A former manufactured gas plant (MGP) facility located in Valdosta operated between the late 1800s and the early 1950s. An area of concern (approximately 50 acres in total) that was affected by activities at the former MGP facility encompassed the property and several nearby properties. Potentially affected habitats included upland, wetland, and aquatic areas. Drainage from the entire site concentrates in a beaver-dammed cypress swamp, then flows eastward onto adjacent property where it joins a perennial stream. A preliminary assessment and remedial investigation were conducted on the site to assess those releases. Assessment investigations delineated the extent of chemicals of potential concern (COPCs) by collecting and analyzing samples of surface soil, subsurface soil, and groundwater. Site-specific COPCs included volatile organic compounds (VOCs), semi volatile organic compounds (SVOCs), metals, and cyanide. Several VOCs were found in concentrations that exceeded background. SVOCs exceeding background concentrations were limited to polycyclic aromatic hydrocarbons (PAHs) and phenols. Geosyntec was retained to conduct an ecological and functional assessment of the wetland.
Geosyntec's Scope of Services
Geosyntec identified ecological receptors of concern in the study area via surveys of available habitat, animal observations, and signs of animals such as tracks, nests, middens, droppings, etc. We determined that upland areas posed little risk to terrestrial receptors due to lack of wildlife habitat and known low concentrations of COPCs. As determined by ecological screening criteria and areas of known COPC concentrations, we selected fish, amphibians, and raccoons as assessment endpoints in the evaluation. Geosyntec also described an unusually diverse community of amphibians for the wetland site via on-site ecological surveys. We documented no threatened or endangered plants or animals on or near the site.
Geosyntec subjected sediments to arsenic speciation analyses to determine whether available concentrations of oxidized arsenic would pose a higher ecological risk in a reduced state during periods of wetland inundation. We also subjected surface water and sediments from areas of higher COPC concentrations to aquatic toxicity testing.
We used the toxicity and sediment test results, combined with ecological risk-based determinations, to design an isolated removal of contaminated sediments. Significant contaminant mass removal was achieved through mechanical excavation of a relatively small volume of sediment. Significant risk reduction was achieved while at the same time preserving the important hydrologic function and ecological value of the site wetlands.