Salt Water Intrusion

Topic(s):

Hydrosphere, Oceans

Scenario:

"Seven tablespoons of salt will make the water in a 55-gallon bathtub too salty to be safe for drinking."

Can you imagine filling your glass with water from your faucet and taking a drink of salt water? Most of us take the ready availability of freshwater in our homes for granted. Yet, in many of the world's coastal areas, the sustainability of freshwater is threatened by saltwater intrusion, which is the movement of saline water into fresh water aquifers.

Since the 1940's saltwater intrusion has forced the abandonment of more than 100 wells on the Cape May Peninsula, a popular vacation destination in New Jersey. Nearly all of the demand for water on the Peninsula is met by pumping ground water. Once used, most of this water is treated at wastewater treatment plants and then discharged to the ocean. This process results in the removal of millions of gallons of fresh ground water from the aquifers every day. Saline ground water migrates inland as the level of fresh ground water in the aquifers decreases. Continually increasing demand for water in the City of Cape May resulted in more and more wells becoming contaminated with salt water. Consequently, the City of Cape May was forced to find an alternative means of meeting the demand for water and in 1997 constructed a $5 million desalinization plant to remove salt from brackish water pumped from its wells. The desalinization plant has allowed the city to continue using some of its brackish wells and reduce withdrawals at remaining freshwater wells, thereby slowing the inland migration of the saltwater front (Galloway et al., 2003).

While overpumping of ground water is the primary cause of salt water intrusion, other factors can contribute to the problem. In developed areas much of the rainfall flows over impermeable surfaces, such as concrete and pavement, into storm drains, canals, and lakes depriving aquifers of their primary source of fresh water recharge. Rising sea level, whether natural or associated with anthropogenic climate change, and storm surges can also disrupt the equilibrium between fresh and saline ground water in coastal areas.

The problem of salt water intrusion is by no means limited to the northeastern United States. Other cities in the United States that are dealing with salt water intrusion include Savannah, Georgia, Miami and Tampa Bay, Florida, and Los Angeles, California. In the Laizhou Gulf in China saltwater intrusion led to the abandonment of more than 1500 wells between 1990 and 1997, and soil salinization resulting from saltwater intrusion has caused a significant decrease in crop productivity (Shanzhong et al., 2007). In Manila, Philippines rapid growth and urbanization have put intense pressure on fresh water resources. Due to overpumping, ground water levels are decreasing by 6 to 12 m/yr putting the region's aquifers at risk for saltwater intrusion (IDRC)). In Perth, Australia, the government is restricting water use from backyard "garden" wells in an effort to control salt water intrusion (Banks, 2007).

Roughly half of the world's population lives within 200 km of a coastline. In 2003 the average population density in coastal areas, 80 people per square kilometer, was nearly twice the global average population density. Demand for fresh water in densely populated coastal communities is immense. Continued population growth, urban development and climate change are putting increased pressure on coastal water resources. As governments worldwide struggle to supply their citizens with freshwater, they will be forced to contend with saltwater intrusion along their coastlines.

References
Banks, A. 2007. Salt intrusion may force new limit on bores. The West Australian (Perth). July 25, 2007, p. 15.

Galloway, D.L.; W.M. Alley, P.M. Barlow, T.E. Reilly, P. Tucci. 2003. Evolving issues and practices in managing ground-water resources: Case studies on the role of science. U.S. Geological Survey Circular 1247. Reston, Va.

Shanzhong, Q., Z. Zulu, Z. Zhaopei, G.Qiaoyu, Z. Yan. 2007. Saltwater intrusion in the Laizhou Gulf, Shandong Province, China: Causes and its impact on coastal areas. Ambio: A Journal of the Human Environment 36(4):361-362.

Task:

Due to your group's interest and expertise, you have been approached by a coastal state regarding the potential vulnerabilities to it's groundwater resources. Your group should use an Earth system science approach to investigate the possible impacts of saltwater intrusion and make recommendations that the state can disseminate to municipal leaders so they can protect their local drinking water supplies.

Date: 5/13/2008

Scenario Images:

Salt water intrusion caused by overpumping of ground water. Larger image. More info. Image: courtesy USGS

Salt water intrusion into freshwater aquifers is a problem facing coastal communities throughout the United States. Larger image.. Image: courtesy The Center of Advanced Materials for the Purification of Water with Systems

Salt water intrusion and overexploitation of ground water in Europe. Go here for an interactive version (click the image). Image: courtesy European Environmental Agency.

Irrigation well near Tampa, Florida where large withdrawals of ground water have caused the water table to decline leading to salt water intrusion. Full USGS Report. Image: courtesy USGS

Resources:

Earth's Hydrologic Cycle (Cycle A)
This website shows a conceptual view of the Earth's hydrologic cycle. Here you can also learn the definitions of important hydrologic cycle terms.

Ground Water Occurance and Quality (Cycle A)
At this Encyclopedia of Earth site you can read about how ground water occurs, what aquifers are and how saltwater intrusion affects water quality.

