Over a period of decades a former lagoon was used for disposal of used oils (i.e., waste oil), which previously was operated as a sand quarry. The accumulation of waste oil not only displaced water within the lagoon, but also penetrated the surrounding aquifer given the heightened elevation of oil in the lagoon relative to the aquifer groundwater elevation.
Active dewatering around the former lagoon prior to remediation via excavation further increased penetration of oil into the surrounding aquifer. Following remediation, a ring of light nonaqueous phase liquid (LNAPL) remained around the former lagoon caused both by historic waste operations within the lagoon and also the smearing caused by dewatering operations during its removal. Multiple conventional investigations have been completed over the history of the remediation including: groundwater monitoring and sampling, soil borings, monitoring and recovery wells, confirming the ring-like lateral distribution of the LNAPL. More recently laser induced fluorescence (LIF) was used to aid and enhance understanding the vertical distribution. Using a combination of observations during drilling, temporal LNAPL and groundwater gauging, soil lithology, photoionization detector (PID) and flame ionization detector (FID) readings, LNAPL physical and chemical properties, and LIF, a detailed understanding of the LNAPL conceptual site model (CSM) was developed. One piece of data on its own was not able to define the LNAPL CSM; rather, a multiple lines of evidence approach was necessary to best understand the complex LNAPL distribution caused by historic Site operations, heterogeneity caused by fill and reworked land within the former lagoon, and variability of the LNAPL. The LNAPL CSM incorporated 20 years of historic data supplemented with more innovative characterization tools to define both the lateral and vertical extents of the LNAPL body. The LNAPL CSM is being employed with current remediation activities to aid in timing of the LNAPL extraction system during ideal seasonal water table elevations.
- Geosyntec Authors: Derek Tomlinson
- Title: Comprehending LNAPL Body Distribution at a Former Waste Oil Facility Through Multiple Lines of Evidence
- Event or Publication: 39th Annual International Association of Hydrogeologists Congress
- Practice Areas: Groundwater Assessment and Remediation
- Date: 2012
- Location: Niagara Falls, Ontario