Groundwater remediation is a challenging task as many existing technologies do not clean up contaminated groundwater in situ. Photocatalysis can decompose a wide range of organic compounds and in principle could be applied to in situ groundwater remediation. However, photocatalytic reactor designs are typically small in scale and generally focus on process intensification to maximise its efficiency, particularly for high flows in wastewater treatment. These compact reactor designs may not be technically and economically viable for in situ groundwater remediation. This paper aims to propose a reactor design suitable for in situ groundwater remediation and characterise it with respect to the surface area to volume ratio, aeration, flow and reliability. The surface area study showed that arranging additional immobilised catalyst radially around the UVA lamp can also enhance the reactor efficiency. The reactor efficiency remained consistent throughout 5 successive experiments with continuous aeration. Aeration is an essential component of photocatalytic oxidation and it has an immediate impact on the photocatalytic degradation. The study demonstrated that under the conditions tested, there was a critical hydraulic residence time (HRT) of 1 day (corresponding to an average water velocity of 0.21 md(-1)) beyond which the reactor efficiency can be maintained. This paper shows the potential of this reactor configuration for in situ groundwater remediation. (C) 2010 Elsevier B.V. All rights reserved.