Springer Science and Business Media LLC

Accurate estimates of aquifer parameters are necessary for effective groundwater management and for geotechnical engineering applications. Pumping tests may be employed to estimate the hydraulic conductivity in leaky aquifer/aquitard systems. This work introduces a hybrid algorithm with global search capacity (the Genetic algorithm, GA) and local search capacity—the Levenberg-Marquardt (LM) algorithm—coupled with a modified Neuman-Witherspoon solution for leaky aquifers to estimate the aquifer’s hydraulic parameters from pumping-test data. The GA is employed to determine the initial guesses of the aquifer parameter values. The optimal parameter values are then obtained with the LM algorithm, yielding a mixed GA/LM algorithm, herein named GALMA. Results show that the drawdown trends based on the estimated parameters agree well with measured drawdown. The proposed estimation algorithm identifies aquifer parameters with greater reliability than previous approaches. Verification of the GALMA is carried out based on three pumping tests in a layered aquifer in Tianjin, China, and on four historical case studies involving diverse hydrogeological settings. The excellent match between observed drawdown and GALMA-estimated parameters demonstrates the estimation accuracy and superior performance relative to previously reported estimation methods.

Global navigation satellite system (GNSS) and interferometric synthetic aperture radar (InSAR) data, along with exploration well data, are used to investigate elastic and inelastic land displacements across the Salmas plain, northwest Iran. GNSS measurements (2006–2012) show that the long-term and seasonal variability of the hydraulic head in the Salmas confined aquifer system (SCAS) control the vertical land deformation. A combination of drought and overextraction from SCAS led to significant changes in the head and land deformation after the 2006–2008 period. It was observed that the amplitude of the seasonal component of the hydraulic head and land-deformation time series increased about 2.5 times after this period. InSAR analysis over period 2014–2018 also revealed that the SCAS is prone to both long-term subsidence (average ~60 ± 3 mm/year in the line-of-sight direction of the satellite) and seasonal elastic vertical deformation (~60 mm). The seasonal elastic components of the vertical land deformations are used to precisely map the boundary of the SCAS. The average skeletal storativity of the SCAS is estimated to be ~0.028 and the time delay between the change in seasonal hydraulic head and its corresponding elastic deformation in the aquifer system is 0–150 days. The total groundwater storage variation of the aquifer system is computed to be ~18 million m3 from 2015 to 2018. Furthermore, the irreversible component of groundwater storage variations associated with the dewatering of compacted aquitards is estimated to be ~2.33 times greater than its recoverable component from aquifer units.

High-pressure flow-through experiments on solid rock samples are commonly conducted with experimental setups using a confining pressure to restrict the flow to the rock. These setups are often spacious, costly, and difficult to replicate by other researchers due to their individual nature. This work presents the RESECO (resin sealed column) setup which allows flow-through experiments on solid rock without a confining pressure. The column setup is only slightly larger than the sample size and has material costs per sample of a few Euros. The fluid flow is confined to the rock by a cast of epoxy resin using a metal column as an outer casing. The functionality was verified by comparing experimental results with a conventional triaxial cell. Four different rock types with varying hydraulic properties were tested and proven compatible with the setup. Additional endurance tests were performed to investigate the physical limits with regard to pore pressure and temperature. The RESECO setup can be operated with pore pressures of at least 40 MPa and temperatures up to 95 °C, and is therefore suitable for many high-pressure, high-temperature experiments, while being easily reproducible.

