Groundwater Lab
Geology 2
Purpose: An introduction to the analysis of groundwater resources. Skills will include
contouring water tables in unconfined aquifers and determining the direction of
groundwater flow.
Part I Groundwater flow in Florida
Much of Florida is underlain by limestone which forms a Karst topography
consisting of many sinkholes. The water table in the very porus and permeable limestone
is just a few feet below the surface. The level of the water table is marked by the level of
the lakes that fill many of the sinkholes. The slope of the water table, and thus an
indication of which way the groundwater is flowing, can be determined by contouring the
water table. We will contour the slope of the water table by contouring the level of the
water in the lakes.
How to do it: Follow
the example to the right by:
1) Estimate the elevation of
the water in each of the
lakes by examining the
contour lines showing the
elevation of the land. Note
that our estimate of lake
elevation will be imprecise.
Assume that the lake
elevations are halfway
between the lowest contour
closest to the lake and the
next lower contour line. See
the example to the right. For example at Glass Lake, the lowest contour line next to the
lake is 150 feet. Assume the lake level is 145 feet because 145 is halfway between 150
feet and 140 feet. All lake levels will end in the number “5”.
2) Write the elevation of the lake in bold pencil on the lake.
3) Contour the elevation of the water table by drawing lines for elevations that end in “0”
using the numbers you have drawn on the lakes.
4) Water will flow in a direction perpendicular to the contour lines (do you understand
why?), from lines representing high elevations to lines representing lower elevations.
Now draw in these flow lines using an arrow to show the direction of flow. In the
example above, the water flow would be from northwest to southeast.
On the map below, estimate the elevations of all the lakes, write the elevations of the
lakes on the map, and then contour the water table using these elevations. Use a contour
interval of 10 feet and elevations of contour lines that end in “0”. Finally, use arrows to
show the direction of groundwater flow. Answer the following question. (You can see a
color version of this map in the lab book provided by the instructor.)
How deep would you have to drill to obtain water if the well site were located at
the road intersection located 1 mile west of Interlachen?
Part II Polluted Groundwater Flow.
Smith is worried that the horses and corral on Jones’ property is a potential source
of pollution. Could pollution on Jones’ property impact the well on Smith’s property?
Note that the lines are contours of the water table, not contours of land elevation.
1) Use arrows to show the direction of flow of groundwater in the area below.
2) What are the chances that polluted water could ever get from the dump to Jones’ well?
3) What are the chances that polluted water would ever get from the dump to Smith’s
well?
4) What are the chances that polluted water would ever get from Jones’ corral to Smith’s
well?
1. In the diagram above, label the following locations or features. In your labels, please
use the full terms or words, not the letters that identify the terms below.
a) the water pressure surface (or potentiometric surface)
b) the recharge zone
c) a surficial, or unconfined, aquifer
d) a confined aquifer
e) a confining bed
f) the direction that the water will flow in the confined aquifer
g) a good place for a well that taps the confined aquifer.
2. For the well that you placed in “g” above, would the water flow freely to the surface,
or would it need to be pumped to the surface? Please explain the rationale behind your
answer.
3. On the
diagram at
right, mark and
label the
following
items. Assume
that the granite has zero porosity.
a) An area where a single well might encounter two separate aquifers.
b) The surficial aquifer where the water will flow from wells most easily.
c) The surficial aquifer where water will flow from wells with more slowly.