ENVIRONMENTAL
CONSIDERATIONS FOR
NORTHERN
PIPELINE CONSTRUCTION
Compiled by Ken Johnson,
Earth Tech
The coming Mackenzie Valley Gas Pipeline will have significant environmental demands imposed on the construction methods used. Regulatory approval of the 1,500 kilometre pipeline will take about three years, and may include in excess of 16 regulatory agencies; construction will take approximately another two years. On that timeline, gas could begin flowing south from the Mackenzie Delta by 2008. The estimated $5 billion pipeline travels through Inuvialuit, Gwich'in, Sahtu and Deh Cho lands; each of these regions have their own independent land and water boards that must approve the project, and may impose regulatory demands.
It will be interesting to compare this
project to the
The regulatory processes to northern projects of this magnitude have been recently established to some degree with the Ekati, and Diavik diamond mines, however, the linear nature of this project does create some unique regulatory demands.
The following checklist of what were considered appropriate northern pipeline construction techniques approximately 20 years ago may provide some insight on the environmental review process yet to come.
Borrow Sites
1. Where possible, existing borrow pits and associated roads, trails or cut lines will be used in preference to developing new pits.
2. Where practicable, borrow pits for aggregate sources will be located in upland locations and separated from streams and lakes by a 100 metre wide buffer strip of undisturbed terrain in order to minimize siltation. Where upland borrow pits are unavailable or where the environmental disturbances associated with upland aggregate removal would be acceptable, the use of borrow materials from floodplains may be acceptable.
3. Where a borrow site is opened in a floodplain, the development will be above the 150 year high water mark. Dykes and other works will be constructed to minimize the possibility of drainage disruption. A buffer strip of undisturbed floodplain between the channel zone and the pit will be maintained if practicable.
4. Prior to borrow development, site specific plans will be developed to optimize the extraction of granular resources, minimize disturbance and facilitate restoration.
5. Site specific development plans will be used by the operator(s) during development planning, operations, and final restoration.
6. The borrow development area, stockpile area and limits of clearing will be staked to prevent over-extension of the pit area.
7. Topsoil and overburden will be salvaged and placed in separate stockpiles on a level and stable area. Topsoil stripping depth and storage locations will be identified on plan diagrams as final designs become available.
8. A minimum space of 5 metres will be maintained between the clearing edge and the stockpile base. A minimum spacing of 10 metres will be maintained between excavation perimeter and the stockpile base.
9. A minimum firebreak of 30 metres will be maintained around the development area.
10. Equipment movement will be restricted to a 30 metre working area at the pit entrance and to the excavation area during pit development to prevent unnecessary disturbance of the soil stockpiles and surrounding cleared areas.
11. Where practicable, pit excavation will not extend below the water table.
12. In areas where winter excavation in poorly drained areas will result in spring and summer ponding, all granular materials required will be removed and stockpiled during the initial development period.
13. Drainage and erosion associated with each borrow operation will be controlled so as to minimize terrain disturbance and siltation of water bodies.
14. Pit slopes will be contoured to a 2:1 slope or less to minimize erosion instability.
15. Restoration and appropriate drainage and erosion control measures will be implemented following site use and abandonment to prevent erosion and assist the natural recovery. Future potential site uses will be accommodated where practicable.
Facility
Sites
1. Environmental procedures and restrictions for the location, clearing and winter development of facility sites will be itemized for Winter Clearing and Site Development.
2. A minimum firebreak of 30 metres will be maintained between the work pad and the clearing perimeter.
3. Work pads will be constructed of granular fill of sufficient thickness to minimize disturbance of the existing thermal regime. Fill material will be deposited directly over the organic mat. Site grading and disturbance to the organic mat will be minimized to maintain the soil thermal regime.
4. During summer, vehicle movement will be confined to the work pad.
5. Drainage control measures will be implemented to provide adequate surface drainage on and around the pad. If needed, surface waters will be directed into a collection and sedimentation pond before being discharged.
Right-Of-Way
Construction
1. Equipment will not be operated off the right-of-way, ancillary sites, access road, Territorial highways or other areas except as provided for in the design plans or as approved by the regulatory authorities.
2. Ground surface preparation will be conducted in accordance with the appropriate existing land use regulations.
3. In the event of accidental off right-of-way travel, the area affected will be restored to as near the original or equally stable condition.
4. Construction traffic on the right-of-way will travel on winter roads built of packed snow. Grading of the native soils will be minimized and limited to ice-poor soils where practicable. Fill grading using snow will be used as possible in preference to cut grading.
