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1.
Radiocarbon dating of dissolved inorganic carbon in groundwater from confined parts of the Upper Floridan aquifer, Florida, USA 总被引:3,自引:1,他引:3
Geochemical reaction models were evaluated to improve radiocarbon dating of dissolved inorganic carbon (DIC) in groundwater
from confined parts of the Upper Floridan aquifer in central and northeastern Florida, USA. The predominant geochemical reactions
affecting the 14C activity of DIC include (1) dissolution of dolomite and anhydrite with calcite precipitation (dedolomitization), (2) sulfate
reduction accompanying microbial degradation of organic carbon, (3) recrystallization of calcite (isotopic exchange), and
(4) mixing of fresh water with as much as 7% saline water in some coastal areas. The calculated cumulative net mineral transfers
are negligibly small in upgradient parts of the aquifer and increase significantly in downgradient parts of the aquifer, reflecting,
at least in part, upward leakage from the Lower Floridan aquifer and circulation that contacted middle confining units in
the Floridan aquifer system. The adjusted radiocarbon ages are independent of flow path and represent travel times of water
from the recharge area to the sample point in the aquifer. Downgradient from Polk City (adjusted age 1.7 ka) and Keystone
Heights (adjusted age 0.4 ka), 14 of the 22 waters have adjusted 14C ages of 20–30 ka, indicating that most of the fresh-water resource in the Upper Floridan aquifer today was recharged during
the last glacial period. All of the paleowaters are enriched in 18O and 2H relative to modern infiltration, with maximum enrichment in δ18O of approximately 2.0‰.
Electronic Publication 相似文献
2.
Understanding the geologic controls of porosity development and their relationship to the karst aquifer system in the Cambrian
Maynardville Limestone is important in determining possible contaminant transport pathways and provides essential data for
hydrologic models within the Oak Ridge Reservation of east Tennessee. In the Maynardville Limestone, several important factors
control porosity development: (1) lithologic controls on secondary microporosity and mesoporosity are related to dissolution
of evaporite minerals and dedolomitization in supratidal facies; (2) depth below the ground surface controls the formation
of karst features because the most active portion of the groundwater system is at shallow depths, and karst features are rare
below ≈35 m; and (3) structural controls are related to solution enlargement of fractures and faults.
Received: 21 May 1996 · Accepted: 30 August 1996 相似文献
3.
A proposed new diagram for geochemical classification of natural waters and interpretation of chemical data 总被引:13,自引:1,他引:13
D. K. Chadha 《Hydrogeology Journal》1999,7(5):431-439
A new hydrochemical diagram is proposed for classification of natural waters and identification of hydrochemical processes.
The proposed diagram differs from the Piper and expanded Durov diagrams in that the two equilateral triangles are omitted,
and the shape of the main study field is different. In addition, the proposed diagram can be constructed on most spreadsheet
software packages. The proposed diagram is constructed by plotting the difference in milliequivalent percentage between alkaline
earths and alkali metals, expressed as percentage reacting values, on the X axis; and the difference in milliequivalent percentage
between weak acidic anions and strong acidic anions, also expressed as percentage reacting values, on the Y axis. The milliequivalent
percentage differences from the X and Y co-ordinates are extended further into the main study sub-fields of the proposed diagram,
which defines the overall character of water. Examples of hydrochemical analyses of groundwater are given from Karnataka,
India, for each of the three types of diagrams, illustrating the applicability of the proposed diagram in four case histories
having different hydrogeochemical aspects. A comparison indicates that the proposed new diagram satisfies the basic requirement
for a suitable classification of natural waters, and it also can be effectively used for studies of hydrochemical processes.
Received, April 1998 / Revised, February 1999 / Accepted, April 1999 相似文献
4.
Geomorphic aspects of groundwater flow 总被引:3,自引:0,他引:3
Robert G. LaFleur 《Hydrogeology Journal》1999,7(1):78-93
The many roles that groundwater plays in landscape evolution are becoming more widely appreciated. In this overview, three
major categories of groundwater processes and resulting landforms are considered: (1) Dissolution creates various karst geometries,
mainly in carbonate rocks, in response to conditions of recharge, geologic setting, lithology, and groundwater circulation.
