Environmental Analysis Tools - Environmental Impact Analysis: Process and Methods - page 290

Cooper Pt.

Greely Pt.

Pt. Salisbury Bishop Pt.

Tailings perimeter:
Total deposition of
>10 cm over 13 years
(18 km 2 )

Discharge
point

Deposition
rate 4 to 10 cm/yr
(3.52 km 2 )

Plume

Pete's Rock

Deposition
rate >10 cm/yr
(2.72 km 2 )

False
Arden

Admiralty Island

Stephens
Passage deep
basin

BATHYMETRIC CONTOURS IN FEET
0 5,000 10,000 15,000

North

SCALE IN FEET

FIGURE 7.7
AJ mine ecological risk assessment physical stress exposure characterization.

The standard chemical characterization of determining literature values
reported as effects levels was supplemented with toxicity testing on mine
tailings samples. The additional characterization was warranted because of
the relative nonbioavailability of the metals in the tailings, the low chemical
solubility in the deep, cold, salt, and alkaline disposal areas; and the poten-
tial for additive and/or synergistic effects of multiple contaminants in the
tailings. After much discussion with the TAC and research on toxicity test-
ing methods, an extensive bioassay program was implemented. It addressed
both the solid and dissolved phases of the mine tailings and several benthic
as well as pelagic (i.e., living in the water column) species were tested for
toxicity (acute and chronic) and bioaccumulation in tissue. When the test
results were in, the conclusions were very clear: the contaminants associ-
ated with the mine tailings (predominantly heavy metals) were not toxic to
ecological receptors of concern and they had not bioaccumulated in the tis-
sue of prey organisms exposed to the tailings. This was consistent with the
development of benchmarks which were well above the measured levels of
contaminants in the mine tailings; thus no elevated risk was indicated. The
results seem to stem from the relatively low concentrations in the tailings,
at least partially because most of the metals would be extracted with the gold