Environmental Engineering Reference
In-Depth Information
3. Slurry tailings discharge consisting of water and a wide range of inorganic and
organic dissolved constituents obtained from the remnants of reagents used in
the recovery processes and ine fractions of the host ores. Impacts on land use
consist of large open containment facilities such as dammed-up valleys and ponds
containing sludges and slimes that pose health and safety threats to animals and
humans, runoffs from the containment facilities, embankments for the impound-
ments used to contain the sludges and slimes and leachates that contaminate
ground, groundwater, and receiving waters. Most of the slurry tailings' con-
tainment facilities contain slurries and slimes that will not exhibit liquid-solids
separation, i.e., the solids in these facilities will not readily sediment or settle to
the bottom of the containment structure. Typical of the types of tailings ponds
are red-mud ponds, tar sands sludge ponds, phosphatic clay ponds, etc. Many of
these ponds contain slurries and sludges that are toxic in nature. Their presence
will pose potential safety and health threats to the human population within the
immediate area. The strategies for maintaining and operating containment facili-
ties are discussed in the next subsection.
As opposed to the discussion on tailings dam instability in the previous section, holding
ponds embankment stability can be a problem if the containment embankments become
too high and are subject to drawdown pressures when large luctuations occur over a
very short period in the height of the slurry or sludge in the pond. This has happened in
instances when containment ponds are emptied quickly. Collapse of the embankments
can lead to failure of structures located near these embankments. This particular issue
is a geotechnical problem that can be corrected with proper design and management
techniques.
5.3.2 Underground In Situ Hydrocarbon Extraction
We have previously described underground in situ hydrocarbon extraction to mean the
extraction of natural gas from shale and similar geological formations, oil (tight oil) or
heavy bitumen in deep geological deposits (using the SAGD technique or the CSS process).
The procedures common to all of these underground in situ extraction techniques is the
requirement for deep drilling, in most instances, to obtain horizontal wells at the depths
required for extraction of the desired product hydrocarbon. The discussion of sources of
stressors and resultant impact that follows is conined to those sources associated with the
extraction of the product hydrocarbons in the already drilled horizontal wells.
5.3.2.1 Fluid Usage and Stressors
Common to the three types of underground in situ extraction processes is the use of high
volumes or quantities of water—with or without additives. Either with or without prior
addition of additives, water obtained after its accomplished purpose, is contaminated,
i.e., the utilized water is a source for chemical stressors. In the case of steam-injection
water used for softening the bitumen in the host material, contamination of the water
by the hydrocarbons released or luidized by the steaming process occurs—thereby
rendering the used steam water a source of chemical stressors. In the case of fracking
luids used for extraction of shale gas, for example, the additives used in the fracking
luid constitute the sources for chemical stressors. Although the industries involved in
the implementation of these processes make every effort to recover the water used for
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