Denudation and cave formation rates can be estimated from kinetic and hydraulic parameters. (2) Groundwater weathering generates
regoliths of residual alteration products at weathering fronts, and subsequent exhumation exposes corestones, flared slopes,
balanced rocks, domed inselbergs, and etchplains of regional importance. Groundwater relocation of dissolved salts creates
duricrusts of various compositions, which become landforms. (3) Soil and rock erosion by groundwater processes include piping,
seepage erosion, and sapping, important agents in slope retreat and headward gully migration. Thresholds and limits are important
in many chemical and mechanical groundwater actions. A quantitative, morphometric approach to groundwater landforms and processes
is exemplified by selected studies in carbonate and clastic terrains of ancient and recent origins.
Received, May 1998 · Revised, September 1998 · Accepted, October 1998 相似文献
5.
Jonathan Levy Gordon Chesters Daniel P. Gustafson Harry W. Read 《Hydrogeology Journal》1998,6(4):483-499
A field study from October 1989 through July 1992, conducted on a 4.1-km2 area in south-central Wisconsin, USA, examined the distributions of atrazine and its chlorinated metabolites in groundwater
and related those distributions to the groundwater flow system. MODFLOW and PATH3D were used to assess bedrock-aquifer susceptibility
to contamination. Estimated travel time from water table to bedrock surface ranges from <0.25 to >512 yr. Spatial distribution
of the estimates demonstrates that increased travel time to bedrock can result from the presence of shallow surface-water
bodies, greater depths to bedrock, and smaller hydraulic conductivities. Estimated travel times to local domestic wells are
inversely related to atrazine and desethylated atrazine concentrations observed in water from those wells.
The potential impact of long-term atrazine use on aquifer water quality was investigated using MT3D in two best-case scenarios.
Uncertainties associated with predicted atrazine concentrations at various depths and times were estimated. For shallow groundwater,
widespread violations of Wisconsin's current preventive action limit were predicted, but with large uncertainty stemming from
uncertain estimates of input parameter values. The simulations indicate, however, that moderate inputs at the water table
are very unlikely to produce violations of Wisconsin's standards deeper in the aquifer.
Received, October 1997 Revised, July 1998 Accepted, July 1998 相似文献
6.
John P. Hoffmann Donald R. Pool A. D. Konieczki Michael C. Carpenter 《Hydrogeology Journal》1998,6(3):349-364
Land subsidence in the form of sinks has occurred on and near farmlands near Tucson, Pima County, Arizona, USA. The sinks
occur in alluvial deposits along the flood plain of the Santa Cruz River, and have made farmlands dangerous and unsuitable
for farming. More than 1700 sinks are confined to the flood plain of the Santa Cruz River and are grouped along two north-northwestward-trending
bands that are approximately parallel to the river and other flood-plain drainages. An estimated 17,000 m3 of sediment have been removed in the formation of the sinks. Thirteen trenches were dug to depths of 4–6 m to characterize
near-surface sediments in sink and nonsink areas. Sediments below about 2 m included a large percentage of dispersive clays
in sink areas. Sediments in nonsink areas contain a large component of medium- to coarse-grained, moderately to well sorted
sand that probably fills a paleochannel. Electromagnetic surveys support the association of silts and clays in sink areas
that are highly electrically conductive relative to sand in nonsink areas. Sinks probably are caused by the near-surface process
of subsurface erosion of dispersive sediments along pre-existing cracks in predominantly silt and clay sediments. The pre-existing
cracks probably result from desiccation or tension that developed during periods of water-table decline and channel incision
during the past 100 years or in earlier periods.
Submitted, April 1997 · Revised, November 1997 · Accepted, April 1998 相似文献
7.
Groundwater in alluvial aquifers of the Wakatipu and Wanaka basins, Central Otago, New Zealand, has a composition expressed
in equivalent units of Ca2+≫Mg2+≅Na+>K+ for cations, and HCO3
–≫SO4
2->NO3
–≅Cl– for anions. Ca2+ and HCO3
– occur on a 1 : 1 equivalent basis and account for >80% of the ions in solution. However, some groundwater has increased proportions
of Na+ and SO4
2-, reflecting a different source for this water.
