NWT RESEARCH DATABASE

Regions: Sahtu Settlement Area

Tags: physical sciences, geology, stratigraphy, bedrock, lithology, industrial development, watercourse crossing, seismic activities

Project Description: The objective of the program is to collect information regarding the surficial geology of the Great Bear River at the location of the proposed pipeline watercourse crossing. This information will be used to determine the depth to bedrock as part of the information for a river crossing design, and for use in the design of a proposed horizontal directional drill (HDD) crossing at this location. Site investigation procedures will consist of a parallel series of reversed seismic refraction sections, which will be at right angles to the centreline of the proposed pipeline crossing. Each section will be centred on the centreline and extend 200 metres upstream and 200 metres downstream of the centreline. The streamer cable containing 24 geophones will be aligned in the current, parallel to the banks of the river. The length of the survey section will be 200 metres either side of the centreline, with some variation based on the type of system and number of channels to be used. The survey is to be conducted across the full width of the river. The approximate channel width at the crossing point for the Great Bear River is 389 metres. The transverse spacing of each of the sections will not exceed 50 metres. The section spacing and the geophone spacing will be adjusted to clearly demonstrate the presence of bedrock and the near-surface lithology under the crossing down to 30 metres below the mudline. Two boats will be required to perform the work. One boat will tow the streamer cable and its crew will collect the data. The other boat will carry the airgun and its crew will be responsible for positioning the airgun in the correct relationship to the streamer cable orientation. Each boat will carry a crew of three people: a specialist geophysical technician, a boat driver and a wildlife or environmental monitor. The geophones on the streamer cables will be equally spaced. A minimum of 24 channels of data is required. Data will be presented in SEG-2 format for both the interpreted and the raw system data. The boats used for this operation will be of sufficient size in terms of length, beam and draft to safely and effectively operate with the required loads and crews in the shallow water of the Great Bear River. All regulatory requirements, in terms of equipment, safety and personnel training for marine craft shall be fully maintained. Eight section transects will be required for the Great Bear River’s channel width of 389 metres. As the geophone streamer cable length is about 50 metres in length, eight separate observation periods are required along each transect. Each data recording session requires four discharges of the airgun. The geophone streamer remains in one location while the airgun is discharged about 50 metres downstream of the streamer, at the downstream end of the streamer cable, at the upstream end of the streamer cable and 50 metres upstream of the streamer cable. This procedure is then repeated three times for each setting location of the streamer cable. Accordingly, 96 shots will be discharged per section transect resulting in approximately 768 shots for the entire program. Following receipt of all necessary regulatory authorizations, the seismic survey crew will mobilize from Tulita. A non-technical summary report of the program will be submitted to the Aurora Research Institute, copies of which are then made available in each community. If required, a program report will be provided to the regulatory authorities and, where necessary, assistance to the local environmental monitor will be provided in the preparation of similar reports. To ensure that local residents and businesses are informed about and have an opportunity to be involved in the final detailed planning of the program, Imperial will: 1) conduct ongoing community consultation; 2) utilize a local environmental monitor and wildlife monitor for monitoring activities; 3) retain companies for services, including boat rental, from Sahtu-based companies that can provide a competitive bid, are available for the required time period, and can demonstrate adequate capabilities; and 4) retain and utilize the services of a local translator (where necessary) for all meetings and interviews. Program activities will be executed from September 15 to October 7, 2006 at the following locations: Great Bear River, approximately eight km upstream of its confluence with the Mackenzie River.