Many variables in wastewater projections

A series of variable factors is used in calculating how much wastewater can be processed by a treatment plant, while meeting provincial regulations. The numbers limit how many households could be serviced, and therefore how many new homes could be built.

Here are the main issues for a Town of Erin system, as outlined by Ainley staff at the June 22 Public Information Centre. They help explain why the potential urban population for Hillsburgh and Erin village has increased from 6,000 to 14,559 (over 20-30 years). Erin village could go from 3,225 to 8,565 residents, while Hillsburgh could go from 1,391 to 5,994.

Total Phosphorus

A treatment plant improves effluent quality by lowering concentrations of suspended solids, E.coli bacteria, ammonia and nitrates, and maintains desirable levels of acidity and oxygen. But a crucial constraining factor is Total Phosphorus.

When measured in the river, the existing concentration is .016 mg/L, well below the provincial limit of .03 mg/L. In what they call a “conservative approach”, Ainley proposes that the effluent be allowed to increase that concentration to .024 mg/L. If the target were even higher, it could mean less intensive treatment, or more homes being allowed on the system.

When measured in the effluent itself, the original strategy in the Servicing and Settlement Master Plan (SSMP) was to lower phosphorus by a moderate amount to meet the provincial standard. Total phosphorus in the effluent would have been .15 mg/L.

The new proposal is to use the best available technology to reduce phosphorus in the effluent to .046 mg/L, about one third of the previous level. This would translate to the target of .024 mg/L once the effluent was dispersed in the river. Ainley President Joe Mullan says this is the most significant factor in allowing for a higher population to be serviced.

The SSMP predicted a sewage flow of 2,610 cubic metres per day based on 6,000 urban residents. Ainley is now predicting 7,172 cubic metres per day for 14,559 residents.

River Flow

The Assimilative Capacity Study (ACS) in the SSMP came up with a river flow of 202 litres per second during low-flow periods. This measures the river’s ability to absorb effluent in the driest times, and is a major constraint.

A revised ACS done by Credit Valley Conservation, with updated river data, shows a low flow rate of 225 litres per second, 11 per cent higher than before. This could allow for less intensive treatment, or more new homes.

Water usage and infiltration

The SSMP used a water use projection of 435 litres per person, per day. (Water use equates closely to sewage generation.) This is considered very high.

Based on water use trends in the Town of Erin and a review of design standards in similar municipalities, Ainley is assuming a sewage flow averaging 290 litres per person per day. They’ve also included an additional allowance of 90 litres per person per day for possible “infiltration” – the water that often leaks into traditional gravity sewers, increasing the volume that a treatment plant must handle.

Lower water use per household, and possible reduction or elimination of infiltration, would both mean that more people could be on the system.

Not connecting some homes

Most residential properties in Hillsburgh and Erin village are too small for a normal, modern septic system, and so most neighbourhoods would be hooked up to a sewer system. But three areas with larger lots and newer septic systems could be exempt from having to hook up.

These are: the Upper Canada Drive subdivision in Hillsburgh, the Credit River Road – Pine Ridge Road area near the Tenth Line, and the Delarmbro Drive – Patrick Drive – Erinwood Drive area near Eighth Line and Country Road 124.

Not connecting these areas could free up sewage allocation for new subdivisions, though this might not be necessary since capacity is increasing due to other factors. In general, sewers cost less per household if the maximum number of residents are hooked up and paying a share.

Concerns about extra population growth with sewers

Concerns about major additional population growth in Hillsburgh and Erin village – above and beyond the 10,000 new residents already considered feasible in the next 20-30 years – were expressed at a public meeting last Thursday at Centre 2000.

It was a Public Information Centre hosted by the Town of Erin as part of the Wastewater Environmental Assessment, designed to update residents on current developments and provide an opportunity to ask questions.

 “Ensuring the community is both informed and engaged is an important component of this process,” said Mayor Allan Alls. “A sewage treatment plant will unquestionably move our community forward, allowing us to better address our tax imbalance, help our existing businesses, and bring new jobs to our community”. 

All of the information boards and slides presented last week are available in the Wastewater section of the Town’s website, erin.ca.

The project is now moving into Phase 3 of a 5-stage process that had its first public meeting in 2009. Town consultants The Ainley Group will now be exploring more detailed design alternatives, including options for sewage collection and treatment. The ideal location for discharge into the river, the treatment plant and pumping stations will also be analyzed. 

They intend to hold another Information Centre this November, and wrap up the entire EA in March next year.

Last week’s meeting focused on several environmental measurements and wastewater treatment factors, all of which affect how many homes could be serviced by a sewer system. (See article below for an overview.)

Actual decisions on population growth and approval of subdivisions will be made later as amendments to the Official Plan, but the capacity of the sewer system is a key element.

