The role of faulting on surface deformation patterns from pumping-induced groundwater flow (Las Vegas Valley, USA)

Land subsidence and earth fissuring can cause damage in semiarid urbanized valleys where pumping exceeds natural recharge. In places such as Las Vegas Valley (USA), Quaternary faults play an important role in the surface deformation patterns by constraining the migration of land subsidence and creating complex relationships with surface fissures. These fissures typically result from horizontal displacements that occur in zones where extensional stress derived from groundwater flow exceeds the tensile strength of the near-surface sediments. A series of hypothetical numerical models, using the finite-element code ABAQUS and based on the observed conditions of the Eglington Fault zone, were developed. The models reproduced the (1) long-term natural recharge and discharge, (2) heavy pumping and (3) incorporation of artificial recharge that reflects the conditions of Las Vegas Valley. The simulated hydrostratigraphy consists of three aquifers, two aquitards and a relatively dry vadose zone, plus a normal fault zone that reflects the Quaternary Eglington fault. Numerical results suggest that a 100-m-wide fault zone composed of sand-like material produces: (1) conditions most similar to those observed in Las Vegas Valley and (2) the most favorable conditions for the development of fissures to form on the surface adjacent to the fault zone.     

Noble gas recharge temperatures and the excess air component

The calculation of a groundwater recharge temperature based on the dissolved concentrations of Ne, Ar, Kr and Xe requires a correction for noble gas supersaturation due to excess air entrainment. This entrainment is commonly attributed to the recharge process or to air contamination at the wellhead during sample collection. With the exception of some local studies, most work has concentrated on interpretation of the recharge temperature or quantification of the radiogenic content for palaeoclimatic and dating purposes. The magnitude and source of the excess air is not directly relevant to these studies and so is often ignored. In this work, excess air Ne and other data have been calculated from new and published noble gas data sets for several groundwater systems. For younger groundwaters which have been recharged under one broad climatic regime, the amount of air entrainment increases according to lithology in the order granites, sandstones and limestones respectively. A negative correlation between precipitation and excess air entrainment is identified in at least one aquifer, and some of the mechanisms which may influence the entrainment process are discussed.     

Why conceptual groundwater flow models matter: a trans-boundary example from the arid Great Basin, western USA

Spring and Snake valleys, western USA, are scheduled for development and groundwater export to Las Vegas, Nevada (USA). New work, compared to published studies, illustrates the critical role of conceptual models to underpin water withdrawals in arid regions. Interbasin flow studies suggest that 30–55?% of recharge to Snake Valley arrives from adjacent Spring Valley. This study, however, suggest little or no interbasin flow; rather, Spring and Snake valleys comprise separate systems. Contrary to expectation, δD and δ¹⁸O contours are perpendicular to proposed interbasin flow paths. ¹⁴C age gradients up to 10?ka along interbasin flow paths indicate that old waters are not displaced by such fluxes. ¹⁴C and ³H patterns indicate local recharge occurs in adjacent mountain ranges and is transferred to basin-fill by losing streams, mountain front recharge, and upward leakage from carbonate bedrock beneath basins. The choice of conceptual models is critical for groundwater development. Simple analyses of water withdrawals indicate that monitoring discharges at desert springs is an inadequate protective measure. Once flows decline, recovery is lengthy even if pumping is stopped. The conceptual framework behind quantitative evaluations of sustainable yield is critical to determine the ability of a groundwater system to deliver sustained withdrawals.     

Ion exchange and trace element surface complexation reactions associated with applied recharge of low-TDS water in the San Joaquin Valley,California

Stable isotope data, a dissolved gas tracer study, groundwater age dating, and geochemical modeling were used to identify and characterize the effects of introducing low-TDS recharge water in a shallow aerobic aquifer affected by a managed aquifer recharge project in California’s San Joaquin Valley. The data all consistently point to a substantial degree of mixing of recharge water from surface ponds with ambient groundwater in a number of nearby wells screened at depths above 60 m below ground surface. Groundwater age data indicate that the wells near the recharge ponds sample recently recharged water, as delineated by stable O and C isotope data as well as total dissolved solids, in addition to much older groundwater in various mixing proportions. Where the recharge water signature is present, the specific geochemical interactions between the recharge water and the aquifer material appear to include ion exchange reactions (comparative enrichment of affected groundwater with Na and K at the expense of Ca and Mg) and the desorption of oxyanion-forming trace elements (As, V, and Mo), possibly in response to the elevated pH of the recharge water.     

