A Hydrostratigraphic Framework for the Paleozoic Bedrock of Southern Ontario

Groundwater systems in the intermediate to deep subsurface of southern Ontario are poorly understood, despite their value for a number of societal uses. A regional hydrostratigraphic framework is a necessary precursor for improving our understanding of groundwater systems and enabling development of a 3-D hydrostratigraphic model to visualize these groundwater systems. This study is a compilation and integration of published and unpublished geological, hydrogeological, hydrochemical and isotopic data collected over the past 10 years to develop that framework.Bedrock is covered by a thin veneer of surficial sediments that comprise an aquifer/aquitard system of considerable local variability and complexity. Aquifers in the bedrock are thin and regionally extensive, separated by thick aquitards, within a well-defined lithostratigraphic framework and a well-developed hydrochemical depth zonation comprising a shallow fresh water regime, an intermediate brackish to saline sulphur water regime, and a deep brine regime of ancient, evaporated seawater. Occurrence and movement of groundwater in shallow bedrock is principally controlled by modern (Quaternary) karstic dissolution of subcropping carbonate and evaporite rocks, and in the intermediate to deep subsurface by paleokarst horizons developed during the Paleozoic. Flow directions in the surficial sediments of the shallow groundwater regime are down-gradient from topographic highs and down the regional dip of bedrock formations in the intermediate regime. Shallow karst is the entry point for groundwater penetration into the intermediate regime, with paleo-recharge by glacial meltwater and limited recent recharge by meteoric water at subcrop edges, and down-dip hydraulic gradients in confined aquifers. Hydraulic gradient is up-dip in the deep brine regime, at least for the Guelph Aquifer and the Cambrian Aquifer, with no isotopic or hydrochemical evidence of infiltration of meteoric water and no discharge to the surface.Fourteen bedrock hydrostratigraphic units are proposed, and one unit comprising all the surficial sediments. Assignment of lithostratigraphic units as hydrostratigraphic units is based principally on hydrogeological characteristics of Paleozoic bedrock formations in the intermediate to deep groundwater regimes, below the influence of modern meteoric water. Carbonate and evaporite rocks which form aquitards in the subsurface may form aquifers at or near the surface, due to karstic dissolution by acidic meteoric water, necessitating compromises in assignment of hydrostratigraphic units.

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Interactions Between Regional Climate, Surficial Geology, and Topography: Characterizing Shallow Groundwater Systems in Subhumid, Low‐Relief Landscapes

Water Resources Research ◽

10.1029/2018wr023934 ◽

2019 ◽

Vol 55 (1) ◽

pp. 284-297 ◽

Cited By ~ 4

Author(s):

K. J. Hokanson ◽

C. A. Mendoza ◽

K. J. Devito

Keyword(s):

Regional Climate ◽

Shallow Groundwater ◽

Surficial Geology ◽

Groundwater Systems

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Seasonal dynamics of dissolved organic matter in high arsenic shallow groundwater systems

Journal of Hydrology ◽

10.1016/j.jhydrol.2020.125120 ◽

2020 ◽

Vol 589 ◽

pp. 125120

Author(s):

Yijun Yang ◽

Xiaofang Yuan ◽

Yamin Deng ◽

Xianjun Xie ◽

Yiqun Gan ◽

...

Keyword(s):

Organic Matter ◽

Dissolved Organic Matter ◽

Seasonal Dynamics ◽

Shallow Groundwater ◽

Groundwater Systems ◽

High Arsenic

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A meta-analysis and statistical modelling of nitrates in groundwater at the African scale

Hydrology and Earth System Sciences ◽

10.5194/hess-20-2353-2016 ◽

2016 ◽

Vol 20 (6) ◽

pp. 2353-2381 ◽

Cited By ~ 11

Author(s):

Issoufou Ouedraogo ◽

Marnik Vanclooster

Keyword(s):