5. Fill grading may be used on side slopes. Fill material will generally be snow. When sufficient snow is not available onsite, snow may be hauled from a nearby approved source or fill from an approved borrow pit. Cut grading will be minimized and used only with appropriate approval.
6. Frost penetration on terrain will be at least 30 centimetres before heavy machinery and equipment movement will be allowed. In any event, the undercarriage of working equipment will be clear of the ground surface.
7. On surfaces that are cut graded, surface soil material will be salvaged and stored within the cleared right-of-way for use in restoration of the cut slope.
8. Construction procedures will not cause significant changes to natural drainage.
9. Surface preparation during construction activities will be restricted to the areal extent necessary for construction.
10. Grubbing of all roots, stumps and partially embedded rocks or boulders where required will be undertaken in such a manner as to minimize the extent of disturbance to the organic layer and/or topsoil.
11. Pipe stringing, laying and trench backfilling will be coordinated with trenching to minimize disruption of wildlife movements across the line.
12. Excess spoil material will not be deposited in a push pile manner beyond the cleared right-of-way, will not be side-case along streams, will not be disposed above the high water mark within valley breaks and will not be disposed in water bodies.
13. Spent welding rods and any other waste metal shall be collected and disposed of in an approved landfill site.
14. All waste petroleum products will be collected and incinerated or properly stored and disposed outside the slope to any watercourse.
1. Prior to and during construction activities, environmental education will be provided by qualified people to all personnel involved in construction and inspection.
Thaw
Sensitive Slopes
1. On thaw sensitive slopes not to be graded:
a) Machine movement will be kept to a minimum. Vehicles not required for construction purposes will not be allowed on these slopes.
b) Movement of construction equipment will be confined to the ditch line as much as practicable.
c) Removal of vegetation from these slopes and disturbance to the organic mat will be kept to an absolute minimum necessary for construction.
2. Thaw sensitive slopes to be graded:
a) Cutting of grades will be avoided wherever possible.
b) Width and depth of cuts will be kept to an absolute minimum.
c) High ice content spoil should be disposed of and replaced with select backfill.
d) Surfaces of thaw sensitive slopes may be insulated with granular material or wood chips.
Water
Crossings
1. Crossing of water bodies will be conducted in compliance with the authorities having jurisdiction.
2. Activities which encroach upon water bodies, such as pipeline crossings, road crossings and water intakes, will be planned and carried out so as to minimize changes in water quality, flow or level, or morphology of the channel or bank.
3. The movement of machines across water bodies will be via approved access roads. Existing access will be utilized for crossing activities where possible.
4. Temporary winter stream crossings will be constructed of compacted snow or ice of sufficient thickness to protect the banks of the watercourse.
5. Ice bridges will be located to minimize approach grades and to avoid cuts in streams and riverbanks.
6. Soil or vegetation will not be incorporated into ice bridges or ice roads on water bodies.
7. Temporary crossing structures will be removed following completion of use.
8. Ice bridges will be breached by mechanical means prior to spring flooding, where damming and potential flooding could occur.
9. Ground cover vegetation within 10 metres of the high water mark area will not be disturbed until the actual start of crossing construction.
10. Water crossing locations and designs will be chosen to provide for maximum terrain integrity of banks and to minimize erosion potential.
11. Physical disturbance to stream banks and stream substrates will be limited to the minimum area required for installation of the pipe.
12. In stream activities necessary for the movement of men and equipment on the right-of-way across a watercourse will be restricted to a single location.
13. Any water crossing structures that are required will allow uninterrupted movement and safe passage of fish. If culverts are to be installed, designs will accommodate an average cross-sectional velocity through any culvert section not exceeding 0.9 m/s during fish migration periods.
14. Streams with fish over-wintering potential and a discharge less than 1 m³/sec. will be flumed with culverts to prevent heavy sedimentation and to maintain adequate flow. Culverts will remain in place during trenching, pipe laying and backfilling.
15. Pipe trench excavations will be made in a manner which will minimize suspended sediment input into a watercourse. Where necessary, an adequate protective plug will be provided at each bank. Plugs will not be completely removed until absolutely necessary. Trenches in the banks will be backfilled with stable materials immediately after the pipe is laid to avoid the erosion of fine materials from the trench immediately adjacent to the water body. Coarse material will be used to backfill sub-aqueous trenches.
16. Ditch spoil from streambeds will be piled on stream banks where practicable. On wider water crossings, it may be necessary to temporarily deposit spoil on the ice. This spoil will not be piled to the extent that ice is depressed and overflow occurs, resulting in dewatering of the watercourse downstream.
17. At water crossings, the pipeline will be buried below the anticipated channel scour depth and sag bends will be set back to avoid exposure resulting from channel migration.