基于TOUGH2数值模拟软件的延津地区热储采灌研究

本文采用TOUGH2数值模拟软件,根据研究区对井在预设情景下运转30年的模拟结果,对河南省延津县下新近系热储层压力场、温度场进行模拟,在模型验证的基础上,对不同回灌率及不同采灌井间距工况进行模拟研究,结果显示:回灌井的回灌过程会使地下水水温降低,回灌时间越长水温降低幅度越大,影响范围也越大,根据模拟抽水井和回灌井不同间距条件下(55 m、150 m、250 m、300 m)温度场变化情况,建议区域下新近系地层地热回灌项目抽水井和回灌井间距应大于等于250m,以保证抽水井出水温度;而不同回灌率工况下分析化学场和压力场的模拟数据可以看出,回灌率越大,地热水水质、压力影响越大,基本呈线性关系。为区域地热资源回灌-开采提供示范和指导。     

Experimental investigations on the formation of excess air in quasi-saturated porous media

The formation of an excess of dissolved gas (“excess air”) in quasi-saturated media was studied by analyzing and interpreting dissolved noble gas concentrations in laboratory column experiments. Using quartz sand filled columns of 1 m length, two different experimental designs were realized. In the first, groundwater recharge was simulated by a unidirectional vertical water flow through the columns. In the second, groundwater level fluctuations in an aquifer zone without active infiltration were reproduced by cyclic water level fluctuations in the columns. The reproducible generation of excess air under these defined, near natural conditions was successful. Partial or complete dissolution of air bubbles entrapped in the quartz sand could be identified as the mechanism responsible for the generation of excess air. Depending on the experimental design, supersaturation of the dissolved atmospheric noble gases ranging between 1.4% ΔNe and 16.2% ΔNe was found. The measured noble gas patterns were interpreted using inverse modeling and conceptual gas exchange models and were compared to results of numerical simulations of gas bubble dissolution in water filled soil columns. The gas composition in most of the samples resembles either unfractionated pure atmospheric excess air or is fractionated in accordance with closed-system equilibration between entrapped air and surrounding water. In addition to the amount of entrapped air, the hydrostatic pressure exerted on the entrapped air bubbles is the dominating parameter responsible for the total amount of dissolved air. The composition of the excess air component is controlled by the water flow regime, the bubble size distribution, the initially dissolved gas concentrations and the initially entrapped gas composition.     

Solubility of sulfur in some magmas at 1 atmosphere

In order to understand the distribution of sulfur in igneous rooks, we determined the solubility of sulfur in volcanic rock melts (tholeiite basalt, hawaiite and rhyodacite from Hawaii) at various gas compositions and at 1250° and 1300°C and 1 atm total pressure. The solubility of sulfur in the melt passes through a minimum with change in oxygen partial pressure, if other factors are held constant. For the basaltic liquid at 1200°C, most sulfur in the melt is as dissolved sulfide (S^?2) at oxygen partial pressures below 10^?8 atm and as dissolved sulfate at oxygen partial pressures above 10^?8 atm. Based on the present solubility data, 5 per cent is inferred for volcanic gas at 1 atm total pressure in equilibrium with subaerially extruded Hawaiian tholeiite basalt (Pele's hair with 180 ppm S) at 1200°C and 10^?8 atm P_O2.     

高坝工程总溶解气体过饱和与水体含沙量关系

为研究伴随高坝泄水产生的总溶解气体(TDG)过饱和现象与水体中含沙量关系的问题,提出切实可行的减缓TDG过饱和影响的措施,通过实验的方法,对含沙水体中TDG过饱和的生成和释放进行了研究分析。结果表明:同样初始条件下,在含沙水体与清水中的TDG过饱和生成过程中,TDG过饱和度没有明显变化。在TDG释放过程中,含沙水体中TDG释放速率明显快于清水中TDG释放速率,据此提出可通过开启排沙孔等泄洪调度方式使泄流中悬沙含量增加,促使TDG沿程释放加快,降低其对鱼类的影响。     

Hydrogeological characterization of Gold Valley: an investigation of precipitation recharge in an intermountain basin in the Death Valley region, California, USA

