Anatomy of a hazardous waste site in a paleosink basin

For 30 years the Brown Wood Preserving Company treated timber with creosote and pentachlorophenol, disposing waste to a three acre unlined lagoon in a paleosink basin. This basin has been naturally filled with reworked Hawthorn clays and a thin veneer of sand. The lagoon is dependent on rainfall for its water supply. A thick layer of creosote sludge had accumulated in the deepest part of the lagoon. Recent subsidence occurred along the west shore line of the lagoon. The upland areas are underlain by slightly sandy Hawthorn clays which contain extensive secondary fracturing. The Suwannee Limestone is encountered at variable depths and dips into the basin. The area is semi-artesian with regional groundwater flow to the south and southwest. Monitor wells were installed and geophysical techniques employed to determine the local geologic conditions. The monitor wells and residential wells were sampled, no creosote products were found. Water level data were analyzed and mapped. This information indicated that the potentiometric surface was relatively flat with flow lines that indicated a slight bulge in the contours under the site. Analysis of data indicated anomalies in the ground water levels and the stratigraphic column. Subsequently, additional monitor wells were installed. Sampling indicated no water quality problems. Because questions remained about groundwater flow direction, sinkhole development and recharge, another level of geologic investigation was initiated. Split spoon samples were taken and the geologic information was mapped and interpreted. Based on the new information additional monitor wells were installed. When sampled, one of the two new wells and one of the old wells was found to have creosote products present.