Phase I: Initially, the impact of mine waters on the receiving watercourse
is assessed by physicochemical means. The severity of impact is measured
sequentially in six categories:
1. Area affected (by deposition of metal precipitates; assessed visually)
(m2
)
2. Length affected (m)
3. Substrate quality for salmonid reproduction
4. Iron deposition (the intensity of discoloration, assessed visually)
5. Total iron concentration (mg/l)
6. pH, dissolved oxygen concentration (mg/l), aluminum concentration
(mg/l)
These categories are listed in what is perceived to be a decreasing order
of importance. Each category is subdivided to indicate the severity of impact
measured, as illustrated in Table 1.
In its first application, for mine waters in South Wales, this method was