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1.
Orientation surveys were conducted over five deposits to test the potential of determining helium in overburden gas as a pathfinder for uranium mineralization and other deposits containing uranium or thorium. Samples were collected via fixed tubes emplaced at depths of 6 m in backfilled holes drilled for this purpose. Compared to the atmospheric background value of 5.24 ppm v/v He, a variable weak anomaly (maximum 5.45–5.65 ppm He) was found over part of the Angela uranium deposit, N.T., in an arid area where mineralization is mostly at a depth of 60–90 m, at or below the water-table. Helium contents were mostly at background levels over a uranium deposit in the Officer Basin, W.A., where mineralization is at the water-table at 30–35 m, although radon gave a marked anomaly. Neither helium nor radon indicated the Manyingee deposit, W.A., which has uranium mineralization in a confined aquifer at 60–110 m. Similarly, no helium anomalies were found over the uranium- and thorium-rich Mt. Weld carbonatite or mineral sands at Eneabba.There appeared to be no correlation between helium distributions shown by groundwater and overburden-gas sampling at Manyingee or Mt. Weld. At Mt. Weld, groundwaters contained 0.06 to 13.60 μ/l He and overburden gases 5.24–5.47 ppm He, with the higher gas concentrations over country rock, where waters had background helium contents. It is presumed that equilibration between overburden gas and the atmosphere is far more rapid than that between overburden gas and groundwater, so that any helium released from the water is quickly dispersed.Overburden-gas helium concentrations were found to vary according to overburden type, being 5.24–5.32 ppm where sandy and porous and 5.30–5.50 ppm where clay-rich and less permeable. These background variations, which are greater than the total background-anomaly contrasts reported in the literature for shallow soil gases, have not been accounted for in most trial surveys, nor has the possibility of similar variations being due to analytical error. From the data obtained, there is little evidence that helium can be considered an effective pathfinder for blind or concealed deposits using soil gas or overburden gas as sample media. Previous work on the use of soil and soil-gas helium determinations in uranium exploration is reviewed in the light of these findings and the concept and techniques assessed.  相似文献   

2.
The study reports the age evolution of groundwater as it flows from the recharge area through a regional alluvial aquifer system in North Gujarat-Cambay region in western India. Radiocarbon (14C), 4He and 4He / 222Rn dating methods have been employed. Sediments from a drill core in the Cambay Basin were also analysed for uranium (U) and thorium (Th) concentrations and the measured values have been used to estimate the 4He and 222Rn production rate for groundwater age calculations. Additionally, factors controlling the distribution of 222Rn, 4He and temperature anomalies in groundwater, vis-à-vis their relation to the tectonic framework and lithology of the study area, have also been examined.The multi-isotope study indicated a reasonable correspondence in groundwater age estimates by the three methods employed. The groundwater 14C ages increased, progressively, in the groundwater flow direction: from the foothills of Aravalli Mountains in the east, and reached a value of ∼35 ka towards the region of lowest elevation, linking Little Rann of Kachchh (LRK)-Nalsarovar (NS)-Gulf of Khambhat (GK) in the western part of the study area. In this region, groundwater ages obtained for free flowing thermal wells and springs employing 4He and 4He / 222Rn systematics are in the order of million years. Such anomalous ages are possibly due to enhanced mobilisation and migration of ‘excess helium’ from hydrothermal circulation vents along deep-seated faults. Excluding such anomalous cases and considering all uncertainties, presently estimated 4He and 4He / 222Rn groundwater ages are in reasonable agreement with 14C age estimates in the Cambay Basin for helium release factor (ΛHe) value of 0.4 ± 0.3. The 4He method also indicated west-southwards progression of groundwater ages up to ∼100 ka beyond the Cambay Basin.Large ‘excess helium’ concentrations are also seen to be generally associated with anomalous groundwater temperatures (> 35 °C) and found to overlie some of the basement faults in the study area, particularly along the east and the west flanks of the Cambay Basin. Groundwater 222Rn activities in most of the study area are 800 ± 400 dpm/l. But, a thermal spring at Tuwa on the east flank of the Cambay Basin, having granitic basement at shallow depth, recorded the highest 222Rn activity (∼63,000 dpm/l).  相似文献   

3.
Groundwater samples from 288 domestic wells in Barry County, Michigan, were analyzed for 33 inorganic chemical parameters. Variations in chemical composition were investigated by considering the possible effects of human impact, aquifer type (bedrock vs glacial drift), chemical evolution along groundwater flow paths, and glacial landform type (moraine vs outwash). Approximately 25 percent of the glacial drift wells were classified as degraded by human impact and were excluded from further analysis of chemical variation. Two-sample tests comparing individual concentrations from drift and bedrock aquifers suggest that groundwater in the Marshall Sandstone aquifer is derived from local recharge through the glacial drift. This conclusion is supported by generalized groundwater flow patterns recognized for the two aquifers.Concentrations in both aquifers were examined in relation to generalized flow paths derived from water level data and also by classification of wells as recharge, transition, and discharge. No spatial concentration trends in major ions were detected, although iron concentrations do appear to increase from recharge to discharge areas. Declining redox potential along groundwater flow paths may explain this trend.The possible influence of glacial landform type was investigated by comparing concentrations of wells in moraines with those in outwash deposits. Wells in moraines have significantly higher concentrations of most parameters, perhaps due to higher content of finer, more chemically reactive sediment grains.  相似文献   

4.
Shallow groundwater collected in Chaozhou,Huizhou,and Guangzhou allowed testing of concentrations and the isotope ratios of noble gases.Based on the calculated noble gas temperature(NGT)and the ratio of noble gas isotopes,the recharge temperature,recharge source,and residence time of groundwater can be calculated.In addition,the contribution of noble gas components from different sources to the sample components can be assessed.In the Huizhou area,according to the 1/Xe vs.Ne/Xe and NGT data,the shallow sandstone-confined water samples in the Shiba area and the unconfined water samples of the Huangshadong are in different temperature ranges,indicating that they have different recharge sources,both in time or space.The He components in the samples are calculated to obtain the content of radiogenic 4He in the crust and to simulate the groundwater ages.The noble gas isotope ratios show the addition of mantle components into the basalt aquifers and sandstone aquifers in Chaozhou and Huizhou.Except for atmospheric and crustal sources,there is a certain proportion of mantle-derived components in the shallow underground cold water in Huizhou and Chaozhou.The noble gases in the Chaozhou groundwater have an obvious mantle signature,allowing speculation that there is a deep fluid carrying mantle characteristics.This upwelling of mantle-derived material might be caused by the India-Eurasia collision or that between the Philippine Sea Plate and the Eurasian Plate.  相似文献   

5.
In Canada’s western Arctic, perennial discharge from permafrost watersheds is the surface manifestation of active groundwater flow systems with features including the occurrence of year-round open water and the formation of icings, yet understanding the mechanisms of groundwater recharge and flow in periglacial environments remains enigmatic. Stable isotopes (δ18O, δD, δ13CDIC), and noble gases have proved useful to study groundwater recharge and flow of groundwater which discharges along rivers in Canada’s western Arctic. In these studies of six catchments, groundwater recharge was determined to be a mix of snowmelt and precipitation. All systems investigated show that groundwater has recharged through organic soils with elevated PCO2, which suggests that recharge occurs largely during summer when biological activity is high. Noble gas concentrations show that the recharge temperature was between 0 and 5 °C, which when considered in the context of discharge temperatures, suggests that there is no significant imbalance of energy flux into the subsurface. Groundwater circulation times were found to be up to 31 years for non-thermal waters using the 3?H-3He method.  相似文献   

