Understanding the health risks with reclaimed wastewater

 By Karen A. Phillipps, Nino Devdariani and Claire McAuley

There is increasing concern regarding the sustainability of public water supplies for drinking, industry and agriculture. Options for water reuse are available, including reclaimed wastewater for the irrigation of green spaces and agricultural crops, and for household use.

Harmony is a unique residential and commercial development project that was recently approved by Alberta Environment and Sustainable Resource Development (ESRD) in Rocky View County, west of the City of Calgary. This master planned community will include a self-contained system that will treat residential wastewater and collect it for irrigation within the development. Concerns were expressed by regulatory stakeholders regarding the protection of public health. Cyanobacteria, indicator organisms, turbidity and chlorine residuals were also raised as issues of interest, given the design of the wastewater system and the novelty of the project.

The existing Guidelines for Municipal Wastewater Irrigation in Alberta (2000) outline several requirements regarding water quality, buffer zones and setbacks. These guidelines indicate that a 15 metre setback is required from all adjacent properties, unless permission is obtained from landowners. Also, a buffer zone of 60 – 100 metres is recommended between occupied dwellings and irrigated land. The guidelines also stipulate that wastewater irrigation may only take place on suitable agricultural land from May 1 to September 30, and only when wind speeds are less than 30 km/hr.

Health Canada has developed Canadian Guidelines for Domestic Reclaimed Water for Use in Toilet and Urinal Flushing (2010) that are applicable to some domestic applications. However, some of the concerns raised by the regulatory stakeholders were not completely addressed by Health Canada’s guidelines, due to the potential differences in the exposures that people might receive.

Neither set of guidelines provided the basis to adequately inform regulators, or the project team, regarding adverse health risks from the proposed reclaimed water irrigation. As a result, ESRD requested that a risk assessment be completed for this project.

Risk Assessment

Risk assessment is a tool that can be used to organize and analyze information to enlighten regulatory decision making and the development of risk management and monitoring programs. Intrinsik Environmental Sciences Inc. was contracted to complete a screening-level human health risk assessment of the proposed reclaimed water and its use for irrigation.

For the purposes of the risk assessment, it was assumed that people within the development could be exposed to the reclaimed water following irrigation through:

1. Direct skin contact: People in the vicinity of the golf course may come into contact with the reclaimed water through contact with aerosols or touching surfaces impacted by the water or aerosol (e.g., golf turf, landscaping).
2. Inhalation: People in the vicinity of the golf course (e.g., on adjacent public or private property) may inhale aerosols in the event of spray drift from the irrigation sites.
3. Incidental ingestion: Consideration was given to the possibility that people may either consume home-grown garden produce that could be impacted by spray drift from the irrigation, or have hand-to-mouth behaviour following skin contact with impacted surfaces (e.g., small children).

These assumptions may have resulted in over-estimates of potential exposure, as some of these routes of exposure assume that there is no setback or buffer between the irrigated land and adjacent properties. Also, it is assumed that no restrictions regarding irrigation times and conditions were in place (although several restrictions are required by the ESRD guidelines). The consideration of a zero metre setback for a wastewater irrigation project was unique to this project.

As Harmony’s wastewater treatment plant had not yet been constructed, information available regarding the water quality at the plant, in the reclaimed water storage pond and what would be withdrawn from the storage pond and used for irrigation, was based primarily on performance estimates.

To evaluate potential risks associated with direct contact, inhalation and ingestion, various criteria relating to agricultural uses or recreational water were identified from other jurisdictions and compared with the proposed reclaimed water quality.