Section 5: Limitations

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Section 5 Limitations
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ISCO Limitations

• Saturated Zone vs Unsaturated Zone
• Chemistry
• CoSolvents
• Geology /Geochemistry/Hydrogeology
• NAPL

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ISCO Saturated Zone vs Unsaturated

• All ISCO are Aqueous Phase Technologies
• Ozone is also an Unsaturated Zone Technology
• In order for treatment to occur, both the
  contaminant and the oxidant must be in solution
  together.
• Permanganate, solid peroxides, activated sodium
  persulfate can be used to treat the unsaturated
  zone if zone or soils are hydrated during
  treatment.
• Percent saturated is dependent on the contaminant
  and the soil type

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What about Chemistry
Oxidant Amenable contaminants of concern Reluctant contaminants of concern Recalcitrant contaminants of concern
Peroxide/Fe TCA, PCE, TCE, DCE, VC, BTEX, chlorobenzene, phenols, 1,4-dioxane, MTBE, tert-butyl alcohol (TBA), high explosives DCA, CH2Cl2, PAHs, carbon tetrachloride, PCBs CHCl3, pesticides
Ozone PCE, TCE, DCE, VC, BTEX, chlorobenzene, phenols, MTBE, TBA, high explosives DCA, CH2Cl2, PAHs TCA, carbon tetrachloride, CHCl3, PCBs, pesticides
Ozone/ Peroxide TCA, PCE, TCE, DCE, VC, BTEX, chlorobenzene, phenols, 1,4-dioxane, MTBE, TBA, high explosives DCA, CH2Cl2, PAHs, carbon tetrachloride, PCBs CHCl3, pesticides
Permanganate (K/Na) PCE, TCE, DCE, VC, TEX, PAHs, phenols, high explosives Pesticides Benzene, TCA, carbon tetrachloride, CHCl3, PCBs
Activated Sodium Persulfate PCE, TCE, DCE, VC, BTEX, chlorobenzene, phenols, 1,4-dioxane, MTBE, TBA, PAHs, PCBs PAHs, explosives, pesticides None
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What About CoSolvents

• All organic Mass is addressed by ISCO
• Chlorinated Solvents dissolved into oils
  generally behave as the oil. ( sink or float)
• Cosolvent must be oxidized to reduce target
  analytes
• BETX is only a 20 portion of fuel contamination
  so remaining solvent must be oxidized

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What About Geology, Geochemistry, and Hydrogeology

• If you cant contact the contaminant with ISCO
  you can not treat it.
• Tight Clays require special treatment
• Heterogeneity requires special consideration for
  well locations and screen intervals.
• High Flow Aquifers need to use recirculation to
  maintain contact
• Carbonate formations can be treated but need to
  be tested for best ISCO approach

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What about NAPL

• Very rarely does NAPL exist as free floating
  product
• If NAPL can be recovered effectively, it should
  be
• NAPL occupies the pore spaces of soil and exists
  in the colloidal spaces in the soil
• Effective short-term ISCO treatment requires
  dissolution of the sorbed and NAPL phase in the
  colloidal spaces with heat- Only peroxide
  provides that heat in ISCO Treatments
• NAPL has been and can be effectively and safely
  treated with ISCO using controlled temperatures
  at low pressures
• NAPL must be treated with Submerged application
  of chemicals below NAPL Zone.

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Total Mass EvaluationNature of Contamination

• Contamination mass exists in four phases in the
  contaminated zone
• Soil gas
• Sorbed
• Dissolved
• Non-aqueous phase liquid (NAPL) or
  phase-separated
• Geochemistry, partitioning coefficient (Kow)
  determines the relationship between phases in
  the saturated zone
• Majority of mass (normally gt80) is sorbed and
  phase-separated

Graphic source Suthersan, 1996
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ISCO Pilot PAH DNAPL SITE, TRENTO, IT
Site information Old Petroleum Tar Chemical
Distillation Plant Contamination from Closed
Treatment Ponds Geology 0 2 m bgs till, stone
and heterogeneous soil with brick fragments 2
-5m silty/sandy soil black color and heavy
hydrocarbon and naphthalene smell, 5 to 14.3 m
sandy, 13.30 to 16.30 colour black w/
hydrocarbon smell. Flowing DNAPL tars are
present in the last 10 cm. Hydrogeology The
water table is 2.7 m bgs but locally confined
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ISCOPAH DNAPL, TRENTO, IT
Pilot Test Area
Future Treatment Area
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ISCO PAH DNAPL SITE, TRENTO, IT
AW-03
Creek
Concrete Wall
PZ-01
AW-02
PZ-02
AW-01
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ISCO PAH DNAPL SITE, TRENTO, IT
DNAPL in AWs prior to Treatment
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ISCO PAH DNAPL SITE, TRENTO, IT
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DNAPL Reduction PAH DNAPL SITE, TRENTO, IT

• Observations
• Flow was 2 l/min and increased to 5 l/min after
  hydrogen Peroxide application through Concurrent
  Application in All AWs
• Temperatures were increased to 40 C in all AWs
• All DNAPL was removed from AW wells and PZ 01
  within 2 days
• All hydrocarbon odor eliminated from all wells
• Secondary indications of Sodium Persulfate
  Oxidation Activity for 6 weeks
• Dissolved concentrations less than 100 ppb and
  no residual sheen or NAPL

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DNAPL Reduction PAH DNAPL SITE, TRENTO, IT

• Observations
• Controlled Applications of Hydrogen Peroxide can
  effectively dissolve large amounts of NAPL and
  Dissolved Mass by agitation and addition of heat
  at low pressure
• Controlled application at low pressure controls
  migration of NAPL
• Persistence of Activated Sodium Persulfate
  consumes dissolved organics for over six weeks
  eliminating repartitioning and rebound potential.
• Augmentation of additional sodium Persulfate
  after initial application can be performed before
  repartitioning of dissolved mass.

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Conclusions

• ISCO and the contaminant must be in an Aqueous
  solution for successful Treatment
• ISCO can treat all organics
• ISCO is not selective, it treats all organics
  including non-target Cosolvents and Natural
  Occurring Organics
• ISCO can safely and effectively treat
  non-recoverable NAPL and prevents rebound