Signatures Of Groundwater Research Articles

Hydrograph separation using stable isotopes: Review and evaluation

The separation of storm hydrographs using stable isotope tracers dates back to the late 1960s. These studies ushered in a paradigm shift in how hydrologists conceptualized runoff generation as most showed a large preponderance of pre-event water in the storm hydrograph, even at peak flow. This forced a fundamental re-examination of the processes of water delivery to streams during rainfall and snowmelt events. Whilst the simplicity of the two-component hydrograph separation was a powerful tool for showing the importance of stored water effusion, the assumptions implicit in the two-component model have now become limiting for further advancement of the approach. Here we review the use of stable isotopes for hydrograph separation with particular reference to studies completed since the last comprehensive review of the subject in 1994. We review critically the contributions to new field knowledge gained by isotope hydrograph separation applications. We focus specifically on the current issues regarding the limitations of the two-component approach. We examine the role of soil water as a contributor to channel stormflow and the issues raised by differences in the soil water and groundwater signatures at the watershed scale. Finally, we offer ideas on how to overcome the limitations of the two-component approach and present a vision for future directions for isotope based hydrograph separation. These future directions are focused on high frequency analysis of rainfall-runoff structures and dual isotope analysis of catchment end-members including comparison of lysimeter-based soil water sampling of mobile soil water versus cryogenic and vapor-based analysis of tightly bound water.

Hydrochemical characteristics of coastal aquifers of Kadaladi, Ramanathapuram District, Tamilnadu, India

Geochemical signatures of groundwater in the coastal aquifers of Kadaladi block of Ramanathapuram District, Tamilnadu, India were used to identify the chemical processes that control hydrochemistry. The parameters such as pH, EC, TDS and major ion concentrations Na, K, Ca, Mg, Cl, HCO3, SO4, PO4 and NO3 of the groundwater were analyzed. Abundances of these ions are in the following order Na > Ca > Mg > K and Cl > HCO3 > SO4 > NO3 > PO4. Na–Cl is the dominant hydrochemical facies of the study area. Interpretation of the hydrochemical data suggests that hydrochemistry of the study area is controlled by mixing of fresh water with relict saline water, ion-exchange processes, silicate weathering and evaporation are responsible for the groundwater chemistry of the study area. Above statement is further supported by Gibbs plot where most of the samples fall within the evaporation zone. Good quality groundwater is restricted to coastal sand dunes running parallel to the coast and it is important to conserve these dunes.

Strontium Isotopic Signature of Groundwater from Adamantina Aquifer, Bauru Basin, Brazil

Using 87Sr/86Sr ratios and the geochemistry of groundwater we were able to identify different hydrochemical facies in the Adamantina aquifer, Bauru Basin (Brazil). Samples from shallow wells show Cl-NO3-Ca-Mg water with low pH due to natural and anthropogenic recharge. The 87Sr/86Sr ratios are greatest in the shallower parts of the aquifer (0.7134) and decrease with increasing well screen interval depth. The nitrate concentration gradually decreases with depth and aquifer pH increases, HCO3 predominates as the main anion, and the groundwater becomes saturated with respect to calcite, with average 87Sr/86Sr ratios of 0.708694 at depth.

Geological Control upon Groundwater Flow and Major Ion Chemistry with Influence on Basin Management in a Coastal Aquifer, South Australia

Estimation of natural recharge and potential for seawater intrusion are critical considerations for management of coastal freshwater aquifers. We show hydrochemical signatures of groundwater to identify the influence of geological control on chemical processes in a coastal groundwater system. We used dominant hydrochemical facies, salinity and magnesium ions to determine two main groundwater flow paths with different origins and ages. Mixing of groundwater with different origins and ages results in unreliable recharge estimates using chlorofluorocarbon (CFC) and chloride mass balance (CMB) methods, thus limiting available methods for recharge assessment. Interpretation of hydrochemical data suggests that calcium carbonate dissolution, ion exchange processes and mixing with sea aerosol in coastal zones are the main influencing factors on groundwater chemistry. Restricted groundwater flows due to occurrence of a basement high at the southern side of the basin boundary influence the distance to the toe of the saline wedge. Thus, knowledge of geological control over groundwater systems forms an important part of characterising basins and contributes toward effective management of groundwater resources.