Gold Valley is typical of intermountain basins in Death Valley National Park (DVNP), California (USA). Using water-balance calculations, a GIS-based analytical model has been developed to estimate precipitational infiltration rates from catchment-scale topographic data (elevation and slope). The calculations indicate that groundwater recharge mainly takes place at high elevations (>1,100?m) during winter (average 1.78?mm/yr). A resistivity survey suggests that groundwater accumulates in upstream compartmentalized reservoirs and that the groundwater flows through basin fill and fractured bedrock. This explains the relationship between the upstream precipitational infiltration in Gold Valley and the downstream spring flow in Willow Creek. To verify the ability of local recharge to support high-flux springs in DVNP, a GIS-based model was also applied to the Furnace Creek catchment. The results produced insufficient total volume of precipitational infiltration to support flow from the main high-flux springs in DVNP under current climatic conditions. This study introduces a GIS-based infiltration model that can be integrated into the Death Valley regional groundwater flow model to estimate precipitational infiltration recharge. In addition, the GIS-based model can efficiently estimate local precipitational infiltration in similar intermountain basins in arid regions provided that the validity of the model is verified.     

The water balance for the Basin of the Valley of Mexico and implications for future water consumption

The Basin of the Valley of Mexico is a closed basin of 9600?km2, where average annual precipitation (1980–85) is 746?mm (226.7?m3/s). Calculated actual evapotranspiration is 72–79% of the precipitation. The surrounding mountain ranges of the Sierra de Las Cruces, Sierra Nevada, and Sierra Chichinautzin are the main recharge areas for the enclosed Basin, in decreasing order. Calculated recharge rate is a maximum of 19?m3/s in the Metropolitan Zone, whereas a recent estimate of the groundwater exploitation rate indicates that 51.35?m3/s is being withdrawn from the Basin aquifer systems, resulting in a deficit of more than 30?m3/s. Taking into account infiltration processes by leaking water-supply systems, the calculated deficit is reduced to 20.5?m3/s. Overexploitation of the natural aquifer systems is also indicated by an average annual decline of 1?m of the potentiometric levels of the shallow groundwater systems. Possible solutions include: (1) the use of surface runoff water (unused amount in 1995?:?17.6?m3/s) for consumption purposes, which is currently pumped to areas outside the Basin; (2) an increased number and capacity of treatment plants; (3) the renovation of the leaky water-distribution network; (4) the reinjection of treated water; and (5) possible exploitation of deep regional aquifer systems.     

紫坪铺坝下游过饱和溶解气体原型观测研究

在总结国内外关于水电站大坝下游总溶解气体(TDG)过饱和问题的研究现状的基础上,对紫坪铺坝下游河段的过饱和气体进行了原型观测,指出下泄流量与下游TDG饱和度有着较好的相关关系;河道水深是影响过饱和气体消减速率的重要因素;在同样单宽流量下,含沙水体比清水有更高的TDG饱和度。这一研究为更深入的开展高坝下游过饱和溶解气体的产生及消减过程理论研究提供了依据,对高坝下游水生生物保护具有重要作用。     

Groundwater resources assessment using numerical model: A case study in low-lying coastal area

The impacts of climate change and human pressure in groundwater have been greatest threats facing small islands. This paper represents a case study of groundwater responses towards the climate change and human pressures in Manukan Island Malaysia. SEAWAT-2000 was used for the simulations of groundwater response in study area. Simulations of six scenarios representing climate change and human pressures showed changes in hydraulic heads and chloride concentrations. Reduction in pumping rate and an increase in recharge rate can alter the bad effects of overdrafts in Manukan Island. In general, reduction in pumping rate and an increase in recharge rate are capable to restore and protect the groundwater resources in Manukan Island. Thus, for groundwater management options in Manukan Island, scenario 2 is capable to lessen the seawater intrusion into the aquifer and sustain water resources on a long-term basis. The selection of scenario 6 is the preeminent option during wet season. The output of this study provides a foundation which can be used in other small islands of similar hydrogeological condition for the purpose of groundwater resources protection.     

铁岭城区水源热泵可行性研究

水源热泵是一种高效、节能且无污染的新型中央空调系统。银州区地处北温带,气候四季分明,冬季寒冷,夏季炎热,冬夏季节温差达75℃。而地下水温度年际变化很小,一般在15℃左右,利用这一地温能源,冬季取暖、夏季降温,应这一资源广泛应用的理想绿色技术。分析区域地质和水文地质条件和含水层状况,经抽水回灌试验,以潜水完整井计算渗透系数、回灌渗透系数及回灌影响半径,分析取用水量、水质的可行性、取水、退水的第三者影响等,闸述科学合理使用这一技术的可行性。     

Mountain-block recharge, present and past, in the eastern Espa?ola Basin, New Mexico, USA

