Impacts on groundwater quality from abandoned hydrocarbon wells - final report

This report details a reconnaissance investigation carried out between 2016 and 2018 from a British Geological Survey (BGS)–Environment Agency (EA) collaboration on the impacts of abandoned hydrocarbon (HC) wells on groundwater quality in England. The investigation involved collation of a database of HC wells that were identified from records provided by DECC (Department of Energy & Climate Change; now BEIS: Business, Energy & Industrial Strategy) as being abandoned (as opposed to operational or unspecified), categorising according to factors such as oil or gas designation, depth of HC resource, time since abandonment, productive life, absence of active wells nearby, and occurrence and type of overlying aquifer(s). From this categorisation, a subset of 27 sites were shortlisted for further investigation and fact sheets were produced for each outlining regional geology, hydrogeology and potential groundwater monitoring points in the area. Using these factsheets, four study areas were assessed as being most suitable for further field investigation. These comprised two gas fields: Nooks Farm (Staffordshire), and Ashdown (Sussex), and two oil fields: Hemswell (Lincolnshire) and Lomer (Hampshire). Groundwater sampling campaigns were conducted in 2016–2017 in the four study areas, with potential sampling points identified within a 5 km buffer zone around (downstream of) the HC well or HC field. In several areas, the number of sampling points was very limited as locations of HC wells do not necessarily have any relationship with locations of overlying aquifers. In others, large numbers of sites were deemed unsuitable for sampling, for reasons including disuse, decommissioning, safety or lack of access. This made representative sampling of groundwater a severe challenge. Suitable sites from the four study areas were sampled twice during the project, with a total of 48 groundwater samples being collected over the two campaigns. Results from both sampling rounds have shown th