&EFA
                 United States
                 Environmental Protection
                 Agency
                  Solid Waste and
                  Emergency Response
                  5403W
EPA510-F-93-018
October 1993
Groundwater
Remediation  For
UST  Sites
In Situ Bioremediation
                   In situ bioremediation is a technique for removing
                   biodegradable contaminants from groundwater. The
                 technique relies on microorganisms and supplemental
                 oxygen and nutrients to break down petroleum products
                 in the groundwater.

                 In situ bioremediation offers the advantage of being able
                 to treat contamination in place, without the need for
                 pumping or the subsequent treatment of pumped
                 groundwater. The technique is most effective in
                 permeable aquifers.
                    Petroleum Types And Constituents

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

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

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In Situ Bioremediation
Advantages
Limitations
System
Components
Wastestream
Treatment
Parameters to
Monitor1
Cleanup Levels
and Timing2
Costs5
• Degrades contaminants in place
• Achieves lower concentration levels than pump and
treat
• Effectiveness is limited in low permeability or
heterogeneous media
• Ability to transport nutrients and oxygen might be
limited by soil and groundwater mineral content or pH
• Targets only biodegradable constituents
• Groundwater containment system
• Oxygen delivery equipment
• Nutrient delivery equipment
• Injection trenches
• Recovery walls or trenches
• Pumps
• Monitoring points
• Recirculated groundwater treatment options:
• Air stripping
• Granulated activated carbon
• Bioreactors
• Constituent concentrations in groundwater
• Microbial population in aquifer
• pH and total organic carbon
• Dissolved oxygen
• Nutrient concentration
• Flow rates
• Generally, can achieve maximum contaminant levels
(MCLs)
• Achieves £ 90% reduction of biodegradable constituents
• For an ideal site3, ~90% in 6 months to 1 year
• For an average site4, ~90% in 6 months to 4 years
• Longer time required to degrade heavier hydrocarbons
• For an ideal site3, $150,000 to $250,000
• For an average site4, $200,000 to $500,000
'"Parameters to mentor* are for performance purposes only; compliance monitoring parameters vary by state.
3An Ideal site" assumes no delays in corrective action and a relatively homogeneous, permeable subsurface.
Vn •average stW assumes mWnal delays h corrective action and a modmtelyheterogerieous and pameabte surface.
'Costs include equipment, and operation and maintenance.

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