Mining has serious environmental impacts including effects on water quality. Slate quarrying is
neglected as with regards environmental impacts in the literature. Specifically, the geochemical effect
of slate quarrying on water is an under-researched field. The effects of climate change may have
future impacts with regards mining perhaps worsening any effects. Two metals which are of prime
importance in this dynamic are Aluminium (Al) and Copper (Cu), which are found to be the most
enriched in the river Barlwyd, they are also the most toxic to aquatic life. This thesis explores the
geochemistry, hydrology, sediment effects and remediation in the Ffestiniog area, an area
synonymous with historical and current slate mining.

The first aim was to quantify the temporal and spatial pollution of Al/Cu from slate quarrying on the
rivers Barlwyd and Bowydd in line with the European Water Framework (EWFD) guidelines. This
involved a yearlong study which was completed to establish a baseline. Samples were taken at 20
different sites throughout the year during different weather conditions. On the Bowydd concentrations
of Al were 0.0015-0.8698 mg/L. Sample concentrations ranged for the Barlwyd ranged between 0.020
mg/L at B1 and 21.2656 mg/L at B12 and were spatially dependent. pH ranged between 3.4 at B12
and 7.62 at B1. Turbidity was negligible. Geochemical parameters were correlated to metal
concentrations. This demonstrated that slate quarrying influences river water quality. This effect is
most pronounced in the summer months when metal sample water concentrations are at their peak, as
the water is more concentrated due to water availability. Geographically, Al and Cu were found to be
enriched in the river Barlwyd and in the river Bowydd near sources of slate pollution/slate tips. Al/Cu
also showed a temporal pattern of expression in this riverine environment, with higher concentrations
in summer months when there was less rainfall. Al and Cu concentrations found by this research place
the river in this area are poor status as with regards to the EWFD and are outside guidelines.
Geochemical parameters also showed extreme tendencies, with low pH and high
electroconductivities, outside recommended guidelines. Flux illustrated heavy loads on the river,
explaining the poverty of aquatic life found in the river. It is concluded that slate mining has a
significant impact on the river water quality.

Chapter 4 in this study aimed to establish the influence of storm-driven hydrological change on Al/Cu
concentrations and associated aqueous geochemistry of the of the Afon Barlwyd. Samples collected
from 20 sites during storm events, showed an initial increase in Al and Cu concentrations (Site B4
0.319 mg/L and Cu 20.2 μg/L, Site B12 8.563 mg/L and 216.64, Site B14 0.0265- 0.0544 mg/L,
1.7523-2.72) and increase in pH to circa neutral levels over the course of the storm. This is evidence
of a flushing effect, and as the storm progresses there is a physical dilution. Concentration: time
relationships during the storm events demonstrated a clockwise hysteresis relationship, indicating that
it could be as Doty and Carter (1965) claim that that the material decreases because of hydrological
processes, or as Novotny (1980) suggests that the decrease in rainfall levels in the storm retreat means
there is less polluted material carried into the water channel. Eh/pH relationships indicate that the
speciation of Cu and Al are found in free ion states, suggesting it is more toxic to aquatic life. The
key overall conclusion is that storms have a negative effect on aquatic life in the river as a flush of
material causes toxicity from quarrying activity.

The aim of Chapter 5 was to estimate the sorption/desorption of the metals Al/Cu from sediment into
the dissolved water fraction. The end goal was to work towards establishing better guidelines for the
EWFD, by estimating the relative contribution of slate quarrying sediment to the Al/Cu load in the
river. To examine the effect of sediment on the river water in the Barlwyd, sediment – aquatic phase
exchange experiments modelling natural conditions were conducted. The study showed ambiguous
results between sites and temperature and there was no overall clear pattern as there could sometimes
be absorption and sometimes be desorption. This study indicated that sediment was not enough to
explain the levels of metals in the water. Sediment analysis using TxRF revealed that the rock was
rich in Al, and Cu, and laser ablation showed and that it was enriched in clay particles. To explain the
results, it is concluded that a pH dependent mechanism is responsible for the dissolution of minerals,
and this could be due to clay presence in the rock.

The final aim was to evaluate two methods of remediation, biochar and zerovalent iron on removal of
Al/Cu from samples of slate quarrying affected river water. Modelled lab trials with microcosms
revealed that biochar was effective at removal of Cu but not as effective at removal of Al. Percentage
removal of Al ranged from 44-97% biochar and 34-86.9% with FeO. The removal of Cu with biochar
was not as efficient as with biochar with 44-76.9% removal. Percentage removal of Cu with FeO was
63-97 %. It is concluded that again the pH of the river water may play a crucial part in the mechanism
of removal. It is demonstrated that viable remediation options could include the use of Biochar and
FeO in the future.