A study on groundwater geochemistry and water quality in layered aquifers system of Pondicherry region, southeast India

Geochemical signatures of groundwater in the Pondicherry region, south India, were determined. The coastal aquifers are fragile and this situation becomes more intense in layered aquifer systems like that of the Pondicherry region. In this region, groundwater occurs in alluvium, Lower Cuddalore, Upper Cuddalore, Tertiary, Cretaceous and mixed aquifers. The geochemical signature of groundwater in these formations was studied by collecting 93 groundwater samples. The collected samples from specific formations were analysed for physical parameters, such as electrical conductivity (EC), pH and major ion concentrations, such as Ca, Mg, Na, K, Cl, HCO3, PO4 and SO4. The results of the analysis were interpreted with geology; the ionic concentrations in the groundwater vary spatially and temporally. The abundance of these ions are in the following order: Na > Ca > Mg > K = Cl > HCO3 > SO4. Interpretation of analytical data shows that Ca–Na and Cl–SO4–HCO3 is the dominant facies in all the formations. Groundwater in the area is generally hard and fresh-brackish in most of the formations and brackish in nature in alluvium formation. The sodium absorption ratio shows that most of the samples are grouped under excellent category to good category in all the formations. The residual sodium carbonate also are in good category in all the formations. Chloro-alkaline indices reveal that the majority of samples show negative values in all the litho units indicating the exchange of Na and K in groundwater with Mg or Ca in rock. Scholler classification of water indicates that longer residence time of water with more prominent base exchange. High EC and TDS values in certain locations of alluvial, Upper Cuddalore and Cretaceous formations prove to be unsuitable for drinking and irrigation purposes.

The effect of tidal fluctuation on ground water quality in coastal aquifer of Saijo plain, Ehime prefecture, Japan

This study is an effort to trace the implication of tidal fluctuation on coastal groundwater quality for different aquifers in case of Saijo plain, western Japan, through major ion, heavy metal and isotopic chemistry as well as to estimate aquifer parameters by tidal response method. Time series analysis for chemical characteristics depicts that tidal fluctuation at diurnal basis significantly affects ionic signature of groundwater along with piezometric level for unconfined aquifer whereas effect is less prominent for confined aquifer. Different plots (e.g. 87Sr/ 86Sr vs 1/Sr and BEX vs Cl) were drawn in order to deduce mechanisms responsible for water quality change with tidal phase and it was found that cations exchange and local sea water–fresh water (SW–FW) mixing along with oxidation–reduction are likely to be main processes responsible for water quality changes. Using tide aquifer interaction technique, calculated hydraulic conductivities for different monitoring sites were 0.01 and 2.8 × 10 − 6 m/s which appropriately address geological properties of aquifers, and thus it can be concluded that tide aquifer technique is a reliable technique to estimate aquifer properties.

Identification of probable groundwater paths in the Amargosa Desert vicinity

In this study, the hydrogeochemical program PHREEQC was used to determine the chemical speciation and mineral saturation indices (SIs) of groundwater in the vicinity of the proposed high-level nuclear waste repository at Yucca Mountain, Nevada (USA). In turn, these data were used to interpret the origin and recharge mode of groundwater, to elucidate the mechanisms of flow and transport, and to determine potential sources of groundwater contamination. PHREEQC was run to determine aqueous dissolved species and minerals that would be in equilibrium with the study area’s groundwater. Selected major ions, associated SI, F− and Ca/Na ion exchange were then examined using the multivariate statistical methods of principal component factor analysis and k-means cluster analysis. Analysis of dissolved ion concentrations, SIs, and Ca/Na ion exchange allows simultaneous consideration of arithmetic (raw concentrations) and logarithmic (SI, ion exchange) variables that describe the hydrochemical system and, therefore, can provide further insight into the system’s behavior. The analysis indicates that the dominant processes and reactions responsible for the hydrochemical evolution in the system are (1) evaporative concentration prior to infiltration, (2) carbonate equilibrium, (3) silicate weathering reactions, (4) limited mixing with saline water, (5) dissolution/precipitation of calcite, dolomite and fluorite, and (6) ion exchange. Principal component factor analysis and k-means cluster analysis of factor scores allow the reduction of dimensions describing the system and the identification of hydrogeochemical facies and the processes that defined and govern their evolution. Statistical analysis results indicate that the northern, west face and southern Yucca Mountain groundwater is fresh water with low concentrations of Ca2+, Mg2+, Cl−, Ca2+/(Na+)2, and CaF2. The Fortymile Wash groundwater is dilute. The carbonate signature is shown in the Ash Meadows and Death Valley waters with high fluorite SI. Finally, the Crater Flat, Stripped Hills, and Skeleton Hills are dominated by Ca/Na ion exchange, Mg and Ca. The hydrochemical and statistical analyses showed three main groundwater signatures or hydrochemical processes indicating groundwater evolution, potential flowpaths, and recharge areas. The flowpaths are the trace of the Amargosa River, the trace of Fortymile Wash, and its convergence with the Amargosa River. This appears to represent not just a groundwater flow path, but traces of surface runoff infiltration as well.

