What is Site Excavation?
Excavation is a process that removes soil, rock, and other materials from a particular location. It involves digging the material up for “ex-situ” (above-ground) treatment or disposal in a landfill. Excavation may also involve removing old drums of chemicals or other buried debris that might be contaminated. Removing these potential pollutants prevents people from coming into contact with harmful chemicals and it eliminates a potential source of groundwater contamination.
How Does Excavation Work?
Heavy earthmoving equipment such as excavators, bulldozers, backhoes and excavator trackhoes are used to dig up contaminated soil. Long-arm excavators can reach as deep as 100 feet below ground, but excavations are generally limited to much shallower depths due to safety concerns and difficulty in keeping the hole open. Sometimes soil is excavated below the water table, which requires walling off the contaminated area and pumping out accumulating water.
Excavated soil may be placed directly in a dump truck for transport to an appropriate landfill or treated in an above-ground facility at the site. If the soil is stockpiled for future processing it is stored on plastic tarps or in containers and covered with tarps to prevent wind and rain from blowing or washing the contaminated soil away. Excavation is complete when test results show that the remaining soil around the hole meets established cleanup levels.
Excavated soil may be cleaned using a mobile treatment facility brought to the site or it can be transported to an alternative site where soil washing equipment is available. Treated soil may be used to fill in the excavated area or clean soil obtained from other locations. After an excavation is filled in, the area may be landscaped to prevent soil erosion and make the site more attractive.
Why is Excavation Used?
Excavation is commonly used where in situ (at site) cleanup methods will not work quickly enough or will be too expensive. Offsite disposal and ex-situ treatment are often the fastest ways to deal with high levels of contamination that pose an immediate risk to people or the environment. Excavation is also a cost-effective approach for small amounts of contaminated soil.
How Long Does Excavation Take?
This process may take as little as one day or as long as several years. The actual time is dependent upon specific factors unique to each site.
Is Excavation Safe?
Handling contaminated soil requires precautions to ensure safety. Only trained site workers who know the proper safety procedures should conduct this work.
Site workers typically wear protective clothing such as rubber gloves, boots, hard hats, and coveralls. These items are either washed or disposed of before leaving the site to keep workers from carrying contaminated soil offsite via their shoes and clothing. The tires and exteriors of trucks and other earth-moving equipment are also washed before leaving the site so that the contaminated soil is not tracked through neighboring streets.
During excavation, workers monitor the air to make sure dust and contaminant vapors are not present at levels that may pose a breathing risk to workers and surrounding areas. Monitors may also be placed around the site to ensure that contaminated dust and vapors are not leaving the site. Workers close to the excavation may need to wear “respirators,” which are face masks equipped with filters that remove dust and contaminants from the air. Contaminant vapors are also be suppressed with foams or other materials.