Groundwater Survey Research Articles

Combining continuous monitoring and High-Precision altitude measurements in forensic groundwater surveys: a case study of chlorinated solvent pollution in an urban context

This paper describes a forensic investigation of groundwater in an urban context in Italy. The present case study was conducted to detect the hydraulic flow path between a sportfishing pond and a nearby industrial plant’s contaminated groundwater site. The investigation was performed to evaluate the potential for diffusion of contaminants through groundwater flow into a fishing pond located downstream from a chemical factory. High-precision altitude measurements of monitoring stations combined with continuous water level monitoring were crucial to understand the groundwater flow dynamics and define the hydrogeological conceptual model. The study verified that the fishing pond, dug in low-permeability volcanic rock, was not hydraulically connected to the groundwater flow. The presence of contaminants in the pond may be related to the periodic topping-up activity performed using water from an existing well. The identified groundwater flow paths were consistent with the possible contaminant migration from the chemical factory to the water well near the fishing pond.

Discussion on Sampling Method of Soil and Groundwater Survey

Discussion on Sampling Method of Soil and Groundwater Survey

Changes of groundwater flow field of Luanhe River Delta under the human activities and its impact on the ecological environment in the past 30 years

The Luanhe River Delta is located in the center of the Circum-Bohai Sea Economic Zone. It enjoys rapid economic and social development while suffering relatively water scarcity. The overexploitation of groundwater in the Luanhe River Delta in recent years has caused the continuous drop of groundwater level and serious environmental and geological problems. This study systematically analyzes the evolution characteristics of the population, economy, and groundwater exploitation in the Luanhe River Delta and summarizes the change patterns of the groundwater flow regime in different aquifers in the Luanhe River Delta according to previous water resource assessment data as well as the latest groundwater survey results. Through comparison of major source/sink terms and groundwater resources, the study reveals the impacts of human activities on the groundwater resources and ecological environment in the study area over the past 30 years from 1990 to 2020. The results are as follows. The average annual drop rate of shallow groundwater and the deep groundwater in the centers of depression cones is 0.4 m and 1.64 m, respectively in the Luanhe River Delta in the past 30 years. The depression cones of shallow and deep groundwater in the study area cover an area of 545.32 km2 and 548.79 km2, respectively, accounting for more than 10% of the total area of the Luanhe River Delta. Overexploitation of groundwater has further aggravated land subsidence. As a result, two large-scale subsidence centers have formed, with a maximum subsidence rate of up to 120 mm/a. The drop of groundwater level has induced some ecological problems in the Luanhe River Delta area, such as the zero flow and water quality deterioration of rivers and continuous shrinkage of natural wetlands and water. Meanwhile, the proportion of natural wetland area to the total wetland area has been decreased from 99% to 8% and the water area from 1776 km2 to 263 km2. These results will provide data for groundwater overexploitation control, land subsidence prevention, and ecological restoration in plains and provide services for water resources management and national land space planning.© 2021 China Geology Editorial Office.

A Novel Three-Dimensional Mine Area Hydrogeological Model Based on Groundwater Modeling Systems

Zhang, L.; Dong, D.; Zhang, F., and Xu, Z., 2020. A novel three-dimensional mine area hydrogeological model based on groundwater modeling systems. In: Hu, C. and Cai, M. (eds.), Geo-informatics and Oceanography. Journal of Coastal Research, Special Issue No. 105, pp. 141–146. Coconut Creek (Florida), ISSN 0749-0208.Three-dimensional(3D) geological modeling has received extensive attention and research in the fields of energy exploration, geological survey, disaster prevention, and groundwater simulation. In this article, a novel 3D visualization geological model of the mining area based on the groundwater modeling system (GMS) is proposed. Also, 3D spatial combination characteristics of the hydrogeological structure of the mining area are analyzed and investigated. To attain better optimization parameters, the spatial distribution of water flow field and the temporal variation characteristics of groundwater level are derived. The simulation shows that the model is of theoretical value for 3D visualization of mine geology and numerical survey of groundwater.

