Section 5: Limitations

1
Section 5 Limitations
2
ISCO Limitations

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

3
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

4
What about Chemistry
5
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

6
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

7
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.

8
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
9
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
12
ISCO PAH DNAPL SITE, TRENTO, IT
DNAPL in AWs prior to Treatment
13
ISCO PAH DNAPL SITE, TRENTO, IT
14
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

15
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.

16
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