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                        spill response

 

Liquid and solid chemicals, when disposed of by burial or direct release onto the ground surface, can migrate down into the soil structure and come in contact with groundwater. Final disposition of these chemicals depends on their volatility and water solubility. Aqueous phase chemicals, chemicals that are soluble in water, dissolve in and move with groundwater. Non aqueous phase chemicals (NAPLs) do not dissolve in water and may be either lighter than water (light non aqueous phase liquids or LNAPLs) or heavier than water (dense non aqueous phase liquids or DNAPLs). The distinction between DNAPLs and LNAPLs has a significant impact on the detection and remediation of organic contamination.

LNAPLs such as petroleum products (e.g., gasoline, diesel, oils) are common contaminants in urban, industrial, and agricultural areas. DNAPLs such as chlorinated solvents—trichloroethylene (TCE) and perchloroethylene (PCE)—are found also in urban and industrial areas, most commonly in association with the dry cleaning industry, where previous management practices often resulted in the spilling or dumping of these chemicals. These NAPLs pool above (LNAPL) or below (DNAPL) groundwater bodies, dissolving slowly into, and potentially contaminating, enormous volumes of water. In states that rely heavily on ground water for drinking water, billions of dollars have been spent in the last two decades to replace leaking underground gasoline storage tanks (LUSTs) and to clean up historical contamination.

When contamination is detected in groundwater, one common cleanup approach is to drill wells, then pump out and purify the contaminated water using a variety of methods, including air stripping , where compounds are volatized from the water into the air. This technique does not rid the environment of the pollutants, however, as the contaminants are merely transferred from the water to the air. Less volatile compounds, or those at low concentrations, may be removed by filtration through a solid sorbent , such as activated carbon. This “pump and treat” approach addresses only the dissolved, aqueous phase of contamination, while leaving the concentrated, nonaqueous “pool” as a continuing source of groundwater contamination. As a result, “pump and treat” may be a prolonged process. The detection and elimination of NAPL source zones of contamination are more desirable where feasible.

In order to remove sources of groundwater contamination, technologies are needed to accurately detect and measure the amounts of these chemicals. Well drilling is commonly used to investigate or remediate contaminated sites, though it is relatively slow and expensive, and it brings up contaminated soil that must be disposed of properly. Direct push technologies use large vehicles equipped with hydraulic rams or percussion equipment to push metal tubes into the ground.

 

 

Page, G.W. (1997). Contaminated Sites and Environmental Cleanup: International Approaches to Prevention, Remediation, and Reuse. San Diego, CA: Academic Press.

Tedder, D.W., and Pohland, F.G. (2000). Emerging Technologies in Hazardous Waste Management. New York: Kluwer Academic/Plenum.

Testa, S.M., and Winegardner, D.L. (2000). Restoration of Contaminated Aquifers: Petroleum Hydrocarbons and Organic Compounds, 2nd edition. Boca Raton, FL: Lewis.

U.S. Department of Energy. (1999). Groundwater and Soil Cleanup: Improving Management of Persistent Contaminants. Washington, DC: National Academy Press.