A well that pumps at a constant rate of 78,000 ft'/ d has achieved equilibrium so that there is no change in the draw down with time. (The cone of depression has expanded to include a recharge zone equal to the amount of water being pumped.) The well taps an unconfined aquifer that consists of sand overlying impermeable bedrock at an elevation of 260 ft above sea level. An observation well 125 ft away has a head of 277 ft above sea level; another observation well 385 ft away has a head of 291 ft. Compute the value of hydraulic conductivity using the Thiem equation.