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Question 4
Three identical boreholes fully penetrate the depth of a 25m confined aquifer. The wells are pumped at a constant rate for 20 hours after which time the drawdown at the observation point is 5m. Each of the pumping wells is positioned at a distance of 160m away from a central observation point. The permeability of the aquifer is 7.5m/day and its storage coefficient is 0.001.
It becomes necessary to increase the drawdown at the observation point requiring a fourth borehole, previously drilled and prepared at a distance of 125 m from the observation borehole, to be pumped at the same rate as the existing boreholes.
Calculate the additional drawdown achieved at the observation well after a further 28 hours of pumping all four active boreholes. You may use the Well Function table given and assume all wells are within the field of influence.
Question 4 Three identical boreholes fully penetrate the depth of a 25m confined aquifer. The wells are pumped at a constant rate for 20 hours after which time the drawdown at the observation point is 5m. Each of the pumping wells is positioned at a distance of 160m away from a central observation point. The permeability of the aquifer is 7.5m/day and its storage coefficient is 0.001. It becomes necessary to increase the drawdown at the observation point requiring a fourth borehole, previously drilled and prepared at a distance of 125 m from the observation borehole, to be pumped at the same rate as the existing boreholes. Calculate the additional drawdown achieved at the observation well after a further 28 hours of pumping all four active boreholes. You may use the Well Function table given and assume all wells are within the field of influence.