In-Situ Remediation at Silver Lake

1. In-Situ Remediationat Silver Lake Region 4 Hazardous MaterialsGeo/Bridge/Environmental Unit

2. LUSTs and Sustainability • Limited groundwater resources • Once impacted from petroleum hydrocarbons, subsurface ecosystem can take decades to recover • Limited financial resources

3. 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 = $$$!

4. 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.

6. Silver Lake Maintenance Facility

7. Late 1980s • 6,000 gallons of diesel spilled from newly installed AST 1992 • 5 USTs decommissioned • Unknown amount of fuel spilled from USTs • 3,500 yd3 of Petroleum Contaminated Soil excavated 1993 • Subsurface investigation, Corrective Action Plan

13. Silver Lake In-Situ Cleanup 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 What went wrong?

14. 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?

15. Fresh Start • Delineate full extent of diesel contamination • Chemistry • Evaluate in-situ remedial options • Pilot Test • Final Design • Construction • Operation

16. Drilling – Expanded Subsurface Investigation

17. Groundwater Sampling

18. Groundwater Contours

19. Extent of Contamination

20. Aerobic Conditions Anaerobic Conditions

21. Aerobic Biodegredation HC Molecule (electron donor) e- Oxygen (electron receptor) Secondary receptors => Fe, SO4, NO3 “oxidized” Energy Released HC + O2 -> CO2 + H2O “reduced”

22. Anaerobic Biodegradation HC Molecule (electron donor) e- Carbon (electron receptor) “oxidized” Energy Released HC + CO2 -> CH4 + H2O Methanogenesis “reduced”

23. Remedial Alternatives No 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

24. 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!

25. DO Injection Wells GroundwaterRecovery Wells

26. In-Situ DO Remediation Installation • Install injection points • Gnd wtr recovery wells • Trenching and piping • Super-OxTM system

27. Injection Well Installation

28. Trenches and Piping

29. Questions?

30. Beer Molecule e- O2 “oxidized” Beer + O2 -> CO2 + H2O Energy Released “reduced”