HYDRO31360

• Permit No: C1981071
• IBM Index Class Name: Hydrology
• Doc Name: EVALUATION OF WATER QUALITY DATA FROM SEDIMENTATION POND D INFLOW AND DISCHARGE POINTS
• Permit Index Doc Type: CORRESPONDENCE
• Media Type: D
• Archive: No

~ i •
3.0 CONCLUSIONS APID RECOMMENDATIONS
3.1 Conclusions
The variability of analytical results, and questionable validity
of total metals analyses, resulted in some difficulty in the
evaluation of the water quality data. The following conclusions
are consequently based on trends in the data, rather than
individual absolute values. By necessity, the evaluation is
based on the assumption that the analytical data, for the most
part, are approximately correct. A quality control program
initiated in early September should indicate whether this
assumption is correct. The following major conclusions may be
made from evaluation of the existing data base:
1) The only NPDES permit exceedences noted are in total silver
and total zinc concentrations (Table 2). Concentrations of both
zinc and silver in water at NPDES discharge point 005, the
underground mine discharge and the pit overflow are associated
with suspended material. Dissolved concentrations of these
metals are generally below the analytical detection limits. The
Wedge sump is the only water source which shows a consistent
significant dissolved concentration of zinc which generally makes
up a large proportion of the total zinc concentrations in this
( source.
1 2) There is no apparent correlation between total suspended
solids (TSS) and total concentrations of zinc and silver.
Significantly high values of total zinc and silver are noted when
the dissolved contents of these metals are negligible and when
the TSS of the sample was less than the detecton limit (4 mg/L)
This indicates that the metal concentrations are predominantly
associated with an extreamly fine fraction of the suspended
material in the water. This would also explain the relatively
small increase noted in total concentrations of zinc and silver
with large increases in TSS.
1 3) Minor disturbances of water at all sampling sites could have
significant effects on the concentration of the fine suspended
fraction with consequent increases in the total concentrations of
i zinc and silver. This would explain some of the large
variability of analytical values since disturbances do occur at
all sampling sites at various times. The time of water sampling
in relation to the timing of these disturbances may have a
significant effect on the water quality represented by the
sample.
4) Pond D reduces the TSS load by an average of 870 (Table 6).
Total zinc reduction ranges wider' but averages 330 (Table 7).
Reduction of total silver also ranges widely with an average
reduction of 57~ (Ta61e 8). The lesser average reductions in
total metals concentrations compared taith TSS reductions may be
explained by conclusion 2. Gravity settlement in the pond is
very efficier,: at removing most of the suspended material