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Remediation of Mixed Petroleum Hydrocarbon and Chlorinated Hydrocarbon Plume

Project Highlights:
  • Phase I & II Environmental Site Assessments (ESAs) identified environmental concerns (PCE and Stoddard solvent) at site
  • Soil gas sampling and analysis
  • Human Health Risk Assessment (HHRA) evaluation
  • Feasibility testing and remedial action plan preparation and implementation
  • Design-build soil vapor extraction (SVE) systems
  • SCAQMD permitting and compliance
  • SCAQMD Rule 1401 Risk Assessment Program evaluation
  • SCAQMD Rule 304 source testing and Rule 1147 NOx testing
  • Operation, maintenance, and monitoring of SVE system, including system data analysis, optimization of system performance, and regulatory agency reporting

EEC Environmental (EEC) was retained by the client to conduct a Phase I ESAs at the site to evaluate any potential environmental concerns in advance of a proposed property sale. The results of the Phase I investigation and a subsequent Phase II investigation identified Tetrachloroethene (PCE) and Stoddard solvent as environmental concerns.  Based on these results, the client requested EEC fast-track an HHRA evaluation, feasibility testing, and remediation to facilitate a sale of the property. Although the mass of PCE was relatively small compared to the mass of Stoddard solvent, the HHRA concluded that the PCE was the primary risk driver.

Based on contaminant levels in soil and HHRA results, soil remediation was deemed necessary. A feasibility study and SVE pilot test conducted by EEC indicated that SVE was the most cost-effective remedial option for the site. However, remediation options/costs were complicated because the two contaminant classes, chlorinated solvents and petroleum (Stoddard solvent), were concentrated in separate areas of the site, but also had significant overlap.  The pilot test indicated that the most cost-effective approach was to implement two-stage remediation due to the separate, but overlapping, locations of the two primary contaminants.

Stage 1 involved remediation of the primary constituent of concern, PCE. The purpose was to remove a significant portion of the chlorinated solvent mass using conventional SVE with carbon adsorption and minimize the amount of Stoddard solvent removal. A cost/benefit analysis was performed to determine the breakpoint at which the system could be changed to an SVE with thermal treatment without the need for acid-gas wet-scrubbing equipment.

Stage 2 was then implemented and involved the removal of Stoddard solvents and trace PCE using conventional thermal SVE without specialized acid-gas scrubbers. Sampling during pilot testing of Stage 2 confirmed the potential acid-gas generated by the thermal destruction of PCE was below the acceptable levels that could be discharged based on South Coast Air Quality Management District (SCAQMD) Rule 1401.

Using the results of the SVE pilot test, a full-scale granular activated carbon (GAC) SVE system was designed and installed, consisting of three 2,000-pound vapor-phase carbon vessels and a 500-cubic-foot-per-minute blower package. Upon a two order of magnitude reduction of PCE vapor, the transition to Stage 2 remediation began. This remedial approach involved a cooperative effort with SCAQMD, who approved all activities and testing procedures. Air testing per SCAQMD Rule 304 was conducted to confirm that trace PCE levels did not exceed SCAQMD Rule 1401 guidelines. Upon successful completion of the Rule 304 test, the SVE with thermal treatment was implemented. EEC is currently performing routine operation and maintenance of the SVE system.