1. Tom Wilson, Department of Geology and Geography Environmental and Exploration Geophysics I tom.h.wilson tom.wilson@mail.wvu.edu Department of Geology and Geography West Virginia University Morgantown, WV Wrap up resistivity methods

2. Tom Wilson, Department of Geology and Geography Not used as often because of recent computer and hardware developments AGI’s Sting and Swift

3. Tom Wilson, Department of Geology and Geography High or low resistivity zones depending on the concentration of dissolved electrolytes

4. Tom Wilson, Department of Geology and Geography A simple 4-electrode system offers an alternative approach to fracture zone location – the Tri-potential resistivity method Switching current electrode positions in the Wenner array

5. Tom Wilson, Department of Geology and Geography Normal Wenner array configuration CPPC A conductive fracture zone would likely be one that was water filled High conductivity = low resistivity What is the geometrical factor?

6. Tom Wilson, Department of Geology and Geography CPCP The CPPC and CPCP electrode configurations both reveal the presence of a low resistivity zone What is the geometrical factor?

7. Tom Wilson, Department of Geology and Geography CCPP The CCPP electrode arrangement reveals the opposite response What is the geometrical factor?

8. Tom Wilson, Department of Geology and Geography Tripotential resistivity measurements help establish the association of a topographic lineament with a possible fracture zone The work of Dr. Rauch and some of his students

9. Tom Wilson, Department of Geology and Geography Good Devonian shale wells are located near fracture zones Dr. Rauch and students

10. Tom Wilson, Department of Geology and Geography CCPP The fracture zone response Is this a wet or dry fracture zone? Dr. Rauch and students

11. Tom Wilson, Department of Geology and Geography

12. Wet or dry?

13. Tom Wilson, Department of Geology and Geography Once the approach is validated, 3D coverage helps resolve the vertical and horizontal extents of contamination 2 meter a-spacing reveals the upper tip of the conta- minant plume 16 meter a-spacing reveals the base of the contaminant plume

14. Tom Wilson, Department of Geology and Geography Limestone bedrock 7 meter thick gravel Sand with some clay  thicknessdepthInterp 253.53.2 1038.812 402335 75 ft & control

15. Tom Wilson, Department of Geology and Geography What hypothesis could you test in SS2 Run equivalence. Put your model and hypothesis to the test.

16. Interval below the gravel aquifer? Tom Wilson, Department of Geology and Geography What are the range of possible resistivities of this zone? Possible depths? What parameters could you fix? Hold constant?

17. Tom Wilson, Department of Geology and Geography If you already haven’t, please hand in your work from Tuesday.

18. Tom Wilson, Department of Geology and Geography 1.Construct a cross section derived from your modeling of soundings SS1 through SS5. (5 points). Cross sections must accurately portrayed on graph paper. 2.Develop and describe your interpretation of the subsurface. Use the cross section to illustrate your interpretation. Refer to it. Are aquifers present across the area? Explain your results. (6 points) 3.Develop two hypotheses to be tested using the equivalence computations. What do the equivalent models suggest about the viability of your hypothesis – about the limits of your interpretation? For example, does the range of equivalent answers support the presence of a shallow and/or deep fresh-water aquifer? What did you find about the possible presence of bedrock and the range in depth to the bedrock/channel interface? (4 points)

19. Tom Wilson, Department of Geology and Geography 4. Describe your hypotheses and the range of possible answers you obtained. Show equivalent models generated by IX1D and discuss how the results of equivalence analysis could give rise to more than one possible subsurface interpretation. Refer to labeled figures. Remember figures should have captions. (part of 3).

20. Tom Wilson, Department of Geology and Geography 5. After you complete your cross section, compare your interpretation to Frohlich’s (i.e. discuss in your lab report). Make direct comparisons to Frohlich’s result. Have you been able to better define the extent of basal gravel aquifers than Frohlich did in his cross section (see Figure 7 of his paper) Have you been able to more accurately define the boundary between bedrock and overlying, less resistive, intervals? If the resistivity increases at the base of your model did you feel confident that you could tell the difference between gravel and limestone bedrock? (Approximately 7 points)

21. Tom Wilson, Department of Geology and Geography 6. Number and caption your figures for easy reference in your lab discussion. The captions don’t have to be lengthy, but should succinctly inform the reader what they are looking at. 7. Organize your discussions in the requested abstract, introduction, results and conclusions format. (Roughly 8 points out of 30)

22. Tom Wilson, Department of Geology and Geography Your report should be a minimum of 3-4 pages double spaced (12pnt with 1 inch margins and the length does not include figures). AGAIN - Number your figures and make specific reference to them in the text of your report. Be sure to label important features on those figures when they are mentioned in your text. Use of captions is recommended.

23. Tom Wilson, Department of Geology and Geography We will be getting into gravity methods and I’d like for you to start reading Chapter 6 pages 349-373. Hand in the resistivity lab next Friday, October 21 st. Resistivity paper summaries will be due this Friday in my mailbox by noon (October 13 th ). Those in the writing section should carefully read and follow the 1 page guidelines handed out to you Tuesday.