INNOVATION Mar-Apr 2020

The well as it was in 2015, before the start of the plugging operation, with the 30-inch and 16-inch casings. Historically, artesian flow from both casings was collected into a concrete cistern (centre), and then distributed to buried discharge piping.

with flowable grout that migrated through perforations in the casing into the aquifer. After the grout in the CRW had cured, pumping from the dewatering wells was halted, and RW3 was shut in using valves that were installed at the well head to withstand the artesian pressure. For the first time in 50 years, water stopped flowing from the artesian aquifers underlying the Coldstream Ranch. The team kept a close watch on the water pressure in RW3, because high pressure inside this relief well meant that water wasn’t escaping elsewhere. As the water pressure in RW3 grew, so did the project team’s excitement. The gauge pressure in RW3 soon reached 48 pounds per square inch (equivalent to a water level over 30 metres above ground surface), with no seepage at surface. In late 2018, after groundwater monitoring indicated that the CRW had been successfully closed, the site monitoring wells were decommissioned. Since then, RW3 has provided water for ranch operations. According to CBC News, the total cost for the well closure program from 2009 to 2015 was at least $3.9 million; the cumulative costs since 1965 were even higher. The flowing artesian conditions in the Coldstream Valley are not unique. Many areas, both explored and unexplored, have potential for unidentified flowing artesian conditions. In most cases, these conditions can be mitigated through an understanding of the local hydrogeology, development and implementation of proper well designs, and use of appropriate drilling equipment and methods to prevent losing control of a flowing well. Landowners, consultants, and drillers should all be aware of the potential risks and their responsibilities under the Groundwater Protection Regulation and the Water Sustainability Act . Pattie Amison, P.Geo., the primary author, is a Senior Hydrogeologist, formerly with Golder, and part of the CRW project team. She is now with Teck Resources at the Highland Valley Copper Operations as Lead, Water Resources. Nick Sargent, P.Geo., is a former Golder Project Director and hydrogeology technical lead. In 2019 he retired as a Principal and currently works as a contract consultant. Jacqueline Foley, Geo.L., is an Associate and Senior Hydrogeologist at Golder, and currently works as a Project Director for oil and gas projects.

and bring the water level in the CRW below ground surface during closure. This included designing a temporary water management system to handle sustained flows of up to 95 litres per second from dewatering using several wells, including CRW, RW3, and a nearby municipal supply well. The water management system included several options for water disposal under foreseeable circumstances, including the potential for settling turbidity and containing cement-contaminated water using the temporary tanks. The CRW plugging operation took place from May to June, 2015. After artesian flow from the CRW had been stopped, the shallowest aquitard was stabilized by compaction grouting, a process where the grout is injected into the ground under pressure to increase the density of the surrounding soils. To decommission the CRW, the existing 16-inch well screen and casing were removed, and the bottom of the hole was compaction grouted. The existing 30-inch casing was left in place and filled

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