1 ES202 Lab 7 - Groundwater Processes, Resources, and Risks Part 1. Station 1 Static Groundwater Model At Station 1, examine the physical model of a simple groundwater aquifer system. The basic components of the model include three wells (Well A, B, and C), and a sequence of unconsolidated, layered sediments (Units 1, 2, and 3). Answer the following questions. 1. Make some basic stratigraphic observations regarding the physical sedimentology of Units 1, 2, and 3. Refer to your sedimentology notes as needed. Fill in the table below. Unit No. Bed Thickness (cm) Grain Size (mm) Sediment Name Sorting 1 _____________ ____________ ______________ ______ 2 _____________ ____________ ______________ ______ 3 _____________ ____________ ______________ ______ 2. On the graph provided on the next page, draw a cross-section to scale, showing the basic configuration of the layered sediments. Use a fractional scale of 1:2 (1 unit on the cross-section = 2 units on the groundwater model). Use a ruler to measure the thickness of the sediment beds to the nearest millimeter. Include in your cross-section a diagrammatic illustration of grain size for each unit, label all parts of your cross-section appropriately. 3. Pour a small volume of water (about 5 ml) onto the surface of Unit 3. Describe your observations of Unit 3 in terms of texture, porosity, and permeability. Is Unit 3 presently saturated with respect to groundwater? Explain your observations and answer. How about Units 1 and 2? Explain as above; draw diagrams as necessary.2 Cross-sectional profile of groundwater model. Scale the model 1:2 (1 unit on model = 2 units on graph)3 4. Based on grain size and sorting characteristics, identify the relative porosity and permeability of the three stratigraphic units comprising the model. Use descriptive terms such as highly porous/permeable, moderately porous/permeable, low porosity/permeability. Fill in the table below. Unit Porosity Permeability 1 ____________ ____________ 2 ____________ ____________ 3 ____________ ____________ 5. Based on your observations from the physical model, which of the following tend to make good aquifers and aquitards. Your choices for answers include "good" or "poor". Aquifer? Aquitard? Poorly Sorted Clayey Sand ____________ ____________ Clay ____________ ____________ Well-Sorted Gravel ____________ ____________ Well-Sorted Sand ____________ ____________ Shale ____________ ____________ Fractured Limestone ____________ ____________ 6. Perform the following measurements on the groundwater model, fill in the data table. A) Measure the stick-up (above ground surface) of the well casings (the distance from the ground surface to the top of the well). Measure in centimeters to the nearest decimal place. B) Use the "dip stick" to measure the depth to the top of water in each well. C) Determine the depth to water below "ground surface" (total depth to water minus well stick up). Measure in centimeters to the nearest decimal place. D) Measure the total depth to the bottom of the well. Measure in centimeters to the nearest decimal place. E) Calculate the height of the column of water in each well (in centimeters, to the nearest decimal).4 Well Well Casing Depth to Water DTW below Total Well Height of I.D. Stick-up (cm) from top of well (cm) ground surface (cm) Depth (cm) Water Column (cm) A __________ __________ __________ __________ __________ B __________ __________ __________ __________ __________ C __________ __________ __________ __________ __________ 7. Are any of the wells "dry" with no ground water? Which ones? Which stratigraphic unit is associated with the dry well (hint: compare your well depth to the depth of strata in the model). By looking at the model, what would be the minimum depth that you would have to drill to find an abundant supply of ground water (answer in cm below ground surface). Which stratigraphic unit is the best aquifer in this case? 8. By looking at the model, do you see any visible flow of the ground water through the system? (is the ground water flowing "like an underground river"). 9. Let's create an imaginary frame of reference with respect to elevation. Let's assume that the ground surface of the model lies at an elevation datum of +500 cm above relative sea level. From your table of data above, determine the elevation of the top of the ground water surface at each of the wells. Fill in the table below. Well I.D. Depth to water Elevation of Elevation of top Elevation of from ground surface (cm) ground surface of well casing top of water (cm) (cm) (cm) A _______ _______ _______ _______ B _______ _______ _______ _______ C _______ _______ _______ _______5 10. Compare your calculations in question 9 to your observations in question 8, what can you conclude about changes in elevation of the ground water surface and ground water flow velocity? Write a conceptual equation that relates water surface elevation change to ground water flow velocity. Station 2 Activities. Visit Station 2 and examine the display. There are four types of porosity that can be found in rock and sediments. These include (1) intergranular porosity (open pore spaces between grains, primarily the result of deposition), (2) solution porosity (open pore spaces result from chemical dissolution of salt and limestone deposits by ground water), (3) fracture porosity (open pore spaces result from fracturing of rocks by tectonic forces, the fractures form opening through which fluids can migrate), and (4) vesicular porosity (open pore spaces associated with vesicular volcanic rocks). Fractures are typically arranged in geometric patterns (rectangular shapes, etc.), depending on the orientation of tectonic forces at the time of fracture. There are five earth materials samples at Station 2 with examples of different types and degrees of porosity and permeability. Use the water bottle and make observations for each sample with regards to its ability to store and transmit water. Use terms like Low, Medium, High for degree of porosity and permeability. For porosity type, your choices include intergranular, fracture, solution, and vesicular. Fill in the data table below. Sample I.D. Degree of Porosity Degree of Permeability Porosity Type A _______________ _______________