Aquifers Interaction in the Southwestern Foot of Mt. Fuji, Japan, Examined through Hydrochemistry and Statistical Analyses

Major ion chemistry, oxygen isotope and multivariate statistical method were used to investigate aquifers interaction in the southwestern foot of Mt. Fuji, the largest Quaternary stratovolcano in Japan. Groundwater samples were taken from different aquifers which are in descending order: the superficial aquifer, aquifers residing in the New Fuji Lava and the Old Fuji Aquifer. The geochemical signatures of groundwaters, notably the molar Na/Cl and Na/Ca ratios, oxygen stable isotope and the nitrate contents evolution, in conjunction with the hierarchical cluster analysis allowed to highlight three groundwater systems differing by their hydrochemical facies and residence time: 1) The shallow and highly polluted groundwaters of the superficial aquifer, 2) Groundwaters of the New Fuji Lava moderately mineralized and polluted, 3) The non-polluted groundwaters of the Old Fuji Aquifer. Waters of these systems are interacting. In fact, nitrate contamination, in provenance from the superficial aquifer, was detected in the New Fuji Lava layers and the deep groundwaters of the Old Fuji. Furthermore, many samples taken from the Old Fuji Aquifer were characterized by a relatively enriched δ18O. These results prove that groundwaters of the New Fuji layers could be mixed with groundwaters of the overlaying superficial aquifer and that these groundwaters, supposed to flow only horizontally, can flow vertically through the cracks, causing the mixing of deep and old groundwater of the Old Fuji with groundwaters recently recharged and polluted.

Strontium isotope geochemistry of groundwater affected by human activities in Nandong underground river system, China

Abstract The Nandong Underground River System (NURS) is located in a typical karst area dominated by agriculture in SE Yunnan Province, China. Groundwater plays an important role in the social and economical development in the area. The effects of human activities (agriculture and sewage effluents) on the Sr isotope geochemistry were investigated in the NURS. Seventy-two representative groundwater samples, which were collected from different aquifers (calcite and dolomite), under varying land-use types, both in summer and winter, showed significant spatial differences and slight seasonal variations in Sr concentrations and 87Sr/86Sr ratios. Agricultural fertilizers and sewage effluents significantly modified the natural 87Sr/86Sr ratios signature of groundwater that was otherwise dominated by water–rock interaction. Three major sources of Sr could be distinguished by 87Sr/86Sr ratios and Sr concentrations in karst groundwater. Two sources of Sr are the Triassic calcite and dolomite aquifers, where waters have low Sr concentrations (0.1–0.2 mg/L) and low 87Sr/86Sr ratios (0.7075–0.7080 and 0.7080–0.7100, respectively); the third source is anthropogenic Sr from agricultural fertilizers and sewage effluents with waters affected having radiogenic 87Sr/86Sr ratios (0.7080–0.8352 for agricultural fertilizers and 0.7080–0.7200 for sewage effluents, respectively), with higher Sr concentrations (0.24–0.51 mg/L). Due to the overlapping 87Sr/86Sr ratios, it is difficult to distinguish the sources of Sr in groundwater samples contaminated by agricultural fertilizers or sewage effluents based only on their 87Sr/86Sr ratios. However, 87Sr/86Sr ratios do provide key information for natural and anthropogenic sources in karst groundwater.

