To:             Harvey Snyder Harvey.Snyder@consulting.fujitsu.com
From:         Susan Springthorpe
Subject:      Risk Issues With Forcemain Through Richmond And Potential Breakage
Date:          2004/03/10
cc:              sspring@uottawa.ca

This is in response to your request for some comments from me on this issue. It should be noted that these comments relate strictly to ‘what is in the pipe’ and cannot speak to pipe breakage because I have no engineering expertise to speak on the probability of this happening. However, from previous enquiries I have made, I understand that although some of these newer pipes are nominally stronger, they remain to be proven over the longer term, so you would have to rely on other expertise for this issue.

Neither can I speak strictly to risk if a breakage occurs, because knowledge of what pathogenic microorganisms will be in the pipe at any one time does not exist, nor can anyone predict the exact paths that fluids underground will take. These comments are therefore both general and theoretical in nature.

With the above caveats in mind I make the following points in relation to the sewage forcemain going through Richmond:

·   Water generally travels much faster horizontally through soils than it does vertically. It moves relatively fast through preferential flow channels since soils are not homogeneous. These preferential flow channels or macropores are of different sizes and form a meshwork through the soils as a result of historical events in the soils including dead root holes, worm, insect and rodent burrows, cracks forming in dried clay soils, etc.

·   Vertical transport does occur however and is facilitated by rainfall and therefore tends to be somewhat pulsed in nature. Bacteria, viruses attached to fine particulates and other microorganisms generally travel with the water front, though it is recognized that motile organisms can travel ahead of the water front if there is sufficient soil moisture present.

·   There are potentially large numbers of pathogenic microorganisms in sewage -including viruses, bacteria, fungi and protozoan parasites. During a pipe break or leakage these would be released into surrounding soils. They adhere to soil particles and penetrate soil matrices to varying degrees. In general, viruses adhere less well than other microbial types and hence have been believed to pose a greater threat for groundwater contamination than some other bacteria or protozoa. They also occur in large numbers (up to 10⁹ per gram of feces) in infected individuals and have a very low minimal infective dose (often a single virus particle may be sufficient to cause an infection). Many bacteria will die or be preyed upon by soil microorganisms, especially protozoa, ciliates, etc. However, some bacteria, including a number of pathogens (e.g. legionellae and mycobacteria, helicobacter, E. coli O157:H7, etc) have the ability to survive and multiply within vacuoles of protozoa and hence can become part of the microflora in the soils and in groundwater. Therefore it is possible that disease-causing microorganisms once in the soils can become ‘resident’ there.

·   How is a sewage force main different than the normal sewage collectors that run through Richmond or the septic systems that used to be present in the context of the above? I suspect the matter is mainly one of degree. Individual septic systems have a much smaller area that is potentially likely to be affected. Moreover, the range of pathogens likely to be present may be restricted to those intermittently excreted by an individual household rather than the collective fecal output of the entire community. Also, in an efficiently operating septic system there is some active digestion of the sewage that should result in lower numbers of pathogenic organisms in the effluent. The risk therefore may be lower. In sewage collectors from whole communities the range of pathogens may be higher, and in sewage pipes the weakest points are often the joints. Whereas the sewage collectors in Richmond have been recognized, particularly during the spring snow-melt, to be net importers of water to the sewer system, it is clear that the same portals allowing infiltration can permit leakage if the conditions were suitable for this to occur. Force mains, by their nature, are under a certain degree of pressure. Therefore any minor breaches in pipe integrity or misalignment can result in leakage even in the absence of a major pipe break. Pipe integrity is an issue wherever pipes are used to transport fluids. Drinking water was always believed to be a system under pressure and therefore problems were with leakage rather than infiltration. However, it is now recognized that infiltration of microorganisms can occur during pressure fluctuations/surges. I am not sure what if any studies have been done with sewer forcemains to investigate minor continuous leakage. The potential for impacts on wells from actual breaks in pipe integrity is much more obvious.

·   Groundwater contamination is very much of an evolving issue everywhere. In parts of the US many wells are heavily contaminated. One utility with whom we work has wells that are all more than seven hundred feet deep and these sources are contaminated. How does the contamination get that deep is anyone’s guess. Clearly wells can only be grouted for a certain distance and so it is unclear whether the contamination is from the surface or from underground sewers or other sources. Ideally, persons relying on wells for their drinking water should be able to do so without fear of their contamination. However, legislation in the province of Ontario makes well owners themselves responsible. Usually these owners have septic systems that need to be maintained. However, the situation in Richmond is unusual. Since sewers have replaced septic systems in Richmond, the principal source of potential contamination is now in the hands of the Municipal authorities rather than the well owners themselves.

I am not sure if the information provided is what you wanted but it a snapshot view from that of an environmental microbiologist. There are other issues that relate to the flaws in using enteric bacteria as indicators of soil contamination that I do not have time to go into at the moment. Please let me know if you need any more information in this matter.

Susan Springthorpe
Director of Research
Centre for Research in Environmental Microbiology
University of Ottawa
Ottawa, K1H 8M5, Canada
613-562-5800 (ext. 8313)
613-562-5452 (fax)