Underground Storage Tanks: Assessing the Levels of Contamination

Environmental Training Resource
January 4, 2013 — 920 views  
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An underground storage tank (UST) is a system in which an underground pipe is connected to a tank that has at least 10 percent of its combined volume under the ground. These tanks are used to store petroleum products and hazardous chemicals. If the contents of an underground storage tank get released, they can act as a threat to the environment and human health. These tanks are found to be a major source of groundwater and soil contamination.

Causes of Leakage

The leakage of an underground tank can result from overfilling of the tanks or unsuitable geotechnical conditions. Not maintaining and inspecting the tank on a regular basis can lead to its leakage. Human errors such as negligent delivery of the fuel into the wrong piping system like an abandoned groundwater well piping or a disconnected line can lead to fuel spill. Improper installation of the tank can also cause leakage.

Ground Water Contamination by USTs

Fuels or stored wastes that seep from USTs are capable of contaminating the ground water. Gasoline, a fuel which is stored in USTs, contains many hazardous chemicals and certain additives which are added to boost octane and reduce carbon monoxide emissions. Benzene, ethyl benzene, toluene, and xylene are some of the chemicals present in gasoline. These chemicals are water-soluble and can cause potential health problems, if they are leaked into drinking water. These water-soluble chemicals can cause severe damage to the nervous system, kidneys, and the liver. Also, long-term exposure of drinking water to benzene increases the risk of cancer.

Groundwater Assessment

Groundwater assessment is very important to understand the effects of storage tanks contamination on the environment. Site hydrology, potential for preferential flow, mobility, products stored at the site and their breakdown products, and plunging groundwater plumes are some of the factors to be considered before performing the assessment. As a part of the assessment, groundwater monitoring wells can be constructed.

Soil Assessment

The leakage of USTs can also lead to the presence of non-detectable or low amount of contaminants in the soil. Soil samples from storage tanks contamination sites are collected and then sent for further assessment. The number of soil samples to be collected depends on factors like the average concentration of an analyte and the level of contamination. The size of the contaminated area should also be considered while performing the assessment.

The place of intersection of the backfill with the natural soil is one of main locations to be assessed in the UST site. However, there are many factors which hinder the process of soil assessment. These include soil permeability and porosity, heterogeneity, presence of fill, state of the leaking material, extent of weathering, and presence of lenses of different types of soil.

Clean-up Programs

The underground clean-up of UST contamination sites can be a very costly affair and the clean-up budget will depend on the level of contamination. The first step of any clean-up program will be to stop the release of the fuel and to make sure that the leakage doesn’t happen again. There may be many programs which are suitable for cleaning up the contamination site. A site characterization of the contaminated area will be performed by professionals, so that the best underground clean-up method can be used.

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