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1.
A. KamyshnyJr. M. Zilberbrand I. Ekeltchik T. Voitsekovski J. Gun O. Lev 《Aquatic Geochemistry》2008,14(2):171-192
Zerovalent sulfur and inorganic polysulfides were determined in nine sulfide-rich water wells in central and southern Israel.
Although the two locations belong to the same aquifer, they are characterized by different pH and hydrogen sulfide levels.
Hydrogen sulfide in the central Israel wells ranged between 19 and 32 μM, and the pH was 7.26 ± 0.07. The southern basin is
characterized by lower water circulation, lower pH (around 6.8), and higher hydrogen sulfide levels (>470 μM). Polysulfides
were determined by a rapid single-phase methylation using methyl trifluoromethanesulfonate (methyl triflate) reagent. The
summary polysulfide concentration for S42−–S72− species was found to be around 0.14–0.75 μM in the central region of Israel and substantially higher, 2.3–4.6 μM in the southern
region. The sum of polysulfide zerovalent sulfur and colloidal sulfur was quantitatively detected by cyanide derivatization
and compared to polysulfide sulfur determined by methyl triflate derivatization and to the chloroform extraction of zerovalent
sulfur. A method for the determination of sulfur undersaturation level—the ratio between dissolved elemental sulfur and its
equilibrium concentration in the presence of solid sulfur—based on the observed levels of the major polysulfide species is
described. The observed polysulfide speciation was compared with the predicted speciation under sulfur saturation conditions
taking into account the water temperature, its ionic strength, and pH. Criteria for sulfur saturation versus unsaturated conditions
were established based on (1) the chain length dependence of the ratio between the observed polysulfide concentrations and
their predicted value under sulfur saturated conditions, and (2) the difference between the concentration of zerovalent sulfur,
as determined by cyanolysis, and the total polysulfide sulfur. According to this dual criterion five of the water wells were
classified as being undersaturated with respect to sulfur, though for all the examined water wells the majority of the zerovalent
sulfur was in the form of polysulfide sulfur. 相似文献
2.
Proposed groundwater withdrawals in the San Luis Valley of Colorado may lower the water table in Great Sand Dunes National
Monument. In response, the National Park Service initiated a study that has produced a generalized conceptual model of the
hydrologic system in order to assess whether a lowering of the water table might decrease the surface flow of lower Medano
Creek. Based upon information obtained during the drilling of several boreholes, there appear to be five important hydrostratigraphic
units underlying lower Medano Creek within the upper 30 m of the ground surface: 1. a perched aquifer overlying an aquitard
located between about 5 and 6 m below the ground surface; 2. the aquitard itself; 3. an unconfined aquifer located between
the upper and lower aquitards; 4. an aquitard located between about 27 and 29 m below the ground surface; and 5. a confined
underlying the lower aquitard. Because the areal extent of the aquitards cannot be determined from the borehole data, a detailed
conceptual model of the hydrogeologic system underlying lower Medano Creek cannot be developed. However, a generalized conceptual
model can be envisioned that consists of a complex system of interlayered aquifers and leaky aquitards, with each aquifer
having a unique hydraulic head. Water levels in the perched aquifer rise rapidly to their annual maximum levels in response
to the arrival of the flow terminus of Medano Creek during the spring runoff event, and the location of the flow terminus
is directly dependent upon the discharge of the creek. Water levels in the deeper, non-perched aquifers do not appear to fluctuate
significantly in response to the arrival of the flow terminus, demonstrating that it is unlikely that the proposed groundwater
withdrawals will decrease the surface flow of lower Medano Creek.
Received: 27 December 1995 · Accepted: 20 February 1996 相似文献
3.
