Systematic assessment of field-scale unconfined aquifer heterogeneity using multiple hydraulic test methods

• Main Authors: Chih-Yi Chen, 陳芝儀
• Other Authors: Chuen-Fa Ni
• Format: Others
• Language: zh-TW
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/9424y4

碩士 === 國立中央大學 === 應用地質研究所 === 107 === Accurate and efficient remediation policies highly rely on the understanding of hydrogeological conditions at sites. This study aims to conduct assessment of aquifer heterogeneity using multiple hydraulic tests at the same well field, comparing the estimations by different data analysis methods, and then carrying out the insight into the use of hydraulic surveys at the field-scale site. Cross-hole pumping tests and Multi-level slug tests(MLST) are conducted at the well field. The well field has 19 installed wells, including five 4’’ wells that are considered to be the pumping wells. The pumping and slug tests produce multiple types of observations from well field. The single- and multiple-well pumping tests are analyzed with Neuman(1975) model. All the cross-hole hydraulic test data are involved in the sequential successive linear estimator(SSLE) model to estimate the transmissivity(T) distribution. Drawdown data from MLSTs are analyzed with Hvorslev(1951) to obtain the hydraulic conductivity(K) and the results of MLSTs are interpolated with the Kriging method to obtain 3D K distribution. Results of the single-well hydraulic tests show that the mean T value is 66.81m2/day, the variance of ln(T) is 0.067, and results of the MLSTs show that the correlation length of the T field is 3.3m. These results are the input parameters in SSLE for estimating 2D T at the well field. Results show that the K values from four different hydraulic tests are in the same order. Under the same tests data source, the patterns of T heterogeneities are similar for single-well pumping tests, multi-well pumping tests, and SSLE hydraulic tomography. The MLST shows the patterns slightly different from other pumping tests. The results show that the average K value from the single-well pumping tests (7.62E-05 m/sec) is between the minimum and the maximum K(z) values obtained from MLST. The well field is mainly composed of gravel and embedded with fine sand, loam, and silt layers. The obtained K values at the site show relatively smaller than typical K values obtained from previous studies. Results also show that the SSLE can provide the most detailed information of the aquifer heterogeneities. However, the study site is relatively homogeneous. The single and multi-well pumping tests might be sufficient to resolve the aquifer properties at the site. Additionally, the MLSTs show that the lnK variance in the vertical direction is very small, indicating that the depth-averaged slug test can be used to for the well hydraulic test. The sensitivity analysis of SSLE model shows that the T estimated errors for the site is between 0.0016 and 0.0543 m2/min, which is relatively small.