Investigation and Mitigation of a Complex Source of Vapor Intrusion Using an Iterative Investigative Approach
Christopher J. Milone, Brown and Caldwell , 110 Commerce Drive , Allendale , NJ 07401 , Tel: 201-574-4700, Fax: 201-236-1601, Email: cmilone@brwncald.com
Scott D. MacMillin, Brown and Caldwell , 110 Commerce Drive , Allendale , NJ 07401 , Tel: 201-574-4700, Fax: 201-236-1601, Email: smacmillin@brwncald.com
Stephen A. Kessel, Brown and Caldwell , 110 Commerce Drive , Allendale , NJ 07401 , Tel: 201-574-4700, Fax: 201-236-1601, Email: skessel@brwncald.com
Sharon M. Stecker, Brown and Caldwell , 110 Commerce Drive , Allendale , NJ 07401 , Tel: 201-574-4700, Fax: 201-236-1601, Email: cmilone@brwncald.com

Indoor air samples consistently detected concentrations of tetrachloroethene (PCE) above the NJDEP Indoor Air Screening Level (IASL) and periodically above the NJDEP Rapid Action Level (RAL) at a critical communications switching facility in northern New Jersey .  This paper presents the challenges and approaches associated with assessing and mitigating the complex vapor intrusion issue.  Investigations are being conducted by Brown and Caldwell to complete the delineation of chlorinated solvents in soil and groundwater likely associated with a former cleaning supply manufacturer.  Soil and groundwater contamination is associated with a former dry well and underground piping that was discovered during building renovation and construction activities conducted at the site in 1996.  Data gathered during ongoing remedial investigations revealed the presence of elevated concentrations of PCE in sub-slab soil vapor samples which exceeded 10 times the applicable NJDEP Soil Gas Screening Level.  In addition, indoor air samples collected within the site building over a two year period revealed concentrations of PCE consistently in excess of the IASL with periodic exceedances of the RAL.  With approval from NJDEP, a sub-slab depressurization system was implemented in the known source area as an interim remedial measure (IRM) intended to be protective of on-site workers while remedial investigation activities continued at the site.  Four weeks following installation and activation of the sub-slab depressurization system confirmation indoor air sampling was conducted to verify the effectiveness of the system.  Based on the results of this and two subsequent rounds of indoor testing, concentrations of PCE had not decreased since the sub-slab depressurization system was activated and continued to exceed the applicable IASL with one sample location exceeding the RAL.

This paper describes the methods and findings of a multimedia, investigation undertaken to evaluate, characterize and mitigate a complex source of vapor intrusion using an iterative investigative approach.

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