6.
Deuterium, oxygen-18 and chloride were analyzed for 84 samples from deep and shallow wells, precipitation and the river White Nile to investigate groundwater recharge/discharge relations in the semi-arid central Sudan. Spatial and vertical variation in isotopic signature and chloride concentration in the groundwater show similar patterns and indicate local recharge and evaporative discharge. Progressive decrease in isotopic composition along the regional groundwater flow path demonstrates aquifer continuity down the NW–SE recharge-discharge path. Isotope-heavy recharged water progressively mixes with lighter older groundwater formed during cooler and humid conditions in the late Pleistocene. However, evaporative fractionation in the flow path’s final reach in the southeast re-enriches the isotopic composition and suggests evaporative loss of groundwater as the plausible discharge mechanism. Chloride concentration increases down the gradient from the recharge area and reaches its peak in the discharge zones indicating: lack of recharge from direct infiltration down the gradient, evaporation and prolonged rock/water interaction. Head differences and increased isotopic concentration in the vicinity of the White Nile suggest recharge from the river from subsurface flow. Reduced chloride content and relatively heavier isotopic composition in the deep groundwater beneath the wadi of Khor Abu Habil indicate recharge from the streambed into the deep aquifer.  相似文献   

7.
A mobile mass spectrometer to measure He concentrations has been developed by the U.S. Geological Survey. This instrument has been tested in areas of known uranium deposits, and He anomalies have been found in both soil gas and water. A gas sample is collected in a hypodermic syringe, injected into the spectrometer, and analyzed for He. Over 100 analyses a day can be performed with a sensitivity of 10 parts per billion (ppb). One detailed study conducted in Weld County, Colorado, shows that values for He in soil gas can be contoured to outline an anomalous area and that the anomaly is displaced from the deposit in the direction of groundwater flow. Other studies include the Schwartzwalder uranium mine, Jefferson County, Colorado, where He anomalies may be related to geologic structure; near Ambrosia Lake, New Mexico, where the location of He anomalies are related to groundwater movement; and tests for diurnal effects showing only slight variations probably related to soil-moisture content.  相似文献   

8.
To test the usefulness of groundwater for U prospecting, 130 domestic wells were sampled from a 22,000 km2 rectangular area extending south and west from Ottawa, Ontario. The waters were analyzed for twenty variables including ten gases and five trace elements.The dissolved gases give information on subsurface chemical and geological environments. Carbon dioxide highs occur at the contact of granites and limestones; He highs are along major faults; CH4 and H2S reveal strongly reducing environments, and O2 in wells indicates shallow wells or active water turnover. Rn reveals U mineralization and granitic rocks.The South March U-Cu surface occurrence gives coincident U, Cu, Zn, Pb and Rn highs. A weak U-Rn-Cu high in the Richmond-North Gower area suggests more radioactive subcropping March formation there.A strong regional He anomaly coincident with the outcropping Rockcliffe Formation and controlled by the Hazeldean Fault is believed to be due to deep-seated He, but its coincidence with a weak regional Cu anomaly, a Rn anomaly in the Bells Corners area, its linear northeast trend, the presence of Helikian U-rich source rocks to the southwest, and northeast-dipping Paleozoic sandstones provide both indications of, and the right environment for epigenetic type U-Cu occurrences.  相似文献   

9.
Potassium chloride (KCl) and potassium bromide (KBr) tracers were used to explore the role of geologic structure on groundwater recharge and flow at the Fractured Rock Research Site in Floyd County, Virginia, USA. Tracer migration was monitored through soil, saprolite, and fractured crystalline bedrock for a period of 3 months with chemical, physical, and geophysical techniques. The tracers were applied at specific locations on the ground surface to directly test flow pathways in a shallow saprolite and deep fractured-rock aquifer. Tracer monitoring was accomplished with differential electrical resistivity, chemical sampling, and physical monitoring of water levels and spring discharge. KCl, applied at a concentration of 10,000 mg/L, traveled 160 m downgradient through the thrust fault aquifer to a spring outlet in 24 days. KBr, applied at a concentration of 5,000 mg/L, traveled 90 m downgradient through the saprolite aquifer in 19 days. Tracer breakthrough curves indicate diffuse flow through the saprolite aquifer and fracture flow through the crystalline thrust fault aquifer. Monitoring saline tracer migration through soil, saprolite, and fractured rock provided data on groundwater recharge that would not have been available using other traditional hydrologic methods. Travel times and flowpaths observed during this study support preferential groundwater recharge controlled by geologic structure.  相似文献   

