98
• According to the water footprint framework formalized in ISO 14046 standard
for LCA. No consensus-based approach exists for applying this standard.
Furthermore, results are not always comparable when different scarcity or stress
indicators are used for the characterization of impacts (Boulay et al. 2017).
Additionally, regionalized assessment is still a challenge with current databases
and software, referring to a “global” region without specific geographic
information (Boulay et al. 2017).
• A range of methodological and data limitations hamper the efforts to conduct
water footprint studies of mining, such as private mining companies not releasing
data to the public (Northey et al. 2016). General life cycle assessment studies,
which include “water use,” are mainly focused only on water consumption and
neglect the environmental impacts of this consumption.
Table 7.1 compares the life cycle assessment water indicators of both open-pit
and alluvial mining combined with mining processes taken from the Ecoinvent 3.1
database. It shows that for all water impact categories, alluvial mining technology
presented the lowest value in relation to open-pit mining and the standard results
from Perú, Papua New Guinea, and ROW (from the Ecoinvent 3.1 database). This is
of course excluding water depletion where it obtained the highest values for its
excessive water usage.
The unusual behavior presented by alluvial mining in comparison with other
mining systems could be explained by the stark difference in its extractive technique.
Conventional extractive processes such as open-pit mining and those presented by
Ecoinvent 3.1 all seem to have similar environmental impacts as they all use a
similar conventional ore extractive method. However, it is worth noting that values
for all impact categories showed in Table 7.2 are higher for the open-pit technology
than in the Ecoinvent processes.
Figure 7.7 shows the contribution of each process to open-pit mining’s water
environmental impact categories. From the figure, 98.9% of the total impacts to the
water resource (9.63 × 10
4
) are generated by sulfide tailings. This is a direct result
of its huge need of area and its contents of toxic substances. Tailings generate almost
99% of total impacts in the following impact categories: freshwater ecotoxicity,
freshwater eutrophication, marine ecotoxicity, and marine eutrophication.
In the case of alluvial mining technology (see Fig. 7.8), 99.9% of the total water
impacts (2.82 × 10
4
) come from water extracted from the river to build the digging
pond and use in the physical separation of gold by gravimetric concentration, which
mainly affected water depletion. The rest of the impact categories are largely
affected by the run-of-river electricity production.
In regard to mining technologies’ impact on water resources, freshwater ecotoxicity and marine ecotoxicity were clearly the most affected impact categories in
comparison to freshwater and marine eutrophication indicators.
It is also clear that according to the laboratory values for the tailings composition, specific substances cause the high toxicity values from the open-pit mining
process. The phosphorus content of the tailings slug contributes to nearly 75% of
open-pit mining’s impact on freshwater ecotoxicity and close to 99% of freshwater
N. A. Cano Londoño et al.
• According to the water footprint framework formalized in ISO 14046 standard
for LCA. No consensus-based approach exists for applying this standard.
Furthermore, results are not always comparable when different scarcity or stress
indicators are used for the characterization of impacts (Boulay et al. 2017).
Additionally, regionalized assessment is still a challenge with current databases
and software, referring to a “global” region without specific geographic
information (Boulay et al. 2017).
• A range of methodological and data limitations hamper the efforts to conduct
water footprint studies of mining, such as private mining companies not releasing
data to the public (Northey et al. 2016). General life cycle assessment studies,
which include “water use,” are mainly focused only on water consumption and
neglect the environmental impacts of this consumption.
Table 7.1 compares the life cycle assessment water indicators of both open-pit
and alluvial mining combined with mining processes taken from the Ecoinvent 3.1
database. It shows that for all water impact categories, alluvial mining technology
presented the lowest value in relation to open-pit mining and the standard results
from Perú, Papua New Guinea, and ROW (from the Ecoinvent 3.1 database). This is
of course excluding water depletion where it obtained the highest values for its
excessive water usage.
The unusual behavior presented by alluvial mining in comparison with other
mining systems could be explained by the stark difference in its extractive technique.
Conventional extractive processes such as open-pit mining and those presented by
Ecoinvent 3.1 all seem to have similar environmental impacts as they all use a
similar conventional ore extractive method. However, it is worth noting that values
for all impact categories showed in Table 7.2 are higher for the open-pit technology
than in the Ecoinvent processes.
Figure 7.7 shows the contribution of each process to open-pit mining’s water
environmental impact categories. From the figure, 98.9% of the total impacts to the
water resource (9.63 × 10
4
) are generated by sulfide tailings. This is a direct result
of its huge need of area and its contents of toxic substances. Tailings generate almost
99% of total impacts in the following impact categories: freshwater ecotoxicity,
freshwater eutrophication, marine ecotoxicity, and marine eutrophication.
In the case of alluvial mining technology (see Fig. 7.8), 99.9% of the total water
impacts (2.82 × 10
4
) come from water extracted from the river to build the digging
pond and use in the physical separation of gold by gravimetric concentration, which
mainly affected water depletion. The rest of the impact categories are largely
affected by the run-of-river electricity production.
In regard to mining technologies’ impact on water resources, freshwater ecotoxicity and marine ecotoxicity were clearly the most affected impact categories in
comparison to freshwater and marine eutrophication indicators.
It is also clear that according to the laboratory values for the tailings composition, specific substances cause the high toxicity values from the open-pit mining
process. The phosphorus content of the tailings slug contributes to nearly 75% of
open-pit mining’s impact on freshwater ecotoxicity and close to 99% of freshwater
N. A. Cano Londoño et al.