An unconfined aquifer is comprised of two main layers: a well-sorted sand from 0 – 50 ft below the ground surface and a well-sorted gravel from 50 – 78 ft below the ground surface. The aquifer is underlain by a clay aquitard. Recently, the Maryland Dept. of Environment discovered that in 1990 illegal, toxic chemicals was put into a disposal well that is 5900 ft upgradient of the water supply wells for a town. Some of the water supply wells are slotted in the sand and some in the gravel layer. Assuming that the toxic chemical travel at the same rate as the groundwater and that water does not move between the sand and gravel layers, calculate the time (in years) that it might take water to flow from the disposal well to the water supply wells. The town will determine if they should start testing the wells for the toxic chemicals based on your calculations. Disposal well Water supply wells
Ground surface elevation (ft) 148 142
Water table depth below ground surface (ft) 31 34