H. Khérici-Bousnoubra N. Khérici E. F. Derradji C. Rousset R. Caruba 《Environmental Geology》2009,57(7):1619-1624
Industrial wastewater is characterised by the presence of a great quantity of metallic micro-pollutants, among which chromium
by its mobility, contaminates the surface and groundwater. The study of different aquifers within the area of Annaba (Algeria)
shows extremely variable chromium concentrations in the unconfined aquifer (0–0.22 mg l−1), which becomes practically null in dry period; on the other hand, they remain relatively constant in the deep confined aquifer
(about 0.04 mg l−1). To specify the mechanisms of chromium migration in the aquifer system, a study of space–time evolution of chromium concentrations
in unconfined aquifer was undertaken, while considering the kinetics of diffusion in the deeper aquifer. Chromium, indirectly
reduced microbiologically by sulphate-reducer bacteria in the upper aquifer, is likely to anticipate the auto-depuration capacity
of the ground and to reduce the quality of groundwater. 相似文献
4.
Geology and hydrogeology of the Dammam Formation in Kuwait 总被引:2,自引:0,他引:2
The Dammam Formation of Middle Eocene age is one of the major aquifers containing useable brackish water in Kuwait. Apart
from the paleokarst zone at the top, the Dammam Formation in Kuwait consists of 150–200 m of dolomitized limestone that is
subdivided into three members, on the basis of lithology and biofacies. The upper member consists of friable chalky dolomicrite
and dolomite. The middle member is mainly laminated biomicrite and biodolomicrite. The lower member is nummulitic limestone
with interlayered shale toward the base. Geophysical markers conform to these subdivisions. Core analyses indicate that the
upper member is the most porous and permeable of the three units, as confirmed by the distribution of lost-circulation zones.
The quality of water in the aquifer deteriorates toward the north and east. A potentiometric-head difference exists between
the Dammam Formation and the unconformably overlying Kuwait Group; this difference is maintained by the presence of an intervening
aquitard.
Received, February 1997 Revised, June 1997, September 1997 Accepted, January 1998 相似文献
5.
The aim of this study was to identify the complex hydrogeological and hydrochemistry conditions of Damt region, through determining
hydrochemical properties of groundwater in the study area. According to the results of hydrochemical analyses, sampled waters
can be divided into three groups: cold, thermal, and mixed waters. Thermal waters in the area are characterized by Na–HCO3, while the cold waters by CaHCO3 facies. HCO3 indiscriminate cation and/or Na-indiscriminate anion are present in many places in the region and indicate generally mixing
water. Only three villages with dental fluorosis observed using water elevated in F− for drinking. Agricultural and liquid waste disposal are the main sources of pollution, leads to increase of Na, Cl, NO3, Cd, and Iron. The groundwater flow is from north, northwest, and northeast to the south. Within this regional trend, structural
controlling groundwater flow along Wadis and it flows from upper reaches of tributaries toward the main channel, then downward
to the south of the study area. The similarity of TDS and Cl concentration at Qa’a Al Haql and Al Nadirah between aquifers
indicates hydraulic continuity between alluvial and the underlying volcanic, while at Damt no hydraulic continuity found between
alluvial, volcanic and Sandstone aquifers. The temporal variation shows slight decrease in the concentration of nitrate and
sulfate of thermal water indicating previously high gas content of nitrogen, hydrogen sulfide in the thermal active region.
The developed conceptual model of water circulation indicates flood waters infiltrate slowly through the wadi bottoms in the
East where Sandstone aquifer outcrops. These waters flow westward, following the westerly dip of the Sandstone through the
effects of gravity, gains heat and dissolve materials as it comes in contact with the numerous dykes, which are the feeders
to the overlying volcanoes and sputter cones. All thermal water samples from Damt region fall into immature water field in
NA–K–Mg diagram. Therefore, the results obtained from the cation geothermometers should be taken into account as doubtful. 相似文献
6.
