INVESTIGATION OF A SOLVENT POLLUTED INDUSTRIAL SITE ON A DEEP SANDSTONE MUDSTONE SEQUENCE IN THE UK .2. CONTAMINANT SOURCES, DISTRIBUTIONS, TRANSPORT AND RETARDATION

A single industrial site has been investigated in detail to gain information on sources and movement of chlorinated hydrocarbon solvent (CHS) pollutants in groundwater under the industrialized city of Coventry in the UK. A soil gas survey identified the most polluted area of the site where two types of investigation borehole were drilled; open boreholes lined with plain and slotted casing, and a single dedicated borehole incorporating gas samplers and gas-driven water samplers. Specially designed sampling techniques using pumps and packers were employed to determine vertical pollution profiles in the open boreholes. Core material was collected for sorption and diffusion experiments. An assessment of field investigation procedures suggests that soil gas sampling is a useful method for reconnaissance surveying of pollution by volatile organic compounds, but the results reflect only shallow pollution in the vertical profile. Open boreholes were found not to be satisfactory for accurate groundwater profile sampling and dedicated boreholes are recommended for such studies. Many uncertainties are involved in such a study of solvent pollution owing to the limited number of boreholes drilled and the complex spatial and temporal variations of pollutants. Despite the limitations of the investigation, several useful conclusions are drawn concerning sources and movement of solvent pollution. The main pollution source at the site is identified as the solvent storage tanks and pollution has resulted from poor use practices. Vertical pollution profiles indicate that the downward migration of 1,1,1-trichloroethane is following that of trichloroethene, reflecting their history of use on the site. The overall quality of groundwater abstracted in the system is set to deteriorate, as high pollution loads, presently at shallow levels in the system penetrate deeper, little attenuated by sorption or degradation. Diffusion of pollutants between mobile fissure and immobile pore waters will result in poor quality groundwater under this site for the foreseeable future. This trend is expected to be reflected throughout the urban area as a whole, with most groundwaters falling below drinking water standards for CHSs.