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1.
The purpose of this study was to trace the groundwater flow system in the Nagaoka area using subsurface temperature distribution, stable isotopes and water quality. Temperature-depth profiles were measured four times in observation wells during the period 2000–2002. Water was sampled from both observation and pumping wells during the same period. A combination of tracers was used to conceptualize the groundwater flow system. The flow system appears to be divided into shallow, intermediate and deep systems. It is clear that land use, pumping and the infiltration rate are affecting the shallow flow system.An erratum to this article can be found at 相似文献
2.
In porous sediments of the Ishikari Lowland, there is a gradual increase in the background geothermal gradient from the Ishikari
River (3–4 °C 100 m–1) to the southwest highland area (10 °C 100 m–1). However, the geothermal gradient at shallow depths differs in detail from the background distribution. In spite of convective
heat-flow loss generally associated with groundwater flow, heat flow remains high (100 mW m–2) in the recharge area in the southwestern part of the Ishikari basin, which is part of an active geothermal field. In the
northeastern part of the lowland, heat flow locally reaches 140 mW m–2, probably due to upward water flow from the deep geothermal field. Between the two areas the heat flow is much lower. To
examine the role of hydraulic flow in the distortion of the isotherms in this area, thermal gradient vs. temperature analyses
were made, and they helped to define the major components of the groundwater-flow system of the region. Two-dimensional simulation
modeling aided in understanding not only the cause of horizontal heat-flow variations in this field but also the contrast
between thermal properties of shallow and deep groundwater reservoirs.
Electronic Publication 相似文献
3.
Groundwater-flow modeling in the Yucatan karstic aquifer, Mexico 总被引:1,自引:0,他引:1
Roger González-Herrera Ismael Sánchez-y-Pinto José Gamboa-Vargas 《Hydrogeology Journal》2002,10(5):539-552
The current conceptual model of the unconfined karstic aquifer in the Yucatan Peninsula, Mexico, is that a fresh-water lens
floats above denser saline water that penetrates more than 40 km inland. The transmissivity of the aquifer is very high so
the hydraulic gradient is very low, ranging from 7–10 mm/km through most of the northern part of the peninsula. The computer
modeling program AQUIFER was used to investigate the regional groundwater flow in the aquifer. The karstified zone was modeled
using the assumption that it acts hydraulically similar to a granular, porous medium. As part of the calibration, the following
hypotheses were tested: (1) karstic features play an important role in the groundwater-flow system; (2) a ring or belt of
sinkholes in the area is a manifestation of a zone of high transmissivity that facilitates the channeling of groundwater toward
the Gulf of Mexico; and (3) the geologic features in the southern part of Yucatan influence the groundwater-flow system. The
model shows that the Sierrita de Ticul fault, in the southwestern part of the study area, acts as a flow barrier and head
values decline toward the northeast. The modeling also shows that the regional flow-system dynamics have not been altered
despite the large number of pumping wells because the volume of water pumped is small compared with the volume of recharge,
and the well-developed karst system of the region has a very high hydraulic conductivity.
Electronic Publication 相似文献
4.
Vuthy Monyrath Yasuo Sakura Akinobu Miyakoshi Takeshi Hayashi 《Environmental Earth Sciences》2010,60(5):923-932
Previous studies and borehole temperature measurements suggest that subsurface temperature distribution on the west side of
Tokyo Bay (from Tokyo to Yokohama) is higher than that of the east side (Chiba side). To understand the groundwater flow and
other factors which may contribute to the subsurface temperature discrepancy such as geological setting in the study area,
groundwater temperature profiles were measured in 119 boreholes around the Tokyo Bay from 2002 to 2007. The data were analyzed
and compared with previous studies. Horizontal distribution of subsurface temperature at the depths of −50 and −100 m was
made to show the distribution of thermal regime. A cross-section across the bay of Tokyo was made to see the isothermal lines
and distribution of hydraulic heads in a vertical perspective. These results show that the highest subsurface temperature
zone is in the Tokyo area, along the river valley. Subsurface temperature at the depth of 50- and 100-m below sea level in
the western part of the bay is comparatively higher than its eastern side at the same elevation and distance from the bay.