Natural and Anthropogenic Groundwater Contamination in a Coastal Volcanic-Sedimentary Aquifer: The Case of the Archaeological Site of Cumae (Phlegraean Fields, Southern Italy)

Archeological sites close to coastal volcanic-sedimentary aquifers are threatened by groundwater contaminated by natural and anthropogenic processes. The paper reports on a hydrogeological, chemical (major, minor and trace elements) and isotopic (δD-H2O, δ18O-H2O, δ15N-NO3, δ18O-NO3, δ11B, 222Rn) survey of groundwater at the Cumae archaeological site, which is located in the coastal north-western sector of the volcanic district of Phlegraean Fields (southern Italy), where groundwater flooding phenomena occur. Results show the presence of a complex coastal volcanic-sedimentary aquifer system where groundwater quality is influenced mainly by: (i) aquifer lithology and localized ascent of magmatic fluids along buried volcano-tectonic discontinuities, (ii) mixing of groundwater, deep mineralized fluids and seawater during groundwater pumping, and (iii) nitrate contamination >50 mg/L from non-point agricultural sources. Moreover, δD and δ18O point toward fast recharge from seasonal precipitations, while the isotopic ratios of N and O in nitrate reveal the contribution of mineral and organic fertilizers as well as leakage from septic tanks. Results can assist the local archaeological authority for the safeguarding and management of the archaeological heritage of the Cumae site.

An integrated electrical resistivity and geochemical approach to delineate groundwater contamination due to seawater intrusion in the southern part of Mangalore, Karnataka, India

In this paper, integration of electrical resistivity survey and chemical analyses of groundwater has been executed in Mangalore’s southern part, Karnataka to delineate seawater intrusion phenomena. About 11 locations representing different hydrogeological and geomorphological setups were selected for the vertical electrical sounding (VES) to identify the subsurface formations and the extent of seawater intrusion. With the VES, the contaminated groundwater zones and the depth to fresh and saline water interface have been demarcated. Overall, 59 groundwater samples were subjected to various geochemical analysis viz; pH, electrical conductivity (EC), total dissolved solids (TDS), salinity, total hardness, alkalinity, calcium (Ca2+), magnesium (Mg2+), chloride (Cl−), sodium (Na2+), potassium (K+)and sulfate (SO4 2-) to understand the nature of salinity in the aquifer. The geochemical analyses show that good groundwater conditions characterize the study area except for the southern part. The southern part is under the moderate to high salinity hazard risk, possibly due to its proximity to the sea and hydraulic connection with the seawater through the tidal creek. Two among the VES locations situated in this region show a saline water trend towards the bottom, and in the rest of the VES locations, a freshwater trend is encountered towards the depth.

Origin and hydrochemical characteristics of groundwater in the Northeastern Patagonia, Argentina: the relationship with geomorphology and soils

In arid zones, geomorphology and soils play a fundamental role in groundwater surveys as they condition the recharge phenomenon and some processes that modify water chemistry. The objective of this work was to identify the groundwater provenance and the relationship between its chemistry and isotope contents with the geomorphology and soil in the northeastern Patagonia, Argentina. Over an area of 10,600 km2, groundwater levels and major ionic and stable isotopic contents were measured. The main geomorphological units were mapped using satellite images and digital elevation models. In soils, pedogenetic carbonate contents (PC) and clay accumulation index (CAI) were measured. Different hydrochemical facies were identified in relation to geomorphological units, being the Cl–SO4–Na and Cl–Na ionic types dominant in fluvial terrace plains (terrace associations, TAs). The Cl–SO4–Na types are the most saline groundwaters and are coincident with the TA where Petrocalcids are the dominant soils. With less salinity contents, Cl–SO4–Na and Cl–Na types are the groundwaters associated with TA where the dominant soils are Natrargids and Haplocalcids. The only sector with Cl–HCO3–Na is those with fresh water coincident with the Aeolian field unit, where Psamments soils develop. Likewise, groundwater is isotopically differentiated in response to the origin being mostly allocthonus in the fluvial terrace plains and from local recharge in the Aeolian fields. The fluvial terraces are gravel deposits that would favor a local recharge, but this is prevented both by pedogenic carbonate and clay contents which developed in the upper part of the deposit. In this way, the measurement of pedogenetic carbonates and clays becomes soil properties of utmost importance to be considered in groundwater prospecting in arid regions worldwide.

