Regional Groundwater Flow System Research Articles

From streambed temperature measurements to spatial-temporal flux quantification: using the LPML method to study groundwater-surface water interaction

Knowledge on groundwater–surface water interaction and especially on exchange fluxes between streams and aquifers is an important prerequisite for the study of transport and fate of contaminants and nutrients in the hyporheic zone. One possibility to quantify groundwater–surface water exchange fluxes is by using heat as an environmlental tracer. Modern field equipment including multilevel temperature sticks and the novel open-source analysis tool LPML make this technique ever more attractive. The recently developed LPML method solves the one-dimensional fluid flow and heat transport equation by combining a local polynomial method with a maximum likelihood estimator. In this study, we apply the LPML method on field data to quantify the spatial and temporal variability of vertical fluxes and their uncertainties from temperature–time series measured in a Belgian lowland stream. Over several months, temperature data were collected with multilevel temperature sticks at the streambed top and at six depths for a small stream section. Long-term estimates show a range from gaining fluxes of −291 mm day−1 to loosing fluxes of 12 mm day−1; average seasonal fluxes ranged from −138 mm day−1 in winter to −16 mm day−1 in summer. With our analyses, we could determine a high spatial and temporal variability of vertical exchange fluxes for the investigated stream section. Such spatial and temporal variability should be taken into account in biogeochemical cycling of carbon, nutrients and metals and in fate analysis of contaminant plumes. In general, the stream section was gaining during most of the observation period. Two short-term high stream stage events, seemingly caused by blockage of the stream outlet, led to a change in flow direction from gaining to losing conditions. We also found more discharge occurring at the outer stream bank than at the inner one indicating a local flow-through system. With the conducted analyses, we were able to advance our understanding of the regional groundwater flow system. Copyright © 2015 John Wiley & Sons, Ltd.

Hydrochemical characteristics and geothermometry applications of thermal groundwater in northern Jinan, Shandong, China

Carbonate rock thermal reservoirs are important geothermal resources but lack systematical study on a regional scale. This paper integrated hydrochemical and isotopic data to outline thermal water resources in carbonate rock aquifers as part of deep regional groundwater flow system. Hydrochemical characteristics of thermal groundwater in northern Jinan geothermal field, where Ordovician carbonate rocks are the main thermal reservoir, were examined and characterized by SO4–Ca, SO4–Ca·Na, SO4·Cl–Ca·Na and Cl·SO4–Na·Ca types. Hydrochemical evolution was revealed by analyzing correlation between different chemical constituents and their relative changes in various waters. Isotopic data allowed the origin of thermal water to be determined and presented different recharge elevations. Thermal groundwater was originated from precipitation in the northern piedmont of Tai Mountain with elevation of 708–1493m.a.s.l.. Reservoir temperature was estimated by chemical geothermometry and validated by fluid–mineral equilibria calculations. The feasibility of different geothermometers was verified, indicating that quartz geothermometers were more suitable for the geothermal system and yielded reservoir temperatures of 60–80°C. Finally, a conceptual hydrogeological model of the geothermal field was proposed: thermal groundwater was derived from regional flow system with high recharge areas, deep circulation depth and slow flow velocities, confirmed by its depleted stable isotopic contents, high chloride and TDS concentrations and long residence time. The improved understanding of this geothermal system is fundamental for the better management of this karst geothermal resource.

Isotopic and geochemical characterization of fossil brines of the Cambrian Mt. Simon Sandstone and Ironton–Galesville Formation from the Illinois Basin, USA

