In-Situ Remediationat Silver Lake

Region 4 Hazardous MaterialsGeo/Bridge/Environmental Unit

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.

Silver Lake Maintenance Facility

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

Drilling – Expanded Subsurface Investigation

Groundwater Sampling

Groundwater Contours

Extent of Contamination

Anaerobic ConditionsAerobic Conditions

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!

GroundwaterRecovery Wells

DO Injection Wells

In-Situ DO Remediation Installation

• Install injection points• Gnd wtr recovery wells• Trenching and piping• Super-OxTM system

Injection Well Installation

Trenches and Piping

Questions?

Beer Molecule

e-

O2

Energy Released

“oxidized”

“reduced”

Beer + O2 -> CO2 + H2O