in-situ remediation at silver lake region 4 hazardous materials geo/bridge/environmental unit
TRANSCRIPT
LUSTs and Sustainability• Limited groundwater
resources• Once impacted from
petroleum hydrocarbons, subsurface ecosystem can take decades to recover
• Limited financial resources
LUSTs – Why So Bad?
• Petroleum Fuel – contains known or suspected carcinogens
• Released fuel doesn’t stay put – migrates
• Travels with groundwater• Difficult to see• Difficult to cleanup = $$$!
What is In-Situ Remediation?In-Situ means “in place”.
Remediation – providing remedy. Treatment or removal contaminants in soil and groundwater.
In Situ – in place remedy. Remove, treat, change, transform contaminants in subsurface.
Late 1980s– 6,000 gallons of diesel spilled from newly installed
AST1992
– 5 USTs decommissioned– Unknown amount of fuel spilled from USTs– 3,500 yd3 of Petroleum Contaminated Soil excavated
1993– Subsurface investigation, Corrective Action Plan
1995– Groundwater extraction (“pump and treat”)– Operated for total of 6 weeks– No measurable hydrocarbon recovery
1996 - 1998– Soil Vapor Extraction (SVE) system installed– Horizontal trenches– Operated for 21 months– Only recovered total of 25 lbs of petroleum
hydrocarbons
Silver Lake In-Situ Cleanup
What went wrong?
Restoring Aquifers
Enhanced Naturally Occurring Biological Degradation• Use natural healing forces of nature• Microbes dismantle petroleum hydrocarbons (HC)
deriving energy from that process• Give nature a helping hand• What does the system lack? O2? Nutrients? Use
mechanical technology to distribute electron receptors and nutrients.
• What is occurring now under the “Do Nothing” Technology?
Fresh Start• Delineate full extent of diesel contamination• Chemistry• Evaluate in-situ remedial options• Pilot Test• Final Design• Construction• Operation
HC Molecule (electron donor)
e-
Oxygen (electron receptor)
Secondary receptors => Fe, SO4, NO3
Energy Released
Aerobic Biodegredation“oxidized”
“reduced”
HC + O2 -> CO2 + H2O
HC Molecule (electron donor)
e-
Carbon (electron receptor)
Energy Released
Anaerobic Biodegradation“oxidized”
“reduced”
HC + CO2 -> CH4 + H2OMethanogenesis
Remedial AlternativesNo Action
– doesn’t remove risk or future liability
Air Sparging– uncertainty of uniformity of air injection
Dissolved Oxygen Injection– enhancement of natural attenuation
Dual Phase Extraction– removes groundwater and vapors
Ozone Injection– uncertainty of uniformity of air injection
O2 as an electron receptor is primary limiting factor in bioremediation.
To promote faster bioremediation, dissolved O2 must be supplied in large quantities.
Solution – Provide dissolved O2 and lots of it!
In-Situ DO Remediation Installation
• Install injection points• Gnd wtr recovery wells• Trenching and piping• Super-OxTM system