St Michael’s Jubilee Golf Course in Widnes was constructed between 1964 and 1986, by re-grading chemical waste deposits generated from local industries, which were then covered with a thin layer of topsoil and grassed over. An estimated 4.5 million tonnes of waste materials are present beneath the golf course. The site is underlain by alluvium and a major aquifer, the Sherwood Sandstone. The alluvium and Sandstone aquifers are thought to be separated by boulder clay, the thickness of which beneath the site has not been proven. Arsenic on the site presented a human health risk to site users, visitors and site workers.
Jacobs was undertaking remediation assessment and design works, part of which was a requirement to address human health risks arising from high concentrations of arsenic in shallow soils on the golf course. ESI was asked to provide a sensitivity analysis to the human health risk assessment in order to select remediation targets which were protective of human health, but not unduly conservative.
ESI’s tasks were to design further soil sampling, assess the arsenic concentration data and obtain an appropriate human health screening value for the remediation design. Arsenic soil results were obtained during a shallow hand auger investigation.
Analysis of the data was undertaken using a software tool developed by ESI, released with the latest Defra guidance. This new guidance for the comparison of soil contamination data with assessment criteria replaces the CLR 7 guidance. ESI staff are principal authors of the guidance, which sets out a formal statistical approach for assessing contaminated land, in order to determine with a quantitatively estimated level of confidence whether a site is contaminated. ESI’s software tool has been thoroughly tested and confirmed to accurately perform all the tests that the Defra guidance relies upon.
On the basis of the actual arsenic concentrations, the presence of clay and the presence of chemical waste, three geographic zones with distinct arsenic concentration ranges were identified. Four hotspots were also identified, which required further delineation, through sampling. Zone 2, comprising about one third of the golf course, was un contaminated and suitable for continuing use without remediation. Analysis found that zones 1 and 3 were, on the balance of probabilities, contaminated. Further sampling was recommended to provide a higher degree of confidence in this conclusion and to focus remediation efforts.