The hydrogeology of granitic rocks in deep boreholes used for compressed air storage

The compressed air energy storage(CAES) is a much-awaited new system for load leveling power supply. An economical system must be developed, preventing leakage of stored air (with pressures of more than 20 atm) using groundwater pressure surrounding an unlined cavern in hard rock. The air tightness of the rock around the cavern must be confirmed. In this study, the hydrogeology of the test site was examined prior to field air tightness tests in the borehole. The results indicate that, when evaluating the hydrogeology of the test site related to the air tightness of rocks, it is necessary to understand the geological structure and fracture characteristics of the site. This is done by means of a field survey, investigations and tests in and between the boreholes, and the examination of the distribution of permeability and pore water pressures.     

Constraining the uncertainty in fracture geometry using tracer tests

In fractured-rock aquifers, the geometric and hydraulic properties of the fractures commonly have a dominant influence on transport. Tracer tests are often used to estimate directly the gross transport properties of a fractured rock mass. The prospects for understanding characteristics of the heterogeneities in a fractured porous medium were explored from evidence provided by tracer experiments. The approach was to simulate flow and transport on a large set of prescribed fracture networks in a two-dimensional homogeneous permeable medium, thus generating synthetic tracer test data. The fracture orientation, aperture, spacing and network geometry were systematically altered from one case to the next. A classification scheme was devised for the tracer breakthrough curves using principal component analysis and this classification was linked to the fracture pattern properties. Even under highly simplified and controlled conditions, quite different fracture patterns can produce very similar breakthrough curves. The classification scheme thus demonstrates that a single breakthrough curve cannot reveal the fracture geometry with any precision. However, the scheme provided a methodology for rejecting geometric properties that do not belong to the fracture pattern under investigation, thus reducing the uncertainty in fracture geometry.     

岩溶热储井间连通性的示踪研究

岩溶热储储层的不均匀性强,采灌井之间的连通性不易确定。示踪技术可以将运移参数量化,有效刻画储层流体的特征,研究回灌井和开采井之间的水力联系,包括导水通道,流体流速等信息,对长期回灌可能引起的开采井的冷却进行预测,是岩溶热储井间连通性研究十分有效的技术。本文以华北牛驼镇地热田雄县地区为例,针对蓟县系雾迷山组岩溶热储,采用荧光素钠示踪剂,进行了1口井注入,10口井观测的群井示踪试验。采用裂隙介质溶质运移模型,对示踪试验数据进行了解释,得到优势通道的长度、渗透流速、纵向弥散度、回收率等储层性质,获得了试验区内采灌井之间的连通特征。对调整采灌井布局提出了建议。     

温度探测土坝圆柱状集中渗漏模型研究

渗漏是堤坝破坏主要形式之一，只有确定渗漏发生的确切位置和集中渗漏通道的大小和强度，才能对其有效治理。本文基于渗流和渗漏情况下堤坝温度场特征及温度示踪基本原理，对复杂的实际问题进行科学简化合理假设，把集中渗漏通道简化为圆柱状并作为边界条件，结合钻孔探测温度实际，运用稳定热传导理论，建立了圆柱状堤坝渗漏温度示踪模型。利用测井温度曲线的最大异常温度，该模型可以计算渗漏通道的位置，渗漏通道大小，流速等参数。工程实践表明，对于垂向流速较小的地下水渗漏进行温度场示踪是有效的方法。     

Characterization of karst conduits by tracer tests for an artificial recharge scheme

Challenged by rapidly changing climate in combination with an increase in anthropogenic pressures, karst groundwater resources in the Old Town of Lijiang (OTLJ), SW China, are diminishing. Higher frequency and longer duration of dried-up periods have been observed at the Heilongtan Park (HP) Springs in recent years. Thus, there is an urgent need for an artificial recharge scheme, aimed at replenishing groundwater in the aquifer and increasing the outflow of the springs to ensure effective water resources management. Evaluation of the scheme feasibility, prior to its implementation, is important. In this study, tracer tests were conducted between the recharge area and receiving springs in order to gain insight into the transport mechanisms of karst groundwater and the structural characteristics of the aquifer. Multiple underground flow paths, exhibiting high conductivity between the recharge area and HP Springs, were revealed by the interpretation of tracer breakthrough curves. Three springs considered as the leakages of the scheme were identified. Moreover, the outflow of springs at HP and OTLJ were predicted to be increased by the artificially recharged water after 9.2 and 12.5 days, respectively. Quantitative analysis of tracer recoveries demonstrates that the springs to be recharged and the springs considered as leakages, respectively, share 45 and 55% of the increased outflow. The feasibility of the scheme has been confirmed by the tracer tests. This report provides references for the evaluation of artificial groundwater recharge and protection strategies, particularly in large and poorly investigated karst spring fields.

