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1.
Flexible-wall hydraulic conductivity tests were carried out on bottom ash, fly ash and compacted specimens of sand with additions of 0, 3, 6, 9 and 18% of bentonite. In order to study the effect of bentonite inclusion and particle morphology on the hydraulic conductivity of the admixtures, an investigation was undertaken based on thin section micrographs. It was found that, for both bottom and fly ash admixtures, bentonite addition reduced only one order of magnitude the hydraulic conductivity, from 1.78 × 10−6 m/s to 1.39 × 10−7 m/s. On the other hand, the sand hydraulic conductivity was reduced five orders of magnitude, from 3.17 × 10−5 m/s to 5.15 × 10−10 m/s. Among several factors that can be responsible for the difficulty in reducing hydraulic conductivity, such as ash grain size distribution and elevated cation concentration (leached from the ash) in pore water, it can also be recalled the high particle voids observed in the ash by means of microscopic analysis. The same is not true with the sand, which has solid particles, without inner voids.  相似文献   

2.
Biosurfactants are frequently used in petroleum hydrocarbon and dense non-aqueous phase liquids (DNAPLs) remediation. The applicability of biosurfactant use in clayey soils requires an understanding and characterization of their interaction. Comprehensive effects of surfactants and electrolyte solutions on kaolinite clay soil were investigated for index properties, compaction, strength characteristics, hydraulic conductivities, and adsorption characteristics. Sodium dodecyl sulfate (SDS) and NaPO3 decreased the liquid limit and plasticity index of the test soil. Maximum dry unit weights were increased and optimum moisture contents were decreased as SDS and biosurfactant were added for the compaction tests for mixtures of 30% kaolinite and 70% sand. The addition of non-ionic surfactant, biosurfactant, and CaCl2 increased the initial elastic modulus and undrained shear strength of the kaolinite–sand mixture soils. Hydraulic conductivities were measured by fixed-wall double-ring permeameters. Results showed that the hydraulic conductivity was not significantly affected, but slightly decreased from 1×10−7 cm/s (water) to 0.3×10−7 cm/s for Triton X-100 and SDS. The adsorption characteristics of the chemicals onto kaolinite were also investigated by developing isotherm curves. SDS adsorbed onto soil particles with the strongest bonding strength of the fluids tested. Correlations among parameters were developed for surfactants, electrolyte solutions, and clayey soils.  相似文献   

3.
Physical and hydraulic properties of sediment from two karst aquifers were measured to determine (1) the similarity of sediment between karst aquifer systems and (2) the importance of sediment in modeling flow through karst aquifers. The sediment from the two systems was similar in size and composition. Within both aquifers, the silt-sized sediment was composed primarily of quartz, with minor amounts of plagioclase and clays. Hydraulic conductivity of the sediment measured directly (falling-head test) ranged from 1.61×10−7 to 1.33×10−6 m s–1 and estimated using the Campbell equation ranged from 8.30×10−8 to 8.98×10−7 m s–1. These values of hydraulic conductivity fall within the span of hydraulic conductivities for carbonate rocks, indicating that the sediment and carbonate matrix could be represented as one mathematical unit in modeling flow through karst aquifers. Statistical agreement in the hydraulic conductivity values generated by the two methods indicates that the estimation technique could be used to calculate hydraulic conductivities; thus allowing karst scientist to collect bulk sediment samples instead of having to collect cores from within karst aquifers. Electronic Publication  相似文献   

4.
This research describes the goals, design and implementation of a quasi natural gradient, laboratory scale, sand tank (aquifer) model experiment. The model was used to study the transport of an inorganic tracer (Chloride) in groundwater, within a tropical aquifer (porous medium) material. Three-dimensional sand tank (1.8 m × 0.3 m × 0.8 m) experiments were conducted to investigate contaminant transport and natural attenuation within the sand tank. In all, 360 samples were collected during 24 sampling sessions, for the three days of the tracer experiments in the Sand Tank. The Owena sand is a poorly graded sand with 88.1 % sand and 11.9 % gravel. Geotechnical properties including; coefficient of uniformity Cu = 2.53, coefficient of gradation Cz = 0.181, hydraulic conductivity K = 5.76 × 10?4 m/s, bulk density p = 1.9 Mg/m3, effective porosity ne = 0.215 and median grain diameter D50 = 0.55 mm, were determined. Other relevant hydraulic and solute transport parameters, such as dispersion coefficients and dispersivities were also established for the tropical soil.  相似文献   