Geochemical and isotopic characteristics of deep-seated saline groundwater provide valuable insight into the origin and evolving composition, water–rock interaction, and mixing potential of fossil brines. Such information may yield insight into intra- and interbasinal brine movement and relationships between brine evolution and regional groundwater flow systems. This investigation reports on the δ18O and δD composition and activity values, 87Sr/86Sr ratios and Sr concentrations, and major ion concentrations of the Cambrian-hosted brines of the Mt. Simon Sandstone and Ironton–Galesville Formation and discusses the evolution of these brines as they relate to other intracontinental brines. Brines in the Illinois Basin are dominated by Na–Ca–Cl-type chemistry. The Mt. Simon and overlying Ironton–Galesville brines exhibit total dissolved solids concentrations of ∼195,000mg/L and ∼66,270mg/L, respectively. The δD of brine composition of the Mt. Simon ranges from −34‰ to −22‰ (V-SMOW), and the Ironton–Galesville is ∼−53.2‰ (V-SMOW). The δ18O composition of the Mt. Simon brine ranges from −5.0‰ to −2.8‰ (V-SMOW), and the Ironton–Galesville brine is ∼−6.9‰ (V-SMOW). The 87Sr/86Sr values in the Mt. Simon brine range from 0.7110 to 0.7116. The less radiogenic Ironton–Galesville brine has an average 87Sr/86Sr value of 0.7107. Evaluation of δ18O and δD composition and activities and 87Sr/86Sr ratios suggests that the Mt. Simon brine is likely connate seawater and recirculating deep-seated brines that have been diluted with meteoric water and influenced by the dissolution of evaporites with a minimal halite contribution based on Cl/Br ratios. The Ironton–Galesville brine is also likely originally connate seawater that mixed with other brines and meteoric waters, including possibly Pleistocene glacial recharge. The Ca-excess vs. Na-deficiency comparison with the Basinal Fluid Line suggests the Mt. Simon and Ironton–Galesville brines have been influenced by the effects of albitization and plot very close to the Basinal Fluid Line. These Cambrian-hosted brines appear to have a different albitization history than other regional basin brines and a strong component of seawater. The Ironton–Galesville brine appears more geochemically associated with other Illinois Basin brines than the Mt. Simon brine which appears more geochemically conservative. Comparisons with other extrabasinal North American brines suggest that the Michigan basin brines are geochemically most similar to the Mt. Simon brines with the exception of the influence from carbonates in the Michigan Basin. Analyses of 87Sr/86Sr values in the Mt. Simon brine suggest that brine Sr has isotopically equilibrated with clay minerals in the Lower Mt. Simon and underlying bedrock formations and not with whole rock suggesting the influence of recirculating brines from the crystalline basement. Overall, the geochemistry of these Cambrian-hosted brines suggests an evolution from original seawater-like compositions. This investigation shows that intracratonic basins do not behave as closed systems but can be strongly affected by water–rock interaction and regional groundwater flow systems that circulate deep crystalline basement brines and brines from nearby basins.

Hydrologic framework of the Santa Clara Valley, California

The hydrologic framework of the Santa Clara Valley in northern California was redefined on the basis of new data and a new hydrologic model. The regional groundwater flow systems can be subdivided into upper-aquifer and lower-aquifer systems that form a convergent flow system within a basin bounded by mountains and hills on three sides and discharge to pumping wells and the southern San Francisco Bay. Faults also control the flow of groundwater within the Santa Clara Valley and subdivide the aquifer system into three subregions. After decades of development and groundwater depletion that resulted in substantial land subsidence, Santa Clara Valley Water District (SCVWD) and the local water purveyors have refilled the basin through conservation and importation of water for direct use and artificial recharge. The natural flow system has been altered by extensive development with flow paths toward major well fields. Climate has not only affected the cycles of sedimentation during the glacial periods over the past million years, but interannual to interdecadal climate cycles also have affected the supply and demand components of the natural and anthropogenic inflows and outflows of water in the valley. Streamflow has been affected by development of the aquifer system and regulated flow from reservoirs, as well as conjunctive use of groundwater and surface water. Interaquifer flow through water-supply wells screened across multiple aquifers is an important component to the flow of groundwater and recapture of artificial recharge in the Santa Clara Valley. Wellbore flow and depth-dependent chemical and isotopic data indicate that flow into wells from multiple aquifers, as well as capture of artificial recharge by pumping of water-supply wells, predominantly is occurring in the upper 500 ft (152 m) of the aquifer system. Artificial recharge represents about one-half of the inflow of water into the valley for the period 1970–1999. Most subsidence is occurring below 250 ft (76 m), and most pumpage occurs within the upper-aquifer system between 300 and 650 ft (between 91 and 198 m) below land surface. Overall, the natural quality of most groundwater in the Santa Clara Valley is good. Isotopic data indicate that artificial recharge is occurring throughout the shallower parts of the upper-aquifer system and that recent recharge (less than 50 yr old) occurs throughout most of the basin in the upper-aquifer system, but many of the wells in the center of the basin with deeper well screens do not contain tritium and recent recharge. Age dates indicate that the groundwater in the upper-aquifer system generally is less than 2000 yr old, and groundwater in the lower-aquifer system generally ranges from 16,700 to 39,900 yr old. Depth-dependent sampling indicates that wellbores are the main path for vertical flow between aquifer layers. Isotopic data indicate as much as 60% of water pumped from production wells originated as artificial recharge. Shallow aquifers not only contain more recent recharge but may be more susceptible to anthropogenic and natural contamination, as evidenced by trace occurrences of iron, nitrate, and volatile organic compounds (VOCs) in selected water-supply wells. Water-resource management issues are centered on sustaining a reliable and good-quality source of water to the residents and industries of the valley. While the basin has been refilled, increased demand owing to growth and droughts could result in renewed storage depletion and the related potential adverse effects of land subsidence and seawater intrusion. The new hydrologic model demonstrates the importance of the aquifer layering, faults, and stream channels in relation to groundwater flow and infiltration of recharge. This model provides a means to analyze water resource issues because it separates the supply and demand components of the inflows and outflows.

