St. Mildred's Tannery, Canterbury

Project Summary: Sevenoaks Environmental Consultancy recently completed several phases of a geo- environmental assessment of a former Tannery, located in Canterbury on behalf of Jubb Consulting Engineers Ltd (overall project engineers). It is currently proposed to redevelop this 3.4 Ha site for residential flats with some commercial premises by a major national property developer. Project Description: The site, which is of great archaeological significance and is located within the former City Wall, was originally developed some time before 1640 as a frontage on the northern side of Stour Street. It became a tannery in c. 1860 under the operation of J.J. Williamson and Sons (Canterbury) Ltd. In the 1880's the site expanded north onto marshland between two channels of the Great Stour River. Operations carried out at the site included the preparation and tanning of imported hides, and from 1988 the dressing, softening and dying of hides but never the finishing of hides. The site continued these operations until recently. Potential contaminants, including chloride, sulphate, ammonium, phenols, hydrocarbons and land gases, were identified from extensive previous intrusive investigations undertaken by several different companies. These contaminants originated from historic escapes of tannery effluent, historic land filling practices and hydrocarbon storage on site. Sevenoaks Environmental Consultancy reviewed the data from these investigations and updated data from a previous Desk Study to assist in the construction of an up to date Conceptual Model. Risks to receptors identified from the conceptual model included the risk to controlled waters such as underlying aquifers and the northern branch of the Great Stour River. Sevenoaks Environmental Consultancy carried out a quantitative groundwater risk assessment in accordance with the Environment Agencies R and D Publication 20 to assess the risk posed to these receptors and the need for, or degree of, groundwater remediation required. The groundwater modelling (taking into account the effects of dilution, dispersion and natural attenuation) was able to identify acceptable Site Specific Target Levels (SSTL's) for each of the contaminants of concern. The SSTL's were then used by Sevenoaks Environmental Consultancy to determine the degree of groundwater remediation currently required and to design an effective groundwater remediation scheme.