Ground Water Principles (Cycle A)
This website provides a basic explanation of ground water principles and aquifers. This website applies these basic principles to Kingman County, Kansas, but the principles apply universally.

Relation of salt water to fresh water in aquifers (Cycle A)
This National Ground Water Association website describes the relationship between fresh water and saline water in coastal aquifers.

Seawater Intrusion is the First Cause of Contamination of Coastal Aquifers (Cycle A)
This Science Daily news article discusses saltwater intrusion as a consequence of freshwater aquifer overexploitation in the Mediterranean basin.

The Groundwater Foundation (Cycle A)
This Groundwater Foundation website provides links to a variety of reference materials, community programs and educational information/activities.

Global Climate Change Impacts on Saltwater Intrusion (Cycle B)
In this Encyclopedia of Earth you can read about how global climate change impacts saltwater intrusion of aquifers.

Ground Water in Freshwater-Saltwater Environments of the Atlantic Coast (Cycle B)
The United States Geological Society (USGS) is one of the world's foremost authorities in all aspects of Earth systems. This USGS publication provides detailed information about Ground Water in Freshwater-Saltwater Environments of the Atlantic Coast.

Saltware Intrusion in Europe (Cycle B)
This website provides a map of European areas affected by saltwater intrusion and discusses groundwater over-exploitation throughout Europe.

Saltwater Intrusion in Los Angeles (Cycle B)
This USGS site discusses the problems Los Angeles, California faces with saltwater intrusion.

Saltwater Intrusion in Puget Sound (Cycle B)
This report discusses the struggle Island County, located in the waters of the Puget Sound, has with saltwater intrusion of its drinking water supplies. This report provides an overview of the current science and policies for the county and provides recommendations for potential resource protection plans.

Ground Water Adventures (Cycle C)
Teachers will find a large variety of K-12 education resources about groundwater at this website.

Kid's Corner at The Groundwater Foundation (Cycle C)
Teachers and students alike will find the "Kid's Corner" at The Groundwater Foundation website both exciting and interesting. The website contains a variety of student activities and lesson plans.

USGS Water Resources for Students (Cycle C)
This USGS website provides student friendly access to a multitude of water related topics.

Water Kids (Cycle C)
The "Water-Kids" website provided by the Water Education Foundation provides elementary level descriptions of important groundwater concepts.

Water Related Lesson Plans (Cycle C)
The Saint John's River Water Management District provides student and teacher resources. Water Ways is a complete online curriculum.

Sample Investigations:

Water Ways: More About Water Below the Ground (Cycle A)
In this lesson students will define ground water; identify ground water's relationship to springs, artesian wells, ordinary wells and sinkholes; define saltwater intrusion and explain its causes.
Difficulty: intermediate

Aquifer Model in a Tank (Cycle B)
In these hands on labs, students create an aquifer model in a fish tank and then use it to understand how human activities can make an impact on surface and ground water.
Difficulty: intermediate

The Underground Flow (Cycle C)
In this lesson, students will investigate the basic concepts of groundwater and saltwater intrusion, including using Darcy's Law to calculate rates of groundwater flow to understand how long a well can be used to provide fresh water.
Difficulty: intermediate

Standards:

• Science
  National Science Education Standards - Science Content Standards http://www.nap.edu/readingroom/books/nses/html/overview.html#content The science content standards outline what students should know, understand, and be able to do in the natural sciences over the course of K-12 education.
  • K-12 UNIFYING CONCEPTS AND PROCESSES
    The understandings and abilities associated with the following concepts and processes need to be developed throughout a student's educational experiences:
    • Systems, order, and organization
    • Evidence, models, and explanation
    • Constancy, change, and measurement
    • Form and function
  • GRADES 5-8 CONTENT STANDARDS
    • Science as Inquiry (Std A)
      • Abilities necessary to do scientific inquiry
      • Understanding about scientific inquiry
    • Earth and Space Science (Std D)
      • Structure of the earth system
    • Science in Personal and Social Perspectives (Std F)
      • Populations, resources, and environments
      • Natural hazards
      • Risks and benefits
  • GRADES 9-12 CONTENT STANDARDS
    • Science as Inquiry (Std A)
      • Abilities necessary to do scientific inquiry
      • Understanding about scientific inquiry
    • Science in Personal and Social Perspectives (Std F)
      • Natural resources
      • Environmental quality
      • Natural and human-induced hazards
      • Science and technology in local, national, and global challenges
• Geography
  Geography for Life: National Geography Standards, 1994
  • PHYSICAL SYSTEMS
    Physical processes shape Earth’s surface and interact with plant and animal life to create, sustain, and modify ecosystems. The geographically informed person knows and understands:
    • The physical processes that shape the patterns of Earth’s surface
  • ENVIRONMENT AND SOCIETY
    The physical environment is modified by human activities, largely as a consequence of the ways in which human societies value and use Earth’s natural resources, and human activities are also influenced by Earth’s physical features and processes. The geographically informed person knows and understands:
    • How human actions modify the physical environment
    • How physical systems affect human systems