REP28887

• Permit No: M1985029
• IBM Index Class Name: Report
• Doc Date: 6/8/1990
• Doc Name: RESPONSE TO MLRD-HYDROLOGY CONCERNS AT ALMA PLACER MINE
• Media Type: D
• Archive: No

combination of these two soils was noted. Standard Proctor tests
the two soil samples. The bulk of the embankment is the sandy-si:
which has an optimum moisture content of 7.SX and a maximum dry d~
133.5 pounds per cubic foot. The fine soil, which was quite limi
extent, had an optimum moisture content of 19.4X and a maximum dr;
109.5 pounds per cubic foot. It is not anticipated that signific,
of this clayey soil trill be Found on the project site. The SW-SN
more representative of what is found on site, although a higher c:
is typically found and reflected in the sample that was tested.
In-place testing of the compacted embankment material has reveale
125 to 135 pounds per cubic foot and about 6X •oisture content.
to 100X of the standard Proctor density, which is in accordance w
geotechnical construction. Although the embankment nay utilize s
of the historic berm as a foundation, the density found in the hi
was also in the vicinity of 135 pounds per cubic foot. This indi
resulting compacted embankment can be considered a well construct
structure. the embankment can be generally classified as a homog
embankment rather than a zoned dam. For this classification it i
for some seepage to appear in the downstream face of the dam duri
state high water level conditions. As long as no piping (washing
out of the dam) occurs, such seepage is a common, expected situat
not endanger the structure.
• Embankment Slope Design
were run on
ty material,
nsity of
ed in
density of
nt amounts
soil is much
ay content
values of
is is 95X
h good
ie portions
oric berm
tea the
. reliable
customary
steady-
f material
n that does
As shown on Plate No. lA, the revised embankment is called for to ave a 3:1
slope upstream and downstream, a 15 foot wide crest, and a maximum height of
approximately 20 feet above the downstream toe of the embankment. The
structural height of the dam will be significantly less since natu al ground
rises significantly and probably is on the order of 10 to 14 feet t the
center line of the embankment. The embankments were laid out acco ding to the
standardized slopes presented in the Bureau of Reclamation's Des of Sma 1
ams, a standard reference text for small earth embankments. Thre -to-one
slopes may actually be conservative, since 2.5 or 2:1 slopes would be wit6ln
those accepted guidelines. However, it was decided that conservat sm was
preferred. Since standard, commonly accepted embankment slopes ar being used
in accordance with the onsite materials found at the Alma Placer p oject, e
stability analysis has not been performed. A stability analysis t ically is
only performed when an attempt is made to optimize the embankment nd utilize
steeper slopes than those recommended by the guidelines noted abov .
• Pond Capacity
It is anticipated that the bottom of the ponds will De enlarged so ewhat
upslope of the embankments. At this time, we estimate that the ma imu^ depth
of storage water will be on the order of 8 feet, and the maximum s rface area
will encompass an area 800 Eeet long by 200 feet wide.
2