Identification of different groundwater flowpaths within volcanic aquifers using natural tracers for the evaluation of the influence of lava flows morphology (Argnat basin, Chaîne des Puys, France)

Hydrochemical and stable isotopic (2H, 18O) data were used to characterize the groundwater flow and major chemical features within a complex fractured volcanic aquifer system, the Argnat basin, which is located in the Chaine des Puys (French Massif Central). From 10 sampling points, the study of the transfer into the saturated zone from upstream to downstream, given the geological context and topography, allows to estimate the role of supply from high and low altitudes to the recharge processes. This work shows the existence of different types of supply between pahoehoe and a’a flows. Therefore, the morphology of volcanic flows impacts the chemical and isotopic signatures of groundwater, enhancing or reducing the influence of the unsaturated zone on the pathways of infiltrated water. Pahoehoe flows imply horizontal water flows of low discharge at the top of the lava whereas a’a flows seems to be much more heterogeneous and locally able to promote the existence of perched water bodies and further vertical circulations. Taking into account these two types of behaviour, a conceptual scheme of the functioning of this heterogeneous environment is proposed, which will help towards a sustainable management of volcanic aquifers in relation with the European Union Groundwater Directive (2006/118/CE) (2006).

Hydrochemical and isotopic investigation of the groundwater composition of an alluvial aquifer, Cap Bon Peninsula, Tunisia

In the Grombalia region, Cap Bon Peninsula, northeastern Tunisia, increasing population and development of agricultural activity during the last few decades have engendered large expansion of groundwater pumping from the shallow, unconfined aquifer. Recently, the water table has displayed some signs of overexploitation such as decline in the water level in boreholes and considerable deterioration of water quality. Hydrochemical and isotopic data were used in conjunction with hydrogeological characteristics to investigate the groundwater composition in this aquifer. It has been demonstrated that groundwaters, recharged mainly in the surrounding foothills, acquire their mineralization principally by water–rock interaction, i.e., dissolution of evaporites and reverse cation exchange, and secondarily by return flow of irrigation waters. The isotopic signature of groundwaters permits identification of two different types. Water with depleted δ18O and δ2H contents is interpreted as recharge by non-evaporated rainfall, originating from a mixture of Atlantic and Mediterranean air masses. However, water with relatively enriched δ18O and δ2H contents is thought to reflect contamination by return flow of irrigation waters. Tritium contents, ranging between 1.2 and 4.5 TU indicate that groundwaters in an unconfined aquifer derive from post-nuclear recharge or contain a significant component of post-1950s water. The recent origin of these groundwaters is confirmed by the high carbon-14 activities, exceeding sometimes 100%, indicating the existence of a significant fraction of organic 14C. This younger source of radiocarbon is, however, highlighted by the depleted δ13C contents, corresponding to a system where CO2 of C4 plants predominates.

CO2 supersaturation along the aquatic conduit in Swedish watersheds as constrained by terrestrial respiration, aquatic respiration and weathering

AbstractWe tested the hypothesis that CO2 supersaturation along the aquatic conduit over Sweden can be explained by processes other than aquatic respiration. A first generalized‐additive model (GAM) analysis evaluating the relationships between single water chemistry variables and pCO2 in lakes and streams revealed that water chemistry variables typical for groundwater input, e.g., dissolved silicate (DSi) and Mg2+ had explanatory power similar to total organic carbon (TOC). Further GAM analyses on various lake size classes and stream orders corroborated the slightly higher explanatory power for DSi in lakes and Mg2+ for streams compared with TOC. Both DSi and TOC explained 22–46% of the pCO2 variability in various lake classes (0.01–>100 km2) and Mg2+ and TOC explained 11–41% of the pCO2 variability in the various stream orders. This suggests that aquatic pCO2 has a strong groundwater signature. Terrestrial respiration is a significant source of the observed supersaturation and we may assume that both terrestrial respiration and aquatic respiration contributed equally to pCO2 efflux. pCO2 and TOC concentrations decreased with lake size suggesting that the longer water residence time allow greater equilibration of CO2 with the atmosphere and in‐lake mineralization of TOC. For streams, we observed a decreasing trend in pCO2 with stream orders between 3 and 6. We calculated the total CO2 efflux from all Swedish lakes and streams to be 2.58 Tg C yr−1. Our analyses also demonstrated that 0.70 Tg C yr−1 are exported to the ocean by Swedish watersheds as HCO3− and CO32− of which about 0.56 Tg C yr−1 is also a residual from terrestrial respiration and constitute a long‐term sink for atmospheric CO2. Taking all dissolved inorganic carbon (DIC) fluxes along the aquatic conduit into account will lower the estimated net ecosystem C exchange (NEE) by 2.02 Tg C yr−1, which corresponds to 10% of the NEE in Sweden.

