Environmental Impact Assessment(EIA) Registration for the ...

REVISED PROJECT DESCRIPTION AND ENVIRONMENTAL IMPACT ASSESSMENT (EIA) REGISTRATION
FOR THE NEPISIGUIT FALLS GENERATING STATION MODIFICATION AND REHABILITATION PROJECT
such sediments in the headpond might be exposed and result in a secondary episode of toxicity
to fish as a result of the alternative option. Changes to flow patterns during dewatering may also
cause these sediments to be disturbed and transported downstream.
Dewatering of the headpond also has the potential to result in a large area of HADD (though
temporary), which could be unfeasible to compensate. The temporary HADD would be a direct
result of the lowered water level in the headpond that would expose fish habitat to the elements
(e.g., drying from the sun, heavy rainfall events) prior to re-watering.
This alternative would also limit access to the local recreational fishery upstream of the NFGS
(R. Baker, pers. comm. 2010; D. Haché, pers. comm. 2010; Scott and Crossman 1993).
Consultation with DFO during the planning stages of the Project indicated that a fishery closure
may be recommended to mitigate potential health and safety concerns associated with the
public accessing the river by traveling over the exposed muddy banks.
As described in Section 2.2, the nature of the replacement of the coarse trash rack system and
intake deck require that part of the Project be completed in dry conditions. In order to replace
the coarse trash rack system, access to the upstream face of the power house in the dry is
required, to allow for personnel and machinery access. The installation of a Coffer Dam
upstream of the spillway provides a reasonable way to create dry conditions required complete
the work, while minimizing the environmental effects.
The potential environmental effects of dewatering are considered more substantial that its
benefits to the Project. Therefore, in light that a reasonable alternative (i.e., Coffer Dam) has
been identified that also meets the overall Project objectives, NB Power, in consultation with
DFO has settled on the Coffer Dam option as the Preferred Option.
2.6.4 Other Alternative Options
Other alternative options (e.g., installation and removal of the Coffer Dam in dry conditions, use
of a temporary access road without draw down or dewatering) were considered, and deemed to
be not technically and/or economically feasible. These were rejected at an early stage due to
clear deficiencies in terms of scheduling, potential environmental effects, and/or cost. It would
be possible to construct a Coffer Dam in dry conditions, with less effort than described above for
construction in the wet, and without the issues of sedimentation. However, the basic design
presented in Drawing 9 (Appendix C) would still be preferred, and thus the time required to
dewater and build the structure would interfere with the overall construction schedule. In
addition, as the primary reason for investigating the Coffer Dam option would be to remove the
requirement to dewater, this option is considered to be less viable than those presented, as it
would require 2 dewatering events, with the first one lasting between 2 to 4 weeks.
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