2003 CPEO Military List Archive

From: themissinglink@eznetinc.com
Date: 14 Apr 2003 16:26:02 -0000
Reply: cpeo-military
Subject: [CPEO-MEF] 30 Year Feasibility Timeframe
Can someone tell me the legal reasoning behind the 30 year time frame for
these base closure environmental assessments?  At Yucca Mountain the geology
was assessed over a period of tens and hundreds of thousands of years which
seems appropriate given the duration of the toxicity.

My issue is that Landfill 7, at the former Fort Sheridan, was created in a
ravine along the bluffs of the North Shore along Lake Michigan.  The bluffs
are eroding at a rate of 20-25cm per year during the 130 year time frame
studied by the USGS.  That is about 100 feet of bluff recession which will
surely affect Landfill 7 over the next 100 years since the waste is right at
the edge of the bluff.  Even if the waste is set back the 150 feet of the
bluff lateral distance(which is not a sure thing given the incomplete Army
data on the landfill boundaries), the rest of the bluff will recess leaving
Landfill 7 as a jut in the lake.  This is assuming that the engineering
controls are really going to be effective at stopping erosion along a single
point when no such stretch of bluff has ever been shown to be impervious no
matter what erosion controls have been put in place as referenced below.

I found this interesting :

"Between 1872 and 1987,  rates of bluff retreat from Wilmette to Waukegan
vary from 10 to 75 cm/yr between discrete segments of bluffs [figure_3].
The average rate of retreat for the entire area, however,  does not vary
significantly between 1872-1937 and 1937-1987 and ranges from 20-25 cm/yr.
No obvious correlation appears to exist between lake levels, rainfall,
abundance of groins, and retreat rate.   Local variations in retreat rate
do, however, correlate closely with lithologic variations.  Bluffs that
contain lake-plain sand and silt have higher retreat rates than clay-till
bluffs.  However, the bluffs  have little curvature across these boundaries
indicating that the variations average out over time, producing long- term
parallel bluff retreat. (Jibson and Staude)."

Also, from http://jglr.org/1994/num1/20_1_135-152.pdf

Rates and Processes of Bluff Recession Along the Lake Michigan Shoreline in

Randall W. Jibson and Jackson K. Odum

U.S. Geological Survey
Box 25046, MS 966, Denver Federal Center
Denver, Colorado 80225

Discussion and Conclusion

".........What are the human consequences of the 20-25cm/yr bluff recession
rates in this area?  Development in most of the area consists of
medium-density single-family housing(large homes of fairly large
lots)ranging in age from new to nearly 100 yr old.  Setbacks from the bluff
vary from almost zero to a few tens of meters.  If the regional retreat rate
prevailed everywhere(which it does not), then a house would need a 20-25 m
setback from the bluff to survive 100 yr.  Few houses have such large
setbacks.  Even though regional retreat rates are fairly constant, Figure 9
shows that retreat rates vary substantially from place to place for a given
50-100 yr period.  The retreat that a specific part of the bluff might
experience in any 50-100 yr period probably  depends on several factors at
that site and at nearby parts of the bluff: (1) the type and quality of
shore protection, (2) the rate of retreat in the previous 50-100 yr period,
(3) the local lithology and geotechnical properties of the bluff material,
(4) the width of the fronting beach, and (5) the geometry of the shoreface
in front of the bluff.  Therefore, the data and conclusions from this study
are relevant for regional planning rather than site-specific engineering.
Any planning for construction near the bluffs, however, must anticipate some
amount of bluff recession and stipulate sufficient setback to insure the
integrity of structure for it's anticipated life."

This would seem to indicate that the Army concept of protecting a single
point against bluff-wide erosion is a fiction.  I guess it comes down to
what the Army's requirement is for the stability of the engineering controls
after the thirty year time frame.  Is the time frame a yardstick to measure
geologic stability after which time the Army gets to walk away with the
assumption that if the cap lasted thirty years then it will last forever?
Or is the thirty years just some arbitrary number and the Army is still
responsible to take corrective action when the erosion begins to disturb the
erosion controls?

Steven Pollack

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