The proportion of trace elements in biosolids requiring careful monitoring is very small (less than 1/10 of 1 percent). These include such things as copper, lead, mercury and zinc. These elements enter the sewer system from residences and storm water runoff. Most of these minerals actually benefit plant growth, but they can be harmful in excess concentrations. That is why the composition of biosolids used in land applications is carefully analyzed and controlled. Only biosolids which meet the Ministry of Environment's Organic Matter Recycling Regulation are used in land application projects.
Research performed by Vancouver Island University has shown that trace elements introduced into the soil through biosolids projects generally do not move far below the soil surface, usually within 5 to 10 centimetres. Even during a very severe rainstorm, biosolids that have not yet been absorbed into the soil will move only a few metres. This would not affect the nearest residence to our project site, 1 km away. Nevertheless, to assure the safety of water supplies, application sites are away from steep slopes and 30 to 60 metres from any watercourse.
To protect public health and the environment, we: