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It is estimated that around 30,000 sites requiring active remediation are present across the UK. Amongst active remediation technologies, pump and treat (PAT) is one of the most widely used, however, its value in stimulating in-situ bioremediation is often overlooked. Using multi-level samplers this thesis provides further hydro-chemical and stable isotopic data for a plume of phenolic compounds within a sandstone aquifer which is under the effect of PAT. Analysis of this data indicates that near to the areas of PAT operation, a consistent 50%-70% decrease in contaminant concentrations is enacted. In addition, contaminant turnover is raised from < 200 mg L-1 to ~400 mg L-1 , indicating enhanced bioremediation. Enrichment of δ³⁴S-SO₄, by up to 15 ‰, is indicative that bacterial sulphate reduction (BSR) is stimulated by the PAT system within regions of reduced contamination. In contrast, further data shows that in regions where the PAT does not operate, contaminant concentrations remain high and contaminant turnover low. Furthermore, in regions where PAT ceases operation, in-situ hydrochemistry returns to pre-pumping values in less than 2 years, with contaminant turnover returning to < 200 mg/L. Data gathered from microcosm studies indicate δ³⁴S-SO₄ enrichment factors during BSR range from -6 ‰ and -10 ‰, with slightly stronger enrichment found at lower contaminant concentrations. Utilising the calculated enrichment values, an enhanced carbon balance model is created defining the proportions of BSR, methanogenesis and other respiration within separate regions of the plume. This model indicates that ~75 % of the increased contamination turnover is attributable to BSR. However, methanogenesis remains dominant in areas of high contamination due to toxic inhibition of BSR. Furthermore, an oxic/nitrate reducing fringe persists. A plume model based upon the parameters above may have applicability to contaminant plumes in the wider environment, particularly in circumstances where there is the potential for BSR and/or toxic inhibition.