Recharge contribution to the Guarani Aquifer System estimated from the water balance method in a representative watershed.

The contribution of recharge to regional groundwater flow systems is essential information required to establish sustainable water resources management. The objective of this work was to determine the groundwater outflow in the Ribeirão da Onça Basin using a water balance model of the saturated soil zone. The basin is located in the outcrop region of the Guarani Aquifer System (GAS). The water balance method involved the determination of direct recharge values, groundwater storage variation and base flow. The direct recharge was determined by the water table fluctuation method (WTF). The base flow was calculated by the hydrograph separation method, which was generated by a rain-flow model supported by biweekly streamflow measurements in the control section. Undisturbed soil samples were collected at depths corresponding to the variation zone of the groundwater level to determine the specific yield of the soil (drainable porosity). Water balances were performed in the saturated zone for the hydrological years from February 2004 to January 2007. The direct recharge ranged from 14.0% to 38.0%, and groundwater outflow from 0.4% to 2.4% of the respective rainfall during the same period.

Hydrogeochemical characterization of groundwater flow systems in the discharge area of a river basin

Summary The lowest reaches of a large-scale basin could be the discharge area of local, intermediate and regional groundwater flow systems with different travel distances and travel times. However, little research has been devoted to identify the flow systems in such a site. In this study, 44 groundwater samples were collected from wells with different depths in the discharge area of the Dosit River Watershed in the Ordos Cretaceous Basin. Using the major ions and pH as the input, hierarchical cluster analysis was conducted, which leads to five clusters (from C1 to C5) with distinct geochemical compositions. The relationship between δ D and δ 18 O shows that clusters C1 and C2 were recharged during the cold time while clusters C3, C4 and C5 were recharged recently. According to the Gibbs scheme, groundwater samples in all clusters except for C5 were controlled by rock–water interaction. Both hydraulic and geochemical perspectives were considered to identify the mechanisms of groundwater evolution. Both hydrochemistry and isotopes versus depth show a three-part structure with boundaries around depths of 200 m and 600–750 m, which were assumed to be associated with the circulation depths of local and intermediate flow systems. After excluding C4 with highly variable water-types, three geochemical indicators (Cl − , SO 4 2− , and the slope of (Ca 2+ + Mg 2+ ) − (SO 4 2− + HCO 3 − ) versus (Na + − Cl − ) imply that the processes of water–rock interaction for clusters C1, C2 and C3 include dissolution of halite and gypsum, weathering of feldspar, and ion-exchange. Moreover, it was found that C3 from local flow system, C1 from intermediate flow system, and C2 from regional flow system has increasingly higher concentrations of Cl − and lower values of Chloro-Alkaline index, which indicate increasingly higher degrees of dissolution and ion-exchange. This study not only reveals the mechanisms of groundwater evolution in the study area, but also provides a method to identify nested flow systems using hydrochemistry and isotopes.

