8. (25 points) estimati ng direction and hydraulic gradient in a sand and silt layer beneath a low-level radioactive waste burial site. you have been tasked to determine the direction and hydraulic gradient in a sand and silt layer that underlies a low-level radioactive-waste burial site in western new york. the location of the western new york nuclear service center where the low-level radioactive wastes were buried is shown in figure i an extensive geologic survey was done in the vicinity of the waste burial area. wastes were buried in trenches excavated into a clay-rich till (hydraulic conductivity both vertical and horizontal- of about 2 x 10 centimeters per second) that overlies a sequence of sand and silt, (figures 2 and 3). the till beneath the bottom of the burial trenches is about 25 m thick; the gradient is strongly vertical and is about 0.8 m per m. the underlying fine sand and silt has a hydraulic conductivity of about 2 x 104 centimeters per second. the effective porosity of the till is 0.15 and the effective porosity of the fine sand and silt is 0.20. the sequence of sand and silt acts as a drain to the till beneath the burial trenches and causes vertical flow through the till beneath the burial trenches. the upper part of the sand and silt sequence is unsaturated because there simply is insufficient flow from the overlying till. three piezometers were installed in holes drilled into the saturated sand and silt (wells j, v, and w, figure 2). the water-level elevation in meters above mean sea level is listed next to each well. a. (10 points) use figure 2 to determine the direction of ground-water flow in the sand and silt layer and estimate the gradient.