A study on the hydrogeology and hydrogeochemistry of groundwater from different depths in a coastal aquifer: Annamalai Nagar,Tamilnadu, India 总被引:3,自引:0,他引:3
S. Chidambaram G. Senthil Kumar M. V. Prasanna A. John Peter AL. Ramanthan K. Srinivasamoorthy 《Environmental Geology》2009,57(1):59-73
Chemical characterization of groundwater is essential to bring out its nature and utility. Samples from shallow and deep ground
water of the same location were collected and studied for their geochemical characteristics following standard procedures
(APHA 1998). Sediment samples from different depths were collected and analysed for minerals using FTIR and SEM. Resisitivity logging
was carried out in the bore well to understand the variations in depth to fresh water potential. The shallow ground water
is dominated by Na–Cl–HCO3–SO4 and deeper groundwater by Na–HCO3–SO4–Cl types. It is observed that there is a significant ionic variation with depth. The ionic strength of the deeper samples
is lesser than in the shallower samples. Wide pH variations in the shallow water samples are due to ion exchange process.
Thermodynamic stability plot was used to identify the state of stability. It is inferred that there is no major significant
difference in the thermodynamic state of stability in the shallow and the deeper aquifers as the aquifer matrix for the shallow
and deeper aquifers are almost similar. Saturation index of Gibbsite, Kaolinite, Calcite, Dolomite and anhydrite, were studied
for shallow and deep aquifers, to identify the difference in hydro chemical signatures. The Si/Al ratios of shallow samples
are less when compared with the deeper samples. Leaching of secondary salts was the chief mechanism controlling the ground
water chemistry of the region. 相似文献
7.
A. Lawrence D. Gooddy P. Kanatharana W. Meesilp V. Ramnarong 《Hydrogeology Journal》2000,8(5):564-575
Many cities and towns in South and Southeast Asia are unsewered, and urban wastewaters are often discharged either directly
to the ground or to surface-water canals and channels. This practice can result in widespread contamination of the shallow
groundwater. In Hat Yai, southern Thailand, seepage of urban wastewaters has produced substantial deterioration in the quality
of the shallow groundwater directly beneath the city. For this reason, the majority of the potable water supply is obtained
from groundwater in deeper semi-confined aquifers 30–50 m below the surface. However, downward leakage of shallow groundwater
from beneath the city is a significant component of recharge to the deeper aquifer, which has long-term implications for water
quality. Results from cored boreholes and shallow nested piezometers are presented. The combination of high organic content
of the urban recharge and the shallow depth to the water table has produced strongly reducing conditions in the upper layer
and the mobilisation of arsenic. A simple analytical model shows that time scales for downward leakage, from the surface through
the upper aquitard to the semi-confined aquifer, are of the order of several decades.
Electronic Publication 相似文献
8.
Delineation of saltwater intrusion into the freshwater aquifer of Lekki Peninsula,Lagos, Nigeria 总被引:2,自引:0,他引:2
A. A. Adepelumi B. D. Ako T. R. Ajayi O. Afolabi E. J. Omotoso 《Environmental Geology》2009,56(5):927-933
Recently, the deterioration of water quality in the coastal zones of Lekki Peninsula area of Lagos due to saltwater infiltration
into the freshwater aquifer has become a major concern. With the aim of providing valuable information on the hydrogeologic
system of the aquifers, the subsurface lithology and delineating the groundwater salinity, vertical electrical resistivity
(VES) sounding survey was carried out utilizing surface Schlumberger electrode arrays, and electrode spacing varying between
1 and 150 m. The DC resistivity surveys revealed significant variations in subsurface resistivity. Also, the VES resistivity
curves showed a dominant trend of decreasing resistivity with depth (thus increasing salinity). In general, the presence of
four distinct resistivity zones were delineated viz.: the unconsolidated dry sand (A) having resistivity values ranging between
125 and 1,028 Ωm represent the first layer; the fresh water-saturated soil (zone B) having resistivity values which correspond
to 32–256 Ωm is the second layer; the third layer (zone C) is interpreted as the mixing (transition) zone of fresh with brackish
groundwater. The resistivity of this layer ranges from 4 to 32 Ωm; while layer four (zone D) is characterized with resistivities
values generally below 4 Ωm reflecting an aquifer possibly containing brine. The rock matrix, salinity and water saturation
are the major factors controlling the resistivity of the formation. Moreover, this investigation shows that saline water intrusion
into the aquifers can be accurately mapped using surface DC resistivity method. 相似文献
9.
