With the rising concern with respect to the quality of drinking water in Ontario, more and more attention is being paid to nitrate concentrations in the treated effluent from onsite sewage systems. The Ontario Ministry of the Environment requires nitrate concentrations to be a factor in selecting treatment processes in systems with projected flows that are greater than 10,000 litres per day. However, The Ontario Building Code, the regulatory legislation that governs the systems with flows that are less than 10,000 litres, does not specify a nitrate concentration requirement. Ministry guidelines however may be enforced if an impact is found to occur to the ground water.

In this case, an existing property of 2.27 acres in size in the Town of Bradford West Gwillimbury was to be separated into two lots. The existing residence is serviced by means of a private sewage disposal system and an existing drilled well that remained in the boundaries of the severed lot in accordance with setback requirements of the OBC. The retained lot however needed to be serviced by means of a private well and private sewage disposal system. The proposed residential severance consists of a 1.09 acre retained lot and a severed lot that is 1.19 acres in size.

A preliminary impact assessment on the new proposed residential lot found that predicted nitrate concentration would not meet MOE guidelines set on the property boundary. Thus, in order to secure a severance approval, the nitrate concentration out of the septic had to be less then 10 mg/L. The property owner retained the services of Jagger Hims Limited for the sewage system design for the new lot severance. Jagger Hims Limited specified a Norweco Singulair Treatment Plant with advanced nitrogen removal, due to its ease of installation and cost effectiveness. The Norweco Treatment Plant de-nitrifies effluent to the drinking water standard of 10 mg/L.

Norweco recently completed NSF testing on the Singulair with a recirculating pump which sends the treated effluent back to the head of the treatment plant with the objective of enhanced denitrification. The set up is simple, the treatment plant is followed by a basin with a pump in the bottom. While the basin has a gravity outflow to send liquid to the disposal bed, a portion of the liquid is pumped back to the head of the plant.

NSF testing shows an average nitrate concentration of 6 mg/l.