Historic mining processes were inefficient and unregulated, leading to a legacy of pollution in fluvial systems in formerly mined areas of the UK. Wales is no exception, the Water Framework Directive (WFD) and Natural Resources Wales (NRW) identified 50 sites of concern requiring remediation in the Metal Mines Strategy for Wales (MMSW) which are demonstrating legacy pollution of Potentially Harmful Elements (PHEs) and are failing water quality standards. In 2016 NRW stated that they are aiming to achieve good ecological status by 2027 using remediation techniques at 50 metal mine sites. The 50 mines have been identified as the worst polluters inputting 200 tonnes of Zn, 32 tonnes of Cu, 15 tonnes of Pb and 600 Kg of Cd to environment on annual basis. To achieve this accurate assessment of water quality variation and remediation requirements would be required. Previous studies on water quality impacts from legacy metal mines have only evaluated data of short-term snapshot metal concentrations or fluxes and associated hydro-climatic conditions. This paper will aim to evaluate the temporal variability of water quality in response to hydro-climatic controls at a range of monitoring resolutions and evaluate the potential effectiveness of current and future mine water treatment schemes. The study will use the mine sites of Parc mine and Cwm Rheidol mine. The study utilized remote data loggers to monitor hydroclimatic and chemical conditions at each mine site supplemented by analysis of anion and cations via ICP-OES and ion chromatography to assess PHEs and define temporal and spatial variation in water quality. Hourly monitoring highlighted the potential for underestimated PHEs loads demonstrating an increased PHE load of 36.1% in comparison to weekly monitoring. This was due to diel cycling that was identified at Parc mine exemplifying increased PHE concentrations during night-time periods. The study found Zn and Cd to be the primary cause for concern at both mine sites, failing water quality standards with concentrations that exceed guidelines defined by the WFD (The Water Framework Directive, 2015). The current passive remediation system in place at Cwm Rheidol was found to be 75.9% effective for Zn, the effectiveness varied temporally with changes in discharge. The study identified hydroclimatic variability to have a significant effect on water quality. The study highlights the requirement of high-resolution hourly monitoring to aid accurate load calculations to enable identification of the correct remediation system to manage PHE concentration reduction in light of a temporally varied PHE load.