Distribution and Transportation of Coal Tar Contaminants in the Chattanooga Creek Floodplain

In Chattanooga, Tennessee, tens of thousands of tons of coal tar were disposed of in Chattanooga Creek during operations of the Chattanooga Coke Plant (1918-1987). Coal tar is composed of thousands of organic compounds, which span a wide range of molecular weight. Many of these compounds are polycyclic aromatic hydrocarbons (PAHs) and are known carcinogens. Chattanooga Creek is an urban creek, which runs through the southern part of the city of Chattanooga and is surrounded by industrial development, residential neighborhoods, parks, and schools. Due to the hazardous nature of coal tar and coal tar constituents, portions of the creek and the adjacent floodplain have been placed on the National Priority List for Superfund Sites (U.S. EPA, 1999a; U.S. EPA, 1999b; U. S. EPA, 1999c). The focus of the research described in this thesis is to assess the influence of flooding on redistribution of PAHs, which are an integral part of coal tar, from the creek-bottom sediments of Chattanooga Creek. Specifically, we hypothesize that creek bottom sediments contaminated with PAHs and related compounds are re-suspended during flood events and deposited in the floodplain. To test this hypothesis soil core samples were extracted, from depths of up to 189 cm, at two transects located in the floodplain approximately 0.5 and 1.0 Km downstream of the coke plant, to determine the distribution and concentration of coal tar contaminants, and to assess transport processes. Petrographic analyses indicate the presence of trace amounts of small (\u3c 2 mm) fragments of coal, slag, and possible solidified tar in the floodplain sediments. These fragments are likely from the coke plant or from other industrial sites along the creek. Sediment age dates, based on 137Cs measurements, indicate that the floodplain soils are relatively young and that depositional rate ranges from 0.7-2.0 cm/yr. Concentrations of the 16 US EPA Priority Listed PAHs in the sediments were measured by extracting the PAHs with a Soxhlet Extractor and analyzing the extract with a Gas Chromatograph coupled with a Mass Spectrometer. The results indicate the PAHs are widespread and concentrations are relatively high, ranging from total PAH (tPAH) concentrations (for the 16 priority compounds of 0 – 1,950 mg/Kg of soil. The zone of high tPAH concentration extended from ground surface to depths of 22 to 87 cm with generally greater contaminated thickness occurring nearest the creek. The only exception was one core, where tPAH concentrations decreased with depth, then sharply increased due to the presence of large amounts of immiscible coal tar (possibly due to local dumping of tar on the floodplain). Thickness of the zone of measurable 137Cs (indicative of post-1959 deposition) is less than the thickness of the zone of PAH contamination and also decreases with distance from the creek. This indicates that deposition of PAH contaminated sediments is ongoing and its onset pre-dates the 1959 occurrence of 137Cs in the atmosphere, as would be expected if the coke plant was the principal source of PAHs. The widespread occurrence of PAH contamination in the floodplain sediments without corresponding widespread tar occurrence, suggests that PAHs from the tarry-stream bottom sediments are sorbing to non-tarry sediments (mineral and organic matter) in the creek prior to being entrained during flood events and deposited in the floodplain. It is expected that flooding may be an important mechanism for transporting PAHs into floodplains at many other sites where coal tar or related compounds occur in stream bottom sediments