Noble gas recharge temperatures (NGTs) and radiocarbon ages were determined for 43 groundwater samples collected in the eastern Espa?ola Basin, New Mexico (USA), to identify mountain-block recharge in waters <10 thousand years (ka) old and to evaluate possible changes in mountain-block recharge over the past ??35?ka. For Holocene samples from the southeastern area, NGTs are dominantly 2?C4° cooler than the measured water-table temperature near the mountain front. Computed minimum mountain-block recharge fractions are dominantly 0.2?C0.5, consistent with previous large mountain-block recharge estimates. NGTs do not display the distinct low during the last glacial maximum observed in other paleorecharge studies; samples recharged 15?C25?ka ago are on average only 1.3° cooler than Holocene samples. Instead, samples with the coldest NGTs were recharged 25?C35?ka ago. A proposed explanation is that higher precipitation rates during the last glacial maximum resulted in a lower mean recharge elevation for the basin, essentially buffering the effect of the lower mean annual air temperature and producing NGTs similar to the Holocene. In the period preceding the last glacial maximum, precipitation rates more like today??s resulted in Holocene-like mountain-block recharge fractions, producing a mean NGT ??5° cooler than the Holocene, as expected.     

Sources of oxygen flux in groundwater during induced bank filtration at a site in Berlin, Germany

The microbial degradation of pharmaceuticals found in surface water used for artificial recharge is strongly dependent on redox conditions of the subsurface. Furthermore the durability of production wells may decrease considerably with the presence of oxygen and ferrous iron due to the precipitation of trivalent iron oxides and subsequent clogging. Field measurements are presented for oxygen at a bank filtration site in Berlin, Germany, along with simplified calculations of different oxygen pathways into the groundwater. For a two-dimensional vertical cross-section, oxygen input has been calculated for six scenarios related to different water management strategies. Calculations were carried out in order to assess the amount of oxygen input due to (1) the infiltration of oxic lake water, (2) air entrapment as a result of water table oscillations, (3) diffusive oxygen flux from soil air and (4) infiltrating rainwater. The results show that air entrapment and infiltrating lake water during winter constitute by far the most important mechanism of oxygen input. Oxygen input by percolating rainwater and by diffusive delivery of oxygen in the gas phase is negligible. The results exemplify the importance of well management as a determining factor for water oscillations and redox conditions during artificial recharge.     

Field experiments yield new insights into gas exchange and excess air formation in natural porous media

Gas exchange between seepage water and soil air within the unsaturated and quasi-saturated zones is fundamentally different from gas exchange between water and gas across a free boundary layer, e.g., in lakes or rivers. In addition to the atmospheric equilibrium fraction, most groundwater samples contain an excess of dissolved atmospheric gases which is called “excess air”. Excess air in groundwater is not only of crucial importance for the interpretation of gaseous environmental tracer data, but also for other aspects of groundwater hydrology, e.g., for oxygen availability in bio-remediation and in connection with changes in transport dynamics caused by the presence of entrapped air bubbles. Whereas atmospheric solubility equilibrium is controlled mainly by local soil temperature, the excess air component is characterized by the (hydrostatic) pressure acting on entrapped air bubbles within the quasi-saturated zone. Here we present the results of preliminary field experiments in which we investigated gas exchange and excess air formation in natural porous media. The experimental data suggest that the formation of excess air depends significantly on soil properties and on infiltration mechanisms. Excess air was produced by the partial dissolution of entrapped air bubbles during a sprinkling experiment in fine-grained sediments, whereas similar experiments conducted in coarse sand and gravel did not lead to the formation of excess air in the infiltrating water. Furthermore, the experiments revealed that the noble gas temperatures determined from noble gases dissolved in seepage water at different depths are identical to the corresponding in situ soil temperatures. This finding is important for all applications of noble gases as a paleotemperature indicator in groundwater since these applications are always based on the assumption that the noble gas temperature is identical to the (past) soil temperature.     