This fact suggests that there is a regional groundwater flow system in the area and it is strongly affected by the geological
structure, particularly buried valley systems of the bay during the Paleo-Tokyo River and the topographical driving force
which is the result of the different elevation of recharge areas. Groundwater discharge is concentrated along the buried valley of Paleo-Tokyo River. 相似文献
5.
Temporal monitoring of the pesticide 1,2-dibromo-3-chloropropane (DBCP) and nitrate and indicators of mean groundwater age were used to evaluate the transport and fate of agricultural chemicals in groundwater and to predict the long-term effects in the regional aquifer system in the eastern San Joaquin Valley, California. Twenty monitoring wells were installed on a transect along an approximate groundwater flow path. Concentrations of DBCP and nitrate in the wells were compared to concentrations in regional areal monitoring networks. DBCP persists at concentrations above the US Environmental Protection Agency’s maximum contaminant level (MCL) at depths of nearly 40 m below the water table, more than 25 years after it was banned. Nitrate concentrations above the MCL reached depths of more than 20 m below the water table. Because of the intensive pumping and irrigation recharge, vertical flow paths are dominant. High concentrations (above MCLs) in the shallow part of the regional aquifer system will likely move deeper in the system, affecting both domestic and public-supply wells. The large fraction of old water (unaffected by agricultural chemicals) in deep monitoring wells suggests that it could take decades for concentrations to reach MCLs in deep, long-screened public-supply wells, however. 相似文献
6.
A three dimensional steady-state finite difference groundwater flow model is used to quantify the groundwater fluxes and analyze
the subsurface hydrodynamics in the Akaki catchment by giving particular emphasis to the well field that supplies water to
the city of Addis Ababa. The area is characterized by Tertiary volcanics covered with thick residual and alluvial soils. The
model is calibrated using head observations from 131 wells. The simulation is made in a two layer unconfined aquifer with
spatially variable recharge and hydraulic conductivities under well-defined boundary conditions. The calibrated model is used
to forecast groundwater flow pattern, the interaction of groundwater and surface water, and the effect of pumping on the well
field under different scenarios. The result indicates that the groundwater flows regionally to the south converging to the
major well field. Reservoirs and rivers play an important role in recharging the aquifer. Simulations made under different
pumping rate indicate that an increase in pumping rate results in substantial regional groundwater level decline, which will
lead to the drying of springs and shallow hand dug wells. Also, it has implications of reversal of flow from contaminated
rivers into productive aquifers close to main river courses. The scenario analysis shows that the groundwater potential is
not enough to sustain the ever-growing water demand of the city of Addis Ababa. The sensitivity and scenario analysis provided
important information on the data gaps and the specific sites to be selected for monitoring, and may be of great help for
transient model development. This study has laid the foundation for developing detailed predictive groundwater model, which
can be readily used for groundwater management practices. 相似文献
7.
Volatile organic compound (VOC) contamination of subsurface geological material and groundwater was discovered on the Nortel
Monkstown industrial site, Belfast, Northern Ireland. The objectives of this study were to (1) investigate the characteristics
of the geological material and its influences on contaminated groundwater flow across the site using borehole logs and hydrological
evaluations, and (2) identify the contaminants and examine their distribution in the subsurface geological material and groundwater
using chemical analysis. This report focuses on the eastern car park (ECP) which was a former storage area associated with
trichloroethene (TCE) degreasing operations. This is where the greatest amount of volatile organic compounds (VOCs), particularly
TCE, were detected. The study site is on a complex deposit of clayey glacial till with discontinuous coarser grained lenses,
mainly silts, sands and gravel, which occur at 0.45–7.82 m below ground level (bgl). The lenses overall form an elongated
formation that acts as a small unconfined shallow aquifer. There is a continuous low permeable stiff clayey till layer beneath
the lenses that performs as an aquitard to the groundwater. Highest concentrations of VOCs, mainly TCE, in the geological
material and groundwater are in these coarser lenses at ∼4.5–7 m bgl. Highest TCE measurements at 390,000 μg L−1 for groundwater and at 39,000 μg kg−1 at 5.7 m for geological material were in borehole GA19 in the coarse lens zone. It is assumed that TCE gained entrance to
the subsurface near this borehole where the clayey till was thin to absent above coarse lenses which provided little retardation
to the vertical migration of this dense non-aqueous phase liquid (DNAPL) into the groundwater. However, TCE is present in
low concentrations in the geological material overlying the coarse lens zone. Additionally, VOCs appear to be associated with
poorly drained layers and in peat <3.0 m bgl in the ECP. Some indication of natural attenuation as VOCs degradation products
vinyl chloride (VC) and dichloromethane (DCM) also occur on the site. 相似文献
8.
