Environmental Engineering Reference
In-Depth Information
the adit (S5) that shows 436 mg/L alkalinity and 20 L/s flow (Table
2
). Even though
this effluent is insufficient to neutralize the water of La Silva, it is capable to raise
the pH from 3.6 to 4.5. Only after La Silva flows into the Tremor and having cov-
ered 8,000 m from the headwaters, the water reaches neutrality. In spite of this situ-
ation, the plume of contamination, noticeable due to the drag of Fe and Al
precipitates, reaches Bembibre Village, 15,500 m downstream.
In the current environmental conditions, the biodiversity in La Silva is very
poor. A comparison of the physicochemical and biological characteristics in differ-
ently polluted sampling points is showed in Table
3
. B3 sampling point (Boeza
River) is not affected by mining and shows a high environmental quality. B0
(Boeza River) is located downstream from the confluence of Tremor River. T0, T1
and T4 are located in the Tremor River, which is affected by old mining but have
almost recovered. R1 sampling point is located in the Rodrigatos Stream, on the
process of recovery. In both Tremor and Rodrigatos, the past mining activity is only
noticeable by the high concentration of sulphates and of iron oxides. In order to
compare results, S1 and S10 sampling points (affected by ARD) have been
included. As can be seen in Table
3
, La Silva Stream (S1 and S10) shows much
lower IBMWP and EPT index values than the reference point (B3), being always
lower than 5 (very poor biological quality). On the other hand, the sampling points
T4 (Tremor River upstream from the confluence with La Silva) and R1 (Rodrigatos
Stream) show values closer to B3 (very good biological quality and good biological
quality, respectively). The negative effect of La Silva is also observed downstream
from the confluence of the Tremor River and spreads much further up to the conflu-
ence of Boeza River. Thus, T1 and T0 show lower values than T4 (fair biological
quality). The effect is still visible at B0, in Boeza River downstream from the con-
fluence of Tremor (good biological quality).
Regarding the ichthyofauna, the point B3 has a healthy brown trout population
whereas in La Silva Stream none specimen was found. In the Tremor River,
upstream from the confluence of La Silva (T4), the ichthyofauna is present.
However, as a result of the flowing water from La Silva, in T1 and T0 (downstream
from La Silva) the ichthyofauna is nonexistent. It is necessary to get to the Boeza
River (B0) to find brown trout.
Table 3
Physicochemical features and biological indexes in several sampling points
Sampling point pH SO
4
2−
Cond. Turb. Alk. Al Fe Fe (S) IBMWP EPT
B0 Boeza 7.1 39 122 35 31.7 60.8 22 8,976 89 9
B3 Boeza 6.9 2 22 0.05 12.2 <10 <10 7,592 174 13
T0 Tremor 6.8 105 244 91 34 64.5 66 12,506 54 3
T1 Tremor 7.25 135 293 12.69 42.7 64.1 19 12,277 48 5
T4 Tremor 7.6 126 301 2.53 60 43.6 24 9,701 139 11
R1 Rodrigatos 7.2 304 575 5.52 65 98 83 10,037 86 6
S1 La Silva 3.45 438 781 0.21 0 52,644 10,640 175,178 0 0
S10 La Silva 4.73 289 507 25 0 8,548 808 12,665 5 2
Cond: co
nductivity, unit in µS/cm; Turb: turbidity, unit in FTU; Alk: alkalinity, unit in mg/L
CaCO
3
; Al, Fe: concentration in water samples, units in µg/L, Fe (S): concentration in Fraction III
in sediments samples
[7]
, units in µg/g.