J. Jiménez-Martínez K. Tamoh L. Candela F. J. Elorza D. Hunkeler 《Mathematical Geosciences》2012,44(2):187-208
Tritium is a short-lived radioactive isotope (T
1/2=12.33 yr) produced naturally in the atmosphere by cosmic radiation but also released into the atmosphere and hydrosphere
by nuclear activities (nuclear power stations, radioactive waste disposal). Tritium of natural or anthropogenic origin may
end up in soils through tritiated rain, and may eventually appear in groundwater. Tritium in groundwater can be re-emitted
to the atmosphere through the vadose zone. The tritium concentration in soil varies sharply close to the ground surface and
is very sensitive to many interrelated factors like rainfall amount, evapotranspiration rate, rooting depth and water table
position, rendering the modeling a rather complex task. Among many existing codes, SOLVEG is a one-dimensional numerical model
to simulate multiphase transport through the unsaturated zone. Processes include tritium diffusion in both, gas and liquid
phase, advection and dispersion for tritium in liquid phase, radioactive decay and equilibrium partitioning between liquid
and gas phase. For its application with bare or vegetated (perennial vegetation or crops) soil surfaces and shallow or deep
groundwater levels (contaminated or non-contaminated aquifer) the model has been adapted in order to include ground cover,
root growth and root water uptake. The current work describes the approach and results of the modeling of a tracer test with
tritiated water (7.3×108 Bq m−3) in a cultivated soil with an underlying 14 m deep unsaturated zone (non-contaminated). According to the simulation results,
the soil’s natural attenuation process is governed by evapotranspiration and tritium re-emission. The latter process is due
to a tritium concentration gradient between soil air and an atmospheric boundary layer at the soil surface. Re-emission generally
occurs during night time, since at day time it is coupled with the evaporation process. Evapotranspiration and re-emission
removed considerable quantities of tritium and limited penetration of surface-applied tritiated water in the vadose zone to
no more than ∼1–2 m. After a period of 15 months tritium background concentration in soil was attained. 相似文献
10.
Geochemical and isotopic investigation of the aquifer system in the Djerid-Nefzaoua basin, southern Tunisia 总被引:2,自引:0,他引:2
In the Djerid-Nefzaoua region, southern Tunisia, about 80% of agricultural and domestic water supply is provided by the complex terminal (CT) aquifer. However, 20% of this demand is provided by other hydraulically connected aquifers, namely the continental intercalaire (CI) and the Plio-Quaternary (PQ). Overexploitation of the CT aquifer for agricultural practices has contributed to the loss of the artesian condition and the decline of groundwater level which largely increased the downward leakage from the shallow PQ aquifer. Excess irrigation water concentrates at different rates in the irrigation channels and in the PQ aquifer itself. Then, it returns to the CT aquifer and mixes with water from the regional flow system, which contributes to the salinization of the CT groundwater. A geochemical and isotopic study had been undertaken over a 2-years period in order to investigate the origin of waters pumped from the CT aquifer with an emphasis on its hydraulic relationships with the underlying and the overlying CI and PQ aquifers. Geochemistry indicates that groundwater samples collected from different wells show an evolution of the water types from Na-Cl to Ca-SO4-Cl. Dissolution of halite, gypsum and anhydrite-bearing rocks is the main mechanism that leads to the salinization of the groundwater. Isotopic data indicate the old origin of all groundwater in the aquifer system. Mixing and evaporation effects characterizing the CT and the PQ aquifers were identified using δ2H and δ18O relationship and confirmed by the conjunction of δ2H with chloride concentration. 相似文献
11.
