1. Soils, Hydrogeology, and Aquifer Properties
Philip B. Bedient
2006
Rice University

2. Basin Hydrologic Cycle
Charbeneau, 2000.

3. Global Water Supply Distribution
3% of earth’s water is fresh - 97% oceans
1% of fresh water in lakes, streams, rivers
29% of the world’s fresh water exists in aquifers and 70% in glaciers

4. 1. Hydrogeology: What is it?
Hydrogeology examines the relationships of geologic materials and flowing water
Volume, water fluxes, and water quality are important

5. Basin Hydrologic Cycle – GW/SW Interaction

6. U.S. Hydrogeologic Units

7. Artesian Zone of Edwards Aquifer
The artesian zone is a complex system of interconnected voids that can discharge water to the surface - stream
Located between two relatively less permeable layers that confine and pressurize the system
Underlies 2100 square miles of land

8. 2. Soil Horizons

9. porosity
Charbeneau, 2000.

10. Figure 15.1

11. 3. Porosity and Density

12. Types of Porous Media n = VV / VT = Vol Voids / Total Vol
Freeze and Cherry, 1979.

13. Porosity - not good indicator of flow
Bedient et al., 1999.,

14. 4. Hydraulics & Wells

15. Hydraulic Conductivity K
K represents a measure of the ability for flow through porous media:
K is highest for gravels to 1 cm/sec
K is high for sands to 10-3 cm/sec
K is moderate for silts to 10-5 cm/sec
K is lowest for clays to 10-9 cm/sec

16. 4. Hydraulic Conductivity
Darcy’s Set up for Analysis

17. Pressure and Elevation Heads - Laboratory
 = pressure head
z = elevation head
h = total head
Freeze and Cherry, 1979.

18. Pressure and Elevation Heads - Field
 = pressure head
z = elevation head
h = total head
Freeze and Cherry, 1979.

19. Two Confined Aquifers with Different Heads
Groundwater will tend to flow from the top aquifer to the bottom aquifer.
We can’t make any conclusion about horizontal head gradients from this picture.
Charbeneau, 2000.

20. Horizontal and Vertical Head Gradients
Freeze and Cherry, 1979.

22. Occurrence of Ground Water
Ground water occurs when water recharges the subsurface through cracks and pores in soil and rock
Shallow water level is called the water table

23. Example Layered Aquifer System
Bedient et al., 1999.

24. Geology & Pumping Impacts

25. Other Aquifer Features

26. 5. Aquifers Types
Definition: A geological unit which can store and supply significant quantities of water.
Principal aquifers by rock type:
Unconsolidated - Gulf Coast
Sandstone - oil reserves
Sandstone and Carbonate
Carbonate-rock - Edwards
Volcanic - Hawaii

27. The Major Aquifers of Texas
Ogallala
Carrizo-Wilcox
Edwards
Gulf Coast

28. Recharge Artificial Natural Precipitation Recharge wells melting snow
Infiltration by streams and lakes
Artificial
Recharge wells
Water spread over land in pits, furrows, ditches
Small dams in stream channels to detain and deflect water

29. 6. The Edwards Aquifer

30. Formation History

31. Hydrologic Features Pumpage to Date: 33,035.30 mg
    
                 
                                     
                                                                                         
      
                                                                                                                 
   
                                                      
                           
                       
                            
                  
                      
                                  
               
    
                 
                                     
                                                                                         
      
                                                                                                                 
   
                                                      
                           
                       
                            
                  
                      
                                  
               
: OUR WATER : EDWARDS AQUIFER : MAIN
: OUR WATER : EDWARDS AQUIFER : MAIN
Hydrologic Features
Pumpage to Date: 33, mg
Average Daily Pumpage: mg
Historic minimum level (1956): ’
Historic maximum level (1992): ’
Minimum Edwards Level for 2000: ’
Maximum Level for 2002: 690.5’
    
                                                      
                                                                                                
                                                                                                                 
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© 2002 San Antonio Water System • 1001 E. Market St. • P.O. Box 2449 • San Antonio, TX Customer service inquiries: Web site issues: Click here to participate in our visitor survey or join the SAWS mailing list.

32. The Edwards Limestone
When the limestone was exposed, it was extensively eroded creating cavities and conduits making it capable of holding and transmitting water
Then it was covered over with relatively impermeable sediments forming a confining unit

33. Geology of Edwards Aquifer
Primary geologic unit is Edwards Limestone
one of the most permeable and productive aquifers in the U.S.
The aquifer occurs in 3 distinct segments:
-The drainage zone
-The recharge zone
-The artesian zone

34. Artesian Wells A well whose source of water is a confined aquifer
The water level in artesian wells is at some height above the water table due to the pressure of the aquifer
Water Table Well
Artesian Well
Pot. Surface
Flowing Well
Confined Aquifer and
Confining Unit Above
Bedrock Zone

35. Drainage Zone of Edwards Aquifer
Located north and west of the aquifer in the region referred to as the Edwards Plateau or Texas Hill Country
Largest part of the aquifer spanning 4400 sq. miles
Water in this region travels to recharge zone

36. Recharge Zone of Edwards Aquifer
Geologically known as the Balcones fault zone
It consists of an abundance of Edwards Limestone that is exposed at the surface
-provides path for water to reach the artesian zone

37. Artesian Zone of Edwards Aquifer
The artesian zone is a complex system of interconnected voids varying from microscopic pores to open caverns
Located between two relatively less permeable layers that confine and pressurize the system
Underlies 2100 square miles of land

38. The Edwards Group

39. The Edwards Group The Edwards limestone is 300-700 ft. thick
Outcrops at the surface is tilted downward to the south and east and is overlain by younger limestone layers and thousands of feet of sediment
The immense weight of this sediment layer caused faulting in the region

40. Typical Dip Section

41. Regional Dip Section

42. Flowpaths of the Edwards Aquifer

43. The Ogallala Aquifer
Deposition of the Ogallala formation began in the late Miocene to early Pliocene
During the Pliocene eroded sediment from the Rockies was deposited on the existing surface of Triassic and Permian rocks until the whole surface was covered with Ogallala sediments up to 900 ft. thick

44. Characteristics
Consists primarily of heterogeneous sequences of coarse-grained sand and gravel grading upward to fine clay, silt and sand
Saturated thickness ranges from a few feet to more than 525 ft.

45. Aquifer Size
The Ogallala supplies water for eastern New Mexico, much of west Texas, as well as parts of Colorado, Oklahoma, Kansas, Nebraska, Wyoming and South Dakota
Approximately 170,000 wells draw water from the aquifer
Contains 3.3 billion acre feet of water (1 acre foot = 326,000 gallons)

46. Water Level Change before 1980

47. Water Level Change to 1994

48. The Ogallala Problem
Water level declines of 2-3 feet per year in some regions are drawing concern of the aquifer drying up - first one in the U.S.
This is due to pumping more water than is replaced through recharge, and only 10% is restored by rainfall.
Large issues exist over contamination and salt water intrusion problems as well.

49. Sample Hydrograph

50. The Ogallala Future
Drawdown from 1998 to 2050 is predicted to be more than 150 feet in some areas given the forecast amount of pumping.
By 2010, parts of the aquifer in Oklahoma and Kansas are simulated as going dry.
Dutton, A.R., Reedy, R.C., and Mace, R.E. (2001). Saturated Thickness in the Ogallala Aquifer in the Panhandle Water Planning Area: Simulation of 2000 through 2050 Withdrawal Projections.
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