Abstract:The hydrogeochemistry of shallow groundwater has been characterized in the Allt a' Mharcaidh catchment in the Scottish Cairngorms in order to: (i) assess the spatial and temporal variation in groundwater chemistry; (ii) identify the hydrogeochemical processes regulating its evolution; and (iii) examine the in¯uence of groundwater on the quality and quantity of stream¯ow. Shallow groundwater in super®cial drift deposits is circumneutral (pH $ 7 . 1) and base cation concentrations are enriched compared with precipitation and drainage water from overlying podzolic soils. Modelling with NETPATH suggests that the dominant geochemical processes that account for this are the dissolution of plagioclase, K-feldspar and biotite. Groundwater emerging as springs from weathered granite underlying high altitude (4900 m) alpine soils shows similar characteristics, though weathering rates are lower, probably as a result of reduced residence times and lower temperatures. Chemical hydrograph separation techniques using acid neutralizing capacity (ANC) and Si as tracers show that groundwater is the dominant source of base¯ow in the catchment and also buers the chemistry of stream water at high¯ows: groundwater may account for as much as 50±60% of annual runo in the catchment. Climate and land use in the Cairngorms are vulnerable to future changes, which may have major implications for hydrogeological processes in the area. #

Polluted discharges from abandoned mines are a major cause of freshwater pollution in central Scotland, often contributing high Fe, SO 4 2- and acidity to receiving streams. The Central coalfield has been extensively mined for over a century and Polkemmet was the last colliery to close in 1985. Recent monitoring indicates that the rate of groundwater recovery is approximately 0.15 to 0.2 m per week. Without intervention, this trend would result in complete recovery by 2000 and probable discharge into the River Almond. Geochemical modelling indicates that pyrite oxidation, calcite dissolution and goethite precipitation are primarily responsible for the evolution of groundwater chemistry currently observed at Polkemmet. Predictive modelling using PHREEQE suggests that unregulated minewater discharges will have marked effects in the River Almond, with goethite being initially precipitated at a rate of up to 36 kg/day, dissolved sulphate concentrations ranging between 170 and 800 mg/l and pH being depressed to 6.5. Combined active lime flocculation and passive aerobic wetlands may be the most effective means of treating the predicted minewater discharges. Keywords: abandoned mines, hydrochemistry, surface water, underground mining, water quality

Groundwater resources in Scotland are receiving increasing attention because of the high costs of surface water treatment and the stringent water quality requirements of the EC Drinking Water Directive. On the River Spey, a unique abstraction scheme has been developed, involving a wellfield comprising 36 production boreholes in the river gravels of the lower catchment. The scheme aims to provide a maximum of 27 000 m 3 /d to meet increasing water demands in northeast Scotland by 2011. This yield is equivalent to one-third of the current total public groundwater abstraction in Scotland. This paper describes a steady-state quasi-three-dimensional numerical model of the Spey river-aquifer system which was used in conjunction with a particle tracking program to delineate travel time related capture zones of the Spey abstraction wellfield. Three scenarios were simulated: pre-development, current pumping rate (16 000 m 3 /d) and projected maximum pumping rate. The pre-development water budget indicates that 940f total groundwater inflow is discharged into the river, whereas the budgets for stressed conditions give the percentage of water abstracted from the river as 69% and 74 0.000000or current and maximum pumping rates respectively. Capture zones of 50-day (Zone 1) and 400-day (Zone 2) travel time to the wellfield are defined for the projected maximum pumping rate. These indicate that the river itself is the primary potential polluting source. However, extensive areas of the river floodplain also contribute significantly to the abstraction, thus certain restrictions on potentially polluting activities are needed. It is concluded that rigorous programmes for monitoring water quality both in the river upstream, and within the modelled catchment are required to protect the Spey Abstraction Scheme.

The Lower Old Red Sandstones in northern Strathmore have favourable hydrogeological conditions for ground‐water development. A scheme was proposed to abstract water in the north Esk catchment in order to augment water supplies to local villages, and a production borehole was drilled into the Edzell Sandstones to give a design yield of 2420 m3/d. However, this scheme has been abandoned because of concern that the abstraction would significantly reduce the flow in a nearby stream which is an important salmonid fishery. This study demonstrates the potential value of using a stream‐aquifer numerical model in an environmental risk assessment for the proposed scheme.