DWR_3391241

• Document Date: 3/1/1983
• Document Type - Dam Safety: Report
• Division: 3
• Dam ID: 200224
• Subject: HOMESTAKE TAILING POND, LOWER DAM - ENGINEER'S REPORT, STABILITY EVALUATION
• DWR Send/Recipient: DSB
• Outside Send/Recipient: DAPPOLONIA CONSULTING ENGINEERS, INC.

2-4
In 1979, Envirologic Systems, Inc. (1979) investigated the downstream
seep areas by drilling and installing piezometers in seven borings. As
a result of these investigations, eight 12 inch diameter pumping relief
wells were installed by Homestake in February of 1980, in the area
downstream of the dam toe. The intent was to pump the wells contin—
uously to lower the water table in the area and to return the pumped
water to the lower tailings pond. The wells did not function properly
for long, primarily because of pump damage caused by small amounts of
sand entering the wells. Well pumping was abandoned in December of
1980. '
In 1981, D'Appolonia was asked to investigate the seepage problem and
recommend remedial measures for the lower tailings dam. As part of the
Investigations (D'Appolonia, 1981a, 1981b), six borings were drilled and
six piezometers were installed from the dam crest and the downstream toe
During all of the investigations, exit locations and quantities of
seepage were difficult to record due to the general areal nature of most
of the seepage. From conversations with Homestake personnel and
D'Appolonia observations during their involvement in 1981 and 1982, the
seepage exiting as general wetness on the ground surface tends to change
location. No general trend of movement was discernable but the area of
greatest wetness moved from one side of the valley to the other and
back. Concentrated seepage outflows, such as in the ravine to the east
of the toe area appear to have remained relatively constant.
area of the dam.
The water levels in these piezometers and others are
shown as a
function
of time in
Figure 2. The levels are fairly constant
over the
period shown (July
1981 to November 1982), reflecting a
relatively
constant
pond level.
Erratic piezometer readings in July and
August of
1982 are
attributed
to experimental grouting beneath the dam
during this period.
During all of the investigations, exit locations and quantities of
seepage were difficult to record due to the general areal nature of most
of the seepage. From conversations with Homestake personnel and
D'Appolonia observations during their involvement in 1981 and 1982, the
seepage exiting as general wetness on the ground surface tends to change
location. No general trend of movement was discernable but the area of
greatest wetness moved from one side of the valley to the other and
back. Concentrated seepage outflows, such as in the ravine to the east
of the toe area appear to have remained relatively constant.