The rock material of the alluvial aquifers of both basins is derived from the erosion and weathering of metamorphic Otago
Schist (grey and green schists). Calcite is an accessory mineral in both the grey and green schists at <5% of the rock. Geological
mapping of both basins indicates that dissolution of calcite from the schist is the only likely mechanism for producing groundwater
with such a constant composition dominated by Ca2+ and HCO3
– on a 1 : 1 equivalent basis. Groundwater with higher proportions of Na+ and SO4
2- occurs near areas where the schist crops out at the surface, and this groundwater represents deeper and possibly older water
derived from basement fluids. Anomalously high K+ in the Wakatipu basin and high NO3
– concentrations in the Wanaka basin cannot be accounted for by interaction with basement lithologies, and these concentrations
probably represent the influence of anthropogenic sources on groundwater composition.
Received, June 1996 Revised, March 1997, July 1997 Accepted, July 1997 相似文献
8.
Aquifers in the arid alluvial basins of the southwestern U.S. are recharged predominantly by infiltration from streams and
playas within the basins and by water entering along the margins of the basins. The Tucson basin of southeastern Arizona is
such a basin. The Santa Catalina Mountains form the northern boundary of this basin and receive more than twice as much precipitation
(ca. 700 mm/year) as does the basin itself (ca. 300 mm/year). In this study environmental isotopes were employed to investigate
the migration of precipitation basinward through shallow joints and fractures. Water samples were obtained from springs and
runoff in the Santa Catalina Mountains and from wells in the foothills of the Santa Catalina Mountains. Stable isotopes (δD
and δ18O) and thermonuclear-bomb-produced tritium enabled qualitative characterization of flow paths and flow velocities. Stable-isotope
measurements show no direct altitude effect. Tritium values indicate that although a few springs and wells discharge pre-bomb
water, most springs discharge waters from the 1960s or later.
Received, February 1997 · Revised, September 1997 · Accepted, September 1997 相似文献
9.
Paul F. Hudak 《Hydrogeology Journal》1998,6(3):341-348
A method was devised for designing configurations of monitoring wells, consisting of vertically nested intakes in boreholes.
The network-design method involves analyzing a subset of potential contaminant plumes emerging from the downgradient margin
of a landfill. Plume widths are evaluated along selected equipotential lines and compared to the lengths of those lines. The
method was applied to a 32-ha solid-waste landfill in Tarrant County, Texas, USA. Sixtynine potential source nodes were considered.
A 15-borehole network devised by the method registered 93 detections in total, detecting all 69 model-generated plumes by
at least one borehole. Based on an enumeration procedure, a minimum of 10 boreholes was needed to detect all of the model-generated
plumes. However, the less conservative 10-borehole network had little capability for backup detection. An existing monitoring
network of seven downgradient wells detected only 38 model-generated plumes. Results of this study illustrate a practical
need for structured approaches to designing detection-based groundwater-monitoring configurations.
Received, February 1997 · Revised, July 1997, December 1997 · Accepted, November 1997 相似文献
10.
On Hatteras Island, North Carolina, USA, complex stratigraphy results from surficial sediments being superimposed on an inherited
Pleistocene platform. Numerical simulations used to simulate water-table profiles on the island illustrate the influence that
the complex stratigraphy has on water-table elevations. Field data consist of water-table profiles collected from a cross-island
transect of wells. These profiles show unusually high water-table elevations in the south-central portion of Hatteras Island.
Geophysical data are used to constrain the subsurface stratigraphy. Simple analytical solutions to the groundwater flow equation
using laterally varying recharge rates cannot match mean water-table profiles. More complex numerical simulations, which do
match the profiles, indicate that the elevated water levels result from a low-permeability unit that extends several kilometers
along the longitudinal axis of the island. Island geomorphology and ground-penetrating radar (GPR) data suggest that this
unit is a former interdunal wetland that has been buried by a series of parabolic dunes.
Received, September 1999 / Revised, March 2000 / Accepted, March 2000 相似文献
11.