5.
 Rock and flow parameters of three karstic-fissured-porous aquifers in the Krakow-Silesian Triassic formations were measured using various methods and compared. Though cavern and fissure porosities are shown to be very low (cavern porosity below 0.5% and fracture porosity below 0.2%), they contribute dominantly to the hydraulic conductivity (from about 1.3×10–6 to about 11×10–6 m/s). Matrix porosity (2–11%) is shown to be the main water reservoir for solute transport and the main or significant contributor to the specific yield (<2%). Though the matrix porosity is shown to be much larger than the sum of the cavern and fissure porosities, its contribution to the total hydraulic conductivity is practically negligible (hydraulic conductivity of the matrix is from about 5×10–11 m/s to about 2×10–8 m/s). On the other hand, the matrix porosity (for neglected cavern and fissure porosities) when combined with tracer ages (or mean travel times) is shown to yield proper values of the hydraulic conductivity (K) by applying the following formula: K≅(matrix porosity×mean travel distance)/(mean hydraulic gradient×mean tracer age). Confirming earlier findings of the authors, this equation is shown to be of great practical importance because matrix porosity is easily measured in the laboratory on rock samples, whereas cavern and fracture porosities usually remain unmeasurable. Received: 21 February 1997 · Accepted: 13 May 1997  相似文献   

6.
Recent work in southern Ontario, Canada, demonstrates anomalously high vertical groundwater flow velocities (>1 m/year) through a thick (as much as 60 m), sandy silt till aquitard (Northern till), previously assumed to be of very low permeability (hydraulic conductivity <10–10 m/s). Rapid recharge is attributed to the presence of fractures and sedimentary heterogeneities within the till, but the field-scale flow regime is poorly understood. This study identifies the nature of physical groundwater pathways through the till and provides estimates of the associated groundwater fluxes. The aquitard groundwater flow system is characterized by integrating details of the outcrop and subsurface sedimentary characteristics of the till with field-based hydrogeologic investigation and numerical modeling. Outcrop and subsurface data identify a composite internal aquitard stratigraphy consisting of tabular till beds (till elements) separated by laterally continuous sheet-like sands and gravels (interbeds) and boulder pavements. Individual till elements contain sedimentary heterogeneities, including discontinuous sand and gravel lenses, vertical sand dikes, and zones of horizontal and vertical fractures. Hydrogeologic field investigations indicate a three-layer aquitard flow system, consisting of upper and lower zones of more hydraulically active and heterogeneous till separated by a middle unit of relatively lower hydraulic conductivity. Groundwater pathways and fluxes in the till were evaluated using a two-dimensional aquitard/aquifer flow model which indicates a step-wise flow mechanism whereby groundwater moves alternately downward along vertical pathways (fractures, sedimentary dikes) and laterally along horizontal sand interbeds within the till. This model is consistent with observed hydraulic-head and isotope profiles, and the presence of tritiated pore waters at various depths throughout the till. Simulations suggest that a bulk aquitard vertical hydraulic conductivity on the order of 1×10–9 m/s is required to reproduce observed hydraulic-head and tritium profiles. Electronic Publication  相似文献   

