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
are a primary food source for many fish species. High levels of suspended solids in the water
column can occlude fish gills, causing suffocation. Therefore, erosion and sedimentation control
measures and mitigation will be implemented as part of the Project. These measures include
installation of the Coffer Dam itself, installation of silt curtains on the upstream face of the twospan
bridge and over the intake structures (during construction of the Coffer Dam, and
dewatering of the PDA), and installation of a check dam and settling pond (and drainage
channels as necessary) within the PDA to catch water that may accumulate in the work area as
a result of heavy rain as well pumping of water from the forebay area over vegetation away from
watercourses.
Turbid water pumped from the forebay area will be routed through a check dam/settling pond
where it will be allowed to settle, and then pumped over existing vegetation a sufficient distance
away (at least 30 m from the watercourse) to remove suspended sediments and prevent
sediment from entering the watercourse. Pumping will be conducted in accordance with
NB Power’s WAWA Permit (Condition of Approval No. 13) to prevent TSS in the watercourse
from increasing more than 25 mg/L above background levels.
Historically, an accidental release of sulphidic sediments from the former Bathurst Mine entered
the headpond and resulted in mortality of fish downstream. The possibility has been identified
that a residual deposit of such sediments in the headpond might be exposed, or suspended and
result in a secondary episode of toxicity to fish. As discussed above, by choosing the Coffer
Dam alternative, the likelihood that sediments will be suspended and transported from the
riverbed is low. Although considered unlikely, in the event that such sediments are identified
and are exposed to the atmosphere following draw down, it would be prudent to remove them in
order to prevent possible sulphide oxidation and acid generation, with associated potential
leaching of heavy metals. Therefore, following draw down, an evaluation of exposed sediments
will be undertaken in the vicinity of the former Bathurst Mines. The evaluation will include a
walk over of the area between the outfall from the Bathurst Mines site and the NFGS to identify
any potential deposits which may be present. If exposed sulphidic sediments are identified as
being present, NB Power will notify DFO and consult with them to develop an appropriate action
plan and mitigation.
If draw down of the headpond results in loss of access to tributary streams by brook trout or
other fish, then spawning areas may be rendered inaccessible. The New Brunswick Atlas
shows approximately seven (7) tributary streams entering the headpond, although most of these
are very small, and only one (Austin Brook, approximately 2 km upstream from Bathurst Mines)
is named. It is presently unknown whether these tributary streams provide spawning habitat, or
whether such habitat is accessible by fish in the headpond. Based on the proposed vertical
draw down of 2.1 m (7 ft) of the headpond, and because stream channels extending to the
historical river elevation would have existed prior to flooding of the headpond, it is unlikely that
these tributaries will be rendered inaccessible as a result of the lower water levels. NB Power
will have an aquatic biologist monitor the water levels in the headpond and tributary access to
confirm fish passage is available. Access conditions between the river and the normal water
level of the headpond will be investigated after the headpond is drawn down. If blockages are
June 15, 2011 Page 57