Oscar Escolero Luis E. Marin Eloisa Domínguez-Mariani Sandra Torres-Onofre 《Environmental Geology》2007,51(5):719-723
A hydraulic analysis of the interface between freshwater–saltwater behavior was done in the Merida Yucatan zone, two machines
that constantly register the groundwater levels were installed, and three electric conductivity logs were taken from wells.
When comparing the measured results with the ones obtained using theoretical equations developed to calculate the freshwater–saltwater
interface position, it was proved that in some cases these equations can be applied, and in others not. Two effects that rule
the behavior of karst aquifers in extraordinary conditions were found. 相似文献
9.
Radon in groundwater as a tracer to assess flow velocities: two test cases from Israel 总被引:1,自引:1,他引:1
U. Kafri 《Environmental Geology》2001,40(3):392-398
Two test cases from Israel are presented herein employing the decay rate of radon along the flow path to assess groundwater
flow velocities. Groundwater flow reaching the fault zone emerges in several places along the rift fault zone as thermal springs
because of deep water confinement. The high water temperature of the surface is indicative of high vertical flow velocities,
which maintains the original high temperatures. Knowing the Rn content at a source point and at a given down-gradient, and
assuming no Rn addition from the water itself or along the flow path, one can calculate the flow velocity based on the Rn
half-life time. The decay of Rn in western Galilee was found to be ∼570–150 pCi/l, and in the Dead Sea area from 5000–2000 pCi/l
along a respective flow path of 1000 and 200 m, Based on the above, the calculated flow velocities were compared with those
obtained from pumping tests in the study area. The method is applicable, because of the short Rn half-life, to cases of high
Rn contents, short distances and high flow velocities.
Received: 18 January 2000 · Accepted: 21 March 2000 相似文献
10.
Water samples were collected from the Yellow River and from wells for chemical and isotopic measurement in the counties of
Yucheng and Qihe, to which 6–9×108 m3 of water is diverted annually from the Yellow River. A zone of high electrical conductivity (EC) in groundwater corresponds
well on the regional scale with a ridge in groundwater level, which is the main flow path through the region, but has a low
gradient. The zone of highest EC along this ridge occurs at a position with the lowest ground altitude in the study area.
The unique characteristic of the groundwater is the linear relationship among the principal anions as the result of mixing.
The mixing effect is confirmed by its isotopic signature, which was then used to calculate the contributions from three sources:
rainfall, old water, and diverted water with an average mixing rate of 18, 17, and 65%, respectively. As an indicator of water
movement, Cl– content varies across a wide range in the profile from 30–10 m with a maximum concentration at about 1.2 m depth. Concentrations
are relatively stable at about 2 m, which is the average boundary of the saturated and unsaturated zone. The water from the
Yellow River has proved to be dominant in mixing in the aquifer in terms of groundwater flow and geochemistry.
Electronic Publication 相似文献
11.
