Chemical Oxidation: Lessons Learned from the

Remediation of Leaking UST Sites

Jerry Cresap, PE

Groundwater & Environmental Services

gcresap@gesonline.com

Agenda

• Overview of In-Situ Chemical Oxidation

• Lessons Learned from 300+ Projects

• Detailed Analysis of 19 Sites

• Application of Findings

2

Oxidation Potentialof various oxidizing species

3.03

2.80

2.60

2.07

2.01

1.77

1.70

1.69

1.38

1.20

0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50

Fluorine

Hydroxyl Radical

Activated Persulfate

Ozone

Persulfate

Hydrogen Peroxide

Perhydroxyl Radical

Permanganate

Chlorine

Oxygen

Oxidation Potential (Volts)

3

Ozone/Peroxide/Persulfate Chemistry

1. Hydrogen peroxide will react with ozone to form hydroxyl radicals:

2 O3 + H2O2 → 2 (•OH) + 3 O2

2. Hydrogen peroxide will react with iron to form hydroxyl radicals:

H2O2 + C → • OH+ OH- + C+

C = Iron or Metal Catalyst; • OH = Hydroxyl Radicals

3. Hydrogen peroxide will react with persulfate to form sulfate radicals and

hydroxyl radicals:

S2O82- + H2O2 → 2SO4• + 2(•OH)

Note: Addition of persulfate can lower local pH, which will enhance the first and

second chemical reactions above.

GES Max-Ox Process

• Safe end products: carbon dioxide and water

• Extremely aggressive for MTBE, BTEX, TBA,

naphthalene, PCE, TCE, vinyl chloride

• Treats dissolved, adsorbed, and separate

phase

• No pH adjustment

• Not highly exothermic

5

Prefabricated

Max-Ox

Nested

Point

Hydrogen

Peroxide

Injection

Point

Ozone

Injection

Point

Injection Methods: HypeAir

• Process

> Short duration events

> Inject peroxide Air/Ozone

• Advantages

• Enhanced mixing

• Expanded ROI

• Limitations

> Subsurface utilities

> Receptors

6

What makes it such an effective technology?

1. The combination of aggressive remediation technologies

> Strong oxidizers (ozone, peroxide, persulfate)

> Soil scrubbing/washing

> Soil vapor extraction

> Dissolved oxygen enhances bioremediation

2. The injection process

> Nested injection of gas and liquid

> Pulsed operation

> Permanent injection points = expanded ROI

Lessons Learned from 300+ Sites

• Pre-Injection Characterization

• Oxidant Efficiency Factors

• Calculate Oxidant Demand

• Feasibility Testing

• Chemical Compatibility, Handling, Storage, and Delivery

• Ideal Site Conditions

• Injection Strategies

Lessons Learned:Pre-Injection Characterization

• Conceptual site model

• Soil Samples

> Vadose zone

> Upper saturated zone

> Lower saturated zone

> Fraction Organic Carbon

• Water Samples

> COCs

> Chemical oxygen demand

> Transition metals (e.g., iron)

9

Lessons Learned:Oxidant Efficiency Factors

• Oxidant efficiency is a function of:

> Oxidant type

> Subsurface distribution

> Presence of catalysts

> Natural humic matter

> Reaction rate with the COCs

• Oxidant efficiencies can be 30% or lower depending on

these variables

10

Lessons Learned:Oxidant Demand Calculation

• Determine COC mass in soil and groundwater

• LNAPL

• Select oxidant

• Determine moles of electrons required

• Determine mass of oxidant required

• Estimate efficiency

11

Lessons Learned:Feasibility Testing is Essential

12

Lessons Learned: ISCO Feasibility Testing

Always select the most appropriate technology – test traditional technologies

• Purpose

> Oxidant concentration

> Injection flow rate

> Injection pressure

> Radius-of-Influence

• Not the Purpose

> Prove that ISCO works

13

Lessons Learned:Feasibility Test Monitoring

• Groundwater Monitoring – Recommended Minimum

> Record pH, temp, DO, and ORP via YSI meter

> Peroxide concentration via field test kits

> Depth to water

• Vapor Monitoring – Recommended Minimum

> Well headspace readings with an LEL/O2 meter & PID

> Headspace & ambient monitoring with O3 meter (if

applicable)

> Compliance vapor treatment monitoring (if applicable)

14

Lesson Learned: Ideal Site Conditions

• Moderate to High Permeability

• Homogenous Soils

• DTW > 10 ft

• Limited Underground Utilities

• No Receptors

> > 10 ft from UST system (prefer > 20 ft)

• Low Organic Soils

• Few Oxidizer “Sinks”

• No chlorinated ethanes

• Minimal or no NAPL

15

Lessons Learned: Injection Strategies

• Use oxidation enhancers

> sodium persulfate

> ferrous sulfate

> EDTA iron

• Post-ox enhancers, such as nutrients

• Sodium persulfate may be injected at the end of an injection event to

further enhance free-radical production following the injection event.

When is short-term chemical oxidation not likely to be effective?

• Significant contaminant mass (> 5,000 lbs COC) may require significant volume of oxidant or # events.

• Large plumes may require a full-scale chemical oxidation system.

