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 that the presence of hydrocarbons in the groundwater
is limited. In the first sampling round, a maximum dissolved methane (CH4) concentration of 407 μg/L
was recorded. However, this relatively high value was not repeated when the site was visited during the
second round of groundwater sampling. The value was below the threshold required for δ13CCH4 isotopic
analysis. Some groundwater samples showed detectable quantities of organic compounds including
VOCs (volatile organic compounds) and PAHs (polycyclic aromatic hydrocarbons) as well as
pesticides, herbicides, fungicides, surfactants, analgesics and veterinary compounds. These were,
however, almost invariably present in low concentrations, none could be linked unequivocally to the
presence of abandoned HC wells and many were clearly due to other anthropogenic activities.
As a result of the difficulties finding representative and suitable groundwater sampling sites, a further
reconnaissance was undertaken in May 2017 to identify potential alternative gas and oil fields. This
confirmed further the difficulties in finding suitable areas for investigating groundwater quality and
further groundwater sampling was therefore not attempted. An alternative approach was used to
investigate two abandoned HC well areas: Ashdown, one of the original study areas, and a new location
at Bolney (also Sussex). A soil gas survey was completed at each of these locations in order to
investigate whether soil gas proximal to the former well location contained any evidence of HC leakage.
Due to poor ground conditions at the time of sampling, the results are ambiguous, but do show elevated
concentrations of both CO2 and CH4. Further work in dry ground conditions would be required to say
with certainty that these concentrations are linked directly to the presence of the gas wells