United States           Solid Waste and          EPA510-F-93-026
Environmental Protection     Emergency Response       October 1993
Agency              5403W


Soil Remediation  For

UST Sites


In Situ  Passive

Biodegradation

(Natural Attenuation)


 In situ passive biodegradation (natural attenuation) is
 an approach for removing biodegradable contaminants
from soil. This method of remediation relies on
microorganisms to break down petroleum products in the
soil. It does not require the addition of oxygen or nutrients
to facilitate the process.

In situ passive biodegradation is extremely slow. It is most
appropriate when expedient remediation is not needed
and nearby receptors will not be affected by
contaminated soil. To date, few sites have been fully
remediated using this approach.

This technique offers low cost and minimal disruption to
business operations. In addition, this method generates
no wastestreams.
   Petroleum Types And Constituents

   • Fresh or weathered gasoline, diesel, jet fuel,
    kerosene

   • Volatile organic compounds (VOCs) such as
    benzene, toluene, etnylbenzene, and xylene (BTEX);
    residual semivolatile organic compounds (SVOCs)
    such as polynuclear aromatic hydrocarbons; and
    nonvolatile constituents

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In Situ Passive Biodegradation (Natural Attenuation)
Advantages
Limitations
System
Components
Wastestream
Treatment
Parameters to
Monitor1
Cleanup Levels
and Timing2
Costs3
• Costs substantially less than other methods
• Eventually degrades volatile organic compounds (VOCs),
semivolatile organic compounds (SVOCs), and
nonvolatile organic compounds
• Causes minimal disruption to business operations
• Generates no wastestreams
• Reduces potential for human contact with contaminated
soil or soil vapor
• Targets only biodegradable constituents
• Is an extremely slow process
• Requires sufficient nutrients, moisture, active
indigenous microbial population, and pH of 6-9 to
degrade contaminants
• To date, few sites have been fully remediated
• Monitoring wells
• Soil borings
• Soil vapor probes
• None
• Soil and groundwater contaminant concentrations
• Oxygen and carbon dioxide
• Can achieve risk-based cleanup levels
• Computer models project average remediation times of
50 to 200 years
• Longer time required to degrade heavier hydrocarbons
• Costs vary depending on monitoring frequency and risk
assessments
• Average risk assessment costs: $10,000 to $50,000
• Average monitoring and reporting costs: $10,000 to
$60,000
'"Parameters to monitor" are for performance purposes only; compliance monitoring parameters vary by state.
'Cleanup standards are determined by the state.
3Costs include equipment, and operation and maintenance.

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