Control of artesian pressure by bleeder wells

Deep test bleeder wells were installed in an artesian aquifer underlying the Bridge River No. 1 hydroelectric generating station in southern British Columbia to determine whether seasonal peak artesian pressures could be controlled.The Bridge River complex, built in the early 1950's, consists of two powerhouses located about a kilometre apart on the shore of Seton Lake, a system of power tunnels, and surface penstocks, which conduct water from the Carpenter Lake reservoir in Bridge River valley to the powerhouses. The No. 1 powerhouse is founded on consolidated deposits of clayey silt, underlain by sand and gravel. Shortly after the powerhouse was constructed, ground and powerhouse movements occurred. It was later determined that such movement was caused by high artesian pressures in the sand and gravel aquifer under the powerhouse.Attempts to install bleeder wells in 1952 were unsuccessful and an offshore fill was constructed as a toe weight, which functioned adequately until 1974 when additional ground cracking was observed. After further study and additional drilling at the site, test bleeder wells and piezometers were installed in 1976.Tests conducted to assess the effect of the bleeder wells indicated that control of excessive artesian pressures by a system of bleeder wells was feasible.