We are pleased to announce the publication of a new article in Science of the Total Environment, 622-623: 1178-1192, from the G360 Institute Team.
High resolution spatial and temporal evolution of dissolved gases in groundwater during a controlled natural gas release experiment.
Cahill*, A.G., Parker, B.L., Mayer, B., Mayer, K.U., Cherry, J.A.
Funding for this study was provided by the Natural Sciences and Engineering Research Council of Canada (NSERC) under grant STPGP 463045 – 14 awarded to Professors John Cherry and Beth Parker. Special thanks for field and laboratory assistance are given to Michael Nightingale, Andreas Haggman, Bethany Ladd, Dylan Klazinga, Terri Cheung, Leon Halwa and Alyssa Verdin.
Fugitive gas comprised primarily of methane (CH4) with traces of ethane and propane (collectively termed C1–3) may negatively impact shallow groundwater when unintentionally released from oil and natural gas wells. Currently, knowledge of fugitive gas migration, subsurface source identification and oxidation potential in groundwater is limited. To advance understanding, a controlled release experiment was performed at the Borden Research Aquifer, Canada, whereby 51 m3 of natural gas was injected into an unconfined sand aquifer over 72 days with dissolved gases monitored over 323 days. During active gas injection, a dispersed plume of dissolved C1–3 evolved in a depth discrete and spatially complex manner. Evolution of the dissolved gas plume was driven by free-phase gas migration controlled by small-scale sediment layering and anisotropy. Upon cessation of gas injection, C1–3 concentrations increased to the greatest levels observed, particularly at 2 and 6 m depths, reaching up to 31.5, 1.5 and 0.1 mg/L respectively before stabilizing and persisting. At no time did groundwater become fully saturated with natural gas at the scale of sampling undertaken. Throughout the experiment the isotopic composition of injected methane (δ13C of − 42.2‰) and the wetness parameter (i.e. the ratio of C1 to C2 +) constituted excellent tracers for the presence of fugitive gas at concentrations > 2 mg/L. At discrete times C1–3 concentrations varied by up to 4 orders of magnitude over 8 m of aquifer thickness (e.g. from < 0.01 to 30 mg/L for CH4), while some groundwater samples lacked evidence of fugitive gas, despite being within 10 m of the injection zone. Meanwhile, carbon isotope ratios of dissolved CH4 showed no evidence of oxidation. Our results show that while impacts to aquifers from a fugitive gas event are readily detectable at discrete depths, they are spatially and temporally variable and dissolved methane has propensity to persist.
We are pleased to announce the publication of a new article in Groundwater for Sustainable Development from the G360 Institute Team.
Integrative management of saltwater intrusion in poorly-constrained semi-arid coastal aquifer at Ras El-Hekma, Northwestern coast, Egypt.
Eissa*, M.A., De-Dreuzy, J.R., Parker, B.L.
This study was supported by the Campus France of the French Institute in Cairo, Egypt. The Authors gratefully acknowledge the Science & Technology Development Fund (STDF) in Egypt for funding the project # 6723. Authors would like to thanks the Editors of the journal as well as the reviewers who have generously given up valuable time to review the manuscript.
