2013-07-25_REVISION - M2008078

• Permit No: M2008078
• IBM Index Class Name: Revision
• Doc Date: 7/25/2013
• Doc Name: GP Aggregates LLC West Farm Pit Technical Revison no 2 Request
• From: J&T Consulting Inc
• To: DRMS
• Type & Sequence: TR2
• Media Type: D
• Archive: No

CESARE, INC.
Rapid drawdown of the reservoir was analyzed with a drawdown rate of 1 foot per day. Pore
pressures were computed using transient seepage analysis. Slope stability analyses were performed
during drawdown which generated a minimum factor of safety versus time plot.
SECTIONS ANALYZED
Two sections were chosen for analysis to capture stratigraphic differences across the site. Boring
IT-B9 at Station 31 +52 was chosen to represent areas within the site covered by relatively deep
sand and gravel deposits. This section contains a relatively deep deposit of permeable soil and
represents areas where seepage potential is expected to be the highest. This section was analyzed
for both steady state seepage and slope stability during rapid drawdown.
Boring IT-B12 at Station 44 +60.39 was chosen to represent areas within the site covered by
relatively deep clay deposits. Because the clay soils were assigned the lowest shear strength
values, this section will represent areas where the risk of slope instability is the highest during rapid
drawdown. This section was analyzed for slope stability during rapid drawdown.
Bedrock and groundwater elevations were judged to be relatively stable across the site and were
not significant factors in the choice of sections for analysis. For conservatism, a groundwater
elevation located at the top of the gravel /sand layer was used in our analyses.
MATERIAL PROPERTIES
Hydraulic conductivity values for analysis were developed. For the weathered shale bedrock,
hydraulic conductivity values were based on the Packer test results performed in Borings IT-B1, JT-
B3, JT -B5, JT -B7, IT-B9, IT-B11, and 3T -B13. The results are presented in Table 2.
TABLE 2. Packer Test Results
soling
—61
K (Crr1 )
-- - --
Layer (fea below
ground level)
-8
T-
0
_ 72 - 9 --
3T -B3
72.5-82.5
8.46 x 10'
JT -B5
70-83
1.59 x 10'5
- JT -B7
76.5-85.5
1.44 x 10 "5
3T -B9
69-76
9.53 x 10'5
lT -B11
72 -8 4
72,90-
2 - 90
9.74 x 10-1
0
JT -B13
For sand, clay, and gravel, hydraulic conductivity values were based on Seepage, Drainage, and
Flow Nets, 3rd Edition by Cedergren. For the slurry cutoff wall, the hydraulic conductivities of 1x10-
6 and 1x10'' were evaluated. Presumptive ratios of horizontal to vertical hydraulic conductivity for
each material were assigned as found in the USACE /CA DWR guidance document.
The unit weight, cohesion, and friction angles of the materials encountered are estimated values
based on published literature and our experience in the area.
11.124 GP Ranches Memo 03.21.1303.21.13 2