Groundwater Quality

Groundwater quality reflects substances that are dissolved or suspended in the water. Suspended material is not transported far in most subsurface materials, but it is usually filtered out.   In general, groundwater flow is very slow and depends on the permeability (water transmitting ability) 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 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:

• Landfill solid waste disposal
• Liquid waste disposal basins
• Septic waste infiltration systems
• Highway deicing with chemicals (eg. salt)
• Gasoline service stations
• Petroleum bulk storage facilities
• Underground storage tanks
• Many industrial activities
• Livestock feed lots

• Urban stormwater infiltration

The illustration on the above-right 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 (eg. 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).

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