Consequences and mitigation of saltwater intrusion induced by short-circuiting during aquifer storage and recovery in a coastal subsurface
Coastal aquifers and the deeper subsurface are increasingly exploited. The accompanying perforation of the subsurface for those purposes has increased the risk of short-circuiting of originally separated aquifers. This study shows how this short-circuiting negatively impacts the freshwater recovery...
Main Authors: | , |
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Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2017-02-01
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Series: | Hydrology and Earth System Sciences |
Online Access: | http://www.hydrol-earth-syst-sci.net/21/1173/2017/hess-21-1173-2017.pdf |
Summary: | Coastal aquifers and the deeper subsurface are increasingly
exploited. The accompanying perforation of the subsurface for those purposes
has increased the risk of short-circuiting of originally separated aquifers.
This study shows how this short-circuiting negatively impacts the freshwater
recovery efficiency (RE) during aquifer storage and recovery (ASR) in
coastal aquifers. ASR was applied in a shallow saltwater aquifer overlying a
deeper, confined saltwater aquifer, which was targeted for seasonal aquifer
thermal energy storage (ATES). Although both aquifers were considered
properly separated (i.e., a continuous clay layer prevented rapid groundwater
flow between both aquifers), intrusion of deeper saltwater into the
shallower aquifer quickly terminated the freshwater recovery. The presumable
pathway was a nearby ATES borehole. This finding was supported by field
measurements, hydrochemical analyses, and variable-density solute transport modeling (SEAWAT version 4; Langevin et al., 2007).
The potentially rapid short-circuiting during storage
and recovery can reduce the RE of ASR to null. When limited mixing with
ambient groundwater is allowed, a linear RE decrease by short-circuiting
with increasing distance from the ASR well within the radius of the injected
ASR bubble was observed. Interception of deep short-circuiting water can
mitigate the observed RE decrease, although complete compensation of the RE
decrease will generally be unattainable. Brackish water upconing from the
underlying aquitard towards the shallow recovery wells of the ASR system
with multiple partially penetrating wells (MPPW-ASR) was observed. This
<q>leakage</q> may lead to a lower recovery efficiency than based on current ASR
performance estimations. |
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ISSN: | 1027-5606 1607-7938 |