Assessment and prediction of contaminant migration in ground water from chromite waste dump 总被引:3,自引:0,他引:3
Sukinda chromite valley is one of the largest chromite deposits of the country and produces nearly 8% of chromite ore. It
greatly contributes towards the economic development but at the same time deteriorates the natural environment. It is generally
excavated by opencast mining method. In the Sukinda mining area, around 7.6 million tons of solid waste have been generated
in the form of rejected minerals, overburden material/waste rock and sub-grade ore that may be resulting in environmental
degradation, mainly causing lowering in the water table vis-à-vis deterioration in surface and ground water quality. The study
conducted in and around one of the chromite mine of the valley reveals that the concentration of hexavalent chromium is found
in the water samples of ground and surface water, mine effluents and seepage water. Hexavalent Chromium (Cr+6) have been found varying between 0.02 mg/l and 0.12 mg/l in mine effluents and 0.03–0.8 mg/l in shallow hand pumps and 0.05
and 1.22 mg/l in quarry seepage. The concentration of Cr+6 in Damsal nalah, the main surface water source in the area, is found varying between 0.03 mg/l and 0.14 mg/l and a increasing
trend, which is in the downstream of mining activities, has been observed. Leachate study clearly shows that the soil lying
in the vicinity of mine waste dump shows highest concentration of Cr+6. Contaminant migration in ground water depends upon various geohydrological conditions of the area. The study shows that
aquifer resistivity varies between 15 Ωm to 150 Ωm and aquifer depth varies from 4 m to 26 m below ground level. The ground
water flow and mass transport models were constructed with the help of geo-hydrological and geophysical informations using
Visual Modflow software. Contaminant migration and path lines for 20 years have been predicted in two layers model of ground
water. The study provided an insight into the likely migration of contaminant in ground water due to leaching from overburden
dump of chromite ore and will be helpful in making strategic planning for limiting the contaminant migration in the ground
water regime in and around the mining areas. 相似文献
12.
Hydrogeological and hydrochemical framework of regional aquifer system in Kali-Ganga sub-basin, India 总被引:5,自引:0,他引:5
The central Ganga Basin is one of the major groundwater reservoirs in India. The Kali-Ganga sub-basin is a micro watershed
of the central Ganga Basin, containing a number of productive aquifers. A detailed hydrogeological investigation was carried
out, which reveals the occurrence of a single-tier aquifer system down to 163 m bgl (metres below ground level), but at places
it is interleaved with clay layers; thus imparting it a two-to three-tier aquifer system. These aquifers are unconfined to
confined in disposition. The transmissivity, storage coefficient and hydraulic conductivity are determined as 2178 m2/day, 1.12×10–5 and 120 m/day, respectively. The groundwater of the basin is fresh, of an alkali-bicarbonate type and is suitable for irrigation
and domestic use. However, in certain areas, extensive agricultural activities, and domestic and industrial effluents have
caused some deterioration of groundwater quality. This study contains data of where the concentration of Fe, Pb, Cd, Cr and
Ni are higher than the permissible limits, which may be hazardous to public health.
Received: 2 March 2000 · Accepted: 3 July 2000 相似文献
13.
D. V. Reddy P. Nagabhushanam M. R. Rao D. S. Mitra B. M. Tripati S. K. Sinha B. Bhadu 《Journal of the Geological Society of India》2011,77(3):239-242
The Oil and Natural Gas Corporation Limited (ONGC), India, embarked upon exploration and exploitation of deep groundwater
under the project named as “Saraswati” in arid Thar desert, Rajasthan, with a societal mission of providing water to the local
people and cattle. A 555 m deep well drilled by the ONGC near Jaisalmer town in 2006 encountered a potential aquifer at a
depth of 450–500 m. Radiocarbon dating of this well water indicated paleorecharge to be >40,000 yr BP (uncorrected) (Before
Present with respect to 1950 AD), while the medium depth (∼200 m) well waters around that area showed an age range of ∼9,000
to 17,000 yr BP (uncorrected). These waters represent pre-Saraswati era recharge, because the mighty Saraswati flowed in this
region between 7000–4000 yr BP. The stable isotope (δD and δ18O) and Total Dissolved Solids (TDS) data of these waters clearly indicated absence of communication between the two aquifers
(deep and medium depth). However, the extension of this deep aquifer needs to be determined. 相似文献
14.