Determining groundwater inflow and Si behavior in a wetland using 222Rn mass balance and multidisciplinary approach

Studying groundwater inflow and quantifying its flux into aquatic systems remain challenging because of geological and topographical heterogeneities. In this study, we measured the 222Rn activities in the surface water and porewater of a shallow wetland, the Baekseok Reservoir Wetland, to investigate the groundwater flow system and quantify the groundwater inflow rate. Three field campaigns were carried out in April 2018, September 2018, and February 2019 to determine the spatial and temporal variations in the 222Rn activity. The 222Rn activities were significantly higher along the western boundary of the wetland than the eastern boundary, suggesting a significant difference in the groundwater inflow rate, which reflects different hydrological characteristics on the two boundaries of the wetland. The results of hydrogeological investigations (electrical resistivity survey and monitoring of groundwater and surface water levels) and microbiological analyses were consistent with the 222Rn distribution results, supporting our hypothesis that the groundwater inflow qualitatively and quantitatively exhibits a spatial difference. Based on the mass balances of water and 222Rn under a steady-state condition, the groundwater inflow rates were estimated to be 3.2 × 102, 1.7 × 103, and 7.6 × 102 m3 day−1 in April, September, and February, respectively. The highest groundwater inflow rate in September may be due to the relatively high hydraulic gradient resulting from intense rainfall events. The water residence time of the wetland estimated from the 222Rn mass balance results was approximately one month regardless of the seasons. In addition, the groundwater-derived dissolved silica flux accounted for ~60% of the total dissolved silica input flux of the wetland, highlighting the importance of groundwater-derived dissolved silica. Our multidisciplinary approach to identify and quantify groundwater inflow has important implications in determining groundwater sources in aquatic systems and the behaviors of other substances, such as dissolved nutrients.

Measurement of Apparent Electrical Impedance of Soil with Water Flow Inside

Understanding the flow of groundwater is very important, not only for water management but also for the prevention and mitigation of natural disasters. The electrical resistivity method has been established as an effective groundwater exploration method in geological surveys. The purpose of this study is to develop an accurate investigation method for groundwater flow using soil impedance fluctuations. As a preliminary experiment, the apparent soil impedance was measured by applying a low-frequency current through a soil column with water flow inside. The apparent impedance showed fluctuations due to water flow at frequencies above 20 Hz, and the fluctuation range increased with the flow rate of water. It has been proposed that groundwater flow can be detected by measuring impedance fluctuations, and it is considered that this method can be applied to groundwater surveys and embankment and reservoir leak surveys.

Distribution and Geochemical Controls of Arsenic and Uranium in Groundwater-Derived Drinking Water in Bihar, India.

Chronic exposure to groundwater containing elevated concentrations of geogenic contaminants such as arsenic (As) and uranium (U) can lead to detrimental health impacts. In this study, we have undertaken a groundwater survey of representative sites across all districts of the State of Bihar, in the Middle Gangetic Plain of north-eastern India. The aim is to characterize the inorganic major and trace element aqueous geochemistry in groundwater sources widely used for drinking in Bihar, with a particular focus on the spatial distribution and associated geochemical controls on groundwater As and U. Concentrations of As and U are highly heterogeneous across Bihar, exceeding (provisional) guideline values in ~16% and 7% of samples (n = 273), respectively. The strongly inverse correlation between As and U is consistent with the contrasting redox controls on As and U mobility. High As is associated with Fe, Mn, lower Eh and is depth-dependent; in contrast, high U is associated with HCO3−, NO3− and higher Eh. The improved understanding of the distribution and geochemical controls on As and U in Bihar has important implications on remediation priorities and selection, and may contribute to informing further monitoring and/or representative characterization efforts in Bihar and elsewhere in India.

