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Utility Corridor Risk Assessment
Closure activities are being completed for a former manufactured gas plant (MGP) site located in northcentral Pennsylvania under the PA Land Recycling and Environmental Remediation Standards Act (Act 2). A unique aspect of this MGP site is that the historic MGP structures not only were on the on-site property, but also extended across the adjacent street and onto the opposing property owned by a separate entity. Investigative activities that were conducted within the adjacent street and opposing property verified the presence of MGP-residual material from the historic MGP structures. A major piece of the risk assessment for this site included the evaluation of the utility corridor within the adjacent street.
There were existing utility lines within the eastern side of the street (adjacent to the site) and a scheduled project for the western side of the street to extend a force main sanitary sewer line. Therefore, the risk assessment included in part the evaluation of potential construction/utility workers who may excavate within the utility corridor to repair or maintain the existing/future utilities. Accordingly, a dual construction worker and utility worker scenario was evaluated.
Therefore, in order to assess the utility corridor adjacent to the site, the characterization data along the property boundary was conservatively utilized in the risk assessment, while discrete sampling was completed along the western side of the street to delineate and “clear” a utility corridor for the new force main.
As additional information regarding the plans to install the force main became available, the original direction of the force main changed and was re-directed off of the street and onto the opposing property within an easement area before crossing over a bridge. Additional investigative activities were completed within the easement area to “clear” this part of the utility corridor. Subsurface structures from the historic MGP facility were encountered during the investigative activities, and part of these structures were removed to make room for the force main. Therefore, a third quantitative risk assessment was completed for a construction worker and utility worker within the easement area.
Because of the complexity of this project, significant communication with several organizations was necessary, including the local municipality, sewer authority and several property owners. In order to complete this portion of the project successfully, the conceptual site model was repeatedly refined through an intricate iterative process to complete the risk assessment.