MAPPING: TRACK GROUNDWATER POLLUTION
Background: You can use a topographic map to estimate the direction of groundwater flow. Groundwater pollution spreads out from its source and follows the flow of groundwater. The spread and movement of the pollution resembles a plume that stems from its source.
Question: How can you determine the movement of a pollution plume?
U. S. Geological Survey topographic map of Forest City,
Florida transparent paper ruler graph paper calculator
6. Draw a small line at each place where a contour line intersects the line from Lake Lotus to Lake Lucien. Also note the elevation at each hash mark and any rivers crossed.
7. Draw a table to use for your topographic profile, using the width representing the distance between Lake Lotus to Lake Lucien. For the y-axis, use the elevations 60, 70, 80, 90, and 100 ft.
8. Now take your paper where you marked your lines and place it along the base of the table.
9. Mark a corresponding dot on the table for each elevation, and mark the position of Jim's gas station.
10. Connect the dots to create a topographic profile.
11. Note the elevations of the nearby bodies of water to approximate the distance from the ground surface to the water table. Use dots to indicate those distances on the topographic profile. Connect the dots to draw the water table on the topographic profile.
Imagine that Jim's Gas Station has discovered a major gasoline leak from one of its underground tanks. As the local hydrogeologist, you are asked to determine the path that the gasoline will take through the groundwa-ter, and to notify the residents of the areas that might be affected by the contamination.
2. Identify the lakes and swamps in the southwest corner of the map and list their names and elevations in a data table. (Note: The elevations are given or can be estimated from the contour lines. The elevation of the water table in each area can be estimated from the elevations of nearby bodies of water).
3. Note the location of Jim's gas station on Forest City Rd., about 1400 feet north of the Seminole County line (at the 96-foot elevation mark).
4. Take out a piece of paper to construct a cross section of the surface topography and the water table. Lay the paper on the map from Lake Lotus to Lake Lucien (through Jim's Gas Station).
5. On this piece of paper, mark the location of Jim's gas station.
Analyze and Conclude
1. Calculate the slope of the ground surface on either side of Jim's Gas Station.
2. Estimate the slope of the water table at Jim's Gas Station.
3. Infer the direction toward which the pollution plume will move.
4. Identify the houses and bodies of water that are threatened by this pollution plume.
5. Conclude Prepare a written statement to present to the local community. Explain the path the plume is predicted to take, and how this was determined.
Was this article helpful?