7.
Compacted sewage sludge as a barrier for tailing impoundment   总被引：1，自引：1，他引：0  
The feasibility of compacted sewage sludge serving as a barrier for tailing impoundment was evaluated by the batch test and hydraulic conductivity test with respect to heavy metal retardation and impermeability. The batch test results showed that the effective removal of heavy metals approached 97.8 and 93.4% for Zn and Cd, respectively. Formation of precipitation of oxy(hydroxide) and carbonate minerals was mainly responsible for the attenuation of heavy metals in the early period of the test. Nevertheless, the further removal of heavy metals can be attributed to the sulfate reduction. The hydraulic conductivity test indicated that almost all of the heavy metals contained in simulated acid pore water were retarded by compacted sewage sludge. The hydraulic conductivity of the compacted sewage sludge ranged from 3.0 × 10−8 to 8.0 × 10−8 cm s−1, lower than 1.0 × 10−7 cm s−1, which is required by regulations for the hydraulic barrier in landfill sites. Thus, this study suggested that compacted sewage sludge could be used as a bottom barrier for tailing impoundment.  相似文献   

8.
The present study assesses groundwater resources in the semiarid central Sudan, where 20 deep productive wells were installed to supply a major city in the region, El Obeid. The wells, which has an average 20 L/s discharge each, are taping a deep semiconfined to confined aquifer of fluvial silisiclastics deposited in the Tertiary–Pleistocene. Groundwater modeling was used as a technique to interpret the hydrologic system in arid to semiarid central Sudan and to simulate the future influence of the project on the hydrogeologic system. The simulation confirmed that steady-state flow conditions have been currently reached as indicated by consistency of computed heads. It also calibrated the values of the conductivity and recharge and ensured the sustainability of the El Obeid water supply project. A total of 3.5 × 107 m3/year can be continually extracted from the deep aquifer to supply El Obeid city without endangering the groundwater resources in the region. The decline in water level will not exceed 25 m during the first 10 years, while indefinite continuous pumping will affect only the vicinity of the wells in a circle of 30 km diameter. Therefore, aquifer storage capacity and hydraulic properties encourage further groundwater exploitation. The present use of groundwater is extremely lower than the present demand, and it can potentially cover future demands without introducing significant changes to the system. The increase of pumping cost due to the decline in head subsequent to project operation was found to be minimal and of local effect.  相似文献   

9.
 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  相似文献   

10.
Zakynthos, an island of 408 km2 in the Ionian Sea, is completely dependent on its groundwater resources for fulfilling the demands of the water supplies. The use of groundwater resources has become particularly intensive during the last decades because of the intense urbanization, the tourist development and the irrigated land expansion that took place. The main aquifers are developed in limestones (karstic), sandstones of neogene deposits (confined) and alluvial deposits (phreatic). This paper focuses on the assessment of their hydrogeological characteristics and the groundwater quality. For this investigation, groundwater level measurements, drilling data, pumping tests and chemical analyses of groundwater samples were used. The average annual consumption that is abstracted from the aquifer systems, is 4.9 × 106 m3 year−1. The exploitable groundwater reserves were estimated to be 3.3 × 106 m3 year−1. In the last decades, the total abstractions exceed the natural recharge, due to the tourist development; therefore the aquifer systems are not used safely. The results of chemical analyses showed a deterioration of the groundwater quality. According to the analyses the shallow alluvial aquifer and the confined aquifer are polluted by nitrates at concentrations in excess of 25 mg L−1. High sulphate concentrations might be related to the dissolution of gypsum. Seawater intrusion phenomena are recorded in coastal parts of aquifer systems. The increased Cl− concentrations in karstic aquifer indicate signs of overexploitation. Strengths, weaknesses, opportunities and threats (SWOT) analysis was applied in order to evaluate the SWOT of the groundwater resources. Moreover, some recommendations are made to assist the rational management that aim at improving the sustainability of the groundwater resources of Zakynthos Island.  相似文献   

11.
Yang  Heejun  Tawara  Yasuhiro  Shimada  Jun  Kagabu  Makoto  Okumura  Azusa 《Hydrogeology Journal》2021,29(6):2091-2105