Typology of Sounding Curves and Lithological 1D Models of Mineral Prospecting and Groundwater Survey within Crystalline Basement Rocks in the East of Cameroon (Central Africa) Using Electrical Resistivity Method and Koefoed Computation Method

Resistivity method using seventy-sixth (976) Schlumberger vertical electrical soundings along forty-one (41) profiles are conducted in the Batouri and Ngoura subdivisions, East region of Cameroon, to investigate the subsurface layering, mineral potential, and groundwater resource characteristics. Results of quantitative and qualitative interpretation of data using Koefoed computation method reveal two to five layers having geometrical and electrical characteristics of geological layer models: topsoil (0.5 m<ep<3 m; 600<ρ<3000 Ω.m), lateritic soils (3<ep<20 m; 1000<ρ<4000 Ω.m); conductive layer (5<ep<110 m; 100<ρ<1000 Ω.m); fractured/weathered granite (20<ep<60 m; 1000/5000<ρ<3000/9000 Ω.m); clayey layer (5<ep<20 m; 600/1500<ρ<2000/3500 (dry) Ω.m); and fresh granites (ρ>4000 Ω.m). From the qualitative interpretation of VES curves, the subsurface layering is depicted by nine (09) types of sounding curves (G, H, A, QH, KH, HK, HA, HKH, and KHK) characterizing the vertical changes and the typology of sounding curves in the East Cameroon crystalline basements. The lithology of the subsurface is dominated (more than 80%) by geoelectrical and lithological 1D models derived by the H, QH, KH, HK, HA, HKH, and KHK curve types. These models are characterized by the presence of conductive layers and fractured/weathered granites derived from tectonic activities of the region. Also, the resistivity method (VES) applied in this study bring information about variation of the resistivity with depth, geological structures, fractures, and rupture zones in the underground until 120 m depth. These abovementioned information reveal proper hydrogeological and mining conditions for an efficient evaluation of the mineral potential and groundwater resources.

Major and trace (including arsenic) groundwater chemistry in central and southern Myanmar

Myanmar, in Southeast Asia, is categorized as a Least Developed Country, facing substantial challenges towards meeting 2030 Sustainable Development Goal targets, including ensuring access to safe water and sanitation. The occurrence of geogenic contaminants, notably arsenic, in Myanmar groundwaters is relatively poorly understood, particularly as compared to other countries in South/Southeast Asia. Improving the understanding of groundwater quality in Myanmar is hence a major concern and relevant to the health of millions of local inhabitants who extensively use groundwater. A groundwater survey was undertaken at 85 sites across five distinctly contrasting zones within three of Myanmar's main river basins (Chindwin-Ayeyarwady, Sittaung, and Salween) to assess the occurrence of arsenic and other potentially harmful elements, and to study the dominant geochemical controls in each zone/basin. A significant number of samples were affected by water quality issues, based on World Health Organization (WHO) guidelines, including elevated arsenic (>10 μg.L−1) in 14% of all samples within the basins studied. Fluoride, nitrate, salinity, iron, manganese, and aluminum also exceeded WHO drinking water guidelines in some locations. Arsenic typically occurred as inorganic AsIII and largely arose from the reductive dissolution of Fe(Mn)-(hydro)xides and was broadly associated with relatively high HCO3 and NH4. Variable dominant geochemical controls on groundwater composition were identified, notably (i) calcite and dolomite dissolution in the Salween basin; (ii) cation exchange, carbonate dissolution and saline intrusion in the Ayeyarwady delta; and (iii) gypsum dissolution, silicate weathering, and cation exchange in Chindwin-Middle Ayeyarwady. This reconnaissance study provides new information on groundwater composition and corresponding geochemical controls across contrasting, and previously underrepresented, areas of Myanmar and may help to inform further hazard assessment, monitoring and/or mitigation strategies.

