Macleod, Alison Catherine; (1998) Organic matter in UK aquifers. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Natural Organic Matter: A robust sampling and storage method for dissolved organic carbon (DOC) at natural abundances involves acidifying to pH 3.00 and sparging with nitrogen gas for 15 minutes; this preserves samples at room temperature for up to one month. Concentrations of DOC in two major UK aquifers are: in the Lower Greensand aquifer of Sussex and Surrey, 0.51 ± 0.05 mg/l (range 0.459), in the Lower Greensand aquifer of Kent, 0.28 ± 0.05 mg/l (range 0.300), in the Chalk aquifer of Berkshire, 0.51 ± 0.05 mg/l (range 0.277). Concentrations of DOC do not differ significantly between the unconfined and confined parts of the aquifers, despite the fact that oxygen and nitrate reduction occurs in the confined part of the aquifers. If DOC is sourced solely at outcrop, the concentrations of DOC in these aquifers is insufficient to drive microbial reduction reactions. Redox reactions may be driven in the Chalk by iron sulphide oxidation and in the Lower Greensand by oxidation of Fe(II) in glauconite. Contaminant Organic Matter: Contaminant migration beneath a landfill site in southern England has occurred to differing extents, vertically between, and laterally within, each of the three shallow aquifers that underlie the site. Vertical contamination may have occurred mostly by leakage through seals in multi-level boreholes. Lateral migration is predominantly eastward, in the direction of regional groundwater flow, but some westward (historical) migration has occurred. Lateral migration eastward is greatest (up to 1004 metres) in the middle of the three aquifers. The lateral migration of contaminants to the nearby coastline (approximately 650 m) will take between 202 and 239 years, and hence the contaminants do not pose an immediate environmental hazard. Within the anoxic plume core, degradation occurs of many organic compounds (benzene, ethylbenzene, toluene, o-xylene, chloroform, PCE, a butyl-methyl ketone, an aldehyde and an alkyl amine), but others appear not to be degraded (TCE, p-chloro-m-cresol, bromophenol, phenol, an acetate, chloro-methyl-phenyl ether and an acetate).

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