Geophysical study of historical landfill at Wishingwell Park, St. John’s, Newfoundland and Labrador, Canada

The Empire Avenue landfill, approximately 3 km from downtown St. John’s, was used as the city’s official landfill from approximately 1947 until its official closure in 1963. The highly mixed waste, evidenced via photo records, was reported to be covered by soil every day in trenches. Following its abandonment, the area was eventually transformed into the present day Wishingwell Park. However, there are no detailed records about the landfill. Consequently, a thorough integrated geophysical investigation was carried out using magnetic, geoelectrical, electromagnetic and ground penetrating radar surveys to map and investigate the possible locations and extent of the buried waste. A magnetic survey was carried out over the entire park. The data clearly suggest the presence of metallic waste underneath much of the study area. There are four linear magnetic features representative of the axes of buried trenches. Six resistivity profiles were measured over the entire park. The geoelectrical results revealed numerous conductive anomalies (75-190 mS/m), mostly observed where the profiles crossed the magnetic linear features. These geoelectrical anomalies could indicate the vertical extents of the trenches with their depths ranging from about 4 m (top) to 12 m (bottom). The spatially coincidental anomalies in both methods help conclude that these anomalies are due to metallic waste, although some conductive anomalies could be from leachates and increased ground water contents in loose till. A frequency-domain electromagnetic survey was conducted over the soccer and rugby fields in the western part of the park. The lowest frequency data show significant inphase responses mostly from those regions where the anomalies were recorded for magnetic and geoelectrical surveys. A ground penetrating radar survey was conducted over almost the same area as the electromagnetic survey, with a penetration depth of about 1-1.5 m. The data indicated the existence of near-surface layers and a dipping layer in the vicinity of the strongest magnetic anomaly, likely depicting the top of the ground surface before construction of the playing fields. Thus, this integrated geophysical study found evidence of buried waste, including significant metal, over the extent of Wishingwell Park. The waste is buried in subparallel, covered trenches occurring at a depth of approximately 4 m (top) to 12 m (bottom) below the current ground surface.