DOUBLE TROUBLE IF NORTH SPUR COLLAPSES

Guest Post Written by Cabot Martin


Minister’s August 26, 2015 Letter Confirms James L. Gordon’s Concerns


The attempt to bring some clarity to the North Spur
landslide issue seems to be making headway – if in a very disturbing way.


Attached is a letter from Minister Dan Crummell (Minister responsible for Dam Safety) dated August 26, 2015 in answer to my
letter to him of August 7,2015 together with my reply of September 11, 2015 to the Minister’s latest letter. (Both letters are shown below.)


While this letter exchange with the Minister involves
some pretty technical matters, this should not deflect us from the conclusion
that an independent, engineering-based and technically competent review is
needed. My latest letter closes with a call for a “Hydro Review Board” that
would do just that.


That such a Board can, even at this late date, “add
value” can be illustrated by the major issues that arise from the Minister’s
latest letter and the findings of the recent, long-called for, North Spur Dam
Break Analysis.  

According to the Hatch Consultants June 26,2015 North
Spur Dam Break Analysis, the gap in the North Spur upon failure would be 600 m
long and, as the Minister now admits, such failure  “ may indeed increase in depth below an
elevation of 10 m” – a point that hydro expert Jim Gordon made in a previous
piece on Uncle Gnarley.


The creation of such a deep and wide gap alone would
be bad enough as it would result in the creation of a brand new Lower Churchill
river course on the north side of Spirit Mountain, leaving all Muskrat Falls
generating assets currently under construction high and dry and of no economic
value; our billions of dollars of investment would simply evaporate.


But this would be just the start in a predictable
chain of events, for:


“…
should the North Spur fail, the erosion cut will remove all support that the
North Spur currently provides to the very large sensitive clay deposit on the
North Bank and its adjacent upslope area, exposing the bank to a massive
landslide likely to engulf the powerhouse on the south bank, and cause a large
tsunami wave moving rapidly downstream to inundate Goose Bay and Happy Valley.”


The newly exposed and highly unstable stretch of north
side riverbank would rise some 150 to 200 feet high and stretch about a
kilometer in length leaving lots of potential for both “retrogressive” slides that
start at the river bank and even larger Downhill Progressive Slides that would
be initiated far upslope as postulated by Dr. Bernander.


It is inexplicable why Nalcor has not, and does not,
consider these two issues to be major project risks.


Such a situation clearly makes the case for the
immediate creation of a “Hydro Review Board”.



This is the Minister’s reply to my letter of August 7, 2015.










I have responded to the Minister with the letter shown below:


September 11, 2015.

The Honourable Dan Crummell
Minister of Environment and Conservation
4th Floor, West Block
Confederation Building
St. John’s, NL   A1B 4J6
Dear Mr. Minister:

Thank you
for your letter of August 26, 2015 in response to my letter of August 7, 2015
concerning the North Spur stability problem at the Muskrat Falls hydro project
on the Lower Churchill River in Central Labrador.

 On a technical but important point I
should point out that your reference on page 1 to “sensitive marine clays”
should properly state “sensitive glacio-marine clays” as it is the latter class
of particularly sensitive clays that are present at the North Spur and it’s
adjacent up slope area.

I note that at page 2 of your letter, you state that Nalcor
plans to avoid “human activity such as pile driving that could induce
landslides “by which I assume that all parties now apparently understand how
risky the situation at the North Spur really is.

In the second paragraph of you letter, you emphasize that the
geotechnical investigations have been undertaken according the CSA guidelines.
Also you have acknowledged that the North Spur is part of the reservoir
containment structures. This is correct. However, the North Spur “dam” will
contain quick “marine” clay, a very unstable material, and the CSA guidelines
do not cover such a structure for the reason that no such structure has ever
been built which includes quick clay within the dam structure.

This basic non- applicability of the CDA Guidelines is not
offset by characterizing  the kilometer long
50 m high North Spur  as a “reservoir
rim”; and I should say that in any event the North Spur constitutes 50% in
length of the entire Muskrat Falls reservoir 

Page 1 of 4



containment system – hardly a
“rim”.

In the third to fifth paragraphs, you outline the
measures that will be taken to improve the safety of the Spur dam. The question
is will they be sufficient? For example:-
·        
Will all the
sensitive clay be removed? Or will the clay removal be confined to certain
areas.
·        
Will there be a
backup to the cut-off wall? Cement-bentonite
sand cut-off walls are very difficult to construct with 100% impermeability.
They usually contain several permeable holes formed during the backfill process
when sand sloughs off the vertical wall. A backup usually consists of grouting
or an upstream blanket.
·        
Will the cut-off
wall be excavated through sensitive clay? – A difficult task.
·        
Are the lower
slopes of the dam sufficiently flat to distribute the load onto the lower quick
clay?