18. Burial of all pipelines through waterways will be undertaken so as not to restrict or eliminate winter flows.
19. All channels, including intermittent drainages, capable of supplying some concentrated flow, will be returned as close as practicable to their natural configuration, and the channel bed and bank protected with coarse granular material.
20. Slope cuts through riverbanks will be designed and constructed to minimize erosion and prevent slides. The banks will be stabilized upon completion of construction and prior to spring break up.
21. Suitable cobbles or boulders removed from the riverbank during the grading operations will be stockpiled.
22. Debris, logs and soil from approach slopes will not be deposited in or pushed through any watercourse.
23. Any spoil material or other foreign material, such as rocks or timber, will be removed from the ice during cleanup.
Summer
Crossings
1. Spoil removed from the pipeline trench will be stockpiled out of the water or in piles in the water in areas of relatively low water velocity.
2. All pipe used to cross a major waterway will be pre-tested on the bank prior to installation.
Drainage and
Erosion Control
1. Drainage and erosion control measures will be applied in accordance with existing land use regulations and permit and license requirements as applicable.
2. Design and implementation of construction will ensure that requirements for drainage control are minimized and natural drainage patterns are maintained.
3. Drainage and erosion control measures will be designed, constructed and monitored so as to ensure fish and wildlife habitat quality are maintained.
4. All permanent drainage and erosion control measures will be maintained and/or repaired as required. Temporary drainage control measures will be removed from roads, borrow sites and spoil disposal sites during restoration.
5. Erosion control measures will be provided to minimize the siltation of water bodies utilized by important fish species. Settling basins, sediment traps or other devices will be constructed on approaches to crossings, where necessary.
6. Devices such as rock riprap or gabions will be placed on the banks and bottom of river, stream and floodplain crossings as necessary to control erosion. Riprap will be composed of rocks large enough to withstand peak runoff velocities.
7. Diversion berms will be used to divert or to intercept runoff upslope of the pipeline, across or away from the right-of-way.
8. Diversion berms will be extended randomly 1 to 3 metres beyond the edge of the cleared right-of-way to prevent concentrated flow and to direct water onto undisturbed terrain.
9. Diversion berms may be constructed of sacks placed on the organic mat or soil armoured with pit-run gravel.
10. When erosion of the backfill from water flowing within the ditch is possible, ditch plugs will be provided across the ditch with a mound break and diversion berm.
11. Ditch plugs will be constructed of materials placed in sacks keyed into the walls of the trench to direct groundwater to the surface.
12. Mound breaks will be located to minimize ponding along the backfill mound. Mound breaks will typically be 2-3 metres wide, and will be protected by granular materials and/or vegetation.
13. In non-permafrost and thaw stable permafrost terrain, drainage ditches may be used as adjuncts to the diversion berms where large flows are anticipated. Where required, the ditches will be protected with a layer of non-erodible material.
14. Ditch checks will be used in drainage ditches for velocity or sediment control. Ditch checks may be temporary or permanent measures. Temporary ditch checks could be made of sacked free-draining material. Permanent ditch checks will be made of free-draining granular material.
15. In ice-rich terrain, vertical cut slopes will be allowed to slump naturally to a stable angle. Parallel interceptor ditches will be installed a distance from the initial toe of the cut equal to about the height of the cut. Vertical cuts in excess of 5-6 metres will require site specific design. Sloped cuts will be reduced to stable angles and protected from thermal erosion with granular fill or wood chips.
Archaeological
Sites
1. Project activities and personnel will not be allowed to enter within 40 metres of the identified archaeological sites.
2. The boundary of each restricted area will be clearly flagged and signed during the survey phase.
3. If unusual objects or features, which may be of historical significance, are found in any area during clearing or construction, contingency plans developed for such incidents will be implemented.
Wildlife
1. Licensed trap line operations and associations in the vicinity of the right-of-way will be notified by registered mail and by the Community Consultation Officer at least five days prior to the commencement of clearing or construction.
2. Slash will be burned simultaneously with the advance of the clearing operations to minimize obstruction of wildlife movement across the line.
3. Pipe stringing and backfilling will advance with the opening of the trench to minimize obstruction of wildlife movement across the line.
Raptor Nest
Sites
1. Ground and air access within 3.2 kilometres of an identified raptor nest will be restricted during the period from April 15 to September 15 unless otherwise directed by an authority having jurisdiction. Access during this time period will be permitted only under the approval and supervision of an Environmental Inspector.
2. If over flight of raptor nests cannot be avoided, aircraft will maintain a minimum altitude of 760 metres above ground level over such areas.