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Feasibility of Using Effluent from the Comox Wastewater Treatment Plant to Irrigate Farm Land and Golf Courses in the Comox Valley

Executive Summary

This report examines the technical, economic, and environmental feasibility of using effluent from the Comox Wastewater Treatment Plant to irrigate farm land and golf courses in the vicinity of the wastewater treatment plant.

Available literature on the use of reclaimed water for farm, golf course, and landscape irrigation was reviewed and summarized in the report. Literature on wastewater treatment, health risks, environmental risks, site requirements, costs and regulations were reviewed.

The effluent from the Comox Wastewater Treatment Plant is the product of primary and secondary treatment. The total volume of effluent produced during the irrigation season of May to September is 1561 acre-feet, or an average flow of 2309 gpm.

The irrigation requirements of the participating farms and golf course were determined and compared to the effluent flow from the treatment plant. It was found that peak demand for irrigation water among the participants exceeded the average daily discharge from the plant. Annual irrigation requirements of the participants would likely be within the volume of effluent produced during the irrigation season in an average year.

According to new regulations from the BCMoELP, sewage treatment plant effluent requires at least secondary treatment followed by disinfection prior to use for irrigation in restricted land use cases (crops that are not consumed raw, pastures that are not grazed within set lag times). For unrestricted public access, the effluent must be the product of tertiary treatment followed by disinfection. In both cases, there are quality and monitoring guidelines that must be followed. Unrestricted public access would include irrigation of all crops, with no lag times for grazing or harvest, and would also include golf courses and landscape irrigation. For most of the study's participants, unrestricted access wastewater would be required.

A system was designed to treat and deliver reclaimed water from the treatment plant to the farms and golf course participating in the study. To allow for future growth and peak use of the effluent, a system was designed for 4000 US gpm. For restricted public access irrigation, the cost of a pumping station, disinfection equipment, and pipeline was estimated at $3,505,280, and operating costs (based on current flow rates) are estimated to be $48.88 per acre-foot. For unrestricted public access, the additional equipment required brings the total capital cost to $4,425,280, and operating costs rise to $112.95 per acre-foot. If the capital costs are amortized over a 20 year period at 6% interest, then the total cost of the reclaimed water would be $295.63 per acre-foot for restricted public access and $424.46 per acre-foot for unrestricted public access use.

The economic benefit of the reclaimed water, including its nutrient value, was determined for each farm ($122.03 to $198.29 per acre-foot) and was found to be significantly lower than the estimated cost of delivering that water. Other economic factors, such as the potential increase in salmon spawning in Little River and Brooklyn Creek, were also investigated and found to be minimal.

The potential environmental impacts from irrigating with reclaimed water were discussed, including risks to human and animal health, risk of soil and water contamination, and possible benefits to fish habitat, and improved soil and crop health. It was concluded that environmental risks would be very low if the BCMoELP guidelines were followed, and that these risks would be more than offset by the potential environmental benefits.

The report concludes that irrigating farms and golf courses in the vicinity of the Comox Wastewater Treatment Plant with treated effluent is technically feasible, would likely have a net environmental benefit, but, given current conditions, would not give an economic benefit that would offset the cost of treating and delivering the effluent to the farms and golf courses. It is recommended, however, that the project be re-evaluated if economic or environmental factors change in a manner that may affect the viability of the project.

For more information, or for a copy of the complete 50 page document, please contact Dennis Lightfoot.