     

Interpretation of single-well tracer tests using fractional-flow dimensions. Part 2: A case study

Generalized equations using fractional-flow dimensions were derived to estimate the Darcy and groundwater-flow velocities obtained from the point-dilution and the single-well injection-withdrawal field tests. Flow velocities can only be estimated from single-well tests if the kinematic porosity or the hydraulic conductivity and hydraulic gradient are known a priori. A pumping test performed on the boreholes will yield an estimate of the fractional-flow dimension and the extent of the flow region by applying the generalized radial flow (GRF) model of Barker [Barker JA (1988) A generalized radial flow model for hydraulic tests in fractured rock. Water Resour Res 24(10):1796–1804]. These parameters are used in the generalised equations for the single-well tracer tests to estimate the flow-through area and, therewith, the Darcy or flow velocity. The generalized procedure, described in detail in Part 1 of this paper, is applied to two boreholes on the Campus Test Site located at the University of the Free State, Bloemfontein, South Africa, and it is shown that the two independent tests (i.e. the point-dilution and the single-well injection-withdrawal tests) yield similar estimates of the natural-seepage velocity in the aquifer. The estimated natural-flow velocity obtained by using fractional dimensions is about two times higher than the velocity estimated by using the standard method (i.e. flow dimension n=2, flow thickness equal to length of the sealed-off section of the borehole). Electronic Publication     

Soil column infiltration tests on biomediated capillary barrier systems for mitigating rainfall-induced landslides

Rainfall-induced landslide is a common geohazard in tropical and humid regions. Capillary barrier system (CBS) is a popular and widely studied mitigating measure for rainfall-induced landslides. However, several previous studies have shown that the performance of the conventional CBS under intense rainfalls has not been particularly convincing. This paper aims to explore the feasibility and effectiveness of a newly proposed system, known as “biomediated capillary barrier system” (B-CBS) in minimizing water infiltration into soil. A one-dimensional soil column was used to investigate the infiltration characteristics of the proposed system. The results showed that the B-CBS of biomediated residual soil overlying original residual soil (Test IV) could effectively control the infiltration into soil by taking advantage of the less-permeable biomediated soil cover. The B-CBS of biomediated residual soil overlying gravelly sand (Test V) and the three-layered B-CBS of fine sand overlying gravelly sand and biomediated residual soil (Test VI) showed the best performance in terms of minimizing the water infiltration. A suction of about 5 kPa still remained in the soil column after 60 min of infiltration from the ponded water on the soil surface.     

Applicability of the ACE algorithm for multiple regression in hydrogeology

This paper introduces the alternating conditional expectation (ACE) algorithm of Breiman and Friedman (J Am Stat Assoc 80:580–619, 1985) for estimating the transformations of a response and a set of predictor variables in multiple regression problems in hydrogeology. The proposed nonparametric approach can be applied easily for estimating the optimal transformations of different hydrogeological data to obtain maximum correlation between observed variables. The approach does not require a priori assumptions of a functional form, and the optimal transformations are derived solely based on the data set. The advantages and applicability of this new approach to solve different multiple regression problems in hydrogeology or in Earth Sciences are illustrated by means of theoretical investigations and case studies. It is demonstrated that the ACE method has certain advantages in some fitting problems of hydrogeology over the traditional multiple regression. Based on our knowledge, this is the first application of the ACE algorithm to analyze and interpret groundwater data.     