Heli 4He tích tụ trong các chất lỏng là một dấu vết địa hóa đã được thiết lập rõ ràng, được sử dụng để nghiên cứu động lực học chất lỏng trong vỏ trái đất. Mẫu chất lỏng trực tiếp không phải lúc nào cũng có thể thu thập; do đó, một phương pháp để chiết xuất khí hiếm từ các chất lỏng lưỡng tính của đá toàn phần thông qua sự khuếch tán đã được điều chỉnh. Heli đã được đo trên các chất lỏng lưỡng tính được chiết xuất từ đá cát và đá sét thu hồi trong quá trình khoan Đài quan sát Đứt gãy San Andreas ở độ sâu (SAFOD) tại California, Mỹ. Mẫu thường được thu thập dưới dạng lõi phụ hoặc từ các mảnh lõi khoan. Nồng độ heli và tỷ lệ đồng vị đã được đo 4-6 lần trên mỗi mẫu, cho thấy hệ số khuếch tán 4He tổng thể là 3,5 ± 1,3 × 10–8 cm2 s–1 ở 21°C, so với các hệ số khuếch tán đã được công bố trước đó từ 1,2 × 10–18 cm2 s–1 (21°C) đến 3,0 × 10–15 cm2 s–1 (150°C) trong cát và đất sét. Việc sửa đổi hệ số khuếch tán của 4He nước cho độ rỗng của lưới (∼3%) và độ rối (∼6–13) tạo ra các hệ số khuếch tán hiệu quả là 1 × 10–8 cm2 s–1 (21°C) và 1 × 10–7 (120°C), cách ly hiệu quả khí 4He trong lỗ rỗng khỏi 4He chứa trong khung đá. Tính toán mô hình cho thấy <6% heli hòa tan ban đầu trong chất lỏng lỗ rỗng đã bị mất trong quá trình lấy mẫu. Việc chiết xuất hoàn chỉnh và định lượng các chất lỏng lỗ rỗng cung cấp giá trị độ rỗng tại chỗ tối thiểu cho đá cát là 2,8 ± 0,4% (SD, n = 4) và đá sét là 3,1 ± 0,8% (SD, n = 4).

Groundwater monitoring and pumping wells set in anoxic aquifers require attention to keep the groundwater free of dissolved oxygen (DO). In properly constructed monitoring or pumping wells, two processes can however still introduce oxygen to anoxic groundwater: (1) permeation of oxygen through polymer materials such as silicone, PVC, HDPE or Teflon, and (2) thermally driven convection, which can occur in all types of piezometers or wells, regardless of construction material, when the water table or pressure head is close (<10 m) to the land surface. Here, field measurements (temperature and DO well loggings) from a monitoring well in Bilthoven, the Netherlands, are combined with analytical and numerical modelling to investigate the role of both processes on oxygenation of anoxic groundwater in wells. The results of numerical and analytical modeling show that both permeation and convection can introduce oxygen into anoxic wells to near saturation concentrations. In the field data gathered, convection is primarily responsible for oxygen intrusion up to a depth of around 12 m. Oxygen intrusion through convection and permeation in monitoring and pumping wells may influence groundwater sampling and analyses, and may contribute to well clogging, depending on site conditions. The combination of field and modelling provides new insights into these processes, which can be used for both groundwater sampling and pumping well design.

There are multiple flow paths with different flow directions in fracture intersections. A general flow model synthetically describing the nonlinear flow behavior of multiple flow paths in different directions in two-dimensional fracture intersections was proposed for the analysis of fluid flow in rock fracture networks. The flow behavior of seven typical fracture intersection models, according to a geological investigation, was simulated. Through numerical simulations and experimental observations, it was validated that the flow model was capable of describing the nonlinear flow behavior in each flow direction in the fracture intersections at the same time. In this flow model, the coefficient matrices include linear coefficients for each fracture branch and nonlinear coefficients for each flow path. The relations between the hydraulic pressure drops and the flow rates reflect the influence of intersection configurations and flow directions on flow behavior in the fracture intersections. Based on the flow model and corresponding non-Darcy effect factor for fracture intersections, the critical Reynolds numbers to describe the transition of the flow regime in fracture intersections were determined and found to range from 51 to 105. Furthermore, the transition of the flow regime in the fracture intersections calculated with the proposed model was found to be closely related to the evolution of microscopic flow structures in the numerical simulations.