The 428-acre Paoli Rail Yard site is a maintenance, storage, and repair facility located north of Paoli in Chester County, Pennsylvania. The site consists of the 28-acre rail yard and the surrounding 400-acre watershed. The site, which is mainly wooded, is bordered to the north by residential areas and to the south by commercial developments. Since 1915, the rail yard has provided general maintenance and repair support for rail cars. The site operates five track areas used for multiple rail lines, a power house, a freight house, and a repair shop. Prior to 1968, the site was owned by Pennsylvania Railroad, after which it changed hands several times.

Contamination of the soil in and around the car shop is attributed to releases of fuel oil and PCB-laden transformer fluid from rail cars during maintenance and repair activities. In 1985, EPA identified PCB contamination in soil and sediment, and on building surfaces. The rail companies agreed to address site clean-up activities, including erosion, sedimentation, and storm water characteristics and control, decontamination, soil sampling, excavation of 3,500 cubic yards residential soil and implementation of worker protection measures. Further EPA investigations identified soil samples in and around the car shop, parallel to the rail tracks, and 10 feet below the facility that were contaminated by fuel oil in the form of benzene, toluene, ethylbenzene, and xylenes (BTEX). Sediment samples taken from the three creeks that drained the general rail area also showed PCB contamination decreasing further from the rail yard. Soil samples taken from residences lying adjacent to the facility identified topsoil contamination presumably resulting from soil erosion from the rail yard.