The City's Confederate Park, a park of historical significance, is located in downtown Jacksonville. The park has been impacted by operations from the former Main Street manufactured gas plant (MGP), operated from 1875 to 1913, when MGP operations reportedly ceased. Coal tar and its constituent PAHs were found in subsurface soils and groundwater. As a result, Florida Department of Environmental Protection (FDEP) NE District issued a Consent Order for Confederate Park, and the City retained Geosyntec to prepare and implement a Contamination Assessment (CA) Plan. The objective of CA was to evaluate hydrogeological conditions, define the distribution of tar and PAHs in the subsurface, characterize release/leaching potentials, predict the transport and fate of dissolved PAHs in groundwater, and provide preliminary evaluations of remedial alternatives.
Geosyntec's Scope of Services
Geosyntec initially reviewed historical MGP processes, Sanborn maps from the late 1800's and early 1900's, aerial photographs, newspaper articles, and a set of building plans for realignment of Hogan Creek (an on-site waterway) which provided key information to assist in streamlining the site investigation. We theorized that the former creek bed likely contained historical MGP waste products, and designed an expedited source investigation to evaluate this theory. CA work completed to date has included: i) extensive soil, groundwater and sediment sampling; ii) a tidal influence study of Hogan creek (an on-site waterway) and the surficial aquifer; iii) a risk-based evaluation of surficial soil data; and iv) an ecological receptor survey.
Although MGP free product residuals have been delineated on the City of Jacksonville property, the next phase of the CA will require 1) the delineation of free product that extends to at least three neighboring properties, and 2) the delineation of the dissolved plume off-site. Geosyntec has begun evaluating the feasibility of various remedial options, which include both in situ and ex situ alternatives. Selection of appropriate remedial alternatives will be complicated by the existence of a utility corridor through the impacted area.
Geosyntec conducted field investigations to evaluate subsurface lithology and evidence of staining or contaminated media. We developed a "3D solids model" using the Department of Defense Groundwater Modeling System (GMS) to estimate the volume of MGP residuals at Confederate Park. Geosyntec also used Personal Digital Assistants (PDAs) to collect data for development of the 3D model. Based on the field logs, the absence or presence of MGP residuals was imported into GMS for interpretation. We extrapolated volume estimates from the solids model, which estimated the volume of subsurface material containing MGP residuals ranged from 15,691 to 39,425 cubic yards.