As published in The Erin Advocate
It should be possible to build a gravity-based sewer system for Erin village and Hillsburgh, despite the many hills in town, according to consultants running the Servicing and Settlement Master Plan (SSMP) study.
There is still no estimate of the cost, or when it would be built, but details of how it could work were outlined at a meeting of the SSMP Liaison Committee on October 17, hosted by Project Manager Matt Pearson of B.M. Ross and Associates.
Launched in May 2009 and originally expected to take two years, the SSMP is finally entering its home stretch. Engineering work is being done to explore various alternatives and assess the capacity of the river to handle treated effluent. Pearson hopes to have a draft plan by the end of January, which would be the focus of a public meeting.
To complete the study, which is currently holding back all subdivision development, town council will have to choose one of the possible strategies. Actual construction of a sewage system would be a separate decision at a later date.
For the plan to work, said Pearson, it will need the support not only of the current Town Council, but of future councils, since the process will take many years. Solmar Development Corp has a subdivision plan in the north of Erin village that could add 1,240 homes over 30 years. It is prepared to build its own modular sewage plant on the 10th Line, which could be expanded to service other parts of Erin.
"You don't need to rush in and do it all at once, if it makes sense to phase it," said Pearson. "A master plan lets you get out of the reactive mode...not just lying around waiting for the government to come along and give you money."
While sewers will definitely require money from senior governments, the SSMP allows Erin to plan a direction – unlike the sewage plan of 1995 that was not supported by village council. Pearson said the SSMP can help ensure the solution is "technically, financially and environmentally sustainable".
The province will no longer allow new subdivisions on septic systems, and the aging systems for older homes may not be replaceable due to small lot sizes.
"These systems are going to start failing, sooner than later," he said. "You've been lucky so far, but eventually there's a point when you'll get a critical mass. People will not want to put the investment into that back yard, knowing that the sewers should be here, may be here. That's a pretty expensive adjustment, so they'll be looking to the municipality."
A traditional gravity-based sewer system would be the most costly to construct, but the least costly to maintain and operate, since it would have few mechanical and electrical parts.
Road disruption would be substantial with a gravity system, since some of the pipe trenches would have to be quite deep. While a road can go over a rise of land, a gravity sewer pipe has to maintain a continual downslope. To get through a hill, backhoes would have to dig deeper than the nearby low land, so the challenge is to route the system between the hills.
"You're not the first place to get sewers – probably the last place," said Pearson. "This has all been done before."
When necessary, the sewage flows to a pumping station at a low point in the landscape. It is stored temporarily in a large underground tank, then pumped through a pressurized pipe, either to the treatment plant or to a high point of land where it resumes gravity flow.
Pumping stations can cost from $650,000 to well over $1 million, but Erin might need only one, said Pearson.
"Topography plays a big role in where sewers are routed, because the goal is to minimize how deep they go," said B.M. Ross Engineer Dale Erb. "Are gravity sewers realistic for Erin? We think they are."
A pipeline could be built along the Elora-Cataract Trailway to move sewage from Hillsburgh to Erin, along the gentle slope established by railroad engineers in 1879.
One advantage of a traditional deep system is that it would enable direct service to plumbing fixtures in residential basements. If the hook-up is closer to the surface, waste water from basements would have to be pumped up to the sewer pipe.
A modified gravity system, not deep enough to serve basements, could save millions of dollars by enabling shallower road trenches and reducing the number of pumping stations.
An alternative system would require every home to get a new septic tank in their front yard, which would provide the initial waste processing. But instead of the outflow going into a weeping bed, it would go by gravity or pump into a public sewer system.
Pipes for this alternative are smaller, and could be installed beside roadways without large trenches. The pipes are not as deep, and do not require a continuous grade, as long as the overall flow is downhill. The sewage would be lower in volume and easier to treat.
But the septic tanks would have to be maintained and pumped out, and the smaller pipes would be more susceptible to blockages.
A fully pressurized system not likely in Erin, but there could be a hybrid design, with certain low-lying areas having pressurized pipes, delivering the waste water into the main gravity system.
A Low Pressure System would require homes to have an outdoor "grinder pump" buried in the front yard instead of a septic tank. This would chop up the waste before pumping it into the public system.
Road excavation would be reduced, since the pressure would allow the pipes to be installed fairly shallow and on different grades, and there would be less need for pumping stations. Costs would include electricity and maintenance, and there would be more risk of odours.
Maintenance of the sewer system would be done by the Town, but the costs would be recovered through a sewer bill. With all systems, the cost of connection would be paid by the homeowner, normally over time.
Additional study is to be done on issues such as compatibility with existing water lines and other underground services, with ditches, and with high-level groundwater.
There also has to be planning so that future development areas will be able to feed efficiently into the system, ensuring that the pipes are large enough to handle the additional flow and that the river can assimilate that input.
The Ministry of the Environment sets river water quality standards that will effectively limit the number of residents that can be hooked up to an Erin sewer system, based on a standard sewage treatment plant.
The maximum number has not been announced, but it should be in the next SSMP report. It could be increased by upgrading the level of treatment in the plant.
