Cumulative Effects Assessment Practitioners' Guide

Terra Nova Off-Shore Petroleum Project: Cas Study Highlights

VECs: Water and air quality, fish, seabirds, marine mammals

Issues: Changes to water quality, impacts on fish, seabirds and marine mammals; reduced opportunities for fishing; impact of noise from aircraft and project activities on seabird colonies and marine mammals

Approaches: Interaction matrices indicating scale, magnitude, duration and mitigation measures for each potential impact on specific development activities and VECs

Lessons learned: Acknowledgment of lack of information about future offshore projects on the Grand Banks and the difficulty of assessing cumulative effects because of the uncertainties and multi-jurisdictions that are involved; project demonstrated the need for follow-up and monitoring programs supported by many stakeholders


A federal-provincial panel was appointed in 1996 to review and assess an offshore petroleum development southeast of Newfoundland. The project was designed to recover petroleum resources from the Terra Nova oil field located in the northeast section of the Grand Banks. Approximately 1 billion barrels of oil are contained in this reserve. The proponents would use a floating steel monohull production, storage and offloading vessel; semi-submersible drilling rigs; and shuttle tankers to transfer produced oil from the site to storage facilities onshore or directly to markets (Harris et al. 1997). Drilling centres will be located in open glory holes, 10 m deep and 15 m wide, from which flowlines trenched in the ocean floor will carry oil to flexible risers leading to the production platform.

Assessment Approach

The principle cumulative effects issues identified were: impact of discharging drilling muds, cuttings, drilling fluids, deck waste and produced waste on water quality, fish and fish refuge, and marine mammals; impact of oils spills on water quality, fish and fish refuge, and marine mammals; impact of noise from aircraft and project activities on seabird colonies and marine mammals; impact of project activities on the fishing industry; and potential impacts on VECs from the existing Hibernia project and all other potential developments on the Grand Banks. Only factors specific to planned petroleum projects on the Grand Banks throughout the life of the Terra Nova Development were included in the assessment.

Within the proponent's CEA, all possible relationships between project activities and VECs were identified in interaction matrices. Impacts were evaluated after consideration of mitigation measures that were designed into the Terra Nova project and its operational procedures. Results were tabulated for the VECs which included an assessment of the magnitude, scale and duration of potential impacts. The majority of impacts were evaluated as negligible; however, a limited number were rated as moderate to major with respect to noise disturbance to seabird colonies. The proponent stated that with development-specific mitigation measures and monitoring programs these impacts would be reduced to negligible levels.

With respect to cumulative impacts resulting from potential developments and other projects on the Grand Banks, the proponent did not include future activities in the assessment because of the lack of detailed information on their likelihood, timing and scale (Petro Canada 1996). The assessment did address potential cumulative effects from the Hibernia project, the commercial fishery and commercial shipping. Resulting impacts from these activities were determined to be insignificant because the distance between the Terra Nova project and Hibernia would be sufficient to avoid overlap of effects; in the future the two projects would investigate shared logistics to reduce the impacts caused by aircraft and shipping vessels; and the safety zones of the two developments would be large enough to provide a potential refuge for the fisheries and allow for unimpeded fish harvesting.

Within its report, the Panel stated that it was not possible to hold the proponent responsible for potential developments beyond their control that may interact with the Terra Nova project to cause cumulative effects. However the Panel did stress that gradual accumulative degradation of the Grand Banks environment due to collective anthropogenic impacts was a major environmental concern and must be avoided (Harris et al. 1997). Without sufficient information and a defined methodology to identify and measure impacts, the Panel found it difficult to assess the cumulative effects of the project. The multiple jurisdictions involved in the assessment added to their difficulty and it was evident to the Panel that it would be necessary to have cooperation between all stakeholders in order to complete a comprehensive cumulative effects assessment.

Recommendations by the panel to address cumulative effects included the development of a workshop of experts with experience in environmental monitoring, sampling and measurement to examine the potential for cumulative effects of petroleum developments and other activities in the Newfoundland offshore environment and to design an approach to monitor these effects. Once a cumulative effects monitoring program was established, all offshore development projects would be required to incorporate this monitoring program into their individual monitoring plan standards and measures.

Lessons Learned

  • It was difficult to assess cumulative effects of the Terra Nova offshore project because of the uncertainties and lack of information regarding the number and magnitude of future offshore petroleum developments and other activities on the Grand Banks; and the multi-jurisdictions involved in the assessment.
  • Due to the present difficulties in identifying and measuring cumulative effects; the Panel recommended a follow-up monitoring program be developed, implemented and supported by multi-stakeholders for all future offshore developments on the Grand Banks.