10.
Widespread agricultural activity may threaten water quality in fractured bedrock aquifers having little overburden protection. A study in Canada improves the understanding of the potential impact of agriculture on water quality in bedrock aquifers, focusing on spatial and temporal variability of nitrate and bacteria. A research site was developed in and adjacent to a hay field where a gneissic aquifer is overlain by a thin veneer of unconsolidated glacial material. Ten wells were installed, hydraulically tested and completed as multilevel piezometers. Results of monthly sampling for nitrate, dissolved organic carbon, and E. coli show significant temporal and spatial variation in concentrations. Intensive 5-day sampling rounds conducted during baseflow and recharge conditions indicate that bacterial concentrations vary daily, with higher concentrations during recharge periods. The location of the impacted monitoring wells is correlated to an upgradient cattle pasture that is used periodically each summer. It is evident that periodic upgradient sources, dilution from recharge, and heterogeneous flow systems lead to varied and unpredictable contaminant concentrations. The temporal and spatial variability of contaminants in bedrock aquifers with minimal overburden must be considered for the protection of human health, as annual or even monthly groundwater monitoring may not capture unsafe concentrations.  相似文献   

11.
本文利用钻孔水化学数据和地球化学模拟方法,分析了郑家泉泉域基岩裂隙含水层各钻孔之间的水力联系和地下水补迳排特征。研究表明泉域北部的基岩裂隙含水层为条带状分布,到南部逐渐混合,郑家泉水的补给源主要来自西部和北部。  相似文献   

12.
《Applied Geochemistry》2004,19(4):519-560
The hydrogeochemistry of the Lac du Bonnet granitic batholith has been determined for the region of the Whiteshell Research Area (WRA) in southeastern Manitoba, Canada. This work forms part of the geosciences studies performed for the Canadian Nuclear Fuel Waste Management Program over the period 1980–1995 by Atomic Energy of Canada Limited (AECL). Knowledge of the variation of groundwater chemistry and its causes is useful in assessing the performance and safety of a nuclear fuel waste vault located at depths of up to 1000 m in a crystalline rock formation of the Canadian Shield. Groundwaters and matrix pore fluids have been obtained by standard sampling methods from shallow piezometers in clay-rich overburden, from packer-isolated borehole zones intersecting fractures or fault zones in the bedrock, and from boreholes in unfractured rock in AECL's Underground Research Laboratory (URL). Eighty-six individual fracture groundwaters have been sampled and analysed from permeable zones in 53 boreholes drilled to depths of up to 1000 m in the Lac du Bonnet batholith. In addition, 28 groundwaters from piezometers in a large wetland area near the URL have been sampled and analysed to determine the influence of clay-rich overburden on the bedrock hydrogeochemistry. Analyses have been made for major and minor ions, pH, Eh, trace metals, and stable and radioactive isotopes, to characterise these groundwaters and relate them to their hydrogeologic regimes. Shallow groundwaters in the fractured bedrock are generally dilute (TDS <0.3 g/l), Ca–Na–HCO3 waters and show little indication of mixing with Ca–Mg–HCO3–SO4 groundwater from overburden sediments. The near-modern levels of 3H and 14C, and a warm-climate 2H/18O signature in these groundwaters, indicates that the upper ∼200 m of fractured bedrock contains an active groundwater circulation system with a residence time of tens to hundreds of years. Deeper fracture groundwaters (200–400 m depth) in recharge areas, are more alkaline, Na–Ca–HCO3 waters and evolve to Na–Ca–HCO3–Cl–SO4 waters with increasing distance along the flow path. Isotopic data indicate the presence of a glacial melt-water component suggesting that the residence times of these waters are 103–105 a. These waters form a transition zone between the upper, advective flow regime and a deeper regime in sparsely fractured rock where groundwater in fractures and fracture zones is largely stagnant. At these depths (> 500 m), Na–Ca–Cl–SO4 waters of increasing salinity (up to 50 g/l) with depth are found and in some fractures the waters have evolved to a Ca–Na–Cl composition. Isotopic data indicate that these waters are warm-climate and pre-glacial in origin, with residence times of over 1 Ma. Pore fluids observed to drain from the unfractured rock matrix in the URL facility are almost pure Ca–Cl in composition, ∼90 g/l salinity, and have a 2H/18O composition displaced well to the left of the global meteoric water line, about which all other WRA groundwaters lie. This information indicates that these pore fluids have undergone prolonged water-rock interaction and have residence times of 101–103 Ma. Most of the deeper fracture groundwaters and pore fluids have low Br/Cl ratios and moderate to high δ34S values of dissolved SO4 which indicates that their salinity could be derived from a marine source such as the basinal sedimentary brines and evaporites to the west of the batholith. These fluids may have entered the batholith during early Paleozoic times when sedimentary rocks were deposited over the granite and were driven by a hydraulic gradient resulting from higher ground in western Canada. The hydrogeochemical data and interpretations show that below ∼500 m in the WRA, fracture-hosted groundwaters are very saline, reducing and old, and are, therefore, indicative of stagnant conditions over the period of concern for nuclear waste disposal (1 Ma). The intact rock matrix at these depths is extremely impermeable as indicated by the presence of pore fluids with unusual geochemical and isotopic characteristics. The pore fluids may represent basinal brines that have evolved geochemically and isotopically to their current composition over periods as long as 103 Ma.  相似文献   

13.
Groundwater is the major source of water and a critical resource for socioeconomic development in semi-arid environments like the Johannesburg area. Environmental isotopes are employed in this study to characterise groundwater recharge and flow mechanisms in the bedrock aquifers of Johannesburg, which is known for polluted surface water. With the exception of boreholes near the Hartbeespoort Dam, groundwater in the study area was derived from meteoric water that has undergone some degree of evaporation before recharge, possibly via diffuse mechanisms. Boreholes that tap groundwater from the Transvaal Supergroup Formation show depletion in δ18O and δ2H values. This is attributed to diffuse recharge through weathering fractures at high elevation that are undergoing deep circulation or recharge from depleted rainfall from the high-latitude moisture sources. The influence of focused recharge from the Hartbeespoort Dam was observed in the boreholes north of the dam, possibly as a result of the north–south trending fault lines and the north-dipping fractures in the bedding planes of quartzites. This is also supported by a reservoir water budget method which indicated a mean annual net flux of 2,084,131 m3 from Hartbeespoort Dam recharging groundwater per annum. Using tritium in the dam and boreholes located at 750 m and 5400 m downstream, average groundwater flow velocity was estimated as 202 m/year. An open system was observed in shale, andesite and granitic-gneiss aquifers indicating soil CO2 as a dominant source of carbon (δ13C) in groundwater. A closed system was also observed in dolomitic aquifers indicating carbonate dissolution as the predominant source of carbon.  相似文献   

14.
王新娟  韩旭  许苗娟  孙颖  刘久荣 《地质论评》2022,68(3):2022062038-2022062038
利用地下水水化学和同位素测试分析成果,结合区域地质、水文地质条件研究了平谷北山山区侧向补给情况和中桥水源地地区第四系松散孔隙水和下伏岩溶水关系。结果表明：研究区第四系松散孔隙水和基岩岩溶地下水均来源于大气降水,地下水化学类型均为HCO-3-Ca2+?Mg2+ 型;平谷北山山前基岩岩溶水侧向补给平原区第四系松散孔隙水和下伏岩溶地下水;通过D值估算得到中桥水源地第四系浅层地下水的山区岩溶水侧向补给和垂向降水入渗补给比例为57：43;中桥水源地基岩岩溶水接受山区岩溶水侧向补给和第四系孔隙水垂向越流补给比例为87：13。研究成果为平谷地区地下水资源量评价和地下水动力场数值模型的建设提供了关键参数,为区域地下水的合理开采和有序回补涵养提供了科学依据。  相似文献   