Isotopic and geochemical evidence of recharge sources and water quality in the Quaternary aquifer beneath Jinchang city, NW China

Multiple isotopic and hydrogeochemical tracers were utilized to understand the recharge sources and geochemical evolution of groundwater in the Quaternary aquifer beneath Jinchang city and the adjacent Gobi desert area. The groundwater shows markedly depleted stable isotopic composition compared to modern rainfall. The signature of groundwaters from Jinchang and the northern Gobi desert area differ clearly from that of the alluvial fan in the south Yongchang basin and modern rainfall, and has lower or non-detectable (3)H activity, implying that the aquifer is likely maintained by palaeowater. This groundwater in the Gobi desert has a (14)C age older than 12 ka, indicating that the groundwater resources are non-renewable. The build-up of dissolved solids through evaporation is a major control on groundwater composition, and the dominant anion species change systematically from HCO(3)(-), SO(4)(2-) to Cl(-), but cations from weathering of albite, calcite, dolomite and gypsum also make a significant contribution. The scientific results have important implications for groundwater management in Jinchang city and as well as in the Shiyang River basin under China's West Development Strategy. It is recommended that the water allocation program of diverting water from the Dongda river to the Minqin basin be reconsidered. (C) 2010 Elsevier Ltd. All rights reserved.

Groundwater residence time and movement in the Maltese islands – A geochemical approach

The Maltese Islands are composed of two limestone aquifers, the Upper and Lower Coralline Limestone separated by an aquitard, the ‘Blue Clay’. The Lower Coralline Limestone is overlain in part by the poorly permeable Globigerina Limestone. The upper perched aquifers are discontinuous and have very limited saturated thickness and a short water level response time to rainfall. Frequent detections of coliforms suggest a rapid route to groundwater. However, the unsaturated zone has a considerable thickness in places and the primary porosity of the Upper Coralline Limestone is high, so there is likely to be older recharge by slow matrix flow as well as rapid recharge from fractures. Measurement of SF6 from a pumping station in a deep part of one of the perched aquifers indicated a mean saturated zone age of about 15 years. The Main Sea Level aquifers (MSL) on both Malta and Gozo have a large unsaturated thickness as water levels are close to sea level. On Malta, parts of the aquifer are capped by the perched aquifers and more extensively by the Globigerina Limestone. The limited detection of coliform bacteria suggests only some rapid recharge from the surface via fractures or karst features. Transmissivity is low and tritium and CFC/SF6 data indicate that saturated zone travel times are in the range 15-40 years. On Gozo the aquifer is similar but is more-extensively capped by impermeable Blue Clay. CFC data show the saturated zone travel time is from 25 years to possibly more than 60 years. Groundwater age is clearly related to the extent of low-permeability cover. The δ13C signature of groundwater is related to the geochemical processes which occur along the flowpath and is consistent with residence time ages in the sequence; perched aquifers<Malta MSL<Gozo MSL. The 18O and 2H enriched isotopic signature of post 1983 desalinated water can be seen in more-modern groundwater, particularly the urbanised areas of the perched and Malta MSL aquifers. In all aquifers, movement of solutes from the surface travelling slowly through the matrix provide a long term source of groundwater contaminants such as nitrate.

Limits to recharge of groundwater from Tibetan plateau to the Gobi desert, implications for water management in the mountain front