The influence of faults in basin-fill deposits on land subsidence,Las Vegas Valley,Nevada, USA

The role of horizontal deformation caused by pumping of confined-aquifer systems is recognized as contributing to the development of earth fissures in semiarid regions, including Las Vegas Valley, Nevada. In spite of stabilizing water levels, new earth fissures continue to develop while existing ones continue to lengthen and widen near basin-fill faults. A three-dimensional granular displacement model based on Biot's consolidation theory (Biot, MA, 1941, General theory of three-dimensional consolidation. Jour. Applied Physics 12:155–164) has been used to evaluate the nature of displacement in the vicinity of two vertical faults. The fault was simulated as (1) a low-permeability barrier to horizontal flow, (2) a gap or structural break in the medium, but where groundwater flow is not obstructed, and (3) a combination of conditions (1) and (2). Results indicate that the low-permeability barrier greatly enhances horizontal displacement. The fault plane also represents a location of significant differential vertical subsidence. Large computed strains in the vicinity of the fault may suggest high potential for failure and the development of earth fissures when the fault is assumed to have low permeability. Results using a combination of the two boundaries suggest that potential fissure development may be great at or near the fault plane and that horizontal deformation is likely to play a key role in this development. Electronic Publication     

Fractionation of carbon isotopes by phytoplankton and estimates of ancient CO2 levels

Reports of the 13C content of marine particulate organic carbon are compiled and on the basis of GEOSECS data and temperatures, concentrations, and isotopic compositions of dissolved CO2 in the waters in which the related phytoplankton grew are estimated. In this way, the fractionation of carbon isotopes during photosynthetic fixation of CO2 is found to be significantly correlated with concentrations of dissolved CO2. Because ancient carbon isotopic fractionations have been determined from analyses of sedimentary porphyrins [Popp et al., 1989], the relationship between isotopic fractionation and concentrations of dissolved CO2 developed here can be employed to estimate concentrations of CO2 dissolved in ancient oceans and, in turn, partial pressures of CO2 in ancient atmospheres. The calculations take into account the temperature dependence of chemical and isotopic equilibria in the dissolved-inorganic-carbon system and of air-sea equilibria. Paleoenvironmental temperatures for each sample are estimated from reconstructions of paleogeography, latitudinal temperature gradients, and secular changes in low-latitude sea surface temperature. It is estimated that atmospheric partial pressures of CO2 were over 1000 micro atm 160 - 100 Ma ago, then declined to values near 300 micro atm during the next 100 Ma. Analysis of a high-resolution record of carbon isotopic fractionation at the Cenomanian-Turonian boundary suggests that the partial pressure of CO2 in the atmosphere was drawn down from values near 840 micro atm to values near 700 micro atm during the anoxic event.     

石津灌区冬小麦水分生产率的尺度效应

以河北省石津灌区为研究对象,以2007-2009年两季冬小麦生育期为研究时段,基于Hydrus-1D和Modflow模型模拟分析了井渠结合灌溉模式下冬小麦的净入流量水分生产率和净灌溉水分生产率的尺度效应(作物、田间、分干、干渠和灌区尺度)。结果表明:①从作物尺度到灌区尺度,损失水量越来越多,使得净入流量水分生产率和净灌溉水分生产率分别减少了9.49%和16.59%;②由于研究区地下水埋深较大,冬小麦生育期内渗漏补给地下水库的重复利用水量很小,而净灌溉水分生产率因为考虑了这一小部分重复利用水量,比传统的灌溉水分生产率有了小幅提升;③在多年时间尺度上,由于渗漏水量能够全部进入地下水库被重复利用,净入流量水分生产率随尺度增大而增大,而不同空间尺度的净灌溉水分生产率也比冬小麦生育期时间尺度上提高37%~65%。     

具有补给气的异常高压有水凝析气藏物质平衡方程建立及应用

物质平衡法是计算气藏地质储量、水侵量、补给气量的有效方法之一.具有补给气的异常高压有水凝析气藏是气藏开发中最复杂的类型之一, 兼具异常高压气藏、凝析气藏和补给气的边底水气藏的特性.综合考虑开发过程中的凝析油析出, 岩石、束缚水和凝析油弹性膨胀, 水相挥发, 凝析气相中水蒸气增多, 水溶气溢出, 边底水的推进及外来气补给等复杂物理现象, 根据物质平衡原理, 推导了具有补给气的异常高压有水凝析气藏物质平衡方程, 并运用相对海明距离及关联度理论, 以驱动指数均方差、比拟压力与采出程度偏差指数和综合目标函数为分析因素, 分析了各组合方案贴近程度及相似程度, 挑选最佳组合方案并确定出地质储量、补给气量及水侵量, 同时计算了水体倍数.实例计算表明: 中国西北某凝析气藏地质储量为66.80×108 m3, 如果忽略凝析油, 计算地质储量偏大, 误差高达91.77%, 其次是水侵、弹性膨胀和气侵的影响, 误差分别为75.75%、23.95%和12.87%, 而溢出水溶气为2.69%与水蒸气为1.65%, 影响较小, 但也不可忽略.