The hydraulic conductivity of an unconfined carbonate aquifer at the uplifted atoll of Minami-Daito, Japan, was evaluated by a combination of cross-spectral analysis, analytical solution, and density-dependent groundwater modeling based on observed groundwater levels in 15 wells and at sea level. The island area was divided into 10 subregions based on island morphology and on inland propagation of ocean tides. The hydraulic conductivity was obtained for each subregion using analytical solutions based on phase lags of M2 constituents of ocean tides at each well by assuming two aquifer thicknesses (300 and 1,800 m) and two effective porosities (0.1 and 0.3). The density-dependent groundwater model evaluated the hydraulic conductivity of the subregions by reproducing observed groundwater levels. The hydraulic conductivity in the subregions was estimated as 3.46?×?10?3 to 6.35?×?10?2 m/s for aquifer thickness of 300 m and effective porosity of 0.1, and as 1.73?×?10?3 to 3.17?×?10?2 m/s for aquifer thickness of 1,800 m and the effective porosity of 0.3. It was higher in southern and northern areas, and higher in interior lowland than in the western and eastern areas. Fissures and dolomite distributions on the island control differences of the omnidirectional ocean tidal propagation and cause these differences in hydraulic conductivity. The method used for this study may also be applicable to other small islands that have few or no data for hydraulic conductivity.

  相似文献   

12.
The hydrogeologic and hydraulic characteristics of a lateritic terrain in West Bengal, India, were investigated. Test drilling was conducted at ten sites and grain-size distribution curves (GSDCs) were prepared for 275 geologic samples. Performance evaluation of eight grain-size-analysis (GSA) methods was carried out to estimate the hydraulic conductivity (K) of subsurface formations. Finally, the GSA results were validated against pumping-test data. The GSDCs indicated that shallow aquifer layers are coarser than the deeper aquifer layers (uniformity coefficient 0.19–11.4). Stratigraphy analysis revealed that both shallow and deep aquifers of varying thickness exist at depths 9–40 and 40–79 m, respectively. The mean K estimates by the GSA methods are 3.62–292.86 m/day for shallow aquifer layers and 0.97–209.93 m/day for the deeper aquifer layers, suggesting significant aquifer heterogeneity. Pumping-test data indicated that the deeper aquifers are leaky confined with transmissivity 122.69–693.79 m2/day, storage coefficient 1.01?×?10?7–2.13?×?10?4 and leakance 2.01?×?10?7–34.56?×?10?2 day?1. Although the K values yielded by the GSA methods are generally larger than those obtained from the pumping tests, the Slichter, Harleman and US Bureau Reclamation (USBR) GSA methods yielded reasonable values at most of the sites (1–3 times higher than K estimates by the pumping-test method). In conclusion, more reliable aquifers exist at deeper depths that can be tapped for dependable water supply. GSA methods such as Slichter, Harleman and USBR can be used for the preliminary assessment of K in lateritic terrains in the absence of reliable field methods.  相似文献   

13.
A long-term elution experiment to study the saturated transport of pre-accumulated fertilizers by-products, was conducted within a large tank (4 × 8 × 1.4 m) equipped with 26 standard piezometers. Sandy sediments (35 m3), used to fill the tank, were excavated from an unconfined alluvial aquifer near Ferrara (Northern Italy); the field site was connected to a pit lake located in a former agricultural field. To evaluate spatial heterogeneity, the tank’s filling material was characterized via slug tests and grain-size distribution analysis. The investigated sediments were characterized by a large spectrum of textures and a heterogeneous hydraulic conductivity (k) field. Initial tank pore water composition exhibited high concentration of nitrate (NO3 −) sulfate (SO4 2−) calcium (Ca2+), and magnesium (Mg2+), due to fertilizer leaching from the top soil in the field site. The initial spatial distribution of NO3 − and SO4 2− was heterogeneous and not related to the finer grain-size content (<63 μm). The tank’s material was flushed with purified tap water for 800 days in steady-state conditions; out flowing water was regularly sampled to monitor the migration rate of fertilizer by-products. Complete removal of NO3 − and SO4 2− took 500 and 600 days, respectively. Results emphasized organic substrate availability and spatial heterogeneities as the most important constraints to denitrification and nitrogen removal, which increase the time required to achieve remediation targets. Finally, the obtained clean-up time was compared with a previous column experiment filled with the same sediments.  相似文献   

