Blended Cover Treatability Study: Activated Carbon Performance

Chemical contamination is a major environmental concern that deteriorates ecosystems and human health alike. Leakage and poor management of chemical process plants where pesticides are or were produced are a prime example, such as the United Heckathorn Superfund site located in the San Francisco Bay area whichcreate disturbance in marine ecosystems. The risk in the harbor rises primarily from dichlorodiphenyltrichloroethane (DDT), a highly stable, carcinogenic, organic compound whose production was banned decades ago. However, improper management and abandonment allowed DDT to contaminate the surrounding land and marine ecosystem. DDT’s hydrophobic properties suggests it should concentrate in the sediment reducing bioavailability, however, DDT concentration has remained high in the water due partially to natural water flows. Furthermore, persistent boat activity such as from tugboats continuously uplift contaminated sediment allowing mixing with the water above, maintaining a hazardous environment for wildlife and humans alike. Previous efforts to clean up the site included dredging up the contaminated sediment, which failed to significantly reduce DDT contamination in either the water or sediment layer. Therefore, a new engineering solution is required. Research is focused on creating a blended cover which will further reduce DDT’s bioavailability in the marine harbor ecosystem. The blended cover, a mixture of gravel and activated carbon, can be placed on top of the sediment layer. To test activated carbon’s performance to attract and sequester DDT from the water, aquarium tank experiments simulating similar conditions to those in the bay area were constructed in which the activated carbon and gravel size were varied. After a month, a passive sampler was used to test DDT concretion at different layers. Utilizing a Gas Chromatography-Electron Capture Detector (GC-ECD), presence and concentration of DDT and its derivatives was analyzed in different blended cover conditions. Preliminary analysis suggests that the smaller the activated carbon and gravel size, the better performing the blended cover will be at removing DDT. Moreover, physical tests are ongoing to test the erodibility of different blended cover mixtures. Research into alternative clean-up techniques for contaminated sites is of great value for ecosystem remediation where much improvement is left to be made.