BMP 9 – Trenching

Trenching and pitting, either on Crown lands or in Provincial Parks, may be conducted during surface exploration activities to obtain a stronger visual understanding of the rock. Trenching can be conducted with hand tools, but heavy equipment is typically used to remove the surface soil and expose the bedrock, BMP 10 – Surface Stripping. Trenches or pits are then excavated or blasted into the rock to expose more of the mineralized zones for sampling and testing. See information on Blasting BMP 2 – Early Exploration.

Pits are shallow holes, while trenches are generally longer, linear and of variable depth. Excavation can be either by hand, mechanical digger or by bulldozer on sloping ground. Rock and soil removed from the trench or pit is stored on site in a safe and stable manner. There are two main types of exploration trenches, overburden trenches and bedrock trenches.

Overburden trenches: Overburden trenches are commonly used during early exploration activities and are excavated to better observe and map the type of bedrock below the soil or organic material overlaying the rock. Unless further work is planned to test or drill the bedrock, overburden trenches are typically backfilled after mapping or surface sampling has concluded.

Bedrock trenches: Bedrock trenches are excavated to sample and confirm mineralization of the bedrock. These trenches are less common during early exploration activities and are typically created by Blasting. See information on Blasting BMP 2 – Early Exploration.

Manitoba Economic Development, Investment, Trade and Natural Resources accepts trenches by volume removed as evidence of assessment work (the exploration activities that must be conducted annually on mineral dispositions to keep dispositions in good standing), which is one of the reasons bedrock trenches may be left open and not immediately backfilled.

The Department of Economic Development, Investment, Trade and Natural Resources provides approval for Trenching activities prior to starting work through a Work Permit Application.

Details of the proposed Trenching activities, including the dimensions of the trenches, method of excavation, and any backfilling or site decommission planning details should be included in a Work Permit Application. If clearing of forest vegetation is required, BMP 6 – Timber Clearing Activities.

Environmental impacts can be reduced or avoided with the proper safeguards.

Unless otherwise authorized, a minimum 100 metre buffer of undisturbed vegetation must be maintained between a trench and all water bodies.

Unless otherwise approved, all areas stripped of topsoil must be backfilled and restored to as near the original contour as possible BMP 16 – Decommissioning.

The excavation of an exploration trench must take into consideration the safety risks associated with entrapment and must be dug in a manner that allows for easy escape for both humans and wildlife. This includes sloping excavation walls to a slope ratio of 5:1 or gentler.

For the use of explosives, see information related to Blasting BMP 2 – Early Exploration. Blasting activities should be planned outside sensitive timing windows for wildlife such as migratory bird nesting periods and within known caribou calving areas, BMP 15 – Wildlife. Blasting activities should also consider the use of dampening techniques to prevent debris from impacting areas adjacent to the trench.

If present, any topsoil excavated should be stockpiled separately from other materials excavated to be utilized for subsequent backfilling unless otherwise directed.

Materials excavated during overburden Trenching should be backfilled in reverse order, if possible, to match existing soil horizons, with the topsoil replaced last at surface level. Seeding or planting may be necessary depending on topography and likelihood of erosion and should be considered as part of site decommission planning details included as part of a Work Permit Application. This should be discussed with the Permit Office or Reginal Forester. See BMP 16 – Decommissioning.

Advanced exploration project: means a) an excavation of an exploration shaft, adit or decline, b) construction of an all-weather access road to an advanced exploration site, c) diversion, alteration or damming of a natural watercourse for purposes of bulk sampling, mine development or mining, d) dewatering of a shaft, adit or decline for underground exploration and development purposes, e) removal of a bulk sample of at least 500 tonnes of material for testing, and f) any other project that is prescribed as an advanced exploration project.

If during the Trenching process, activities move beyond visual understanding of the rock to sampling and at least 500 tonnes of bulk sample is removed for testing, the activities are no longer considered to be Early Mineral Exploration and would fall under advanced exploration.

Safety measures, further exploration program planning, and future decommissioning strategies should be considered by the Proponent and detailed within a Work Permit Application when requesting trenches be left open.

Contacts

Related Acts and Regulations

M162 – The Mines and Minerals Act
C340 – The Crown Lands Act
P20 – Provincial Parks Act
MR 141/96 Park Activities Regulation
W210 – Manitoba Workplace Safety and Health Act
F150 – The Forest Act
W130 – The Wildlife Act
E111 – The Endangered Species and Ecosystems Act

Contacts

Economic Development, Investment, Trade and Natural Resources

Economic Development, Investment, Trade and Natural Resources

Environment and Climate Change

Economic Development, Investment, Trade and Natural Resources

Economic Development, Investment, Trade and Natural Resources

Department of Labour and Immigration

Related Acts and Regulations