MARINE SCIENTISTS REVIEW OF ENVIRONMENTAL ISSUES RELATED TO PLANS FOR LAND BASED SEWAGE TREATMENT. (This review was published in April 2007) .
In 2006 the provincial government ordered the CRD to proceed towards land-based sewage treatment, replacing the present system which has source control for some contaminants followed by discharge of the screened sewage into the ocean. It remains controversial, however, as to whether land-based treatment is scientifically required to protect human health and the marine environment.
Here, we present an appraisal by a group of scientists familiar with the local marine environment. For each issue, we present first the “argument” that might be presented by those who see the need for land-based sewage treatment, then the “counter-argument” representing the views of those who do not consider the issue as a significant problem or as a basis for land-based sewage treatment, and finally our “analysis” which assesses the issue as objectively as possible. We have chosen to be brief rather than comprehensive; more details of background material can be found in the SETAC report (accessible via http://www.crd.bc.ca/wastewater/reviewpanel.htm) and in publications cited therein. The interested reader may also find it useful to access http://www.crd.bc.ca/wastewater/marine/reports.htm to obtain the 2005 (and later) Annual Reports on the Macaulay and Clover Point Wastewater and Marine Environment Program.
It will be seen that a rational assessment requires focused discussion of a number of separate issues rather than a blanket statement that the sewage is “toxic” or “harmless”. We hope that our analysis will help readers decide for themselves whether we need further research, better source control, land-based treatment, or some combination of these.
As part of this discussion we will also touch on the key questions:
1) Do documented or potential problems in the marine environment arise primarily from the effluent, or from other sources, which should be a priority?
2) Will land-based sewage treatment deal adequately with problems, or will the substances of concern remain in the treated effluent, and thus still be discharged into the ocean, or in contaminated sludge which will present environmental and human health problems on land?
3) If the objective is to protect human health and the environment, could more value for money be obtained from other actions?
ISSUE: Oxygen demand
Argument: The breakdown of organic matter in the effluent consumes oxygen in the water, endangering marine life.
Counterargument: The water is so well oxygenated by tidal currents, and the effluent so diluted by rapid mixing, that the dissolved oxygen in the water does not decrease to harmful levels.
Analysis: The “Biochemical Oxygen Demand” (BOD) of discharged wastewater is a significant issue in many confined waters, but the strong tidal currents off Victoria recharge the local water column with oxygen. Some oxygen depletion could still occur in organic material that accumulates on the sea floor, but marine life is present in the sediments near the outfalls, demonstrating that the depletion is not severe.
ISSUE: Nutrients and eutrophication
Argument: Dissolved nutrients in the effluent, together with those released by the breakdown of discharged organic matter, can fuel the growth of marine plant material which in turn dies and decays, extracting oxygen from the water. This can result in dead zones devoid of oxygen and life. The nutrients can also lead to harmful algal blooms.
Counterargument: This is not a problem off Victoria because the amount of nutrients added is small and anyway flushed out into the Pacific by the average (estuarine) current.
Analysis: This concern (called “eutrophication”, see http://toxics.usgs.gov/definitions/eutrophication.html) is not an issue here because more nutrients than can be used by biological production in Juan de Fuca Strait are already supplied by natural oceanographic processes. Thus the addition of a small amount of extra nutrients is unlikely to make any difference. This conclusion also holds for the Strait of Georgia if some of the effluent from Victoria is fluxed back into that region during storms. (See “Nitrogenous Nutrient Sources and Sinks in the Juan de Fuca Strait/Strait of Georgia/Puget Sound Estuarine System: Assessing the Potential for Eutrophication” by D. L. Mackas and P. J. Harrison in Estuarine, Coastal and Shelf Science, 44, 1997, 1-21.)
Argument: The sediments in the vicinity of the outfalls are contaminated with copper, lead, and mercury compounds (and some other chemicals) at levels which meet the criteria for designation as a “contaminated site”. The contamination represents a risk to the biota. See http://www.env.gov.bc.ca/main/prgs/docs/sq_crd_outfalls.pdf .
Counterargument: Only minor changes in the populations of marine organisms in the vicinity of the outfalls have been observed and the CRD has instituted “source control” to reduce the delivery of many contaminants to the environment.
Analysis: The levels of some metals are indeed higher within 100 metres or so of the outfalls than at reference stations farther away. However, much of the metal seems to be in chemical forms that are not available for uptake. The sediment contamination is an indication of potential effects; the abundance of marine organisms near the outfalls suggests that the actual effects are small. The mercury may be a residue of discharges from dentists’ offices, now reduced by source control. Some of the lead may have come from historical use of leaded gasoline. Some copper and lead may still come from leaching of old domestic water pipes. Sewage treatment does not destroy metals. Many will be concentrated in the sludge and, if this is disposed of on land, may be altered into soluble chemical forms and contaminate surface and ground water.
