Search

Attributing the sources of legacy contamination, including brines, is important to determine remediation options and to allocate responsibility. To make sound remediation decisions, it is necessary to distinguish subsurface sources, such as leaking oil and gas ("O&G") wells or natural upward fluid migrations, from surface releases. While chemical signatures of surface and subsurface releases may be similar, they are expected to imprint specific dissolved noble gas signatures, caused by the accumulation of terrigenic noble gases in subsurface leaks or re-equilibration of noble gases following surface releases. We demonstrate that only a historic surface release influenced the dissolved noble gas signature of groundwater in monitoring wells contaminated with brine near an abandoned O&G well, rather than subsurface leakage from the well. Elevated brine concentrations were associated with lower terrigenic helium concentrations, indicating re-equilibration with atmospheric helium at the surface during the release. Geophysical surveying indicating elevated salinity in surficial soils upgradient of the wells further supported the interpretation of the noble gas data. Eliminating the possibility that subsurface leakage was the source of the plume was critical to selecting the proper remedial action at the site, which otherwise may have included an unnecessary and costly well re-abandonment. This study demonstrates the use of noble gas analysis to compare potential sources of brine contamination in groundwater and to exclude subsurface leakage as a potential source in an oilfield., (© 2024 The Authors. Groundwater published by Wiley Periodicals LLC on behalf of National Ground Water Association.)

This study examines the potential for aquifer storage and recovery (ASR) in the brackish portion of the Edwards aquifer in New Braunfels, Texas. Successful ASR relies on understanding hydraulic properties, aquifer heterogeneity, water geochemistry, and geochemical processes during operations. The research aims to investigate the chemistries of native groundwater and injectant during ASR operation, estimate the hydraulic properties of the aquifer layers, and assess the recovery rate for the recovered groundwater meeting the total dissolved solids (TDS) threshold. The study found that native groundwater is of Na-Cl facies due to halite dissolution and a possible basinal brine migration associated with the zone of greatest fault displacement. High sulfate ions in background native groundwater result from sulfate-bearing minerals' dissolution in the Kainer and Person Formations. The injectant water is of Ca-Mg-HCO 3 facies due to the carbonate-rich composition of the aquifer host matrix and interaction with the Guadalupe River riverbed. During ASR operations, mixing controlled the shift in hydrochemical facies from Na-Cl to Ca-Mg-HCO 3 .The study also suggests a possible connection between Kainer and Person Formations and preferential pathways in the targeted storage zone aquifer. The estimated conductivity values also indicate dominant horizontal flow via possible fracture pathways in both the Person and Kainer Formation storage zones. Recovery of groundwater meeting the TDS of 1000 mg/L requires a recovery rate of 0.03 m 3 /s for 60 days after 40-day storage. This research emphasizes that understanding the hydrogeological conditions and geochemical processes is critical to ASR feasibility in brackish carbonate multi-aquifer fractured systems., (© 2023 The Authors. Groundwater published by Wiley Periodicals LLC on behalf of National Ground Water Association.)

Managed aquifer recharge is an effective strategy for urban stormwater management. Chemical ions are normally retained in stormwater and groundwater and may accelerate clogging during the recharge process. However, the effect of water chemistry on physical clogging has not previously been investigated. In this study, we investigated the hydrogeochemical mechanism of saturated porous media clogging in a series of column experiments. The column was packed with river sand and added suspensions of kaolinite particles. Calcium chloride and sodium chloride are used as representative ions to study chemical effects. We found that an increase in ionic strength resulted in retention of kaolinite solids in the column, with a breakthrough peak of C/C 0 value of 1 to 0.2. The corresponding hydraulic conductivity decreased with increased solids clogging. Divalent cations were also found to have a greater influence on kaolinite particle clogging than monovalent cations. The enhanced hydrochemical-related clogging was caused by kaolinite solids flocculating and increasing the deposition rate coefficient by 1 to 2 times in high ionic strength conditions. Three clogging mechanisms of kaolinite solids are proposed: surface filtration, inner blocking, and attachment. This study further deepens the understanding of the mechanisms of solids clogging during aquifer recharge and demonstrates the significance of ionic strength on recharge clogging risk assessments., (© 2019, National Ground Water Association.)