Environmental Assessment
Volume B-3.7
Mine
Hydrogeology
Ambatovy Project
89
January 2006
(Volume B, Section 3.8). The minor reduction in groundwater inflow volumes
into the wetland will be offset by an increase in surface runoff that will occur
during mining.
3.7.6
Impact Analysis
3.7.6.1 Residual Impacts
During construction, negligible impacts to groundwater resources will occur as
influence to groundwater will be limited to excavation of mine water collection
ponds that could provide minor increased seepage to groundwater.
During operations, extraction of groundwater from the active areas of mining will
result in temporary dewatering of the groundwater aquifers. It will also reduce
groundwater contributions to upper watersheds of affected rivers that feed the
Mokaranana and Torotorofotsy wetlands by up to 7%. The reduction of baseflow
contributions (low impact) will be offset by increased runoff from the mine area.
Increases in surface flows in the Torotorofotsy River at the inlet to the wetlands
will be less than 4% during operations and about 2% for post-closure conditions
(Volume B, Section 3.8).
Groundwater aquifers will recover in Year 20 of operations when active mining
in the open pits ceases. The estimated time for complete recovery of groundwater
levels to pre-mining state is 5 to 20 years (ferricrete aquifer) and 5 to 75 years
(ferralite aquifer), depending upon the location. The remnant open pits and the
removal of materials during mining will result in an altered landscape that will
permanently influence the groundwater regime to some degree. The degree of
reduction of groundwater contributions to river baseflows will lessen from the
6.6% to 8.3% as the groundwater aquifers recover such that the long-term
influence on groundwater flow will be less than that during operations.
Residual impacts are presented in Table 3.7-4. Residual impacts to groundwater
flows and groundwater quality at the mine site is of negligible to low
environmental consequence. Residual impacts of changes in groundwater
contributions to the Mokaranana and Torotorofotsy Wetlands during operations
is of low magnitude, medium-term in duration and of high frequency, ultimately
obtaining a moderate rating in terms of environmental consequence.
