Geology

Lab – Hydrologic Cycle and Groundwater

Pre-Lab Questions

1. Groundwater can be found in the unsaturated zone, immediately below the land surface, in open spaces, or pores. It also can found in the saturated zone where every opening is filled with water. What is the top of the saturated zone in an aquifer called?

2. How can a water table become raised or lowered?

3. What happens if a hole is dug in the gravel below the water table?

Experiment 1: Porosity

Table 1: Rock Porosity Data
Rock Sample Bubbling (in minutes) Dry mass (g) Mass after soaking in water (g) Difference in weight (g)
Granite        
Sandstone        

Post-Lab Questions

1. Which rock produced the most bubbles?

2. Which has more porosity: tightly packed particles or loosely packed particles?

3. Which material is most porous? The least?

4. Why do you think rocks with rounded grains absorb water more than rocks with interlocking grains?

5. Would dolomite make a good aquifer?

Experiment 2: Permeability

Table 2: Rock Porosity Data
Material Distance traveled (cm) Time Elapsed (s) Permeability (cm/s)
Gravel      
Sand    
Soil    
Mix of Sand/ Gravel    

Post-Lab Questions

1. Which material is most permeable? The least? _________________________.

2. What rock type would be good for aquifers?

3. Are parking lots permeable? Porous? How can you tell by sight?

4. Henry Philibert Gaspard Darcy, born in 1803, was assigned to find a water supply for a town in France. Drilling a well didn’t produce enough water, so he used a series of gravity-drive pipes from surface water for water supply. His ongoing research on the rate of flow of groundwater produced this formula:

V = K(G)

V = groundwater velocity

K = hydraulic conductivity; describes how easily groundwater flows through a certain rock or soil

G = hydraulic gradient, the slope of the water table

5. What would Darcy’s Law predict would happen to the rate of flow of groundwater as the hydraulic gradient, (i.e. the slope of the water table) increased?

6. Which variable, or variables, does pumping out water from an aquifer affect?

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