Hydrogeological and mixing process of waters in aquifers in arid regions: a case study in San Luis Potosi Valley,Mexico 总被引:1,自引:0,他引:1
J. A. Ramos-Leal V. J. Martínez-Ruiz J. R. Rangel-Mendez M. C. Alfaro de la Torre 《Environmental Geology》2007,53(2):325-337
The climatic conditions of arid regions are characterized by high temperatures, low precipitation and high evapotranspiration
rates that can explain the reduced recharge of aquifers. Thus, in these regions, there are some problems related to the groundwater
quality and recharge that makes worse the problem of groundwater supply. A model, taking into account ternary mixtures, is
presented and applied to a case study: the aquifer of San Luis Potosi valley located in the highlands of the central part
of Mexico. In this valley, four hydrochemical facies were identified that correspond to the Ca–Na + K–HCO3, Na + K–Ca–HCO3, Ca–HCO3 and Ca–SO4 types. From this characterization, it was found out that the recharge area (known as Bledos Graben) is located at the SE
of the valley; the deep water flow comes from there (Villa de Reyes and Alvarez Range) to the center of the valley. Mixture
fractions were obtained by using chlorides and fluorides as conservative elements, from which it was possible to quantify
the contribution of each member to the groundwater quality. According to these results, the contributions to the water extracted
from this aquifer are as follows: shallow flows 50%, deep flows from Villa de Reyes 27%, and flows coming from the Alvarez
Ranges about 15%. 相似文献
12.
Long-term groundwater monitoring has been carried in the model locality of the landslide area at Třebenice, situated in the
northern part of the Czech Republic in Cretaceous claystones to marlstones. Primarily, long-term fluctuation of the groundwater
and piezometric levels has been monitored. Monitoring of groundwater flow was carried out in selected wells also by the photometry
logging method using a dilution technique of a marked liquid. On the basis of these results, the pattern of the groundwater
flow through the landslide area was determined in lithologically homogeneous Cretaceous claystones to marlstones. Interpretation
of monitoring results indicated that water flows preferentially through the zone of near-surface loosening of the claystone
rock massif, in general parallel to the slope inclination between 8 and 10-m depth below ground level. This zone exhibits
a higher permeability given by 1–2 orders of hydraulic conductivity compared with overlying strata and underlying rock in
which this zone is closed. This verified pattern of groundwater flow has a significant effect on the stability of the sliding
slope and it is one of the main factors affecting the evolution of landslides on the slopes formed by these rocks. 相似文献
13.
An artificial water canal opening is planned between the Agean Sea and the historical Ephesus site for the sake of tourism in the Selçuk sub-basin. In order to predict the effects of the planned canal on freshwater–seawater interface and related contamination in the aquifer, 3-D numerical density dependent flow and solute transport simulations were carried out. The simulations included the pre-pumping and pumping periods without a canal and the prediction period in the presence of the canal. Chloride concentration comparisons of the results obtained from the pre-pumping period and the pumping period indicate that the freshwater-seawater interface in the aquifer has progressed inland due to artificial discharge in the sub-basin. Drawdown during the pumping period is about 15 cm. The planned canal opening could further lower the groundwater levels in the area and would change the groundwater flow directions in the first 4 years. Then the levels and flow directions will nearly recover. However, the canal opening could cause further seawater intrusion into the aquifer to the extent that groundwater would be unfit to use for irrigation after the seventh year of the canal opening in the irrigation cooperative II wells area and would be unfit to use for drinking purposes after the tenth year in the municipality wells area located at the south of the cooperative II wells. On the other hand, the cooperative I wells would not be effected by the opening of the canal. 相似文献
14.
Evaluation of groundwater quality in coastal areas: implications for sustainable agriculture 总被引:4,自引:1,他引:4
Seawater intrusion is a problem in the coastal areas of Korea. Most productive agricultural fields are in the western and
southern coastal areas of the country where irrigation predominantly relies on groundwater. Seawater intrusion has affected
agricultural productivity. To evaluate progressive encroachment of saline water, the Korean government established a seawater
intrusion monitoring well network, especially in the western and southern part of the peninsula. Automatic water levels and
EC monitoring and periodic chemical analysis of groundwater help track salinization. Salinization of fresh groundwater is
highly associated with groundwater withdrawal. A large proportion of the groundwaters are classified as Na–Cl and Ca–Cl types.