Numerical analysis of groundwater flow and potential in parts of a crystalline aquifer system in Northern Ghana

The groundwater flow system in a crystalline aquifer system in parts of Northern Ghana was simulated and calibrated under steady-state conditions. The objective was to estimate the regional distribution of a key aquifer hydraulic parameter (the hydraulic conductivity) and recharge and also to predict possible effects of different abstraction and groundwater recharge scenarios on the sustainability of groundwater resources in the area. The study finds that the hydraulic conductivity field is quite homogeneous and has values ranging between 1.70 and 2.24 m/day. There is an apparent dominance of regional groundwater flow systems compared to local flow systems. This is probably attributed to the homogeneity in the hydraulic conductivity field and the absence of complex local relief. Estimated groundwater recharge ranges between 0.036 and 0.164 m/yr representing 3.6 and 16.4 % of the local annual precipitation, respectively. Substantial subsurface inflows and outflows have also been simulated through general head boundaries. The simulation suggests that under the current conditions of groundwater recharge estimated at calibration, the system can sustain increment in groundwater abstraction by up to 50 % without any significant changes in the groundwater flow geometry and drawdowns in the hydraulic heads. However, significant drawdowns will be expected in the wake of 100 % increment in groundwater abstraction and a reduction in recharge by 10 % during the 20-year period. Under such conditions, the flow geometry will significantly be altered and a reversal in groundwater flow will be observed.

Integrating Hydrogeochemical and Isotope Data in Studying Regional Groundwater flow Systems in the Great Hungarian Plain

Environmental isotopes (δ 18O, δD, δ 13C, 14C, 87Sr/86Sr) combined with hydrogeochemical data have been used in studying regional groundwater flow systems in the Great Hungarian Plain part of the Pannonian Basin. Oxygen and deuterium isotope data show groundwater is of meteoric origin, with isotopic signatures indicative of petroleum producing units in the deeper part of the basin. Based on the carbon isotopes analysed on dissolved inorganic carbon, the groundwater residence times vary from a few thousand to tens of thousands of years. Strontium isotopic signatures show enrichment where carbonate dissolution is indicated by increasing bicarbonate values in Upper Miocene aquifers.

Investigating summer flow paths in a Dutch agricultural field using high frequency direct measurements

The search for management strategies to cope with projected water scarcity and water quality deterioration calls for a better understanding of the complex interaction between groundwater and surface water in agricultural catchments. We separately measured flow routes to tile drains and an agricultural ditch in a deep polder in the coastal region of the Netherlands, characterized by exfiltration of brackish regional groundwater flow and intake of diverted river water for irrigation and water quality improvement purposes. We simultaneously measured discharge, electrical conductivity and temperature of these separate flow routes at hourly frequencies, disclosing the complex and time-varying patterns and origins of tile drain and ditch exfiltration. Tile drainage could be characterized as a shallow flow system, showing a non-linear response to groundwater level changes. Tile drainage was fed primarily by meteoric water, but still transported the majority (80%) of groundwater-derived salt to surface water. In contrast, deep brackish groundwater exfiltrating directly in the ditch responded linearly to groundwater level variations and is part of a regional groundwater flow system. We could explain the observed salinity of exfiltrating drain and ditch water from the interaction between the fast-responding pressure distribution in the subsurface that determined groundwater flow paths (wave celerity), and the slow-responding groundwater salinity distribution (water velocity). We found water demand for maintaining water levels and diluting salinity through flushing to greatly exceed the actual sprinkling demand. Counterintuitively, flushing demand was found to be largest during precipitation events, suggesting the possibility of water savings by operational flushing control.

Condensation-corrosion speleogenesis above a carbonate-saturated aquifer: Devils Hole Ridge, Nevada

The Devils Hole Ridge, a small block of Paleozoic carbonate rocks surrounded by the Amargosa Desert in southern Nevada, is located at the discharge end of the Ash Meadows regional carbonate groundwater flow system. The massif hosts the famous Devils Hole, a near-vertical extensional fracture which intersects slightly thermal groundwater (33.6°C) and whose walls are coated below the water table by thick mammillary calcite. The latter was deposited continuously over the last ca. 600kyr, indicating that the water underneath Devils Hole Ridge was supersaturated with respect to calcite during this time span. Rocks, located more than 9m above the present-day water table, remained in the unsaturated (vadose) zone. Continuous, long-term presence of thermal water and the extensional tectonic setting, creating underground thermal lakes in open fractures, is associated with intense dissolution above the water table. Condensation corrosion is responsible for modifications of the morphology of the subaerial parts of the tectonic caves. We also describe, for the first time, the Devils Hole Prospect Cave, which was created almost entirely by condensation corrosion. Caves and cavities in the Devils Hole Ridge are an interesting example of hypogene speleogenesis, by condensation corrosion, operating above an aquifer which was demonstrably supersaturated with respect to calcite for hundreds of thousands of years.

