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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
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