Eileen Herrstrom

University of Illinois at Urbana-Champaign

Undergraduate class on introductory physical geology or geology and society

Must know how to read topographic maps, draw contour lines, and and use Microsoft Excel (enter formulas, fill down, make charts)

This is a laboratory activity that follows a lecture on groundwater. It falls near the end of the course.

Identify features of karst topography on the Sulphur Springs quadrangle, read depression contours on the map, relate values of hydraulic head from a spreadsheet to positions on a sketch map

Recognize the general orientation of the water table based on lake elevations, draw contour lines on the potentiometric surface, deduce the direction of groundwater flow based on the potentiometric surface

Calculate the velocity of groundwater flow using the results of dye tests, construct a vertical cross section using Microsoft Excel and showing the land surface, water table and hydraulic head, interpret the cross section in terms of flow directions and recharge areas

Groundwater accounts for only 0.75% of all water on Earth, yet it is a precious resource for the biosphere. In the United States, about one-fifth of the population taps into the groundwater reservoir of the hydrologic cycle as their main source of drinking water. However, worldwide, about 40% of all irrigation water comes from groundwater, and up to 80% of groundwater withdrawals are used for agriculture. Groundwater is also at risk and vulnerable to pollution, especially in areas with karst topography such as Tampa FL. Thus, the more people who understand the potential and the problems associated with groundwater, the better are the prospects for this resource.

Student materials for this exercise include a Microsoft Excel spreadsheet with with data for dye tests and elevations, a .zip archive with two versions of the topographic map (PDF and JPG), as well as the instruction sheet. The exercise is divided into three parts.

In Part I, students study the Sulphur Springs topographic quadrangle and identify features of karst topography on the map. This part of the exercise also reviews basic groundwater terminology.

Part II involves transferring hydraulic head information from Microsoft Excel to a simplified sketch map of the quadrange and drawing contour lines on the potentiometric surface. Next, students use the contour lines to add arrows indicating the direction of groundwater flow. Finally, students apply their knowledge to determine which lakes could be affected by a toxic spill within the quadrangle.

In Part III, students study the results of dye tests in the Sulphur Springs quadrangle to analyze the flow of groundwater. They also use elevation data to construct a vertical cross section that illustrates the ground surface, the water table, and the potentiometric surface for the Floridan aquifer, and they relate the cross section to features on the topographic map.

As originally designed for a traditional face-to-face course, this activity is assessed by the quality of the contours and flow arrows on the sketch map, the completeness of the vertical cross section and the answers to the questions. In the online version, only the answers to questions are used to assess student understanding of the exercise, but these questions include choosing the correct map views and alternative presentations of the cross section. It is also possible to have students submit their completed spreadsheets, although this option works best in a small class.

Stewart, J.W., and R.L. Mills, 1984, Hydrogeology of the Sulphur Springs Area, Tampa, Florida: USGS Water Resources Investigations No. 83-4085
https://pubs.usgs.gov/wri/1983/4085/plate-1.pdf

USGS Sulphur Springs FL quadrangle 1:24000 (1995) https://ngmdb.usgs.gov/topoview/viewer/#15/28.0233/-82.4474

The Sulphur Springs Exploration Project http://caveatlas.com/systems/media/sulphur_springs/kur_report_sulphur_springs_1993.pdf

MWH Americas, Inc., 2009, Blue Sink Feasibility Study Augmentation Potential for the Lower Hillsborough River, pp. 11-16
https://www.tampagov.net/sites/default/files/NewsAndNotices/Files/ContractAdmin/11D20TM_BLUE_SINK_Final.pdf

Wallace, R.E., 1993, Dye trace and bacteriological testing of sinkholes: Sulphur Springs, Tampa, Florida: Environmental Geology, v. 22, pp. 362-366.
https://doi.org/10.1007/BF00767510