ISSUE: Man-made chemicals, including pharmaceutical substances and personal care products
Argument: Numerous toxic chemicals, including prescription and other drugs, are found in the effluent and are a hazard to marine life.
Counter-argument: The concentrations are much too low to be a problem.
Analysis: Research to date shows no effects on marine life from levels of these chemicals typically found in the receiving environment. There is, however, a concern that some chemicals that are present in the effluent in very diluted form can be concentrated by various processes, taken up by marine organisms, and further concentrated as they move up the food chain. Given the extreme dilution off Victoria, it is unlikely that this biomagnification leads to significant concentrations in higher organisms such as marine mammals resulting from Victoria’s wastewater discharges, though other sources may be a cause for concern. While some of the chemicals would be rendered harmless during secondary treatment and some would be trapped in the sewage sludge, many would remain in the discharged effluent. There is a need for further research to identify the chemicals of concern, establish their sources (which may be mainly other than sewage discharges), and determine any necessary remedial strategies.
ISSUE: PCBs and related chemicals
Argument: High levels of PCBs have been found in orcas and are thought to be a key reason for the decline in their population. Victoria's sewage disposal has contributed to the problem and it is irresponsible to continue the practice even if the sewage is only a small contributor.
Counterargument: PCB discharges from Victoria’s sewage outfalls are insignificant compared with other sources. Moreover, the levels of PCBs in marine mammals are now declining.
Analysis: PCBs are an example of a persistent organic pollutant (POP) deserving special discussion. PCBs have been banned from open use in Canada since 1977 and levels in the environment have dropped substantially. Recent data show that only a few percent of the PCBs entering the marine environment do so via municipal effluent, whether treated or not. The main transport is via rivers and the atmosphere. “Hotspots” are thought to exist within Victoria and Esquimalt harbours, and other harbours in the region, and may have added significantly to the contamination of local organisms and food webs. The input from these sources is declining due to natural sedimentation. Other POPs, particularly some flame retardants (PBDEs), are emerging as potentially larger threats. Up to 50% of the oceanic input of these may be via wastewater discharge. This could be reduced by secondary treatment, transferring the problem to the sludge, but some compounds would still be discharged. Other significant inputs, such as via rivers and the atmosphere, would be difficult to reduce so that limitation of the use of these chemicals may be the only effective control. For more discussion see “Fireproof killer whales (Orcinus orca): flame-retardant chemicals and the conservation imperative in the charismatic icon of British Columbia, Canada” by Peter S. Ross in Canadian Journal of Fisheries and Aquatic Sciences, 63, 2006, 224-234.
ISSUE: Effects on the biota near the outfalls
Argument: The changes in the mixes of marine organisms near the outfalls clearly show the toxic effects of the wastewater discharges.
Counter-argument: These changes are a consequence of the extra organic material, not of toxic chemicals, and are not of concern.
Analysis: It does seem that the increased abundance of marine worms rather than other marine organisms within 100 metres or so of the outfalls (particularly the one at Macaulay Point) is a consequence of the extra organic material. Most types of organism found in the far field are also found at the outfalls, however. Monitoring by the CRD over many years has not identified any adverse effects of toxic substances and this conclusion was endorsed by the SETAC panel.
ISSUE: Plume surfacing
Argument: The sewage plume which rises from the outfalls sometimes reaches the surface and presents a hazard to recreational water users.
Counter-argument: This is a very rare occurrence and presents no risk because of the very great dilution which has occurred.
Analysis: Most of the year, the effluent plume is dispersed well below the sea surface. In the winter months, model results indicate that the diluted effluent plume (with the wastewater diluted by 500 times or more) surfaces only a few percent of the time. Monitoring of the surface water above the outfalls has found fecal coliform counts to be nearly always well below BC guidelines for recreational waters, though the guidelines are occasionally exceeded. (For more details see the 2005 CRD report cited earlier.)
ISSUE: Oil and grease
Argument: Oil and grease reach the surface above the outfalls and present human health risks as well as a threat to marine life.
Counterargument: There is no evidence of significant harm to marine biota or humans arising from this. Moreover it occurs in a very limited area and is being reduced by the CRD’s program of source control.
Analysis: This is an important issue as we do not know the extent to which toxic chemicals and human pathogens can be contained in surfacing grease particles and so not be as diluted as they would be if in the water. However, the CRD’s program of source control, combined with vacuuming of oil and grease at the screens, has reduced the marine inputs significantly since 1990. The problem does not appear to be serious, but there is a need for further investigation.
ISSUE: Human pathogens
Argument: Bacteria and viruses occur in the effluent and cause sickness among those using local waters for recreation. The wastewater discharges are also responsible for a large area of the Victoria Bight being closed to shellfish harvesting.
Counter-argument: The danger posed by this is estimated from the fecal coliform count in the water. This is nearly always found to be well within safe limits. Moreover, bacteria that pose a risk to human health die quickly in salt water.