Numerical analysis of the hydrogeologic controls in a layered coastal aquifer system, Oahu, Hawaii, USA 总被引:2,自引:1,他引:2
Delwyn S. Oki William R. Souza Edward L. Bolke Glenn R. Bauer 《Hydrogeology Journal》1998,6(2):243-263
The coastal aquifer system of southern Oahu, Hawaii, USA, consists of highly permeable volcanic aquifers overlain by weathered
volcanic rocks and interbedded marine and terrestrial sediments of both high and low permeability. The weathered volcanic
rocks and sediments are collectively known as caprock, because they impede the free discharge of groundwater from the underlying
volcanic aquifers. A cross-sectional groundwater flow and transport model was used to evaluate the hydrogeologic controls
on the regional flow system in southwestern Oahu. Controls considered were: (a) overall caprock hydraulic conductivity; and
(b) stratigraphic variations of hydraulic conductivity in the caprock. Within the caprock, variations in hydraulic conductivity,
caused by stratigraphy or discontinuities of the stratigraphic units, are a major control on the direction of groundwater
flow and the distribution of water levels and salinity. Results of cross-sectional modeling confirm the general groundwater
flow pattern that would be expected in a layered coastal system. Groundwater flow is: (a) predominantly upward in the low-permeability
sedimentary units; and (b) predominantly horizontal in the high-permeability sedimentary units.
Received, October 1996 Revised, August 1997 Accepted, September 1997 相似文献
12.
Hydrogeologic and hydrochemical framework of the shallow groundwater system in the southern Voltaian Sedimentary Basin, Ghana 总被引:4,自引:0,他引:4
The southern Voltaian Sedimentary Basin underlies an area of about 5000 km2 in east-central Ghana. Groundwater in the basin occurs in fractures in highly consolidated siliciclastic aquifers overlain
by a thin unsaturated zone. Aquifer parameters were evaluated from available aquifer-test data on 28 shallow wells in the
basin. Hydraulic-conductivity values range from 0.04–3.6 m/d and are about two orders of magnitude greater than the hydraulic
conductivity calculated using Darcy's Law and the average groundwater velocity estimated from carbon-14 dating. Linear-regression
analysis of the transmissivity and specific-capacity data allowed the establishment of an empirical relationship between log
transmissivity and log specific capacity for the underlying aquifers.
Groundwater chemistry in the basin is controlled by the weathering of albitic plagioclase feldspar. The weathering rates of
various minerals were estimated using 14C-derived average velocity in the basin. The weathering rate of albite was calculated to be 2.16 μmol L–1 yr–1 with the resulting formation of 3.3 μmol L–1 yr–1 of kaolinite and 0.047 μmol L–1 yr–1 of calcite. The low porosity and permeability of the aquifers in the basin are attributed to the precipitation of secondary
minerals on fracture surfaces and interlayer pore spaces.
Received, September 1997 Revised, July 1998, August 1998 Accepted, August 1998 相似文献
13.
Humboldt, Arago, and the temperature of groundwater 总被引:1,自引:0,他引:1
Stanley N. Davis 《Hydrogeology Journal》1999,7(5):501-503
14.
Hans G. Machel 《Hydrogeology Journal》1999,7(1):94-107
This article provides a critical synopsis of the effects of groundwater flow on mineral diagenesis. Emphasis is placed on
those aspects and processes that change porosity and permeability in carbonate aquifers, because they are of particular importance
to human societies as sources of supplies of water for human consumption (drinking, irrigation) and of crude oil and natural
gas.
Diagenetic settings in carbonates as well as clastics are generally ill defined. This paper proposes a new comprehensive classification
of diagenetic settings into near-surface, shallow-, intermediate-, and deep-burial diagenetic settings; hydrocarbon-contaminated
plumes; and fractures. These settings are defined on the basis of mineralogy, petroleum, hydrogeochemistry, and hydrogeology.
This classification is applicable to all sedimentary basins.
Diagenesis is governed by various intrinsic and extrinsic factors that include thermodynamic and kinetic constraints, as well
as microstructural factors that may override the others. These factors govern diagenetic processes, such as dissolution, compaction,
recrystallization, replacement, and sulfate–hydrocarbon redox-reactions. Processes such as cementation, dissolution, and dolomitization
require significant flow of groundwater driven by an externally imposed hydraulic gradient. Other processes, such as stylolitization
and thermochemical sulfate reduction, commonly take place without significant groundwater flow in hydrologically nearly or
completely stagnant systems that are geochemically "closed."
Two major effects of groundwater flow on mineral diagenesis are enhancement and reduction of porosity and permeability, although
groundwater flow can also leave these rock properties essentially unchanged. In extreme cases, an aquifer or hydrocarbon reservoir
rock can have highly enhanced porosity and permeability due to extensive mineral dissolution, or it can be plugged up due
to extensive mineral precipitation.
