AQUATIC ENVIRONMENT: IMPACTS
Impacts
This section includes a description of the potential effects of the New Darlington Project on the aquatic environment.
The Environmental Impact Assessment addressed two primary effects: the physical changes to aquatic habitat and organism-level effects involving intake losses and thermal discharge.
Each of the project's works and activities were considered in order to determine whether there is a mechanism for them to interact with the aquatic habitat or biota.
This section includes a description of the potential effects of the New Darlington Project on the aquatic environment.
The Environmental Impact Assessment addressed two primary effects: the physical changes to aquatic habitat and organism-level effects involving intake losses and thermal discharge.
Each of the project's works and activities were considered in order to determine whether there is a mechanism for them to interact with the aquatic habitat or biota.
Summary of the effects on the aquatic environment during the two phases of the project
Site preparation and construction phase
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Operation and maintenance phase
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Most of these effects, which are discussed below, can be mostly grouped in three different groups: habitat loss, thermal discharge, as well as impingement and entrainment of biota.
Habitat
Another effect on the aquatic environment is the direct loss of the site's aquatic habitat during the preparation of the site and construction phase.
Another effect on the aquatic environment is the direct loss of the site's aquatic habitat during the preparation of the site and construction phase.
- Site development will involve the removal of three of the four ponds present on-site (Treefrog, Dragonfly, Polliwog), as well as the removal of the uppermost portions of two intermittent Darlington creek tributaries. These actions will only result in the loss of habitat of low sensitivity, since those ponds and tributaries do not support fish. However, it is still considered by the EIA as a negative effect of the project.
- Lake infilling and shoreline protection at the new site will result in the permanent loss of approximately 40 ha of nearshore habitat. This area is currently productive to varying degrees for various aquatic invertebrates and fish species.
- Loss of 2 ha of nearshore habitat due to the construction of the intake and discharge structures. However, the EIA states that the area of affected habitat will be negligible considering the total habitat that is available for the aquatic species in the area.
Thermal Discharge
There are two options for plant condenser cooling at the New Darlington Nuclear Power Plant: once-through water cooling or the use of cooling towers. When using the once-through water cooling option, water will be drawn from Lake Ontario through metal tubes into the condenser in order to cool off the turbine. This water, now warm, will then be released back into the lake. The cooling tower option also takes up lake water and releases it back into the lake, the only difference is that by using this method, it is possible to reuse the same water for a longer period of time by cooling it off at the towers before sending it back to the condenser. The once-through water cooling option discharges 10 times more water and at higher temperatures, than the cooling tower system (nirs.org).
Discharge of heated water lake will result in measurable changes to water temperature conditions, specially close to the discharge diffuser. The once-through cooling water discharge is similar to the one at the DNGS, and it has met performance expectations to prevent dispersion of water at temperatures 2 degrees C above ambient temperatures beyond a narrow mixing zone close to the diffuser. No increase in temperature is expected beyond the mixing zone of 50m east or west of the discharge diffuser. In the case that the cooling tower option is used, the mixing zone will extend only up to 15m beyond the water discharge outlet.
For species living in the water column, there would be no significant effects from thermal discharge since the temperatures close to the diffuser were within their preferred range. However, summer temperatures around the diffuser are not suitable for cold-water species such as whitefish, lake trout and other salmonid species.
Warm water discharge can also have the potential to increase substrate temperature in spawning habitat of fish species. Species such as the round whitefish or lake trout are particularly susceptible to increases in substrate temperature during incubation.
There are two options for plant condenser cooling at the New Darlington Nuclear Power Plant: once-through water cooling or the use of cooling towers. When using the once-through water cooling option, water will be drawn from Lake Ontario through metal tubes into the condenser in order to cool off the turbine. This water, now warm, will then be released back into the lake. The cooling tower option also takes up lake water and releases it back into the lake, the only difference is that by using this method, it is possible to reuse the same water for a longer period of time by cooling it off at the towers before sending it back to the condenser. The once-through water cooling option discharges 10 times more water and at higher temperatures, than the cooling tower system (nirs.org).
Discharge of heated water lake will result in measurable changes to water temperature conditions, specially close to the discharge diffuser. The once-through cooling water discharge is similar to the one at the DNGS, and it has met performance expectations to prevent dispersion of water at temperatures 2 degrees C above ambient temperatures beyond a narrow mixing zone close to the diffuser. No increase in temperature is expected beyond the mixing zone of 50m east or west of the discharge diffuser. In the case that the cooling tower option is used, the mixing zone will extend only up to 15m beyond the water discharge outlet.
For species living in the water column, there would be no significant effects from thermal discharge since the temperatures close to the diffuser were within their preferred range. However, summer temperatures around the diffuser are not suitable for cold-water species such as whitefish, lake trout and other salmonid species.
Warm water discharge can also have the potential to increase substrate temperature in spawning habitat of fish species. Species such as the round whitefish or lake trout are particularly susceptible to increases in substrate temperature during incubation.
Impingement and Entrainment of Biota
Large numbers of fish and their larvae are killed by being entrained and impinged in the cooling systems of thermal power plants. Entrainment and impingement is expected to be the principal source of mortality on fish and invertebrates as a result of this project. For this reason, the EIA considers them as important adverse effects of the project.
- Impingement
- Entrainment
On the other hand, the entrainment of other fish species is expected to be low with only the risk of incidental capture.
Invertebrate entrainment will be limited to the abundant chironomids and amphipods and their populations are unlikely to be affected.
Mitigation Measures
Mitigation measures of these impacts will be discussed in the Aquatic Environment critique section of this website.
For more information, please refer to the Aquatic Environment - Assessment of Environmental Effects Technical Support Document