Multiple isotopic and hydrogeochemical tracers were utilized to understand the limits to recharge from Tibetan plateau to Gobi desert. The average direct recharge rate according to chloride mass balance is between 0.9-2.5 mm yr(-1) based on an annual rainfall of 120 mm yr(-1), indicating that this has negligible impact on groundwater. The groundwater shows markedly depleted stable isotopic composition compared to modern rainfall. The signature of groundwaters (around -10.4 parts per thousand to -9.6 parts per thousand delta(18)O in several wells) from Dajing and South Lake playa differ clearly from that of the alluvial fan and modern rainfall, and has lower or undetected tritium activity, implying that the aquifer in the desert is maintained by palaeowater. This groundwater has an estimated (14)C age of similar to 4 kyr, with a recharge temperature of 7.3 degrees C. At current hydraulic head gradients, transit time from the recharge zone (Wuwei-Gulang alluvial fan) to South lake is approximately 2200-3500 yrs, indicating that groundwater flow is relatively slow and that the water resources are non-renewable. The geochemical information is comparable to the isotopic results of limit recharge sources of groundwater from Tibetan plateau to the Gobi desert. The buildup of dissolved solids through evaporation is a major control on groundwater composition, and the dominant anion species change systematically from HCO(3)(-), SO(4)(2-) to Cl(-), but the dissolved ions from albite, calcite, dolomite and gypsum also have a significant contribution. It is advised to re-consider seriously the immigration policy of South lake to meet the groundwater management in the mountain front to Gobi desert. (C) 2008 Elsevier B.V. All rights reserved.

Radium isotopes reveal seasonal groundwater inputs to Cockburn Sound, a marine embayment in Western Australia

Summary The mass balance and activity ratios of naturally occurring radium (Ra) iso-topes ( 223 Ra, 224 Ra, 226 Ra, 228 Ra) were investigated in Cockburn Sound (Western Australia)to further understand submarine groundwater discharge (SGD) into these coastal waters.Water samples from 11 marine stations and 20 groundwater sites (encompassing threeaquifer layers) were analysed for Ra at four times, at the end of winter (September2003), early summer (December 2003), late summer (March 2004) and mid-winter (July2004). Variable isotopic signatures of groundwater suggested that vertical mixing mayoccur between different aquifer layers and two isotopically different water sources wereidentified in marine waters both inside and outside of Cockburn Sound. A mass balance ofthe long lived radium isotopes ( 228 Ra and 226 Ra) produced a range of discharge estimatesfrom 0.8 · 10 7 L day 1 in late summer to 2.7 · 10 7 L day 1 at the end of winter. Signaturesof radium isotopes in the coastal waters suggested that groundwater discharge was notconfined to the shoreline and may have occurred from a number of aquifer sources at atemporally variable scale.a 2007 Elsevier B.V. All rights reserved.

Chloride and the environmental isotopes as the indicators of the groundwater recharge in the Gobi Desert, northwest China

The long term recharge in Gobi Desert from Hexi Corridor to Inner Mongolia Plateau was estimated to be 1 mm year−1 by using the chloride mass balance method from one unsaturated zone profile, which shows that no effective modern recharge is taking place. A good rainfall database from Zhangye provides definition of the stable isotopic composition of modern rainfall. The signature of groundwater from the late Pleistocene differs markedly from that of the Holocene, shown clearly by the compositions of −10.5‰ δ18O as compared with values of −7‰ at the present day. It is apparent that the groundwaters in the Minqin Basin, Ejina Basin and feeding the lake system of the Badain Jaran are part of a regional flow network related to a wetter past climate as source of recharge. The recharge source in the past and to a limited extent in the more arid conditions of the present day included the foothills of the mountains of the Tibetan Plateau. The tritium age determinations accurate to the year are impossible and of no meaning to groundwater studies. A tritium value in the groundwater means multiple recharge ages in this region.

Interaction between different water bodies in a small catchment in the Paris basin (Brévilles, France): Tracing of multiple Sr sources through Sr isotopes coupled with Mg/Sr and Ca/Sr ratios

Abstract Intensive monitoring of the Cuise Sands Aquifer in a small agricultural catchment (3 km2, where agricultural practices are well documented) over nearly 5 a showed significant disparities for major element concentrations, Sr concentrations, isotopic compositions and 3H values, depending on the groundwater sampling locations. Lower 87Sr/86Sr values (0.7079–0.7085) associated with low NO 3 - concentrations, low Mg/Sr molar ratios ( 0.7085) and higher Mg/Sr molar ratios (>250) suggest a contribution of Sr from anthropogenic sources. Strontium isotopes coupled with Mg/Sr and Ca/Sr ratios of groundwater in this catchment successfully demonstrated the capacity to trace fertilizer contributions, which significantly modify the natural Sr isotopic signature of groundwater. The specific geochemical signature of groundwater revealed by Sr isotopes, in addition to major and trace element concentrations (in particular Mg/Sr and Ca/Sr molar ratios), demonstrated the partial isolation of groundwater bodies in this catchment. Compartmentalisation of the aquifer is compatible with fault distribution as defined by geological and geophysical investigations. Thus, the Sr isotopic tool coupled with Mg/Sr and Ca/Sr ratios has been applied with success to trace water pathways and recharge and to provide scenarios for the hydrological functioning of the system.