14.
This study integrated surface and subsurface stratigraphic data with geophysical logs and hydrogeologic data in order to characterize the hydraulic properties of the Silurian dolomite in northeastern Wisconsin. Silurian stratigraphy consists of predictable alternations of characteristic facies associations. A vertical profile of hydraulic conductivity, obtained from short-interval packer tests in a core hole that penetrates a majority of the Silurian section, indicates that hydraulic conductivity ranges over five orders of magnitude (10–1 to 10–6 cm/s). Matrix conductivity is generally low and varies with texture; the finer-grained restricted-marine and transitional facies being less permeable than the coarser-grained open-marine facies. High-conductivity values are generally associated with bedding-plane fractures, and fracture frequency is greater in the restricted-marine facies. High-flow features in 16 wells were identified using fluid-temperature/resistivity and heat-pulse flowmeter logs. Natural-gamma logs were used to identify the stratigraphic position of flow features in each well and to correlate flow features to specific stratigraphic horizons. By combining stratigraphic, geophysical, and hydrogeologic data, 14 high-permeability zones within the Silurian aquifer have been identified and correlated in wells more than 16 km apart. These zones parallel bedding, appear most pronounced at contacts between contrasting lithologies, and are most abundant in restricted-marine lithologies. Electronic Publication  相似文献   

15.
The generation of massive volume of slimes from sand mining industry ascertains the need for effective waste treatment. The application of slimes in landfill barrier construction works has been identified as one of the processes that can be used to reduce their volume, enabling in this way the rehabilitation of dangerous sites. This article presents a modified triaxial cell specially built to investigate high water content soils and discusses the results obtained from the investigation of the hydraulic properties of two slimes. The results of laboratory filter cake tests show that the slimes have reasonably good sealing capacities due to the formation of a cake layer on other porous materials upon draining. A relatively low hydraulic conductivity (1.5–3 × 10−9 m/s) was achieved, once the cake layer was formed. This is close to the prescribed 1 × 10−9 m/s required by the local environmental governmental authority for a landfill hydraulic barrier material, indicating their potential suitability as landfill barrier.  相似文献   

16.
Water-table elevation measurements and aquifer parameter estimates are rare in alpine settings because few wells exist in these environments. Alpine groundwater systems may be a primary source of recharge to regional groundwater flow systems. Handcart Gulch is an alpine watershed in Colorado, USA comprised of highly fractured Proterozoic metamorphic and igneous rocks with wells completed to various depths. Primary study objectives include determining hydrologic properties of shallow bedrock and surficial materials, developing a watershed water budget, and testing the consistency of measured hydrologic properties and water budget by constructing a simple model incorporating groundwater and surface water for water year 2005. Water enters the study area as precipitation and exits as discharge in the trunk stream or potential recharge for the deeper aquifer. Surficial infiltration rates ranged from 0.1–6.2×10?5 m/s. Discharge was estimated at 1.28×10?3 km3. Numerical modeling analysis of single-well aquifer tests predicted lower specific storage in crystalline bedrock than in ferricrete and colluvial material (6.7×10?5–2.0×10?3 l/m). Hydraulic conductivity in crystalline bedrock was significantly lower than in colluvial and alluvial material (4.3×10?9–2.0×10?4 m/s). Water budget results suggest that during normal precipitation and temperatures water is available to recharge the deeper groundwater flow system.  相似文献   