The city of Scarborough lies on the eastern margin of the Greater Toronto Area of southern Ontario, Canada, along the northern
coastline of Lake Ontario. The City has a population of 500,000 and is presently one of the fastest growing communities in
Canada. The City is expanding northwards onto rural land on the south slope of the large Pleistocene glacial Oak Ridges Moraine
system. The moraine system is underlain by a thick (150 m) succession of tills, sands and gravels and is a regionally-significant
recharge area for three principle aquifer systems that discharge to numerous watercourses that flow to Lake Ontario. Protection
of deeper aquifers from surface-generated urban contaminants is a particular concern.
A groundwater flow model using Visual MODFLOW was developed for the 350-km2 Rouge River–Highland Creek (RRHC) drainage basin using an extensive GIS-based collection of subsurface geological, geophysical
and hydrogeological data, maps of land use and surficial geology. The RRHC model was calibrated against point water level
data, known potentiometric surfaces of the principal aquifers and baseflow measurements from streamflow gauging stations and
determined to be within acceptable limits. Water balance calculations indicate that 70% of the basin recharge (106,000 m3/day) enters the Upper Aquifer along the crest and immediate flanks of the Oak Ridges Moraine. To the south, Upper Aquifer
water moving through fractured till aquitards accounts for more than 75% of recharge to deeper aquifers. Water quality data
confirm previous observations that urban- and rural-sourced contaminants (chlorides and nitrates) present in Upper Aquifer
waters are moving rapidly into deeper aquifers. Some 83% of total RRHC recharge water is ultimately discharged as baseflow
to creeks draining to Lake Ontario; the remainder discharges to springs and along eroding lakeshore bluffs. Model results
demonstrate that deeper aquifers are poorly protected from urban contaminants and that long-term protection of ground and
surface water quality has to be a priority of municipal planners if the resource is not to be severely degraded.
Electronic Publication 相似文献
15.
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
16.
Historically, the arid conditions of La Rioja, Argentina have been the main controlling factor in its development. The shortage
of surface water, which is fully used, makes groundwater a potential source for development. The government encouraged investment
in early 1979, resulting in a 20-fold increase of groundwater extraction by 1998 (0.076–1.450 m3/s, respectively) to cover related needs of agriculture, industry and population growth. This extraction created unjustified
uncertainties derived from negative results obtained in hydrological balances. However, a 0.5 m lowering of the water-table
surface was experienced. A knowledge of groundwater functioning was required to establish a reliable frame of reference for
development and, at the same time, to find possible scenarios of feasible economic activities in harmony with accessible water
resources and aptitude of the environment. The flow regime was found to be composed of three main systems: a regional, an
intermediate and several local. The intermediate system provides water for the extraction boreholes, and discharges naturally
in Salina La Antigua. From the chemical perspective the intermediate system has three groundwater groups. Group I has an outstanding
fluoride concentration (1.98–3.10 mg/l) defined to the north of the City of la Rioja and the highest temperature (26.8–33.0°C),
the lowest lithium content (0.029–0.059 mg/l) and moderate arsenic (≤0.038 mg/l). Group II has the moderate arsenic content
(≤0.38 mg/l) detected to the south of the City of La Rioja and high lithium (0.024–0.085 mg/l), Group III has the lowest TDS
(456–931 mg/l) and arsenic (0.007–0.012 mg/l) and the highest lithium (0.067–0.141 mg/l). to A regional flow is represented
by Group IV with one order of magnitude higher strontium (4.870 mg/l), lead (0.021 mg/l) and uranium (0.362 mg/l) content
than the other groups. Results provide evidence to eliminate several well-established hydro-myths such as “the boreholes are
getting dry” and “boreholes are getting saline water”. The aquifer (granular Tertiary and Quaternary material) thickness (≈750m)
was defined with the aid of the geological framework, geothermometers and Modflow modelling. The aquifer extent extends far
beyond the limits of the study area. Several economic activities were found to be feasible with available groundwater resources
and without bordening the environment (fish farming, bottled-water marketing, SPA activities and farming of endangered species). 相似文献
17.
