediation. Although its release history may be unknown, contaminant plume distribution can be calculated using a geostatistical approach with groundwater flow modeling. Understanding of hydrogeological structure is important to predict plume transportation and take appropriate countermeasures. Identification of hydraulic parameters from a limited number of in-situ measurements include uncertainty in general. Therefore, reduction of the uncertainty has been considered by accounting hydrogeophysical measurements such as hydraulic heads and tracer data. However, for the contaminated area, tracer test is difficult because it can make a disturbance of the site. In this study, we estimate heterogeneous hydraulic field using the transient monitoring data of contaminant concentration. Joint inversion method of transmissivity distribution and contaminant plume using head and concentration was developed. For the 2D synthetic case, we confirmed that the prediction accuracy of contaminant plume was increased by the proposed method.