17.
Quantitative evaluation of management strategies for long-term supply of safe groundwater for drinking from the Bengal Basin aquifer (India and Bangladesh) requires estimation of the large-scale hydrogeologic properties that control flow. The Basin consists of a stratified, heterogeneous sequence of sediments with aquitards that may separate aquifers locally, but evidence does not support existence of regional confining units. Considered at a large scale, the Basin may be aptly described as a single aquifer with higher horizontal than vertical hydraulic conductivity. Though data are sparse, estimation of regional-scale aquifer properties is possible from three existing data types: hydraulic heads, 14C concentrations, and driller logs. Estimation is carried out with inverse groundwater modeling using measured heads, by model calibration using estimated water ages based on 14C, and by statistical analysis of driller logs. Similar estimates of hydraulic conductivities result from all three data types; a resulting typical value of vertical anisotropy (ratio of horizontal to vertical conductivity) is 104. The vertical anisotropy estimate is supported by simulation of flow through geostatistical fields consistent with driller log data. The high estimated value of vertical anisotropy in hydraulic conductivity indicates that even disconnected aquitards, if numerous, can strongly control the equivalent hydraulic parameters of an aquifer system.  相似文献   

18.
Within carbonate systems, the working hypothesis suggests that when a conduit is flooded fluid and solute migrate from the conduit into the matrix. This flux of fluid and solute into the matrix creates a reservoir that can be slowly released once the flooding recedes. Although hypothesized, these fluxes have never been measured. To quantify the distance that a fluid and solute would move into a matrix, the fluxes of fluid and solute from a conduit into a matrix were simulated for nine different carbonate aquifer systems. Two independent numerical approaches were used to simulate (1) fluid flux into the matrix and (2) solute flux into the matrix during a flooding event. When flooding occurs within the conduit, the volume of water transported into and stored in the matrix with a high porosity and high hydraulic conductivity (Floridan Aquifer) was less than 0.34 m3 along a 1 m length of conduit, resulting in a penetration depth of 7.2×10−2 m into the matrix. In a low porosity and low hydraulic conductivity matrix (Ozark Plateau), the volume of water transported into and stored in the matrix was less than 6.85×10−5 m3 along a 1 m length of conduit, resulting in a penetration depth of 2.0×10−4 m into the matrix. Simulated solute flow shows that less than 0.1% of the solute moves in to the matrix. The two approaches demonstrate that during high flow conditions fluid and solute are forced through the conduits, with very little moving into the carbonate matrix. Once the fluid and solute enter a conduit and are moving, they will remain in the conduit until they are discharged at an outlet. Thus, a carbonate matrix does not become a reservoir for solute and fluid during a high-flow event.  相似文献   

19.
Groundwater recharge by natural replenishment for the unconsolidated alluvial aquifer in Wadi Al-Yammaniyah is estimated on a daily basis instead of the conventional monthly basis The study reveals that during the two-year period (1978 and 1979), the estimated recharge in the area is about 40% of the total average annual rainfall of 155 mm Subsurface underflow estimated at 36×10−6 m3/yr from the Wadi Al-Yammaniyah aquifer occurs in the vicinity of Wadi Ash-Shamiyah A comparison of the recharge and extracted volumes of water from the aquifer indicates that there is a net increase of 10 million m3 and 38 million m3 of water in the storage for 1978 and 1979, respectively  相似文献   

20.
A simple, single-well push-pull test was conducted at a TCE-contaminated site to estimate the site-specific TCE degradation and permanganate (MnO4−) consumption rate. Known quantities of a conservative tracer (Br−) and permanganate were rapidly injected into a saturated aquifer then periodically sampled during extraction from the same well. Concentrations of Br−, TCE, and MnO4− were measured; breakthrough curves (BTCs) for all species of solute were determined. Data analysis of BTCs for bromide and TCE showed that the first-order rate constant of TCE degradation by MnO4− is 1.67 ± 0.152 h−1. Further, the in situ MnO4− demand rate by TCE and aquifer materials is estimated to be 0.54 ± 0.371 h−1. This study demonstrates that in situ push-pull tests are useful and economical tools for field investigations to determine contaminant reaction and oxidant consumption rates, which may then be used to optimize groundwater remediation designs.  相似文献   

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