2011-02-04_PERMIT FILE - M2010071

• Permit No: M2010071
• IBM Index Class Name: PERMIT FILE
• Doc Date: 2/4/2011
• Doc Name: Slope Stability Analyses Review- MEMO
• From: DRMS-tc1
• To: DRMS-mac
• Email Name: MAC
• Email Name: TC1
• Media Type: D
• Archive: No

Slope Stability - Goose Haven Reservoir No. 2
Page 2
February 4, 2011
slope (as discussed on page 17 in the first paragraph under "Stability Analysis"), the
slurry wall should only be about 40 feet deep. Please correct or clarify the scale.
Also indicate whether the vertical scale is exaggerated or the same as the horizontal
scale. ii) The light blue gravelly sand (SP) and darker blue sandy gravel (GP) layers
shown above bedrock for the East Slope figures do not correspond with the TH-21
borehole log shown on Figure E-14. TH-21 indicates there is about 23 feet of silty
sand (SM) on top of the claystone bedrock, with a five-foot layer of clay on top of
that, and nine feet of silty or clayey sand (SC/SM) above that to the surface. No SP
or GP is indicated in the borehole log for TH-21. Please either correct the analysis to
reflect the borehole log properties or explain what data was used to select materials
for the slope stability analyses. iii) The slip/failure surfaces shown in Figures C-3
and C-5 suggest surface sloughing only. The Division is concerned with slope
failures that may affect the overall slope and what if any structures may be near the
top of the slope failure, such as those shown in Figures C-2 and C-6. Please provide
factors of safety for significant slope failures. iv) Please indicate where the phreatic
surface elevations are obtained.
b. Please provide slope stability analyses such as computer output, spreadsheets or
manual calculations for all five conditions.
c. The locations of the existing power line and ditch should be represented' on the
figures for reference purposes.
6. West Slope:
a. Figures C-7 through C-11: i) The approximate scale (1"=100') appears to be off by
an order of magnitude. According to that scale, the slurry wall is about 200 ft from
the crest of the slope and is 320 feet deep. Based on Drawing 3, the slurry wall is
about 15 feet from the crest of the slope. Based on borehole locations (e.g., Figure 4)
and the borehole log for the hole (TH-19/Figure A-1) closest to the middle of the west
slope (as discussed on page 17 in the first paragraph under "Stability Analysis"), the
slurry wall should only be about 32 feet deep. Please correct or clarify the scale.
Also indicate whether the vertical scale is exaggerated or the same as the horizontal
scale. ii) The light blue gravelly sand (SP) and darker blue sandy gravel (GP) layers
shown above bedrock for the West Slope figures do not correspond with the TH-19
borehole log shown on Figure E-24. TH-19 indicates there is about 13.5 feet of
gravel (GP) on top of the claystone bedrock, with a two-foot layer of silty sand on top
of that, and 13.5 feet of clayey sand (SC) above that to the surface. No SP is
indicated in the borehole log for TH-19. Please either correct the analysis to reflect
the borehole log properties or explain what data was used to select materials for the
slope stability analyses. iii) The slip/failure surfaces shown in Figures C-S and C-10
suggest surface sloughing only. The Division is concerned with slope failures that
may affect the overall slope and what if any structures may be near the top of the
slope failure, such as those shown in Figures C-7 and C-11. Please provide factors of
safety for significant slope failures. iv) Please indicate where the phreatic surface
elevations are obtained.
mAmin\tc1\m-2010-071 goose haven\stabilitycomments_mem04feb11.docx