Investigation of the persistence and degradability of chlorophenol and chlorophenoxy acids in groundwater

Groundwater at an industrial site near Perth, Australia, is contaminated with a herbicide/pesticide mix of chlorophenols (e.g. 2-chlorophenol, 4-chlorophenol (4-CP), 2,4-dichlorophenol (2,4-DCP), 3,4-dichlorophenol) and chlorophenoxy acids (e.g. 2,4-dichlorophenoxy acetic acid (2,4-D)). The mobility of components of the plume was investigated to determine the threat to water supply extraction wells and the nearby marine environment. Historic data for the site was collated, especially the chemical and water level data from two groundwater sampling surveys in 2000 and 2003. Plumes that were indicated from contours of the 2000 and 2003 data were compared, along with depth transects through the source areas and along the groundwater flow direction. Aquifer material was recovered from two locations for radiometric determination of biodegradation rates in the laboratory, and possible treatment options. Treatments examined included: (a) sterilised controls, (b) added glucose, (c) natural (anaerobic) attenuation, and (d) aerobic conditions. Both zero-order and first-order (half life) degradation rates were calculated. The historic and depth data indicated that the plume resides principally near the base of the Safety Bay Sand aquifer, and some of the mono-chlorinated compounds and some other compounds appeared to be persistent and have migrated further westward between 2000 and 2003. Despite some uncertainties, biodegradation/ biotransformation and attenuation of 2,4-DCP and 2,4-D was shown to occur under the simulated aquifer conditions in laboratory microcosms. There was significant inhibition of the degradation of 2,4-DCP under aerobic conditions, compared to natural (anaerobic) conditions. Degradation of 2,4-D was enhanced under aerobic conditions. Glucose addition did not enhance degradation.