In your 6th paragraph, you mention that the
North Spur dam break is not the worst case scenario in regard to downstream
impacts. This point is debatable. The warning time for a “slow erosion” North
Spur break may well be significantly longer that for the concrete dam break.

However,
this does not take into account that should the North Spur fail, the erosion
cut will remove all support that the North Spur currently provides to the very
large sensitive clay deposit on the North Bank and its adjacent upslope area,
exposing the bank to a massive landslide likely to engulf the powerhouse on the
south bank, and cause a large tsunami wave moving rapidly downstream to
inundate Goose Bay and Happy Valley.

This scenario has not been studied, and is likely to
be far more dangerous than the concrete dam failure. Also, since there have
been many recent collapses on the North Bank, the risk of such an occurrence is
far higher than a failure in the concrete dam. This scenario has not been
investigated at all.

These concerns are heightened by the potential in this
area for Downhill Progressive Landslides as described by Dr. Bernander.

In your 7th paragraph, you assert that my breach
assumptions were incorrect, since they did not take into account the cement-bentonite-sand
cut-off wall halting the 

Page 2 of 4


downward erosion of the breach. This is partially
correct. However, the cement-bentonite-sand wall will only provide a
temporarily non-erodible surface, eventually crumbling when the downstream
material erodes out, removing support for the wall. The result will be a “slow”
erosion down to about or below sea level. The warning time for Happy Valley –
Goose Bay – Mud Lake in such a “slow erosion” case may well be significantly
longer than that for the concrete dam break case.

However, even the “slow erosion” case constitutes a very
significant project risk that must be considered
.

I
have been informed by an experienced hydro engineer that the consequences of a
North Spur failure,
“from
a financial perspective would be unimaginably catastrophic due to the very
large expenditure required for a repair due to erosion of the Spur clay
foundation down to below sea level. …” … “The cost would be so high, that a
more economical alternative would likely be to abandon the site and spend the
repair moneys on a re-design and construction of the Gull Island Dam, taking
advantage of the lower tailwater level resulting from a dam break in the North
Spur to increase the capacity.”
Turning now to your second last paragraph wherein you state
that – “The engineering design for the
North Spur stabilization works has been reviewed by three different independent
third parties, who have advised that the design is adequate”.
I cannot find any corroboration for this statement and
would appreciate being directed to where I might find a public source for such
opinions.
The Muskrat Development is being built without an
independent “Review Board”. This is unusual, since most large hydro projects
have review boards to ensure that all aspects have been foreseen. Moreover, the
North Spur has unique challenges with a dam being built on a quick clay
foundation, with quick clay included within the dam structure.
An independent Review Board should be immediately
appointed comprising the most qualified engineers with experience in soft
clays. To my knowledge these would be Dr. S. Bernander, and Professor (retired)
N. Morgenstern who recently served as Chair of the Panel investigating the
failed Mount Polly Dam – it was found to be due to an undetected layer of soft
clay below the dam.

Page 3 of 4


In closing, I urge you to immediately advocate within
cabinet and generally support the establishment of such a Hydro Review Board.
Sincerely,
Cabot Martin
151 Waterfordbridge Road
St. John’s , NL
A1E 1C7

Cc Mr Jamie
Chippett Deputy Minister Department of Environment and Conservation.




Page 4 of 4



THE PROOF MUSKRAT FALLS IS NOVA SCOTIA’S PROJECT

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2 COMMENTS

  1. I was watching the weather channel today. There was a special about earthquakes. It mentioned that in hydroelectric projects around the world, there have been countless earthquakes caused by adding the weight of the reservoir. I have not seen many people discuss this possibility as it relates to the quick clay. As quick clay is so very susceptible to disruption during earthquakes. I tried to look at the earthquake studies for muskrat falls, and did not notice any extra precaution taken for the added weight of the reservoir. It seems to be a very common and well known issue with hydroelectric projects. Knowing that earthquakes are often caused(albeit smaller ones) by the change in pressure from a reservoir, makes the North Spur truly an emergency issue. Even a small earthquake after the reservoir is created would be an event that could kill countless people. https://en.wikipedia.org/wiki/Induced_seismicity#Artificial_lakes

  2. I appreciate your informative posts, and they would be even better if you used the proper name for the "knob" on the north side of Muskrat Falls. Some locals do call it spirit mountain, but that name doesn't really do it justice. It is called Manitu-utshu, and it is the home of Uenitshikumishiteu. At the LCP JRP hearing in Sheshatshiu the old Innu warned that Uenitshikumishiteu was strong enough to destroy the damn if it wanted, and requested that Nalcor ask it for permission before doing work at that location. http://www.innuplaces.ca/fiche.php?id=494