Saltwater intrusion is a major concern in coastal aquifers, particularly in arid and semiarid regions, where recharge is limited and groundwater withdrawal is the main source of potable water. In Ras El Hekma groundwater occurs in the Pleistocene aquifer as a thin lens of freshwater where groundwater quality is very sensitive to pumping stresses. High groundwater withdrawals from the Pleistocene aquifer deteriorate the groundwater quality along the coast due to upwelling of saltwater into the thin lens freshwater. The Pleistocene aquifer is poorly-constrained; the hydrological and geochemical records are sparse. Therefore, a simple analytical approach has been used in order to address local and regional groundwater management issues, for cases of data scarcity using little known and well defined parameters. The model assumes steady state flow as an initial condition in an isotropic and homogeneous medium, with a sharp interface between the freshwater and seawater wedge. The model combines the hydrogeological and geochemical characterization, adapted to the aquifer geometry, in order to provide global salt and freshwater balances to the Ras El Hekma scale site. The model shows progressive extension of the seawater intrusion zone (x-toe) upon increasing the groundwater withdrawals from 250 m3/day to an order of magnitude of this amount. The x-toe distance has been extended from 1700 to 5000 m from the tip of Ras El Hekma to inland. Such model could be applied to estimate the volume of the freshwater and seawater wedge along the coast as well as to predict the groundwater withdrawals under different pumping scenarios. Seawater intrusion, in the Ras El Hekma area, is caused by the unbalance between the pumping withdrawal rates and the natural recharge from precipitation. The model can be applied for similar hydrogeological systems, specifically, coastal aquifers located in semiarid to arid environments where limited aquifer data is available.
We are pleased to announce the publication of a new article in Groundwater Monitoring and Remediation from the G360 Institute Team.
Novel Well Completions in Small Diameter Coreholes Created Using Portable Rock Drills:
Pierce*, A.A., Parker, B.L., Ingleton, R., Cherry, J.A.
We thank Neil Shaw, CEO of Shaw Drills, for his devotion to quickly advancing his drill to make 2-inch diameter holes, which allows use of down-hole pressure transducers, and his continued work on modifying the drill technology to enhance its capabilities for use in hydrogeological studies. Dale Emerson of Cascade Drilling and Ryan Kroeker of the University of Guelph provided able assistance during field work at the Los Angeles site that was critical to fine tuning the small drills methodology for monitoring well clusters. Funding for development of this methodology and its application was provided by The Boeing Company, National Aeronautics Space Administration, United States Department of Energy, and Natural Science and Engineering Research Council of Canada Industrial Research Chair grant to Dr. B.L. Parker (IRC 363783-11).
The Boeing Company
National Aeronautics Space Administration
United States Department of Energy
Natural Science and Engineering Research Council of Canada. Grant Number: IRC 363783-11
Difficult access conditions have limited techniques for groundwater system characterization and monitoring in bedrock exposed landscapes. This condition is common in the mining industry and resulted in the development of lightweight portable drills. This paper describes how these drills were used at a contaminated site to understand the groundwater flow system by adapting piezometer designs, ensuring effective seals to obtain reliable hydraulic head, hydrochemistry, and contaminant concentrations. Two drilling machines were evaluated: the Shaw Portable Core Drill™ fits in a backpack and can advance continuously cored rock holes, nominal 51 millimeters (mm) diameter, to depths up to approximately 15 meters (m); and the larger Winkie Drill™ requires a two or more people to mobilize and can advance continuously cored holes, nominal 48 mm diameter, to depths of approximately 45 m. The resulting small diameter coreholes were accommodated in the design of each well using a seal created by injecting grout into a semipermeable fabric sleeve. This “fabric sleeve” serves as a means to contain the grout and ensures that the entire annulus above the screen is sealed without loss of grout into the formation, allowing the well to perform as a piezometer. To develop and demonstrate this methodology for groundwater monitoring in bedrock, the two drills were used in drainages located along the slopes of an elevated sandstone outcrop near Los Angeles, California. Unique insights into the groundwater flow system of this bedrock environment, which would otherwise be unattainable, were achieved. This methodology overcomes the accessibility limitations of conventional drilling methods that prevent installation of wells in remote and rugged mountainous terrains.
We are pleased to announce the publication of a new article in the Journal of Hydrology from the G360 Institute Team.
Cross-hole fracture connectivity assessed using hydraulic responses during liner installations in crystalline bedrock boreholes:
Persaud*, E., Levison, J., Pehme*, P., Novakowski, K., Parker, B.L
The authors would like to acknowledge time and effort of G360 staff, especially Ryan Kroeker and James Hommersen, for the field activities involved in this study. Thank you also to Peter Kitanidis, Paul Hsieh and three anonymous reviewers whose constructive comments helped to improve the quality of this manuscript.
