Groundwater • aquifer / aquitard • water table • groundwater flow • groundwater contamination Groundwater: aquifers • Any geologic unit through which water can move easily (i.e it’s permeable) (= high permeability) • Porosity: how much water a geologic material can hold Opposite of an aquifer? • Aquitard / aquiclude – retards the flow of groundwater (it’s almost never really zero) Groundwater: aquifers • What would be the properties (porosity/permeability) of conglomerate? • High porosity, high permeability Groundwater: aquifers • What would be the properties (porosity/permeability) of unfractured granite? • Low porosity, low permeability Groundwater: aquifers • Can you think of a rock/sediment with high porosity and low permeability? Groundwater: aquifers • Can you think of a rock/sediment with low porosity and high permeability? discharge=2000 ft3/s No tributaries here discharge=4000 ft3/s How is this possible? Ground Water and Surface Water • These are almost always connected • If a stream contributes water to the aquifer it’s called a “losing stream” • If a stream receives water from the aquifer it’s called a “gaining stream” • Same stream can be both at different places or at different times Pumping Animation • Go to animation at: http://almandine.geol.wwu.edu/~dav e/courses/2003/spring/101/lectures/w ater_level.swf What is happening here? • In the low permeability case the water is pumped primarily from the area directly around the well, whereas with the higher permeability the water seems to be drawn from a more broad area surrounding the well "hole" Since permeability refers to the ability of a material to let a fluid move through it, the low permeability doesn't allow the water to venture far from the path of pressure change (the "hole" of the well) • What happens when this well is heavily pumped? Groundwater Flow • Groundwater velocity – Depends on permeability and hydraulic gradient (slope of water table) – Ranges from 100 m/day to mm/day – A good round number: ft/day • What happens when a new well here is heavily pumped? Flow direction can change [...]...discharge=2000 ft3/s No tributaries here discharge=4000 ft3/s How is this possible? Ground Water and Surface Water • These are almost always connected • If a stream contributes water to the aquifer it’s called a “losing stream” • If a stream receives water from the aquifer it’s called a “gaining stream” • Same stream can be both at different places or at different times... permeability doesn't allow the water to venture far from the path of pressure change (the "hole" of the well) • What happens when this well is heavily pumped? Groundwater Flow • Groundwater velocity – Depends on permeability and hydraulic gradient (slope of water table) – Ranges from 100 m/day to mm/day – A good round number: 1 ft/day • What happens when a new well here is heavily pumped? Flow direction can... happening here? • In the low permeability case the water is pumped primarily from the area directly around the well, whereas with the higher permeability the water seems to be drawn from a more broad area surrounding the well "hole" Since permeability refers to the ability of a material to let a fluid move through it, the low permeability doesn't allow the water to venture far from the path of pressure