Toward mapping potential groundwater recharge zones across Viti Levu and Vanua Levu (Fiji islands)

Water access in Fiji is a critical issue as not everyone can access reticulated water sources which poses heavy dependence on groundwater sources. Along with its various uses, groundwater sources have been left vulnerable to contamination and depletion over the years due to changes in climatic patterns and human influence. Traditional hydrometric groundwater survey is performed monthly to help determine recharge potential areas in Fiji but doesn’t cover all the water sources nor considers all the factors contributing to groundwater recharge. GIS, presents a contemporary approach to identify potential recharge areas which has been used in this study. In this study, the Multi Influencing Factor technique was used to determine the weightage of the factors aspect, slope, soil drainage, drainage density, parent materials and rainfall which are believed to have potentially contribute to groundwater recharge. The basic GIS tools of overlaying and reclassification was used to denote the relationships between the factors and groundwater recharge and the potential groundwater recharges areas for Viti Levu and Vanua Levu. Results have shown that higher potential areas are mostly areas with lower altitudes such as plains, wet areas (windward side), water bodies, excessively drained soils and parent materials with high exposure to weathering. Low ground water recharge potential areas are mostly mountainous, poorly drained soils, dense vegetation and poorly permeable bedrocks. These information is compared against existing boreholes and findings are to assist the government to invest more in those areas that have high recharge areas.

Potential for co-metabolic oxidation of TCE and evidence for its occurrence in a large-scale aquifer survey

Trichloroethylene (TCE) is a groundwater pollutant that is prevalent worldwide. In contaminated groundwater, TCE can be biodegraded following either reductive dechlorination or aerobic co-metabolic oxidation. However, since the co-metabolic process is not accompanied by indicative and easily detectable transformation products, little is known about its prominence in the environment. To estimate the environmental importance of the oxidative process, a regional groundwater survey was conducted. In this survey, polluted water from 100 wells along the Israeli Coastal Aquifer was sampled. Geochemical data indicated oxic conditions prevailing in most sites. The sampled groundwater was used for microcosm experiments, functional gene analysis, and TCE compound-specific isotope analysis (δ13C and δ37Cl).Enrichments of methane and toluene oxidizers in microcosms indicated the high potential of the indigenous microbial community to co-metabolically oxidize TCE. This was further reinforced by the high abundance of mmoX and PHE functional genes quantified in some of the sites (yet lower abundance of TOD functional gene was found).Finally, compound-specific isotope analysis was used to assess the magnitude of TCE oxidation in practice. Applying the isotopic tool for scattered points on a regional scale demanded the consideration of a wide δ13C range of source TCE, hampering the ability to detect small shifts of a single permil. Thus, despite the high potential for the oxidation process, no evidence was attained for the natural occurrence of the process, and significant isotopic shifts were restricted to actively treated sites only. This limitation should be considered in future regional scale studies, in which no single source is defined.

A survey of trace metal burdens in increment cores from eastern cottonwood (Populus deltoides) across a childhood cancer cluster, Sandusky County, OH, USA

A dendrochemical study of cottonwood trees (Populus deltoides) was conducted across a childhood cancer cluster in eastern Sandusky County (Ohio, USA). The justification for this study was that no satisfactory explanation has yet been put forward, despite extensive local surveys of aerosols, groundwater, and soil. Concentrations of eight trace metals were measured by ICP-MS in microwave-digested 5-year sections of increment cores, collected during 2012 and 2013. To determine whether the onset of the first cancer cases could be connected to an emergence of any of these contaminants, cores spanning the period 1970–2009 were taken from 51 trees of similar age, inside the cluster and in a control area to the west. The abundance of metals in cottonwood tree annual rings served as a proxy for their long-term, low-level accumulation from the same sources whereby exposure of the children may have occurred. A spatial analysis of cumulative metal burdens (lifetime accumulation in the tree) was performed to search for significant 'hotspots', employing a scan statistic with a mask of variable radius and center. For Cd, Cr, and Ni, circular hotspots were found that nearly coincide with the cancer cluster and are similar in size. No hotspots were found for Co, Cu, and Pb, while As and V were largely below method detection limits. Whereas our results do not implicate exposure to metals as a causative factor, we conclude that, after 1970, cottonwood trees have accumulated more Cd, Cr, and Ni, inside the childhood cancer cluster than elsewhere in Sandusky County.

Students’ understanding of a groundwater system and attitudes towards groundwater use and conservation

ABSTRACTThe purpose of this study was to investigate students’ understanding of groundwater as a system, and to further examine whether and how their understanding is related to attitudes towards groundwater use and conservation. A total of 676 junior high school students completed a groundwater survey including a drawing activity and a questionnaire. An additional group of university students with environmental science majors were recruited for the survey for the purpose of determining reasonable expectations and validating interpretations of the results. Analysis of student drawings indicated that students generally held an incomplete and unconnected understanding of the groundwater system. Correlation analysis showed that student levels of understanding were associated with their perceptions of environmental impacts as well as environmental concern regarding groundwater problems. These findings re-emphasised the importance of promoting students’ understanding of environmental systems, as well as their ability to think systemically.

Formation mechanism of large sinkhole collapses in Laibin, Guangxi, China

On June 3, 2010, a series of karst sinkholes occurred at Jili village surrounded by Gui-Bei highway, Wu-Ping highway and Nan-Liu High-Speed Railway in Laibin, Guangxi, China. The straight-line distances from an large sinkhole pit, 85 m in diameter and 38 m in depth, to the above mainlines are 200, 600 and 500 m, respectively. Several investigation methods including geophysical technology, borehole and well drilling, groundwater elevation survey and hydrochemistry analysis of groundwater were used to study the formation mechanisms of these sinkholes. Based on the results, the spatial distribution of the Jili underground river was confirmed with a strike of SN along the middle Carboniferous limestone bedrock and the Quaternary deposits controlled the sinkhole formation. In addition, both historical sinkhole events and analysis of the groundwater–air pressure monitoring data installed in the underlying karst conduit system indicate that sinkholes in this area are more likely induced by extreme weather conditions within typical karst geological settings. Extreme weather conditions in the study area before the sinkhole collapses consisted of a year-long drought followed by continuous precipitation with a daily maximum precipitation of 442 mm between May 31 and June 1, 2010. Typical geological conditions include the Jili underground river overlain by the Quaternary overburden with thick clayey rubble. Especially in the recharge zone of the underground river, a stabilized shallow water table was formed in response to the extreme rainstorm because of the presence of the thick clayey rubble. When the underground conduit was flooded through the cave entrance on the surface, air blasting may have caused the cave roof collapse followed by formation of soil cavities and surface collapses. Borehole monitoring results of the groundwater–air pressure monitoring show that the potential karst sinkhole can pose threats to Shanbei village, the High-Speed Railway and the Wu-Ping highway. Local government needs to be aware of any early indicators of this geohazard so that devastating sinkholes can be prevented in the future. The results also suggest that groundwater–air pressure monitoring data collected both the Quaternary deposits and the bedrock karst system provide useful indicators for potential sinkhole collapses in similar karst areas where sinkholes usually occur during rainy season or karst groundwater level is always under the rockhead.

Survey and zoning of nitrate-contaminated groundwater in Iran

Survey and zoning of nitrate-contaminated groundwater in Iran

Contribution of phosphorus to Georgian Bay from groundwater of a coastal beach town with decommissioned septic systems