The Na–Cl types represent effects of seawater intrusion. The highest EC level was over 1.6 km inland and high Cl values were
observed up to 1.2 km inland. Lower ratios of Na/Cl and SO4/Cl than seawater values indicate the seawater encroachment. A linear relation between Na and Cl represents simple mixing
of the fresh groundwater with the seawater. The saline Na–Cl typed groundwaters showed Br/Cl ratios similar to or less than
seawater values. The Ca–HCO3 type groundwaters had the highest Br/Cl ratios. Substantial proportions of the groundwaters showed potential for salinity
and should be better managed for sustainable agriculture. 相似文献
15.
In the rural Guatemalan Central Highlands, drinking water wells are a rare commodity due to lack of data regarding depth and sustainability of groundwater. At a study well in Lemoa, aquifer sustainability and other characteristics were estimated using hydrograph data and Theiss recovery method for pumping tests. These tests showed that while specific capacity remained fairly constant, transmissivity increased, indicating development of the well subsequent to installation of the study well. The time domain electromagnetic (TDEM) method was evaluated at the site as a prospective groundwater prospecting technique. Characterization of subsurface conditions using TDEM is feasible with local subsurface data for correlation; however, it is limited to delineating low electrical resistive zones without geologic data for correlation. Data showed that groundwater produced from volcanic alluvium at approximately 79 m in depth is sustainable at the study area at current use rates. 相似文献
16.
Erik Espinosa María Aurora Armienta Olivia Cruz Alejandra Aguayo Nora Ceniceros 《Environmental Geology》2009,58(7):1467-1477
High arsenic (As) groundwater is widely distributed in northwestern Hetao Plain, an arid region with sluggish groundwater
flow. Observed As concentration in groundwater from wells ranges from 76 to 1,093 μg/l. Most water samples have high total
dissolved solids, with Cl and HCO3 as the dominant anions and Na as the dominant cation. The major hydrochemical types of most saline groundwaters are Na–Mg–Cl–HCO3 and Na–Mg–Cl. By contrast, fresh groundwaters generally belong to the Na–Mg–HCO3 type. High concentrations of arsenic in shallow aquifers are associated with strongly reducing conditions, as evidenced by
high concentrations of dissolved organic carbon, ammonium, as well as dissolved sulfide and Fe, dominance of arsenite, relatively
low concentrations of nitrate and sulfate, and occasionally high content of dissolved methane (CH4). High As groundwaters from different places at Hetao Plain experienced different redox processes. Fluoride is also present
in high As groundwater, ranging between 0.40 and 3.36 mg/l. Although fluorosis poses an additional health problem in the region,
it does not correlate well with As in spatial distribution. Geochemical analysis indicates that evapotranspiration is an important
process controlling the enrichment of Na and Cl, as well as trace elements such as As, B, and Br in groundwater.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
17.
S. J. Appleyard 《Environmental Geology》1996,28(2):106-110
Drilling of 15 boreholes at a disused liquid waste disposal site near Perth, Western Australia, has indicated that a contamination
plume extends about 1000 m in a southerly direction from the site in the direction of groundwater flow. The plume is up to
600 m wide and 5–40 m thick. Chemical and microbiological analyses have indicated that contaminated groundwater contains high
concentrations of ammonia, iron, and bacteria at levels that commonly exceed national drinking water guidelines. It is likely
that a proposed water supply production well in the path of the contamination plume will have to be abandoned, and additional
wells may have to be abandoned if the plume continues to extend in the direction of groundwater flow. There is currently insufficient
information to indicate whether the plume is continuing to expand, but studies on similar plumes in the Perth metropolitan
area have indicated that contaminated groundwater can move at rates up to 100 m yr–1. Several other liquid waste disposal sites are now located in residential areas of Perth where wells are used for garden
irrigation. Further work is required to ensure that there is no potential impact of groundwater contamination on public health
in these areas.
Received: 31 July 1995 · Accepted: 18 September 1995 相似文献
18.