Case study of contaminated groundwater discharge: How in situ tools link an evolving conceptual site model with management decisions

In this paper, we show how simple in situ tools provide key insights into groundwater transport and exposure pathways. We illustrate how integration between managers, hydrogeologists, and ecologists, through the use of an evolving conceptual site model, helps direct management decisions. An initial conceptual site model was used to guide a preliminary investigation to determine the extent to which contaminant exposure from discharging groundwater occurs in a waterway. Regulatory agency managers, informed by phased input of data, supported extending the site investigation subtidally to identify the nature and extent of waterway contamination and to provide the basis for developing remedial alternatives. Approaches and tools used in this reconnaissance investigation included monitoring ambient surface water for groundwater signatures, installing minipiezometers within the sediment, and installing diffusion samplers and seepage meters. Despite high concentrations of contaminants in nearby piezometer samples, the diffusion sampler array indicated few locations with contaminant accumulation in the top 20 cm of the sediment. At the location where deployed, seepage meters demonstrated a high degree of connectivity and the potential for mass loading in the waterway. In the collective experience of the authors, this is one of the 1st sites where this comprehensive suite of tools has been applied in a regulatory setting to evaluate the movement of industrial contaminants beneath and into a waterway. This approach was effective because of integration of disciplines, unification of previously separate groundwater and sediment investigations, and collaboration across separate agencies and programs. In large part because of the results, the facility and agency managers agreed, and have begun a comprehensive subtidal investigation, to characterize the distribution of sediment and groundwater contamination and to quantify the groundwater flux to the surface water.

Low-temperature serpentinization processes and kimberlite groundwater signatures in the Kirkland Lake and Lake Timiskiming kimberlite fields, Ontario, Canada: implications for diamond exploration

Groundwaters from diamondiferous kimberlite pipes in the Kirkland Lake and Lake Timiskaming regions display unusual geochemical characteristics and signatures compared with groundwaters from the surrounding host rock. Reaction modelling was used to better constrain water/rock ratios, alteration mineralogy and groundwater geochemistry. A soil-zone Ca-HCO 3 − water from glacial till was reacted, using a reaction-modelling program, with three different suites of minerals: a kimberlite suite, a felsic intrusive suite and a mafic intrusive suite. Decreasing pH and alkalinity with increasing water/rock ratios in model reactions with the kimberlite suite suggest that sampled groundwaters are from both the hypabyssal facies (high pH and alkalinity; low water/rock ratios) and the diatreme facies (low pH and alkalinity; high water/rock ratios). Geochemical concentrations of sampled groundwaters from kimberlites were compared to modelled waters; results indicate that these waters are different from those flowing through local felsic or mafic intrusive rocks. The kimberlitic groundwaters, and modelled waters, contain low concentrations of Mg and Fe, high concentrations of K and Ca, have elevated pH (up to 12.45), and are defined as a Ca-OH − water for the A4 and B30 kimberlites. In contrast, the C14, Diamond Lake and 95-2 kimberlites contain groundwaters that have higher Mg and Fe, lower Ca and K concentrations, and relatively low pH (8.5–10). The reaction model suggests that different minerals precipitate where the water interacts with different kimberlite facies and/or where a different water/rock ratio exists. More hydroxide phases form where pH and hydroxide alkalinity are high. Where kimberlite waters interact with host-rock waters, minerals not likely to be found otherwise, such as magnesite, brucite and magnetite, may be detected along fractures, or near seeps or springs where groundwater comes to surface. Exploration for kimberlites can benefit from the use of groundwater. Groundwater interaction with kimberlitic rocks produces characteristic aqueous geochemical anomalies due to low-temperature serpentinization reactions. The identification of geochemical anomalies in the groundwaters down-flow of a kimberlite and the unusual mineral assemblages that may precipitate from these groundwaters may aid in the location of undiscovered kimberlites.