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posted August 21, 2006

Responses to Technical Concerns Raised

regarding the earthen sculpture and composting toilet facility in Dufferin Grove Park


This toilet facility – the Phoenix 201 PF (Public Facilities) – is installed in several national and provincial parks in Ontario, as well as a couple of YMCA camps. It is a well-accepted alternative to standard sewage or septic options, where there is concern about minimizing environmental impact and encouraging environmental stewardship.

The Cob Courtyard NE side
Size Impact

The building has been designed to minimize its visual impact on the park, and to blend in as completely as possible.

  • The walls are curved, so the building takes up less space than a rectilinear building of comparable dimensions
  • It is nestled in amongst trees, instead of out on the open green space
  • The colour of its plaster will help it to blend in with the surrounding trees
  • A clerestory roof will minimize overall height
  • A green roof will further integrate the structure into the park’s greenery

Parks, Forestry and Recreation is working in tandem with park users to create this facility. Park users and friends are providing materials, the toilet system and labour to build the facility. PFR is providing materials such as it has available, (sand, clay, gravel), and is involved in permissions and facilitation. PFR will maintain the facility, while park users will maintain the building, as they are currently doing with the cob wall.


Staff and park users will keep a close eye on the unit’s effectiveness. Safeguards in place include:

  • Slow, measured implementation: Can include opening the unit for short periods to start, to ensure that the unit is used below recommended capacity
  • Ability to lock the unit down in case of misuse
  • Monitoring use: Taking door counter readings will allow staff to monitor number of uses. If uses approach capacity on any particular day, the facility will be closed for the rest of the day.
  • Watching for foreign objects: A door in the mechanical room gives access to the top of the compost medium, so that any foreign objects can be removed and disposed of. Standard equipment for this job includes a stick with a clasper on the end, so that staff never touches the toilet bin’s contents. This check is done before the daily turning of the pile.
  • Paying attention to potential odors: All will be on the lookout for undue odors; any questionable emissions will mean closure of the facility to look into the problem.

A unit used year-round will likely have compost ready in about two years. It is possible that a seasonal-use facility such as this might take several more years than that to produce its first compost. Tests have shown that compost produced from this type of unit is safe for use on gardens, and indeed that is the intention of the unit’s designers. To be safe, compost from the facility would be destined for use on flower gardens only, away from food-producing crops.

Day-time use:

A toilet that is used in the daytime only has, as a rule, fewer solid deposits than one available 24 hours a day. This actually increases the daily use threshold, although use will be kept under the published recommendations, to be on the safe side.

Additional units:

The proposal of one unit is the culmination of several years of goodwill offered to the park from several parties, including anonymous donors. It is unlikely for this confluence of goodwill to occur again, so there is little expectation that another unit would be installed here, even if need proved to be great. The “several new cob structures” mentioned in the proposal refers to benches built on existing asphalt bench pads, many of which are missing their benches through age and/or use, for which there is no Parks budget for replacement.


The manner of dealing with leachate is the same as is common in Ontario’s many national and provincial parks where this facility is installed.

From the Phoenix installation guide literature:

After filtering through the compost pile, liquid receives secondary treatment in the well-aerated, stable, peat moss medium beneath the bottom baffle. The stability and tremendous surface area of peat provides an excellent filtering medium for treating liquid. The amount of liquid discharged from the Phoenix depends upon the amount of use it receives, and the temperature and relative humidity of the ventilation air. Approximately 20 liters (five gallons) of liquid is added to the Phoenix for every 100 uses. Incoming ventilation air circulating above the secondary liquid treatment medium can evaporate some of this liquid. The remaining liquid draining from the tank should be directed to a leaching field. The liquid end product contains considerable bacteria and dissolved salts, but generally has a low coliform indicator concentration (<200 org/100 ml), low BOD, (<50mg/liter) and low TSS (<100 mg/liter) compared to septic tank effluent, so a short (8-foot) leach line is all that is necessary.

As a comparison, monitored swimming areas are required to not exceed 200 cfu (coliform forming units) per 100 ml of sample over a long period and 400 over 24 hours. Septic tank sampling would probably yield about 6,000,000 cfu/100 ml. The Phoenix leachate consistently tests at less than 10 cfu/100 ml.; usually negative, which means undetectable.

This line will run under an ornamental garden located to the immediate west of the structure, six inches under the surface of the soil. The line will be made of PVC weeping tile surrounded by filter cloth. It will be pumped there by a condensate pump which has a small reservoir and float switch and will pump the liquid up to the leach line. The garden will keep people from walking near the leach line, although the line will be buried and no evidence of it or its contents will appear above ground. The soil and plants will integrate the minerals; the liquid will evaporate and be used for plant growth.

At a maximum five gallons per 100 uses, it is exceedingly unlikely that this tiny amount of leachate would migrate laterally across the park, over the concrete collar and into the pool. Undoubtably, there is already bacteria of many kinds already in the pool, but that comes from the pool’s users, and a chlorination schedule is already in place to deal with that. Currently, there is likely five gallons of liquid effluent per day being added to the trees around the southern playground by young children who cannot make the trek to the north washrooms without wetting themselves. A washroom close by would offer the chance to give primary and secondary treatment to the leachate before dispersal.

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