A multiple-tracer approach to understanding regional groundwater flow in the Snake Valley area of the eastern Great Basin, USA

Groundwater in Snake Valley and surrounding basins in the eastern Great Basin province of the western United States is being targeted for large-scale groundwater extraction and export. Concern about declining groundwater levels and spring flows in western Utah as a result of the proposed groundwater withdrawals has led to efforts that have improved the understanding of this regional groundwater flow system. In this study, environmental tracers (δ2H, δ18O, 3H, 14C, 3He, 4He, 20Ne, 40Ar, 84Kr, and 129Xe) and major ions from 142 sites were evaluated to investigate groundwater recharge and flow-path characteristics. With few exceptions, δ2H and δ18O show that most valley groundwater has similar ratios to mountain springs, indicating recharge is dominated by relatively high-altitude precipitation. The spatial distribution of 3H, terrigenic helium (4Heterr), and 3H/3He ages shows that modern groundwater (<60yr) in valley aquifers is found only in the western third of the study area. Pleistocene and late-Holocene groundwater is found in the eastern parts of the study area. The age of Pleistocene groundwater is supported by minimum adjusted radiocarbon ages of up to 32ka. Noble gas recharge temperatures (NGTs) are generally 1–11°C in Snake and southern Spring Valleys and >11°C to the east of Snake Valley and indicate a hydraulic discontinuity between Snake and Tule Valleys across the northern Confusion Range. The combination of NGTs and 4Heterr shows that the majority of Snake Valley groundwater discharges as springs, evapotranspiration, and well withdrawals within Snake Valley rather than continuing northeastward to discharge at either Fish Springs or the Great Salt Lake Playa. The refined understanding of groundwater recharge and flow paths acquired from this multi-tracer investigation has broad implications for interbasin subsurface flow estimates and future groundwater development.

Seismic and structural geology constraints to the selection of CO2 storage sites—The case of the onshore Lusitanian basin, Portugal

Abstract The Lusitanian sedimentary basin, in Portugal, has a complex tectonic history and a seismic activity determined by its proximity to the Eurasian–Nubian tectonic plate boundary. Seismic activity and geological structure impose serious constraints to the selection of CO 2 storage sites. This article focuses on the constraints imposed by active seismicity, geological structure and, as a direct consequence of the latter, by the hydrogeology and geothermal framework on the identification of onshore CO 2 storage sites in deep saline aquifers of the Lusitanian basin (central and north sectors). Several active faults and areas of higher seismic hazard have been defined, favouring the selection of storage sites in the northern part of the basin. The halokinetic tectonics, responsible for emplacement of salt domes, constrains the regional groundwater flow system, and suggests that it is unreasonable to consider post-salt reservoirs. In most of the Lusitanian basin the pre-salt Silves Formation is the only reservoir worth considering. Four areas have been selected where the reservoir is at adequate depth, but given the other criteria for site selection, the area designated as S. Mamede is the most interesting one for CO 2 injection.

Partitioning a regional groundwater flow system into shallow local and deep regional flow compartments

Key Points This work studies the groundwater flow structure as a function of recharge in 3D A two‐compartment model quantifies local and regional transfers Partitioning of recharge and volumes associated to both compartments are studied

広域地下水流動の実態を踏まえた熊本地域における地下水の持続的利用を目指した新たな取り組み

地下水をその水道水源として利用している熊本地域では，地下水資源の持続的な利用のための様々な取り組みを実施してきている。過去30年以上にわたる地域自治体による調査研究と観測により火砕流帯水層の広域地下水流動の詳細が把握されると共にその長期低減傾向が把握され，それに対する対応策である越境地下水管理としての転作水田水張り事業が実施され良好な成果が確認されつつある。これを踏まえ熊本県においては，これまでの地下水保全条例を改定して新たに地下水揚水許可制が導入されそれを運営するための新たな組織が設立された。この地下水条例は，特段の地下水災害は存在していない地域であるにも拘らず地下水資源の持続的利用のための保全措置として施行された全国で初めての採取規制条例であることに特徴を持つ。

Knowledge, transparency, and refutability in groundwater models, an example from the Death Valley regional groundwater flow system

