Texas Grain Elevator Fumigant Site
A fumigant containing carbon tetrachloride (CT) was used at this elevator from 1965 to 1986. CT was discovered in the groundwater and just above the groundwater adjacent to the grain elevator where the fumigant was likely stored.
Initial concentrations were high enough that un-dissolved free product, both above and below the water table, was suspected but not observed. Source area CT levels were as high as 153 mg/L.
Groundwater is approximately 25 feet below ground surface (bgs) and flows north toward the adjacent river. The top 25 ft are predominantly brown and gray clays, with silty sand between 26 to 30 ft bgs, which is the upper water bearing zone. Hydraulic conductivity within this saturation zone ranged from 10⁻³ to 10⁻⁴ cm/sec.
Simple biological anaerobic dechlorination was not considered due to the extremely high CT concentrations, which were inhibitory to bacteria growth. The suspected un-dissolved free product made EZVI the logical remediation choice, as the free product would partition into the vegetable oil and then react with the suspended iron, providing a significant reduction in CT concentrations (and toxicity) before the biological degradation began.
- July 2006: 58 borings, 8,750 pounds of EZVI (18-33 ft bgs)
- June 2010: 70 injection borings, 35,400 pounds of EZVI, treating over 3,000 cu yds
Source Area Well MW-205:
- CT declined from over 150 mg/L to less than 30 mg/L immediately after first injection
- Chloroform increased from 12 mg/L, peaked at 70 mg/L in 2008, then declined
- Methylene Chloride increased from 0.100 mg/L, peaked at 32 mg/L in 2011, then declined
- After second injection (2010): CT declined to 14.9 mg/L
- Objective of 0.005 mg/L first achieved in December 2012
Downgradient Well MW-102:
- CT declined steadily after first EZVI injections
- Temporary increase to 5.9 mg/L after second injection (September 2010)
- Continued decline since 2010
Chloride Evidence of Free Product Destruction:
- First injection: Chloride increased 400 mg/L (equivalent to 400 mg/L CT destroyed)
- Second injection: Chloride increased 1,190 mg/L (equivalent to 1,190 mg/L CT destroyed)
- Clear evidence of un-dissolved free product being destroyed by EZVI
This Texas project demonstrates EZVI's unique capability to destroy chlorinated solvent free product (NAPL) that is inhibitory to biological treatment. The site had extremely high carbon tetrachloride (CT) concentrations with suspected un-dissolved free product — conditions under which simple biological anaerobic dechlorination was not considered viable due to CT's toxicity to dechlorinating bacteria. EZVI was the logical choice because the free product partitions into the vegetable oil emulsion and then reacts with the suspended iron, providing significant CT concentration reduction before biological degradation begins.
The two-phase injection strategy — July 2006 (58 borings, 8,750 lbs EZVI at 18–33 ft bgs) and June 2010 (70 injection borings, 35,400 lbs EZVI treating over 3,000 cubic yards) — demonstrates the value of phased treatment for high-concentration source zones. The first injection rapidly reduced CT concentrations (from 150+ mg/L to less than 30 mg/L), while the second injection drove concentrations down to the treatment objective of 0.005 mg/L — first achieved in December 2012.
The chloride evidence of free product destruction is particularly compelling: the first injection generated a 400 mg/L chloride increase (equivalent to 400 mg/L CT destroyed), and the second injection generated a 1,190 mg/L chloride increase. This stoichiometric relationship between chloride generation and CT destruction provides clear evidence that the EZVI emulsion is directly contacting and destroying un-dissolved free product — not just treating dissolved-phase contamination.
The clay geology noted in the Key Success Factors is a significant factor in the remediation design. Clay soils have low permeability, which limits reagent distribution through conventional gravity-fed injection. EZVI's emulsion-based formulation can be distributed under pressure through clay matrices, and the biodegradable oil phase provides sustained treatment as it slowly releases ZVI particles over months to years. The 128 total injection borings across the two phases ensured comprehensive lateral coverage of the source zone within the clay formation.
Carbon tetrachloride (CT) is a chlorinated solvent historically used as a cleaning agent, fire suppressant, and refrigerant. It is a known carcinogen with a high density (1.59 g/cm³), making it a DNAPL that migrates downward through soil and accumulates at lithologic interfaces. The extremely high concentrations at this site — with suspected free product — represent a challenging treatment scenario that EZVI is specifically designed to address. The achievement of the 0.005 mg/L treatment objective in December 2012, approximately 6 years after the initial injection, demonstrates the sustained long-term treatment provided by the EZVI emulsion system.