Contamination of the Paleozoic carbonate aquifer at Walkerton (Ontario, Canada) by pathogenic bacteria following heavy rain in May 2000 resulted in 2,300 illnesses and seven deaths. Subsequent tracer testing showed that there was rapid groundwater flow in the aquifer, and also rapid exchange between the aquifer and the ground surface. Electrical conductivity (EC) profiling during a 3-day pumping test showed that most flow was through bedding-plane fractures spaced about 10 m apart, that there were substantial contrasts in EC in the major fracture flows, and that there were rapid changes over time. Total coliform sampling revealed transient groundwater contamination, particularly after heavy rain and lasting up to a few days. These characteristics can be understood in terms of the dual-porosity nature of the aquifer. Most of the storage is in the matrix, but this can be considered to be static in the short term. Almost all transport is through the fracture network, which has rapid groundwater flow (~100 m/day) and rapid transmission of pressure pulses due to the high hydraulic diffusivity. Rapid recharge can occur through thin and/or fractured overburden and at spring sites where flow is reversed by pumping during episodes of surface flooding. These characteristics facilitated the ingress of surface-derived bacteria into the aquifer, and their rapid transport within the aquifer to pumping wells. Bacterial presence is common in carbonate aquifers, and this can be explained by the well-connected, large-aperture fracture networks in these dual-porosity aquifers, even though many, such as at Walkerton, lack karst landforms. 相似文献
18.
Hydrogeochemistry of the Koyna River basin,India 总被引:1,自引:1,他引:0
Pradeep Kumar Naik A. K. Awasthi A. V. S. S. Anand P. N. Behera 《Environmental Earth Sciences》2009,59(3):613-629
Hydrogeochemistry of the Koyna River basin, famous for the Koyna earthquake (magnitude 7) of 1967, has been studied. Basalt
is the primary aquifer; laterites, alluvium, and talus deposits form aquifers of secondary importance. Groundwater generally
occurs under water table conditions in shallow aquifers. Deeper aquifers are associated only with basalts. One hundred and
87 water samples were collected from various sources, such as dugwells, borewells, springs, and surface water, including 40
samples for analysis of iron. Only major constituents were analyzed. Analyses show that the concentrations of Ca2+ exceed that of Mg2+ in almost all water samples; the concentrations of Na+ are generally next to Ca2+ and are always higher than that of K+; and CO3
2– and SO4
2– are very low and are often negligible. Groundwater in borewells tapping deeper aquifers has higher mineralization compared
to that in dugwells representing shallow aquifers. Majority of the water samples are dominated by alkaline earths (Ca2+, Mg2+) and weak acids (HCO3
−, CO3
2–). Groundwater from shallow aquifers is generally calcium-bicarbonate type (53%) and calcium-magnesium-bicarbonate type (27%).
In case of deeper aquifer, it is mostly calcium-magnesium-bicarbonate type (29%), sodium-bicarbonate type (24%), calcium-bicarbonate
type (19%), calcium-magnesium-sodium-bicarbonate type (19%) and sodium-calcium-bicarbonate type (9%). Groundwater water is
generally fit for drinking and irrigation purposes, except in the lower reaches of the Koyna River basin, which is affected
by near water logging conditions. 相似文献
19.