This work demonstrates how available knowledge can be used to build more transparent and refutable computer models of groundwater systems. The Death Valley regional groundwater flow system, which surrounds a proposed site for a high level nuclear waste repository of the United States of America, and the Nevada National Security Site (NNSS), where nuclear weapons were tested, is used to explore model adequacy, identify parameters important to (and informed by) observations, and identify existing old and potential new observations important to predictions. Model development is pursued using a set of fundamental questions addressed with carefully designed metrics. Critical methods include using a hydrogeologic model, managing model nonlinearity by designing models that are robust while maintaining realism, using error-based weighting to combine disparate types of data, and identifying important and unimportant parameters and observations and optimizing parameter values with computationally frugal schemes. The frugal schemes employed in this study require relatively few (10–1000s), parallelizable model runs. This is beneficial because models able to approximate the complex site geology defensibly tend to have high computational cost. The issue of model defensibility is particularly important given the contentious political issues involved.

The application of isotope and chemical analyses in managing transboundary groundwater resources

Managing transboundary groundwater resources requires accurate and detailed knowledge of aquifers and groundwater bodies. The Pannonian Basin is the largest intracontinental basin in Europe with a continuous succession of more than 7km of Miocene to Quaternary sediments and with an average geothermal gradient of about 5°C/100m. Geographically the Pannonian basin overlaps eight countries (Hungary, Romania, Serbia, Croatia, Slovenia, Austria, Slovakia and Ukraine), so the issue of transboundary cold and thermal water resources is regionally very important. The T-JAM bilateral Hungarian–Slovenian (HU–SLO) project is the first to apply modern isotopic and chemical analyses in the characterization and correlation of a number of shared groundwater resources in the Mura-Zala Sub-basin of the Pannonian. The aims of this work were the identification of groundwater flow paths, the delineation of transboundary aquifers based on thermal and cold groundwater geochemical and isotope properties in the Mura-Zala Basin, and providing input to calibrate a hydraulic numerical model. Following a common groundwater sampling campaign, 24 cold and thermal groundwater samples from seven aquifers were collected for chemical, isotope, gas and noble gas analyses. Chemical analyses, and D, O and C isotopes were used to correlate cross border aquifers. A regional groundwater flow is hydrogeologically possible in some aquifers in the Mura-Zala Basin, and has been confirmed by hydrogeochemistry. The Újfalu (HU) and Mura (SLO) Formations are a part of the active regional thermal groundwater flow system, probably hydraulically separated from the shallower flow system of the Ptuj-Grad (SLO), Zagyva and Somló-Tihany (HU) Formations. The thermal water is of meteoric origin, reductive and alkaline. The predominant water type in the Quaternary and Pliocene aquifers is Ca–Mg–HCO3, changing to Na–HCO3 in the main Pannonian geothermal aquifer, and Na–Cl brine in deeper and older Miocene aquifers. Total dissolved solids and Na content generally increase with depth. Deuterium is in the range −87‰ to −75‰, 18O from −11.9‰ to −10.4‰, while 14C values are less than 6.1pmC in the samples of the active regional thermal groundwater flow system. These and results of noble gas analyses indicate recharge during the Pleistocene interglacial period with temperatures around 6–7°C. Regional thermal water resources are limited and environmental isotopes can be used as an early warning in the management of thermal water.

On Modeling Weak Sinks in MODPATH

Regional groundwater flow systems often contain both strong sinks and weak sinks. A strong sink extracts water from the entire aquifer depth, while a weak sink lets some water pass underneath or over the actual sink. The numerical groundwater flow model MODFLOW may allow a sink cell to act as a strong or weak sink, hence extracting all water that enters the cell or allowing some of that water to pass. A physical strong sink can be modeled by either a strong sink cell or a weak sink cell, with the latter generally occurring in low-resolution models. Likewise, a physical weak sink may also be represented by either type of sink cell. The representation of weak sinks in the particle tracing code MODPATH is more equivocal than in MODFLOW. With the appropriate parameterization of MODPATH, particle traces and their associated travel times to weak sink streams can be modeled with adequate accuracy, even in single layer models. Weak sink well cells, on the other hand, require special measures as proposed in the literature to generate correct particle traces and individual travel times and hence capture zones. We found that the transit time distributions for well water generally do not require special measures provided aquifer properties are locally homogeneous and the well draws water from the entire aquifer depth, an important observation for determining the response of a well to non-point contaminant inputs.