15.
The distribution and controls of trace elements (Cd, Cr, Cu, Ni, Pb, Zn and U) in shallow groundwater in discharge and recharge zones were analysed at two sites on the Baltic coast of Sweden; one granite-dominated and one with a significant addition of calcite. Although the study sites differ in overburden geochemistry and groundwater trace metal concentrations, which were well reflected in the general groundwater composition, the relative hydrochemical differences between recharge and discharge ground waters were similar at both sites, and temporally stable. The concentrations of Cd, Cu, Ni and U were higher in soil tubes in recharge areas, but Cr was higher in discharge zones. Also concentrations of HS, Fe, Mn and NH4 were higher in discharge samples, which in combination with increased 34S values provide strong evidence of a transition from oxidizing to more reducing conditions along the groundwater flow gradient. In terms of trace metals, this might mean either mobilisation due to dissolution of trace-metal carrying Fe(III) and Mn(IV) phases, or immobilisation caused by precipitation of discrete trace-metal sulfides or co-precipitation with Fe sulfides. The results from this study show that the latter is dominant in both the carbonate and granite environments for the metals Cd, Cu and Ni. Chromium concentrations were likely coupled to organic complexation and were higher in discharge groundwater, where DOC was also more abundant. As the concentration of several potentially toxic trace metals were found to differ between recharge and discharge areas, a climate driven change in hydrology might have a substantial impact on the distribution of these metals.  相似文献   

16.
海原盆地地下水咸化特征和控制因素   总被引：1，自引：0，他引：1       下载免费PDF全文
地下水是海原盆地唯一的供水水源,近年来部分地区地下水溶解性总固体(TDS)增高,引起了有关部门和水文地质工作者的高度关注。通过分析69组地下水样品的水化学和氢氧稳定同位素数据,对地下水补给来源和咸化的水文地球化学过程进行了研究。结果表明:地下水TDS值198.2~6 436.4 mg/L,沿着地下水流向,咸化程度增加,水化学类型从基岩区的HCO3—Ca·Mg型演化至滞留—排泄区的SO4·Cl—Na·Mg型。地下水补给来源主要为大气降雨和基岩裂隙水侧向径流,补给源—对地下水咸化贡献较小。溶滤作用具空间差异,基岩区和补给区以碳酸盐、硅酸盐风化为主,径流区和滞留—排泄区则为蒸发岩风化,硫酸盐是地下水中阳离子的主要来源。补给水、溶滤和蒸发对第四系地下水TDS的贡献比率分别为4.8%~81.2%、11.9% ~85.9%、1.7%~29.5%,溶滤作用是控制海原盆地地下水咸化的首要因素。当地有关部门应加大对基岩泉水的综合利用,同时注意控制海原县和西安镇等地区地下水开采量,防止地下水进一步咸化。另外,在微咸水分布区可引进地下水去除硫酸盐技术,提高微咸水利用程度。  相似文献   

17.
A field study was undertaken on the Florida Bay side of Fiesta Key, Florida, to identify the chemical characteristics of a previously unexplored offshore groundwater system and to define the critical parameters affecting groundwater movement and interaction with sediment pore fluids and bedrock. Emphasis was placed on the upper 2 meters of bedrock, where groundwater recharge and discharge potentials are maximized, along a 100 meter transect extending from the island margin. Bedrock cores were used to describe Pleistocene depositional textures, and were sampled at discrete depths to determine the extent of water-rock interaction. Piezometers installed into each core hole were used to monitor surface and ground water tide levels, and for the systematic collection of water samples for a large suite of chemical determinations.Aqueous chemical data indicate that these groundwaters are marine in origin, anoxic, and moderately hypersaline (S = 36–40). Exchange of bedrock pore fluids with overlying Bay waters is restricted by a layer of Holocene sediment and a discontinuous soilstone crust formed at the modern bedrock surface. Groundwater chemistry near the sediment/bedrock interface is marked by elevated concentrations of total alkalinity and Ca2+, and by significant Mg2+ depletion. These waters likely acquired their unusual chemistry by mixing between deeper groundwaters and overlying, early diagenetically altered, sediment porewaters. High alkalinity and calcium concentrations presumably result from the combination of the effects of aerobic metabolism, carbonate dissolution, and sulfate reduction. Mg-depletion most likely resulted from the precipitation of Mg-calcite. These unusual chemistries disappear by 2 m depth in the groundwater system, where Ca2+ and Mg2+ concentrations are similar to those expected for seawater under slightly hypersaline conditions.The Pleistocene bedrock contains low Mg, Sr, F, and P concentrations relative to the overlying unconsolidated Holocene carbonate sediments. This is consistent with the diagenetic recrystallization processes that the bedrock has undergone. Hydraulic conditions favor the net recharge of Florida Bay seawater to the groundwater system, but there are insufficient tide data to identify cyclical water exchange rates or groundwater flow patterns.  相似文献   

