Environmental Engineering Reference
In-Depth Information
This pollution may occur as a result of poor practice, accident or unexpected
circumstances that lead to pathways being created between the source of
the pollution and the receptor. Receptors in this case include humans,
groundwater, surface water and ecosystems. The pathways may be
created by:
Run-off or infiltration to the ground arising from spills and leaks of li-
quids, chemicals and operational wastewater being transported to/from
the site, stored on the site or during use in the hydraulic fracturing
process/operation;
Uncontrolled releases of drilling muds/fluids into non-target geological
formations containing groundwater and aquifers during installation of
exploration and production wells;
Migration of drilling muds/fluids or hydraulic fracturing fluids injected
at high pressures along natural geological discontinuities (faults and
fractures);
Hydraulic fracturing creating interconnected fractures that extend be-
yond the intended zone and provide migration pathways for drilling
muds/fluids, hydraulic fracturing fluids and formation water to leak
into non-target geological
formations containing groundwater and
aquifers;
Well failure arising from poor construction or loss of well integrity
during the lifetime of operation, including damage resulting from in-
duced seismicity or other ground movement, leading to uncontrolled
releases of drilling muds/fluids, hydraulic fracturing fluids and for-
mation waters
into non-target geological
formations containing
groundwater and aquifers; and
Existing infrastructure such as wells (active or abandoned), mine
workings and adits providing pathways for drilling muds/fluids,
hydraulic fracturing fluids and formation water to leak into non-target
geological formations containing groundwater and aquifers.
Multiple pathways may potentially exist and interact. It is therefore
essential that an appropriate level of risk assessment is carried out and
effective risk management procedures established. This will require a
combination of actions, some of which are engineering-based and will be
addressed by ensuring that industry good practice is adopted; others will
require site-specific investigation, characterisation and monitoring.
5.1 Natural Sub-surface Pathways
Myers
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identifies two possible mechanisms by which pollutants may mi-
grate from fractured shale to shallow aquifers along natural pathways in the
sub-surface: advective transport through the rock matrix, and preferential
flow through fractures and other discontinuities. He suggests that there is
substantial geological evidence that natural hydraulic gradients can drive