A parsimonious approach for large-scale tracer test interpretation

Hydrogeology Journal - Dye tracing is an efficient method for spring watershed delineation, but is also used in surface waters to assess pollution migration over several kilometers. The aim of this...     

井间分溶示踪估计重非水相污染物残留量的影响因素数值分析

对于重非水相污染场地,传统的钻孔取样方式因经费和取样个数的限制,往往无法准确估计含水层中重非水相污染物的残留量。井间分溶示踪法费用较低,且不会对污染源区造成破坏,可适用于推估重非水相污染物残留量,但目前该方法的准确性尚未得到验证。本文基于数值模拟方法探讨了示踪剂注入速率、示踪剂类型以及污染源区结构等多因素对井间分溶示踪估计重非水相污染物残留量准确性的影响。数值算例结果表明:井间分溶示踪实验估计重非水相污染物残留量的误差小于15%;降低示踪剂的注入速率使得分溶性示踪剂在非水相和水相流体间作用更充分,能够提高井间分溶示踪估计重非水相污染物残留量的精度,实验中示踪剂注入速率由500 m3/d降为250 m3/d后,多种情景的平均精度由91.68%提高至93%;选取低分溶系数的示踪剂有利于提高示踪剂的回收率,从而提高推估精度,实验中示踪剂由2,2-二甲基-3-戊醇改为己醇后,平均精度由87.83%提高至96.85%;复杂的重非水相液体污染源区结构易于出现示踪剂绕流等现象,导致井间分溶示踪估计重非水相污染物残留量的误差增大,实验中含水层由均质变为非均质后,平均精度由93.03%变为91.65%。重非水相污染场地调查时,建议结合数值模拟方法选择适宜的示踪剂和示踪剂注入速率,以提高污染场地的刻画精度。     

水文地质及灾害地质监测新仪器介绍

本文介绍了地下水监测和滑坡监测的两种新型仪器。ＷＬＴ－１０２０地下水动态监测仪器的突出特点是高分辨率、长期稳定、微功耗、全自动工作。ＨＹＪ－３００８滑坡诱发因素监测仪通过监测滑体内的水分变化来预测预报暴雨滑坡。     

CoFIS and TELog: New downhole tools for characterizing dispersion processes in aquifers by single-well injection-withdrawal tracer tests

Contaminant migration in aquifers is one of the most debated issues in hydrogeology, as most experimental results display large deviations from the standard (asymptotic) Fickian dispersion theories. Multi-scale investigation and high-resolution sensors are required to determine the origin of non-asymptotic dispersion and validate models. For this, a set of multi-scale Single-Well Injection-Withdrawal (SWIW) tracer tests using a new dual-packer probe CoFIS, including a high resolution optical sensor TELog, are presented. When compared to standard techniques such as salinity measurements, it is shown that high-resolution optical measurements allow an improved characterization of the long-lasting non-asymptotic dispersion mechanisms.     

Determination of bioavailable Fe(III) content in column experiments with the reactive tracer phosphate

Different methods were compared to evaluate the oxidation capacity of ferric iron in column studies. The specific adsorption of the reactive tracer phosphate on the Fe(III) oxide surface was used as an alternative approach to determine the oxidation capacity utilizing the linear correlation between the long-term extent of Fe(III) reduction and the specific surface area of the oxide. Although a low crystalline form of ferric iron (two-line ferrihydrite) was used as electron acceptor and toluene as a carbon source, only 31 and 24% respectively of the total iron was reduced by Geobacter metallireducens in parallel experiments. The results of the phosphate tracer tests were in good agreement with the Fe(III) that was actually reduced and the microbially oxidized toluene. The oxidation capacity of ferric iron is therefore overestimated by the chemical extraction methods, which completely dissolve the ferrihydrite and neglect surface-dependent limitations.     

