M. Selvans, GEOL 9, after A. Priewisch Groundwater Lab The objectives of this lab are: · identify the water table and evaluate groundwater flow · analyze groundwater contamination · determine the...

California's Groundwater Information Center Interactive Map (also linked within the lab):https://gis.water.ca.gov/app/gicima/(Links to an external site.)


M. Selvans, GEOL 9, after A. Priewisch Groundwater Lab The objectives of this lab are: · identify the water table and evaluate groundwater flow · analyze groundwater contamination · determine the safest approach to provide drinking water to a town Please record your ANSWERS in a color other than black. PART A - Understanding Water Table Location and Groundwater Flow Groundwater flows in complicated looping, three-dimensional paths through an aquifer. In map view, however, we can determine the general, overall direction of flow by examining the water table contours which are lines of equal elevation of the water table surface. Let’s start with an analogy of surface elevation contours: Water flowing at the surface always flows directly downslope because of the force of gravity. Similarly, groundwater flows from high elevations on the water table surface toward low elevations. Example The map above shows contour lines (contours) of water table elevations and the direction of groundwater flow, indicated by flow arrows. Note that the flow arrows cross a contour line at a right angle. The inset diagram shows an example of how to calculate the depth to the surface of the water table which is important when it comes to drilling a well. 1. You have just purchased the land at location “X”. You plan to build a home here and you’ll need to drill a well for drinking-water. From a topographic map you know that the land-surface elevation of your property is 825 m above sea level. a. Draw the water table contour line below your land at “X”. What is the elevation of the water table represented by this contour line? b. How deep (in meters) will you need to drill your well in order to intersect the saturated zone? This is the depth to water in the example provided in the diagram. Show your work. c. Discuss briefly whether a drilling a well as deep as you calculated in (b) is deep enough to ensure your long-term drinking water supply. Explain your reasoning. d. What is the compass direction of groundwater flow at location “X”, your new home? (North is up on the map.) Draw some arrows on the water-table-elevation contours near this location in order to be confident in your answer (use the ‘Draw’ feature in Word/Office 365). PART B - Groundwater Flow and Groundwater Contamination This portion of the lab will allow you to apply your understanding of groundwater flow to the analysis of a hypothetical groundwater contamination problem, near the town of Los Hypotéticos shown below. This map shows contour lines of the water table in the area. 2. To accurately show the flow directions of the groundwater, draw flow arrows on each contour line, at approximately half-inch intervals and at right angles (in other words, perpendicular to the water table contours). 3. Toxic seepage has been discovered at the Industrial Site. This contamination has probably infiltrated the unsaturated zone and has entered the groundwater. Highlight or circle the well/s that is/are at risk of being affected by this pollution. Well 1Well 2Well 3 4. A cattle feed lot is located on the east side of the Rio Imaginación. If groundwater below the feed lot is polluted by manure from the cattle feed lot, will this pollution reach the Rio Imaginación? Explain why or why not. 5. You need to select a safe drinking-water source for the city of Los Hypotéticos. Explain which of the following sources is the best choice: Well 1, Well 2, Well 3, or the Rio Imaginación within Los Hypotéticos. PART C - Groundwater Depth in the Fresno area Visit the Groundwater Information Center Interactive Map for California. Zoom in on the Fresno area. Groundwater level data can be viewed in 3 different ways; you will look at it as depth below the surface. Depth information is represented in feet below the ground surface. Increasing values indicate increasing depth to groundwater (or deeper/lower water levels).  6. First, select the ‘Points’ option in the ‘Show layers’ menu on the left. Find the data point closest to Clovis Community College. What is the depth, in feet, of the water table below our campus? 7. Next, add the ‘ColorRamp’ option to the display. a. What color are the areas with the shallowest water table depths? b. Is the water table in the vicinity of Madera (NW of Fresno) deeper or shallower in general than it is in Fresno? c. What is the smallest depth to the water table that you can find in the greater Fresno area (hint: look for the color that indicates a shallow water depth, and then look at data points to find the smallest value)? PART C – Video “How Does Fracking Work?” (https://www.youtube.com/watch?v=Tudal_4x4F0) 1. Briefly explain why fracking can pose a threat to groundwater. 2. What in the video surprised you most? 3. What further questions do you have about fracking? 4