18.
Occurrence and evolution of the Xiaotangshan hot spring in Beijing, China   总被引：1，自引：0，他引：1  
Thermal groundwater occurs in bedrock aquifers consisting of the dolomite of the Wumishan Group of the Jixianin System and the Cambrian carbonate in the Xiaotangshan geothermal field near the northern margin of the North China Plain, China. The hot water in the geothermal field of basin-type discharges partly in the form of the Xiaotangshan hot spring under natural conditions. The hot water has TDS of less than 600 mg/L and is of Na·Ca-HCO3 type. The geothermal water receives recharge from precipitation in the mountain area with elevation of about 500 m above sea level to the north of the spring. Thermal groundwater flows slowly south and southeast through a deep circulation with a residence time of 224 years estimated with the Ra–Rn method. The Xiaotangshan hot spring dried up in the middle of the 1980s owing to the increasing withdrawal of the hot water in the geothermal field in the past decades. The water level of the geothermal system still falls continually at an annual average rate of about 2 m, although water temperature changes very little, indicating that the recharge of such a geothermal system of basin-type is limited. Over-exploitation has a dramatic impact on the geothermal system, and reduction in exploitation and reinjection are required for the sustainable usage of the hot water.  相似文献   

19.
Proper management of groundwater resources requires knowledge of the processes of recharge and discharge associated with a groundwater basin. Such processes have been identified in the Jakarta groundwater basin, Indonesia using a theory that describes the simultaneous transfer of heat and fluid in a porous medium. Temperature-depth profiles in monitoring wells are used to determine the geothermal gradient. To examine the rules of groundwater flow in the distortion of the isotherms in this area, several methods are compared. Subsurface temperature distribution is strongly affected by heat advection due to groundwater flow. Under natural flow conditions, the recharge area is assumed to occur in the hills and uplands, which are located on the periphery of the Jakarta basin, and the discharge area is located in the central and northern part of the Jakarta groundwater basin. A transition area, which could act as local recharge and discharge areas, occupies the middle of the lowland. Subsurface temperatures show good correlation with the groundwater flow conditions, and the data yield important information on the location of recharge and discharge areas.  相似文献   

20.
Atmospheric deposition of S in Sweden has decreased by some 80% over the last 15 a, resulting in a general reduction of SO4 concentrations in ground and surface water. This project, however, shows that artificial hydrological alteration in an acid wetland can reverse this trend and increase acidity and SO4 concentrations. The experiment involved the monitoring of two catchments in relatively virgin conditions. In one of the catchments, an experiment with intensive groundwater extraction from the bedrock was carried out. During the experiment, the runoff from the catchment decreased by 50%. Furthermore, the extraction of groundwater resulted in increased seasonal aeration of the centrally located wetland, leading to oxidation of reduced S bound to the soil layers of the wetland. The S changed to solute SO4, with a subsequent SO4 surge. Thus, the experiment resulted in an induced acidification of the wetland and runoff waters. The extraction of groundwater significantly increased the recharge of water from the overburden, glacial till and organic soils to groundwater in the bedrock, which in turn reduced the retention time in the bedrock aquifer. These changes resulted in the chemical signature of the groundwater in the bedrock becoming similar to those of the wetland. The findings revealed deterioration in the water quality in the bedrock due to increased concentrations of dissolved organic C and SO4, as well as a decrease in pH.  相似文献   

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