Alternative water resources in granitic rock: a case study from Kinmen Island,Taiwan 总被引:1,自引:1,他引:0
Tai-Sheng Liou Yuan-Hsi Lee Li-Wei Chiang Wayne Lin Tai-Rong Guo Wen-Shan Chen Jeng-Ming Chien 《Environmental Earth Sciences》2010,59(5):1033-1046
Kinmen Island is a small, tectonically stable, granitic island that has been suffering from a scarcity of fresh water resources
due to excessive annual evapotranspiration over annual precipitation. Recent studies further indicate that shallow (0–70 m)
sedimentary aquifers, the major sources of groundwater supply, have already been over-exploited. Therefore, this preliminary
study is to investigate the existence of exploitable water resources that can balance the shortage of fresh water on this
island. Site characterization data are obtained from island-wide geophysical surveys as well as small-scale tests performed
in a study area formed by three deep (maximum depth to 560 m) vertical boreholes installed in mid-east Kinmen northeast to
Taiwu Mountain. Vertical fracture frequency data indicate that the rock body is fractured with a spatially correlated pattern,
from which three major fracture zones (depths 0–70, 330–360, and below 450 m) can be identified. Geologic investigations indicate
that the deepest fracture zone is caused by the large-scale, steeply dipping Taiwushan fault. This fault may have caused a
laterally extensive low-resistivity zone, a potential fractured aquifer, near Taiwu Mountain. The middle fracture zone is
induced by the Taiwushan fault and intersects the fault approximately 21 m southeast of the study area below a depth of 350 m.
Slug testing results yield fracture transmissivity varying from 4.8 × 10−7 to 2.2 × 10−4 m2/s. Cross-hole tests have confirmed that hydraulic connectivity of the deeper rock body is controlled by the Taiwushan fault
and the middle fracture zone. This connectivity may extend vertically to the sedimentary aquifers through high-angle joint
sets. Despite the presence of a flow barrier formed by doleritic dike at about 300 m depth, the existence of fresh as well
as meteoric water in the deeper rock body manifests that certain flow paths must exist through which the deeper fractured
aquifers can be connected to the upper rock body. Therefore, groundwater stored within the Taiwushan fault and the associated
low-resistivity zone can be considered as additional fresh water resources for future exploitation. 相似文献
20.
Evaluation of groundwater environment of Kathmandu Valley 总被引:1,自引:1,他引:0
Vishnu Prasad Pandey Saroj Kumar Chapagain Futaba Kazama 《Environmental Earth Sciences》2010,60(6):1329-1342
Kathmandu Valley aquifer in central Nepal is continuously under stress since the commencement of mechanized extraction of
groundwater resources in early 1970s. Many wells have been drilled in shallow and deep aquifers of the valley; and numerous
studies have been made in last four decades to understand the aquifers. However, up-to-date information on well inventory,
water extraction, water quality and overall situation of groundwater environment are not yet known in the absence of institutional
responsibility in groundwater management. This study attempts to evaluate current state of the groundwater environment considering
natural and social system together; to better understand origin of stresses, their state, expected impact and responses made/needed
to restore healthy groundwater environment. The analysis reveals increasing population density (3,150–4,680 persons/km2), urbanization (increase in urban population from 0.61 to 1.29 million) and increasing number of hotels due to tourism (23–62
hotels) during a decade are acting as driving forces to exceed groundwater extraction over recharge (extraction = 21.56 and
recharge = 9.6 million-cubic meter-a-year), decrease in groundwater levels (13–33 m during 1980–2000 and 1.38–7.5 m during
2000–2008), decline in well yield (4.97–36.17 l/s during mid-1980s to 1998) and deterioration in water quality. In the absence
of immediate management intervention with institutional responsibility for groundwater development, regulation and knowledgebase
management (i.e. to facilitate collection, integration and dissemination of knowledge); situation of groundwater environment
are expected to deteriorate further. Groundwater modeling approach may help to suggest appropriate management intervention
under current and expected future conditions. 相似文献