http://almandine.geol.wwu.edu/~dave/courses/2003/spring/101/lectures/water_level.swf

• 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: 1 ft/day

• Groundwater pollution is a function of the type of contaminant and the medium into which it is found.

• What happens when a new well here is heavily pumped?

Flow direction can

change

Back to the Civil Action Case…

Could the contaminants in the water have come from the named polluters and reached wells G & H prior to 1979?

Legend:

H = municipal well H

G = municipal well G

U = Unifirst Properties

G = W.R. Grace

B = Beatrice (Riley Tannery)

red = outcrop of fractured schist

pink (Qgm) = ground moraine (mixtures of sand-silt-clay)

beige with blue plant symbols (Qsd) = wetland deposits (mixtures of peat-sand-silt)

white (Qo) = glacial outwash (mixtures of sand and gravel with silt)

yellow (Qf) = artificial fill

This geologic cross-section is much more detailed than what is expected from the assignment, however…

Groundwater flow is perpendicular to the water-table contours.

The slope of the groundwater table is equal to the change in elevation between two reference points on the water table divided by the horizontal distance between these reference points.

Darcy’s Law relates the velocity of groundwater flow to the slope of the water table (hydraulic head) and the hydraulic conductivity (permeability).

Darcy’s Law can be written mathematically where:

Velocity of groundwater flow = hydraulic conductivity x hydraulic gradient.

Area is introduced into the equation to determine discharge.