Physics of Groundwater Movement

Other point sources of groundwater pollution include both deep injection wells and shallower dry wells used to inject chemical wastes (including radioactive waste) directly into the subsurface environment. While it is customary to make waste injections into deep aquifers that are salty or otherwise unusable for potable water, it is not unusual for injection wells to leak, or to force the flow of water from one layer of aquifer into another, resulting in contamination of an otherwise usable source of groundwater. 

Agriculture is an important nonpoint source of groundwater pollution in rural areas. Widespread application of agricultural chemicals such as fertilizers and pesticides often leads to groundwater degradation due to the downward percolation of chemicals to the water table. 

In all cases, an understanding of the physics of groundwater movement is necessary to adequately estimate the direction and rate at which contaminated water is moving in an aquifer. An analogy can be made with tracking a contaminant in a river, as discussed in Chapter 2, except that the underground water flow is out of sight and much more expensive to sample. 

The rate at which groundwater moves through an aquifer is not usually directly measurable, and thus it must be estimated from known relationships among measurable parameters. The discussion of groundwater flow presented here is only an introduction to the topic many of the relationships described are approximations, and most are restricted in their applicability to situations in which the flow of groundwater is steady over time. When a more detailed analysis is necessary, the reader is referred to the following texts on ground-water Bear (1972, 1979), Freeze and Cherry (1979), Heath (1984), Strack (1989), McWhorter and Sunada (1977), and Davis and de Wiest (1966). 

---

The physics of groundwater movement and the dispersion of substances is described in an easily understandable way by Hemond and Fechner (1994). 

---