Sensitivity to Formation Porosity of Contaminant Transport from Nevada Test Site to Yucca Mountain

This study quantified the sensitivity of advective contaminant arrival time to the porosity of hydrogeologic units (HGUs) for groundwater transport from the Nevada Test Site (NTS) to the Yucca Mountain (YM) area in the United States. Advective arrival time of contaminants associated with underground nuclear detonations was obtained by using particle tracking on the basis of flow velocities from the Death Valley Regional Groundwater Flow System (DVRFS) model and porosity information for the HGUs along the flowpaths. The objectives were to (1) determine which HGU’s porosity is influential in contaminant advective arrival time from the NTS to the YM, and (2) apportion uncertainties in contaminant advective arrival time to the uncertainty contributions from individual HGU porosity. Over 90% of the uncertainty in advective transport arrival time from the NTS to YM could be described by uncertainties in porosity values of two of the 27 HGUs present in the DVRFS model. The study was significant for optimizing re...

Distribution of 36Cl in the Yoro River Basin, Central Japan, and Its Relation to the Residence Time of the Regional Groundwater Flow System

This study investigates the potential of 36Cl in tracing young groundwater with residence times of up to ~50 years. Groundwater samples were obtained from 16 irrigation wells in paddy fields located within an upland–lowland system in the Yoro River basin, Central Japan. The 36Cl/Cl ratios were in the range of 17 to 362 × 10−15. Among the samples with higher Cl− concentrations (&gt;10 mg/L), two samples showed high nitrate concentrations as well (&gt;30 mg/L). Except for these samples, the distribution of 36Cl in groundwater was essentially consistent with previous tritium concentration data measured in 1982 and 1994, considering the time that has elapsed since these earlier measurements were performed. 36Cl/Cl values were less than 30 × 10−15 in lowland areas, with higher values in and around upland areas. The results indicate longer residence times in the regional groundwater flow system (&gt;50 years) than those estimated in previous studies, especially in the area west of the Yoro River. The results demonstrate the ability of 36Cl to trace young groundwater flow, particularly because high values of bomb-derived 36Cl/Cl are easily discriminated from pre-bomb water with low 36Cl/Cl values. Because of its very long half-life (3.01 × 105 years), 36Cl remains even after tritium is no longer available.

Environmental isotopic and hydrochemical characteristics of groundwater systems in Daying and Qicun geothermal fields, Xinzhou Basin, Shanxi, China

AbstractThe conceptual hydrogeological model of the low to medium temperature Daying and Qicun geothermal fields has been proposed, based on hydrochemical characteristics and isotopic compositions. The two geothermal fields are located in the Xinzhou basin of Shanxi, China and exhibit similarities in their broad‐scale flow patterns. Geothermal water is derived from the regional groundwater flow system of the basin and is characterized by Cl·SO4‐Na type. Thermal water is hydrochemically distinct from cold groundwater having higher total dissolved solids (TDS) (&gt;0·8 g/l) and Sr contents, but relatively low Ca, Mg and HCO3 contents. Most shallow groundwater belongs to local flow systems which are subject to evaporation and mixing with irrigation returns. The groundwater residence times estimated by tritium and 14C activities indicate that deep non‐thermal groundwater (130–160 m) in the Daying region range from modern (post‐1950s) in the piedmont area to more than 9·4 ka BP (Before Present) in the downriver area and imply that this water belong to an intermediate flow system. Thermal water in the two geothermal fields contains no detectable active 14C, indicating long residence times (&gt;50 ka), consistent with this water being part of a large regional flow system. The mean recharge elevation estimated by using the obtained relationship Altitude (m) = − 23·8 × δ2H (‰ ) − 121·3, is 1980 and 1880 m for the Daying and Qicun geothermal fields, respectively. The annual infiltration rates in the Daying and Qicun geothermal fields can be estimated to be 9029 × 103 and 4107 × 103 m3/a, respectively. The variable 86Sr/87Sr values in the thermal and non‐thermal groundwater in the two fields reflect different lithologies encountered along the flow path(s) and possibly different extents of water‐rock interaction. Based on the analysis of groundwater flow systems in the two geothermal fields, hydrogeochemical inverse modelling was performed to indicate the possible water‐rock interaction processes that occur under different scenarios. Copyright © 2010 John Wiley &amp; Sons, Ltd.