Halifax Harbour Cleanup Inc. - Halifax Regional Municipality

Issues 17
4.2.3 The Diffuser Site
According to the description of the proposed Project, after
wastewater from the STP/OFS facility has undergone primary
treatment and disinfection, it will be discharged via an
under-Harbour tunnel through a diffuser to the marine
environment.
The location of the diffuser site has been a major issue in the
review process, because of potential impacts of the large
volume of treated effluent to be released somewhere within
Halifax Harbour. In particular, there is concern about the dispersal
of toxic and hazardous wastes into the marine environment.
To summa&e, the wastewater constituents of greatest
concern are
• persistent toxic organic chemicals and metals associated
with sewage particles
• pathogens such as viruses and enterococci bacteria, which
will not be entirely eliminated by the disinfection process
• nutrient loadings which promote excessive growth of
phytoplankton
The Task Force used the following criteria in making its selection
of the diffuser location:
• Harbour use objectives
• principles established following consultation, with the
community
• available scientific information on dilution and dispersion
rates
• human and ecological health hazards posed by particulate-borne
toxics that would settle on the Harbour floor
• possible distribution and impacts of effluent-derived
sediments
• the need to locate the diffuser a minimum of 2 kilometres
from swimming beaches, to avoid possible human contact
with sewage-derived pathogens
One important factor was apparently not considered by the
Task Force: the relationship between the diffuser location and
designated shipping anchorages.
The Task Force adopted Guideline 6 of the Guidelines for the
Protection of the Marine Environment Against Pollution From
Land-Based Sources (Montreal Guidelines):
In taking measures to prevent, reduce and control
pollution from land-based sources, States have the
duty to act so as not to transfer directly or indirectly,
damage or hazards from one area to another or
transfom, such pollution into another type of pollution.
(Guideline 6 does not prevent transfer or transformation
of pollotion in order to prevent, reduce and
control pollotion of the environment as a whole.)
On the grounds that the responsible way to address sewage
treatment and disposal is to clean it up at home, and based on
community consultation, resulting Harbour use criteria, and
critical scientific and engineering information, the Task Force
concluded that the optimum location of the diffuser was in the
Inner Harbour at a minimum depth of 20 metres, on the hard
bottom between Georges Island and the Dartmouth shore.
In coming to this conclusion, the Task Force deliberately opted
for a strategy that would promote retention of sewage particulates
in the Inner Harbour sediments, while at the same time
providing adequate dilution and dispersal of dissolved contaminants
and pathogens remaining in the effluent. Containment
of sewage-derived particulates contaminated with toxics
within the already polluted Inner Harbour was thus made the
priority concern. This decision recognized that the Inner Harbour
waters and sediments would continue to serve as an
“extended natural treatment system” for the Halifax-Dartmouth
metropolitan area, although the sewage loadings
in the effluent from the new regional treatment system
would be much reduced over the present situation.
The virtual absence of commercial fishing in the Inner Harbour,
the distance from swimming beaches, and the relative
ease of monitoring also contributed to the decision by the
Task Force to locate the diffuser by Georges Island.
With Ives Island designated as the preferred STP/OFS site,
HHCI then examined potential locations for the diffuser site.
Four sites were proposed to the port authority (Halifax Port
Corporation) and the Canadian Coast Guard, who also involved
the Atlantic Pilotage Authority. It appears from the
correspondence made public by HHCI and information
presented at the hearings that only these three agencies
made the September-October 1991 decision to reject the Task
Force’s recommended diffuser site on the grounds of navigational
safety and access to designated anchorages. They
identified “the only acceptable” diffuser site as the one within
the main shipping channel to the west of McNabs Island.
Other Harbour interests were not consulted in this decision.
At the public hearings, the diffuser location decision was challenged
by a number of review participants. The Halifax Port
Corporation and the Canadian Coast Guard defended retention
of existing anchorages for reasons of economics and
marine safety.
Concern was expressed for both diffuser integrity and ship
safety if an anchor caught on the diffuser. The Coast Guard
referenced the primacy of the Navigable Waters Protection
Act over all other uses. At public hearings they acknowledged
ihat if an alternative diffuser site was put forward they would
need to carry out a more detailed examination, including consultation
with other government departments.
After reviewing all the information provided, the Panel confirms
that a diffuser location off Georges Island would better
meet the requirements of Inner Harbour containment recommended
by the Task Force.
At any diffuser site, consideration should be given to the alternative
diffuser design recommended in the Halifax Harbour
Cleanup Project Quality and Value Engineering Audit by Gore
and Storrie. It provides for greater security of operations, less