Azraq Oasis in the eastern Jordanian desert is an important freshwater resource of the country. Shallow groundwater reserves are heavily exploited since the 1980s and in consequence the groundwater table dropped significantly. Furthermore, some wells of the major well field drilled into the shallow aquifer show an increasing mineralization over the past 20 years. A previous study using conventional tracers did not result in a satisfactory explanation, from where the salt originates and why only a few wells are affected. In this study, the application of dissolved noble gases in combination with other tracer methods reveals a complex mixing pattern leading to the very localized salinization within the well field. It is found that primarily the wells affected by salinization 1) contain distinctly more radiogenic 4He than the other wells, indicating higher groundwater age, and 2) exhibit 3He/4He ratios that argue for an imprint of deep fluids from the Earth's mantle.However, the saline middle aquifer below is virtually free of mantle helium, which infers an upstream from an even deeper source through a nearby conductive fault. The local restriction of the salinization process is explained by the wide range of permeabilities of the involved geologic units. As the wells abstract water from the whole depth profile, they initially pump water mainly from the well conductive top rock layer. As the groundwater table dropped, this layer fell progressively dry and, depending on the local conductivity profile, some wells began to incorporate more water from the deeper part of the shallow aquifer into the discharge. These are the wells affected by salinization, because according to the presented scheme the deep part of the shallow aquifer is enriched in both salt and mantle fluids. 相似文献
19.
Analyses of 126 samples collected from 18 dug wells in the shallow basaltic aquifer over a period of 7 months have revealed
spatial as well as temporal changes in the chemical properties of groundwater. While the temporal changes have been attributed
to dilution and concentration phenomena governed by climatic factors, the spatial variations in the geochemical characteristics
of groundwater appeared to be related to pollution due to effluents from the Mula Sugar Factory. The cause of groundwater
pollution is the effluent carried by a stream flowing through the area. Fluctuations in the groundwater table, influent water
quality character of the stream, less capacity to accommodate large volume of effluent and occurrence of zero base flow (under
natural conditions) in the stream are the factors favoring infiltration of constituents of waste water into the underlying
weathered basaltic aquifer. Pollutants have entered into the shallow aquifer by downward percolation through the zone of aeration
to form a recharge mound at the water table and, further, lateral movement below the water table. The plume of polluted groundwater
has a lateral extent of a few meters in the upstream area and more than 400 m on either side of the stream in the downstream
part. The zone of polluted groundwater has an areal extent of more than 3.5 km2. Groundwater is the only source available for drinking and agricultural purposes. It is recommended that the base of the
lagoons and the stream used for release of plant effluent should be waterproofed for the protection of groundwater in the
Sonai area.
Received: 30 April 1997 · Accepted: 23 September 1997 相似文献
20.
Jichun Wu Xiaoqing Shi Yuqun Xue Yun Zhang Zixin Wei Jun Yu 《Environmental Geology》2008,55(8):1725-1735
Land subsidence in China occurs predominantly in 17 provinces (cities) situated in the eastern and middle regions of the country,
including Shanghai, Tianjin and Jiangsu, and Hebei provinces. It is primarily caused by groundwater overpumping. One of the
areas most severely affected by land subsidence is the Yangtze Delta, most of which consists of Shanghai City, the Su-Xi-Chang
area (Suzhou, Wuxi and Changzhou cities) of Jiangsu Province, and the Hang-Jia-Hu area (Hangzhou, Jiaxing and Huzhou cities)
of Zhejiang Province. The excessive exploitation of groundwater forms in a large regional cone of depression and, consequently,
land subsidence is also regional, currently centered in the Shanghai and Su-Xi-Chang areas. In 2002, the maximum cumulative
subsidence of Shanghai, Su-Xi-Chang and Hang-Jia-Hu were 2.63 m, 2.00 and 1.06 m, respectively. The land subsidence area is
continuing to expand throughout the Yangtze Delta. To study the characteristics and the pattern of this land subsidence, the
government has implemented a monitoring system involving the placement of 37 groups of extensometers (layers marks) and drilling
of more than 1000 observation wells. These provide an invaluable historical record of deformation and pore water pressure
and facilitate studies on the special features of soil deformation when the groundwater level changes due to pumping. Several
measures have been taken in recent years to control the development of the land subsidence in the different areas; these include
groundwater injection, prohibition of pumping deep confined groundwater, and an adjustment of the pumping depth and magnitude
of the groundwater withdrawn. At present, although the subsidence area is still increasing slowly, the subsidence rate is
controlled. 相似文献