April 30, 2014

Small pipes could mean big savings on sewers

As published in The Erin Advocate

In the quest for a sewer system that could actually be acceptable to Erin residents, both in terms of cost and community impact, the Town is learning more about alternatives to traditional systems.

One option presented at a recent workshop in the council chambers, organized by Roy Val of Transition Erin, showed councillors, staff and community members a dramatically different approach to wastewater.

The Small Bore Sewer (SBS), patented by Ottawa-based Clearford Industries, employs a septic tank on each property to digest solid wastes, similar to what most Erin residents use now.

Instead of a drainage bed on the property, a public system of small pipes would drain the liquid from those tanks to a treatment facility. Because the tank intercepts the initial discharge, peak flows in the pipe system would be reduced.

“Innovation is overdue,” said Clearford Senior Associate Peter Rupcic. “We remove solids at the source. Water is easier to move than solids and water.”

Servicing and Settlement Master Plan (SSMP) Consultant BM Ross has expressed doubts about whether an alternative system like SBS would be acceptable to the Ministry of the Environment  (MOE), since there are relatively few of them. But Rupcic said SBS systems are designed by professional engineers and have a 20-year track record, including provincial funding.

“There is nothing experimental about it,” said Rupcic. “There is no risk in the design.”

Clearford's Small Bore Sewer Design

Clearford has 11 installations in Canada, plus active projects in China, India, Columbia and Peru. Rupcic said their system is fully understood by the MOE and is eligible for infrastructure grants.

“The Clearford system is less expensive to purchase and install than conventional sanitation systems,” says the company website, www.clearford.com. “But the largest savings will come through lower operating and maintenance costs.”

Rupcic said the cost of a traditional system could make it very challenging for Erin to move forward with a wastewater solution.

“The Town should be giving serious consideration to an alternative method,” he said. “At the end of the day, it’s about what you are discharging.”

He said SBS allows municipalities to avoid problems of traditional systems, including concrete or PVC pipes breaking in harsh conditions, and being invaded by tree roots.

SBS pipes are designed to last 90 years and never get blocked up with solid material, since they carry only liquid. They could be as small as 3 inches in diameter, though pipes in some parts of the system could be as wide as 8 inches, depending on the design, with allowance for future growth.

They are buried only deep enough to avoid freezing, with shallow trenches or horizontal drilling beside the roadway where possible. This avoids the deep, middle-of-the-road trenches of traditional systems, which are very expensive and disruptive for the community.

SBS and traditional systems both operate primarily via gravity, with the help of pumping stations in low areas, but SBS pumping stations are much smaller.

One of the issues with traditional sewers is infiltration – the amount of fresh water that leaks into the pipes. BM Ross estimates that with each Erin resident using about 350 L of water per day, a treatment plant would have to be oversized, designed to handle 440 L per person. The extra 90 L per person per day capacity is required by the MOE.

During major storms or spring runoff, leakage into sanitary sewers forces many municipalities to bypass their treatment plants. This happened recently in Orangeville, meaning that raw, untreated sewage flowed into the Credit River.

The SBS system has fewer joints since the flexible pipe comes in 350-metre rolls, and incoming connections are fused and sealed like a gas line to prevent infiltration.

“Treat only what you produce and do it in the most efficient manner available,” said Rupcic. “The big pipe is old thinking.”

Erin would still need a treatment facility designed to handle both the daily urban flow, plus the septage pumped out of rural and urban tanks, but the plant would be much smaller than a traditional one. Normally a plant represents 20% of the system cost, and the collection system 80%.

Each household would get new single-chamber polypropylene digester tank, normally in the back yard using existing plumbing. Where necessary, a larger concrete tank could serve more than one household, including apartments or condos, and restaurants may need a grease trap on the inlet side.

The tanks do not use chemicals, grinders, pumps or electrical devices. Clearford’s original tanks needed pumping every 7-12 years (instead of the current 3-5 years) and their new design will have a longer pump-out cycle.

The resident would own the pipe leading to the tank, but the Town would own the tank and everything downstream, and would also be responsible for pumping out the tank.

One of the Clearford installations is in Wardsville, Ontario, a village of about 420 people between London and Chatham. A traditional sewer system there would have cost $7 million, but Clearford built that system for $3.6 million, said Rupcic, and it took 10 months instead of two years. That installation is 14 years old, and more than half the tanks have not needed to be pumped out yet.

BM Ross gave a rough estimate of $65 million for system to serve Hillsburgh plus Erin village (not counting grants that could cover a major portion). Town council will soon get an analysis of what it might cost per household to build a traditional system versus an SBS system (with a breakdown on servicing Erin village only or Hillsburgh only).

Rupcic said it would be possible to design a hybrid system, using SBS in some areas and traditional sewers in other areas. SBS is also suitable for light industrial development, of the type being sought by Erin.

SBS technology is not just for small populations. A community of more than 10,000 uses a similar system Australia, and a Clearford project to serve 6,000 in India could be expanded to 100,000, he said.

While SBS is a patented, proprietary design, potential repair or expansion of the system could be done by any general contractor who understands how it works.