Site Assessment and Subsequent Remediation via In-Situ Thermal Treatment
Former Dry Cleaner (Nelson Cleaners)
Santa Clara, CA
During dry cleaner facility closure required soil sampling, the 
dry cleaning solvent Tetrachloroethylene (PCE) was detected in shallow soils at concentrations exceeding applicable commercial/industrial screening thresholds confirming that a release of this chemical had occurred. Weber, Hayes and Associates was retained to complete subsequent site characterization and remediation. Work tasks completed following the release discovery included:
- Assisting the responsible party with a State Site Cleanup Subaccount Program (SCAP) grant application which resulted in a $1.23M grant award for site assessment and remediation.
- Correspondence and close coordination with the Santa Clara Valley Department of Environmental Health (lead agency) for all site assessment and remediation tasks.
- Complete characterization of PCE chemical impacts to all affected media (i.e., soil, groundwater, soil vapor and indoor air) via CPT soundings, soil borings, monitoring wells and indoor air sampling, which led to successful completion of a Conceptual Site Model that was utilized as the basis for subsequent remedy selection.
- Preparation of a Feasibility Study to assess the technical and economic advantages / disadvantages of several remediation approaches for the site-specific limited access conditions (i.e., mass of PCE impacts situated beneath the former dry cleaner building to depths of 25 feet within a multi-unit strip mall) and selecting In-situ thermal remediation (ISTR) as the most viable option based on site conditions, both above and below grade, contaminant concentrations, associated costs and relatively fast timeframe for achieving Cleanup Goals.
- The ISTR wellfield was comprised of over 60 wells, the majority of which were installed within the former dry cleaner building via limited access drilling equipment, and included 21 heater wells, 31 vapor extraction wells, 6 multi-phase extraction wells, and 4 temperature and pressure monitoring wells. The target treatment volume was actively heated for 135 days at which point multiple converging lines of evidence confirmed that the ISTR treatment remediated the source zone to the extent practicable.
- ISTR treatment significantly reduced the mass of PCE contamination (nearly 100% mass reduction within the most heavily impacted soils from 0-15 feet below the surface) and post-remediation monitoring has confirmed PCE concentrations in groundwater and soil vapor have been reduced by orders of magnitude.
Notes:
In-situ Thermal Remediation (ISTR) is a technique for source zone remediation of organic compounds with a high degree of certainty for achieving remedial objectives and refers to the application of high heat (80 to greater than 100 degrees Celsius) to subsurface groundwater and soil by various methods, with a focus of remediating source zone contamination by vaporizing the contaminants via sub-surface heating, followed by contaminant extraction and treatment. Relative to other conventional remedial alternatives, ISTR technology is capable of rapidly treating organic compounds below screening thresholds and even non-detectable concentrations in many instances.
