Risk assessment and risk communication to populations near former manufactured gas plant sites in New York City

The Consolidated Edison Company of New York, Inc. (Con Edison) has identified 50 former manufactured gas plant (MGP) sites and associated gasholder stations within its service territory, which includes New York City and Westchester County. Of the 50 identified sites, 24 lie encased within the foundations of the extensively developed and ever-changing urban landscape of Manhattan. Extensive post-war development coincided with the cessation of gas manufacturing and storage operations. Many of the former MGP sites and holder stations were sold by Con Edison and redeveloped in the late 1940s and 1950s. Current uses of these properties include residential apartment complexes, schools, and parks. Con Edison pioneered a multi-faceted risk assessment approach to prioritize and screen the sites, which culminated in a comprehensive indoor air-sampling program at schools and residential structures. The approach assessed the exposure risk at each of the properties quicker than the regulatory process could accommodate a full-site remedial investigation. Vapor intrusion was identified as a potential exposure pathway. An indoor air-sampling program was developed and a management system was devised to rapidly assess the data and communicate with stakeholders. The review team included environmental scientists and occupational physicians. Indoor air data was reviewed in the context of ambient outdoor air, soil gas, and an inventory of chemical storage within the building. The indoor air-sampling program was completed in 2004, with no increased exposure risk identified from any residual contamination present beneath the foundations at any of the residential or school properties.