Review of data relevant to the characterisation of leachate from Burgess Field waste dump, Oxford

White, D.; Macdonald, D.M.J.. 2015 Review of data relevant to the characterisation of leachate from Burgess Field waste dump, Oxford. Nottingham, UK, British Geological Survey, 136pp. (IR/15/037) (Unpublished)

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This report provides a summary of data available for the Burgess Field waste dump, Oxford. These include historical data records held by the Oxford City Council for free gas concentrations, selected inorganic chemistry and groundwater levels (between 1989 and 1996). They also include inorganic chemistry and groundwater levels collected from selected piezometers by the British Geological Survey at the site since 2011. These data are used to characterise the leachate in groundwaters within and below the dump, addressing spatial variability and long term changes. Burgess field is an unlined historical waste dump located on the floodplain of the River Thames on the eastern side of Port Meadow, in the vicinity of the city of Oxford. The waste dump was closed in 1980 and the area is now a mixed grassland and woodland nature reserve. Subsequent monitoring of the site included a network of seven boreholes installed into the waste dump in 1991; of the seven original sites, only three could be located for the field campaign from 2011 onwards. Groundwater levels at Burgess field exhibit spatial and temporal variability and have been found to rise above the base of the dump at some borehole locations, producing a saturated zone within the waste material. There is potential interaction of leachate with groundwater under all of the waste material as the dump is unlined. Uneven settling and the heterogeneous composition of waste is highlighted by spatial and temporal variation in the dissolved gas, groundwater level data and the inorganic chemistry. Free gas concentrations between 1989 and 1996 show the following: • CO2 and O2 are highly variable and mirror each other at all sites; where one increases in concentration the other is seen to decrease in concentration • Methane concentrations are variable: there was no methane detected in the southern sites; methane was detected in the northern sites, indicating the occurrence of methanogenisis, apart from the most northerly site where is has not been detected. Long term trends in inorganic chemistry for the three sites that were sampled during both the 1990s and the 2010s show: • Spatial variation in the concentrations of Fe, Mn and B is maintained across the two sampling periods; • Conductivity is generally higher in the current period than during the 1990s, reflecting higher SO4 and HCO3 concentrations; • Dissolved N concentrations vary spatially and temporally but the reduced form of nitrogen (NH4) is dominant. Concentrations of NH4 were high during the two periods of study showing a large plume of NH4 below/within the landfill. In summary, this points to a heterogeneous waste dump where fill is spatially variable in composition, and breakdown of the material is at different stages. This reflects the long period during which waste was dumped in the area (1930s-1980) and the potentially varied nature of this material, for which there is very limited information. The data collected on Burgess Field shows: it is a source of pollution in the form of NH4, SO4, Fe, and Mn; that conditions are anaerobic; and HCO3 concentrations are buffering the pH so acidic conditions are not occurring.

Item Type: Publication - Report (Technical Report)
Funders/Sponsors: British Geological Survey
Additional Information. Not used in RCUK Gateway to Research.: This item has been internally reviewed, but not externally peer-reviewed. Report made open by authors in March 2021.
Additional Keywords: GroundwaterBGS, Groundwater
Date made live: 04 Mar 2021 15:20 +0 (UTC)

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