The current rural population of the Town is about 7,800 and expected to grow very slowly. The urban population is now about 4,500, and was previously expected to grow by only 1,500, to a total of 6,000. Recent changes to the proposed parameters have resulted in the growth projection over 20-30 years being revised to 10,000 new urban residents, for a total of 14,500.

This would allow for “full build-out” of lands inside the urban boundaries already designated for development, while still meeting provincial regulations for treated effluent entering the river.

Ainley Project Manager Joe Mullan said that BM Ross, the firm that conducted the Servicing and Settlement Master Plan, was “very conservative” in its proposed removal of phosphorus from sewage effluent. This was a factor in the 6,000 cap, which was vigorously defended by Credit Valley Conservation (CVC).

Mullan said that more aggressive treatment, accepted in the wastewater industry, could cut the total phosphorous by 70 per cent. This would be a major factor in allowing more population, but the strategy does not yet have provincial approval.

“It’s a very high quality effluent,” said Mullan. “This has been reviewed by CVC and the Ministry of the Environment and Climate Change, and I am quite confident that these numbers will be acceptable to those agencies.”

Jay Mowat, a member of the Public Liaison Committee and Transition Erin, noted that Ainley says it is still using “conservative” numbers. He asked how much population the sewage plant could actually handle, if the parameters were to change again.

“Could we be expecting 20,000 people, 25,000 people?” he said.

Mullan said even if there was a technical opportunity to handle more people, the treatment intensity could be cut back to conform to the current population projection.

If the County were to ask Erin to take 25,000 more people, Mullan said he didn’t think the proposed plant could handle it. But he could not give an actual maximum number, since the analysis has been focused on the current projection.

“We don’t want to get into the What If’s and What If’s,” he said. “This is a viable solution we are presenting to the Town that will allow you to make some serious decisions on your growth moving forward. We don’t want this to be your driver for growth. We want this to not be a constraint.”

Mayor Alls has been suggesting that rural residents of Erin should be expected to help pay for the cost of a sewage treatment plant, even though they would not get the direct benefit of sewer service and the higher property values that would result in urban zones.

In response to a question on this, Ainley Technical Team Lead Gary Scott said that Ontario’s Sustainable Water and Sewage Systems Act requires that the local cost of the sewer system and treatment plant (after any grants or developer contributions) to be paid by the residents who are actually hooked up to the system.

Rural residents will get some benefit, since the plant will be equipped to process septage – the waste pumped out of septic tanks. Currently, disposal firms charge to transport this waste to plants in distant locations such as Collingwood.

There is a risk that these plants could stop accepting the waste at any time, resulting in even higher disposal costs at more distant sites.

Hillsburgh sewage plant considered impractical

The possibility of building a sewage treatment plant in Hillsburgh has been rejected as impractical and too costly by the consultant conducting a Wastewater Environmental Assessment for the Town of Erin.

Joe Mullan, President of Ainley Group, presented a technical report to Town Council last week. He said there is insufficient data on the quality and quantity of the river flow near Hillsburgh to determine if treated sewage effluent could be safely discharged there.

Gathering the data for a new Assimilative Capacity Study could take 10 years and $500,000 – with no certainty that a Hillsburgh plant would eventually get provincial approval. Council requested the analysis last month, since the option had not be fully explored in the Servicing and Settlement Master Plan (SSMP).

Ainley is recommending that the Town stick with the original plan from the SSMP to have a single wastewater plant discharging downstream of Erin village. Council has made no final decision on this.

A Public Information Centre on the wastewater situation will be held on Thursday, June 22, at Centre 2000. It runs from 6 p.m. to 9 p.m., with a presentation at 7 p.m. It will describe the scope of possible work, and present the results of studies done so far – including alternatives not covered in the SSMP.

“The industry trend is towards less and larger treatment plants in order to reduce operational and compliance costs,” said Mullan.

Having two plants would save the estimated $5.2 million cost of a forcemain to pump Hillsburgh’s sewage along the Elora Cataract Trailway to the Erin village plant. But building two plants (for the full projected population increase) would cost $98.3 million, compared to $60.7 million for just one plant.

In addition, operation and maintenance costs estimated over 50 years would be about $75 million for a single plant – 32 per cent cheaper than for two plants.

“Subject to development of a cost sharing plan with developers, the full build out cost allocation to the existing community could substantially reduce the per capita cost to existing residents,” the Ainley report says.

Previously, growth within the urban areas of Hillsburgh and Erin was to be limited to 1,500 new residents – based on providing sewer service to all existing residents. As reported last November, a new strategy could exclude several areas from getting sewers. This would help free up capacity for developers, and could allow about 10,000 new urban residents over 20-30 years.

This is referred to as “full build out”, allowing housing growth in areas identified in the Town’s Official Plan. Council has been delaying a decision on exactly where new subdivisions will be allowed.