United States            Solid Waste and           EPA 510-F-93-022
Environmental Protection      Emergency Response        October 1993
Agency               5403W

Soil  Remediation  For

UST  Sites

In  Situ Bioremediation:


  In situ bioremediation—bioventing—is a technique for
  removing biodegradable contaminants from
unsaturated soils. The technique injects oxygen into
contaminated soil. The oxygen stimulates the aerobic
biodegradation of the organic contaminants in the soil.
Oxygen is delivered at a low rate to encourage
biodegradation rather than volatilization.

Bioventing is most effective in coarse-grained soils such as
sand and gravel. It requires a minimum 5-foot-thick
unsaturated zone. This technique can be used in
conjunction with air sparging or groundwater pumping

This technique is able to treat large volumes of soil
effectively and with minimal disruption to business
operations.  It also can remove contamination from near
or under fixed structures. Bioventing also reduces the
need for aboveground treatment because it works to
degrade contaminants in place.
   Petroleum Types And Constituents

   » Fresh or weathered gasoline, diesel, jet fuel,
     kerosene, motor oil, heavy fuel oil, lubricating oils,
     and crude oils

   « Volatile organic compounds (VOCs) such as
     benzene, toluene, ethylbenzene, and xylene fBTEX);
     residual semlvolatfle organic compounds (SVOCs)
     such as polynuclear aromatic hydrocarbons; and
     nonvolatile constituents

   In Situ Bioremediation:  Bioventing
  Degrades semivolatile organic compounds (SVOCs) and
  nonvolatile organic compounds
  Effectively treats large volumes (> 1,000 cu yd) of soil
  Causes minimal disruption to business operations
  Degrades contaminants near or under fixed structures
  Degrades volatile organic compounds (VOCs) in place, which
  reduces air emissions and subsequent need for treatment
  Targets only biodegradable constituents
  Is a relatively slow process
  Requires sufficient nutrients, moisture, active indigenous
  microbial population, and pH of 6-9 to degrade contaminants
  Effectiveness limited in heterogeneous soils
• Vertical or horizontal extraction wells
• Trenches
• Vacuum blower or pump
• Injection and passive inlet wells
• Vapor treatment (optional)
• Nutrient delivery equipment (optional)
  Vapor treatment options (might be needed for high
  concentrations of contaminants):
   •  Vapor phase biofilter
   •  Granulated activated carbon
   •  Internal combustion engine
   •  Catalytic oxidation unit
   •  Thermal incinerator
   Parameters to
• Vapor concentration
• Airflow rate
• In situ respiration rate (oxygen consumption and carbon dioxide
• Soil contaminant concentration
• Microbial population
• Soil pH, moisture, and nutrients
   Cleanup Levels
   and Timing2
• Treats > 90% of biodegradable constituents
• For an ideal site3, ~90% in 1 to 2 years
• For an average site4, ~90% in 1 to 4 years
• Longer time required to degrade heavier hydrocarbons
  For an ideal site3, $40,000 to $120,000
  For an average site4, $100,000 to $150,000
  Vapor treatment and longer treatment times increase costs
''Parameters to monitor" are for performance purposes only; compliance monitoring parameters vary by state.
An Ideal site" assumes no delays in corrective action and a relatively homogenous, permeable subsurface.
4An "average sle" assumes mWmal (Ways in cotredive action andarrKxleratelyrieteroc^nec)usandpemieablestJMurface.
^Costs include equipment, and operation and maintenance.