• Low permeability formations may make injection difficult (works best for formations where >1,000 gallons/day of oxidant injected).

• Should not be considered near active UST systems or shallow utilities unless appropriate engineering controls are used.

17

Lessons Learned: Chemical Compatibility, Handling, Storage, and Delivery

• Chemical compatibility

> tanks, utilities, potable wells

> Some oxidants are VERY Corrosive!

• Handling & storage considerations

> secondary containment

> spill response

> notification

• Logistical considerations

• Dry chemicals may not always be ready to inject (clumps).

• Mixing oxidants above grade not recommended.

Understand Corrosive Properties of Chemicals

Persulfate Corrosion of Steel Geoprobe Rods Damage to Galvanized Steel Fittings After

10 hours of contact with 10% persulfate.

New

After

10 hrs

Persulfate Corrosion of Mixing Tank Fittings

Recent Chemical Oxidation Evaluation

Goals:

• Detailed analysis of ISCO work performed at UST sites

• Determine trends and lessons learned

• Sites evaluated

> 19 UST sites

> 3 separate events

• Investigators

> Chuck Whisman, Denise Good, Mark Lankford

> Jim Higinbotham, Payal Shah

Key Questions:

• Can short-term chemical oxidation achieve closure?

• Can benzene, BTEX, and MTBE be reduced effectively?

• Does the volume of peroxide used affect results?

• Does the oxidizer concentration make a difference?

• How effective is gas injection?

• Do dedicated injection points improve performance?

• What is the optimal injection well spacing?

• Does it only work following other remediation technologies?

• How can a chemical oxidation remediation event be optimized?

Can short-term chemical oxidation achieve

closure?

• 74% attainment monitoring or closed (14 of the 19 sites)

• 21% regulatory closure (4 of the 19 sites)

> 4.25 injection events

> 4,821 gallons of hydrogen peroxide

21%

53%

21%

5%

Closed

Attainment Monitoring

Short-Term Injection

Events in Progress

Upgraded to Full-Scale

Chemical Oxidation

Can dissolved benzene, BTEX, and MTBE be reduced effectively?

• Benzene-impacted sites

> 72% had >70% reduction

> Similar results for BTEX

> Ave decrease = 86% for closed sites

• MTBE-impacted sites

> 71% had > 88% reduction

> Ave decrease = 94% for closed sites

Benzene (18 Sites)

>84%

Reduction

70-84%

Reduction

<70%

Reduction

MTBE (14 Sites)

>97%

Reduction

88-97%

Reduction

<88%

Reduction

Does the volume of peroxide used affect results?

• Sites with >90% Concentration Reduction:

Parameter Ave. Tot. Gallons of Peroxide

BTEX 8,901

MTBE 6,317

Does the oxidizer concentration make a difference?

Injecting 10% to 15% concentration of hydrogen peroxide achieved

much better success than 5% to 8% concentration.

Impact of Injection Solution Strength to Achieve >80% BTEX

Reduction

0

10

20

30

40

50

60

70

80

90

100

10-15% 5-8%

Hydrogen Peroxide Percent Solution

% o

f S

ites W

ith

>80%

BT

EX

Red

ucti

on

1/2 of these sites

achieved 99-100%

reduction; no rebound

almost 1/4 of these

sites had significant

rebound

How effective is gas injection?

• Gas injection using air, oxygen, and/or ozone significantly

increased the success and also minimized the potential for

rebound.

Ozone w/ Air & OxygenHydrogen Peroxide

maximum ROI

Groundwater

Flow Direction

Hydrogen Peroxide

How effective is gas injection?

Percentage of Sites Achieving > 95% BTEX Reduction

57%

27%

0%

10%

20%

30%

40%

50%

60%

Peroxide w Air or Ozone Peroxide Only

% B

TE

X R

ed

ucti

on

No significant

rebound

18% showed

significant rebound

Using air/ozone injection was highly effective.

Do dedicated injection points improve performance?

Percentage of Sites With >90% Reduction

Benzene

Benzene

MTBE

MTBE

30

35

40

45

50

55

60

65

70

Injection Wells Monitoring Wells

% O

f S

ites w

>90%

Red

ucti

on

What is the Optimal Injection Well Spacing?

• Injection well spacing <30 ft. (i.e., 15 ft. ROI) is

recommended.

• The successful chemical oxidation sites were performed

with an average injection well spacing of approximately 32 ft.

(16 ft. ROI).

• For BTEX-impacted sites, where existing monitoring wells

were used with >30 feet spacing, only 20% of those sites

achieved >75% reduction.

Does the process only work following other remediation technologies?

• MTBE sites can be remediated regardless of previous remediation.

• BTEX sites showed more success if previous remediation occurred.

• BTEX sites may require more injection events or volume of oxidant than MTBE sites.

• Sites where SVE was used for off-gas control during the injection event did not appear to show an increase in remediation success.

Summary

• ISCO is an effective and known remediation technology

• Conduct feasibility testing and pre-injection sampling

• Select oxidant(s) and calculate demand

• Select ISCO method

• Maximize effectiveness of selected remedy

32

Chemical Oxidation: Lessons Learned from the

Remediation of Leaking UST Sites

Jerry Cresap, PE

Groundwater & Environmental Services

gcresap@gesonline.com