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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

6What About Geology, Geochemistry, and Hydrogeology

If you can’t 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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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 >80%) is sorbed and phase-separated

Total Mass EvaluationNature of Contamination

Graphic source: Suthersan, 1996

9ISCO Pilot PAH DNAPL SITE, TRENTO, IT

Site information

Old Petroleum Tar Chemical Distillation Plant

Contamination from Closed Treatment Ponds

Geology0 –2 m bgs till, stone and heterogeneous soil with brick fragments2 -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.

HydrogeologyThe water table is –2.7 m bgs but locally confined

10ISCOPAH DNAPL, TRENTO, IT

Pilot Test Area Future Treatment Area

11ISCO PAH DNAPL SITE, TRENTO, IT

Concrete Wall

Creek

AW-02

AW-03

AW-01

PZ-01

PZ-02

12ISCO PAH DNAPL SITE, TRENTO, IT

DNAPL in AW’s prior to Treatment

13ISCO 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 AW’s Temperatures were increased to 40 °C in all AW’s 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 NAPLPersistence 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