Sediment is the soft solid material that lies under the water at the bottom of a harbour, lake, or stream. Similar to how soil can move with the wind and rain, sediment also moves and mixes over time from waves, water currents, or disturbance by people and animals.

Sediment contamination refers to the presence of chemicals in sediment at levels higher than they would normally be. Many chemicals are naturally occurring, so the presence of a chemical in sediment does not necessarily mean that contamination exists. Scientists have identified levels of chemicals in sediment that can be used to help determine what is contaminated and what is not. Presence of contamination does not mean that the sediment is polluted to dangerous levels. Instead, sediment contamination needs to be studied to determine whether it is safe or not for people and the environment, which is dependant on the area, the chemicals, and the site uses.

Past studies of water quality of the harbour have concluded that water quality is generally good compared to provincial and federal guidelines designed to protect people, fish, and wildlife. The main concern is the contaminants in the sediment that may be harmful to people, fish, and wildlife.

The chemicals of potential concern in the sediment are varied, but fall into a few categories: metals, PAHs and PCBs.

• Metals, (such as chromium, copper, mercury, and arsenic) at different parts of the site match the types of metals used in the past from nearby industries.
• Polycyclic aromatic hydrocarbons (PAHs)—this is a group of related chemicals that are commonly present in fuel products. For example, the former coal gasification plant in downtown Kingston released PAHs in the wastes related to plant operations.
• Polychlorinated biphenyls (PCBs)—this is a group of organic chemicals containing chlorine, historically used as coolants and lubricants, for which production has been banned North America. They are persistent, resist chemical breakdown, and accumulate in the bodies of animals.

Metals in the harbour that are elevated include chromium, mercury, arsenic, and copper in some areas. These metals mainly came from historical industry along the harbour front, by either being directly deposited or washed into the harbour with surface water or ground water. For example, chromium in the harbour comes from the chrome tanning process used at the Davis Tannery that was immediately adjacent to the harbour for much of the 20th century. Metals in the harbour can pose both ecological and human health risks depending on the type and where they occur.

PAHs occur naturally in coal, crude oil, and gasoline, and are produced from burning. PAHs are a common contaminant in urban waterways, and come from numerous sources, including storm sewer outlets from road run-off, automobile exhaust, furnace/stack emissions, or spills from fuel depots/marinas. Historical coal stockpiles, oiling docks, and rail yards in Kingston Inner Harbour, along with the former coal gasification plant in downtown Kingston, are thought to be the most significant sources of PAHs to the harbour. These chemicals break down naturally (i.e., biodegrade) in the environment, but this process can take a very long time depending on the type and amount of PAHs present. PAHs in the harbour pose risks to both ecological and human health.

PCBs are human-made chemicals that were used widely in electrical equipment like capacitors and transformers, and previously found in hydraulic fluids, heat transfer fluids, lubricants, and plasticizers. PCBs were mostly washed into the harbour with surface water and groundwater running through the former Belle Landfill. Because they are toxic to people, fish, and wildlife, the import, manufacturing, and sales of PCBs were made illegal in Canada in 1977. In Kingston Inner Harbour, PCBs were most likely released into the environment through leaks from a former landfill, scrap yard, and demolition yard. Once in the environment, PCBs stick strongly to soils and lake bottoms and can be transported long distances from their original source. They also bind strongly with fatty animal tissues and magnify in the food chain, meaning they are passed into and accumulate in larger animals when they eat smaller animals. These chemicals break down (i.e., biodegrade) very slowly and can last a very long time in the environment. PCBs in the harbour pose risks to both ecological and human health.

What ongoing sources are there and how are they controlled?