Statistical Model ◽

Nitrate Concentration ◽

Regional Scale ◽

Shallow Groundwater ◽

Statistical Modelling ◽

Nitrate Pollution ◽

Nitrate Contamination ◽

Data Set ◽

Nitrate Concentrations ◽

Groundwater Systems

Abstract. Contamination of groundwater with nitrate poses a major health risk to millions of people around Africa. Assessing the space–time distribution of this contamination, as well as understanding the factors that explain this contamination, is important for managing sustainable drinking water at the regional scale. This study aims to assess the variables that contribute to nitrate pollution in groundwater at the African scale by statistical modelling. We compiled a literature database of nitrate concentration in groundwater (around 250 studies) and combined it with digital maps of physical attributes such as soil, geology, climate, hydrogeology, and anthropogenic data for statistical model development. The maximum, medium, and minimum observed nitrate concentrations were analysed. In total, 13 explanatory variables were screened to explain observed nitrate pollution in groundwater. For the mean nitrate concentration, four variables are retained in the statistical explanatory model: (1) depth to groundwater (shallow groundwater, typically < 50 m); (2) recharge rate; (3) aquifer type; and (4) population density. The first three variables represent intrinsic vulnerability of groundwater systems to pollution, while the latter variable is a proxy for anthropogenic pollution pressure. The model explains 65 % of the variation of mean nitrate contamination in groundwater at the African scale. Using the same proxy information, we could develop a statistical model for the maximum nitrate concentrations that explains 42 % of the nitrate variation. For the maximum concentrations, other environmental attributes such as soil type, slope, rainfall, climate class, and region type improve the prediction of maximum nitrate concentrations at the African scale. As to minimal nitrate concentrations, in the absence of normal distribution assumptions of the data set, we do not develop a statistical model for these data. The data-based statistical model presented here represents an important step towards developing tools that will allow us to accurately predict nitrate distribution at the African scale and thus may support groundwater monitoring and water management that aims to protect groundwater systems. Yet they should be further refined and validated when more detailed and harmonized data become available and/or combined with more conceptual descriptions of the fate of nutrients in the hydrosystem.

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Research on Hydrogeochemical Characteristics and Transformation Relationships between Surface Water and Groundwater in the Weihe River

10.5194/hess-2017-654 ◽

2017 ◽

Cited By ~ 3

Author(s):

Jihong Qu ◽

Shibao Lu ◽

Zhipeng Gao ◽

Wujin Li ◽

Zhiping Li ◽

...

Keyword(s):

Surface Water ◽

Major Ions ◽

Shallow Groundwater ◽

Hydrograph Separation ◽

Surface Water And Groundwater ◽

Piper Trilinear Diagram ◽

Close Relationship ◽

Weihe River ◽

Groundwater Systems ◽

Δd And Δ18o

Abstract. The transforming relationship between surface water and groundwater as well as their origins are the basis for studying the transport of pollutants in river-groundwater systems. A typical section of the river was chosen to sample the surface water and shallow groundwater. Then, a Piper trilinear diagram, Gibbs diagram, ratios of major ions, factor analysis, cluster analysis and other methods were used to investigate the hydrogeochemical evolution of surface water and groundwater and determine the formation of hydrogeochemical components in different water bodies. Based on the distribution characteristics of hydrogen and oxygen stable isotopes δD and δ18O and discharge hydrograph separation methods, the relationship between surface water and groundwater in the Weihe River was analyzed. The results indicated that the river water is a SO4·Cl—Na type and that the groundwater hydrogeochemical types are not the same. The dominant anions are HCO3− in the upstream reaches and are SO42− and Cl− in downstream reaches. Hydrogeochemical processes include evaporation and concentration, weathering of rocks, ion exchange, and dissolution infiltration reactions. The δD and δ18O of surface water change little along the river and are more enriched than are those of the groundwater. With the influences of precipitation, irrigation, river recharge and evaporation, the δD and δ18O of shallow groundwater at different sections are not the same. There is a close relationship between the surface water and groundwater. Surface water supplies the groundwater, which provides the hydrodynamic conditions for the entry of pollutants into the aquifer.