Received, April 1998 · Revised, July 1998 · Accepted, September 1998 相似文献
15.
Assessment of natural attenuation of aromatic hydrocarbons in groundwater near a former manufactured-gas plant, South Carolina, USA 总被引:1,自引:0,他引:1
J. E. Landmeyer F. H. Chapelle M. D. Petkewich P. M. Bradley 《Environmental Geology》1998,34(4):279-292
Shallow, anaerobic groundwater near a former manufactured-gas plant (MGP) in Charleston, South Carolina, USA, contains mono-
and polycyclic aromatic hydrocarbons (MAHs and PAHs, respectively). Between 1994 and 1997, a combination of field, laboratory,
and numerical-flow and transport-model investigations were made to assess natural attenuation processes affecting MAH and
PAH distributions. This assessment included determination of adsorption coefficients (K
ad
) and first-order biodegradation rate constants (K
bio
) using aquifer material from the MGP site and adjacent properties. Naphthalene adsorption (K
ad
=1.35×10–7 m3/mg) to aquifer sediments was higher than toluene adsorption (K
ad
=9.34×10–10 m3/mg), suggesting preferential toluene transport relative to naphthalene. However, toluene and benzene distributions measured
in January 1994 were smaller than the naphthalene distribution. This scenario can be explained, in part, by the differences
between biodegradation rates of the compounds. Aerobic first-order rate constants of 14C-toluene, 14C-benzene, and 14C-naphthalene degradation were similar (–0.84, –0.03, and 0.88 day–1, respectively), but anaerobic rate constants were higher for toluene and benzene (–0.002 and –0.00014 day–1, respectively) than for naphthalene (–0.000046 day–1). Both areal and cross-sectional numerical simulations were used to test the hypothesis suggested by these rate differences
that MAH compounds will be contained relative to PAHs. Predictive simulations indicated that the distributions of toluene
and benzene reach steady-state conditions before groundwater flow lines discharge to an adjacent surface-water body, but do
discharge low concentrations of naphthalene. Numerical predictions were "audited" by measuring concentrations of naphthalene,
toluene, and benzene at the site in early 1997. Measured naphthalene and toluene concentrations were substantially reduced
and the areal extent of contamination smaller than was both observed in January 1994 and predicted for 1997. Measured 1997
benzene concentrations and distribution were shown to be relatively unchanged from those measured in 1994, and similar to
predictions for 1997.
Received: 26 June 1997 · Accepted: 25 August 1997 相似文献
16.
The 1995 Water Consumer Protection Act of Tucson, Arizona, USA (hereafter known as the Act) was passed following complaints
from Tucson Water customers receiving treated Central Arizona Project (CAP) water. Consequences of the Act demonstrate the
uncertainties and difficulties that arise when the public is asked to vote on a highly technical issue. The recharge requirements
of the Act neglect hydrogeological uncertainties because of confusion between "infiltration" and "recharge." Thus, the Act
implies that infiltration in stream channels along the Central Wellfield will promote recharge in the Central Wellfield. In
fact, permeability differences between channel alluvium and underlying basin-fill deposits may lead to subjacent outflow.
Additionally, even if recharge of Colorado River water occurs in the Central Wellfield, groundwater will become gradually
salinized. The Act's restrictions on the use of CAP water affect the four regulatory mechanisms in Arizona's 1980 Groundwater
Code as they relate to the Tucson Active Management Area: (a) supply augmentation; (b) requirements for groundwater withdrawals
and permitting; (c) Management Plan requirements, particularly mandatory conservation and water-quality issues; and (d) the
requirement that all new subdivisions use renewable water supplies in lieu of groundwater. Political fallout includes disruption
of normal governmental activities because of the demands in implementing the Act.
Received, December 1996 · Revised, October 1997 · Accepted, October 1997 相似文献
17.
The Heretaunga Plains, Hawke's Bay, New Zealand, is underlain by Quaternary fluvial, estuarine-lagoonal, and marine deposits
infilling a subsiding syncline. Within the depositional sequence, river-channel gravels form one of the most important aquifer
systems in New Zealand. An interconnected unconfined–confined aquifer system contains groundwater recharged from the Ngaruroro
River bed at the inland margin of the plain, 20 km from the coast. At the coast, gravel aquifers extend to a depth of 250 m.
