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Soil and Groundwater Cleanup from Petroleum Spills

 Soil and Groundwater Investigations

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Typical removal of a used oil or fuel tank when leaks and contamination are discovered.

Upon confirmation of a release, it is generally required to conduct a soil and groundwater investigation (subsurface assessment) to determine the full impact of the release on the surrounding soils and groundwater. In some cases, these investigations may span several months and consist of more than one or two phases of investigation. A simple investigation may consist of the placement of three soil borings in the vicinity of the release. If sampling and analyses indicate no product has escaped the tank cavity, further investigation should not be required. A more complex investigation may consist of the placement of 15 to 20 (or more) on-site and off-site wells.

Soil and Groundwater Treatment Technologies

The UST agency may require you to prepare a corrective action plan in response to elevated levels of contaminants in soils and/or groundwater found during the assessment. A simple plan may consist of excavation and disposal of localized soils which have been affected or the removal of free product from the tank cavity. A complex plan may include a combination of free product removal from several wells, vacuum extraction to clean the soils and groundwater treatment, in addition to some excavation.

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Depiction of how a fuel leak behaves underground.

Costs for corrective action on soils typically range from $10,000 to $50,000 for excavation and landfilling, but can exceed $100,000. Where groundwater has been severely impacted, assessment costs alone may range from $25,000 to $100,000 while corrective action may range from $100,000 to $250,000 and more. Therefore, it is vital you seek a second professional opinion on the need for  extensive remediation. The completion of a thorough risk assessment may be sufficient to conclude that only continued periodic monitoring or limited remediation of the primary sources (hot spots) is necessary.

Where no action (natural biodegradation), periodic monitoring or limited excavation is not acceptable and cannot achieve the desired clean-up goals, soil and/or groundwater treatment will need to be employed.

Technologies for the treatment of contaminated soils and groundwater continue to evolve as more experience is gained in this relatively new field. The more common soil treatment methods employed at petroleum UST sites include:

*  Treatment of excavated soils on site by:

* Aboveground venting
*  Bioremediation
*  Natural aeration
*  Thermal treatment and recycling

*  Treatment of soils off site by:

* Landfilling
* Landfarming
* Thermal treatment and recycling

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A groundwater treatment system at a truck fleet refueling station that discovered diesel fuel had leaked during UST removal.

* Treatment of soils in place (called in situ) does not require excavation and includes:

* Soil venting (also termed vacuum extraction or vapor extraction)

* Natural bioremediation

* Enhanced bioremediation

* Soil washing

The most common groundwater treatment methods include:

* Pump and treat—Where groundwater is pumped to the surface and free product is collected through an OWS. The water may be further treated and discharged to a municipal sewer, to a  receiving stream or reinjected into the ground. Water treatment equipment, depending on the discharge requirements, may include:

* Oil-water separation

* Carbon adsorption (Note: Spent carbon may be considered a hazardous waste)

*  Air-stripping

* Vacuum distillation

*  Biological treatment

* Combination of the above

* Reinjection—Water may be reinjected in the ground, with or without treatment, but make sure this is permitted in your state. This also enhances soil treatment through biological action and soil washing.

* Vacuum extraction—This method may be used for both contaminated groundwater and soils to extract free product and hydrocarbon vapors and enhance biodegradation of the contaminants.

Vapor streams from the treatment of groundwater and soils will generally require treatment to remove hydrocarbons. Common treatment methods include carbon adsorption or incineration.

Some states require approval of corrective action plans prior to beginning corrective action. Other states, realizing delayed action may exacerbate the problem and increase clean-up costs, desire the tank owner/operator to commence corrective action as soon as possible.

In all cases, it is not recommended to proceed with corrective action (above and beyond the initial r

esponse action and free product removal) until a complete assessment is made and the extent of contamination is well defined. However, it is generally advisable to proceed with additional limited excavation and digging of test pits, if the equipment is already on site (during tank removal, construction, etc.). In these cases, it is sometimes possible to determine the extent of contamination is limited to a small area, and further excavation may completely resolve the problem quickly and cost-effectively.

In all cases, it is recommended careful review of the corrective action plan be made and each item and associated costs in the scope of work understood.

 

 

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