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Current Status and Trend of Nitrate-N and Factors Affecting Its Concentration in Shallow Groundwater Systems of Kathmandu

World Environmental and Water Resources Congress 2011 ◽

10.1061/41173(414)102 ◽

2011 ◽

Cited By ~ 2

Author(s):

Dhundi Raj Pathak ◽

Akira Hiratsuka ◽

Yosuke Yamashiki

Keyword(s):

Shallow Groundwater ◽

Current Status ◽

Factors Affecting ◽

Nitrate N ◽

Groundwater Systems

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A fluoride borehole dilution apparatus for groundwater velocity measurements

Canadian Geotechnical Journal ◽

10.1139/t77-056 ◽

1977 ◽

Vol 14 (4) ◽

pp. 554-561 ◽

Cited By ~ 29

Author(s):

G. E. Grisak ◽

W. F. Merritt ◽

D. W. Williams

Keyword(s):

Large Scale ◽

Shallow Groundwater ◽

Tracer Test ◽

Dilution Method ◽

Groundwater Velocity ◽

Low Concentrations ◽

Groundwater Systems ◽

Chloride Profiles ◽

Fluoride Electrode ◽

Tracer Dilution

A borehole dilution method using fluoride in low concentrations as the tracer and an adapted, commercially available fluoride ion electrode to measure the tracer dilution has been developed and employed at two sites. The sites are shallow groundwater systems consisting of alluvial surficial gravels near Fort Macleod, Alberta, and glaciodeltaic sand deposits at the Chalk River Nuclear Laboratories, Ontario. Zones of relatively high groundwater velocities determined at Fort Macleod with the fluoride apparatus are also evident in the results of a large-scale tracer test that documented chloride profiles over the saturated gravel thickness from point samples at 0.3 m depth intervals. The performance of the fluoride electrode compared favorably with a radio tracer (131I) technique in a simultaneous dilution experiment at the Chalk River site. Other ion-selective electrodes such as the chloride electrode may provide an alternative sensor in areas where hydrochemical conditions may restrict the use of the fluoride electrode.

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Geochemical Approaches to Understanding a Shallow Groundwater Flow in the Kanamaru Uranium Mineralization Area (Japan)

MRS Proceedings ◽

10.1557/proc-0893-jj09-07 ◽

2005 ◽

Vol 893 ◽

Author(s):

Regis Bros ◽

Yoji Seki ◽

Atsushi Kamei ◽

Yutaka Kanai ◽

Koichi Okuzawa ◽

...

Keyword(s):

Groundwater Flow ◽

Flow System ◽

Shallow Groundwater ◽

Shallow Waters ◽

Vertical Diffusion ◽

Deep Groundwater ◽

Fresh Groundwater ◽

Activity Ratios ◽

Alkaline Earths ◽

Groundwater Systems

AbstractPredicting the behaviour of radioactive wastes can be facilitated by comparison with the evolution of natural groundwater systems. During a study of the Kanamaru U mineralization (Japan), geochemical approaches for understanding a shallow (0-50 m) fresh groundwater flow system are being assessed. Deep granitic waters are Ca-HCO3-dominated and slightly acidic to slightly alkaline. Shallow waters within sediments display lower pH and they are more dilute. Halide concentrations suggest the existence of a non marine Br-rich and Cl-depleted deep groundwater in the basement. 234U/238U and 230Th/234U activity ratios in the mineralized sedimentary rocks indicate that U mobilization took place within the last 350,000 years. U dissolution currently continues and it is controled by lateral groundwater flow whereas vertical diffusion appears negligible. Dissolved alkaline earths concentrations and the 87Sr/86Sr ratio indicate that solutes exchanges take place through uppermost low permeable granite followed by mixing with more dilute and Cl-type shallow groundwater.

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