Characterizing groundwater salinity patterns in a coastal sand aquifer at Magilligan, Northern Ireland, using geophysical and geotechnical methods

Abstract

Tidal forcing influences groundwater flow and salt distribution in shallow coastal aquifers, with the interaction between sea level variations and geology proving fundamental for assessing the risk of seawater intrusion (SI). Constraining the relative importance of each is often confounded by the influences of groundwater abstraction and geological heterogeneity, with understanding of the latter often restricted by sampling point availability and poor spatial resolution. This paper describes the application of geophysical and geotechnical methods to better characterize groundwater salinity patterns in a tidally dominated ~ 20 m thick sequence of beach sand, unaffected by groundwater abstraction. Electrical resistivity tomography (ERT) revealed the deposit to consist of an upper wedge of low resistivity (< 3 Ωm), reaching over 8 m thick in the vicinity of the low water mark, overlying a higher resistivity unit. Cone penetrometer testing (CPT), and associated high-resolution hydraulic profiling tool system (HPT), coupled with water quality sampling, revealed the wedge to reflect an intertidal recirculation cell (IRC), which restricts freshwater discharge from a relatively homogeneous sand unit to a zone of seepage within the IRC. The application of CPT and HPT techniques underscored the value of geotechnical methods in distinguishing between geological and water quality contributions to geophysical responses. Survey results have permitted a clear characterization of the groundwater flow regime in a coastal aquifer with an IRC, highlighting the benefit of combining geophysical and geotechnical methods to better characterize shallow SI mechanisms and groundwater flow in coastal hydrogeological environments.

Polymer Coatings Affect Transport and Remobilization of Colloidal Activated Carbon in Saturated Sand Columns: Implications for In Situ Groundwater Remediation

“…Quartz sand is a primary component found in many coastal aquifer sites. , We used quartz sand (Sigma-Aldrich, 50–70 mesh) as the media for all column experiments. Based on the particle size and terminology adopted by the United States Department of Agriculture (USDA, 1993), this quartz sand falls within the range of fine sand and medium sand .…”

Comparison of saturated hydraulic conductivity estimated by empirical, hydraulic and numerical modeling methods at different scales in a coastal sand aquifer in Northern Ireland

“…Groundwater models are commonly used to estimate aquifer properties by calibration processes or inverse modeling (Zhou and Li 2011;Moharir et al 2017;Águila et al 2019). One of the most widely used groundwater flow codes is MODFLOW, which solves the three-dimensional groundwater flow equation for porous media by using the finite-difference method (Harbaugh et al 2000).…”

“…As such K plays a crucial role influencing groundwater flow and contaminant migration and can vary up by more than 10 orders of magnitude from coarse to very fine grained solids. Moreover, hydraulic conductivity typically varies within natural geological units (Mitchell and Soga 2005), with this spatial heterogeneity giving rise to considerable scaledependent uncertainties in determining an appropriate value (Mallants et al 1997;Boschan and Noetinger 2012;Piña et al 2019;Águila et al 2022a). Consequently, determining realistic values of K can prove essential in fields including civil engineering (Liu and Rowe 2016;Tan et al 2017;Chen et al 2021), mining (McCoy et al 2006Meiers et al 2011), chemical engineering (Francisca and Glatstein 2010;Wu et al 2020), agronomy (Peña-Haro et al 2011;Picciafuoco et al 2019) and environmental geology (Akcanca and Aytekin 2014;Gao et al 2018).…”

Four-Dimensional Electrical Resistivity Imaging for Monitoring Pumping-Induced Saltwater Intrusion in a Coastal Aquifer

“…1A). The site has been described in detail in previous studies (Carter, 1975;Robins and Wilson, 2017;Águila et al, 2022). Twenty metres of relatively homogenous, fine-medium grained Holocene sands underlain by low permeability Lower Jurassic Mudstone (McCann, 1988) occur adjacent to an intertidal zone up to 100 m wide (Pingree and Griffiths, 1981).…”