Sequential tracer tests for determining water seepage paths in a large rockfill dam, Nakdong River basin, Korea

The rockfill dam of this study has a clay core, filter zone, and sandy gravel shell, and it is located in the Nakdong River basin in Korea. Filling the reservoir began in August 1994 and it was full by April 1998. When the reservoir level was approximately 150 m, three settlement holes were found in the dam crest. To determine possible seepage paths and potential damaged areas within the rockfill dam, 15 tracer tests were performed during two periods. During the two test periods, six and nine tracer tests were conducted when the average water levels of the reservoir were 145 m and 142 m, respectively. Rhodamine WT (RWT) and bromide ion were used as tracers. For each test, 1800 to 4000 L of tracer solution were injected into the riprap for about 5 h. The 15 injection points were uniformly distributed from the right to left sides of the embankment and the two tracers were injected alternately. Tracer concentrations were monitored at 26 observation wells, which were divided into four groups by their geographical positions: right side of the crest, left side of the crest, right side of the dam toe, and left side of the dam toe. For each tracer test, more than 30 water samples were taken during a period of 96 h at each observation well. Based the breakthrough curves obtained from the sequential tracer tests, it was inferred that the most probable seepage paths and potential damaged area were in the left side of the crest (tongue wing zone) and, to a lesser extent, in the right side of the dam abutment.     

Source-to-site distance distributions for area type of seismic sources used in PSHA applications

The use of recent ground motion prediction equations in probabilistic seismic hazard analysis (PSHA) with area type of seismic sources requires defining the probability distributions of various source-to-site distance metrics with finite fault rupture taken into account. This task is rendered very difficult due to large epistemic uncertainties involved in specifying the details of the causative faults for area sources of diffused seismicity. However, it may generally be possible to constrain the strike and dip angles for fault ruptures in area sources from regional seismotectonic and geological information. This paper proposes to estimate the various finite fault distance measures from a site to a location in an area source by averaging the distances for several fault rupture scenarios with randomly distributed strike and dip over specified ranges. To consider the spatial distribution of the seismicity, the paper then provides the guidelines for defining the distance distributions by assigning suitable weight factors to the distance estimates for a grid of locations in the source area. The PSHA computation based on the distance distributions thus defined is shown to provide quite realistic and objective estimate of the hazard.     

Delineation of groundwater protection zones based on tracer tests and transport modeling in alluvial sediments

 Regulations aiming to protect exploitable groundwater resources were edicted in Belgium a few years ago. Therefore, prevention and protection zones are defined by law and must be determined practically around each pumping well or spring, based on local hydrogeological conditions. The determination of hydrodynamic and hydrodispersive parameters, characterizing the local flow and transport properties of the aquifer, requires pumping and tracing tests. The interpretation of these field experiments, considering the heterogeneity of the geological layers, is performed through the use of numerical FEM simulations of the groundwater flow and pollutant transport conditions in a deterministic framework. After calibration of the model on experimental measurements, multiple simulations with contaminant injections at various points of the modeled domain allow the determination of the transfer time of the pollutant in the studied aquifer whilst taking the updated heterogeneity into account. On the basis of the computed transfer times in the saturated zone, the various prevention and protection areas can be assessed based on provisions of the law. Received: 27 June 1997 · Accepted: 29 July 1997     

Interpretation of tracer tests performed in fractured rock of the Lange Bramke basin, Germany

 Two multitracer tests performed in one of the major cross-fault zones of the Lange Bramke basin (Harz Mountains, Germany) confirm the dominant role of the fault zone in groundwater flow and solute transport. Tracers having different coefficients of molecular diffusion (deuterium, bromide, uranine, and eosine) yielded breakthrough curves that can only be explained by a model that couples the advective–dispersive transport in the fractures with the molecular diffusion exchange in the matrix. For the scale of the tests (maximum distance of 225 m), an approximation was used in which the influence of adjacent fractures is neglected. That model yielded nearly the same rock and transport parameters for each tracer, which means that the single-fracture approximation is acceptable and that matrix diffusion plays an important role. The hydraulic conductivity of the fault zone obtained from the tracer tests is about 1.5×10^–2 m/s, whereas the regional hydraulic conductivity of the fractured rock mass is about 3×10^–7 m/s, as estimated from the tritium age and the matrix porosity of about 2%. These values show that the hydraulic conductivity along the fault is several orders of magnitude larger than that of the remaining fractured part of the aquifer, which confirms the dominant role of the fault zones as collectors of water and conductors of fast flow. Received, April 1997 Revised, January 1998, August 1998 Accepted, August 1998