April 16, 2014

Phosphorous levels limiting population growth

As published in The Erin Advocate

The amount of phosphorus contamination in the West Credit River is “a key parameter of concern” that will limit the future population of Erin village and Hillsburgh to 6,000 people, according to a presentation from SSMP Consultant BM Ross.

At a meeting of the Liaison Committee for the Servicing and Settlement Master Plan on April 9, factors surrounding the Assimilative Capacity Study (ACS) were discussed.

Early last year, BM Ross Project Manager Matt Pearson was estimating that the ACS could result in an urban population cap of more than 9,000, depending on treatment methods and comments from the Ministry of the Environment (MOE) and Credit Valley Conservation (CVC).

Additional stream monitoring, plus a reduction to account for climate change, has resulted in a more conservative cap of 6,000. Town Council recently endorsed the strategy of reserving sewage capacity for the 4,500 existing residents of the villages, leaving 1,500 (33%) for growth.

A detailed financial analysis of costs per household will now be done, for both traditional gravity based sewers and the alternative small bore collection method.

The final SSMP report will examine the implications of three scenarios, including the status quo – no sewers. That could lead to a rigorous inspection system and upgrading of septic systems. For those with large enough properties to upgrade, the cost could be similar to a sewer system.

Mayor Lou Maieron has speculated that the Town might have to try to get special permission to allow new housing on septic systems. A new housing development is being allowed in Cheltenham on medium sized lots close to the river, but strict effluent criteria mean that each septic system will cost about $40,000.

The scenario of a “big pipe” delivering waste to another municipality would allow a much higher population in Erin, but BM Ross says this option is very expensive, and may not be desirable or practical.

Building sewers for existing urban homes, plus about 500 new homes, will be the prime scenario for discussion. Pearson says it will only work if all the urban households are obliged to contribute to the cost, though he said those with newer septic systems could be offered a grace period to delay hook-up.

“There are going to be some people who are going to have to take one for the team,” said Pearson, who has always contended that substantial funding from senior governments would be essential to the feasibility of a sewer project. “Communal servicing is cheaper in the long run, if you get some help.”

Many river contaminants were analyzed as part of the SSMP, but there was particular concern about phosphorous and nitrates, nutrients that can come from fertilizers and other human activity. Certain amounts exist naturally, but excessive levels can increase vegetation growth such as algae and deplete dissolved oxygen, affecting fish and other aquatic life.

Phosphorous levels are always changing. Concentrations have been measured monthly over the last 35 years, with readings tracked at their 75th percentile level according to MOE standards.

Levels drop every April, August and November, but spike high in June, September and December. Having 6,000 people on sewers would put those peaks at the MOE maximum of 0.03 mg of phosphorus per litre of river water.

Nitrates are the next limiting factor, so the treatment plant may need special de-nitrification technology to keep levels in a safe range. There is also the possibility of storing fully-treated effluent in lagoons during months when river contamination is already high, and releasing it later when levels drop.

Any technology that reduces the impact on the river could be used to argue in favour of more housing, but no dramatic changes to the 6,000 limit are expected.

Even an aggressive water conservation system (mandatory low-flow toilets, for example) could lower the amount of sewage and create extra capacity.

Discharging effluent at the Tenth Line has been discussed in the past, but river water quality is better at Winston Churchill Blvd., making it a better discharge point. The sewage treatment plant does not have to be the discharge point. It could be piped to another spot for discharge – although John Kinkead of CVC warned against a pipe next to the West Credit, since river flows can shift over time.