Synoptic monitoring as an approach to discriminating between point and diffuse source contributions to zinc loads in mining impacted catchments

One of the global legacies of industrialisation is the environmental impacts of historic 9 mineral exploitation. Recent national initiatives to manage the impacts on ground and 10 surface waters have driven the need to develop better techniques for assessing 11 understanding of the catchment-scale distribution and characterisation of the relative 12 contribution of point and diffuse contaminant sources. The benefits of a detailed, 13 multidisciplinary investigation are highlighted through a case study focused on the 14 Rookhope Burn, a tributary of the River Wear, which falls within a significantly mine 15 impacted area of the North Pennines Orefield, UK. Zinc (Zn) has been identified as 16 the contaminant of concern within this catchment, which is judged by the 17 Environment Agency to be at risk of failing to achieve good water quality status in the 18 context of the Water Framework Directive. The results of synoptic flow monitoring 19 and sampling for chemical determinations of major and trace elements have been used 20 to calculate mass balances of instream and inflow chemical loads in the Rookhope 21 Burn. Despite a dominant impact on the water quality from a mine outburst 22 (especially Zn [1.45 to 2.42 mg/l], Fe [2.18 to 3.97 mg/l], Mn [3.69 to 6.77 mg/l], F 23 [3.99 to 4.80 mg/l] and SO4 [178 to 299 mg/l]), mass balance calculations combined 24 with geological mapping have facilitated the identification of significant, previously 25 unknown, subsurface contributions of Zn contaminated groundwater (with Zn 26 concentrations in excess of 0.4 to 0.9 mg/l and 0.18 to 0.36 mg/l) to the Burn. The 27 subsurface contributions exhibit spatial correspondence to mine workings with 28 associated mineral veins and adits, or to points of suspected karst groundwater 29 resurgence. These findings reiterate the challenges posed in decision making with 30 Page 2 of 41 respect to remediation, in this case in the context of the management of significant 31 subsurface contributions.