Electromagnetic‐Induction Logging to Monitor Changing Chloride Concentrations

Abstract

Water from the San Joaquin Delta, having chloride concentrations up to 3590 mg/L, has intruded fresh water aquifers underlying Stockton, California. Changes in chloride concentrations at depth within these aquifers were evaluated using sequential electromagnetic (EM) induction logs collected during 2004 through 2007 at seven multiple-well sites as deep as 268 m. Sequential EM logging is useful for identifying changes in groundwater quality through polyvinyl chloride-cased wells in intervals not screened by wells. These unscreened intervals represent more than 90% of the aquifer at the sites studied. Sequential EM logging suggested degrading groundwater quality in numerous thin intervals, typically between 1 and 7 m in thickness, especially in the northern part of the study area. Some of these intervals were unscreened by wells, and would not have been identified by traditional groundwater sample collection. Sequential logging also identified intervals with improving water quality-possibly due to groundwater management practices that have limited pumping and promoted artificial recharge. EM resistivity was correlated with chloride concentrations in sampled wells and in water from core material. Natural gamma log data were used to account for the effect of aquifer lithology on EM resistivity. Results of this study show that a sequential EM logging is useful for identifying and monitoring the movement of high-chloride water, having lower salinities and chloride concentrations than sea water, in aquifer intervals not screened by wells, and that increases in chloride in water from wells in the area are consistent with high-chloride water originating from the San Joaquin Delta rather than from the underlying saline aquifer.

Delineation of Salt Water Intrusion through Use of Electromagnetic-Induction Logging: A Case Study in Southern Manhattan Island, New York

“…The unconsolidated sediments underlying Manhattan Island are of Pleistocene age based upon core analysis and previous work [1]. EM conductivity logs provided an electrical conductivity profile of the formation, from which ground-water conductivity and chloride concentrations can be inferred [25,26].…”

“…The main purpose of using the relation between EM conductivity log response and chloride concentration is to allow the conversion of EM log response in wells where chloride sampling is not possible to estimate the chloride concentrations in the aquifer. A similar technique was used in California in PVC cased wells where groundwater samples for chloride concentration measurement were available with EM conductivity logs, and in Florida to map the saltwater interface using surface and borehole EM methods to produce logarithmic equations relating EM response to chloride concentration [25,33].…”

Evaluación multiparamétrica de un esquema MAR (Managed Aquifer Recharge) en un acuífero costero salinizado (Plana de Castellón, España)

“…These authors assigned resistivity values of between 75 (Baharuddin et al 2011) and 360 Ωm (Sherif et al 2006) to freshwater saturated zones. Gravel sediments (Sherif et al 2006;Himi et al 2007b;Duque et al 2008;Ogilvy et al 2009) or gravelly sand aquifers (Wilson et al 2006;Baharuddin et al 2011; showed resistivity values that were greater than those in fine-grained aquifers (Ebraheem et al 1997;Choudhury and Saha 2004;Metzger and Izbicki 2013). In particular, Duque et al (2008) reported a groundwater EC of~1500 μS/cm and resistivities of 100-150 and of 20-60 Ωm in saturated gravel layers and detrital sediments, which varied widely in grain size, respectively.…”

“…Changes in bulk ER, monitored twice, are attributed to changes in groundwater quality. The uncertainty associated with the estimation of the properties of aquifer materials is therefore minimized (Metzger and Izbicki 2013).…”

“…Geophysical data have been interpreted along with groundwater quality data to characterize the groundwater salinity as either fresh, brackish, saline, or brine. Empirical relationships have been established between subsurface resistivity and groundwater electrical conductivity (EC), total dissolved solids (TDS), and chloride concentrations (Guo 1986;Ebraheem et al 1997;Sherif et al 2006;Wilson et al 2006;Baharuddin et al 2011;Metzger and Izbicki 2013).…”