Pump and Treat Permeable Reactive Barrier Former Intersil, Inc. Site Sunnyvale, California Presented by Daniel Cheung

Outline of Presentation  Site Background  Geotechnology Alternatives  Science/Principles Involved (PRB)  Evaluation on Remediation  Conclusion

Site Background  Historical Activities Former Intersil, Inc. (Sunnyvale, California) Former Intersil, Inc. (Sunnyvale, California) 1970s–1983 Semiconductor manufacturing 1970s–1983 Semiconductor manufacturing 1972 Concrete, epoxy-lined, in-ground neutralization system installed 1972 Concrete, epoxy-lined, in-ground neutralization system installed 1986 Identified as potential contaminant source 1986 Identified as potential contaminant source 1987-Present Remediation 1987-Present Remediation

Site Background

 Hydrogeology of the Site (2.4 acres) Semi-confined aquifer Semi-confined aquifer Upper silty clay (9-12 feet)Upper silty clay (9-12 feet) Lower clay and silty clay (~65 feet)Lower clay and silty clay (~65 feet) Interfingering zones of (~1-8 feet, porosity = 0.3) Interfingering zones of (~1-8 feet, porosity = 0.3) Silty fine grained sandSilty fine grained sand Fine to medium grained sandFine to medium grained sand Gravelly sandGravelly sand Average flow rate = 0.8 ft/dayAverage flow rate = 0.8 ft/day Not usable for consumption (high TDS) Not usable for consumption (high TDS)

Site Background  Contamination Halogenated volatile organic compounds (VOCs) Halogenated volatile organic compounds (VOCs) Maximum concentrations in 1986 Maximum concentrations in 1986 Halogenated VOCs μg/L Halogenated VOCs μg/L Trichlorethene (TCE) 13,000Trichlorethene (TCE) 13,000 cis-1,2-dichloroethene (cis-1,2-DCE) 19,000cis-1,2-dichloroethene (cis-1,2-DCE) 19,000 Vinyl chloride (VC) 1,800Vinyl chloride (VC) 1,800 Freon-13316,000Freon-13316,000 Only detected in the upper aquifer Only detected in the upper aquifer

Geotechnology Alternatives  Pump and Treat, P&T (11/87 – 02/95) 4 extraction wells (pump) 4 extraction wells (pump) 13 monitoring wells 13 monitoring wells 1 Air stripper (treat) → Storm sewer (discharge) 1 Air stripper (treat) → Storm sewer (discharge) 2 Carbon adsorption (unused) 2 Carbon adsorption (unused)  Permeable Reactive Barrier, PRB (02/95 – Ongoing) Granular iron treatment zone Granular iron treatment zone Flow control zone Flow control zone Hydraulic barrier system (2 slurry walls) Hydraulic barrier system (2 slurry walls)

Science/Principles Involved (PRB)

Abiotic Reductive Dehalogenation

Evaluation on Remediation  Pump and Treat HVOCs < MCLs (NPDES) HVOCs < MCLs (NPDES) Inward hydraulic gradient contained the plume Inward hydraulic gradient contained the plume Removal rate declined exponentially Removal rate declined exponentially $1,343,800 (24% capital cost, 76% O/M cost) $1,343,800 (24% capital cost, 76% O/M cost) $24,000/kg of total contaminant $24,000/kg of total contaminant  1993 evaluation Minimise cost & Increase effectiveness Minimise cost & Increase effectiveness Return the site to leasable conditions Return the site to leasable conditions

Evaluation on Remediation  Permeable Reactive Barrier TCE & Freon-133 < MCLs (California & EPA) TCE & Freon-133 < MCLs (California & EPA) Cis-1,2-DCE & VC >> MCLs (California & EPA) Cis-1,2-DCE & VC >> MCLs (California & EPA) Natural attenuation & Non-migrated Natural attenuation & Non-migrated Plume has been contained Plume has been contained $762,000 (78% capital cost, 22% O/M cost) $762,000 (78% capital cost, 22% O/M cost) $108,900/kg of total contaminant $108,900/kg of total contaminant The site was released in 1995 The site was released in 1995

Evaluation on Remediation PRB 2M gallons 7kg in 1.5yrs P&T 36M gallons 56kg in 7.25yrs 98% Total Removal

Conclusion  Both P&T and PRB were used  Satisfactory overall clean up performance  Appropriate methods were adopted Hydrogeology Hydrogeology Seriousness of contamination Seriousness of contamination Cost effectiveness Cost effectiveness Legal requirement Legal requirement

Q&A