In 1994–95, 66 Mm3 of high quality groundwater was abstracted for city and rural water supply, agriculture, industry, and horticulture. Use
of groundwater, particularly for irrigation, has increased in the last 5 years. Concern as to the sustainability of the groundwater
resource led to a research programme (1991–96). This paper presents the results and recommends specific monitoring and research
work to refine the groundwater balance, and define and maintain the sustainable yield of the aquifer system. Three critical
management factors are identified. These are (1) to ensure maintenance of consistent, unimpeded groundwater recharge from
the Ngaruroro River; (2) to specifically monitor groundwater levels and quality at the margins of the aquifer system, where
transmissivity is <5000 m2/d and summer groundwater levels indicate that abstraction exceeds recharge; (3) to review groundwater-quality programs to
ensure that areas where contamination vulnerability is identified as being highest are covered by regular monitoring.
Received, January 1998 / Revised, August 1998, March 1999 / Accepted, April 1999 相似文献
18.
The aquifer system of the Upper Triassic Keuper Sandstone, an important source of drinking water in northern Bavaria, is
affected by elevated arsenic concentrations. Within the study area of 8000 km2, no evidence exists for any artificial source of arsenic. Data from about 500 deep water wells show that in approximately
160 wells arsenic concentrations are 10–150 μg/L. The regional distribution of arsenic in the groundwater shows that elevated
arsenic concentrations are probably related to specific lithofacies of the aquifers that contain more sediments of terrestrial
origin. Geochemical measurements on samples from four selected well cores show that arsenic has accumulated in the rocks.
This indigenous arsenic is the source of arsenic in the groundwater of certain facies of the middle unit of the Keuper Sandstone.
Received, June 1998 / Revised, January 1999, May 1999 / Accepted, June 1999 相似文献
19.
Land-use changes on the Sheyenne Delta in southeastern North Dakota, USA, have prompted research on impacts to the unconfined
Sheyenne Delta aquifer (SDA). This study examines effects of the saline discharge of a flowing artesian well that taps the
Dakota aquifer (DAK) on SDA groundwater chemistry and soil salinity. Objectives were to map the saline plume in the SDA using
induction techniques, to assess chloride migration in the SDA, and to evaluate induction sensitivity to moderately saline
sands. Induction data, collected in a 2.9-ha grid, were compared to 31 soil profiles analyzed for gravimetric moisture, electrical
conductivity, and chloride. Soil salinization is widespread, but only 7% of the area meets the 4-dS/m threshold for saline
soils. SDA chloride distribution was determined on transects oriented with and perpendicular to the flow path determined from
induction readings. Chloride was detected in the aquifer 550 m from the source, indicating a transport rate of 21 m/yr. Complex
recharge and discharge patterns and hummocky relief contribute to a wide chloride plume at this site. A mass balance based
on soil-water content and chloride concentration shows that only 4% of the chloride from the DAK well remains in the grid
volume.
Received, January 1998 · Revised, January 1999 · Accepted, March 1999 相似文献
20.
Conceptual model of the evolution of groundwater quality at the wet zone in Sri Lanka 总被引:1,自引:1,他引:1
The evolution of groundwater quality at a wet zone in Sri Lanka was made clear using field investigation, chemical and isotopic
analyses methods. In the wet zone, the concentrations of major ions and electrical conductivity (EC) in the groundwater are
low with small seasonal change. Except for sodium, silica and chloride, the EC and other major ion concentrations increase
along the groundwater flow direction. The contributions of bicarbonate and calcium ions to the increase in EC are the largest
among the major ions. The groundwater quality shows calcium-bicarbonate type, the initial stage of the Chebotarev series.
There is a seasonal change in isotopic composition. The isotopically lighter groundwater was found at the valley bottom in
the rainy season. Under the very heavy precipitation conditions, the slope of the regression line between δD and δ18O and deuterium excess for groundwater are close to 8 and 10, respectively. In other cases, the slopes of the regression lines
and deuterium excess are, less than 8 and 10, respectively.
Received: 5 August 1998 · Accepted: 19 October 1998 相似文献