Chemical Oxidation: Lessons Learned from the Remediation of Leaking UST Sites

Transcription

1 Chemical Oxidation: Lessons Learned from the Remediation of Leaking UST Sites Jerry Cresap, PE Groundwater & Environmental Services

2 Agenda Overview of In-Situ Chemical Oxidation Lessons Learned from 300+ Projects Detailed Analysis of 19 Sites Application of Findings 2

3 Oxidation Potential of various oxidizing species Oxygen Chlorine Permanganate Perhydroxyl Radical Hydrogen Peroxide Persulfate Ozone Activated Persulfate Hydroxyl Radical Fluorine Oxidation Potential (Volts) 3

4 Ozone/Peroxide/Persulfate Chemistry 1. Hydrogen peroxide will react with ozone to form hydroxyl radicals: 2 O 3 + H 2 O 2 2 ( OH) + 3 O 2 2. Hydrogen peroxide will react with iron to form hydroxyl radicals: H 2 O 2 + 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: S 2 O H 2 O 2 2SO 4 + 2( OH) Note: Addition of persulfate can lower local ph, which will enhance the first and second chemical reactions above.

5 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 Prefabricated Max-Ox Nested Point Hydrogen Peroxide Injection Point Ozone Injection Point 5

6 Injection Methods: HypeAir Process > Short duration events > Inject peroxide Air/Ozone Advantages Enhanced mixing Expanded ROI Limitations > Subsurface utilities > Receptors 6

7 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

8 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

9 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

10 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

11 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

12 Lessons Learned: Feasibility Testing is Essential 12

13 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

14 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

15 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

16 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.

17 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

18 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.

19 Understand Corrosive Properties of Chemicals Persulfate Corrosion of Steel Geoprobe Rods Damage to Galvanized Steel Fittings After 10 hours of contact with 10% persulfate. Persulfate Corrosion of Mixing Tank Fittings New After 10 hrs

20 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

21 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?

22 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 Closed 21% 5% 21% Attainment Monitoring Short-Term Injection Events in Progress 53% Upgraded to Full-Scale Chemical Oxidation

23 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 <70% Reduction 70-84% Reduction Benzene (18 Sites) >84% Reduction MTBE (14 Sites) <88% Reduction >97% Reduction 88-97% Reduction

24 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

25 % of Sites With >80% BTEX Reduction 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 /2 of these sites achieved % reduction; no rebound almost 1/4 of these sites had significant rebound % 5-8% Hydrogen Peroxide Percent Solution

26 How effective is gas injection? Gas injection using air, oxygen, and/or ozone significantly increased the success and also minimized the potential for rebound. Hydrogen Peroxide Ozone w/ Air & Oxygen Hydrogen Peroxide maximum ROI Groundwater Flow Direction

27 % BTEX Reduction How effective is gas injection? Using air/ozone injection was highly effective. Percentage of Sites Achieving > 95% BTEX Reduction 60% 50% No significant rebound 57% 40% 30% 20% 18% showed significant rebound 27% 10% 0% Peroxide w Air or Ozone Peroxide Only

28 % Of Sites w >90% Reduction Do dedicated injection points improve performance? Percentage of Sites With >90% Reduction MTBE Benzene Benzene MTBE 30 Injection Wells Monitoring Wells

29 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.

30 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.

31 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

32 Chemical Oxidation: Lessons Learned from the Remediation of Leaking UST Sites Jerry Cresap, PE Groundwater & Environmental Services