1. Groundwater Pollution
Groundwater and
Groundwater Pollution
Lecture by Dr. Ken Galli, Boston College
EESC Environmental Issues and Resources
July 26, 2016
Please do not distribute beyond the EESC Class.

2. 1 m = 100 cm = 1000 mm. ----- Meeting Notes (7/10/12 07:33) -----
76cm = 30inches per year
1 m = 100 cm = 1000 mm.

3. AVERAGE PRECIPITATION OF THE UNITED STATES
accessed 3/18/16.

4. U.S. average annual precipitation
Note: 20 inches = 51cm
100th meridian
>20 in/yr
<20 in/yr
(inches)
(Understanding Earth, 2004)

5. Semi-arid to Humid Arid 20in =51cm
Two Major Soil Types in the United States as result of Average Precipitation
Pedocals—soils formed in semi-arid to arid areas. Rich in Calcium.
Made of thin A horizon with underlying calicite-rich B horizon called Caliche
Pedalfers—soils formed in humid areas. Rich in Aluminum and Iron Oxides.
Made of organic-rich (humus) A horizon (zone of leaching), B-horizon rich in Al and
Fe-oxides (zone of accumulation), and C-horizon—Regolith/slightly decomposed
bedrock or parent material.
Semi-arid to
Arid
Humid
20in =51cm

6. Chemical weathering makes soil
(Understanding Earth, 2004)

7. Mechanical Weathering increases Surface Area available for Chemical Attack!

8. U.S. average annual runoff: lots of water evaporates and infiltrates
(inches)
(Understanding Earth, 2004)

9. Global Water Cycle Cyclic nature Global distribution
Global movement of water between different water storage compartments
Global distribution
Abundance not a problem
Distribution in space and over time a problem
Supply vs. Use a problem

10. Global Water Cycle Water’s vertical movement
Upflow: Evaporation, transpiration
Downflow: Precipitation and infiltration
Water’s horizontal movement
Surface runoff
Shallow subsurface through flow
Groundwater flow

11. t = Global Water Supply Residence Time (t) V q
is the average amount of time that a particle spends in a particular system. V
{The capacity of a system to hold a substance}
t = q
{The rate of flow of the substance through the system}

12. Idealized diagram showing the hydrologic cycle’s important processes and transfer of water.
(Modified after Council on Environmental Quality and Department of State The Global 2000 Report to the President. Vol.2)

13. 505,000
Units are thousands of cubic kilometers (km3) per year. (Data from Gleick, P. H An introduction to global fresh water issues.
In Water in Crisis, ed. P. H. Gleick, pp. 3–12. New York: Oxford University Press)

14. Map shows Two Drainage Basins Drainage density is controlled
By underlying
Bedrock.

16. Porosity and permeability
(Understanding Earth, 2004)

17. Joints- fractures without movement Faults- fractures with movement
Hawk Mountain, Pennsylvania (2004)

18. Water table
(Understanding Earth, 2004)

24. Discharge of groundwater from Fern Spring at the
southern end of Yosemite Valley, California.
This spring emerges at the base of a hill slope, as do
many springs. The small stream emerging from the
spring pool in a short cascade or falls is about 2 m
(6.6 ft) wide. (Edward A. Keller)

25. Perched aquifer
(Understanding Earth, 2004)

26. Water rises in homes because of pressure created by the water level in the tower.
If there is only a small amount of friction in the pipes, there will be little drop in pressure.
(b) The pressure surface, or water table, in natural systems declines away from the source
because of friction in the flow system, but water may still rise above the surface of the ground
if impervious particles such as clay create a confining layer and cap the groundwater.

27. Cone of depression in the water table,
resulting from pumping water from a well.

28. Groundwater Movement (1)
Hydraulic gradient: The gradient of water table, generally following the topographic gradient
Hydraulic conductivity: Ability of rock materials to allow water to move through (m3/day/m2)
Porosity: Percentage of void (empty) space in sediment or rock to store water
Permeability: Measuring the interconnection of pores in a rock material

29. Groundwater Movement (2)

31. Hydraulic Gradient is the inclination of the water table surface.

35. 439
-15 feet
= 424 feet

37. This amount is temporarily (seasonally) stored,
but it will be given up to plants and streamflow and lakes.

41. Groundwater Use and Supply (1)
Available GW estimated above the total flow of the Mississippi during the last 200 years
GW as primary drinking water source for ~50% of the U.S. population
GW overdraft problems (extraction rate exceeding recharging rate) in many parts of the country, particularly some states in the Great Plains region
Estimated 5% of GW depleted, but water level declined more than 15 m (50 ft) in some areas

43. Ogallala Aquifier
Groundwater overdraft for the contiguous United States.
(b) A detail of water level changes in the Ogallala aquifer, Texas-Oklahoma-High Plains area. (U.S. Geological Survey)

44. Interactions b/w SW and GW
Overdraft of GW: Leads to lower water levels of streams, lakes, reservoirs, etc.
Overuse of SW: Yields lower discharge rates of GW
Effluent stream (in GW discharge zone): Tends to be perennial
Influent stream (in GW recharge zone above the water table): Often intermittent or ephemeral
Special linkage area: Sinkholes and cavern systems in the karst terrains

51. Interceptor wells create
Cone of depression which
Can change direction of
Flow of contaminated
Groundwater.

60. Sinkhole

61. The Colorado River basin, showing major reservoirs and the division of the watershed for management purposes.
The delta, once a large wetland area, at the head of the Gulf of Mexico has been severely degraded as a result of
diversion of water for various uses.