Abstract Groundwater inputs of phosphorus (P) to the Laurentian Great Lakes are poorly known, but may contribute to eutrophication and algal bloom issues. This study's objective was to assess the contribution of P to Nottawasaga Bay from the surficial sand aquifer at Wasaga Beach, representing a coastal cottage area with decommissioned septic systems, and how this might change with time. The first part of the study involved site-scale groundwater sampling beside 4 provincial park public washrooms. Legacy P plumes were detected at two of these sites, with one being > 30 years since decommissioning. P transport calculations including sorption onto aquifer sediments indicate the majority of P plumes from the town's decommissioned septic systems have likely not yet reached the shoreline, > 50 years since installation, and will likely contribute P to the bay for many decades. The second part of the study consisted of broader-scale (town-wide) surveys of shallow beach groundwater. Dissolved P concentrations were ~ 50 μg/L for background groundwater (in town and reference area), which is similar to literature values. This P may have been sourced from degrading organic matter, bird droppings, or soil-aquifer minerals. Sporadic elevated concentrations up to 420 μg/L may be from legacy septic systems and/or natural sources. A rough calculation suggests groundwater P loading along Nottawasaga Bay's eastern shore (Wasaga Beach, 10-km; adjacent similar beaches, 40-km) is a few percent at most of that from the Nottawasaga River. Thus, it more likely affects localized periphyton and macrophyte growth rather than significantly affecting the Nottawasaga Bay P budget.

Redox controls on methane formation, migration and fate in shallow aquifers

Abstract. Development of unconventional energy resources such as shale gas and coalbed methane has generated some public concern with regard to the protection of groundwater and surface water resources from leakage of stray gas from the deep subsurface. In terms of environmental impact to and risk assessment of shallow groundwater resources, the ultimate challenge is to distinguish (a) natural in situ production of biogenic methane, (b) biogenic or thermogenic methane migration into shallow aquifers due to natural causes, and (c) thermogenic methane migration from deep sources due to human activities associated with the exploitation of conventional or unconventional oil and gas resources. This study combines aqueous and gas (dissolved and free) geochemical and isotope data from 372 groundwater samples obtained from 186 monitoring wells of the provincial Groundwater Observation Well Network (GOWN) in Alberta (Canada), a province with a long record of conventional and unconventional hydrocarbon exploration. We investigated whether methane occurring in shallow groundwater formed in situ, or whether it migrated into the shallow aquifers from elsewhere in the stratigraphic column. It was found that methane is ubiquitous in groundwater in Alberta and is predominantly of biogenic origin. The highest concentrations of biogenic methane (> 0.01 mM or > 0.2 mgL−1), characterized by δ13CCH4 values < −55 ‰, occurred in anoxic Na-Cl, Na-HCO3, and Na-HCO3-Cl type groundwaters with negligible concentrations of nitrate and sulfate suggesting that methane was formed in situ under methanogenic conditions for 39.1 % of the samples. In only a few cases (3.7 %) was methane of biogenic origin found in more oxidizing shallow aquifer portions suggesting limited upward migration from deeper methanogenic aquifers. Of the samples, 14.1 % contained methane with δ13CCH4 values > −54 ‰, potentially suggesting a thermogenic origin, but aqueous and isotope geochemistry data revealed that the elevated δ13CCH4 values were caused by microbial oxidation of biogenic methane or post-sampling degradation of low CH4 content samples rather than migration of deep thermogenic gas. A significant number of samples (39.2 %) contained methane with predominantly biogenic C isotope ratios (δ13CCH4 < −55 ‰) accompanied by elevated concentrations of ethane and sometimes trace concentrations of propane. These gases, observed in 28.1 % of the samples, bearing both biogenic (δ13C) and thermogenic (presence of C3) characteristics, are most likely derived from shallow coal seams that are prevalent in the Cretaceous Horseshoe Canyon and neighboring formations in which some of the groundwater wells are completed. The remaining 3.7 % of samples were not assigned because of conflicting parameters in the data sets or between replicates samples. Hence, despite quite variable gas concentrations and a wide range of δ13CCH4 values in baseline groundwater samples, we found no conclusive evidence for deep thermogenic gas migration into shallow aquifers either naturally or via anthropogenically induced pathways in this baseline groundwater survey. This study shows that the combined interpretation of aqueous geochemistry data in concert with chemical and isotopic compositions of dissolved and/or free gas can yield unprecedented insights into formation and potential migration of methane in shallow groundwater. This enables the assessment of cross-formational methane migration and provides an understanding of alkane gas sources and pathways necessary for a stringent baseline definition in the context of current and future unconventional hydrocarbon exploration and exploitation.