# Solution to Exercise 14

14) Ten wells are located in a valley setting. Glacial material underlies the land surface and a confined sandstone aquifer underlies the region. All wells shown in the accompanying diagram tap the confined aquifer. DATA: All water levels (WL) are measured depths below the top of casing (TOC) elevation. TD is the total well depth below land surface. The head measurement is at the bottom of each well.
Well A TD 150 m, TOC 1105 m, WL 57 m
Well B TD 160 m, TOC 1100 m, WL 39 m
Well C TD 170 m, TOC 1108 m, WL 76 m
Well D TD 150 m, TOC 1100 m, WL 59 m
Well E TD 180 m, TOC 1098 m, WL 67 m
Well F TD 160 m, TOC 1090 m, WL 57 m
Well G TD 180 m, TOC 1080 m, WL 53 m
Well H TD 170 m, TOC 1079 m, WL 41 m
Well I TD 180 m, TOC 1070 m, WL 50 m
Well J TD 170 m, TOC 1100 m, WL 41 m

14a) Create a potentiometric surface map view.

It is best to copy this map view figure of the confined aquifer well locations, plot the head values, contour the head values to create equipotential lines, and draw flow lines perpendicular to the equipotential lines. The heads at each well are computed by taking the measuring point elevation, TOC and subtracting the depth to water (WL). This head value is then plotted at the mapped location of well (x,y). The total well depth information is not used in the head calculation. As the head is the elevation of the water level in the well. The value of having the TD would be to confirm that the well is monitoring the confined sandstone aquifer.

Calculate head values and plot on map:
Well A TOC 1105 m – WL 57 m = 1048 m
Well B TOC 1100 m – WL 39 m = 1061 m
Well C TOC 1108 m – WL 76 m = 1032 m
Well D TOC 1100 m – WL 59 m = 1041 m
Well E TOC 1098 m – WL 67 m = 1031 m
Well F TOC 1090 m – WL 57 m = 1033 m
Well G TOC 1080 m – WL 53 m = 1027 m
Well H TOC 1079 m – WL 41 m = 1038 m
Well I TOC 1070 m – WL 50 m = 1020 m
Well J TOC 1100 m – WL 41 m = 1059 m

14b) If the confined aquifer water at the orange rectangle became contaminated with dissolved nitrate from downward leakage of water in the overlying unconfined aquifer, would any other monitoring wells become contaminated under steady state flow conditions? Construct equipotential lines and flow lines to support your answer.

The position of the equipotential lines will be slightly different depending on whether they are hand drawn (and these will differ between individuals) or a computer code is applied. The lines shown here were drawn by hand by estimating their positions between data points by approximate linear interpolation. The flow lines encompassing the orange contaminated groundwater area show flow would be to the southwest-south. In this diagram well E would be impacted. Depending on your results, E may or may not be in the direct flow path.