GEO-FORENSIC CHARACTERIZTION OF A GASWORKS DUMP AT AVENTURA, FLORIDA

In 2001, our client land developer purchased 1.1 ha. of prime real estate occupied by a 1963-era light-manufacturing plant site sold by a bankrupting company located in Ohio. The site was within a former mangrove swamp reclaimed (1955-1960) in the course of construction of Intercoastal Waterway, now new town of Aventura (formerly part of North Miami Beach). The demolished factory was to be replaced by a driven-pile-capped foundation for a mid-rise residential condominia building. The required Grading Soil Assessment revealed a two-meter blanket of Holocene-aged, calcareous sandy silt laced with tars, light tar oils, wood chips and fragments of refractory bricks of the types typical of carburetted water gas and oil-gas generating sets. The new landowner was drawn into an expensive Source Removal Action (SRA) and the wastes and associated contaminated soils were transported to an approved land disposal facility. At this point, the authors began to verify the origin and apparent source of the contamination. Much prime evidence had been destroyed by the excavation and SRA, but we discovered, along two sides of the site, a continuation of the waste blanket projecting under the adjacent properties. We examined and sampled this exposure, a continuous vertical cut of about 1.5 m in height and about 100m in length, and then compiled a face geologic map (scale of 1:12) with overlapping panoramic color photography and vertical and horizontal scale markings. Just 3.5 km distant, and also adjacent to Dixie Highway (U.S. 1) was the still extant 1924-1960 gas works of the former North Miami Beach Gas Co. (now under successor ownership). The gas works site has two parcels, one of which was accessible through an accommodation with an optioned purchaser, while the present owner utility denied us access to the other site. The accessible site parcel turned out to be, in part, an operational-era gasworks dump and also the later staging ground for a 1980s cleanup ordered by the Miami-Dade County EPA/DERM, which allowed us the freedom of inspection of its case file. We were able to make definitive “matches” for the gas-manufacturing debris/wastes, and the soils bearing the contamination at the client's construction site. Even though “aged and weathered,” the tars also proved diagnostic through MS organic fingerprinting.