• Groundwater is water in rocks below the earth's surface
• Most cave systems are formed by groundwater
• A major court case in Woburn, Massachusetts, revolved around the rate of flow of solvents through a groundwater system
• Most groundwater used in the U.S. is pumped for irrigation

hat do the world's largest cave, resurgent movie actor John Travolta, and agricultural economics have in common?  In a word, groundwater.

Groundwater, water in rocks or sediment below the earth's surface, is just one element in the hydrologic cycle. The cycle, discussed in the first section of this chapter (Hydrologic Cycle), ties together the processes that cause water to change state (vapor, liquid, solid) as it moves between different elements of the earth system.

A recent movie,A Civil Action, (adapted from the best-selling book by Jonathan Harr) highlighted the real story of a legal battle essentially decided by the geology of a groundwater system.  The law suit was filed on behalf of a group of families from Woburn, Massachusetts. Children of the families were diagnosed with leukemia after their mothers drank water from two polluted wells (wells G and H) during pregnancy. The families' attorney, Jan Schlichtmann (played by John Travolta in the movie), tried to show that the wells were contaminated by industrial solvents (trichloroethylene [TCE] and tetrachloroethylene [PCE]) dumped illegally by nearby companies.

Relative locations of wells H and G and potential sources of pollution at Woburn, MA. Leukemia cases were clustered in the Pine Street neighborhood south of the wells. Properties near the wells included: W.R. Grace, NEP (Plastics), Olympia (trucking), UniFirst (dry cleaning), Wildwood (tannery). Click here for a more detailed map

The case revolved around how quickly specific solvents could travel through the groundwater system to reach the wells. Lawyers representing the plaintiffs and defendants called geologists as expert witnesses to determine how factors such as distance from wells, properties of the chemicals, and variations in local geology could be used to establish a timeline for the contamination. The geological interpretations were complicated by lateral variations in sediment character, the presence of fractures in the bedrock, the linkage between groundwater flow and a nearby river, and the role of wetlands and peat deposits in influencing groundwater flow. We will discuss how the natural properties of rock and sediment influence the distribution and flow of groundwater in the second section of this chapter (Rock Properties).

Abandoned 55-gallon drum and excavation of contaminated soil, Wells G & H site, Woburn, Massachusetts. Image source: New England EPA, Wells G & H Superfund Site

After more than two months of often complex scientific testimony, the jury found that chemicals from one company, W.R.Grace, could have contaminated the wells. Soon thereafter, Grace settled with the families for $8 million. The EPA later declared the area a superfund site and several of the surrounding land owners agreed to pay nearly $70 million to clean up the 330 acre site. 

We will examine how water enters and leaves groundwater systems in the third section of the chapter (Groundwater Systems). In particular we will discuss the characteristics of aquifers, underground water storage reservoirs. Approximately two-thirds of all the fresh  groundwater pumped in the U.S. is used for irrigation of crops. Precipitation drops to less than 50 cm (20 inches) per year over much of the western U.S. The paradox is that this semi-arid region is the source of a large proportion of our grain crops. Kansas, the wheat state, is too dry to produce wheat unless water is added by irrigation. The majority of the irrigation waters for the Great Plains states are taken from a single massive groundwater system, the High Plains aquifer.

Uses of fresh groundwater in U.S., 1990. Nearly two-thirds of the 79 billion gallons of groundwater used per day was used for irrigation. Most of this was used in western states with relatively dry climates. Image source: USGS water science for schools web site.

In the last section on groundwater (Human modifications of groundwater systems) we will examine how human interaction with the environment has resulted in a variety of groundwater problems including, depleted water supplies, pollution, and land subsidence.

In the penultimate section of the chapter we will describe the conditions necessary for the formation of wetlands (Introduction of Wetlands). Wetlands provide geological (e.g. moderate flooding, recharge groundwater) and cultural (e.g. recreation), and economic (e.g. breeding grounds for commercial shellfish populations) benefits. Finally, we will discuss why these ecosystems are in decline with reference to the Florida Everglades, the nation's only subtropical ecosystem (Destruction of Wetlands).

Wetland developed in an ox bow lake formed by an abandoned stream meander.