Vapor Intrusion Investigation and Mitigation System Design at a Silicon Chip Manufacturing Facility
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An industrial firm retained Geosyntec through its Malaysian subsidiary, GSM Consultancy, for professional services at an operating electronics manufacturing facility in Kuala Lumpur, Malaysia. The objectives of the work were to characterize the distribution of volatile organic compounds (VOCs) in the subsurface; assess the potential for subsurface vapor intrusion to indoor air; and provide data for the design of a sub-slab depressurization (SSD) system for mitigation optimized for minimal disruption to ongoing production activities at the facility.

Geosyntec's Scope of Services

Geosyntec performed a phased investigation beginning with an initial screening of sub-slab vapor concentrations using quantitative passive diffusive samplers (Waterloo Membrane Sampler, or WMS), which was developed jointly by the University of Waterloo and Geosyntec. The WMS samplers provide low-level reporting limits at about half the cost of the conventional Summa canister sampling method and analysis. The initial phase of investigation identified areas of the building with elevated sub-slab concentrations of VOCs, which justified additional assessment of the extent of the vapor distribution and collection of pneumatic data for mitigation system design. The second phase of work was conducted using a Geosyntec proprietary method referred to as High Purge Volume (HPV) sampling, which involves removal of a large volume of soil gas from selected locations and monitoring of the vapor concentrations as a function of the volume removed to assess concentrations between and beyond the points of withdrawal. Monitoring of the vacuum response also provides the necessary information to design an SSD or soil vapor extraction (SVE) system. We also used WMS samplers to provide an average concentration of subsurface VOCs during each HPV test. Geosyntec also performed a mathematical analysis of the transient vacuum response data to develop an optimal design of a mitigation system to only those portions of the building with elevated subsurface concentrations with flushing rates tailored to achieve remedial goals within the client's time-frame.

Notable Accomplishments

Geosyntec used two proprietary investigative and sampling methods, HPV testing with WMS samplers, to cost-effectively characterize the concentrations of VOCs in the subsurface, significantly reducing the client's costs associated with characterizing a large manufacturing facility. These methods were also easier to implement considering the challenges of shipping samples to and from Malaysia. At the same time, we collected a wealth of subsurface vacuum response data to allow us to design a custom-tailored mitigation system to treat only the necessary portions of the building and achieve remedial goals within a time period that minimized disruption to site production activities.

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Project Summary

  • Location: Kuala Lumpur, Malaysia
  • Client: Confidential
  • Project Practice Areas: Contaminated Sites
  • Type of Facility: Manufacturing Site
  • Services Provided: Interpretation of Existing Data; Vapor Intrusion Assessment; Recommended Mitigation and Remediation Options
  • Type of Work: Vapor Intrusion Assessment
  • Governing Regulation: International Standards