GroundwaterPub Date : 2026-01-26DOI: 10.1111/gwat.70048
Michael R. Shultz, Colin Plank
{"title":"The Geology of Aquitards in Alluvial Aquifers: A Predictive Approach Based on Facies Models","authors":"Michael R. Shultz, Colin Plank","doi":"10.1111/gwat.70048","DOIUrl":"10.1111/gwat.70048","url":null,"abstract":"<p>A sophisticated understanding of the three-dimensional distribution of silt- and clay-rich bodies of strata (elements) in aquifers is critical given that they not only have the potential to act as aquitards or semi-confining units and vertically partition groundwater flow into separate aquifer zones, but also provide lateral barriers to groundwater flow, impacting contaminant distribution and groundwater flow dynamics. Additionally, when in prolonged contact with dense nonaqueous phase liquid (DNAPL) or contaminated groundwater, fine-grained elements may become storage zones for contaminant mass via matrix diffusion and thus serve as long-term secondary sources of contamination to groundwater that can confound remediation strategies and render remedy performance projections unreliable. The stratigraphic architecture of aquifer systems, including fine-grained facies architecture, is complex but is not random and can be effectively predicted through application of facies models. This paper reviews depositional models (“facies models”) for common depositional environments with a focus on alluvial end-members of braided fluvial, meandering fluvial, and alluvial fan facies models. We examine the facies models from the perspective of aquitards and present case studies to provide an overview of the expected aquitard dimensions and characteristics. The critical yet underappreciated role of the paleosol as a potential aquitard is also examined, and basic criteria for differentiating ancient floodplain clay units with high lateral continuity from other laterally discontinuous clay units are provided.</p>","PeriodicalId":12866,"journal":{"name":"Groundwater","volume":"64 1","pages":"30-40"},"PeriodicalIF":2.0,"publicationDate":"2026-01-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12857526/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146055704","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
GroundwaterPub Date : 2026-01-13DOI: 10.1111/gwat.70045
M. J. Hinton, S. Alpay, H. L. Crow
{"title":"Groundwater Transport in a Glaciomarine Aquitard: Paleosalinity and Landslide Implications","authors":"M. J. Hinton, S. Alpay, H. L. Crow","doi":"10.1111/gwat.70045","DOIUrl":"10.1111/gwat.70045","url":null,"abstract":"<p>Leaching of marine salinity in the porewater of glaciomarine muds is one precursor to landslide hazard. In this study, groundwater modeling is used to quantify vertical groundwater flow, constrain paleosalinity, and characterize past and future progression of leaching with depth in Champlain Sea sediments. The Breckenridge Creek site, ~15 km northwest of Ottawa, Canada, was cored within a thick sequence (up to 98 m) of Champlain Sea muds that form a regional aquitard in the St. Lawrence Lowlands and Ottawa Valley. Porewater chloride concentrations ([Cl]), up to 12,250 mg/kg, and δ<sup>18</sup>O as high as −7.18‰, indicate remnant seawater. One-dimensional groundwater transport modeling simulates porewater [Cl] and δ<sup>18</sup>O with depth simultaneously and constrains specific discharge, q, from 2.40 to 2.51 mm/a. Groundwater transport modeling and three-component mixing of seawater, glacial meltwater and meteoric water constrain the range of initial [Cl] between 14,000 and 15,700 mg/kg (72–80% seawater) and initial δ<sup>18</sup>O between −5.99 and −5.61‰. The glacial meltwater component of Champlain Sea bottom waters at the Breckenridge site has a maximum δ<sup>18</sup>O value of −22.4‰. Downward leaching to the salinity threshold of <2 g/L for geotechnical sensitivity development reached a depth of 20.6 m. Modeling indicates the leaching front currently progresses at a rate of 2.5 m/1000 years, slower than advection of freshwater infiltration because of upward diffusion and dispersion of marine solutes. Notably for landslide hazard, the highest measurements of geotechnical sensitivity coincide with the leached zone.</p>","PeriodicalId":12866,"journal":{"name":"Groundwater","volume":"64 1","pages":"49-63"},"PeriodicalIF":2.0,"publicationDate":"2026-01-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12857530/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145961045","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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