This work was supported by a Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant [grant number 03973]; the NSERC Canada Graduate Scholarship Program (Master’s); and the Ontario Graduate Scholarship Program.
In order to continually improve the current understanding of flow and transport in crystalline bedrock environments, developing and improving fracture system characterization techniques is an important area of study. The presented research examines the installation of flexible, impermeable FLUTe™ liners as a means for assessing cross-hole fracture connectivity. FLUTe™ liners are used to generate a new style of hydraulic pulse, with pressure response monitored in a nearby network of open boreholes drilled in gneissic rock of the Canadian Shield in eastern Ontario, Canada. Borehole liners were installed in six existing 10–15 cm diameter boreholes located 10–35 m apart and drilled to depths ranging between 25–45 m. Liner installation tests were completed consecutively with the number of observation wells available for each test ranging between one and six. The collected pressure response data have been analyzed to identify significant groundwater flow paths between source and observation boreholes as well as to estimate inter-well transmissivity and storativity using a conventional type-curve analysis. While the applied solution relies on a number of general assumptions, it has been found that reasonable comparison can be made to previously completed pulse interference and pumping tests. Results of this research indicate areas where method refinement is necessary, but, nonetheless, highlight the potential for use in crystalline bedrock environments. This method may provide value to future site characterization efforts given that it is complementary to, and can be used in conjunction with, other currently employed borehole liner applications, such as the removal of cross-connection at contaminated sites and the assessment of discrete fracture distributions when boreholes are sealed, recreating natural hydraulic gradient conditions.
We are pleased to announce the publication of a new open access journal article in the Journal of Hydrology from the G360 Institute Team.
Mechanisms of recharge in a fractured porous rock aquifer in a semi-arid region: Ferdinando Manna, Kenneth M.Walton, John A.Cherry, Beth L.Parker
Funding for this work was provided by an NSERC Industrial Research Chair (n. IRCPJ 363783) to Professor Beth Parker in partnership with the Boeing Company. Field work was supported by the site owner, their consultants (MWH Inc., now Stantec), and University of Guelph colleagues, especially Amanda Pierce from the G360 Institute for Groundwater Research. The authors also thank Dr. Nicholas M. Johnson from Stantec for helpful comments.
Eleven porewater profiles in rock core from an upland exposed sandstone vadose zone in southern California, with thickness varying between 10 and 62 m, were analyzed for chloride (Cl) concentration to examine recharge mechanisms, estimate travel times in the vadose zone, assess spatial and temporal variability of recharge, and determine effects of land use changes on recharge. As a function of their location and the local terrain, the profiles were classified into four groups reflecting the range of site characteristics. Century- to millennium-average recharge varied from 4 to 23 mm y−1, corresponding to <1–5% of the average annual precipitation (451 mm over the 1878–2016 period). Based on the different average Cl concentrations in the vadose zone and in groundwater, the contribution of diffuse flow (estimated at 80%) and preferential flow (20%) to the total recharge was quantified. This model of dual porosity recharge was tested by simulating transient Cl transport along a physically based narrow column using a discrete fracture-matrix numerical model. Using a new approach based on partitioning both water and Cl between matrix and fracture flow, porewater was dated and vertical displacement rates estimated to range in the sandstone matrix from 3 to 19 cm y−1. Moreover, the temporal variability of recharge was estimated and, along each profile, past recharge rates calculated based on the sequence of Cl concentrations in the vadose zone. Recharge rates increased at specific times coincident with historical changes in land use. The consistency between the timing of land use modifications and changes in Cl concentration and the match between observed and simulated Cl concentration values in the vadose zone provide confidence in porewater age estimates, travel times, recharge estimates, and reconstruction of recharge histories. This study represents an advancement of the application of the chloride mass balance method to simultaneously determine recharge mechanisms and reconstruct location-specific recharge histories in fractured porous rock aquifers. The proposed approach can be applied worldwide at sites with similar climatic and geologic characteristics.