Impact of farm waste stores on groundwater quality. Final report

Gooddy, D.C.; Hughes, A.G.; Armstrong, A.C.; Williams, A.T.; Griffiths, K.J.; Nicholson, R.A.; Williams, J.W.; Jones, H.K.; Chilton, P.J.. 2000 Impact of farm waste stores on groundwater quality. Final report. British Geological Survey, 92pp. (WD/00/009) (Unpublished)

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This report details the findings of a three year study into the impacts of farm waste stores on groundwater quality. This is a joint project between the British Geological Survey and ADAS and began in April 1997. Funding has been from the Ministry of Agriculture, Fisheries and Food, Environment, Fisheries and International Science Division, under contract number WA0517 as part of their ongoing research and development programme into farm wastes. Unlined earth-banked farm slurry stores pose a particular threat to groundwater since recent research suggests that the waste and its constituents is able to leach from the bottom of these stores. After investigating a potential 68 sites, we have undertaken a detailed field programme at 3 sites on the Chalk and 5 sites on the Permo-Triassic Sandstone, the two principal aquifers in the UK, beneath unlined slurry stores. Seven of the sites (2 Chalk and 5 Permo-Triassic) concentrated on unlined cattle slurry lagoons whilst one site examined the effects of a turkey manure store. Boreholes were drilled at an angle of 45° so as to obtain material from directly beneath the stores at several of the sites. In addition, a vertical hole was often drilled adjacent to the slurry stores so as to assess the degree of lateral spreading. Vertical boreholes were also drilled through the centre of the turkey litter store since the management of solid manure heaps left a period of the year where the storage area was free from waste. Cores from the boreholes were centrifuged so as to extract the interstitial waters and selected samples were taken for microbial examination. At one Sandstone site and one Chalk site, specially designed gas samplers were installed beneath the slurry lagoons to investigate the aquifer gas composition. Cores taken from beneath the two cattle slurry store Chalk sites showed visual staining from slurry material along fracture faces in the rock. In addition, porewaters from all of the Chalk sites and one of the Sandstone sites showed distinct coloration. These samples showed very high concentrations of nitrate, ammonia, organic carbon, potassium and chloride. The cores taken from beneath two cattle slurry lagoons situated on Chalk exhibited different chemical characteristics with the inference that the least contaminated of these two had formed a sealed base. Gas samplers installed at this Chalk site showed very high rates of denitrification. The physical and chemical properties of the different aquifers were also shown to impact on contaminant movement and attenuation. Microbial studies showed contamination from clostridia in all of the sites studied, however this contamination extended to a depth of 18 m in the two Chalk sites beneath cattle slurry lagoons. Cryptosporidia was found in cattle slurry from five sites, whereas E.coli O175 was found in cattle slurry from just one of the six sites tested for these pathogens. Neither Cryptosporidia nor E.coli O157 was found in any of the rock samples taken for microbiological examination. This may however relate to the small sample size and limits of detection rather than their absence. Taking data obtained from the field site investigation, we attempted to model mathematically the impact on local groundwater concentrations as a result of a leaking farm waste store. Modelling studies showed that concentrations in theoretical nearby production boreholes would be expected to rise only very slightly, typically by 0.5 mg/L for nitrate. Two maps assessing the risk to the principal aquifers in England and Wales have been generated by overlaying the volume of slurry stored in a given region over the aquifer outline and combining this with either the HOST classification system of soils or the geological drift map. These maps identify the Chalk outcrop of the Dorset and small parts of the Permo-Triassic Sandstone in the West Midlands as the regions most at risk from farm waste stores. Areas with a shallow water table are also considered to be at higher risk to groundwater contamination from unlined slurry lagoons.

Item Type: Publication - Report
Programmes: BGS Programmes > Groundwater Management
Funders/Sponsors: NERC
Additional Information. Not used in RCUK Gateway to Research.: This item has been internally reviewed but not externally peer-reviewed
Additional Keywords: GroundwaterBGS, Groundwater, Point source pollution
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Date made live: 14 Dec 2010 09:57 +0 (UTC)

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