Groundwater quality describes the condition of groundwater relative to substances that are dissolved or suspended in the water. Suspended material is not transported far in most subsurface materials, but it is usually filtered (blocked by pore-size or by adhesion to aquifer material) as the water circulates through small openings in the soil or bedrock. In general, groundwater flow is very slow and depends on the permeability (water transmitting properties) of the subsurface materials, as wells as the hydraulic gradient (slope of the water-table or pressure gradient for artesian conditions). The rate of groundwater flow is usually measured in feet (or meters) per day or feet (or meters) per year. In some situations where flow is very slow it is measured in inches (or centimeters) per year. Groundwater usually contains higher concentrations of natural dissolved materials than surface water. The materials dissolved in the water usually reflect the composition and solubility of the earth materials (soil or rock) that the groundwater is in contact with and time that it has been in the subsurface. A number of the activities of man pose threats to water quality. Some of these activities include:
The illustration above presents an example of how a source of groundwater contamination can pollute millions of gallons of groundwater in an underlying aquifer. The "industrial area" is presented as a typical source of contamination. In the illustration, the groundwater contaminants are volatile organic chemicals (e.g. trichloroethene or TCE) that are used as solvents or degreasers in various industrial processes. The degree of contamination is indicated by the concentration of total volatile organics by contours. Degree of contamination is also illustrated by varying colors in the aquifer. Those closest to the industrial area have the highest concentrations, while those at a distance or upgradient have lower concentrations. The downgradient water supply well is being impacted by the contamination from the industrial area and may have to be shut down until the aquifer is remediated (cleaned up).
The groundwater properties of
temperature and conductivity can be used to rapidly delineate bodies
of varying water quality. The quality of water in
wells and boreholes
that penetrate the groundwater may be characterized by a new
instrument by Heron Instruments called the
Plus. It is a combination conductivity (or specific
conductance), temperature, and water level meter.
It comes in lengths from 100 feet (or 30 m) to 1,000 feet (or 300 m)