Treat the Source of Contamination

A source of contamination can be discovered in many ways. A leaking underground storage tank (LUST) at a chemical plant can be discovered after several days, or even years, of record-keeping showing that the tank has less fuel than expected. In other cases, a source of contamination is only discovered after people or the environment have suffered from its effects. The scenarios below are the same as the ones from the previous section, where now the source of contamination is known. We offer reasoning for handling the source of contamination.

A drinking water well has become contaminated with no warning. Engineers review the fueling records from a nearby gas station and discover that one UST has a slow leak that went undetected for several years.

Excavating around the leaking UST reveals a crack in the UST and fuel in the surrounding soil. The UST should be removed, and contaminated soil excavated. A new tank with secondary containment and a leak detection system (see Figure 2.2) should be installed, with clean soil as backfill. Groundwater in the vicinity of the tank is highly contaminated and can be treated with a combination of in situ bioremediation and pump-and-treat.

Following a detailed remedial investigation (RI), a drinking water well is expected to become contaminated in 5 years. Groundwater contamination is discovered to be coming from landfill leachate

The leachate collection system of the landfill should be repaired. As for the soil and groundwater contamination near the landfill source, soil vapor extraction (SVE) combined with air sparging (AS) will treat volatile organic compounds (VOCs). Other types of chemicals can be treated from the groundwater using pump-and-treat, with extraction wells in the “hot spots” providing hydraulic containment to prevent the plume from moving farther. Because contamination of the downgradient well is not imminent, slower but less-expensive technologies can be used, such as in situ bioremediation or monitored natural attenuation.

A tanker truck rolls over on a highway and spills a chemical on soil adjacent to a sensitive lake.

Before the chemical reaches the lake, it’s important to excavate the contaminated soil as quickly as possible and dispose of it appropriately. This scenario was also shown in the previous section, and the same technique treats the source and prevents contamination of a sensitive receptor at the same time.

Students and teachers in an elementary school notice a chemical odor and experience headaches. An RI discovers that the source is a crack in the liner of a waste pond from a hydraulic fracturing (fracking) operation in the adjacent property.

Initially, the fracking operation should stop so that the pond can be emptied and repaired. The resulting soil and groundwater contamination can be aggressively treated with a combination of excavation, in situ chemical oxidation of excavated soils, and groundwater pump-and-treat.

 
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