Ten Bears was chosen for this due-diligence and Brownfields Investigation on behalf of a non-profit organization, after a prospective purchase by Del DOT fell through. Despite expansive funding available to governmental entities under the Brownfields Program, the project was apparently viewed as overly risky. Prior investigation by DNREC, and then two third-party consultants had identified chlorinated solvents and petroleum associated with historical use for a dry-cleaners and a gasoline UST well in excess of DNREC risk screening criteria.

Although the prospective developer entered into the Brownfields program in 2016, Ten Bears was hired to complete a fast-track Brownfields Investigation with less than 6 months left under the 2-year DNREC limit for completion of the investigation. The scope required interactive management and implementation of multiple subcontractors to complete step-wise investigation, including membrane-interface probes (MIPs), followed by soil borings and well construction at multiple depth intervals. Laboratory results and associated Human Health Risk Assessment resulted in unacceptable risks for future users associated with direct soil contact, vapor intrusion, and potential groundwater ingestion. investigation findings were used to refine a Conceptual Site Model indicating surface releases spread horizontally on low-permeability soils, creating near-surface vapor source for building intrusion, and passing to groundwater through 2 discrete ‘windows’ to the groundwater aquifer, with petroleum and dry-cleaning solvent plumes extending off site. While the owner’s demolition of the existing building eliminates the future vapor intrusion pathway, DNREC required remedies for soil contact, groundwater, and potential vapor migration and intrusion.

In consultation with a groundwater remediation contractor, Ten Bears developed a Focused Feasibility Study to address all 3 remedy elements in synergy. The pending selected remedy consists of excavating to remove shallow contaminant sources, passive venting to control vapor migration and mitigate shallow vapor impacts without requiring costly air permitting and treatment, and in-situ groundwater remedy. Project costs~ $150,000