Estimation of PCB contamination in the Twelve Mile Creek arm of Lake Hartwell using GIS and statistical techniques.

摘要

The Lake Hartwell and its Twelve Mile Creek watershed were contaminated with polychlorinated biphenyls (PCBs), mainly Aroclor 1016 and 1254, which resulted in a designation as a Superfund site. The Twelve Mile Creek arm is the most heavily contaminated portion of the lake. The Twelve Mile Creek arm of Lake Hartwell was placed on the National Priorities List (NPL) in the year 1990. In the Record of Decision (ROD) by the EPA in 1994, natural attenuation, primarily through burial by uncontaminated sediment, was declared as the chosen remedy to reach the EPA recommended level of 1 mug/g. Several studies have aimed at understanding the concentrations of PCBs in the sediments and the time required for the concentrations to reach the EPA recommended level. This thesis focuses on documenting results of previous and current contamination levels by Geographic Information System (GIS) modeling to predict when the target sediment concentrations will be reached through statistical techniques.;Results from historic (SD points) sampling points were consolidated on a base map in ArcGIS 10.1. From the historic data, it was observed that the average concentration of the entire study area decreased between 1996 and 2013 due to a number of factors with the average concentration in the year 2013 less than 1mug/g. The concentration at SD011 was the highest through the years with its concentrations considerably higher than the EPA recommended level.;Least squares linear regression was performed on the historic data and was integrated on a GIS map to perform spatial interpolation. Inverse distance weighting interpolation (IDW) in ArcGIS was used to estimate PCB concentrations in areas of the lake arm that have not been sampled. The results indicated a decrease in overall PCB concentration with most areas in the lake reaching the EPA recommended level. However, the removal of Woodside-I and -II dams in 2011 increased the PCB concentrations in the lake with the average PCB concentration of the lake increasing after the dam removal.;The top 10 cm of sediment samples from five new points (named BH) and G-30 were collected to perform particle size analysis on each of the sample. Particle size analysis (PSA) was another estimation technique which was used to estimate the concentration of PCBs at the site based on particle size of the top 10 cm at each sampling location. Results of particle size analysis of BH points were incorporated in ArcGIS 10.1 and spatial interpolation was performed to predict the concentration in the entire arm of the lake. Using PSA, the concentration at G-30 was predicted to be 4.75 mug/g which was more than its concentration of 3.0 mug/g as measured previously in 2004.;Finally, the PCB concentration in the top 10 cm at each BH sampling point was measured by gas chromatography (GC) techniques and compared with the results predicted by the regression and the particle size analysis techniques. A total of 128 congeners distributed over 84 peaks were accounted for in calculating the total PCB concentration at each location. The highest concentration of 3.76 +/- 0.12 mug/g was reported at location G-30 which showed an increase in PCB concentration at G-30 compared to 2004. Overall, particle size analysis established a trend of PCB distribution throughout the lake which was validated by the measured concentrations and proved to be a good estimation technique for the prediction of PCB concentration in the collected samples.