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CE 473/573 Groundwater Fall 2012 Homework 8 Due Friday October 26 *48. Three wells with radius of inﬂuence 450 m are pumping steadily (but at diﬀerent rates). The transmissivity of the aquifer is 430 m2 /d. a. Compute the drawdown at point A. b. Which well has the greatest inﬂuence on the drawdown at point A? 3 Q = 1000 m /d (x,y) = (150, 200) m Point A: (x,y) = (0, 0) m Q = 2000 m3/d (x,y) = (-300,100) m Q = 1500 m3/d (x,y) = (200,-150) m 49. To capture some contaminant, a well is pumped at a rate of 2500 m3 /d in a conﬁned aquifer with a hydraulic conductivity of 1425 m/d, an initial hydraulic gradient of 0.00076, and a thickness of 31 m. a. What is the maximum width of the capture zone? b. What is the maximum distance downgradient of the well that the well will capture contaminant? *50. A contaminant plume of width 65 m is advancing from a leaky underground storage tank in a conﬁned aquifer of conductivity 40 m/d and thickness 14 m. The hydraulic gradient is 0.002. You can install a well 300 m downgradient of the tank. If the plume advances in the x-direction, at what rate must you pump to capture the plume? 300 m x Well Leaking tank Advancing plume *51. A well in a conﬁned aquifer of transmissivity 210 m2 /d sits near a no-ﬂow boundary. The well pumps steadily at 300 m3 /d, and its radius of inﬂuence is 1000 m. The coordinates of several points are shown in meters. The boundary continues beyond the points shown. a. What is the drawdown at point A? b. If the boundary were not there, what would the drawdown at point A be? c. Explain the diﬀerence between the drawdowns in parts a and b. (-550, 900) No -flo w bo un Well (0,0) da ry Pt. A (350,100) (1050, -50) *52. Design a system of wells to lower the water table at a construction site for a rectangular excavation area that has dimensions of 100 m and 500 m. The hydraulic conductivity is 5 m/d, and the initial saturated thickness is 30 m. The water table must be lowered 7 m everywhere in the excavation. Design the system by determining the number, placement, and pumping rate of the wells. The wells must be at least 50 m outside the excavation area. Each well can pump up to 450 m3 /d. Assume steady state and a radius of inﬂuence of 800 m. (Hints: Remember that this aquifer is unconfined. Also, think about where the drawdown will be smallest inside the excavation.)