Analysis: As mentioned earlier, the diluted effluent reaches the surface rarely and has fecal coliform counts usually well below limits set for recreational waters. The relevant bacteria tend to die within a matter of hours, but some viruses can persist for many days. They are likely to be too dilute to be of concern, though it is possible that they may be more concentrated in surface particles. There is anecdotal evidence of infections from exposure to the sea in the vicinity of the present outfalls, but there is no epidemiological evidence for higher incidence of a variety of conditions. The issue requires more research. It is possible that the area closed to shellfish harvesting could be reduced if land-based sewage treatment is introduced, but the presence of other sources of contamination, especially from overflows during high runoff, would likely necessitate the continued closure of some areas. (The international standards for shellfish, which are filter feeders, are set at a low level to ensure that the potential concentration of organisms pathogenic to humans does not cause a human health risk. Moreover, areas around outfalls are routinely closed for shellfish harvesting whether or not there is evidence of any risks from those outfalls.)
ISSUE: Flux into the Strait of Georgia
Argument: The sewage effluent can be carried back into the Strait of Georgia and present a hazard in the more confined waters there.
Counterargument: The highly diluted effluent is nearly always carried out to the Pacific with the prevailing estuarine current off Victoria. Any incursion into the Strait of Georgia is rare and adds a negligible amount to the human input there.
Analysis: The surface outflow in Juan de Fuca Strait can be reversed quite frequently in winter storms, particularly on the south side of the strait, though the effect is weak off Victoria. More research is needed to determine how much of the discharged effluent could end up in the Strait of Georgia, though it is likely a very small fraction. As discussed earlier, the associated nutrients are unlikely to present a problem, but it is possible that some chemical contaminants could be associated with organic particles suspended in the water column, and eventually enter the food chain or be deposited to bottom sediments in the Strait of Georgia. The net input is, nonetheless, likely to be very much less than the contributions from secondary treatment plants in Seattle and Vancouver and from other sources.
ISSUE: The Precautionary Principle
Argument: Given the uncertainty that is still present with respect to the impact of some components of the effluent, we must be precautionary and treat the sewage on land.
Counterargument: The concentrations are so low that we can be confident that the risk is negligible.
Analysis: In the absence of complete scientific certainty, the Precautionary Principle reasonably puts the burden of proving the safety of a practice on the proponent. It can, however, be a recipe for paralysis unless it is limited (as is now usual) to situations where the damage might be severe or irreversible. The discussion above of a number of issues has indicated continuing scientific uncertainty about some, but monitoring programs and basic considerations have given no indication of severe, or even minor, harm to the marine environment from Victoria’s effluent discharges and it is extremely unlikely that any irreversible harm is being done. There is time for further research to identify any real problems and introduce the optimum solutions. Further, secondary treatment and the subsequent production and disposal of sewage sludge have their own environmental costs and uncertain impacts.
Secondary, or possibly more advanced, sewage treatment would be effective in removing or reducing the biochemical oxygen demand, nutrients, and human pathogens prior to wastewater discharge, though none of these is a serious issue in the energetic, naturally nutrient rich, local waters. In other words, a sewage treatment plant would do some things that are necessary elsewhere but not here. The conditions off the present outfall have, in fact, been found to be similar to those off the outfalls from secondary treatment plants in other municipalities.
A sewage treatment plant would also be effective in removing or metabolizing a variety of potentially toxic chemicals in the effluent. Those that are removed but not metabolized would be concentrated in sludge, presenting a new set of problems. Some would not be removed but would still be discharged in the effluent. There is no indication to date that chemicals which have been discharged in the past, both those that would be removed by treatment and those that would not, have caused harm in the marine environment, but a number of issues remain and require further investigation. Further investigation is required whether or not a land-based treatment plant is constructed and should be focused on those contaminants that might present a problem.
Many possible problem contaminants, such as the PBDEs used as fire retardants, enter the marine environment by more than one pathway. For contaminants of concern which would be removed at a sewage treatment plant, it would be wise to establish whether the sewer system is a significant pathway. If not, resources will have been devoted to reducing only a small part of the problem.
This raises the whole issue as to priorities in protecting the marine environment. The 1994 report of the British Columbia Washington State Marine Science Panel attached the highest priority to issues such as habitat protection where current practices seemed to be leading to severe and largely irreversible damage. (See http://www.psat.wa.gov/shared/bcwaswl.html for a summary of the report.) It is likely that the marine science community of BC and Washington would still view Victoria’s current sewage disposal practices as a minor issue, with much more value for money being attainable through a variety of other actions to control degradation of the marine environment or the deleterious input of toxic substances.
This assessment was prepared by Chris Garrett, Lansdowne Professor of Ocean Physics at the University of Victoria, with input from researchers Sophie Johannessen, Rob Macdonald, Dave Mackas, Peter Ross and Rick Thomson at the Institute of Ocean Sciences (though they are not responsible for the final content), Jay Cullen at UVic and Peter Chapman of Golder Associates.