Environmental Assessment
Volume B-3.7
Mine
Hydrogeology
Ambatovy Project
88
January 2006
and sediment quality changes, and reduce likely effects, if such an event should
occur.
3.7.5.5 Results for Key Question HG-2: What Effect Will the Mine
Have on Groundwater Flows and Quality at the Surrounding
Area, particularly the Torotorofotsy Wetlands?
Mine dewatering will influence the volume of water that flows into the
Torotorofotsy and Mokaranana wetland systems. The Mokaranana wetland
system is interconnected to Torotorofotsy and any influence on Mokaranana will
influence Torotorofotsy as well. Groundwater contributions to the baseflow of
affected upper river watersheds that feed Mokaranana or Torotorofotsy will be
reduced by approximately 7%. The affected portions of the watersheds or area of
influence is shown on GCS Drawing No. 3.3.7 in Volume I, Appendix 7.2. The
quality of groundwater contributions to the river watersheds will not be affected
by mining operations.
Based on this reduction in baseflow contribution and actual measured river flow
volumes in the Torotorofotsy and Mokaranana wetlands, the reduction in river
inflow into the wetland systems from the rivers that are affected have been
calculated and are shown in Table 3.7-3.
Table 3.7-3 Reduction in Affected River Inflow into the Wetland Systems due to
Baseflow Contribution Decrease
Dry Season
Wet Season
Average
observed
(10apr2004 to
14dec2004)
calculated
with mining
influence
observed
(15dec2004 to
23feb2004)
calculated
with mining
influence
observed
(10apr2004 to
23feb2005)
calculated
with mining
influence
Mokaranana
Area
(QESF-101)
0.012
3
/sec
0.011m
3
/sec
0.225m
3
/sec
0.209m
3
/sec
0.015m
3
/sec
0.014m
3
/sec
Torotorofotsy
Area
(QESF-103)
0.13 m
3
/sec
0.12 m
3
/sec
0.303m
3
/sec
0.282m
3
/sec
0.155m
3
/sec
0.144m
3
/sec
While up to a 6.6% to 8.3% reduction of groundwater contributions to surface
water baseflows downstream the mine site may occur (7% based on average
flows), groundwater abstracted in mine dewatering during operation will be
released into mine runoff collection ponds and will eventually report to surface
drainage features. In addition, runoff from the mine site is expected to be higher
than under baseline conditions due to land disturbance associated with mine
development. Mine site hydrology is described in the subsequent section
