Detailed Marine Scientists' Review of Environmental Issues.
The provincial government has 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, whether land-based treatment is scientifically required to protect human health and the marine environment.
(Click on heading)
Oxygen Demand
Nutrients and eutrophication
Metals
Man-made chemicals,including pharmaceutical substances and personal care products
PCBs and PBDEs
Effects on the biota near the outfalls
Plume surfacing
Oil and grease
Human pathogens
Flux into the Strait of Georgia
The Precautionary Principle
Conclusions
Acknowledgement
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/documents/2005macclowmepannual.pdf to obtain the 2005 Annual Report 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 then 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 due to mixing by strong tidal currents, and the effluent so diluted by this 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 occurs in organic material that accumulates on the sea floor near the outfalls, as indicated by the presence of large numbers of a particular species of marine worm, but the presence of other species of marine life demonstrates 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 amounts of nutrients added are small and are anyway flushed out into the Pacific Ocean 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.)
ISSUE: Metals
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 localised and primarily a consequence of the added organic matter. 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, partly as a consequence of the extreme dilution. 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 which might be of concern, establish their sources and pathways, and determine any necessary remedial strategies. There is a concern that some persistent organic pollutants (POPs) which are present 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. This is addressed in the next issue.
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 bioaccumulative organic pollutant deserving special discussion. They pose a health risk for marine mammals, including killer whales, because those animals are long-lived, eat high on the food chain and can pass the contaminants on to their young. PCBs have been banned from open use in Canada since 1977 and levels in the local marine 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, largely as a result of long-distance transport, although local “hotspots” exist in the sediments of 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) used in furnishings and computers, are emerging as potentially larger threats. Up to 50% of the input of PBDEs to the local coastal ocean may be via wastewater discharge. This could be reduced by secondary treatment, as most PBDEs stick to particles, but this would not destroy them and they would remain in the sludge, possibly presenting problems elsewhere. Some compounds would still be discharged. Other significant inputs, such as via rivers and the atmosphere, would be difficult to reduce so that banning the production and 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: There is definitely a change in the mix of marine organisms close to the outfalls. The increased abundance of marine worms within 100 metres or so of the outfalls (particularly the one at Macaulay Point) seems to be a consequence of the extra organic material and some resulting oxygen depletion. Most types of organism found in the far field are also found at the outfalls, however. There is nothing approaching a "dead zone". 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.
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.)
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.
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. The effect is considerably weaker 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 and would enter the Strait below the surface layer. 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 harm to the marine environment from Victoria’s effluent discharges and it is 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.